Mathieu Triclot, « Information society before information society », Annual Meeting of the International Association for Computing and Philosophy, Montpellier, 2008-06-16.

Information society before Information Society

Mathieu Triclot, IACAP, Montpellier, 2008/06/16 The discourse on "the information society" developed until the 70's as one of the prevailing discourse in our society; with promises to link information technology and free market with economic growth and human progress. This eventually became something like the official ideology of the European Union as demonstrated by the famous Lisbon strategy to become "the most dynamic and competitive knowledge-based economy in the world" placing "emphasis on the need to adapt constantly to changes in the information society". This discourse about "information society" raised its share of criticism based on technological determinism or the new informational prophecies, Here I think about the works of French authors, like Armand Mattelart, David Forest, Philippe Breton, and so on. This discussion is not intended to review the criticisms, but to go back in time and analyse what can be considered as the first concept of information and society in the wake of the cybernetic movement, in the United States, at the end of the 1940's. Now, briefly, what is cybernetics and how can it claim to be the first discourse about information society? On October 1948 the American mathematician Norbert Wiener publishes Cybernetics, manifesto for a new science based on the merging of several engineering fields, such as automatic computing, telecommunications or feedback control, under the new scientific concept of information. As the science of control and communication in the animal and the machine, cybernetics extends the empire of information to the life, cognition and social sciences. For example we read in Wiener's 1946 conference to the New York Academy of science that "fundamentally the social sciences are the study of the means of communication between man and man or, more generally, in a community of any sort of being. The unifying idea of the diverse disciplines is the message, and not any special apparatus acting on messages."

[Wiener, "Time, Communication, and the Nervous System", Annals of the New York Academy of Scienced, Oct 1948, p. 202] The discourse about the information and society relationship thus appears contemporary to the development of the scientific concept of information.

But what kind of discourse is it?

Even before the publication of Cybernetics, Wiener already drew public attention with an open letter simply entitled "A scientist rebels", published by The Atlantic Monthly magazine in the beginning of 1947. In the midst of the nuclear arms race debate, the letter, whose outraged tones are echoed in several key passages of the 1948 book, warns against the militarization of American science and announces Wiener's commitment to withdraw cybernetics from all researches involving military funding. Thus the Atlantic Monthly's letter not only reminds us that information technology was born in the "World of Belsen and Hiroshima" but that the first information society discourse was, under Wiener's influence, highly critical against the evolutions of American society at the dawn of the Cold War.

The aim of this communication is thus to present the different pieces of the information society discourse in Wiener's writings, to situate them in the conflicting context around the transformations of the American science where they originate, in order to, eventually, draw a parallel between Wiener's old discourse and the newer variants of the information society.

1.1

The idea of information society embraces in Wiener's writings two different dimensions. It first aims at the new information processing devices' social impact (starting with computers). The information society is a society deeply transformed by the appearance of this new set of artefacts that cybernetics taught us to recognize as the unified information technology. More precisely, Wiener thinks that the emergence of information technology leads our societies to a new phase in industrial revolution, characterized by the integral automation of production. I quote: ""What the feedback and the vacuum tube have made possible is not the sporadic design of individual automatic mechanisms, but a general policy for the construction of automatic mechanisms of the most varied type. In this they have been reinforced by our theoretical treatment of communication. […] It is this conjunction of circumstances which now renders possible the new automatic age. […] In its potential significance, the vacuum tube certainly belongs to an industrial revolution different form that of the age of power." [Wiener, The Human Use of Human Beings, 1950, p. 153] Thus, in Wiener's approach, the information society is not a services economy or a dematerialisation of economy through transnational networks, but a complete overhaul of industrial production. The computer, as the new brain of the factory, threatens both white and blue-collar work. On all this issues, Wiener adopted an active attitude, not only warning the public about the information society future dangers, but also trying to secure concrete alliances with trade unions and proposing plans of action.

This first component of the information discourse raises the question of the technical and social change model adopted by Wiener. Is the information society a kind of technological destiny, as Celine Lafontaine for example concludes from the examination of cybernetics conceptions? I don't think so: in reality, Wiener's model is more complex and consistent with his political commitment. Wiener doesn't consider technology or even automation as an autonomous phenomenon making its mark on society from the outside. On the contrary, the path followed by technical change depends on the social forms. Wieners borrows here his arguments from the great narratives on technology and civilization, in particular from Lewis Mumford. He builds an analysis of technical change aware of the systemic effects and political dimensions of artefacts.

1.2

But the question of the relationship between information and society is not restricted to the social impact of technology in Wiener's writings. If one can speak about information society, it is not only because of society is being shattered by the development of new machines, but more importantly because society must be considered as a huge information processing device. In this sense, society becomes itself a cybernetic machine, which can be analysed using the discipline's conceptual toolbox.

Wiener's writings are full of political arguments about the role of secrecy in communications, the drawbacks of intellectual property, the power of media in a free society, the nature of political regimes from the point of view of information processing, all arguments that rest upon the very conceptual core of cybernetics and the definition it gave of the information concept. One of the key arguments consists for example in opposing learning versus rigidity in machines and societies. The design of machines capable of learning serves then as a model for an efficient social organisation. This political cybernetics raises another question, which is the one of models for political analysis and action and the transfer of models originally from the fields of natural or engineering sciences to the social sciences field. Wiener's politics appears at a time when engineers or scientists do not hesitate to offer their services to politicians. Once again, Wiener's model of social analysis tries to introduce a critical alternative to the current models of science's mobilization for action. Wiener is for example highly critical of the use of the game theory in military entities like the Rand Corporation. He explains that his use of cybernetics concepts for social analysis cannot claim to be scientific and need to be understood simply as a tool for analysis. I quote the crucial passage in Cybernetics, chapter 8. It just comes right after the game theory's critic: "Our investigations in the social sciences can never furnish us with a quantity of verifiable, significant information which begins to compare with that which we have learned to expect in the natural sciences. We cannot afford to neglect them; neither should we build exaggerated expectations of their possibilities. There is much which we must leave, whether we like it or not, to the un-"scientific", narrative method of the professional historian." [Wiener, Cybernetics, 1948, p. 164] 2.

The information society project in Wiener's works must be placed in the context of the intense debate on American society's commitment in the Cold War. Wiener's political discourse appears directed mostly against what he calls the militarization of American science and the new relationships between scientists, politicians and military following the Second World War. To a first commitment against nuclear weapons, he adds a critic of the new politics of science at the end of the forties. For Wiener, information society means a new way of designing the organisation of research, from a democratic point of view, opposed to the new science factories where the social responsibility of the individual scientist wanes.

Wiener thus equally rejects the model of a technological development driven by the sole market forces and the current model of nationalization of the research and development effort for the war. He builds a form of ecological socialism, committed to decentralised decision process amongst small autonomous communities in the Jeffersonian tradition.

3.

Eventually, it seems then interesting to compare this first full-length discourse about information society to the discourses about technological change that appear in the 1970's under the motto of information society.

We can now point at 3 main differences: first, Wiener's model doesn't share the idea that technology could completely determine social changes from the outside. Second, Wiener is very sceptical about the idea of reducing policies to a neutral government science. And third he doesn't believe in the efficiency of markets for controlling technological innovation.

In particular, Wiener's information society is build upon the axiom that information is not well suited to become a commodity. This proposal rests upon the very definition of the information measure in cybernetics, as a physical quantity opposed to entropy. Information is an element of order or structure which escapes for a short time the inevitable process towards chaos and thermal death. Information cannot retain its value through time, contrary to the usual commodities.

The contrast is striking with the contemporary conceptions of information society which rest upon precisely the extension of market to the sphere of informational commodities. The comparison between the old and the new discourse about information society offers us a point of view towards the great gap between the conceptions of information, computer and society in the 1950's and the 80's. It accounts for a contribution in the political and cultural history of computing.


Andreas M Hein

Breakthrough Technologies: Principle Feasibility Debates

Breakthrough technologies are technologies that introduce radically new capabilities or a performance increase of at least an order of magnitude. Examples are the turbojet, inertial navigation, and autonomous driving. However, a remarkable pattern for these technologies is that their feasibility seems to have been initially contested. Existing approaches for technology assessment such as the Technology Readiness Levels do not seem to be adequate for capturing the subtle dimension of assessing the potential of breakthrough technologies, as they rather focus on technological maturity. Important aspects such as performance, enabling systems, and contextual factors are not taken into account. This paper addresses the principle feasibility of breakthrough technologies by looking at what arguments for and against principle feasibility were/are used and how the feasibility question was resolved. For this purpose, we reconstruct past and ongoing principle feasibility debates of four exemplary breakthrough technologies using a technology conceptual model and argument maps. For the four technologies analysed, we conclude that sufficient expected performance was a key issue debated in all cases, whereas physical effects and working principles were issues for breakthrough technologies with a relatively low maturity. Principle feasibility issues for breakthrough technologies seem to be resolved by introducing new component technologies and working principles. For future work, we propose the use of case and field studies in order to explore contextual feasibility criteria for breakthrough technologies such as injection into existing system architectures, enabling systems, and market readiness.

