Bureaucracy, "domesticated" elites, and the abolition of capital punishment. Processes of state-formation and the number of executions in England and Habsburg Austria between 1700 and 1914.

Introduction

The paper argues that rise and decline of capital punishment correlate with long-term processes of state formation. In particular, it stresses that with the introduction of a modern bureaucratic apparatus, the death penalty lost importance for the regime of punishment.

The study is based on two empirical sources: 1) an analysis of the numbers of executions and death sentences in England and in Austria from the eighteenth century to the outbreak of World War I; and 2) English and Austrian pamphlet literature and philosophical treatises on the death penalty in the eighteenth and early nineteenth centuries.

Part 2 of the paper discusses the most important theories concerning the role of capital punishment. It will be shown that the theory of civilizing processes is of particular relevance for understanding the relationship between state-building processes and the decline of cruel forms of punishment.

Part 3 presents a comparison of Austrian and English judicial records. These records provide information about the numbers of executions, the numbers of death sentences and the structure of offences for which capital punishment was imposed. This analysis demonstrates that, as of the second half of the eighteenth century, the death penalty was used much less frequently Austria than in England. This evidence prompts reconsideration of some sociological explanations about the rise and the fall of public executions and the death penalty in general.

Part 4 of the paper focuses on processes of state-formation in both countries. It shows: 1) how institutions of social control differed in the two countries; and 2) how the state-building process in Austria was conducive to reforming the regime of punishment.

Part 5 of the paper presents qualitative analyses of pamphlet literature and philosophical arguments. These help to understand attitudes, affects and emotions related to the death penalty. This analytical approach makes it clear that the main responsibility for a reduction in the use of capital punishment lay with protagonists in high administrative positions of the Habsburg Empire. Their disapproval of capital punishment, as well as the political interests of the absolutistic state, served to weaken local elites. In England, the power figuration was different and therefore bureaucratic institutions did not play the same dominant role. This study demonstrates that capital punishment was a key instrument for the English elites to defend their political and economic privileges.

Some theoretical approaches to explain rise and fall of capital punishment

Many sociological explanations do not investigate connections between the behavior of the administrative apparatus and changes in the regime of punishment. They are more concerned with the interplay between economic transformations and their influence on social control and punishment [START_REF] Rusche | Punishment and Social Structure[END_REF][START_REF] Melossi | The Prison and the Factory[END_REF], Hay et.al. 1977[START_REF] Thompson | Whigs and Hunters, The Origin of the Black Act[END_REF][START_REF] Polanyi | The Great transformation. The Political and Economic Origins of our Time[END_REF]). These authors generally consider state-building processes to be marginal phenomena driven by economic developments. These arguments are summarized under the concept of the "political economy of punishment" (Garland 1990: 83-110). Some theoristsincluding, to a certain extent, [START_REF] Foucault | Surveiller et punir: Naissance de la prison[END_REF] see modern justice systems reductionistically, as a device to control the lower classes. Most of these theories focus only on certain single case studies, such as Rusche and Kirchheimer (and Marx) on the English or Foucault on the French case (the exception being Melossi and Pavarini who did an international comparison of prison systems). Subsequently, some of these authors have neglected the idiosyncratic character of sociological investigation because they only focus on a single state-society [START_REF] Weber | Gesammelte Aufsätze zur Wissenschaftslehre[END_REF].

Other theoretical perspectives are more concerned with processes of power formation and their correlation to the regime of punishment; [START_REF] Savelsberg | Knowledge, domination and criminal punishment revisited. Incorporating state socialism[END_REF] focuses on the organization of domination and knowledge, while Durkheim stresses the importance of the evolution of institutions and its relationship to the collective conscience (Durkheim 1899/1900: 65-77, Durkheim 1984, 2001[START_REF] Spitzer | Punishment and Social Organization: A Study of Durkheim"s Theory of Penal Evolution[END_REF]). Durkheim suggests studying changes in the regime of punishments within a process of democratization in which the degree of brutality of punishment decreases.

However, it seems that the theory of civilizing processes develops the clearest understanding how the monopolization of a state"s power impacts the regime of criminal punishment. On the basis of the Dutch experience, [START_REF] Spierenburg | The Spectacle of Suffering. Executions and the evolution of repression. From a preindustrial metropolis to the European experience[END_REF] observed that in the period between the end of the Middle Ages and the second half of the nineteenth century, the use of the death penalty changed dramatically. He formulated three phases of transformation (Spierenburg 1984: 202 -205). In the first phase, the early modern state sought to assert itself. State authorities attempted to monopolize power and to suppress all alternative forms of private violence. Torture and public executions were the means of demonstrating the state"s new power. The early modern states, however, still operated under fairly unstable conditions, and their power institutions were relatively weak. In the second phase, the state"s position was more assured, because a mighty power-center developed. During this period, the aristocracy no longer lived under feudal conditions and, thus, no longer had a fundamental military function. The nobility developed a refined life-style and, along with the high bourgeoisie, they were "domesticated" and "pacified". The living conditions of these "domesticated" elites became more elaborate and cultivated. Spierenburg argues that these two elite groups began to rebel against the bloody rituals of punishment first. Their aversion to violence was a result of a process of conscience formation. Their disgust changed into pity. Spierenburg believes that many of these elites entered a "new stage and identified to a certain degree with the convicts on the scaffold" (Spierenburg 1984: 204). In this period, also the torture disappeared. In the third phase, the nation-state was formed. It expanded the capacity for empathy to a wider spectrum, because more social groups were integrated and could participate in power decisions (democratization). Increasingly, democratized power relationships accelerated the moderation of the penal code. Citizens of different social ranks, too, began to identify with each other and with the suffering of the offender on the scaffold. Public executionsand later, executions in generalcame to be seen as a source of national shame, and were therefore abolished (see also [START_REF] Evans | Rituals of Retribution. Capital Punishment in Germany 1600 -1987[END_REF][START_REF] Gatrell | The Hanging Tree, Execution and the English People 1770 -1868[END_REF] with their national focuses on Germany and England). Thus, Spierenburg argues, harsh punishments (like public executions) were the result of wide class differences that caused social and emotional distance. This promoted the unwillingness or impossibility of identification with the destiny of individuals of different (lower) social background. This lack of empathy ultimately caused a lack pity for the culprits on the scaffold.

The theory of civilizing processes demonstrates the importance of three dimensions for the analysis: First, long-term state building-processes are not necessarily economic epiphenomena. They are essential to understanding institutions and organizations of crime control and correction. Second, the evolution of mentality or what is called the habitus (Elias 1982&1996, Bourdieu 1989[START_REF] Wacquant | Pierre Bourdieu[END_REF])as a kind of bodily imprinting of collective long-term experiencesis useful for explaining the role of emotions like pity for criminal offenders). Third, owing to the process of democratization, civilizing standards were extended down the ladder of social hierarchy. The existence of a feeling of national unity seems to support the idea of a downward progression of civilizing standards. Therefore, in the context of this theory, one would most expect the abolition of brutal punishments in democratic nation-states. In democratic societies, citizens more easily identify with the pain of an offender on the scaffold. Thus, they are more likely to avoid public executionsand to eschew capital punishment in general. Some critics of this theory maintain that it is still unclear how empathy and non-violent attitudes spread downward through the social hierarchy from domesticated elites to the rest of the population [START_REF] Braithwaite | Shame and Modernity[END_REF].

Another problematic factor is that Spierenburg"s work is based on a single case study. This paper shows that the case of the Habsburg Empire does not fit into his patterns of explanation. The Austrian case is quite different from the Dutch or the English experience. The criminal laws of the Habsburg Monarchy were comparatively lenient, despite the fact that it was far from being a democratic nation state, and displayed relatively slow economic development. Under Empress Maria Theresia and the Emperor Joseph II, very progressive reforms were made in the penal system. These reforms included the early introduction of a penitentiary system (Melossi and Pavarini 1981: 71ff), a modern penal code, and a centralized police force. The Habsburg monarchy was also one of the first states to abolish death penalty in the 1780s (although it was reintroduced later, to a greatly reduced extent). Eighteenth-and nineteenth-century England, on the other hand, had established a parliamentary system which evolved (slowly) into a democracy, and the nation exhibited the most advanced economy of its period.

