Keywords: mergers and acquisitions, interpersonal trust, boundary spanning, emerging economies, Malaysia

How does trust develop in new subordinate-leader relationships during post-acquisition integration? Does boundary spanning facilitate or hamper trust? Cultural differences between the acquirer and acquired firm add to integration uncertainty, occurring at multiple, interconnected levels (national, organizational, functional cultures). Multicultural societies add another layer of complexity. This study compares a domestic M&A with a South African cross-border acquisition in the Malaysian financial industry. The analysis reveals that boundary spanning by acquirer and acquired-firm managers facilitated subordinate-leader trust development. I thus posit that boundary spanning mitigates uncertainty and cultural differences during integration. Further and paradoxically, integrating domestic rather than cross-border acquisitions can be more complex when intra-national culture differences are accounted for. This paper offers insights for advancing Western-developed theories and for more successful integration.

INTRODUCTION

Mergers and acquisitions (M&As) are burdened by high failure rates. At best only half succeed [START_REF] Cartwright | The role of culture compatibility in successful organizational marriage[END_REF][START_REF] Haspeslagh | Managing acquisitions: Creating value through corporate renewal[END_REF]. i Post-acquisition integration is a vital process characterized by complexity, uncertainty and unpredictability [START_REF] Cording | Reducing causal ambiguity in acquisition integration: Intermediate goals as mediators ofintegration decisions and acquisition performance[END_REF]Graebner et al., 2017). Birkinshaw et al.'s (2000) seminal paper argues that successful human integration facilitates the effectiveness of task integration, although both processes determine acquisition success.

Cultural differences between the acquirer and acquired firm add to integration uncertainty and complexity, and have long been blamed for unsuccessful domestic and crossborder M&As [START_REF] Buono | When cultures collide: The anatomy of a merger[END_REF][START_REF] Cartwright | The role of culture compatibility in successful organizational marriage[END_REF][START_REF] Chatterjee | Cultural differences and shareholder value in related mergers: linking equity and human capital[END_REF]Nahavandi & Malekzadeh, 1988). Culture is a multifaceted construct incorporating shared assumptions, practices, values, artifacts, and rituals [START_REF] Taras | Half a century of measuring culture: Review of approaches, challenges, and limitations based on the analysis of 121 instruments for quantifying culture[END_REF]2016). Cultural differences often lead to complex trust dynamics and relationships between acquirer and acquired-firm personnel [START_REF] Buono | The human side of mergers and acquisitions[END_REF][START_REF] Stahl | Do cultural differences matter in mergers and acquisitions? A tentative model and examination[END_REF][START_REF] Teerikangas | The culture-performance relationship in M&A: From yes/no to how[END_REF]. Cultural challenges occur at multiple, interconnected levels including national, industrial, organizational, functional and professional cultures in M&As [START_REF] Teerikangas | The culture-performance relationship in M&A: From yes/no to how[END_REF]. Scholars have yet to address this interconnectivity adequately (ibid.), despite pinpointing national and organizational culture differences as the main integration challenges [START_REF] Brannen | Merging without alienating: Interventions promoting cross-cultural organizational integration and their limitations[END_REF][START_REF] Chatterjee | Cultural differences and shareholder value in related mergers: linking equity and human capital[END_REF][START_REF] Shimizu | Theoretical foundations of cross-border mergers and acquisitions: A review of current research and recommendations for the future[END_REF]. Moreover, the M&A cultural 'baggage' [START_REF] Teerikangas | The culture-performance relationship in M&A: From yes/no to how[END_REF]) can be weighed down further by within-country cultural diversity. Recent studies highlight the complexities of multifaith and multilingual societies in cross-border M&As [START_REF] Cuypers | The effects of linguistic distance and lingua franca proficiency on the stake taken by acquirers in cross-border acquisitions[END_REF][START_REF] Dow | The effects of within-country linguistic and religious diversity on foreign acquisitions[END_REF][START_REF] Kroon | Explaining employees' reactions towards a cross-border merger: The role of English language fluency[END_REF][START_REF] Kwok | CEOs we trust: Religious homophily and crossborder acquisitions in multifaith Asian emerging economies[END_REF]. In particular, [START_REF] Dow | The effects of within-country linguistic and religious diversity on foreign acquisitions[END_REF] found that multifaith and multilingual societies can add complexity to behavioral uncertainty and information asymmetry between foreign acquirers and local acquired firms.

Trust is a complex, multilevel [START_REF] Currall | A multilevel approach to trust in joint ventures[END_REF] and multifaceted construct [START_REF] Mayer | An integrative model of organizational trust[END_REF][START_REF] Rousseau | Not so different after all: A cross-discipline view of trust[END_REF]. It refers to positive expectations when the trustor is vulnerable to the trustee's actions (ibid.). Trust is essential in M&As [START_REF] Graebner | Caveat venditor: Trust asymmetries in acquisitions of entrepreneurial firms[END_REF][START_REF] Lander | Boarding the aircraft: Trust development amongst negotiators of a complex merger[END_REF][START_REF] Maguire | Citibankers' at Citigroup: a study of the loss of institutional trust after a merger[END_REF][START_REF] Stahl | Trust dynamics in acquisitions: A case survey[END_REF]2012). During postacquisition integration, trust facilitates cooperation, job performance, resource sharing, and knowledge transfer [START_REF] Bauer | Speed of acquisition integration: Separating the role of human and task integration[END_REF][START_REF] Stahl | Trust in mergers and acquisitions[END_REF]2010). However, unanswered questions remain about how trust develops during integration, especially in subordinateleader relationships (Graebner et al., 2017).

Inspired by calls for a multilayered, multifaceted and contextual view of culture in multiple domains (e.g., [START_REF] Dietz | Unravelling the complexities of trust and culture[END_REF][START_REF] Leung | Culture and international business: Recent advances and their implications for future research[END_REF]Tung, 2008), this study addresses the following research question: How does trust develop in new subordinateleader relationships amidst the uncertainty and cultural differences of post-acquisition integration? The research is contextualized in Malaysia, a multicultural, middle-ranking emerging economy in Southeast Asia for cross-border M&As (UNCTAD, 2017). Emergingeconomy firms actively engage in both domestic and cross-border M&As [START_REF] Aybar | Cross-border acquisitions and firm value: An analysis of emerging-market multinationals[END_REF][START_REF] Bandeira-De-Mello | Theoretical and empirical implications for research on South-South and South-North expansion strategies[END_REF][START_REF] Lebedev | Mergers and acquisitions in and out of emerging economies[END_REF]. Interestingly, Malaysia's M&A volume and value increased in 2017 despite the decline in global deals [START_REF] Duff | Transaction Trail: Annual Issue[END_REF].

Equally, this paper addresses another gap in M&A scholarship, on the difference between integrating domestic vs. international acquisitions. Most researchers contend that integrating cross-border M&As is riskier and more complicated than domestic deals [START_REF] Angwin | Strategic perspectives on European cross-border acquisitions: A view from top European executives[END_REF][START_REF] Barkema | Foreign entry, cultural barriers, and learning[END_REF][START_REF] Olie | Shades of culture and institutions in international mergers[END_REF]. Yet, some demonstrate that domestic M&A integration can be more challenging: despite the merging firms' shared national culture, organizational culture differences can hinder the integration process [START_REF] Véry | A cross-national assessment of acculturative stress in recent European mergers[END_REF]1997). In fact, the differences between domestic and cross-border M&As are still poorly understood [START_REF] Bris | The value of investor protection: Firm evidence from crossborder mergers[END_REF][START_REF] Gregory | Do cross border and domestic acquisitions differ? Evidence from the acquisition of UK targets[END_REF][START_REF] Reynolds | The international experience in domestic mergers-Are purely domestic M&A a myth[END_REF].

I apply a comparative two-case research design in the Malaysian financial services industry, with a domestic M&A and a South African cross-border acquisition. South Africa and Malaysia are newly developed mid-range emerging economies [START_REF] Hoskisson | Emerging multinationals from mid-range economies: The influence of institutions and factor markets[END_REF].

The domestic M&A combines potentially conflicting cultures: two government-linked corporations (GLCs) with majority ethnic Malay personnel, and two entrepreneurial firms with mainly ethnic Chinese personnel. ii Using an abductive approach [START_REF] Timmermans | Theory construction in qualitative research: From grounded theory to abductive analysis[END_REF][START_REF] Welch | Theorising from case studies: Towards a pluralist future for international business research[END_REF], my analysis reveals how boundary spanning by both acquirer and acquired-firm managers facilitated subordinate-leader trust development. I had found puzzling the apparent mismatch between theory-led expectations (complexity of integrating domestic vs. cross-border acquisitions) and interview narratives. Post-acquisition integration had been relatively smooth in both cases except the domestic M&A's first year, when it had been "absolute chaos" and "very stressed and a challenging environment for all the people". How did integration uncertainty and cultural differences dissipate? Moreover, other similar mergers in Malaysia had involved "a lot of infighting… intensified lobbying [and] backstabbing". Abduction led to "a re-description or re-contextualization of the phenomenon" (Welch et al., 2011, p. 748).

The systematic analysis revealed boundary spanning behavior by acquirer and acquired-firm senior and middle managers. This indicates the widening locus of M&A leadership. The manager's relating, scouting, persuading and empowering behaviors [START_REF] Druskat | Managing from the boundary: The effective leadership of self-managing work teams[END_REF]Wheeler, 2003) spanned horizontal, vertical, stakeholder, demographic andgeographical boundaries (Palus et al., 2013), and encompassed cultural differences at national (between-country), intra-national (within-country), organizational and functional levels [START_REF] Teerikangas | The culture-performance relationship in M&A: From yes/no to how[END_REF]. Boundary spanning overcame the 'us and them' mentality between acquirer/acquired-firm subordinates and acquired-firm/acquirer leaders by reducing uncertainty and cultural differences, thus enabling the development of trust. Thus, I posit that boundary spanning mitigates uncertainty and cultural differences during post-acquisition integration. This paper makes two other contributions to M&A scholarship and offers managerial insights for more successful post-acquisition integration. First, it extends the role of boundary spanning in M&As, beyond the pre-M&A negotiation phase [START_REF] Lander | Boarding the aircraft: Trust development amongst negotiators of a complex merger[END_REF] to post-acquisition integration. This complements the process perspective [START_REF] Jemison | Corporate acquisitions: A process perspective[END_REF] and elucidates on the temporality of integrative actions [START_REF] Birkinshaw | Managing the post-acquisition integration process: How the human integration and task integration processes interact to foster value creation[END_REF][START_REF] Froese | Integration management of Western acquisitions in Japan[END_REF][START_REF] Teerikangas | Structure first! Temporal dynamics of structural and cultural integration in cross-border acquisitions[END_REF] from the perspective of South-South M&As. Second, it contributes to the literature on the complexities of multilingual societies in M&As [START_REF] Cuypers | The effects of linguistic distance and lingua franca proficiency on the stake taken by acquirers in cross-border acquisitions[END_REF][START_REF] Dow | The effects of within-country linguistic and religious diversity on foreign acquisitions[END_REF][START_REF] Kroon | Explaining employees' reactions towards a cross-border merger: The role of English language fluency[END_REF]. The domestic M&A was unable to establish a lingua franca for all personnel despite the possibility of speaking in two languages (English and the national language) at meetings. This demonstrates that when intra-national culture differences are taken into consideration, integrating domestic rather than cross-border M&As can be more challenging [START_REF] Véry | A cross-national assessment of acculturative stress in recent European mergers[END_REF]1997).