INTRODUCTION

A breakthrough technology in the following is defined as a technology that offers a radically new capability or a performance improvement of at least an order of magnitude. The innovation literature has considered these technologies in the context of "radical innovation", although radical innovation encompasses a far larger set of technologies than breakthrough technologies, as it is not limited to capabilities and performance [START_REF] Chandy | Innovation typologies[END_REF][START_REF] Garcia | A critical look at technological innovation typology and innovativeness terminology: a literature review[END_REF][START_REF] Kotsemir | Innovation concepts and typology-an evolutionary discussion[END_REF]. The turbojet, inertial navigation, the Google search engine, and autonomous driving are breakthrough technologies. Breakthrough technologies are also considered to be fundamental for sustainable new business models [START_REF] Masters | Zero to one: notes on start ups, or how to build the future[END_REF][START_REF] Teller | A philosophy of technology: from technical artefacts to sociotechnical systems[END_REF]. These technologies can lead to radical changes to the status quo. The turbojet enabled fast and affordable intercontinental travel, inertial navigation enabled a whole class of systems such as long-range aircraft, rocket launchers, and ballistic missiles. The Google search engine enabled almost instant information retrieval from existing knowledge. Fundamental questions about breakthrough technologies are how to assess their feasibility at an early stage, how to quickly reduce key uncertainties regarding feasibility, how to integrate the technology into a product, how to design the enabling systems required for its successful operation, and how to evaluate the readiness of the context into which the product is introduced. These are questions that have been addressed for technologies in general in the technology management literature [START_REF] Burgelman | Strategic Management of Technology and Innovation[END_REF][START_REF] Schilling | Strategic management of technological innovation[END_REF]. Some exploratory proposals have been made regarding uncertainty reduction for breakthrough technologies [START_REF] Drexler | Exploratory Engineering: Applying the predictive power of science to future technologies[END_REF] and feasibility categories [START_REF] Cleaver | On the Realisation of Projects: with Special Reference to O'neill Space Colonies and the like[END_REF]. The product development and systems engineering literature has previously treated the infusion of new technologies into an existing system architecture [START_REF] Moullec | Toward System Architecture Generation and Performances Assessment Under Uncertainty Using Bayesian Networks[END_REF][START_REF] Suh | Technology infusion for complex systems: A framework and case study[END_REF]. Furthermore, the systems engineering literature has proposed various metrics for assessing the maturity of a technology such as the Technology Readiness Levels [START_REF] Mankins | Technology readiness levels[END_REF], Manufacturing Readiness Levels [START_REF] Cundiff | Manufacturing readiness levels (MRL)[END_REF], and System Readiness Levels [START_REF] Sauser | From TRL to SRL: The concept of systems readiness levels[END_REF].

However, breakthrough technologies have often characteristics that make their assessment challenging and most approaches from the literature no longer applicable. For realizing a radically new capability and/or an order of magnitude increase in performance, often, new physical effects and new working principles are used which require the assessment of principle feasibility. Furthermore, to create new business models, new operational principles have to be developed that allow for a proper exploitation of the capability or performance in the market place. There are also numerous cases where breakthrough technologies have been injected into products too early, which lead to a failure in the market place, as, e.g. enabling systems were not present. In successful cases, existing enabling technologies were quickly adapted in order to allow for a proper exploitation of the breakthrough technology, such as aircraft fuselages for the turbojet. For example, initial jet airplane designs were based on straight-wing designs, as they already existed, instead of swept wings that have a better aerodynamic performance but needed to be newly developed. The Google search engine would not have been successful without a large number of internet users and websites. The literature on the sociology of technology and technology history has dealt with this interaction and co-evolution of technologies [START_REF] Bijker | The social construction of technological systems: new directions in the sociology and history of technology[END_REF][START_REF] Constant | The origins of the turbojet revolution[END_REF][START_REF] Mackenzie | Missile accuracy: a case study in the social processes of technological change[END_REF]. Although other domains such as sociology and technology history have addressed breakthrough technologies, we argue that the existing product development and systems engineering literature has not yet addressed these technologies sufficiently to provide companies and policy-makers with guidance on how to assess these technologies. As a first step towards addressing the initially mentioned research questions, in this paper, we deal with the question of principle feasibility. More specifically, with the questions what types of arguments were put forward for / against principle feasibility and how the feasibility issues were resolved. By "principle feasibility" we mean that a technology can possibly be realized regarding its underlying physical effects and working principles. This would correspond to the TRLs 0 to 3, where physical effects are confirmed and technology concepts formulated. Whereas TRL proposes a maturity metric, we are more interested in the debate around the feasibility assessment that enables a proper TRL classification. Principle feasibility seems to be debated before classic feasibility proofs such as prototypes or results from experiments exist. Although it might seem that principle feasibility regarding physical effects and working principles have a clear yes / no answer, we demonstrate by using records from historical and ongoing debates that converting physical effects into applicable engineering knowledge is not trivial and the framing of the feasibility question plays an important role. In the following, we limit our focus on technologies as physical artifacts (hardware) along with their design [START_REF] Hein | Heritage Technologies in Space Programs -Assessment Methodology and Statistical Analysis[END_REF][START_REF] Olechowski | Technology Readiness Levels at 40: a study of state-of-the-art use, challenges, and opportunities[END_REF]. For software and algorithms, feasibility issues are more closely related to logic, proofs, and mathematics, e.g. calculability that seem to be quite different in nature from feasibility issues pertaining to physical artifacts. We first conduct a literature survey on breakthrough technologies. Based on a conceptual model for physical technologies, we reconstruct four past and current feasibility debates to assess the types of arguments that are / were put forward. Finally, we assess, which elements of the conceptual model were subject of the debates, the associated types of arguments, and which technology elements then contributed to the resolution of the issue.

LITERATURE SURVEY

Definitions

In the following, we introduce a set of definitions. First of all, the term "technology" needs to be defined. According to [START_REF] Bijker | The social construction of technological systems: new directions in the sociology and history of technology[END_REF], technologies fall into three categories:

 Physical objects or artifacts: bicycles, lamps, Bakelite;  Activities or processes: steel making or molding (We would put algorithms, methods, instructions into this category);  Knowledge pertaining to the first two categories: What people know as well as what they do. In this paper, we rather focus on technology in the narrow sense of a physical object or artefact. Next, the term "feasibility" needs to be defined. The definition for feasibility which is used in this paper is: "Capable of being accomplished or brought about; possible" (The Free Dictionary, 2016). "Feasible" can be substituted by "possible" or "can be realized" in the context of technologies and technical systems. Typical statements are:

 "Interstellar travel is feasible"  "Artificial intelligence is feasible"  "We have shown that a nuclear-electric mission to Jupiter is feasible." As mentioned in the introduction, by "principle feasibility" we mean feasibility on the conceptual level of a technology, where the applicability or existence of physical effects and working principles for a technology are debated. Typical principle feasibility statements are:

 Is it feasible to use nuclear fusion for fusion reactors?  Are artificial nanomachines feasible?

Feasibility Categories

Despite the importance of assessing principle technological feasibility, only few publications deal with the subject matter. [START_REF] Mankins | Technology readiness levels[END_REF] introduces the Technology Readiness Levels (TRL) that are in widespread use today. Nevertheless, TRL is a metric for technology maturity and does not directly address feasibility. However, we can assume that a technology with a high TRL is feasible and vice versa. [START_REF] Cleaver | On the Realisation of Projects: with Special Reference to O'neill Space Colonies and the like[END_REF] presents four technology feasibility categories along with criteria for putting a technology into these categories. The categories were later adopted by [START_REF] Ruppe | Die grenzenlose Dimension: Raumfahrt[END_REF]. [START_REF] Kaku | Physics of the impossible: A scientific exploration into the world of phasers, force fields, teleportation, and time travel[END_REF] presents three impossibility categories. Although these publications have addressed principle feasibility, they do not seem to specifically address breakthrough technologies and their characteristics.

Next, we will present two methods for systematically increasing the feasibility of a technology.

Exploratory Methodologies

In the following, methodologies that are applicable to the development of breakthrough technologies are presented. In the context of general design theory, CK theory has been specifically presented as a design theory that captures conceptually what is not known (concept) and known (knowledge) in the process of designing [START_REF] Hatchuel | CK design theory: an advanced formulation[END_REF], 2003, 2002).

Regarding more specific methodologies that address breakthrough technologies, Eric Drexler coined the term exploratory engineering [START_REF] Drexler | Exploring future technologies[END_REF], which can be defined as the "process of designing and analysing detailed hypothetical models of systems that are not feasible with current technologies or methods, but do seem to be clearly within the bounds of what science considers to be possible within the narrowly defined scope of operation of the hypothetical system model." (Wikipedia, 2016) Drexler contrasts exploratory engineering with what he calls "standard engineering" [START_REF] Drexler | Nanosystems: molecular machinery, manufacturing, and computation[END_REF][START_REF] Drexler | Radical Abundance[END_REF][START_REF] Drexler | Exploratory Engineering: Applying the predictive power of science to future technologies[END_REF]. According to him, standard engineering leads to the manufacturing of a product. In exploratory engineering, design leads to understanding of what a future manufacturing process could produce. The approach of exploratory engineering shares elements of "feasibility studies" that are common in areas dealing with long-term technology development such as in the space domain [START_REF] Drexler | Radical Abundance[END_REF]. For example, the Concept Maturity Levels (CML) of NASA include an initial level that is called "initial feasibility" [START_REF] Wessen | Space Mission Concept Development Using Concept Maturity Levels[END_REF].