The theory of civilizing processes would suggest that the death penalty would be less prevalent in England than in backward, despotic Austriayet this was not the case. No other Western European country witnessed such frequent executions as England between 1700 and 1830, a time period during which even many property offences were punished with death. Its penal code was old-fashioned and a modern police force was introduced only at a comparatively late stage. These facts must have some relevance for sociological theories of punishment. They could lend themselves to a Marxian argument focusing only on capitalism and treating state organizations as marginal phenomena. However, the argument made here puts the state-building process in the center. This study compares the development of death penalty in England and in the Austrian Monarchy firstly because these two cases seem to challenge both sociological theories. Furthermore, these cases also help to modify the Elias/Spierenburg theory by revising its themes, in particular the absolutism/democratizationpity nexus, and the role of "domestic elites". Moreover, both cases represent two extreme poles in the handling of state punishment: relatively lenient and harsh. The study also provides a comparative and deeper focus on the two cases. Therefore, it enables one to understand (Weber) certain qualities of the state machinery and subsequently to explain their effects on the regime of punishment. The study highlights two different "cultures of control" [START_REF] Garland | The Culture of Control, Crime and Social Order in Contemporary Society[END_REF]) but also long-term processes of state formation that strongly influenced these cultures.

Numbers of executions and numbers of death sentences in both countries 1

Death sentences and executions in England

Before continuing with sociological theory, I will describe the two historical case studies: England and Habsburg Austria from 1700 to the start of World War I. Tables 1 and2 show clearly that until the middle of the nineteenth century, death sentences and executions were more common in England than in Austria. In the beginning of the nineteenth century, both death sentences and executions were much more common in England than in Austria. Statistical data available for eighteenth century London and Middlesex also indicate bloody penal practices (Gatrell 1996: 616;Reicher 2003: 42). 2 These data reveal a steady increase in both the number of executions and the number of death sentences, starting with the last decades of the eighteenth century. The numbers peak in the decade after the Napoleonic Wars. Quite similar patterns can be revealed for all of England and Wales. After the 1830"s, the numbers of executions and death sentences started to decline, even dipping under the Austrian level, which was much lower for most of the period under study. In England only a small fraction of those who were sentenced to death were hanged. Many condemned convicts were transported to the colonies, whichin many caseswas also fatal. Thus, the English death penalty was part of a larger penal framework that, along with actual executions, included forms of forced labor in the hostile environment of the colonies.

The legal regulation of the death penalty in England changed dramatically in the period between 1700 and 1800. At the beginning of the eighteenth century, just a few crimes were punished by death. At the end of the century, there were more than 200 capital crimes (Radzinowics 1948: 3f, Briggs et al. 1996: 73). Most of the new capital crimes were offences against private property. (For more on the expansion of death penalty during this period, see [START_REF] Thompson | Whigs and Hunters, The Origin of the Black Act[END_REF], Hay 1977[START_REF] Gatrell | The Hanging Tree, Execution and the English People 1770 -1868[END_REF][START_REF] Evans | Rituals of Retribution. Capital Punishment in Germany 1600 -1987[END_REF]. Table 3 shows the important role that offences against private property played in the English penal law. It was not until the 1830"s that the system of penal law began to change and gradually the death penalty was abolished for property offences. However, in the period between 1822 and 1855, only 5 percent of all 17420(!) death sentences in England were imposed for murderas against 87 percent for offences against private property. Of these last, the vast majority of death sentences were related to nonviolent property crimes.

Death sentences and executions in Habsburg Austria

In seventeenth-century Austria, penal practices were perhaps even crueler than in England. Beside hangings there were many other types of executions (although these were rarely used). However, executions became rare phenomena in eighteenth century Austria, and it seems they were never imposed for property crimes alone (see e.g. the collection of death penalty announcements published in Vienna). 3 Empress Maria Theresia introduced in the year 1768 a new penal code (the "Constitutio Criminalis Theresiana") which still officially contained numerous brutal penalties such as torture and severe methods of execution (Foregger 1993). However, this new code also marked the beginning of a phase of lasting reforms. In the 1780s, only two decades later, Emperor Joseph II launched major reforms. A new penal code was introduced for some provinces. Most importantly, capital punishment was abolished for all crimes. In some provinces separate reforms were undertaken. The most remarkable and significant of these were the reforms in the 1760s in Tuscany, which introduced a very lenient penal system virtually devoid of capital punishment. In his journey through Tuscany, the English prison reformer Howard counted only 2 executions in 10 years (Melossi and Pavarini 1981: 74f). Grand Duke Pietro Leopoldo, the later Emperor Leopold II, headed this reform movement (which initiated what were known as the Leopoldian reforms) which included figures such as Pietro Verri, Paul Frisi, Cesare Beccaria and others. This group of intellectuals and civil servants from Milan were known as the Caffé. They were tightly connected to Viennese circles representing the highest ranks of bureaucrats, such as Counts Kaunitz and Firmian, or enlightened reformers like Josef von Sonnenfels (the author of a famous treatise on the abolition of the torture).

In Austria, capital punishment was embedded in a larger framework of other punishments that developed during the eighteenth century. The oldest and most brutal substitute for executions was forced labor on Venetian galleys. Joseph II introduced the punishment of pulling ships upriver on the Danube as a penalty for severe offenders. The most important development, however, was the introduction of a penitentiary system in eighteenth century which provided an alternative for the death penalty; some early prisons included the Maison de Force in Ghent, or the Plazzo degli Otto and the Stinche in Florence.

During the Napoleonic threat, capital punishment was reintroduced. Its implementation, however, remained at a low level. It was imposed only for murder, offences against the state"s authority, and in some cases, for financial fraud in relation to issued stocks (which was considered a threat to the state because it could have endangered the weak economy of early nineteenth century Austria). Beccaria and other reformers held the protection of the state as their highest value. For them, the state was the foundation for protecting all other values. Therefore, in the period between 1822 and 1855, eight percent of all Austrian death sentences (984) were imposed for offences against the state"s authorities (Table 3), which was more than in England. However, the vast majority of all death sentences (77 percent) were related to murder. Only a relatively small number were imposed for offences against private property.

Weak and strong states

The focus on the Habsburg Empire reveals that bureaucracy was the most important institution for uniting a realm that consisted of many divergent provinces. Traditionally, many of these territories -spreading from Italy to Belgium and from the Rhine to the today"s Ukrainedid not have much in common. They differed in their political histories as well as in their cultures. In such a situation, the administrative apparatus with its homogeneous staff helped the Viennese power-center, along with its army, to rule over local elites. These local elites stubbornly defended their particular privileges. In many corners of the realm, particular traditional hierarchical systems of ethnic and social dominance prevailed, and the Emperor"s power varied throughout his provinces. He was more influential in some areas than in other parts of his realm. As late as 1848, the aristocracy was under the rule of a separate jurisdiction. In particular, the wealthy high aristocracy could not be taxed successfully. Throughout its entire history, the Habsburg Empire neither developed into a single administrative and jurisdictional unit nor did it form a single economic market. It was also far from being a nation-state. This diversity laid down the foundation of the Austrian-Hungarian Monarchy (Doppelmonarchie) in 1867 and thereafter.

The permanent struggle of the Viennese center to overcome this diversity was a typical characteristic of the Habsburg Empire. In the course of the seventeenth and eighteenth centuries, ministries (and their forerunner organizations), local registrar offices, state court systems, police stations, and other offices began to eclipse provincial parliaments and local forms of feudal domination. In Austria, unlike in England, the power game between aristocracy and an absolutist monarch veered slowly in favor of the latterwithout, however, ending in a fully centralized state such as France. Austria turned into an Empire consisting of many heterogeneous provinces and ethnic groups and did not develop into a nation-state (which was a barrier for the development of the mutual identification posited by Spierenburg). Aside from the army, the administrative machinery was the most important instrument for governing the realm. A bureaucratic elite began to intervene in all sorts of local affairswhich included matters of criminal justice and crime control. Thus, the Austrian Empire came closer to Max Weber"s (1978) type of "bureaucratic domination" than any other Western European state. It cleared a path for the development of modern bureaucracy with its characteristic separation of economic and political/administrative power. In this sense, the Habsburg Monarchy was a strong state.

To speak about weak and strong states implies multidimensional concepts. On the one hand, weakness can refer to a state"s military competence. Strong states, in this sense, must have powerful armies and efficient tax systems (which the Habsburg Monarchy did not have). On the other hand, weakness or strength can be linked to the state"s ability to cope with internal affairs. There are many reasons why states can be weak in their internal affairs, but strong militarily (such as England). Ruling elites may fear the power of a well-organized police (because they might become a state within the state) and thus tolerate a high crime rate. Such states may be unable to fight crime successfully because, for various reasons, they lack the resources to do so. States may be strong internally because they deploy either armed forces or powerful police organizations to prevent, repress, or detect crime ("policing power"). Secondly, states may make use of social welfare programs to deal with poverty and matters of distribution ("welfare power"). This also may have effects on the regime of crime control and crime treatment, since a class of technocrats produced by the welfare expansion may expand its interests into fields of penal correction and criminology [START_REF] Garland | Punishment and Welfare: A History of Penal Strategies[END_REF]. Thirdly, a state finally may have a greater or lesser belief that its rule is just and legitimate ("ideological power"). These capacities may coexist in various and idiosyncratic patterns of relationships in every society. All these aspects are reflections of different sorts of social power [START_REF] Mann | The Sources of Social Power: A History of Power from the begining to A.D. 1760[END_REF]). Although more complex patterns are possible, for the purposes of this paper, I split Mann"s category of military power into two parts: external and internal control (policing power).