LITERATURE REVIEW

Subordinate-leader trust and M&As

The paper adopts the widely quoted definition of trust from [START_REF] Rousseau | Not so different after all: A cross-discipline view of trust[END_REF], as "a psychological state comprising the intention to accept vulnerability based upon positive expectations of the intentions or behavior of another " (p. 395). This definition captures two essential concepts: positive expectations of trustworthiness, including beliefs and perceptions of being able to rely on the trustee; and, willingness to accept vulnerability or a suspension of uncertainty [START_REF] Colquitt | Trust, trustworthiness, and trust propensity: a meta-analytic test of their unique relationships with risk taking and job performance[END_REF][START_REF] Ferrin | Can I trust you to trust me? A theory of trust, monitoring, and cooperation in interpersonal and intergroup relationships[END_REF]. In M&As individual trust can be directed at: a leader, subordinate, or between peers; a group including top management team (TMT) and headquarters (HQ); and, an organization, e.g., during M&A negotiations [START_REF] Currall | A multilevel approach to trust in joint ventures[END_REF]. Interpersonal trust refers to trust between individuals.

In one of the most influential trust models [START_REF] Burke | Trust in leadership: A multilevel review and integration[END_REF][START_REF] Lewicki | Models of interpersonal trust development: Theoretical approaches, empirical evidence, and future directions[END_REF], [START_REF] Mayer | An integrative model of organizational trust[END_REF] proposes three main characteristics for trusting work relationships. Ability refers to the trustee's skills and domain-specific competence. Benevolence represents the trustor's belief that the trustee wants to "do good to the trustor" (p. 718). Integrity refers to the perception that the trustee "adheres to a set of principles that the trustor finds acceptable" (p. 719). These trust antecedents juxtapose with the trust constructs introduced by McAllister (1995): cognition-based trust based on rational information on the trustee's competence, reliability and credibility; and, affect-based trust which refers to an emotional attachment or concern for the other party's interests and welfare. Cognition-based trust precedes affectbased trust in organizations [START_REF] Mcallister | Affect-and cognition-based trust as foundations for interpersonal cooperation in organizations[END_REF][START_REF] Rousseau | Not so different after all: A cross-discipline view of trust[END_REF], and increases job satisfaction and performance [START_REF] Yang | Examining the effects of trust in leaders: A basesand-foci approach[END_REF].

Studies of subordinate-leader trust in the context of M&As emphasize subordinate trust in leaders and emerging economies are still relatively rare [START_REF] Kwok | CEOs we trust: Religious homophily and crossborder acquisitions in multifaith Asian emerging economies[END_REF][START_REF] Stahl | Does national context affect target firm employees' trust in acquisitions? A policy-capturing study[END_REF]. Trust between subordinates and leaders is not necessarily mutual or reciprocal [START_REF] Brower | A model of relational leadership: The integration of trust and leader-member exchange[END_REF][START_REF] Korsgaard | It Isn't Always Mutual: A Critical Review of Dyadic Trust[END_REF][START_REF] Schoorman | An integrative model of organizational trust: Past, present, and future[END_REF]. Their antecedents differ. Leaders emphasize the subordinate's receptivity, availability, and discreteness; whereas, subordinates emphasize the leader's availability, competence, discreteness, integrity, and openness [START_REF] Brower | A closer look at trust between managers and subordinates: Understanding the effects of both trusting and being trusted on subordinate outcomes[END_REF]. This asymmetry may lead to longer-term implications on trust dynamics and post-acquisition integration.

Boundaries, cultural differences, boundary spanning and M&As

Boundaries separate an organization's internal and external environments. Boundaries exist within organizations [START_REF] Palus | Boundary-Spanning Leadership in an Interdependent World[END_REF][START_REF] Schotter | Boundary spanning in global organizations[END_REF]. Managers often face five types of boundaries: horizontal, vertical, stakeholder, demographic, and geographic [START_REF] Palus | Boundary-Spanning Leadership in an Interdependent World[END_REF]. Horizontal boundaries separate functions and units by specialized expertise, and include functional, occupational and professional culture differences. During post-acquisition integration, horizontal boundaries often stem from organizational culture differences (pre-M&A legacies). Vertical boundaries are found across hierarchical levels and define title, rank and power. Stakeholder boundaries refer to shareholders, Boards of Directors, customers, partners, governments, and other communities. Stakeholder boundaries can overlap with organizational culture differences in M&As, and with national cultural differences in crossborder M&As. Demographic boundaries separate people by gender, age, ethnicity, religion, political ideology, etc., and include within-country cultural differences. Geographic boundaries are defined by physical location including countries, regions and East/West, and include national and regional culture differences. Boundaries are linked to identities (i.e., who we are and how we define ourselves; ibid.). Identity has attracted the attention of M&A researchers [START_REF] Clark | Transitional identity as a facilitator of organizational identity change during a merger[END_REF][START_REF] Drori | One out of many? Boundary negotiation and identity formation in postmerger integration[END_REF][START_REF] Maguire | Citibankers' at Citigroup: a study of the loss of institutional trust after a merger[END_REF]. Aldrich and Herker (1977) describe boundary spanning in organizations in terms of information processing -to selectively interpret, filter, summarize, and facilitate the transmission of information; in other words "uncertainty absorption" (p. 219). More recently, [START_REF] Schotter | Boundary spanning in global organizations[END_REF] offers a multidimensional definition of boundary spanning, as "a set of communication and coordination activities performed by individuals within an organization and between organizations to integrate activities across multiple cultural, institutional and organizational contexts" (p. 404). In bridging and mediating across one or multiple contexts, boundary spanners overcome the 'us and them' mentality, thus allowing trust to develop [START_REF] Schotter | Boundary spanning in global organizations[END_REF][START_REF] Yip | The nexus effect: when leaders span group boundaries[END_REF].

Boundary spanners can perform a specific function or responsibility such as public relations, union representation, acquiring/disposing resources and relationship management (Aldrich & Herker, 1977), or improvise his/her actions to get the job done [START_REF] Yagi | Boundary work: An interpretive ethnographic perspective on negotiating and leveraging cross-cultural identity[END_REF]. Boundary spanning contexts include expatriates (Au & Fukuda, 2002), bicultural managers [START_REF] Yagi | Boundary work: An interpretive ethnographic perspective on negotiating and leveraging cross-cultural identity[END_REF], and global vendor-client partnerships [START_REF] Søderberg | Boundary Spanners in Global Partnerships: A Case Study of an Indian Vendor's Collaboration with Western Clients[END_REF].

In M&As, [START_REF] Lander | Boarding the aircraft: Trust development amongst negotiators of a complex merger[END_REF] studied the Air France-KLM merger where chief negotiators acted as "boundary role persons" [START_REF] Currall | Measuring trust between organizational boundary role persons[END_REF], enabling interorganizational collaboration and trust. This contrasts with [START_REF] Drori | One out of many? Boundary negotiation and identity formation in postmerger integration[END_REF] analysis into the process of boundary creation/re-creation in shaping the post-merger identity of an organization, and allowing managers and personnel to maintain key aspects of their previous identities. Anecdotal evidence suggests that leaders engage in boundary spanning during post-acquisition integration, for example, in the Lenovo-IBM merger [START_REF] Stahl | Lenovo-IBM: Bridging Cultures, Languages, and Time Zones-Integration Challenges (B)[END_REF][START_REF] Yip | The nexus effect: when leaders span group boundaries[END_REF].

Outstanding boundary spanning leaders constantly engage in internal (team) and external (organization) oriented initiatives for their teams [START_REF] Druskat | Managing from the boundary: The effective leadership of self-managing work teams[END_REF]. From studying the interactions between external leaders and their team members and managers in a large manufacturing firm, Druskat and Wheeler inductively categorized eleven boundary spanning behavior into four functional clusters. Table 1 summarizes this typology.

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RESEARCH METHODS AND DATA

Empirical design and context

This research applies comparative case-study research and focuses on trust development in new subordinate-leader relationships arising from M&As in multicultural emerging economies. Case study research is particularly suited for in-depth probing into complex concepts such as trust and culture, which quantitative approaches cannot easily reveal [START_REF] Yin | Case study research: Design and methods[END_REF]. I compare a domestic and a cross-border acquisition from Malaysia's financial services industry.

Malaysia is multiethnic, multifaith, and multilingual. There are three main ethnic groups (Bumiputra-comprising Malay and other indigenous groups-63%, Chinese 25%, and Indian 7%), and four main religions (Muslim 61%, Buddhist 20%, Christian 9%, Hindu 6%; Malaysian Department of Statistics, 2010). Generally the Malays are Muslims, the Chinese are Buddhists or Christians, and the Indians are Hindus, Muslims or Christians. Most Malaysians are bilingual in Bahasa Malaysia and English, the national and business languages, but many are trilingual (in Chinese or Indian languages) or quadrilingual [START_REF] Fontaine | Cross-cultural research in Malaysia[END_REF].

The financial services industry was selected to control for environmental variation and a transparently observable phenomenon of interest [START_REF] Eisenhardt | Building theories from case study research[END_REF]. The Malaysian financial industry comprises banking intermediaries, insurance firms and capital market intermediaries (IMF, 2014). As Malaysia's seventh largest sector, it accounts for 4.5% of nominal GDP (IHS, 2016) and has undergone substantial consolidation and rationalization subsequent to the 1997-1998 Asian financial crisis (IMF, 2014). In 2015, the financial industry ranked fourth in terms of emerging economies' M&A activity (Thomson Reuters, 2016) and accounted for 19% of global M&A volume (Bloomberg, 2016). Further, I had worked in the Malaysian financial services industry and am familiar with its characteristics.