The second method was proposed in [START_REF] Szabo | Falsifiable design: a methodology for evaluating theoretical technologies[END_REF]. Szabo argues that as long as experiments have not been conducted to verify or falsify the hypothesis that a technology works, it remains a "theoretical technology". He calls the study of theoretical technologies "exploratory engineering", referring to Drexler. He addresses the common problem of advanced technology that "exploratory engineers" claim that a technology is feasible, on the grounds of theoretical results, whereas scientists and engineers deem it infeasible, as it is not possible to implement it based on existing technology. He therefore proposes that designers "should design not only the technology but also a map of the uncertainties and edge cases in the design and a series of such experiments and tests that would progressively reduce these uncertainties. …We might call this requirement a requirement for a falsifiable design." [START_REF] Szabo | Falsifiable design: a methodology for evaluating theoretical technologies[END_REF] Szabo acknowledges that the approach resembles the systems engineering approach in large novel technology programs. However, he associates the development of theoretical technologies with longer timescales and higher uncertainties. [START_REF] Sandberg | Whole brain emulation[END_REF] use the approach for constructing a roadmap to whole-brain emulation, laying out steps towards this goal and major uncertainties. Both Szabo and Drexler stress the differences between standard engineering practice and a practice that is suitable for assessing the feasibility of theoretical or speculative technologies.

A TECHNOLOGY CONCEPTUAL MODEL

For classifying feasibility arguments pertaining to breakthrough technologies, a proper conceptual model is needed that captures key elements of a breakthrough technology. As a starting point for such a model, the technology conceptual model from [START_REF] Hein | Heritage Technologies in Space Programs -Assessment Methodology and Statistical Analysis[END_REF] is selected. The model was developed for physical technologies in the space domain and is adapted to a breakthrough technology context here.

The resulting conceptual model is shown in Fig. 1. We consider this conceptual model adequate in the context of this paper, as we limit our analysis to physical technologies. The basic elements of the conceptual model resemble previous work in product development, system architecture, and philosophy of technology [START_REF] Arthur | The nature of technology: What it is and how it evolves[END_REF][START_REF] Crawley | Systems Architecture: Strategy and Product Development for Complex Systems[END_REF][START_REF] Otto | Product Design: Techniques In Reverse Engineering And New Product Development[END_REF][START_REF] Pahl | Engineering design: a systematic approach[END_REF][START_REF] Ponn | Konzeptentwicklung und Gestaltung technischer Produkte: systematisch von Anforderungen zu Konzepten und Gestaltlösungen[END_REF][START_REF] Vincenti | Engineering knowledge, type of design, and level of hierarchy: further thoughts about what engineers know. Technological development and science in the industrial age[END_REF][START_REF] Vincenti | What engineers know and how they know it: Analytical studies from aeronautical history[END_REF]. Such elements are the working structure, working principles, effects, and the function. Added elements are in particular the scale of the technology, performance, environment, and economics. "Scale" represents the size of the technology in the sense of its actual physical size or number of components integrated. Classic examples for technologies with different physical size scales are nuclear fusion reactors, rocket engines, and materials. The efficiency of fusion reactors increases with size. By contrast, rocket engines exhibit combustion instabilities at increasing size. Materials at the nano-scale behave differently than at the macro-scale [START_REF] Drexler | Nanosystems: molecular machinery, manufacturing, and computation[END_REF]. Scale in the sense of integrated components are e.g. data centres or server farms where a large number of identical servers is integrated. Scale is important, as scaling up or down in some cases cannot be taken for granted due to potential nonlinearities, emergent behaviour, and changing physical effects.

We expect that performance is a key feasibility issue for breakthrough technologies. For example, the feasibility of inertial navigation was called into question on the grounds of quickly increasing errors in determining the vehicle's position. Hence, measurement accuracy as a performance indicator was a key feasibility issue.

The environment of a technology can be subdivided into its physical environment such as the larger system into which the technology is integrated, and its social and legal context. The social context represents the conventions and norms that may lead to accept, ignore, or reject a technology. This is different from the legal context, where non-compliance can lead to legal penalties. Finally, economics in a broad sense consists of the underlying capital structure of the technology and its exchange value. Some technologies are very capital intensive to develop such as fusion reactors, clean tech, antibiotics. Others require less capital to develop such as most software programs. The exchange value of a technology is in most cases related to selling instances, collecting licensing fees, or transferring the complete of a technology along with personnel, documentation, etc. Using this conceptual model, feasibility debates from the literature are analysed in the following.

PRINCIPLE FEASIBILITY DEBATES: FOUR CASE STUDIES

An exploratory analysis of four technologies with documented principle feasibility debates is conducted.

In this section, we summarize the results of the analysis and discuss its implications. We use the previously presented technology framework and literature on four historical and ongoing principle feasibility debates for (potential) breakthrough technologies. Based on the arguments retrieved from existing literature, argument maps are constructed for representing key arguments and relationships between these. The following four (potential) breakthrough technologies have been selected, due to their significance in the history of technology and due to the extent of available literature: turbojet (enabled airplanes to fly at unprecedented height and speed), inertial navigation (enabled navigation without external references), molecular assemblers (potential for precise manufacturing at a molecular level), EM drive (potential for space propulsion without exhaust mass). We encountered two challenges when going through the literature dealing with these technologies. First, usually different positions exist on feasibility, notably feasibility arguments of advocates and feasibility arguments by critics (Morison, 1966). Second, arguments evolve over time, often with the state of knowledge. We address the first point by reconstructing the sequence of the arguments and counterarguments of advocates and critics. We address the second point by either focusing on arguments around a tipping point in the perception of feasibility (inertial navigation, EM drive, turbojet) or a period where arguments seem to have remained rather stable (Molecular assembler). We acknowledge that for a more thorough temporal representation of the debate, the CK map could be more appropriate in representing the interaction between evolving concepts and knowledge [START_REF] Hatchuel | CK design theory: an advanced formulation[END_REF].

Table 1 shows the main element from the technology concept model for a technology on which the debate was focused and the main references we used for reconstructing the arguments. Some of the debates such as the Drexler-Smalley debate are well-documented. The debate took the form of a written exchange of positions. In other cases, such as Gamow's objection to inertial navigation, the original document is not accessible and has been reconstructed in [START_REF] Mackenzie | Inventing accuracy: A historical sociology of nuclear missile guidance[END_REF]. For the purpose of this paper, it is sufficient to reconstruct the key arguments that were used. We also acknowledge that the documented arguments do not capture implicit biases, ignorance, relationship issues, and risk-aversion that may lead to perceiving feasibility in a favourable or opposite view as has been pointed out prominently by Morison (1966). It is clear that such factors are important to consider but are beyond the scope of this analysis.

Table 1: Technologies and main areas of feasibility debates

Technologies Main area of documented feasibility debate Main references Jet engine

Performance limits of used materials [START_REF] Constant | The origins of the turbojet revolution[END_REF]

Inertial navigation

Performance limits of position measurement [START_REF] Mackenzie | Inventing accuracy: A historical sociology of nuclear missile guidance[END_REF][START_REF] Mackenzie | Missile accuracy: a case study in the social processes of technological change[END_REF]

Molecular assemblers

Viability of precise atomic-level manipulations [START_REF] Bueno | The Drexler-Smalley Debate on Nanotechnology: Incommensurability at Work?[END_REF]Drexler, 2003aDrexler, , 2003b;;[START_REF] Mccray | The visioneers: How a group of elite scientists pursued space colonies, Nanotechnologies, and a limitless future[END_REF]Smalley, 2003aSmalley, , 2003b[START_REF] Smalley | Of chemistry, love and nanobots[END_REF]

EM drive

Validity of physical effect via experiments, theoretical explanation and prediction of effect [START_REF] Millis | Gunfire at sea: a case study of innovation[END_REF] We use an informal argument map to visualize the debates. The main feasibility claim is put at the top of the map, arguments that refute feasibility, mostly from critics, are linked to the claim by arrows with the label "opposes". Rebuttals of these opposing arguments, mostly by advocates, are linked to the opposing arguments by arrows labelled with "refutes".

The arguments for and against the feasibility of the turbojet are depicted in Fig. 2. The main arguments put forward against its practical realization were the availability of materials with sufficient stress and temperature limits and a compressor with a sufficiently high compression ratio of ambient air (Constant, 1980, pp.184-186). These arguments were refuted by the availability of new high temperature alloys and the development of a new compressor with sufficiently high compression ratios by Griffith. Hence, the integration of new technologies into the turbojet lead to its principle feasibility.

Fig. 2: Argument map for and against the feasibility of the turbojet

The feasibility argument map for black-box inertial navigation is depicted in Fig. 3. The main argument against inertial navigation was the so-called "problem of the vertical", put forward by eminent physicist Gamow. Gamow argued that according to the General Theory of Relativity, acceleration in a black box cannot be distinguished from gravitation. Therefore, black box inertial navigation is infeasible with sufficient accuracy, as the error would quickly increase. The argument was refuted by the development of a closed-loop control algorithm that calculates the position of the black box with respect to a spherical model of the Earth and readjusts the box, thereby minimizing the error to an extent where it could be used for practical applications.