This paper focuses on the internal weaknesses and strengths because of their relevance to the authorities" belief in their ability to maintain social control. Thus, "strong" refers to the bureaucracy as an internally powerful actor intervening in many spheres of life. Although its proponents may believe in its efficiency, this does not mean that a strong state is necessarily truly efficient. The Austrian bureaucracy was known for being hesitant and slow to react. However, the rule of the administrative machinery (which is the actual meaning of bureaucracy) organized patterns of relationships between the rulers and the ruled population in a totally new way. It differed from a weak-state structure, which is characterized by direct and personal forms of domination. Administrative rule is more distanced than personal rule.

Bureaucracy is a form of domination characterized by its indirectness. In theory, it does not involve anything other than professional interests. Above allbecause of its impersonal characterbureaucracy is open for new reform projects (sometimes utopian, sometimes realistic).

Structures of state-building: democratization and bureaucracy

Within the theory of civilizing processes, two lines of argumentation explain the process of de-brutalizating (civilizing) the regime of criminal punishment: the democratization argument and the bureaucracy argument. [START_REF] Spierenburg | The Spectacle of Suffering. Executions and the evolution of repression. From a preindustrial metropolis to the European experience[END_REF] and De [START_REF] Swaan | Widening Circles of Identification: Emotional Concerns in Sociogenetic Perspective[END_REF][START_REF] Swaan | Widening Circles of Disidentification. On the Psychoand Sociogenesis of the Hatred of Distant Strangers -Reflections on Rwanda[END_REF] stress the importance of "democratization" for civilizing violent attitudes and brutal punishments (democratization argument). They believe that through a process of "functional democratization," the expansion of mutual identification and empathy is promoted. However, within in the framework of the theory of civilizing processes, an alternative explanation for the de-brutalization process of the regime of punishment seems possible. [START_REF] Elias | The Civilizing Process. State Formation and Civilization[END_REF] stresses the argument that in France, after power was monopolized in the hands of the king an administrative apparatus appeared. Elias ends his history of the French civilizing process with the establishment of the royal court. Thus, he does not say much about what happens afterwards. In particular, he does not address the "second civilizing process" which started within the newly founded bureaucracy, and whose protagonists were no longer the nobility, but rather an administrative staff. Yet, it is essential to understand the development of the administrative machinery to see its impact on this "second civilizing process". The bureaucracy argument claims that a strong and self-confident bureaucracy will very likely find alternatives to brutal punishment. They prefer to use modest but permanent repression to maintain social control. The administrative machinery facilitates professionalism, which helps it withstand the economic interests of capitalism and form a new kind of "domestic elite".

When studying the state-building process within the framework of the civilizing process theory, it is important to acknowledge the idiosyncratic characteristics of each state"s development. Neither the Austrian nor the English development resembles Spierenburg"s subject (the Netherlands) or Elias"s subject (France).

Patterns of state-building in England

The Marxian argument about punishment applies well to eighteenth century England. Not until the Glorious Revolution did the English gentry gain control over political and legal institutions. The gentry began to change laws and property rights to serve their own interests. They combined economic and political power and, thus, decreed capital punishment for many sorts of offences against private property (see [START_REF] Thompson | Whigs and Hunters, The Origin of the Black Act[END_REF].

In England, political and economic power seemed to go hand in hand. However, beginning in the middle of the 1830s, England witnessed political reforms such as new suffrage laws and the introduction of police forces. Before these reforms, the political system was a kind of oligarchy ruled by a powerful land-owning class (the higher nobility and the gentry). The proto-democratic structure of the English political system promoted the death penalty because it linked economic and political interests (as expressed in the high numbers of capital sentences for offences against private property). After the 1830s, the political system was opened up to lower ranks of society. This process of democratization was possible because England, unlike Austria, was a nation-state governed by only one parliament. Here, democratization was intertwined with the process of nation-state building.

England"s development in the eighteenth century is surprising, in a certain way. The country became centralized much earlier than most other European countries. The Tudors undertook serious attempts to install a powerful bureaucratic apparatus. The rise of the landowning class"s power in the seventeenth century, however, blocked further tendencies towards bureaucratization. After coming to power in the year 1689, the English landowning class resisted attempts to establish strong central organizations such as a police force or a multilayer court system. Many of the state"s internal affairs remained in the hands of the local elites and communities. Other tasks that were still in the hands of the state"s bureaucracy were "re-localized" (for instance, the abolishing of the famous "Star Chamber"). The English land-owning class feared the power of any central organization. It saw powerful bureaucracies as a threat to its liberties.

Since medieval times, the English court systemunlike many systems in continental stateshad been centralized and its rules standardized (see [START_REF] Radzinowicz | English Criminal Law and its Administration from 1750[END_REF][START_REF] Beattie | Crime and the Courts in England 1660-1800[END_REF]). After the Glorious Revolution, however, only the local jury courts remained. All higher courts were abolished. The remaining local courts, therefore, became the centers of the legal system. In the eighteenth and the first half of the nineteenth century, there was no court of appeals. Death sentences were reviewed by the Home Office, and no other institutions existed to review the local courts.

The institutions of public social control were restricted to local elite"s influence, too. Thus, Justices of the Peacean honorary functionwere often regarded as clients of the local elites. Edmund Burke, for example, described the JP"s as "elderly, greedy, corrupt [men], who had attained office by improper means." (Skyrme 1994: 410). Eighteenth century London experienced some organizations that formed a kind of police, e.g., the "Bow Street Runners", but these organizations were exceptions [START_REF] Emsley | Crime and Society in England, 1750-1900[END_REF]. For the most part, public social work remained the task of volunteers. It was obvious to many that this system allowed only for low-intensity repression and social control to be deployed. However, it was not changed because of the gentry feared of becoming dependent on these police organizations. Therefore, measures of deterrence, especially public hangings, became an important instrument in fighting crime. The fact that the death penalty also became the major punishment for crimes other than murder may be an expression of the helplessness of the English elites in dealing with crime. Many sorts of crimes against private property became punishable by death. Simultaneously, Austria was taking very different steps.

Patterns of state-building in Austria

Unlike in England, Austrian agricultural structure was dominated by patrimonial relationships (see: [START_REF] Kuzmics | Authority, State and National Character. The Civilizing Process in Austria and England, 1700-1900[END_REF]. Big landowners and powerful peasants were bound by strong obligations to their petty peasantry and farm workers. This circumstance prevented the development of commercialization and the rise of an English-type enclosure movement. The central state administration eagerly tried to narrow the elbowroom of local big landowners, as well. The Habsburgs feared a well organized Gentry. The big landowners were not able to alter property rights in order to subdivide common land among individual owners like in England [START_REF] Polanyi | The Great transformation. The Political and Economic Origins of our Time[END_REF]) because they had no easy access to the law-making process. Both the tight patron-client relationship and the central state intervention established a complicated and indirect system of social control in Austria. Thus, the two fields of economy and politics were separated in many aspects. Already in the course of the seventeenth century, the organized power of the nobility (in parliaments) and the land owning-class was broken up by the monarch and his administration. Unlike its English peers, the Austrian nobility was not able to abolish their small provincial parliaments and to form a common parliament that would oppose the Emperor. Democratization in Austria, therefore, did not take place before the early 1890s.

The Austrian monarchy, on the other hand, developed into a state with a powerful bureaucracy. There was a four-layer court system that had been established in the eighteenth century. Each layer functioned as an appeal court for the layer below. Inquisitional courts based on secrecy that allowed no public access replaced old jury courts. Judges were civil servants and mostly did not have any land-owning origins (Reicher 2003: 127ff), unlike their English counterparts who were recruited from the Gentry up until the end of the nineteenth century [START_REF] Duman | The Judges of England 1730-1875[END_REF]). The legal system in Austria changed systematically so that the ancient common laws of the regions were eventually replaced by a unified penal code. This replacement mainly had the function of reducing the influence of local elites, as Max Weber has described (Weber 1978: 858f).

Policing in Austria changed dramatically toward the end of the eighteenth century. A powerful central police organization began to replace older forms of locally run police forces [START_REF] Gebhardt | Die Grazer Polizei 1786-1850[END_REF]). In the early days, the police carried out a multitude of tasks. 7 In the 1780s a centrally governed police organization was introduced. The police in the provinces came directly under the control of the Viennese headquarters. Unlike in the case of the later English Bobbies, Austrian authorities attempted to minimize local influence on the police (no local participation). Even the governors of each provincewho were directly nominated by the Emperordid not have any official influence on the provincial police organization. Most importantly, a well-organized secret police was established in the 1780s and 1790s. In the 1850s, an additional police-organization was introduced in Austria, called the "Gendarmerie", which was a kind of paramilitary force designed for controlling crime in the countryside.