Case selection and description

This paper compares a domestic M&A "DoeMez" versus a South African acquisition of a Malaysian firm "Cross". Purposive sampling was applied during case selection and care was taken to match them on contextual appropriateness [START_REF] Poulis | The role of context in case study selection: An international business perspective[END_REF][START_REF] Yin | Case study research: Design and methods[END_REF].

Given South Africa's cultural diversity and history of apartheid, the two cases provide an intriguing comparison of cross-cultural trust between acquired-firm and acquirer personnel.

In Malaysia, the Bumiputra have enjoyed special rights since 1971 including in employment, resulting in sensitive although peaceful ethnic relations [START_REF] Bhopal | Ethnicity as a management issue and resource: Examples from Malaysia[END_REF][START_REF] Haque | The role of the state in managing ethnic tensions in Malaysia: A critical discourse[END_REF]IHS, 2016). South Africa introduced a comparable majority-favoring regime in 1998 to eliminate post-apartheid employment discrimination against the 91% black population [START_REF] Thomas | Employment equity in South Africa: Lessons from the global school[END_REF][START_REF] Lee | Affirmative Action in Malaysia and South Africa: Contrasting Structures, Continuing Pursuits[END_REF]. Bumiputra and blacks are increasingly represented in high-level occupations, mainly in the public sector [START_REF] Lee | Affirmative Action in Malaysia and South Africa: Contrasting Structures, Continuing Pursuits[END_REF].

Cross is a Malaysian firm acquired by "SAF", a South African multinational corporation with operations in approximately 40 emerging economies. DoeMez is a domestic acquisition of two sister firms (Mez1 and Mez2) which were then merged with two subsidiaries of the acquirer Doe to create DoeMez1 and DoeMez2. The acquirer and its subsidiaries are majority controlled by GLCs (IMF, 2014) and employ 80% Malay personnel, whereas the acquired firms were founded by an ethnic Chinese entrepreneur, had "Chinaman entrepreneurial" culture, and employed 80% ethnic Chinese personnel. iii Table 2 summarizes the main features of the cases.

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Both acquisitions were friendly deals, had similar motives (business expansion and scaling up), involved experienced acquirers, and were completed approximately two years prior to data collection. To gain access to the firms, personalized invitation letters were sent to the CEOs of the acquired firms and their acquirers/parent firms, together with an offer to share my findings with them. The participating firms and informants were promised complete confidentiality and anonymity.

Data collection

The analysis was based mainly on 35 semi-structured interviews with TMT, senior and middle managers, and supplemented by 2 conference calls with dealmakers, participatory observations, and archival data.

To capture new acquired-firm/acquirer subordinate-acquirer/acquired-firm leader relationships arising from the M&A, I sought individuals who had reported to different managers pre-and post-M&A. The interviewees were selected by their firms-23 from DoeMez and 12 from Cross-and originated from the acquired firm, acquirer, or were 'neutrals' recruited during the focal M&As, as detailed in Table 3. The interviews lasted an hour on average, transpired face-to-face except for one (by conference call), and were recorded with permission and transcribed. All communication was in English except for local expressions sprinkled in some interviews.

- ----------------------------------------- ------------------------------------------The interview questions covered: organizational conditions around the time of the acquisition including the pre-acquisition mood at the individual's firm and the impact of the acquisition on the participant; post-acquisition working relationships with his/her new direct manager and subordinates; and, interactions with the new TMT. An interview protocol was developed beforehand and refined through pilot interviews with 7 Malaysians who were either M&A legal advisors or professionals with M&A experience.

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Due to practical constraints, the interviews were conducted in a tandem arrangement: DoeMez in mid-November 2016, then Cross in late November/mid-December 2016. At DoeMez especially, 23 interviews in 5 consecutive days left little time for reflection.

However, since the interviews were held at the firms' premises, I was able to engage in informal conversations and observe the work environment and personnel interactions.

Further, I participated in one of Cross's day-long workshops in December 2016 when the acquirer's values and culture were introduced. The workshop was facilitated by an external consultant and attended by approximately 100 Cross personnel, its TMT, and 2 senior executives from the acquirer's HQ.

Data analysis

My analysis applied abduction which is partly deductive (theory-driven) and partly inductive (data-driven) [START_REF] Timmermans | Theory construction in qualitative research: From grounded theory to abductive analysis[END_REF][START_REF] Welch | Theorising from case studies: Towards a pluralist future for international business research[END_REF]. Abduction facilitates the discovery of new variables and relationships by moving back-and-forth between framework, data sources and analysis [START_REF] Timmermans | Theory construction in qualitative research: From grounded theory to abductive analysis[END_REF]. Abduction has been used in studies on boundary spanning [START_REF] Søderberg | Boundary Spanners in Global Partnerships: A Case Study of an Indian Vendor's Collaboration with Western Clients[END_REF][START_REF] Yagi | Boundary work: An interpretive ethnographic perspective on negotiating and leveraging cross-cultural identity[END_REF], M&As [START_REF] Monin | Giving sense to and making sense of justice in postmerger integration[END_REF][START_REF] Reynolds | The international experience in domestic mergers-Are purely domestic M&A a myth[END_REF], and international business [START_REF] Barron | Exploring the performance of government affairs subsidiaries: A study of organisation design and the social capital of European government affairs managers at Toyota Motor Europe and Hyundai Motor Company in Brussels[END_REF][START_REF] Maitland | Managerial cognition and internationalization[END_REF].

Initially, I built individual case descriptions by triangulating the multiple sources of evidence [START_REF] Graebner | Caveat venditor: Trust asymmetries in acquisitions of entrepreneurial firms[END_REF]. Next, the interview transcripts were analyzed iteratively in groups: acquirer, acquired-firm and neutral managers; TMT and department heads vs. managers; and, subordinate-leader dyads where possible. For DoeMez's transcripts, withinand between-division analysis was also conducted since its integration involved three 'standards': one division followed Doe's practices, a second division followed Mez's practices, while the third division adopted a mix of both. Multiple examples of TMT and manager boundary spanning were identified. Finally, I categorized the examples according to [START_REF] Druskat | Managing from the boundary: The effective leadership of self-managing work teams[END_REF] typology and identified the boundaries spanned-to reveal the intent or purpose behind each boundary spanning behavior, for clearer linkage to trust development.

FINDINGS

The post-acquisition integration approaches of DoeMez and Cross is described first, followed by the boundary spanning actions of the acquirer and acquired-firm managers and my interpretation of how this behavior facilitated subordinate-leader trust development.

Integration approaches

Cross' integration by SAF corresponds with the light-touch integration approach [START_REF] Liu | Light-Touch Integration of Chinese Cross-Border M&A: The Influences of Culture and Absorptive Capacity[END_REF] of Asian acquirers [START_REF] Kale | Don't integrate your acquisitions, partner with them[END_REF][START_REF] Liu | Light-Touch Integration of Chinese Cross-Border M&A: The Influences of Culture and Absorptive Capacity[END_REF][START_REF] Marchand | Do All Emerging-Market Firms Partner with Their Acquisitions in Advanced Economies? A Comparative Study of 25 Emerging Multinationals' Acquisitions in France[END_REF]. In DoeMez's case, the integration approach resembles symbiosis [START_REF] Haspeslagh | Managing acquisitions: Creating value through corporate renewal[END_REF]. Table 4 compares their integration approaches.

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Boundary spanning behaviors

My analysis identified boundary spanning in the domestic and the cross-border acquisition cases, by TMT and managers of both the acquirers and acquired firms. The boundary spanning behaviors are described below according to [START_REF] Druskat | Managing from the boundary: The effective leadership of self-managing work teams[END_REF] clusters.

Feedback on the behaviors is provided where possible. Horizontal, vertical, stakeholder, demographic, and geographic boundaries [START_REF] Palus | Boundary-Spanning Leadership in an Interdependent World[END_REF] were spanned, representing national, intra-national, organizational and functional culture differences. Tables 5 and6 show boundary spanning examples from Cross and DoeMez, the boundaries and cultural differences spanned, and trust attributes.

- --------------------------------------------------- --------------------------------------------------- Cross managers' social and political awareness spanned all five boundaries and differences in national, organizational, functional and personal cultures (see Table 5). A senior manager enthused: "[SAF are] totally different from shareholders who are American or British. They're very respectful of local cultures and very keen on sharing their knowledge… They don't dictate that they know better than we do, which is a total contrast to where I come from." DoeMez manager's social and political awareness spanned all boundaries, organizational culture differences and especially intra-national culture differences. A Mez leader said, "I go the extra mile to make sure the [Doe] colleagues feel very welcome."

Particular attention was paid to cater for halal food preferences at work, on business trips, annual dinners, and a company trip overseas. Chinese colleagues were reminded eat nonhalal food outside the workplace. Personnel were instructed to speak in English and the national languages only during meetings, for everyone to understand. One senior manager commented, "I heard some departments had [a language-related] problem, [like] immediate separation between [Doe and Mez people who] tend to not mingle [and] seldom talk... There's quite a lot of staff in [X] Department who were from Chinese schools. Their main language… is Cantonese and Mandarin... Sometimes in meetings… it's an issue." Another manager, whose team spanned two locations, introduced a regular weekly conference call and persevered against Asian reticence to seek team members' negative feedback. Other examples are provided in Table 6.

In developing subordinate trust in leaders, Cross leaders showed transparency and willingness to span all boundaries, and national, intra-national and organizational culture differences. Group TMT visited Cross' offices four times in the first eighteen months from the acquisition announcement. Personnel were informed of SAF's intentions and future plans, which dispersed a lot of uncertainty. Managers received regular CEO and CFO performance updates to disseminate in their departments/units. In his first townhall with Cross personnel, the CEO presented his short-term goal and personal interest in being assigned to Malaysia. The CEO's trust-building approach is detailed in Table 5. DoeMez's leaders developed subordinate trust across intra-national and organizational culture differences. Like Cross, this was initiated from early post-acquisition integration and a personal approach was used sometimes (see Table 6).

Cross and DoeMez managers demonstrated their care for subordinates in numerous examples with noteworthy examples in Tables 5 and6. Other caring behavior at DoeMez included a department head covering for subordinates who had exceeded their transaction limits, and a senior manager's insistence that the whole team leaves work by 6:30 pm.

Subordinate-leader bonding at DoeMez and Cross transpired over coffee, drinks and personal chats. Two DoeMez senior managers also organized weekly/daily lunches and outings for within-team bonding.

Cluster 2: Scouting

Scouting involves seeking information within the organization to clarify the manager's understanding or team and organizational needs, and to solve problems. This second function of managerial boundary spanning includes a set of three behaviors: seeking information from managers, peers and specialists, diagnosing subordinate behavior, and investigating problems systematically.