Fig. 3: Black box inertial navigation feasibility argument map

The feasibility of hypothetical molecular assemblers has been debated in the Drexler-Smalley Debate [START_REF] Bueno | The Drexler-Smalley Debate on Nanotechnology: Incommensurability at Work?[END_REF]Drexler, 2003a;[START_REF] Mccray | The visioneers: How a group of elite scientists pursued space colonies, Nanotechnologies, and a limitless future[END_REF]Smalley, 2003aSmalley, , 2003b[START_REF] Smalley | Of chemistry, love and nanobots[END_REF]. A reconstruction of the structure of the debate is shown in Fig. 4 Fig. 4: Molecular assembler feasibility argument map Smalley rejects the feasibility of a molecular assembler that is capable of a) precisely positioning atoms and b) creating objects that are useful for practical applications. He rejects a), as he considers atomically precise positioning by devices made out of atoms impossible. He rejects b), as he considers manufacturing objects sufficiently quickly via molecular assemblers requires self-replicating assemblers, which are more challenging to develop than simple assemblers. Drexler argues against Smalley's points by pointing out that atomically precise positioning is not required, as instead of atoms, molecular chains are positioned, which relaxes the requirements for positioning. Smalley counters by claiming that his argument stays valid even for molecular chains. Drexler counters Smalley's selfreplication argument by arguing that self-replication is not required and proposes possible solutions without self-replication. As a final case, the current debate on the feasibility of the EM Drive is depicted in Fig. 5, which is a yet to be confirmed propulsion system for spacecraft that seems to violate currently known physics. EM Drive proponents claim that they have measured a force when operating an EM Drive on a test stand [START_REF] Shawyer | Second generation EmDrive propulsion applied to SSTO launcher and interstellar probe[END_REF][START_REF] Tajmar | Direct Thrust Measurements of an EMDrive and Evaluation of Possible Side-Effects[END_REF][START_REF] White | Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum[END_REF]. Some of the proponents further claim that the measured force is due to a thrust force generated by the EM Drive, which could indicate a yet unknown physical effect. Opponents are sceptical of these claims based on a) alternative explanations for the measured force, which would not imply that a thrust force has been measured; b) the used methodology and experimental setup to be able to measure a force with sufficient accuracy; c) the lack of theoretical models that predict the measured force [START_REF] Millis | Gunfire at sea: a case study of innovation[END_REF]. The four argumentations for and against the feasibility of the respective technology are quite distinct but can be captured by the technology concept model presented in Fig. 1. The resulting mapping is shown in Table 2. If this observation can be confirmed by further case studies, it could be an important hint at how feasibility issues in breakthrough technologies can be systematically resolved.

We further observe that it is not necessarily the existence of a physical effect (e.g. Lorentz force) that is subject of the debate but its conversion into a working principle that satisfies the performance requirements of the application. Hence, principle feasibility debates are genuine engineering debates in the sense that it is not the knowledge of an effect that counts but its practical applicability, which is consistent with the distinct characteristics of technological knowledge, compared to scientific knowledge, as Vermaas et al. ( 2011) have pointed out.

Another observation is what we call "gap-filling". The many unknowns related to potential breakthrough technologies leads to the use of assumptions, analogies, and premises from existing technologies in order to fill the knowledge gaps. As [START_REF] Kurzweil | The Drexler-Smalley debate on molecular assembly[END_REF] remarked in the context of the Drexler-Smalley debate, arguments based on such premises can lead to straw man arguments that refute a technology concept that does not reflect the technology concept the advocates have in mind. Gap-filling seems to be highly sensitive to the domain, organizational, and cultural context in which the debate takes place along with the origin of its participants. Domain-sensitivity in the context of the Drexler-Smalley debate has been previously discussed in [START_REF] Bueno | The Drexler-Smalley Debate on Nanotechnology: Incommensurability at Work?[END_REF].

CONCLUSIONS

This paper explores principle technological feasibility of breakthrough technologies by proposing a technology conceptual model and analysing four cases of past and present principle feasibility debates using argument maps. The elements of the technology conceptual model that were subject of the debate for a specific technology were identified. Furthermore, the model elements that resolved the principle feasibility issues were also identified. At least for the debates analysed, it seems that the more mature a technology is (turbojet, inertial navigation) performance issues are subject of the debate, whereas for more speculative technologies (molecular assemblers, EM Drive), the physical effects and the working principles seem to be the focus of the debate. However, performance is even relevant for speculative breakthrough technologies. Principle feasibility issues for breakthrough technologies seem to be resolved by introducing new component technologies and working principles. For future work, we propose case and field studies in order to explore the contextual feasibility criteria for breakthrough technologies such as injection into products, enabling systems, and market readiness.

Fig. 1 :

 1 Fig. 1: Technology conceptual model adapted from[START_REF] Hein | Heritage Technologies in Space Programs -Assessment Methodology and Statistical Analysis[END_REF]

Fig. 5 :

 5 Fig. 5: EM Drive feasibility argument map

Table 2 :

 2 Feasibility debates and associated technology framework elements

Technology Elements of technology framework subject of the debate Elements of technology framework that served as the solution

  In the following, the observations and implications of these results are reported. As sufficient performance is a key criteria for breakthrough technologies, as expected, almost all debates focus on performance. Satisfactory performance was achieved for the turbojet via changes to the design, notably the parametric design (compressor), materials (turbine blades), and for inertial navigation by introducing a new working principle (new control algorithm). Hence, in both cases, new technologies on a component level were introduced to solve the feasibility issues. It seems that technology infusion into the architecture of a breakthrough technology is an important aspect. For the molecular assemblers, new working principles were introduced for achieving molecule positioning and sufficient manufacturing speed. The feasibility issues of the EM Drive have not yet been addressed. Despite the small sample size, one can observe that the debates around more mature technologies (turbojet, inertial navigation) were focused on sufficient component and system-level performance, whereas debates around less mature technologies were focused on underlying physical effects and working principles. Nevertheless, performance was an important criteria in almost all cases. Another observation is that the feasibility issues were often resolved by injecting component technologies and working principles into the technology, without fundamentally changing the technology's architecture.

	Turbojet	Component performance (compressor, turbine)	New parametric design (compressor),
			materials (turbine blades)
	Inertial navigation	Performance, working principle	Introduction of new working principle
			(new control algorithm)
	Molecular assemblers Physical effects, working principles, performance	New working principles (molecule
			manipulation)
	EM Drive	Physical effect, working principle	Not resolved

ACKNOWLEDGEMENTS

The authors would like to thank Claudia Eckert and K. Eric Drexler for their comments on an earlier version of this article.


Stéphanie Hajiw

Brigitte Pansu
email: brigitte.pansu@u-psud.fr

Jean-François Sadoc

Evidence for a C14 Frank-Kasper Phase in One-Size Gold Nanoparticle Superlattices

Keywords: Nanocrystals, superlattices, colloids, self-assembly Understanding

The Frank-Kasper phases were already known in 1982 when quasicrystals have been discovered but their complex architectures are now considered as making a link between simple close-packed periodic structures and some quasiperiodic ones. These tetrahedrally close packed structures are observed in many materials from elements to intermetallics as well as self-assembled soft materials like micellar systems, dendritric liquid crystals, star polymers and more recently block-copolymers or heated gold nanocrystal superlattices. We report here the existence of a Frank-Kasper phase with hexagonal symmetry (MgZn 2 type, also labelled C14) in superlattices of monodisperse hydrophobically-coated gold particles at room temperature obtained from suspensions in various solvents. The existence of such a structure in this system is analysed in terms of geometrical parameters including gold core diameter, ligand length and grafting density and an energetic approach based on van der Waals attraction.

Hydrophobically-coated gold nanoparticles is a new system that exhibit a Frank and Kasper phase built by one-size objects. This result opens a route towards nanoparticle superlattice with complex structures and thus original physical properties.