The civilizing process of English and Austrian political elites

The preliminary results lead one to reconsider the role of "domesticated" elites in eighteenth and nineteenth centuries. The English case may follow the patterns of Spierenburg"s study on the Netherlands in some respects (although some noteworthy differences exist as well).

For the English case, pamphlet literature was qualitatively analyzed in order to understand motives and emotions of some protagonists. In the parliamentarian culture of eighteenthcentury England, these pamphlets were intended to influence the public opinion of those who had the right to vote. Thus, the pamphlets provide insight on opinions and emotions of the English upper classes and upper-middle classes related to the issue of the death penalty.

For the Austrian case, no such pamphlet literature exists, owing to Austria"s absolutist political structure. The opinion of political elites in the Habsburg Empire was formed differently. It was mainly the "enlightened" literature that discussed matters of politics and policing. One example is the work of Joseph von Sonnenfels and especially his treatise against torture. This study, however, only concentrates on the work of Cesare Beccaria, and its influence on the administrative elites of the realm.

In reviewing these sources, two main characteristics become obvious. In the English pamphlet literature, an emotionally distanced attitude prevails towards the lower classes (from which most of the offenders derived). This style of writing is referred to here as "Machiavellian". Quite contrary to the English pamphlet literature, Beccaria"s writings often deal with the pain and suffering of offenders on the scaffold. However, his empathy is like that of a father for pain suffered by his children. Beccaria"s perspective is not democratic, but from above looking downwards. It resembles the structure of a paternalistic and hierarchical society in which the state and its protagonists lead the citizens (like fathers their children or shepherds their sheep). Therefore, this authorial attitude is referred to here as "paternalistic".

Machiavellian attitudes of eighteenth and early nineteenth century English upper classes

Eighteenth century English pamphlets only rarely give hints of pity and empathy towards the criminals. The content of these pamphlets expresses emotional distance and cold-blooded thinking. Most of the authors were in favor of the death penalty and even of public executions. However, they were neither blind agitators nor fanatics seeking bloody revenge; they were well aware of the pros and cons of public execution, and discussed them openly. They discuss matters of public executions like any other political topic. Examples of this kind of writing are A. Baldwin"s "Hanging not punishment enough for Murtherers …" (1701), Mandville"s "An Enquiry into the Cases of the frequent Executions at Tyburn" (1725), and Henry Fielding"s "Murders. True Examples of the Imposition of Providences, in the Discovery of Punishment of Murder" (1752). These authors shared some common themes. These were mainly technicali.e. not moralproblems related to the implementation of the death penalty. They recommended executing fewer people in the future, but not because they felt pity towards the convicts, or they thought it unjust or morally problematic to kill someone. They were more concerned about the deflationary effect of excessive executions. They worried that the many public execution events would diminish the intended purpose of deterrence. For them public executions had transformed into spectacles (see also [START_REF] Gatrell | The Hanging Tree, Execution and the English People 1770 -1868[END_REF]. Thus, Baldwin recommended replacing public hangings with more brutal forms of execution in order to reinstate the effect of deterrence. In his pamphlet, there is no notion of shame in expressing these brutal recommendations. His writings reveal an emotional state that lacks feelings such as pity or abhorrence in relation to capital punishment.

To see underclass criminals as objects rather than as humans of equal standing was an unquestioned attitude. It was the habitus and the Weltanschauung of the gentry. These elite were domesticated in the sense of the theory of civilizing processes. They lived in fine manors, they cultivated an elegant lifestyle, they were well educated, and above all, they established a political system that resolved conflicts relatively peacefully (see: Elias 1960, 18ff).

However, the Machiavellian style of thinking about the poor involved a different aspect of their characters. It stood beside the relatively peaceful attitudes towards their own peers. The Machiavellian code towards the lower classes lacks a sense of social responsibility. It reflects the high degree of commercialization in economic relationships that goes along with a lack of responsibility for the poor. This may be a product of the fact that feudal ties were dissolved earlier in England than in parts of Central Europe.

Parliamentary debates about the death penalty reveal similarly distanced emotional patterns standing behind very loose social bonds between the peers and the lower classes. Here, too, it becomes clear that the English elites did not share an empathetic attitude in connection with the many executions. Romilly wrote in his diary:

It is but a few nights ago, that, while I was standing at the bar of the House of Commons, a young man, the brother of a peer, whose name is not worth setting down, came up to me, and breathing in my face the nauseous fun of his undigested debauch, stammered out, "I am against your bill, I am for hanging all … There is no good done by mercy. They only get worse; I would hang them all up at once." (in: Historical Sketch, 1835: 78f)

Romilly, the great reformer, expressed a different emotional attitude towards the death penalty. He condemned the lack of mercy because he felt pity. Lord Ellenborough, argued differently in his speech at the House of Lords in 1811. He used a tone more refined, and even more Machiavellian. He disguised his lack of pity behind the pretense of defending the little man. This speech was made during a House of Lords debate on a bill to abolish the death penalty for all theft of private property with a value of less than 5 shillings. This bill had already been passed by the House of Commons but was rejected by the Upper House after Ellenborough"s speech.

My Lords, if we suffer this bill (as to stealing in shops) to pass, we shall not know where to stand, we shall not know whether we are on our heads or on our feet. If you repeal the Act which inflicts the penalty of death for stealing to the value of five shillings in a shop, you will be called upon next year to repeal a law, which prescribes the penalty of death for stealing five shillings in a dwelling-house, there being no person therein; a law, your lordships must know, on the severity of which, and the application of it, stands the security of every poor cottager who goes out to his daily labour. He, my lords, can leave no one behind to watch his little dwelling … My Lords, there are cases where mercy and humanity to the few would be injustice and cruelty to the many. There are cases where the law must be applied in all its terrors. My Lords, I think this, above all others, is a law on which so much of the security of mankind depends on execution, that I should deem myself neglectful of my duty to the public if I failed to let the law take its course. (in: Historical Sketch, 1835: 80f)

Lord Ellenborough gave the topic of abolishing the death penalty a certain "spin", implying that abolishing capital punishment for these crimes is even crueler than executing a person. Both statements violate today"s standards of political correctness, which would forbid one to speak openly (in the parliament) in such a way about killing people. They also reveal the lack of truly felt pity. Mercy may have played a role amongst some reform-orientated individuals like Samuel Romilly, however, like the majority of political elites, such feelings were less important. They were much too involved in the daily business of defending their economic base. Harsh laws against crimes of poverty were seen as proper measures.

Beccaria and paternalistic attitudes of administrative elites in the Habsburg Empire

Let us revise Spierenburg"s theme of "domesticated elites" by considering the Austrian case.

Here, domesticated elites are identified with high-ranking civil servants and not with nobles or economic upper-classes. For this class of "indifferent middlemen"usually civil servants criminal cases were not of personal but professional interest. Their power increased with the rise of the administrative machinery. The peaceful working conditinos of these new elites fostered conditions for the development of a civilized habitus. Bureaucratic leadership helped to establish an "enlightened" regime of crime prevention and crime fighting.

The example of Cesare Beccaria shows the close links between enlightenment and central government. Alongside his philosophical career, Beccaria was a civil servant in a very high administrative position in Habsburg Milan of the eighteenth century. Later, he became involved in reform programs for introducing a modern code of criminal law for the whole of Austria.

"On Crimes and Punishment" became well-known amongst the political leaders of Europe as one of the most famous treatises against the death penalty. The book is more than a detached discussion about the best regime of punishment. It also features passages written in a highly emotional register against the death penalty and other forms of cruel punishments. It is not hard to detect Beccaria"s disgust and abhorrence with capital punishment. In some passages Beccaria uses the technique of the internal monologue to demonstrate emotions and empathy with poor criminals. These imaginings were intended to evoke empathy amongst the readers of his treatise.

"What are these laws which I have to obey, which leave such a gulf between me and the rich man? He denies me the penny I beg of him, brushing me off with the demand that I should work, something he knows nothing about. Who made these laws? Rich and powerful men, who have never condescended to visit the filthy hovels of the poor, who have never broken mouldy bread among the innocent cries of starving children and a wife"s tears.

[Here, Beccaria uses the rhetoric figure of an anaphora and depicts dramatic scenes of poverty to evoke empathy.]