Seeking information helped to span national, intra-national and organizational culture differences at both Cross and DoeMez, as evidenced from the examples pertaining to incoming expatriates and the expatriate CEO's efforts to develop sensitivity to Malaysian cultural nuances (Table 5), and solving a religion-related problem at DoeMez (Table 6).

Subordinate behavior diagnosis spanned mainly vertical boundaries and, organizational culture differences at Cross and intra-national cultural differences at DoeMez (Tables 5 and6).

Cross and DoeMez managers investigated problems involving horizontal and vertical boundaries. At Cross, this was related to 'silos' where subordinates performed their functions with very little understanding of what happened in other areas of the business. Table 5 provides an example where this where intra-national and functional culture differences were involved. A DoeMez department manager recounted a similar problem when personnel who withhold information, while another manager mediated such a situation involving intranational culture differences (Table 6).

Cluster 3: Persuading

Persuading involves managers seeking resources from within the organization to support their teams' needs, and influencing subordinates' priorities to support organizational objectives.

Successful persuasion enables a manager to align his/her team's objectives with organizational objectives. The data reveals that DoeMez leaders influenced their subordinates more than Cross leaders.

In seeking organizational-level resources for their teams, Cross managers spanned mainly stakeholder boundaries with its two shareholders and Board of Directors. The CEO had monthly engagements and weekly video conferences with various people at HQ, while department managers had a dedicated support person at HQ (e.g., IT coordinator for the IT head, HR coordinator for the HR head). Cross managers were formally and informally linked with Group TMT, e.g., unit heads who also reported to the group's department heads, or the COO and his department manager who liaised regularly with the Group COO. The CEO also recognized the potential of Cross' minority shareholder and its deep local market knowledge (see Table 5). DoeMez managers spanned vertical and horizontal boundaries in seeking their leaders to intervene on critical occasions. Table 6 presents two examples including one with organizational and intra-national culture differences in the attitudes of certain subordinates.

In terms of influencing subordinates, Cross managers did so less than DoeMez managers, perhaps reflecting its light-touch integration approach (cf. DoeMez's symbiotic approach). One Cross senior manager said, "[The TMT] don't bulldoze things. They will [talk to everybody] and see people's acceptance. When a few fellows don't accept, they will try to convince the persons." The TMT encouraged subordinates to span organizational and national culture differences by debating and differing in opinion from their leaders. For example: "I am used to seriously being challenged at [HQ]… whereas here when I make statements, I must say 'You are allowed to disagree. Please disagree if you feel so, talk to me, tell me this is a wrong assumption or this is a wrong statement or whatever.'" The TMT concurred that their people were respectful and uncomfortable with discord, reflecting their Asian culture. Nevertheless, two expatriates noted that subordinates, from watching the TMT challenge one another, began doing so themselves. DoeMez managers influenced their subordinates at organizational-and team-levels through the organization's four core values which were enacted from the outset of the M&A.

First, the core values shaped changes in culture and thought processes across the organization. As one dealmaker/leader explained, "We initiated [culture change] by the new brand. We launched an idea behind that brand, these disciplines, this other culture we want to emulate... We started building new thought processes." Second, the core values guided managers to focus/refocus their teams. For example, one leader reminded his team, "No, no, our core value is to collaborate. Guys, we need to collaborate…" and "We need to be entrepreneurial. That means we need to think how to solve the problem." The core values spanned organizational and intra-national culture differences as seen in the same manager's comment: "Without the core values, everybody will define their own… I think without that, this merger would be a nightmare. I honestly tell you that."

Department heads influenced their subordinates to accept incoming members from the acquirer/acquired firm and fuse horizontal boundaries. One entire team was instructed to treat the newcomers well regardless of the circumstances and to refer back to the manager if any issue arose. Another manager instructed his unit heads similarly. Managers also emphasized the amount of time the two sides would spend together and the need for a pleasant work atmosphere. One subordinate remarked that human integration was "very well-driven…

We're all no longer ex-Mez or ex-Doe people, we're all DoeMez."

Cluster 4: Empowering

Empowering involves delegating authority to subordinates and coaching to improve subordinates' capabilities. This final function of managerial boundary spanning includes a set of three behaviors that span horizontal, vertical and demographic boundaries: delegating authority, flexible on team decisions, and coaching subordinates. My data reveals that the most frequent empowering behavior was coaching subordinates, with some coaching actions implemented through the HR departments.

Delegating was observed in DoeMez and Cross. One DoeMez department head spanned organizational and intra-national culture differences through delegation: "When I first took [the Doe people] in, they weren't comfortable doing a lot of things... They weren't given a lot of freedom in the old days… I found that a lot of them are quite capable... They did make a lot of mistakes and I do hold them accountable for it, but [no] penalties...'" For one Cross expatriate, delegating authority overlaps with being flexible on team decisions behaviors: "If [you] have to change approaches, then we change if it makes sense...

[The initial approach is] not necessarily right. It's only right if it makes sense to you also."

The leader explained, "They'll say something works like this. Then I'll ask 'Why?'… 'Do you think it's right?'… I'm starting to ask questions [but] not telling them what to do." I did not observe any flexible on team decisions behavior in DoeMez.

Subordinate coaching, the most prominent behavior in this cluster, was implemented both through the HR departments and independently. First, HR mobilized and trained managers to be relays: Cross managers were coached to coach their subordinates and thus support them more effectively, while DoeMez senior managers were trained to counsel their teams on how to deal with a different organizational culture, new processes and new workflows. If each HR department had provided support to personnel on an organizational level, more resources would have been required (e.g., more HR personnel, outsourcing). One Cross expatriate introduced a 360-degree feedback system through the HR department, where an individual's leader, peers, and direct subordinates provide confidential and anonymous feedback on "This is what I'd like to see more of you, in…" Second, as a personal initiative, a Cross expatriate coached department managers who had been working in silos on the impact of this behavior on team outcome, and how to deliver as a team. At DoeMez, several managers gave indirect answers to subordinates' questions, for example, a department head: "I say 'I want to hear from you first. Come back to me, say, in

2-3 hours' time and see what you have.'… I put pressure to them to think through properly…

Otherwise they will never learn. Always remember, don't give the man fish all the time. You must teach him how to fish."

DISCUSSION

The objective of this study was to explore how trust develops in new subordinate-leader relationships in the M&A nucleus, amidst the uncertainty and cultural differences of integration. Three bodies of literature are connected to understand the trust development process: M&A, boundary spanning, and trust. The paper's main contribution is to posit that boundary spanning mitigates the uncertainty and cultural differences arising from postacquisition integration. Managerial boundary spanning overcame the 'us and them' mentality between acquirer/acquired-firm subordinates and acquired-firm/acquirer leaders, reduced uncertainty and cultural differences, and thus catalyzed subordinate-leader trust development. Focusing on a domestic and a cross-border acquisition of Malaysian firms, my systematic analysis reveals that both acquirer and acquired-firm managers engaged in boundary spanning behavior. The managers ranged from TMT, integration managers [START_REF] Teerikangas | Integration managers' value-capturing roles and acquisition performance[END_REF] and middle managers in diverse functions. This indicates the widening locus of M&A leadership (Graebner, 2004;[START_REF] Junni | The role of leadership in mergers and acquisitions: A review of recent empirical studies[END_REF] and suggests more widespread managerial influence for smoother and more successful integration.

Second, this research extends the ambit of managerial boundary spanning beyond the pre-M&A negotiation phase [START_REF] Lander | Boarding the aircraft: Trust development amongst negotiators of a complex merger[END_REF] to post-acquisition integration, and adds evidence that effective leaders engage in boundary spanning behavior [START_REF] Druskat | Managing from the boundary: The effective leadership of self-managing work teams[END_REF]. This paper also complements the process perspective of M&As [START_REF] Jemison | Corporate acquisitions: A process perspective[END_REF] and elucidates on the temporality of integrative actions. Birkinshaw et al.'s (2000) influential study argues for a two-phased implementation of effective integration. First, human integration is emphasized while the acquirer and acquired units achieve acceptable performance, and then revisiting task integration so that the existing success of human integration facilitates task integration across units. Other researchers suggest closer interrelation between these elements of integration. [START_REF] Froese | Integration management of Western acquisitions in Japan[END_REF] find that human integration and organizational integration occur simultaneously, from the beginning of post-acquisition integration. [START_REF] Teerikangas | Structure first! Temporal dynamics of structural and cultural integration in cross-border acquisitions[END_REF] observe that cultural integration begins once structural integration is underway, as long as both are implemented in complementarity. In this study, DoeMez implemented extensive organizational integration and human integration rapidly, similar to the Renault-Nissan acquisition [START_REF] Froese | Integration management of Western acquisitions in Japan[END_REF]. In contrast, SAF selectively implemented Cross' organizational integration over time and to a lesser extent, with human integration from the third year post-acquisition. Both deals are considered successful, as are SAF's other similarly integrated South-South acquisitions.

Third, the study's focus on South-South acquisitions extends M&A scholarship which is heavily focused on acquisitions to and from developed economies [START_REF] Lebedev | Mergers and acquisitions in and out of emerging economies[END_REF], and contributes to the literature on the complexities of multilingual societies in M&As [START_REF] Cuypers | The effects of linguistic distance and lingua franca proficiency on the stake taken by acquirers in cross-border acquisitions[END_REF][START_REF] Dow | The effects of within-country linguistic and religious diversity on foreign acquisitions[END_REF][START_REF] Kroon | Explaining employees' reactions towards a cross-border merger: The role of English language fluency[END_REF]. DoeMez exposes that domestic rather than cross-border M&As can be more challenging to integrate [START_REF] Véry | A cross-national assessment of acculturative stress in recent European mergers[END_REF]1997), especially when the intra-national culture differences of a multicultural emerging economy are considered. The language diversity among Malaysian personnel was more problematic for DoeMez than Cross and there was no lingua franca for all DoeMez personnel. Malaysian personnel's proficiency in English varies significantly, particularly in the younger generation [START_REF] Darmi | English language in the Malaysian education system: Its existence and implications[END_REF][START_REF] Yin | Case study research: Design and methods[END_REF]. Some ethnic Chinese personnel were not sufficiently fluent in English or Bahasa, despite the possibility of using both languages in meetings. Malaysian Chinese can be differentiated by their schooling: those with Chinese-school education relate strongly to traditional Chinese values, while those with non-Chineseschool education identify weakly with such values [START_REF] Fontaine | Cross-cultural research in Malaysia[END_REF][START_REF] Ong | Chinese ethnicity: Its relationship to some selected aspects of consumer behaviour[END_REF]. This paradoxical finding draws attention to the intricacy of cultural challenges in M&As [START_REF] Teerikangas | The culture-performance relationship in M&A: From yes/no to how[END_REF], while extending our knowledge of the differences between integrating domestic and cross-border acquisitions [START_REF] Bris | The value of investor protection: Firm evidence from crossborder mergers[END_REF][START_REF] Gregory | Do cross border and domestic acquisitions differ? Evidence from the acquisition of UK targets[END_REF][START_REF] Reynolds | The international experience in domestic mergers-Are purely domestic M&A a myth[END_REF].