particles or atoms behave like hard spheres, the structures that they form are compact structures : face centered cubic (FCC) or hexagonal compact (HCP). Other structures like body-centered cubic structure (BCC) or Frank-Kasper phases (FK) require more complex interactions 1 or anisotropic shapes. [START_REF] Damasceno | Predictive Self-Assembly of Polyhedra into Complex Structures[END_REF] Sixty years ago, Frank and Kasper 3 have investigated many complex alloy structures, constructing packings of polyhedra with large coordination number (Z= 12, 14, 15 or 16) in order to maintain tetrahedral close packing. After the discovery of quasicrystals , [START_REF] Shechtman | Metallic phase with long-range orientational order and no translational symmetry[END_REF] it was recognized that the Frank-Kasper phases complex architectures were the bridging between classical close-packed periodic structures and some quasiperiodic ones. They thus regain much attention in order to understand how to get quasicrystalline materials. In the Frank-Kasper (FK) structures, there are at least two types of sites with different environments. This explains why, in atomic systems, these structures are mainly observed in alloys with at least two types of atoms, with some exceptions such as β-Tungsten (A15 phase) or β-Uranium (σ phase). Since soft particles can adapt their shape to the local geometrical constraints, they are excellent systems to search for FK phases and thus quasicrystalline structures. [START_REF] Ungar | quasicrystalline and related phases in liquid crystals[END_REF][START_REF] Talapin | Quasicrystalline order in self-assembled binary nanoparticle superlattices[END_REF] In these systems, beyond thermodynamic interaction, entropy is suspected to drive new principles of self-organization [START_REF] Ziherl | Maximizing entropy by minimizing area:? Towards a new principle of self-organization[END_REF][START_REF] Iacovella | Self-assembly of soft-matter quasicrystals and their approximants[END_REF] and FCC, HCP and BCC structures but also FK phases are expected as for atomic systems. Frank-Kasper phases have already been found in micellar systems, [START_REF] Seddon | Handbook of Biological Physics: Structure and Dynamics of Membranes[END_REF] liquid crystals, [START_REF] Ungar | quasicrystalline and related phases in liquid crystals[END_REF][START_REF] Ungar | Giant supramolecular liquid crystal lattice[END_REF] star polymers, block-copolymers [START_REF] Lee | Discovery of a Frank-Kasper phase in sphere-forming block copolymer melts[END_REF][START_REF] Sangwoo | Sphericity and symmetry breaking in the formation of Frank-Kasper phases from one component materials[END_REF] and very recently in heated gold nanocrystal superlattices. [START_REF] Goodfellow | Ordered structure rearrangements in heated gold nanocrystal superlattices[END_REF] Micellar systems [START_REF] Seddon | Handbook of Biological Physics: Structure and Dynamics of Membranes[END_REF] exhibit two different FK phases: the A15 phase for direct micelles and the C15 phase for inverted micelles (Figure 1). The A15 phase is a cubic phase with Pm3n as symmetry group, a AB 3 stoichiometry, 8 spheres per cubic cell and Z=12 (icosahedron) or Z=14 coordination numbers. The C15 Laves phase [START_REF] Laves | Crystal Chemistry: Structure of Metals, Metalloids and their Compounds[END_REF] is also cubic with Fd3m as space group, a AB 2 stoichiometry, 24 spheres per cubic cell and Z=16 or Z=12 coordination numbers. In dendrimers 10 as in polymeric sys-tems, [START_REF] Lee | Discovery of a Frank-Kasper phase in sphere-forming block copolymer melts[END_REF][START_REF] Sangwoo | Sphericity and symmetry breaking in the formation of Frank-Kasper phases from one component materials[END_REF] a σ FK phase with tetragonal symmetry (P4 2 /mnm) has also been reported. With 30 spheres per unit cell, it is a dodecagonal quasicrystal approximant structure primarily reported in numerous metal alloys. However, in surfactant or block-copolymer self-assembly, the micelles are not identical and the system is thus closer to alloy structure. For gold nanoparticles, the formation of the FK phases was linked to the growth of some particles upon heating leading to several gold core sizes. Only the dendrimers can be really considered as monodisperse objects building FK phases and dodecagonal quasicrystals. Nevertheless establishing links between all these systems is essential to improve understanding of complex crystallization. This is clearly an important challenge in order to grow materials based on metallic nanoparticles with complex symmetries and thus original physical properties. FCC to BCC structure is the ratio x = L/R where L is the ligand extended length and R the radius of the solid core. When x is smaller than typically 0.7, the FCC packing is favored. [START_REF] Landman | Small is different: energetic, structural, thermal, and mechanical properties of passivated nanocluster assemblies[END_REF][START_REF] Whetten | Crystal Structures of Molecular Gold Nanocrystal Arrays[END_REF] For large x, BCC or BCT (deformed BCC) packings can be observed. Soft nanoparticle superlattices are usually nucleated through the evaporation of the suspending solvant and the nucleation kinetics is also essential in controlling the final structure. [START_REF] Wang | Correlating Superlattice Polymorphs to Internanoparticle Distance, Packing Density, and Surface Lattice in Assemblies of PbS Nanoparticles[END_REF] Recent experiments have shown that superlattices of dodecanethiol-capped 1.8 nm diameter Au nanocrystals (x close to 2) can undergo a non-reversible series of ordered structure transitions at high temperature. [START_REF] Goodfellow | Ordered structure rearrangements in heated gold nanocrystal superlattices[END_REF] Among these phases, several complex pseudo-FK phases have been observed: the cubic NaZn 13 -type structure (Fm3c), the hexagonal CaCu 5 -type structure (P6/mmm). But in this experiment, the structure change is associated to the NP growth and even coalescence leading to various sizes of nanoparticles.

Results and discussion

Experimentals Results

Whatever the crystallization process used and after a certain time, all samples show the same typical SAXS pattern. It is clearly not cubic but compatible with a compact-hexagonal type structure with the first peak located close to 0.12 Å-1 and thus a lattice parameter a ≈ 6.5 nm c = 8/3a ≈ 10.5 nm. The lattice parameter a is always close to twice the distance D P for which the ligands chains are fully interpenetrated. This large cell parameter is very reminiscent of what has been observed 13 on suspension of dodecanethiol-coated gold nanoparticles at high temperature but the authors have attributed the large lattice constant to the NP's growth. Figure 2 shows a diffraction pattern that can be described by a hexagonal lattice with a large cell parameter. The first peaks are less intense. Some peaks close to q = 0.2 Å-1 are more intense. This clearly shows that, in the large cell, the crystallographic motif is rather complex. In emulsions, the observed peaks are larger: the domains, confined in droplets, are smaller and the lattice parameter is less well defined, it could also be not perfectly homogenous. Nevertheless this parameter lies in the same range as for crystals built in capillaries. To confirm the large cell parameter, cryo-TEM experiments have been performed on superlattices built by Oswald ripening of NP suspension-in-water emulsions. Using this method, small crystals stabilized by surfactant can be grown and observed by cryo-TEM . X-ray scattering on these emulsions also shows Bragg peaks around 0.108 Å-1 even if the peaks are large due to the small grain size but perhaps also to a polydispersity in the lattice parameters. Some images as Figure 3a confirm that the lattice parameter is typically twice larger than the particle diameter. Indeed Figure 3a shows a hexagonal pattern with typical distances 6.4 -6.7nm. Figure 3b exhibits layers with a distance d ∼ 3.3nm. Cryo-TEM expriments also show that without heating the nanoparticle core size is constant. The sulphur-gold bond is also very stable and thus, at room temperature, the number of ligands per gold core can reasonably be considered as constant. Thus the system contrary to what is observed in 13 really remains monodisperse.

Determination of the structure X-ray scattering experiments clearly shows that the structure is hexagonal but with a parameter cell twice larger than expected for single spheres. Therefore more complex architec- (first order peak q 0 = q 100 , crystal grain size L C ), the intensity scattered by the disordered suspension in contact with the crystals and a backgound I bg . For the disordered suspension, the Percus-Yevick structure factor S HS (q) of hard sphere with diameter D HS and volume fraction Φ HS has been used. The two first intensities also involve the structure factor of the gold core particles FF(q).

I th (q) = F F (q) * I cryst * S cryst (q, q 0 , L C ) +F F (q) * I liq * S HS (q, D HS , Φ HS ) + I bg

Figure 5 shows a comparison between the measured radial intensity and a theoretical powder pattern for the C 14 and the Z structures. The C14 structure expected intensity corresponds quite well to the experimental pattern even if no real powder pattern could be obtained. The lattice parameter that can be deduced is a = 6.5 nm and the typical size of the crystalline grains built in suspensions is 0.5 µm. The diffraction pattern clearly does not fit with the computed intensity of the Z structure. Moreover, the intensity of the (100) peak in the hexagonal phase vanishes in the Z structure and this is not compatible with Figure 2b where the (100) peak is clearly visible even if its intensity is low. X-Ray experimental results are thus clearly perfectly coherent with a C14 Frank and Kasper structure.

The cryo-TEM experiments do not contredict the C14 FK structure without clearly confirming it. The small grain shown in Figure 3a can be seen either as a slice of the C14 structure with thickness c/2 as shown in Figure 6a or the projection of a Z structure perpendicular to the 3-fold axis. Observing small flat grains instead of quasi-spherical ones could be due to the effect of the cryo-tem grid preparation that could disturb the soft grain shape and induce a grain flattening. However the Z-phase structure is certainly energetically very close from the C14 structure and could thus also be observed in small crystals whereas the larger crystals clearly exhibit a C14 structure as seen by x-ray scattering. The second TEM image can be interpreted by layers piling perpendicular to the (103) direction, one of the densest plane family that produces intense Bragg peaks (Figure 6b). Other projections of the C14 FK structure are shown in Supplementary Information. The emulsions are very sensitive to the electron beam and unfortunately cryo-tomography performed on these emulsions could not really help to confirm the structure. The future challenge is to grow mechanically stable domains that could be analysed by tomography.

Energetic approach

Our experimental results clearly show that gold nanoparticles close to 2nm diameter size covered with hexanethiol build, at room temperature, a non standard stable phase, nor FCC or BCC that has been interpreted as being a C14 hexagonal Frank-Kasper phase. This hexagonal phase with a large lattice parameter is observed for a ratio 2L D ≈ 0.7 that is for a ratio where a transition for which FCC towards BCC structure as been previously observed. This ratio is certainly not the only pertinent parameter. Understanding what parameters can drive the final structure of the NP superlattices is essential to control their self-assembly. For such small nanoparticles, the gold cores are not perfectly spherical but due to the presence of the ligand corona, this effect will be neglected. The parameters that are certainly involved in this problem are: the diameter D of the core diameter, the extended length L of the ligands, their grafting density σ, the volume occupied by each ligand v. For alkane chains wih n = 6 carbon atoms, L is equal to 0.84 nm and v is equal to 0.18 nm 3 . [START_REF] Israelachvili | Intermolecular and Surface Forces[END_REF] The volume occupied by each nanoparticle, when the corona is dense, is given by :

V N P = πD 3 6 + σπD 2 v = πD 3 6 (1 + 6 L D (σA)) (2)
where A = v L can be interpreted as the section of the chain and is roughly independant of the chain length. Let us first assume that there is no solvent still remaining in the crystal and that the soft corona are dense. The lattice parameter of a given structure is therefore deduced from: V cell = N cell V N P . In each structure two geometrical parameters are important.