Let us break these ties, which are pernicious to most people and only useful to a few and idle tyrants; let us attack injustice at its source. [once again an anaphora] I shall return to my natural state of independence; for a while I shall live free and happy on the fruits of my courage and industry; perhaps the day for suffering and repentance will come, but it will be brief, and I shall have one day of pain for many years of pleasure…" [START_REF] Beccaria | On Crimes and Punishments" and other Writings[END_REF](Beccaria [ ] 2000: 69) : 69) In another passage, Beccaria wrote about the abolition of the death penalty. He described establishing merciful laws in correlation to increasing the central government"s power:

How happy humanity would be if laws were being decreed for the first time, now what we see seated on the thrones of Europe benevolent monarchs, inspires of the virtue of peace, of the sciences, of the arts, fathers of their peoples, crowned citizens. Their increased power serves the happiness of their subjects because it removes that crueler, because more capricious intermediary despotism, which choked the always sincere desires of the people which are always beneficial when they may approach the throne! If they leave the ancient laws in place, I say, it is because of the endless difficulty of removing the venerated and centuries-old rust. That is a reason for enlightened citizens to wish all the more fervently for their authorities to continue to increase. [START_REF] Beccaria | On Crimes and Punishments" and other Writings[END_REF] 2000: 71f)

Beccaria"s "capricious intermediary despotism" resembles our type of weak state and its forms of domination. His opinion on the matter of capital punishment and the penal law is written from a bureaucratic elite perspective. The writings of Beccaria and other "enlightened" philosophers in the Habsburg monarchy were addressed directly against the local elites ("intermediary despotism"). They idealized a state bureaucracy run by a corps of civil servants that simply followed the written law (which itself is an expression of natural law) and that were not involved in local networks. These writers formed the ideological base for Josephian utopianism of the This letter expresses more than goodwill toward Beccaria"s ideas from the highest ranks of the imperial administration. It also reflects that enlightenment philosophers were treated by the royal courts of continental Europe like modern professional football players. It improved the reputation of an "enlightened" ruler to place thinkers like Beccaria among his or her staff.

They reflected glory and legitimacy on the leader. This very idea of glory is only to be understood by imagining all absolutist nations of eighteenth century Europe as a network (or as a figuration) within which common symbols of honor and shame are shared by the ruling classes of these states. Unlike in England, the power centers of these states were transformed more and more into an administrative apparatus. Thus, it is no wonder that bureaucrats and rulers began to orientate to each other. They started a process of institutional isomorphism [START_REF] Dimaggio | The Iron Cage Revisited: Institutional Isomorphism and Collective Rationality in Organizational Fields[END_REF]. England lay clearly outside this figuration because her leading class differed from continental power-elites.

The introduction of a new court system followed these ideals. First, judges became civil servants bonded to the code of impartiality. Second, an inquisition court-system was introduced (the older jury system was abolished). Third, the new penal code no longer contained torture or the death penalty.

In the late eighteenth century, continental "enlightenment" also symbolized the lifestyle of civil servants who were no longer dependent on local aristocrats' interests. Civil servants lived and worked in salons, bureaus, agencies, universities and other environments in which direct economic involvement played no role. Their social fields, in the sense of Bourdieu [START_REF] Wacquant | Pierre Bourdieu[END_REF], demanded professionalism and produced the habitus of distance, selfcontrol, routines, non-violent behavior and the belief in "healing" criminality. These social fields discouraged brutality (as a sort of unprofessional solution to their specific problems), rage and anger in relation to criminals. English upper-class thinkers surely also sought to introduce a rational or "enlightened" order. Lord Byron"s statement, however, reveals not so much intellectual as emotional distance to both Beccaria"s advice and his world of continental bureaucracy. Byron wrote 1816 from Milan:

I have just heard an anecdote of Beccaria, who published such admirable things on the punishment of death. A soon as his book was out, his servant (having read it, I presume) stole his watch; and his master, while correcting the press of a second edition, did all he could to have him hanged by way of advertisement. (in: Historical Sketch, 1835: 77)

Byron"s statement reveals not only that he did not know the local laws -since the 1780"s, stealing was no longer punished by death in the Habsburg Empirebut it also clearly indicates spitefulness toward somebody who seems to be a menace for the protection of property.

In England, the reforms of the 1830s promoted an ideal of impartiality, too. However, these reforms were not promoted from "above" (by an enlightened regime) but rather from "below" (from the process of democratization). The English reforms went step by step with the incorporation of new bourgeois and craftsmen classes into the parliamentary system. Thus, in England as in Austria, the death penalty dramatically lost importance due to the process of bureaucratization. However, the two cases showed different patterns of bureaucratization. In Austria the bureaucratization and the abolition of the death penalty resulted from the state"s struggle against local elites and patrimonial domination. In England, bureaucratization was a product of democratization. [START_REF] Greenberg | Siting the Death Penalty Internationally[END_REF] have recently focused on the role of democracy, civil rights, and religion in the abolition of the death penalty. This study argues that modern bureaucracy also plays a prominent role in facilitating a lenient regime of punishment. In the case of the Habsburg Empire, the administrative apparatus was mainly responsible for the decline and eventual abolition of capital punishment. Within the state bureaucracy, a "second civilizing process" was initiated. Thus, professional law enforcement specialists, bureaucrats, civil servants, and detached juridical staff formed a new class of "domesticated middlemen elites".

Conclusion and discussion

In strong states, this new class became a counterweight to other leading groups, especially older economic elites, whose power was based on immediate personal relationships. Out of this new class of bureaucrats a civilizing process was introduced which included the abolition of brutal punishments. On the one hand, the pure logic of bureaucratic routines blocks the involvement of spontaneous emotion while dealing with punishment and social control. On the other hand, peaceful living and working conditions engender disgust and abhorrence towards violence.

England of eighteenth and early nineteenth centuries combined capitalism, proto-democracy, and a weak state-bureaucracy. Here, the two fields of economic and political power were not yet divorced. They were still overlapping. Office-holders and economic elites (mostly landowners) were highly interrelated. This circumstance led to a situation in which elites claimed they had to rely on brutal punishments in order to fight crime. These elites feared the alternative: a strong state with a powerful police organization. The English case also demonstrates that in such liberal capitalistic oligarchies, only reforms in suffrage rights and further steps of "democratization" laid the foundation for introducing a more lenient penal system. Absolute monarchies did not have the same scruples when introducing authoritarian, non-locally based organizations in order to maintain social control. Here, it was in the interest of the centralized state to weaken local elites.

Increasing the power of the state administration promoted a new habitus of leadership with an attitude against brutal punishments. Another component of this habitus was that private interests should not overlap with professional interests. Crime control became a professional field of work demanding objectivity and emotional distance.

This paper has not examined wider international patterns of the death penalty and the statebuilding process, but it has shown that in some respects, the English and the Dutch cases have similarities that indicate the important role of liberal capitalism, in which economic and political power overlap. However, it is much harder to understand, for example, the case of post-revolutionary France, where the death penalty played a more prominent role than in Austria. It would be also interesting to compare the Austrian case with that of other Empires consisting of many heterogeneous parts. Russiawhere Empress Elisabeth abolished the death penalty in 1744 for all crimes, but Catharine II reintroduced itwould be an especially interesting case.

Table 1 :

 1 Death sentences per year and 100,000 inhabitants 4

Table 2 :

 2 Executions per year and 100,000 inhabitants 5

Table 3 :

 3 Death sentences and offences against private property (1822 -1855) 6

	Period	England	Austria
	1805-1824		6,65	0,17
	1825-1844		4,70	0,19
	1845-1864		0,28	0,29
	1865-1884		0,43	1,40
	1885-1904		0,09	0,30
	Period	England	Austria
	1805-1824		0,71	0,06
	1825-1844		0,24	0,06
	1845-1864		0,06	0,03
	1865-1884		0,06	0,04
	1885-1904		0,06	0,01
				in percent (rounded)			abs.
				Offences
			Offences	against	Offences
	Offences
			against privat	private	against the		other
	against				Murder		Total
			property with	property	state's		Offences
	persons
			violence	without	authorities
				violence
	England	5	17	71	2	3	2	17420
	Austria	2	0	13	8	77	0	984

  1780"s. Even earlier, the highest administrator of the Habsburg Empire, Graf Kaunitz, wrote a Letter to Graf Firmian, Governor of the Lombardy and direct supervisor of Beccaria. The letter was spurred by Empress Catherine"s attempt to lure Beccaria to Russia. Kaunitz wrote:

	It

would not be desirable for our country to lose a man, who is not only gifted with esprit but who is used to thinking freely. So much of his book [On Crimes and Punishment] enlightens! … Above all, it would do the ministry credit to honor this genius. We must be sooner than foreign states. (in: Wurzbach 1856: 202) [translation mine]


Ch Y Wang

M Kinzer

S K Youn

N Ramgir

M Kunzer

K Köhler

M Zacharias

V Cimalla

Oxidation behavior of carbon monoxide at photostimulated surface of ZnO nanowires

Keywords: ZnO nanowires, photon stimulation, CO sensing, oxidation behavior, photoluminescence

Normally carbon monoxide is considered to be a reducing agent, which can be used for CO detection. However, oxidizing behavior of CO, to the best of our knowledge, has not been reported. In this work, we find that CO can also act as oxidizing gas at room temperature on photostimulated ZnO nanowires. For photostimulation, the low intensity of light emitting diodes a is used to induce a very low photo current, which, however, leads to a large resistance change due to the ultraviolet light interaction with the nanowire surface. During CO detection, the oxygen vacancies enhance the CO adsorption on the nanowire surface even at room temperature. CO molecules adsorbing on the surface are presumably bound to a zincoxygen vacancy complex, causing a reduction of free electron concentration, which leads to an oxidizing effect of CO gas.