More broadly, my research adds to the literature on multilingual organizations including multinational corporations [START_REF] Bordia | Employees' willingness to adopt a foreign functional language in multilingual organizations: The role of linguistic identity[END_REF][START_REF] Brannen | The multifaceted role of language in international business: Unpacking the forms, functions and features of a critical challenge in MNC theory and performance[END_REF][START_REF] Feely | Language management in multinational companies[END_REF], and the conversation that "context matters". The Malaysian context diversifies the geographic focus of emerging market studies away from China [START_REF] Jormanainen | International activities of emerging market firms[END_REF] and offers tentative insights to advance Western-developed theories in strategy and management [START_REF] Jormanainen | International activities of emerging market firms[END_REF][START_REF] Wright | Strategy research in emerging economies: Challenging the conventional wisdom -Introduction[END_REF][START_REF] Xu | Linking theory and context: 'Strategy research in emerging economies' after Wright et al[END_REF]. The findings support the argument that national cultures are more heterogeneous than homogeneous [START_REF] Shenkar | Cultural distance revisited: Towards a more rigorous conceptualization and measurement of cultural differences[END_REF][START_REF] Taras | Does country equate with culture? Beyond geography in the search for cultural boundaries[END_REF][START_REF] Tung | The cross-cultural research imperative: The need to balance crossnational and intra-national diversity[END_REF][START_REF] Tung | Beyond Hofstede and GLOBE: Improving the quality of cross-cultural research[END_REF].

Fourth, the paper contributes to trust scholarship by diversifying from its reliance (Fulmer & Gelfand, 2012) on WEIRD samples (Western, educated, industrialized, rich, and democratic;[START_REF] Henrich | Most people are not WEIRD[END_REF]. While Mayer et al.'s (1995) model has become one of the most well-known and influential trust models, it remains unclear whether each component of trustworthiness (ability, benevolence, integrity) is equally as important in trust outcomes [START_REF] Burke | Trust in leadership: A multilevel review and integration[END_REF]. My analysis of the linkage between boundary spanning and subordinate-leader trust shows that benevolence and integrity are more prominent than ability, for facilitating Malaysian subordinate-leader trust in M&As. This complements [START_REF] Poon | Effects of benevolence, integrity, and ability on trust-in-supervisor[END_REF] findings on the significance of benevolence for Malaysian personnel to trust their leaders. The precedence of affect-based trust over cognition-based trust is consistent with other emerging economies where personal relationships are important, e.g., China [START_REF] Chua | Guanxi vs networking: Distinctive configurations of affect-and cognition-based trust in the networks of Chinese vs American managers[END_REF][START_REF] Jiang | Effects of cultural ethnicity, firm size, and firm age on senior executives' trust in their overseas business partners: Evidence from China[END_REF], Singapore and Turkey [START_REF] Tan | Understanding interpersonal trust in a Confucian-influenced society: An exploratory study[END_REF][START_REF] Wasti | Cross-cultural measurement of supervisor trustworthiness: An assessment of measurement invariance across three cultures[END_REF].

The importance of building personal relationships was evident in DoeMez and Cross where informal social activities facilitated bonding between subordinates, peers and leaders.

Managerial implications

This research shows that a wider leadership can influence and smoothen M&A processes, outcomes and cultural differences. Regardless of their hierarchical positions, managers from both the acquirer and acquired firm can contribute to reducing post-acquisition uncertainty among personnel, thereby facilitating subordinate-leader trust during integration. The managers should be empowered to play a more central role in human integration from early post-acquisition integration. For example, through awareness-building workshops on where boundaries and cultural differences may lie, with illustrative boundary spanning behaviors.

Moreover, since boundary spanning behaviors are often improvised by managers in doing their jobs [START_REF] Yagi | Boundary work: An interpretive ethnographic perspective on negotiating and leveraging cross-cultural identity[END_REF], integration and HR managers should develop ways to formalize and share such experiences with other managers in the organization so that larger scale benefits can be drawn. This research highlights how language diversity can be an issue not only cross-border acquisitions but in domestic acquisitions in a multicultural society. Boundary spanning behaviors to address this divide includes seeking colleagues to translate or summarize the essential points, and cascading information downwards through department/unit managers so that subordinates have a more accessible point of reference for clarification. In the longer term, personnel should have training and opportunities to overcome their "language anxiety" [START_REF] Darmi | English language in the Malaysian education system: Its existence and implications[END_REF][START_REF] Yin | Case study research: Design and methods[END_REF].

Limitations and future research directions

The study's findings should be interpreted caution. Despite exposing the positive effects of managerial boundary spanning in post-acquisition integration, further research is required to ascertain the conditions under which boundary spanning influences successful integration. First, the analysis compares two M&A case studies within a single industry in Malaysia. Malaysia falls under [START_REF] Schwartz | A theory of cultural value orientations: Explication and applications[END_REF] South Asia cluster of cultural value orientations, which characterize hierarchical and collective societies. Future studies should examine M&As in the same cluster (e.g., Indonesia, India), in other multicultural emerging economies (e.g., Turkey, Nigeria, Chile), as well as vertical acquisitions and acquisitions of financially-troubled firms. Moreover, the integration approach adopted may have a bearing on the extent of boundary spanning. It would be useful to study not only other M&As applying symbiosis and light-touch integration like DoeMez and Cross, but also preservation and absorption [START_REF] Haspeslagh | Managing acquisitions: Creating value through corporate renewal[END_REF]. Second, the managerial boundary spanning behaviors may be related to the individual's job function, level of experience, seniority in the organization, and previous acquisition experience. To analyze this requires a larger sample.

Third, the study relied mostly on interview data to analyze trust development retrospectively.

Despite my efforts to reduce social desirability bias, some interviewees may not have been entirely forthcoming since they were selected by their firms. Ethnographic research or a longitudinal study would be more robust.

Looking beyond, it would be fruitful to enquire into how boundary spanning affects trust between peers during post-acquisition integration, and trust between the acquired firm and HQ personnel. The linkage between boundary spanning, interpersonal trust and identity formation is another interesting research area. I look forward to more active scholarly pursuit along this path.

  -INSERT TABLES 5 AND 6 ABOUT HERE -

-

  Cluster 1: RelatingRelating involves building relationships within the team and organization while showing social and political awareness. This first function of managerial boundary spanning includes a set of three behaviors: social and political awareness, building subordinate trust in leaders, and caring about subordinates.

TABLE 1 : Typology of boundary spanning actions

 1

		(adapted from Druskat & Wheeler, 2003)
	Function	Behavior	Examples
	Relating	Social and political	Building rapport by: understanding the
		awareness	concerns and interests of specific groups,
			appreciating power relationships, politicking
		Build subordinate trust in	Showing that the leader is reliable, fair and
		leaders	honest and focused on the team's best interests
		Care about subordinates	Caring actions towards a team or individual
	Scouting	Seek information from	Making the effort to go beyond the boundary
		managers, peers and	spanner's knowledge or understanding by
		specialists at organizational-	referring to someone in the organization
		level
		Diagnose subordinate	Analyzing a subordinate or team's verbal or
		behavior	nonverbal behavior to understand their needs
		Investigate problems	Solving a problem by breaking it down,
		systematically	systematically tracing the cause of a problem
	Persuading	Obtain organizational	Persuading external groups so that they assist
		support for their teams	or support the needs of the leader's teams
		Influence subordinates	Encouraging subordinates to make choices
			that support team or organizational goals
	Empowering Delegate authority	Giving responsibility, control or authority to
			subordinates
		Flexible on team decisions	When the leader is open-minded about how
			subordinates fulfil a role, assignment, etc.
		Coach subordinates	Developing subordinates' knowledge and
			skills

TABLE 2 : The research cases

 2

	Cross	DoeMez

TABLE 3 : Dealmakers and interviewees

 3

	Position / Firm-of-origin	Cross	DoeMez
	Dealmakers Acquirer	2 2	3 2 a
	Acquired firm	-	1
	Interviewees	12	23
	TMT Acquirer	4 b	2 c
	Acquired firm	-	3
	Neutral	-	1
	Department heads
	Acquirer	-	3
	Acquired firm	4	2
	Neutral	3	1
	Other managers
	Acquirer	-	5
	Acquired firm	1	4
	Neutral a Includes a TMT.	-	2

b Non-Malaysians. c Includes a non-Malaysian.

TABLE 4 : The integration approaches

 4

		Cross	DoeMez
	Integration	Financial controls; HR, operations	Integration of business activities,
	and	and processes were improved or	operations, policies, procedures and
	controls	cleaned up	processes. 3 offices were converged
			into 2
	Corporate	Former shareholder's name was	Launched "DoeMez" (new name, logo,
	rebranding	removed; Cross endorsed as "A	identity, image); new corporate HQ
		member of the SAF Group"
	TMT	4 expatriates from SAF	Acquirer, acquired firm and neutral
			TMT
	Cultural	Initiated during third year post-	None
	integration	acquisition
	Integration
	approach;
	Speed	Light-touch integration; Slow	Symbiosis; Fast

TABLE 5 :

 5 Cross boundary spanning examples(HOD = head of department; SM = senior manager)

		Boundary	Cultural difference Trust attribute Selective quotes
	Relating behaviors
	Social and political	Vertical,	National,	Benevolence,	[P]art of my job is… to cushion off all [issues and]… complement
	awareness	horizontal,	organizational	integrity,	my staff… so everyone works in harmony [with the boss] or SAF…
		stakeholder		ability	I'll do a lot of [consulting], very frequent advice to my staff that this
					is how [the key people] work. (HOD)
		Vertical,	National,	Ability,	[The CFO] is trying to [develop more informal interaction with HQ]
		stakeholder,	organizational	integrity,	through conf calls, updates… We always have this difficulty to align
		geographic		benevolence	[their] understanding of certain topics because their environment,
					perspective, legal and operating environments are different. (SM)
		Horizontal,	Personal,	Benevolence,	Introverts… tend to be more comfortable on email. Very often [after
		vertical	functional	integrity,	a] meeting,… I'll email [a summary]… Extroverts are normally on
				ability	their feet and more direct [but] you have IT people, [actuaries and
					accountants] who are normally introverts. (Expatriate)
	Build subordinate trust	Vertical,	Intra-national,	Benevolence,	You will build trust easier with your senior people than the rest of
		horizontal,	national	integrity,	the company [because of more frequent face-to-face interaction].
		demographic		ability	The rest of the company will be my communications… On [festive
					occasions] I send a nice message… You must do those things
					repeatedly, then people will see 'He genuinely means he embraces
					diversity, he doesn't favor any specific groups.' When we have a
					Divali celebration, I dress like an Indian and those types of things.
					People like that. They start thinking 'Yeah, [he] can walk in my
					shoes, I can trust him.' (CEO)
	Care about subordinates	Vertical	Personal	Benevolence,	People must come and tell me [when problems arise]… then try to
				integrity	fix it themselves… I concentrate on the fixing, not on the blame.
					(Expatriate)

I would draft a speech and say to my secretary-she's a Muslim-and my HR person [who] is Chinese, 'Here is my speech. Please look at it. Am I using the wrong words? Have I said the wrong thing?'...