One is the minimum distance between two neighbouring particles d 1 that must be larger than the core diameter D= 2.4 nm. The other geometrical constraint is due to the fact that the whole volume between the gold cores must be filled by the ligand chains. Thus each point in this volume must be located at a distance from a NP surface smaller than L. Let d 2 be the maximum distance between any point in the structure and a nanoparticle center; d 2 is also the maximum radius of the coordination polyhedra. Thus d 2 must be smaller than D/2 + L = 2.05 nm to avoid empty space in the structure. Table 1 gives the typical value of all these parameters in our system for a given grafting density. The lattice parameters in the five different structures thus correspond to the same NP concentration for which the particles with a dense soft corona are expected to fill totally the space. Table 1: Parameters involved in the different structures with the same NP concentration corresponding to the densest packing (volume fraction equal to 1) of gold nanoparticles with dense soft corona. The NP gold core diameter is D = 2.4 nm and they are covered with hexanethiol with grafing density σ=5.4 nm -2 . N cell is the number of NPs in each cell, Z is the mean coordination number, N n is the mean number of Voronoi polyhedron faces, a is the lattice parameter in nm, d 1 is the smallest distance between NPs, d 2 is the maximum distance between any point in the structure. Table1 clearly shows that assuming that the nanoparticles totally fill the space rules out the FCC phase due to geometrical constraint: d 2 is too large, that means that octahedral sites are too big compared to the the chain length. This is not the case for the BCC structure.

Structure

Nevertheless it is not the final structure. Geometrical parameters are also compatible with the C14, C15 and Z FK structures. The cell parameter deduced from this geometrical approach is smaller than the experimental lattice constant showing that the corona is not dense but swollen and solvent is probably still present. From a purely geometrical point of view, both BCC, C14, C15 and Z structures could be expected for dense soft corona (NP volume fraction equal to 1). FCC is allowed only if solvant is still present between the NPs.

In micellar systems the stability of the BCC structure is explained using entropic arguments. But for metallic NPs, the van der Waals energy between the gold cores cannot be ignored and is much larger than in micellar phases. The Hamaker constant of gold atoms interacting through oil is indeed very large. Its value is still under debate but 75kT is a value that is commonly used. [START_REF] Leff | Thermodynamic Control of Gold Nanocrystal Size: Experiment and Theory[END_REF] We have computed the van der Waals energy for all the structures with the same NP concentration either for dense corona or for the observed NPs concentration derived from SAXS analysis. For both cases, the mean van der Waals energy per nanoparticle is lower for the Frank-Kasper phases. For a volume fraction equal to 1, the van der Waals energy per NP is U F K1 = -8.7 kT for the C15 or C14 structure and U BCC1 = -7

kT for the BCC structure and thus a difference of van der Waals energy per particle of the order of 1.7 kT between the BCC phase and the FK phases. For the NP particle concentration experimentally observed, the van der Waals energy per NP is U F K2 = -3.59 kT for the C14 or C15 structure, U Z = -3.50 kT for the Z phase, U BCC2 = -3.47 kT for the BCC phase and U F CC2 = -3.03 kT for the FCC phase. For short ligand chains, the van der Waals energy difference is certainly large enough to dominate entropic or elastic chain free energy and this explains why Frank-Kasper phases can appear in this system. This is no longer the case for longer ligands for which the distance between the NPs will be larger and entropic effects should become significant compared to van der Waals attraction. For dense systems, the difference of the van der Waals energy per particle, with the same core diameter and covered with dodecanethiol at the same grafting density, is only 0.2 kT between the BCC and the C14 structure. The remaining question is why the C14 structure has been observed

and not the C15 one... These Frank-Kasper phases are very close one from the other and the difference in their energy is certainly very subtle.

Conclusion

In this paper we report the first experimental observation of a hexagonal phase with a large lattice parameter in superlattices of hydrophobically-coated gold nanoparticles at room temperature. This phase has been interpreted as a Frank-Kasper phase (C14) that is the HCP version of the Fd3m structure commonly observed in micellar systems. We show that the van der Waals attraction favors Frank-Kasper phases by comparison with the BCC or FCC structure. However no simple argument can explain why the Frank-Kasper phase that is observed is hexagonal and not cubic. Optical plasmon resonance are observed for larger gold core particles stabilized with longer ligands. For longer ligands, entropic effects have certainly to be considered and it is not clear whether larger NP could exhibit FK phases. Nevertheless this result opens a route towards building complex gold nanoparticles superlattices with original physical properties.

Experimental Materials

In this study we have used small gold nanoparticles with diameter close to 2 nm capped with hexanethiol ligands. They have been synthetized using the Brust procedure. [START_REF] Brust | Synthesis and reactions of functionalised gold nanoparticles[END_REF] They can be suspended in various oils such as n-alkanes, cyclohexane or toluene. Organic solvents and the other chemicals were purchased from Sigma-Aldrich Co., and were used as received. The size and polydispersity of NP gold core have been determined using small angle X-ray scattering (SAXS) on dilute suspensions. The Brust synthesis is very reproducible and the typical gold core diameter is D =2.4 nm (with 16% polydispersity). The grafting density, 5.4 ligands per nm 2 , has been determined by thermogravimetry analysis and is comparable to standard value. The length of the extended ligand chain is 6 = 0.84 nm and thus the maximum external diameter of the gold NPs is D M = D + 2 6 = 4.1 nm. In gold NP superlattices, the interpenetration of the ligand chains is commonly observed. [START_REF] Daniel | Gold Nanoparticles: Assembly, Supramolecular Chemistry, Quantum-Size-Related Properties, and Applications toward Biology, Catalysis, and Nanotechnology[END_REF] A large repulsion between the ligands is predicted when they are fully interpenetrated and the corresponding distance between the spheres is D P = D + 6 = 3.24 nm. For hard sphere with diameter D M = 4 nm (resp: D P = 3.2 nm), the first peak position for classical structures is 0.192 Å-1 (resp. 0.24 Å-1 ) for FCC and BCC and 0.181 Å-1 (resp. 0.226 Å-1 ) for HCP.

Methods

NPs are first suspended in various solvents either volatile solvents (cyclohexane, heptane, toluene) or mixtures of non volatile alkanes (n-dodecane, hexadecane) with a volatile solvent.

The initial NP volume fraction is typically less than 5% (or 30w%) for which no self-assembly in superlattices occurs. The suspensions are poured in flat glass capillaries (VitroCom, USA) that are sealed only at one end. The capillaries are left open at room temperature. Due to the evaporation, the NP concentration in the capillary slowly increases and is followed measuring the x-ray absorbtion as well as weight measurements. The second end of the capillary is sealed when the wished NP concentration is reached. Using flat capillaries has several advantages.

Their thickness (0.1 mm) is well controlled, that is important to determine precisely the NP concentration by X-ray absorbtion. Their flat surfaces can promote the nucleation and growth of monodomains. Oil in water emulsions have also been used. [START_REF] Lacava | On the behaviour of nanoparticles in oil-in-water emulsions with different surfactants[END_REF] Droplets of NP suspension in toluene (5w%) are dispersed in water with the help of a non ionic surfactant (Pluronic P123 from BASF). Ostwald ripening promotes a spontaneous increase of the NP concentration in the smaller droplets and therefore their self-assembly.

Figure 1 :

 1 Figure 1: a) A15 Frank-Kasper structure with space groupe Pm3n (Q223) and AB 3 stoichiometry b) C15 Frank-Kasper structure with space group Fd3m (Q227) and AB 2 stoichiometry.

Figure 2

 2 Figure 2: a) Textured pattern obtained by SAXS on gold NP superlattices, b) Diffraction pattern on a quasi single domain showing a 3-fold axis.

Figure 3 :Figure 4 :

 34 Figure 3: Cryo-TEM image of small grains of hydrophobically-coated gold NP superlattices grown by Ostwald ripening of a doped oil in water emulsion (white scale bar 10 nm). The mean NP diameter determined by SAXS is 2.5 nm. a) Distance between the cell centers: 6.3 to 6.7 nm b) The observed period between the lines is 3.3 nm .

Figure 5 :Figure 6 :

 56 Figure 5: Comparison of the measured radial intensity in suspensions (full line) with the theoretical one (dotted line) : a) for the C14 structure b) for the Z structure. The parameters used are for the crystalline contribution: q 0 =0.112 Å-1 , L C ≈ 500 nm, for the suspension contribution: D HS =3.02 nm, Φ HS =48.8%. The lattice parameters are thus: a = 6.5 nm for both structures, c C14 = 10.6 nm and c Z = 6.45 nm.

  The superlattice structures are determined by SAXS and the experiments have been performed on the Swing beamline of the Soleil synchrotron laboratory (Gif/Yvette, France) and on home set-ups (LPS, Orsay, France). Complementary tests have been done on the D2AM beamline of the ESRF synchrotron laboratory (Grenoble, France). All experiments have been performed at room temperature. The patterns commonly observed are mainly textured patterns produced by several single domains as in 2a. Single domain patterns as that of 2b are rarely observed. Superlattice grains built in emulsion have also been analysed by cryogenic transmission electron microscopy (cryo-TEM). A 3 µl drop of the sample was deposited onto a glowdischarged Quantifoil R2/2 grid (Quantifoil Micro Tools, Jena, Germany) and vitrified in liquid ethane using a home-made cryo-fixation device. The cryo-specimens were transferred to a Gatan 626 cryo-holder (Gatan Inc., Warrendale, PA, USA) and examined at -180 o C with a JEM 2010 Field Emission Gun cryo-Transmission Electron Microscope (Jeol, Tokyo, Japan) using an acceleration voltage of 200 kV and a 50 000 x magnification. Images were recorded with a Gatan 4K x 4K Ultrascan camera with 1 to 1.5 µm of defocus under lowelectron-dose conditions.