An adsorption model for CO is proposed to explain the experimental observations. These results shed light on developing room-temperature CO sensor using oxide nanostructures with the help of high energetic photon replacing the high temperature process normally used in traditional gas sensors.

Comment #6: "The non-equilibrium conditions with desorption of gaseous species at low pressure and inert gases are not close to realistic conditions in the environment. The authors should comment how this technique can lead to an operating room temperature sensor as stated in the manuscript" Answer #6: That's totally right. The measuring conditions described in this work are not close to normal realistic conditions in the environment which contains high concentration oxygen/water vapor as main interfering gases. Thus, we proposed in the conclusion that such sensors working at room temperature will first be easy to be used for special applications, such as for CO detection in fuel cells where H2 is the main gas. For CO detection in H2O and O2 containing environment, the response of H2O and O2 must first be determined for the calculation of pure CO response. However, further experiments will be needed for such applications.

Comment #7: "Authors should include the dipole nature of the CO molecule and the two potential interaction modes with the surface…" Answer #7: We have now proposed one possible mechanism of CO molecules adsorbed on the nanowire surface at the end of 3.3 CO sensing mechanism, and mentioned "However, further experiments are still desired to understand the dipole nature of the CO molecules adsorbed on the surface.".

Sincerely yours,

Chunyu Wang

Introduction

In recent years, nanotechnology research has focused on the understanding of physical properties of nanomaterials and their consequent applications [1], e. g. for gas detection. Metal oxide nanostructures have been demonstrated to be highly sensitive to CO [2], NH 3 [3], H 2 [4], NO x [5], as well as to ethanol [6]. Among 2 them, the detection of CO as one of the major pollutants in the automobile exhaust gases has attracted much interest. Carbon monoxide, normally considered to be a reducing gas [7], can be detected at high temperatures using metal oxides as gas sensing material such as ZnO [8], TiO 2 [9], NiO [10] and CuO [11]. The sensing mechanisms are, however, not fully understood.

For the environmental sensing behavior, two models are used to explain the interaction of CO with a metal oxide surface and adsorbed species. The first model assumes that oxygen molecules adsorb on the surface of metal oxides in a form of O 2-. When CO is present with O 2-at high temperature, the reaction

- - + → + 2e CO O CO 2 2
proceeds on the surface, leading to a release of localized electrons [12]. According to the second model, oxygen adsorbs as O 2 -. At low temperature, CO molecules do not have sufficient thermal energy to react with -

2

O , while at a temperature above 300°C -

2

O is converted to O -and CO reacts via

- - + → + e CO O CO 2 .
In both cases the detection scheme for CO involves the reaction with pre-adsorbed oxygen, and normal CO sensors based on metal oxides work only at high temperature (> 300°C) using its reducing effect [7,13]. However, to the best of our knowledge, oxidizing behavior of CO has not been reported.

In our previous work, we enabled the surface reaction of CO at room temperature by photostimulation [14]. Here, the high energetic photon replaces the high temperature process normally used in high-temperature gas sensors. Thus, the photostimulated sensor, in particular based on nanostructured materials [15], enables gas detection at room temperature, resulting in a reduced power consumption [16]. The gas sensing mechanism stays, however, still controversial due to the interference of remaining residual gases with photostimulated surface. In this work, the effect of photon stimulation on the nanowire surface has been studied at well-defined conditions.

Furthermore, experiments at alternating measuring conditions have been carried out to extract a pure sensing signal. As a result, the oxidizing character of CO on the photostimulated surface of ZnO nanowires and the related sensing behavior have been exhibited. The pure CO response has been calculated based on a simple gas adsorption model. The mechanism of CO adsorption at the photostimulated surface has been proposed.

Experimental Section

The ZnO nanowires were grown using the vapor-solid (VS) method [14] and characterized by highresolution scanning electron microscopy (SEM, Nova NanoSEM, FEI). First, the Si substrate was patterned with Au electrodes by conventional photolithography, physical vapor deposition (Au: 100 nm, Cr: 5 nm) and lift off processing, followed by surface modification of Au by immersing the substrates into a 1 mM ethanol solution of 2-mercaptopropionic acid, MPA (Sigma Aldrich, 99.8%) for 5 h and subsequent washing with ethanol to remove excess MPA. The self-assembled monolayers (SAMs) of MPA, possessing two functional groups, namely, thiol and carboxylic acid, were selectively formed on the gold lines and used to discriminate between Au and Si surface as well as to interact with cationic Zn species in the solution phase. The growth mechanism has been explained in our previous work [14]. The distance between two Au lines was 2 µm. After that, zinc acetate dihydrate (Sigma Aldrich, 98%) in methanol was dropped onto the substrates, followed by drying in air at 70°C and annealing at 350°C for 20 min in air, which resulted in ZnO seeds. Finally, ZnO nanowire arrays were grown at 930°C by vapor-phase deposition using powdered ZnO (Sigma Aldrich, 99.9%) and graphite (Alfa Aesar, 99.9%) as a source material and O 2 as an oxidizing agent.

The CO sensing experiments were conducted in a custom-built equipment [16]. The ZnO nanowires were placed in the measuring chamber with an ultraviolet light emitting diode (UV LED with λ~356 nm and optical power ~200 µW) mounted above the sample. Two electrical contacts were brought onto the two outer Au-lines.

The electrical resistance of the ZnO nanowires between the Au-lines were determined during the sensing experiment, while the UV LED was regularly switched on and off for photostimulation and CO oxidation, respectively. To understand the influence of photostimulation on ZnO nanowires, photoluminescence measurements were carried out using different excitation sources.

Results and Discussion

Optical Properties of ZnO Nanowire Arrays

Figure 1 shows a SEM image of ZnO nanowire arrays grown on an Au-patterned Si substrate.

Mechanical contacts between nanowires grown on two neighboring Au patterns are forming nanowire bridges as shown schematically in the inset of Fig. 1. The abundant nanowire bridges establish a current flow between nanowires deposited on separated neighboring Au electrodes. Furthermore, due to the increased surface area of such arrays of ZnO nanowires, the gas sensing properties are expected to be enhanced. The structural properties of the as grown ZnO nanowire arrays have been reported elsewhere [17]. The grown ZnO nanowires were first investigated by photoluminescence (PL) using different excitation wavelengths and varied excitation intensities. The results are shown in Fig. 2. The four curves (Fig. 2, solid lines) were obtained using a HeCd laser (λ ~325 nm, h ~3.81 eV) at different power densities from 0.01 to 10 W/mm 2 . The excitation area was about 10 -3 mm 2 . A relatively sharp main peak appears at a photon energy of 3.29 eV, which is in agreement with the reported value in literature [18]. This UV emission is normally attributed to the strong band-edge emission [18]. A broad emission peak centered at ~2.45 eV can also be found in Fig. 2.

The origin of this green emission is still under discussion. Very often the green emission has been attributed to defects on the surface of ZnO [18], considering singly ionized oxygen vacancies [19], zinc interstitials [20], zinc vacancies [21], as well as antisite defects [22]. The intensities of both UV and green emission have been found to be dependent on the excitation power density. In case of our ZnO nanowire arrays, both the intensities of the UV and green emission increase by increasing the excitation power density (Fig. 2 (b)). Note that the measurements integrate over a large number of nanowires and are not done on single wires. No saturation effect was seen for both PL contributions. The ratio of the PL intensities (I green /I UV ) decreases with the increase of the excitation power density.

Normally, the UV band edge emission peak increases by increasing the excitation intensity as reported for instance by Shi et al. [23]. In contrast, the intensity of the green emission of high-quality ZnO films grown by metal organic chemical vapor deposition is reported to saturate when increasing the excitation intensity. This effect has been attributed to the perfect crystal structure and the very low number of surface states in single crystalline ZnO films [24]. In the case of ZnO nanostructures, the intensity of green emission was found to increase with the increasing excitation intensity and no saturation was observed [23], which agrees well with our observations as can be seen in Fig. 2 (b). The opposite behavior of the green luminescence in epitaxial films and in nanowires strongly supports the assumption that surface states are the main source for these differences.