TABLE 6 :

 6 DoeMez boundary spanning examples (HOD = head of department; SM = senior manager) People no longer should have that notion of 'I used to manage client A, it's my client'. Today, client A is the firm's clients and is being serviced by a team of people from Doe and Mez... By doing that we avoided a fight, people trying to fight for accounts, for clients, because naturally people want the bigger accounts. (HOD) lot of time trying to tell my acquiree employees that… certain aspects of [their] perception [of our corporate culture]… may not be the reality… Obviously we are a government-linked company [with] Malay mentality and… mindset… What can I dispel? … I can certainly dispel that the management in Doe does not have interference of any sort from the government shareholding that we have, that we are not a racial-biased entity, that we are predominantly merit-based. (Leader) to explain… and remind [my team] what we're going through… [Doe people] have to learn [Mez's] system and now 'I have to lead you.' (DoeMez HOD) The big boss]… was really pushing for [the seller] to accept Doe's bid… because he knows that [if another bidder] were to acquire us, then most of the staff will be jobless. (DoeMez HOD) Muslim [senior management] colleagues together and we brainstormed [on the religion-related problem]… I said 'These are the issues that we have. How should we manage it?' … [The Head of Doe] said, 'Let me talk to [the Muslim staff].' … He helped ease the whole process. (Leader) Some of my people], they are very hierarchical 'I'm the boss, you guys take instructions'… [Other people] are waiting for instructions [or] order-takers. [Another] set of people [are] cookie-cutters,… only can do one thing... [and no more]. (HOD) You have pockets of people who… hold [the] organization to ransom. They know but… don't volunteer the information. For example, 'do we need to do this?' They will say yes. But they never tell you the consequence… I said [to my team], 'You need to probe them further to make sure we don't [miss any details].' (HOD) Two subordinates doing the same job and withholding information from each other: The Chinese guy [from Mez] asked the Malay guy [from Doe] 'Have you done this...?' This Malay guy [felt] 'Why do I have to report to you?'... Then same thing happened [the other way around]. (Manager) [the Group COO] and give her heads-up how to fix the problem… She gave me a lot of air-cover. (HOD) [the] different [corporate] culture [and personal attitude] that I have a problem [with in some of my team]… I discussed it with [my boss]… I think he did talk to the team. Things are better now. (SM)We initiated [culture change] by the new brand. We launched an idea behind that brand, these disciplines, this other culture we want Boundary Cultural difference Trust attribute Illustrative quotes demographic to emulate... We started building new thought processes. (Leader) You have me telling the team that 'you better treat [the Mez] people nicely; I don't care what they do to you, you just treat them nicely. Any [issues], you just come to me.' (HOD) When I first took [them] in, they weren't comfortable doing a lot of things... They weren't given a lot of freedom in the old days… I found that a lot of them are quite capable... They did make a lot of mistakes and I do hold them accountable for it, but [no] penalties...' (HOD) I want to hear from you first. Come back to me, say, in 2-3 hours' time and see what you have.'… I put pressure to them to think through properly… Otherwise they will never learn. Always remember, don't give the man fish all the time. You must teach him how to fish. (HOD) HR Department… arranged training on mergers and acquisitions, post-mergers, and things like that for the senior management team. Then we will go back to our own department and advise or counsel [our teams] on that different culture… the new flow, new process, new way of doing things. (SM)

		Boundary	Cultural difference Trust attribute Illustrative quotes
	Relating behaviors
	Social and political	Horizontal,	Organizational,	Benevolence,	It's not for the acquiring company to reach out to us. Because I'm
	awareness	vertical	intra-national	integrity	the acquirer, I felt it was important for me to reach out to them.
					(Leader)
		Vertical,	Organizational,	Benevolence,
		stakeholder	intra-national	integrity
	Build subordinate trust I take pains Care about subordinates Vertical, horizontal, demographic, stakeholder Organizational, intra-national Benevolence, integrity, ability I spent a Vertical, horizontal, demographic Organizational, intra-national Benevolence, integrity, ability Vertical Personal Benevolence, integrity [Scouting behaviors

ENDNOTES

i The terms "M&As" and "acquisitions" are used interchangeably in this paper, as in extant literature.

ii Malaysian GLCs are usually Malay-owned, controlled and managed, with substantial ethnic Malay managers and personnel (Lee, 2016). GLC shareholding in Malaysia's financial industry is high: four of eight banking groups have direct and indirect government shareholding of 40%-60% (IMF, 2014).

iii This paper refers to Malaysians of Chinese ancestry as ethnic Chinese/Malaysian Chinese to distinguish them from Chinese who are nationals of China; idem for Malaysians of Indian descent.


C Mansuy

Dr J M Nedelec

C Dujardin

R Mahiou

Concentration effect on the scintillation properties of Sol-Gel derived LuBO 3 doped with Eu 3+ and Tb 3+

Keywords: 78.55.Hx, 81.20. Fw, 29.40.Mc, 73.61.Tm scintillators, borate, sol-gel, medical imaging, x-ray conversion

Lu 1-x Eu x BO 3 and Lu 1-x Tb x BO 3 powders have been prepared by a sol-gel process with 0 < x < 0.15 for Eu 3+ and 0 < x < 0.05 for Tb 3+ . The purity of powders has been verified by X-Ray diffraction and the results confirm that all the materials have the vaterite type even if the calcination has been performed at 800°C. Furthermore, the solid solution for LuBO 3 vaterite is observed up to x=0.15 and x=0.05 for europium and terbium ions respectively. So doping with Eu 3+ or Tb 3+ ions does not affect the structure. These materials have also been analyzed by Fourier Transform Infra Red Spectroscopy. The morphology of the powders has been studied by Scanning Electron Microscopy and shows a very nice morphology with small spherical particles with narrow size distribution. Optical properties have then been studied to confirm the effective substitution of Eu 3+ or Tb 3+ for Lu 3+ ions and to determine the materials scintillation performances. The optima, in term of scintillation yield, are obtained for Eu 3+ and Tb 3+ concentration of x=0.05 in both cases. The afterglows have also been measured and confirm the potentiality of these materials as scintillators.

Introduction

Nowadays, research directed towards scintillating materials is in constant development. These materials, that convert high energy radiation into UV-Visible light, are used in various applications: medical imaging, high energy physics, airport security and industrial control. The use of these scintillating materials in medical equipment (X-rays, γrays, positron emission, ... ) requires improvement of their properties, in particular their conversion yield. Soft chemistry routes and in particular the sol-gel process offer an attractive alternative solution for the production of efficient scintillators with a control of the optical properties.

Rare earth activated lutetium orthoborates, which present a high density due to lutetium, appear to be good scintillators [1,[START_REF] Moses | Procceding of the International Conference on Inorganic Scintillators and Their Applications[END_REF]. We consequently decided to prepare LuBO 3 :Eu 3+ and LuBO 3 :Tb 3+ powders by an original sol-gel route. Indeed, the major advantage of this soft chemistry process is that it allows the control of the morphology and the texture of the materials and also the preparation of the material as thin films [START_REF] Schmidt | [END_REF][START_REF] Nedelec | [END_REF]5]. Moreover, the sol-gel route allows the elaboration of materials of different composition and doped easily with different ions, in various concentration and the sol-gel derived materials are synthesized at lower temperature than the ones elaborated by classical solid state synthesis.

The powders have been characterized using various techniques. The purity and the morphology have been respectively analysed by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The scintillation properties of LuBO 3 :Eu 3+ and LuBO 3 :Tb 3+ powders have also been studied.

Experimental section

Powders preparation

LuBO 3 :Eu 3+ and LuBO 3 :Tb 3+ powders have been prepared by a sol-gel process described elsewhere [6]. In a first step, lutetium and Ln (Ln: Eu or Tb) chlorides are dissolved in required amounts in isopropanol during 2 hours. Rare earth chlorides and solvents used were anhydrous and all the experiments were carried out in an argon inert atmosphere to prevent any influence of air moisture.

Potassium isopropoxide was prepared by reacting metallic potassium (Aldrich) with anhydrous 2-propanol (Accros). After dissolution of chlorides, the solution of potassium isopropoxide is added and then Lu/Ln chlorides mixture is reacted with the potassium alcoholate which substitutes for chloride leading to the formation of the rare earth alkoxides and the immediate precipitation of KCl according to:

LnCl 3 + 3 K + + 3 i OPr -→ Ln( i OPr) 3 + 3 KCl↓
This mixture was then refluxed for 2h at 85°C, in order to complete the formation of the rare earth alkoxides. Secondly, an alcoholic solution of boron tri-isopropoxide is added. A homogeneous solution is obtained after 4h-reflux at 85°C.

After cooling down at room temperature, centrifugation is performed in order to separate KCl from the sol. The hydrolysis of the sol with distilled water yields a gel, which is dried at 80°C to obtain a white xerogel. This xerogel is then fired at 800°C for 18h in order to obtain Lu (1-x) Ln x BO 3 (Ln :Eu or Tb) crystalline powders. Samples with 0.005 < x < 0.15 and 0.002 < x < 0.05 have been prepared respectively for LuBO 3 :Eu 3+ and LuBO 3 :Tb 3+ .

Characterization

All powders have been checked by X-Ray diffraction on a Siemens D501 diffractometer working in the Bragg-Brentano configuration with Cu-K α radiation (λ = 1.5406 Ǻ).

Infrared spectra were recorded on a Perkin Elmer 2000 FTIR spectrometer using the KBr pellet technique.

Thermogravimetric analysis was performed using a Metler Toledo 851 apparatus.

Samples were heated in air with a rate of 1 °C.min -1 .

Micrographs were recorded using a Cambridge StereoScan 360 SEM operating at 20 kV. Samples were prepared by depositing a small quantity of powder on adhesive carbon film before coating the surface with gold.