Acknowledgement

The authors thank F. Meneau (Soleil), C. Rochas (ESRF), O. Taché (MOMAC experiment, CEA-LIONS+LPS, funded by RTRA "Triangle de la Physique") for their efficient and kind assistance for collecting the x-ray data. For the cryo-TEM experiments, the authors acknowledge the friendly help of J. Degrouard and the financial support from the french CNRS (FR3507) and CEA METSA network (www.metsa.fr).The authors have benefited from fruitful discussions with M. Impéror-Clerc and J. Schmitt (LPS, Orsay).

Supporting Information Available

Geometric features of the C14 and Z phases. Bragg peak positions and intensities for C14, C15 and Z phases. Projection of the C14 structure along various directions. This material is available free of charge via the Internet at http://pubs.acs.org/.


Avi Oriol

Wissam Ño-Salvado

Cyril Sabbah

Hervé Buttay
email: cyril.buttay@insa-lyon.fr

Pascal Morel

Bevilacqua

Evaluation of printed-circuit boards materials for high temperature operation

Keywords: PCB, ageing, polyimide, FR4, oxygen

This article presents the long term (1000 h) behaviour of two printed-circuit board materials (Panasonic R1755V, a high-T G glass-epoxy composite and Arlon 85N, a polyimide-based laminate) stored at high temperature (190 °C). Tests are performed in air and in nitrogen atmospheres. Electrical and physical measurements are performed regularly (once per week).

Almost no degradation is observed for both materials, when stored in nitrogen. On the contrary, the board stored in air show the consequences of ageing. This is especially true for the glass-epoxy material, which becomes unusable after 2 weeks, because of large swelling.

Introduction

Many applications require electronics systems which can operate in relatively high temperatures. For example, in the oil and gas industry, circuits are required to operate in ambient temperatures of 150 °C, 200 °C, or more [START_REF] Beckwith | Downhole Electronic Components: Achieving Performance Reliability[END_REF]. Depending on their location on the car, automotive electronics can experience ambient temperatures of more than 175 °C [START_REF] Kassakian | The Future of Electronics in Automobiles[END_REF].

Organic substrates such as epoxy-based Printed Circuit Boards (PCBs) are attractive because of their low cost (a few C per dm 2 ), process availability (they can be sourced from many companies), and because they offer a high density of interconnections (50 µm track-width and thinner). This is especially true for the automotive market, where ceramic substrates are often considered too expensive.

High temperature operation is also a key capability for some power electronic systems [START_REF] Buttay | State of the art of high temperature power electronics[END_REF], as they operate in harsh conditions, or because they dissipate a lot of heat (hundreds of W/cm 2 ). Many power electronic chips (diodes and transistors, either made out of silicon or silicon carbide) are rated for a maximum junction temperature of 175 °C. While they are usually mounted on high performance ceramic substrates, not on organic PCBs, these chips require a number of peripheral circuits to be mounted in close vicinity [START_REF] Buttay | Integrated packaging allows for improve-ment in switching characteristics of silicon carbide devices[END_REF]. For example, power MOSFET transistors require some gate drive Integrated Circuits (ICs) to operate. Such ICs can oper-ate at the same junction temperature as the transistors they drive, if not higher [START_REF] Khalil El Falahi | Evaluation of commercial SOI Driver performances While Operated in Extreme Conditions (up to 200C)[END_REF]. However, these peripheral circuits do not carry as much current nor do they dissipate as much power as the power chips. Therefore, they do not require mounting on ceramic substrates, and temperature-capable PCBs can be used instead.

Shaddock et al. [START_REF] Shaddock | Reliability of high temperature laminates[END_REF] investigated the behaviour of several PCB materials at temperatures ranging from 200 to 250 °C, over large periods of time (up to 10000 h). It was found that protecting the boards from oxygen was important to increase lifetime. This was confirmed by Lahokallio et al. [START_REF] Lahokallio | High-temperature storage testing of acf attached sensor structures[END_REF] who found that PCBs (FR4 and hydrocarbon-ceramic laminate) tested from 200 °C to 240 °C suffered strongly from oxidation.

In this paper, we investigate the ageing behaviour of a more standard material (a high-T G FR4) and compare it to a polyimide-based laminate. The experimental protocol is detailed in the next section. A preliminary experiment, presented in section 3, is run to define the test conditions. The results of the tests are presented in section 4 and discussed in section 5.

Experimental Protocol

Test Vehicles

Two materials were tested: a FR4-type material (Panasonic R1755-V, with a T g > 170 °C) and a polyimidetype ( The test boards contain 3 groups of features:

• a surface isolation resistance (SIR) pattern, which is an interdigitated pattern with a 500 µm distance between fingers, and 580 mm total finger length. This pattern is biased during the ageing test to produce an electrical field of 25 V/mm [START_REF]test methods manual -2.6.3.7 surface isolation resistance[END_REF].

• 32 daisy-chained vias (hole diameter 450 µm);

• 2 planar capacitors (electrodes size 20×20 mm 2 ) to detect any change in thickness of the PCB For some of the test described below, some test vehicles were separated in small coupons (≈ 2 × 2 cm 2 ) using shears. No damage (e.g. delamination of the edges of the coupons) was observed after this operation.

Accelerated ageing

After a preliminary drying (6 h at 120 °C [START_REF]IPC. Ipc-1601a -printed board handling and storage guidelines[END_REF][START_REF] Charrier | Moisture pick-up and minimum drying conditions of epoxy and polyimide-glass printed circuit board[END_REF]), the test vehicles are placed in an oven for isothermal ageing (storage test). Two test conditions are evaluated in this paper: ageing in air, using a standard forced-convection oven (MMM Venticell), or in nitrogen with the system presented in Fig. 1 (Termolab). This chamber was especially designed for long term testing: it is gas-tight, requiring only a small flow of nitrogen (0.1 SLM) to prevent oxygen to enter. An oxygen monitor is connected to the exhaust of the chamber to ensure the oxygen concentration remains below 0.1 %, and to inject more nitrogen if required.

The ageing tests are run for 1008 h (6 weeks).

In the ovens, the boards are maintained by edgeboard connectors rated at 200 °C (Vishay EB45-P0K2030X). These connectors are used to bias the SIR patterns of the boards. Alpha Wire PTFE-insulated wires enter the ovens and are soldered (HMP alloy) to the connectors. The reliability of this setup is satisfying, as no failure was observed throughout the tests.

The test temperature was defined through preliminary tests ("step stress tests") which are presented in section 3.

Characterisation

Before the beginning of the ageing test, and then periodically (every week, which corresponds to 168 h), the samples are submitted to the following characterisations:

• Weighting (Ohaus Adventurer Pro 210, 1 mg resolution). The samples are dried before the first measurement.

• Pphotography with a Leica M205 binocular, equipped with a camera and a save/recall system which allows to use identical settings (lightning, white balance, etc.). This produces consistent images throughout the duration of the ageing tests.

• Electrical measurements: The capacitance pattern is measured using an Agilent E4990 impedance analyser. A Keithley 2410 source and measure unit (SMU) is used to measure both the resistance of the vias daisy chain (with a 4-point connection) and the surface isolation resistance pattern. This equipment can indeed measure resistances ranging from 100 µΩ up to 200 MΩ.

• Finally, micro-sections are performed on some test coupons using the following protocol: encapsulation in acrylic resin (Buehler Varikleer); cutting with a low speed diamond saw; grinding with P1200 paper (60 s); polishing on clothes with 6 µm, 3 µm and 1 µm diamond particles (180, 180 and 120 s respectively). Final polishing is performed with 50 nm colloidal silica (60 s), and the sample is rinsed and dried.

t 0 150 • C 170 • C 190 • C 210 • C 230 • C 250 • C Temperature [ • C] -10 -8 -6 -4 -2 0 Weight loss [%]
Polyimide, Nitrogen Polyimide, Air FR4, Nitrogen FR4, Air

Figure 2: Weight loss measured on PCB coupons during stepstress testing (the test temperature is increased every 24 h, one coupon is removed from the test chamber after each step to be characterised). As the coupons are relatively small the nonnegligible error (±1 mg) introduced due to the resolution of the scale is displayed using error bars.

Definition of the Test Conditions

A preliminary experiment was run in order to define the temperature to be used for the ageing tests: in this experiment, 6 coupons of FR4 and polyimide boards are placed in each of the ovens (air and nitrogen atmospheres). Starting at 150 °C (arbitrary value), the temperature is then increased by 20 °C every 24 h. For each step, a coupon is removed from the oven and weighted.

The results are presented in Fig. 2. No weight loss is observed on the samples up to 210 °C. After 24 h at 230 °C, the FR4 coupon stored in air shows a dramatic weight loss (almost 8 %). After 24 h at 250 °C, the FR4 coupon stored in nitrogen also exhibits a comparable weight loss. Regarding the polyimide coupons, a nonnegligible (although much lower than for FR4) weight loss is observed for the coupon stored in air (1.5 %).

As some weight loss is observed between 210 and 230 °C in 24 h (for the FR4 board stored in air), and as our tests are scheduled to run over a much longer period (1000 h), a temperature lower than 210 °C (190 °C, corresponding to the data point immediately before 210 °C in Fig. 2) was chosen for the isothermal tests.

Test Results

The weight loss measurements observed during ageing are presented in Fig. 3. They show a small weight loss after the first week (168 h) for all boards. This weight loss tends to be larger for polyimide boards. Then, the weight tends to stabilise until 500 h. At that point, the FR4 board stored in air shows a strong weight loss (4.5 %). No further change is observed for the remaining 500 h. A small increase in weight is observed for the polyimide board stored in nitrogen at the end of the test, and is unexplained (unfortunately, for this measure- ment, we did not use a control sample, so a measurement error cannot be ruled-out).