Following the interpretation of Ahn et al. [25], oxygen vacancies are assumed to be the major source for these surface defect states. As discussed before, these vacancies are the active centers in the CO adsorption on ZnO and, thus, are also responsible for their sensing mechanism [26,27].

The same PL experiment was carried out by replacing the excitation source HeCd laser with a UV LED (λ ~356 nm), which was also used for photostimulation of ZnO nanowires and which has a much lower power intensity than the laser source. The overall power density of the UV light irradiating the ZnO nanowires was much lower than 1 mW/mm 2 . The respective PL spectrum is the dashed-line curve in Fig. 2 (a) representing the signal for a 5 min excitation with the UV LED. The main peak centered at ~3.48 eV is due to the 356 nm LED excitation, which is not completely blocked in the system. The band gap emission from the ZnO nanowires is negligible for such weak excitation. The observed green luminescence is located at the same energy position as observed if using the HeCd laser as excitation source (Fig. 2 (a)). Although the excitation power is very low, the intensity of the green luminescence is still relatively high indicating the existence and easy excitation of related defects at the surface of ZnO nanowires with its large surface area. The PL experiments only cannot clarify if these defects are pre-existent or have been photostimulated by the UV illumination. Nevertheless, it suggests that the nanowires have a high number of photon active centers at the surface, which are also expected to be responsible for gas sensing, thus, making nanowires ideal candidates for sensing applications.

Oxidizing behavior of carbon monoxide at Photostimulated ZnO Nanowire Surface

The ZnO nanowires were further investigated with respect to CO sensing character at room temperature and the influence of photostimulation. Two main steps are involved in the CO sensing process: (i) gas adsorption at the nanowire surface during CO exposure and (ii) reactivation of the surface via UV illumination. To understand the CO sensing behavior at photostimulated surface, the following four effects have to be considered:

(I) photo current, (II) gas desorption during photostimulation, (III) surface adsorption of CO gas, and (IV) a competing surface adsorption of ambient residual gases (H 2 O and O 2 ) from the measuring chamber during the CO adsorption process [14]. In our previous work, a large resistance change has been observed after photostimulation and CO exposition, which is preliminary assumed to be caused by an interaction between CO and residual water vapor / oxygen molecules at the nanowire surface. In the following, the four main processes are studied to exclude the influence of the residual gases remaining in the measuring system and to understand the interaction between pure CO gas and the surface of photostimulated nanowires.

First, photocurrent has been determined with the help of electrical measurements in different processes, as shown in Figure 3. The black curve represents the resistance change by periodically switching the UV LED "on" (photostimulation) and "off" for 2 hours with a continuous N 2 purge of the system. It must be mentioned here that the gas adsorption/desorption process at room temperature is time-consuming due to the low thermal energy of the gas molecules. Thus, resistance has been measured at non-equilibrium state, i. e. no saturation value of resistance was reached, which, however, has already been proven to be an efficient method to obtain sensing signals, in particular for photostimulated gas sensors operated at room temperature [28]. During photostimulation, the system was pumped down to ~10 -3 mbar, while the system was filled with N 2 after switching off the UV LED (black). Theoretically, a large photocurrent or a large resistance change due to photogenerated carriers should be induced by switching on or off the above-band-gap excitation (E ZnO = 3.37 eV) [29]. As can be seen from the black curve, the resistance change after first photostimulation is nearly two orders of magnitude, then decreased only slightly for the second and third time irradiation with UV light. In particular, it was observed that the resistance increased only insignificantly after switching off the UV light. The same experiments were carried out with different UV LEDs (i.e. h = 3.26 and 4 eV, respectively), and similar resistance changes were obtained independent of the used energy. A very low photocurrent was observed after photostimulation using a UV-LED with photon energy well above the band gap of ZnO (4 eV). This agrees very well with the PL characterization of ZnO nanowire arrays, which has shown a negligible band gap emission using the UV LED as excitation source. The observed large resistance decrease after the first UV-light illumination can be interpreted by a charge transfer at surface defects. According to photoelectron spectroscopy analysis [26,27], these defects are oxygen vacancies. This indicates that the defects observed in the former PL experiments are generated by the UV illumination. In an equilibrium state before the first photoexcitation, adsorbates from environment preferable bond to Zn ions at these oxygen vacancies resulting in a localized negative charge. The UV-light forces desorption of these charged adsorbates, which in turn results in the generation of free electrons and, thus, in an enhanced surface carrier transport. The PL measurements indeed showed the green luminescence observed even at low excitation power densities, hence indicating a high number of optically active centers at the nanowire surface. However, after the first photoexcitation, the oxygen vacancies can only be compensated very slowly by the residual water vapor / oxygen residual gases in the N 2 environment of the experimental setup, leading to a slight resistance increase in repeating LED-off procedures. In contrast, a clear electrical response was observed on ZnO nanowires after repeated photoexcitation cycles in CO with concentrations as low as 40 ppm in N 2 (red curve in Fig. 3). As can be seen in Fig. 3, however, the resistance change decreases gradually with the number of the photostimulation/CO exposure cycles. After 6 cycles, a nearly constant resistance change to the photostimulation/CO exposure cycle was observed as demonstrated in the inset of Fig. 3. Although it has already been reported that the residual gases, such as oxygen or humidity, can oxidize ZnO surface, in particular react with oxygen vacancies even under ultrahigh vacuum conditions [30], this experiment indicates evidently that the CO molecules has obviously been adsorbed on the photostimulated surface at room temperature and has large influence on the electrical properties of ZnO nanowires. Furthermore, the large resistance increase after CO exposure signifies an oxidizing behavior of adsorbed CO molecules at the surface of photostimulated ZnO nanowires.

To determine the influence of residual gas adsorption in the chamber, such as H 2 O and O 2 , the ZnO nanowires were first exposed to 40 ppm CO in N 2 together with the residual gases. Then, the chamber was evacuated down to 10 -3 mbar and purged with N 2 to reduce the residual gas concentration. This process was repeated several times. The corresponding resistance change is shown in Fig. 4 The response towards residual gases (red curve in Fig. 4 (c)) is defined as

res UV S S R R resp = = UV res res , (1)
where R res (S res ) and R UV (S UV ) are the resistance (conductance) of ZnO nanowires after residual gas exposure and UV illumination, respectively, which decreases (increases) with the increase of the photostimulation/oxidation cycle number. This is caused by a reduction of the concentration of residual gases in the system by repeated purging of the chamber with N 2 and pumping the chamber down to ~10 -3 mbar after every gas exposure.

Accordingly, the response towards 40 ppm CO and residual gases (black curve in Fig. 4 (b)) is defined as:

res CO UV res CO S S R

R resp

oxidizing behavior of CO and the residual gases (O 2 or H 2 O) can be concluded, thus, every adsorbed molecule will be negatively charged by localizing one or more electrons. As a consequence, the electron concentration is reduced by n CO or n res after exposure to pure CO or residual gases, respectively. Thereby, the conductance of the ZnO nanowires after gas exposure can be calculated by:

X n n S CO CO ⋅ ∆ - = ) ( max , (6)
X n n S res res ⋅ ∆ - = ) ( max , (7)
X n n n S res CO res CO ⋅ ∆ - ∆ - = ) ( max & . (8)
Based on eq. ( 1) -( 8), the pure CO response is calculated by:

res res CO CO resp resp resp 1 1 1 1 & - + = (9)
This calculated pure CO response (Fig. 4 (b), blue-dashed curve), remains nearly constant during the whole measurements, indicating that CO gas has a stable oxidizing effect at the photostimulated ZnO nanowire surface. Furthermore, the resistance change during CO and residual gas exposure is found to be clearly faster than that during exposure to residual gases alone, caused by the higher CO concentration (40 ppm) compared to the concentration of residual H 2 O or O 2 (< 1 ppm). These experiments clearly prove that pure CO has an oxidizing effect at room temperature if the surface of the ZnO nanowires has been photostimulated by UV light.