The excitation spectra of all the powders, doped with Eu 3+ or Tb 3+ , were recorded at room temperature using a Xenon lamp as continuous excitation source and a Triax 320 monochromator coupled with a CCD detector.

The scintillation spectra were recorded with a Jobin-Yvon Triax 320 monochromator coupled with a CCD camera after excitation of the samples with a tungsten X-ray tube working at 35 kV and 15 mA. The signal was collected near the sample with an optical fiber.

For relative conversion yield estimation, the samples were placed in a quartz tube with a fixed position throughout the measurements. Commercial polycristalline Gd 2 O 2 S:Tb 3+ powder supplied by Riedel de Haën was used as a standard for the scintillation yields measurements. The setup was kept constant between the measurements (excitation and detection), simply changing the sample tube. Equivalent masses of samples were used for measurements and all samples were milled in similar conditions in order to keep the granulometry as constant as possible. Reproducibility was tested on the gadox sample yielding values within a 5 % deviation range.

The afterglow measurements were performed at room temperature on the samples corresponding to concentration optima. The excitation was performed during 10 s with a Xray source working at 40 kV and 35 mA. Gd 2 O 2 S:Tb 3+ powder was used as a reference. presents two crystalline types depending on the thermal treatment. As mentioned in [7] the vaterite form is obtained at 800°C instead of the calcite form when the material is prepared by solid state reaction. However, all the recorded diffractograms are identical and show exclusively the vaterite form of LuBO 3 with no evidence for LuBO 3 calcite, EuBO 3 or TbBO 3 phases. Refinement of powder X-ray diffraction patterns allows deriving the cell parameters for the vaterite phase of LuBO 3 . Plot of the cell volume as a function of Eu 3+ content as shown in Figure 2, clearly shows a linear evolution as expected from Vegard's Law for a solid solution. So rare earth ions (Eu 3+ , Tb 3+ ) substitute for Lu 3+ cation in LuBO 3 vaterite structure and the solid solution is observed up to 15% and 5% for respectively europium and terbium ions. Solid solution limits have not been determined and higher concentration might be possible while keeping the vaterite structure and a monophasic material.

Results and discussion

Characterisation

X-Ray diffraction

FTIR Spectroscopy

Fourier transform Infrared spectroscopy has been carried out on the different samples doped with Eu 3+ or Tb 3+ ions. All recorded spectra, displayed in Figure 3 All the bands observed in the range 500-1200 cm -1 correspond to B-O group vibration modes and the positions agree well with published results [START_REF] Nedelec | [END_REF]8].

Thermal analysis

The evolution of LuBO 3 from the amorphous to crystalline form has been studied by thermal analysis. This study gives informations on the cristallisation of the material. A thermogravimetric analysis has been carried out on LuBO 3 powder elaborated by sol-gel process and the resulting thermogramm is presented in Figure 4. The first derivative is also shown in order to clearly identify the temperatures associated with the different weight losses.

A first weight loss is observed around 100°C and can be allotted to the elimination of adsorbed species such as alcohol or water molecules. A second significant weight loss, observed at about 150°C, corresponds to the condensation of the material. There is a condensation of the alkoxy and hydroxy groups with subsequent alcohol or water elimination. Some residual organic compounds can also be directly pyrolyzed. At this temperature, the inorganic skeleton is formed. A last weight loss is observed at 700°C and corresponds to the crystallisation temperature. From this temperature, the crystalline growth occurs and no more weight loss is observed. This last loss is characteristic of the mineral network reorganization and of the final elimination of residual OH groupments. Total loss of weight is approximately 17%. Thermal behavior appear very consistent with former results concerning sol-gel derived oxides.

Scanning Electron Microscopy

To complete the study, Scanning Electron Microscopy has been performed on vaterite LuBO 3 powders synthesized by sol-gel process and treated at 800°C for 18h.

The micrograph recorded at 30 000 x magnification, given in Figure 5, indicate that LuBO 3 powders are homogeneous and constituted of small spherical particles of about 200nm. The size distribution of these particles is uniform, which is a usual consequence of using the solgel process.

Excitation and emission spectra

Excitation spectra

The excitation spectra of LuBO 3 :Eu 3+ and LuBO 3 :Tb 3+ vaterite powders were recorded for different concentrations of Eu 3+ (0.05 < x < 0.15) and Tb 3+ (0.002 < x < 0.05).

Figure 6 shows the excitation spectra recorded at room temperature by fixing the emission wavelength at respectively 591nm and 541nm for the optima (Lu 0.95 Eu 0.05 BO 3 and Lu 0.95 Tb 0.0 5BO 3 ).

The excitation spectrum recorded for LuBO 3: Eu 3+ powder is constituted of lines corresponding to 4f-4f transitions. The line observed at about 470 nm is attributed to 7 F 0 →5 D 2 transition and the ones situated in the range between 300-430 nm correspond to 7 F 0 → 5 F 2 , 5 H J , 5 D 4 , 5 G J , 5 L 8 , 5 L 6 , 5 D 3 transitions. The excitation band located below 250 nm is assigned to the charge transfer absorption [9]. The excitation lines observed for LuBO 3 :Tb 3+ powder, in the range 300-500 nm, are characteristic of 4f-4f transitions. They correspond to 7 F 6 → 5 H 6 , 5 H 7 , 5 L 8 , 5 L 9 , 5 D 2 , 5 G 5 , 5 L 10 ,

Emission spectra

The emission spectra recorded at room temperature under X-ray excitation for Eu 3+ and Tb 3+ doped LuBO 3 vaterite, with different concentrations of Eu 3+ and Tb 3+ , are presented in Figure 7. Gadox (Gd 2 O 2 S:Tb) emission spectrum has also been recorded in order to calculate the scintillation yields of Eu and Tb doped materials.

In the case of LuBO 3 :Eu 3+ (Fig. 7a), the spectrum is constituted of lines corresponding to 5 D 0 → 7 F J (J = 0-4) transitions of Eu 3+ ions. The spectral distribution of the Eu 3+ doped materials results in a global orange-red emission.

LuBO 3 :Tb 3+ emission spectrum (Fig. 7b) exhibits, in the range between 475-650 nm, several lines characteristic of 5 D 4 → 7 F J (J = 3-6) transitions of Tb 3+ ions. 5 D 4 → 7 F 5 transition is the most intense and confers to the materials an overall green emission.

Scintillation yields

Scintillation yields have been calculated for all the powders by comparing the integrating areas of the emission spectra of the sample and Gadox. Scintillation yields under γ-rays excitation is 78000 photons/Mev [11] for Gadox. The yields of our materials were calculated from reference values, which are obtained under γ-ray excitation. Our measurements have been performed under X-ray excitation, so the results given for the scintillation yields under γ-ray excitation might be under-estimated. Yields have been calculated for concentrations of Eu 3+ and Tb 3+ ions with respectively 0.005 < x < 0.15 and 0.002 < x < 0.05. The scintillation yields for all the samples and their evolution as a fonction of the doping ion concentration is presented in Figure 8.

For Eu 3+ doped LuBO 3 , the optimum is obtained for a Eu concentration of 5% with a scintillation yield of about 8923 photons/MeV. This scintillation yield is 11% of the Gadox one, which is a good value.

In the case of Tb 3+ doped LuBO 3 powders, LuBO 3 :Tb 3+ (5%) present the higher scintillation yield since this one is equal to about 4398 photons/MeV.

Afterglow

Precise knowledge of the afterglow is required for practical applications. Afterglow measurements were recorded at room temperature, using an X-Ray source, which operated at 40kV with an intensity of 25mA. The material was excited for 10s and the signal was collected using a photomultiplier.

The afterglow behaviours for Eu 3+ and Tb 3+ doped LuBO 3 powders are presented in Figure 9. The afterglow of Gadox (Gd 2 O 2 S:Tb 3+ ) was also measured as a reference. The afterglow values, mesured 1 s after X-ray turn-off, are 1%, 0.2% and 0.007% respectively for Lu 0.95 Eu 0.05 BO 3 , Lu 0.95 Tb 0.05 BO 3 and Gadox.

Conclusion

The sol-gel process has been proven to be a good technique for the preparation of scintillating materials doped with different rare earth ions both as powders and thin films.

The advantages of this method compared to traditional syntheses are, the lower temperature of treatment, the good crystallinity and purity of the samples, the morphology control and a homogeneous distribution of the particles size.

The scintillation properties of Eu 3+ and Tb 3+ doped LuBO 3 powders were studied for different concentrations of doping ion and good scintillation yields were obtained.

Sol-gel derived LuBO 3 :Eu 3+ and LuBO 3 :Tb 3+ appear to be promising scintillators.

Figures captions

Figures captions

Figure 1

 1 Figure 1 presents the X-Ray diffraction patterns recorded for LuBO 3 powders heated at 800°C for 18h and doped with Eu 3+ (Fig. 1 a) or Tb 3+ (Fig. 1 b) ions. Orthoborate LuBO 3

  , are similar. No significant change is observed upon doping with Eu 3+ (Figure 3(a)) or Tb 3+ (Figure 3(b)) ions.

Figure 1 :Figure 2 :

 12 Figure 1: X-Ray diffraction patterns recorded for (a) Lu 0.85 Eu 0.15 BO 3 and (b) Lu 0.95 Tb 0.05 BO 3

Figure 3 :Figure 4 :Figure 5 :Figure 6 :

 3456 Figure 3: IRTF spectra of (a) LuBO 3 :Eu 3+ and (b) LuBO 3 :Tb 3+ powders of vaterite form

Figure 7 :

 7 Figure 7: Emission spectra recorded, at room temperature, under X-ray excitation on (a) LuBO 3 :Eu 3+ and (b) LuBO 3 :Tb 3+ of vaterite form, with different concentrations of Eu 3+ and Tb 3+ ions.

Figure 8 :Figure 9 :

 89 Figure 8: Relative scintillation yields of (a) LuBO 3 :Eu 3+ and (b) LuBO 3 :Tb 3+ powders

Figure 1 :

 1 Figure 1: X-Ray diffraction patterns recorded for (a) Lu 0.85 Eu 0.15 BO 3 and (b) Lu 0.95 Tb 0.05 BO 3 with the corresponding ASTM reference patterns (dotted lines)

1 )Figure 3 :Figure 4 :Figure 5 :Figure 6 :Figure 7 :

 134567 Figure 3: IRTF spectra of (a) LuBO 3 :Eu 3+ and (b) LuBO 3 :Tb 3+ powders of vaterite form heated at

Figure 8 :

 8 Figure 8: Relative scintillation yields of (a) LuBO 3 :Eu 3+ and (b) LuBO 3 :Tb 3+ powders.

Figure 9 :

 9 Figure 9: Afterglow measurement on Lu 0.95 Eu 0.05 BO 3 , Lu 0.95 Tb 0.05 BO 3 and Gadox under X-ray

G

, 5 D 3 and 5 D 4 transitions[10].