Regarding the change in capacitance (Fig. 4), the results are comparable, with almost no evolution for the polyimide boards, as well as for the FR4 board stored in nitrogen (two capacitor patterns are monitored per board, producing two curves in Fig. 4). The initial difference between FR4 and polyimide boards is due to the difference in dielectric permittivity (ε r = 5.4 for FR4, ε r = 4.4 for polyimide). For boards of the same material, the intial difference in capacitance can be attributed to manufacturing tolerances (in particular, the thickness of the boards is controlled within ± 10 %). The small changes over time, especially for the first 168 h, are correlated with the weight loss.

For the FR4 board stored in air, however, the capacitance drop is much larger and starts one week sooner than the corresponding weight loss (Fig. 3). The large capacitance drop (≈ 80 %) is related to a noticeable swelling of the board, with large blisters forming (the apparent thickness of the board is more than doubled in some places). Larger blisters tend to concentrate in the capacitance pattern, probably because of the gas-tight area formed by the copper electrodes of the capacitor.

The resistance of the vias is presented in Fig. 5. Again, the evolution is correlated with the change in weight (Fig. 3). The polyimide boards and the FR4 board stored in nitrogen show no noticeable change, while the FR4 board stored in air exhibits a strong increase (15 %). As with the capacitances, this can be related to the swelling of the board. However, contrary to the capacitances (Fig. 4), the change in resistance occurs between the 3 rd and the 4 th week (504 to 672 h), not between the 2 nd and the 3 rd (376 to 504 h). Overall, no rupture of the vias (i.e. fully open circuit, as opposed to gradual increase in resistance) was observed.

The surface isolation resistance (SIR) was found to exceed the capability of our testing equipment (200 MΩ) for the FR4 and polyimide boards in air and in nitrogen atmospheres. Only the FR4 board tested in air showed a drop in SIR after 4 weeks (1.32 MΩ, and 600 kΩ after 5 weeks). The test could not be extended to the 6 th week, as the swelling of the board prevented its insertion in the edgeboard connectors used for the voltage bias in the oven.

Finally, some images of the boards, taken during the course of the ageing tests, are presented in Tab. 2. Many areas of the boards were photographed, and they all show the same evolution: for the boards tested in air, there is a colour change after the first week of test, while the boards tested in nitrogen do not show any colour change over the full duration of the tests. Another change is visible for the FR4 board tested in air, after 4 weeks: the PCB material is no longer uniform in colour, and shows some lighter patches. This is correlated with some corrosion of the Ni/Au plated areas (especially visible after 5 weeks on the via -second line in Tab 2). For the other cases (polyimide boards and FR4 board tested in nitrogen), no such change is visible on the metal areas.

Discussion

Besides the board material, the test atmosphere has a strong influence on the ageing behaviour: the boards tested in nitrogen show no swelling, no discolouration, and almost no change in weight. On the contrary, despite its high T G , the polyimide board tested in air exhibits a non-negligible weight loss (1 %) over the duration of the tests. This confirms the effect of oxygen observed in [START_REF] Shaddock | Reliability of high temperature laminates[END_REF] and [START_REF] Lahokallio | High-temperature storage testing of acf attached sensor structures[END_REF].

The fast degradation of the FR4 material in air could be expected, as the tests were performed at 190 °C, higher than the T G of the material (170 °C). This degradation was detected through all the measurements, but at different times: weight loss (drop after 504 h); capacitance change (drop after 336 h); via resistance (increase after 504 h); SIR (drop after 672 h); visual observation (after 672 h or 4 weeks). Basically, the capacitance measurement was the most sensitive measurement. A possible reason is that the large copper electrodes prevented the decomposition gases to permeate, resulting in an accelerated swelling. This swelling then propagated over the entire board. Eventually, this made it impossible to mount the board in the edgeboard connector. The cross section of a FR4 coupon tested in air is visible in Fig. 6, and shows the extend of the swelling.

The formation of blisters is probably a conjunction of the rubbery state of the FR4 maintained above its T G , and of the thermo-oxidation of the epoxy caused by the diffusion of oxygen [START_REF] Polanský | Determination of the thermal endurance of pcb fr4 epoxy laminates via thermal analyses[END_REF]. It might also be related to other compounds included in the polymer, such as bromide flame retardant [START_REF] Panasonic | R-1755v laminage specification sheet[END_REF], which were found to have a detrimental effect at high temperature in [START_REF] Shaddock | Reliability of high temperature laminates[END_REF]. The gradual embritllement of the thermo-oxidized epoxy [START_REF] Ciutacu | Accelerated thermal aging of glass-reinforced epoxy resin under oxygen pressure[END_REF] might also accelerate the delamination of the glassepoxy composite, expecially above T G , as the CTE of the material increases sharply (from 40 to 240 ppm/K in the z-direction [START_REF] Panasonic | R-1755v laminage specification sheet[END_REF]). Although the vias limited some of the swelling by clamping the board (see Fig. 7), it can be seen that their external annular ring is bent. While no crack could be observed along the barrel of the vias, such bending might explain the increase in resistance measured in Fig. 5.

The FR4 board tested in nitrogen did not show any noticeable ageing, despite it being stored at 190 °C (i.e. above its T G ) for more than 1000 h. Although operating over the glass transition temperature is not recommended because of the reduced mechanical strength of the board and because of its increased coefficient of thermal expansion, this might constitute a "low cost" high temperature prototyping platform: to use a standard high-T G FR4 board instead of a more expensive material, and then to place it in a dedicated test chamber (such as that presented in Fig. 1) to protect it from oxygen. Another solution, as proposed in [START_REF] Shaddock | Reliability of high temperature laminates[END_REF], could be to use a protection layer such as high temperature parylene.

Regarding the polyimide boards, some effects of oxygen could be observed (darkening of the solder resist layer, non-negligible weight loss), but none of these effects translated in changes in electrical performance.

Finally, the Ni/Au finish of the copper tracks was found to have a satisfying stability, with no changes in aspect over the duration of the tests, whether in air or in nitrogen, except for the FR4 boards stored in air. On the latter, the evolution of the Ni/Au finish is probably due to its corrosion by the decomposition products of the board.

Conclusion

The high temperature (190 °C), isothermal ageing of printed circuit board materials is presented in this article. Two materials are investigated, a high-T G FR4 and a polyimide. While polyimide is preferable when operating in air, it is found that FR4 can nonetheless be used over long periods of time (1000 h), providing the tests are performed in a neutral atmosphere (nitrogen).

Several measurements were performed throughout the ageing tests to monitor the condition of the boards. It is found that the capacitance measurements are the most sensitive, as they were the first to detect the degradation of the FR4 board tested in air. Overall, the degradation could be detected through all the measurements (electrical parameters, weight, or visual inspection), albeit one to two weeks later.

As it allows the use of standard PCB materials, operating in nitrogen atmosphere could be an interesting solution for lab experiments and prototyping.

Two distinct topics must be addressed to pursue this study further. First, a more detailed analysis of the various elements in the PCB (laminate and solderresist, mainly) is required. In particular, thermal analyses (thermo-gravimetric analysis, differential scanning calorimetry or thermo-mechanical analysis [START_REF] Smith | Thermochemical and physical properties of printed circuit board laminates and other polymers used in the electronics industry[END_REF]) will measure the degradation temperature of these elements separately to better understand the results presented in this article. The second topic, on the contrary, takes place at board level. It consists in testing the boards in humidity and temperature cycling conditions, to reflect more closely the stresses encountered in real applications.

Figure 1 :

 1 Figure 1: Chamber used for isothermal ageing at low oxygen percentage (<0.1%), using an oxygen monitor and a low flow of nitrogen (0.1 standard litre per minute). The system is 1.4 m tall, 1.2 m wide.

Figure 3 :

 3 Figure 3: Weight loss during isothermal ageing at 190 °C, for polyimide and FR4 boards, tested in air and nitrogen.The error bars corresponding to the measurement error are barely visible because the boards tested here are much heavier (≈ 20 g) than the coupons used in section 3, resulting in a much more accurate measurement with a 1 mg resolution scale.

Figure 4 :

 4 Figure 4: Capacitance change during isothermal ageing at 190 °C, for polyimide and FR4 boards, tested in air and nitrogen.

2 : 2 forFigure 5 :

 225 Figure 5: Resistance change (vias daisy-chain) during isothermal ageing at 190 °C, for polyimide and FR4 boards, tested in air and nitrogen.

Figure 6 :

 6 Figure 6: Cross-section of a FR4 coupon after 5 weeks (840 h) at 190 °C in air, showing the swelling of the board. Darkfield optical microscopy image showing a large blister which formed in the center of the board.

Figure 7 :

 7 Figure 7: Cross section of a large via (1 mm diameter) in FR4 after 4 weeks in air. This shows the bending of the annular ring caused by the swelling of the board close to the via (not visible in this picture). Darkfield optical microscopy image.

Table 1 :

 1 Arlon 85N, T g > 250 °C).

	Both materials were

Main properties of the polyimide

[START_REF] Arlon | Arlon 85n electronic substrates[END_REF]

and FR4 laminates

[START_REF] Panasonic | R-1755v laminage specification sheet[END_REF]

Acknowledgements

This work was funded part of the GENOME-PREMICES initiative.