Based on the results determined by equation ( 9) it can be concluded that for a fixed CO flux the ZnO nanowires have a constant response. Next, ZnO nanowires were exposed to CO with different concentrations in N 2 environment using the same measuring conditions. The measuring chamber was first purged with N 2 for 20 h to reduce the concentration of residual gases. Then the ZnO nanowires were photostimulated for 1 h, followed by CO oxidation for 1 h (Fig. 4 (c). The procedure was repeated by varying the CO concentration from 0.12 to 40 ppm, as shown in cycle 1 in Fig. 4 (c). As expected for oxidizing behavior, the resistance change decreases with decreasing CO concentration in cycle 1. To study the reproducibility of the CO sensing behavior at the photon stimulated ZnO nanowire surface, measurements with increasing CO concentration (cycle 3) as well as with decreasing CO concentration from 40 to 0.12 ppm (cycle 2 and 4 in Fig. 4 (c)) were carried out. Here the sensor response is again due to both residual gases and CO with different concentration. The response to the residual gases during the whole measurement was also determined by setting the CO concentration to 0 at the end of cycle 1 and 3. The pure CO response resp CO has been calculated at different CO concentrations using (9), and is shown in Fig. 4 (d). The CO response increases with the increasing CO concentration from 120 ppb up to 40 ppm indicating that CO at ppb level is detectable at room temperature, which is also an evidence of the oxidizing effect of CO at the photostimulated ZnO nanowire surface at room temperature. Furthermore, although the resistance change by exposure to CO & residual gases, i. e. resp CO&res , in the former cycles is higher than that in the latter cycles, the calculated pure CO response, however, remained nearly the same for the same CO concentration in the different cycles (Fig. 4 (d)), indicating that the sensing signal is quite reproducible, which is very important for real applications.

CO Sensing Mechanism

The mechanism of CO adsorption on ZnO has been widely studied both theoretically and experimentally on a variety of facets with different polarity (polar or non-polar) and different structural properties (single crystalline, defect-rich and highly doped). Using density-functional theory, it was determined that CO can adsorb on both polar (Zn-terminated (0001)) and non-polar (10 _ 10) surfaces, with the C-atoms bound not to O-ions but Zn ions, in particular on step edges and other defects [32]. Photoelectron spectroscopy measurements revealed that CO adsorbs on (0001), (000 _ 1 ) polar and (10 _ 10), (11 _ 2 0) non-polar surfaces at surface defects, in particular oxygen vacancies at steps [27].

In the case of CO adsorption on photostimulated ZnO nanowires, because gas molecules can adsorb both at the surface and on the side wall of ZnO nanowires, CO adsorption on both polar and non-polar ZnO surfaces is possible. There are abundant of wires with a huge surface with defects [33]. Thus, defects including oxygen vacancies are pre-existing on the surface of ZnO nanowires in the initial state [34]. In air, the oxygen vacancies are compensated by chemisorbed -2 O at room temperature which leads to a reduction of free electron concentration and high resistivity of the nanowires, as determined electrically. After photostimulation, the charged adsorbed oxygen species partially desorbs leaving more defects, mostly non-compensated oxygen vacancies V O at the surface. As a result, free electrons are released and the nanowire resistivity decreases. On the other hand, the amount of photo-generated electrons in the core of the ZnO nanowires is relatively small due to the low intensity of the UV light. Thus, photoelectrons have only negligible contribution to the density of free carriers and the large resistance change is basically a surface effect. The corresponding chemical reaction during this process can be described as follows [35]

: e V O O O 2 h 2 + + →  - -. (10)
When CO and residual gases approach the surface, the CO or adsorbed oxygen molecules do not have enough thermal energy to recombine with oxygen vacancies at room temperature, which is reasonable due to the fact that even at high temperatures above 1000 K, the oxygen vacancies cannot be completely annihilated in an oxygen environment [27]. Thus, a possible mechanism is that the ionized CO molecules adsorb at the nanowire surface with the C-atoms weakly bonded to Zn ions at surface defects (oxygen vacancies) at room temperature [32],

leading to a decrease of surface electron density. Thus, the resistance of ZnO nanowires increases after CO exposure. However, further experiments are still desired to understand the dipole nature of the CO molecules adsorbed on the surface.

Conclusion

In conclusion, it has been demonstrated that CO can act as an oxidizing gas on photostimulated ZnO nanowires at room temperature. UV irradiation can effectively desorb charged adsorbates from the surface, which releases free electrons. After CO exposure, CO molecules adsorb at the surface of ZnO nanowires, trapping free electrons and leading to a decrease of surface conductivity. The oxidizing behavior of CO by means of photostimulation opens the way for room temperature CO detection, in particular in fuel cells containing CO as a rest gas in H 2 , while for CO detection in H 2 O and O 2 containing environment, response to residual gases needs to be determined for the calculation of pure CO response. These results shed light on developing roomtemperature gas sensors using oxide nanostructures with the help of high energetic photon replacing the high temperature process normally used in traditional gas sensors. Furthermore, the ZnO nanowires can be directly integrated with UV LEDs, leading to compact miniaturized energy-saving CO sensors [28].

Figure 1 .

 1 Figure 1. SEM image taken at 45 o tilt of ZnO nanowires grown on an Au-patterned Si substrate. The inset shows a schematic view of ZnO nanowire bridges.

Figure 2 .

 2 Figure 2. (a) PL measurements using different exciting sources and excitation power densities: solid lines

Figure 3 .

 3 Figure 3. Resistance change of the ZnO nanowires under photostimulation (black) and photostimulation/CO exposure (red). The inset shows the resistance change after four cycles of photostimulation/CO exposure.

  (a). Again, the resistance strongly decreases after the first UV irradiation due to desorption of charged species from oxygen vacancies and then increases only slightly after residual gas exposure (mainly H 2 O). After exposure to 40 ppm CO and residual gases, the ZnO nanowires show a much higher resistance change in comparison to the exposure to residual gases alone, indicating an oxidizing behavior of the CO gas. A summary of the responses towards different gases is shown in Fig.4 (b). The sensing process involves adsorption of different gas molecules (CO and residual gases) at the photostimulated ZnO surface. Under the assumption according to the Langmuir adsorption isotherm that the surface adsorption sites are equivalent, and the adsorbed molecules do not interact, the pure CO response can be separated from the response to residual gases.

Figure 4 .

 4 Figure 4. (a) Resistance change of ZnO nanowires periodically exposed to residual gases (mainly H 2 O and O 2 ) and 40 ppm CO in N 2 ; (b) measured nanowire response from (a) and calculated response towards 40 ppm CO in dependence on the photostimulation/oxidation cycles, (c) resistance change of ZnO nanowires in CO with different concentration, and (d) ZnO nanowire response in dependence on the CO concentration.

Figure captions:Figure 1 .

 1 Figure captions:

Figure 2 .

 2 Figure 2. (a) PL measurements using different exciting sources and excitation power densities: solid lines

Figure 3 .

 3 Figure 3. Resistance change of the ZnO nanowires under photostimulation (black) and photostimulation/CO exposure (red). The inset shows the resistance change after four cycles of photostimulation/CO exposure.

Figure 4 .

 4 Figure 4. (a) Resistance change of ZnO nanowires periodically exposed to residual gases (mainly H 2 O and O 2 ) and 40 ppm CO in N 2 ; (b) measured nanowire response from (a) and calculated response towards 40 ppm CO in dependence on the photostimulation/oxidation cycles, (c) resistance change of ZnO nanowires in CO with different concentration, and (d) ZnO nanowire response in dependence on the CO concentration.

& UV

Acknowledgment

This work was supported by the Fraunhofer Research Grants "Attract" and "Challenge". The authors thank Crenguta-Columbina Leancu for the PL measurements. Furthermore, we thank B. Raynor for critically reading the manuscript. S. K. Youn acknowledges DIP-K.6.1 and ZA 191/17-3 for financial support. N. Ramgir would like to thank Humboldt Foundation for the fellowship.

where R CO&res (S CO&res ) is the resistance (conductance) of ZnO nanowires after exposure to CO and residual gases, which decreases (increases) similarly but not identically with (1). Furthermore, as can be seen in Fig. 4 (b), the behavior of the two response curves (black and red curves) is very similar, indicating that the decreasing response to CO and residual gases in dependence of the measuring cycle was mainly caused by the reduction of the residual gas concentration. Similar to the definition of responses resp res and resp CO&res , the pure CO response is defined as:

where R CO (S CO ) is the resistance (conductance) of ZnO nanowires after exposure to pure 40 ppm CO. Due to the coexistence of CO and residual gases during the whole measurement, the resistance of ZnO nanowires after pure CO exposure (R CO ) and the pure CO response defined in (3) cannot be directly determined from the resistance change curve shown in Fig. 4 (a). Hence, in this work, a simple model is used to calculate the pure CO response from the other two responses taking into account the resistance change due to exposure to different gases.

For the relatively small measured changes of the resistivity in Fig. 4 (a), the electron mobility is considered to be constant. Then, the resistance and conductance of the nanowires can be expressed by:

where X is a constant and n the electron concentration. The constant value X is expressed by

, where e and µ are the electron charge and mobility, respectively, l the nanowire length, and A the nanowire cross section area. Thus, the nanowire conductance after photostimulation can be described using the simplified equation:

where n max is the maximum electron density in the nanowires after photostimulation. For the response on gases, it is assumed that different gas species occupy individual adsorption sites [31] and that at the low partial pressures used here these adsorption sites are not affecting each other. Furthermore, from the resistance increase, the