Acknowledgements

The authors would like to thanks the French FRT for financial support under project LuminiX (RNTS-01B262).


J Lao

J M Nedelec

Ph Moretto

Edouard Jallot
email: jallot@clermont.in2p3.fr

Biological activity of a SiO 2 -CaO-P 2 O 5 sol-gel glass highlighted by PIXE-RBS methods

Keywords: 68.08.-p, 81.05.Kf, 81.20.Fw, 82.80.Ej, 82.80.Yc, 87.64.Gb, 87.68.+z PIXE-RBS methods, biomaterials, bioactive glass, sol-gel

It is proposed in this study to observe the influence of P 2 O 5 on the formation of the apatite-like layer in a bioactive glass via a complete PIXE characterization. A glass in the SiO 2 -CaO-P 2 O 5 ternary system was elaborated by sol-gel processing. Glass samples were soaked in biological fluids for periods up to 10 days. The surface changes were characterized using Particle Induced X-ray Emission (PIXE) associated to Rutherford Backscattering -2 -Spectroscopy (RBS), which are efficient methods for multielemental analysis. Elemental maps of major and trace elements were obtained at a micrometer scale and revealed the bone bonding ability of the material. The formation of a calcium phosphate-rich layer containing magnesium occurs after a few days of interaction. We demonstrate that the presence of phosphorus in the material has an impact on the development and the formation rate of the bone-like apatite layer. Indeed, the Ca/P atomic ratio at the glass/biological fluids interface is closer to the nominal value of pure apatite compared to P 2 O 5 -free glasses. It would permit, in vivo, an improved chemical bond between the biomaterials and bone.

Introduction

With the development of biologically active materials, new field of applications arise in surgical therapeutics. Clinical operations on bone defects and fractures may call for a filling material that also presents the ability to contribute to the healing process. For this purpose, bioactive glasses are of huge interest. In contact with living tissues, bioactive glasses establish an enduring interface consisting of a calcium phosphate-rich layer that shows a bone-like apatite structure. The bioactivity mechanisms and growth of the layer at the interface deeply depend on the composition of the glass. The biological activity of bioactive glasses is linked to their capability, in aqueous solution, to leach ions from their surface; a porous silica-gel layer is then formed, which will play the part of support for bone-like apatite crystals growth [1]. The development mechanisms of that calcium phosphate-layer lie in the diffusion of calcium and phosphorus ions from the glass and from the aqueous medium to the material surface [2]. As a result, controlling the surface reactions rates and kinetics is of major importance. Optimizing determining parameters such as the material chemical composition and textural properties is in keeping with the concern that the material will be used as an efficient implant, capable of forming a strong interfacial bond with host tissues and stimulating bone-cell proliferation [3].

For this purpose, a SiO 2 -CaO-P 2 O 5 bioactive glass was elaborated using the sol-gel method, which permits the synthesis of materials with higher purity and homogeneity at low processing temperature [4]. Samples of gel-glass powder and glass compacted discs were immersed in biological fluids for varying periods. As a network former, phosphorus was expected to influence the in vitro bioactivity via a modification of the dissolution kinetics [5].

Analyses of major, minor and trace elements present at the biomaterial/biological fluids interface were performed by particle-induced X-ray emission (PIXE) associated to Rutherford backscattering spectroscopy (RBS). Obtaining PIXE elemental maps at a micrometer scale permits the complete follow-up of the bone-like layer formation along with major and trace element quantification. It allows important evaluation for the in vivo bioactivity of such a bone-forming material.

Materials and methods

Preparation of the bioactive glass samples

Gel-glass powders containing 67.5wt% SiO 2 -25wt% CaO-7.5 wt% P 2 O 5 were prepared using the sol-gel process. Tetraethylorthosilicate (TEOS; Si(OC 2 H 5 ) 4 ), triethylphosphate (PO(OC 2 H 5 ) 3 ) and calcium nitrate Ca(NO 3 ) 2 . 4 H 2 O were mixed in a solution of ethanol in presence of water. The prepared sol was then transferred to an oven at 60°C for gelification and aging. Four hours later, the obtained gel was dried at 125°C for 24 hours, then finally reduced to powder and heated at 700°C for 24 hours. The final surface area of the glass was found to be ??? m2/g by nitrogen sorption analysis. Part of the dry gel powder was then compacted into discs of 13 mm diameter and 2 mm height.

In vitro assays

The glass discs were immersed at 37°C for 1, 6 h and 1, 2, 5, 10 days in 45 mL of a standard Dulbecco's Modified Eagle Medium (DMEM, Biochrom AG, Germany), which composition is almost equal to human plasma. 10 mg of gel-glass powder samples were soaked at 37°C for 1, 6 h and 1, 2, 3, 4 d in DMEM, with a surface area to DMEM volume ratio fixed at 500 cm -1 . After interaction, the samples were removed from the fluid, air dried and embedded in resin (AGAR, Essex, England). Before characterization, the glass discs were cut into thin sections of 30 micrometers nominal thickness using a Leica RM 2145 microtome. 1000 nm thin sections of the glass powder samples were prepared by mean of a Leica EM UC6 Ultramicrotome, and laid out on 50 mesh copper grids. Then, the sections and grids are placed on a mylar film with a hole of 3 mm in the centre.

PIXE-RBS analysis

Analyses of the biomaterial/biological fluids interface were carried out using nuclear microprobes at CENBG (Centre d'Études Nucléaires de Bordeaux-Gradignan, France). For PIXE analyses, we chose proton scanning micro-beam of 1.5 MeV energy and 100 pA in intensity. The beam diameter was nearly 2 µm. An 80 mm 2 Si(Li) detector was used for X-ray detection, orientated at 135° with respect to the incident beam axis and equipped with a beryllium window 12 µm thick. PIXE spectra are treated with the software package GUPIX [6] [6]. Relating to RBS, a silicon particle detector placed 135° from the incident beam axis provided us with the number of protons that interacted with the sample. Data were treated with the SIMNRA code [7].

Results and discussion

Glass powder samples

Elemental maps for each immersion time in DMEM were recorded. Figure 1 represents the elemental distribution of a powder grain after 1 h of interaction with biological fluids. The grain is still homogeneous and dissolution has not begun. Its composition is in the order of the primary SiO 2 -CaO-P 2 O 5 synthesized glass. Nevertheless, some grains (not shown) present a gradient of Ca and P concentration from the centre to the periphery of the material, indicating that ionic exchanges are imminent. After 6 h soaking, we note that calcium and phosphorus started to diffuse from the glass (data not shown). Ion exchange between the grains and the solution has occurred and traces of magnesium are detected at the periphery of the material. However silicon is still uniformly distributed through the grains.

The breakdown of the silicate network occurs within 24 h of interaction, and a calcium phosphate-rich layer is formed on particular nucleation sites, located at the periphery of the grains. Calcium and phosphorus ions continue to diffuse from the glass; those are added to the calcium ions and phosphates coming from biological fluids, forming an amorphous calcium phosphate layer on the glass surface. That is illustrated in Figure 2, which shows the multielemental maps of powder grains after 2 days soaking. As visible on the biggest grain, a homogeneous calcium phosphate-rich layer containing magnesium surrounds the material.

The core of the grain is composed of the silicate network enduring dissolution. The smallest grains (in the picture corners) already changed into calcium phosphates.

Glass compacted discs

Glass pastilles react more slowly than powder samples, since their massive powder compacted shape does not grant the same porous-gel open structure as single grains.

However, their retarded behavior is similar to that of powder grain samples. Figure 3 shows the multi-elemental maps across the periphery of a glass pastille after 1 h soaking. Measuring the elemental concentrations in the material reveals no changes in the material composition.

On 6 h immersed samples, we observe the presence of thin Ca-P enriched areas disseminated on the surface of the discs. Growth of those areas is supplied by constant ionic exchanges between the material and biological fluids. It results in the formation of a large calcium phosphate layer after a few days of interaction (Figure 4). We have measured the Ca/P atomic ratio at the periphery of the glass: it is equal to 1.89 after 10 d soaking. That is an essential indication for the formation of bone-like apatite, which Ca/P nominal value is equal to 1.67.

Conclusion

Thanks to micro-PIXE associated to RBS, we are able to specify the role of major and trace elements in physico-chemical reactions occurring at the periphery of the glass. In contact with body fluids, bioactive glasses induce a specific biological response at their surface. The initial SiO 2 -CaO-P 2 O 5 glass network is quickly enduring dissolution. Then, following the different stages of the bioactivity process, a bone-like layer is quickly formed at the material periphery.

The calcium phosphate-rich layer formation and evolution of the glass network are highlighted. Magnesium is proved to be blended into the material: that is new information of capital importance since magnesium can play an important role during spontaneous formation of in vivo calcium phosphates and bone bonding [8,9]. The specific preparation protocol developed permits the characterization of highly porous powders with grains of a few micrometers.

We demonstrate that the presence of phosphorus in the material composition has an impact on the development and the formation rate of the bone-like apatite layer. In a previous work on P 2 O 5 -free glasses, we found that the Ca/P atomic ratio at the material periphery was equal to 2.05 after 10 d of interaction [10]. The Ca/P atomic ratio at the SiO 2 -CaO-P 2 O 5 glass/biological fluids interface is equal to 1.89 after 10 d soaking, which is closer to the 1.67 nominal value of pure apatite. Furthermore, phosphorus-based glass compacted discs present slower dissolution kinetics compared to P 2 O 5 -free glasses (peut on donner une info + quantitative ?). It might permit, in vivo, an improved bonding ability with host tissues.

Biological studies are now being performed to confirm this point.

Figure captions

Figure 1 :

 1 Figure 1: Elemental maps of a SiO 2 -CaO-P 2 O 5 powder grain after 1 h of interaction with biological fluids (53 × 53 µm 2 ).

Figure 2 :

 2 Figure 2: Elemental maps of SiO 2 -CaO-P 2 O 5 powder grains after 2 days of interaction with biological fluids (101 × 101 µm 2 ).

Figure 3 :

 3 Figure 3: Elemental maps at the periphery of a SiO 2 -CaO-P 2 O 5 glass disc after 1 h of interaction with biological fluids (53 × 53 µm 2 ).

Figure 4 :

 4 Figure 4: Elemental maps at the periphery of a SiO 2 -CaO-P 2 O 5 glass disc after 10 d of interaction with biological fluids (179 × 179 µm 2 ).

  Figures

  Figure 2

  Figure 3