1,720,966 research outputs found
Improving the statistical power of AFM with Reverse-Tip-Sample automation
No full textSince their first introduction a few decades ago, Scanning Probe Microscopy (SPM) techniques have emerged as extremely powerful tools to investigate material properties at the nanoscale. Atomic Force Microscopy (AFM) is likely the most diffused SPM, thanks to its ability to precisely and reliably map surface topography and other local properties, and the possibility to be used with a virtually unlimited class of materials without the need of prior surface preparation. Nonetheless, its adoption within industrial settings, for instance those dealing with micro- and nano-electronics, is still limited, mostly because its operation requires dedicated and time wasting operator efforts. As a matter of fact, the geometric features of the probe tip heavily affect the quality of the produced images, resulting in the frequent need for tip replacements.
This thesis examines the inherent limitations of AFM, focusing on the critical dependency of data quality on probe tip characteristics. In AFM, tip shape and sharpness are essential for precise surface characterization. Even slight variations or degradation in tip quality can introduce inconsistencies and biases in both topographic measurements and more advanced material property evaluations. However, as tip quality and, consequently, data quality deteriorate due to wear, the need to use multiple tips becomes inevitable. A significant challenge here is the manual tip replacement process, which may take from ten minutes to several hours, thereby limiting the frequency of exchanges and impeding high-throughput measurements and comprehensive statistical analysis of surface properties.
To address this, the viability of the Reverse Tip Sample (RTS) approach is explored. The RTS configuration reverses the positions of the sample and the tip with respect to the standard SPM configuration. Specifically, for AFM, the sample is now mounted on a tipless cantilever, while the tip is integrated into a nanofabricated RTS probe chip which is placed on the microscope's stage. This reversal enables rapid and seamless tip switching since RTS probe chips host not one, but thousands upon thousands of tips which are easily accessible by the sample through navigation with the piezo and / or coarse motors of the microscope. As such, the RTS configuration not only minimizes experimental downtime but also exploits the inherent variability among tips. Each tip, with its unique geometric characteristics, contributes diverse and complementary data. For example, sharp tips capture high-resolution topography, while blunter tips enhance sensitivity to adhesion forces or stabilize electrical contacts. By continuously cycling through numerous tips, RTS provides a richer statistical representation of tip-sample interactions. Altogether, RTS represents a promising technology, but it is still in its early stages.
This work brings further advances to RTS SPM with the integration of image recognition algorithms, which ensure precise tip alignment with sub-nanometer accuracy after each tip exchange. This automated alignment is essential for repeated measurements of the same region of interest (ROI), where even minor positional inaccuracies can significantly affect measurement consistency. The process begins with a reference scan of the ROI, which is then compared to each subsequent trial scan from a new tip. The image alignment algorithm calculates translational offsets that are applied via piezo motors, thereby ensuring nanometer-accurate centering of the ROI. Moreover, two graphical user interface (GUI) software platforms were developed for a commercial atomic force microscope (AFM) equipped with Python-interfacing APIs. The first platform allows flexible, automated execution of AFM scans using different tips from the RTS probe chip, with each scan configured according to arbitrary parameters for specific target regions. The second platform simplifies the process of running identical scans on the same ROI using different tips, thereby enhancing statistical reliability of the data. Both platforms depend on the above-mentioned precise, automated alignment provided by the image recognition system and both substantially reduce setup / measurement time from several of hours to just a few minutes.
Recognizing that tip quality remains a crucial factor even in the RTS configuration, the thesis explores the development of a tip ranking system. An initial exploratory study identifies surface roughness as a promising, easily obtainable parameter for establishing a quality-based hierarchy among the many tips on a probe chip. The use of surface roughness for tip ranking is further investigated using the previously developed software platforms for experimental automation. The investigation uncovered, and was stalled by, several fundamental scientific questions of current relevance in surface science and nanometrology, namely the dependence of surface roughness on tip size, scan size, and other factors. These issues are addressed and investigated through extensive experimental studies. The experimental results are in line with existing results in AFM literature, and serve to confirm some of the weaker ones with a much higher statistical strength. An analytic computer simulation based on offset curves was developed for simulating the surface roughness measurements of arbitrary line profiles by tips of arbitrary size and shape. The simulation independently reproduces several experimental results, and provides further insights on RMS roughness and on its behaviour against various parameters.
The combination of rapid automated tip exchanges, precise algorithm-driven alignment, and the implementation of a tip ranking system collectively advances the capabilities of AFM for high-resolution nanoscale imaging, and also served for the fundamental investigation of scientific phenomena in surface science
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Densité d'états, alignement de bande et injection de charges dans des nanostructures semiconductrices uni-dimensionnelles étudiées par microscopie à effet tunnel à pointes multiples
No full textThe traditional transistor miniaturization is resulting in devices experiencing quantum effects. Rather than fighting these effect by developing new architectures of conventional silicon-based devices, the long-term solution might be in revisiting existing knowledge of these fundamental concepts and studying them in a well-controlled and methodological manner. Consequently, the newly emergent insights could be applied to the keystones of modern-day electronic devices, such as one-dimensional shape and the presence of heterointerface, but on different materials. This, in fact, has a potential to yield an alternative approach to information processing and computation.Nowadays, it is possible to obtain nanostructures of any shape and size due to recent breakthroughs in nanofabrication. This thesis aims to exploit such possibilities to simulate an experimental environment in which quantum confinement effect can be studied in a controlled manner on different one-dimensional semiconductor nano-heterostructures. At first, a reliable methodology will be developed to accurately determine the band alignment between two dissimilar semiconductors comprising a heterointerface. This will be achieved on planar one-dimensional InGaAs nanostructures grown on InP by selective area molecular beam epitaxy, a nanofabrication method which, to date, offers the best control of nanostructure shape, size, position, and orientation in ultrahigh vacuum. The surface reconstruction, as well as the entire structure morphology will be investigated in great detail by means of atomic force microscopy and scanning tunneling microscopy, while the aforementioned growth will be described by modeling the diffusion dynamics. A combination of low-temperature two-probe scanning tunneling spectroscopy and room-temperature four-probe contact measurements will be utilized to obtain accurate information about the band alignment and charge transport of the heterosystem.Once proven successful, the approach will be employed to study nanostructures of much smaller dimensions, where quantum size effect is ever-present: colloidal CdSe nanoplatelets, which imitate the typical optical characteristics of epitaxial quantum wells, but, due to anisotropic lateral dimensions, make the understanding of the impact of finite lateral confinement on the behavior of the free charge carriers more complex. In addition to the study of the morphology of the nanoplatelets and of their optical transitions, low-temperature scanning tunneling microscopy and spectroscopy investigations will be performed. Once drop-casted onto a gold substrate, the density of states of the nanoplatelets will be directly probed in order to accurately determine the extent of quantum confinement experienced by the carriers as a function of the nanoplatelets thickness, temperature and spatial configuration. The results which are, on one hand, inconsistent with foregoing quantum well-like perception found in literature, while on the other, perfectly in line with our tight binding calculations, will establish a solid baseline for the follow-up study of CdSe/CdS core-crown nanoplatelets.La miniaturisation continue des composants électroniques a atteint un seuil au-delà duquel les effets quantiques deviendront prépondérants. Plutôt que de vouloir supprimer ces effets, il peut être intéressant de les mettre à profit. Mais ce changement de perspective nécessite d’avoir une compréhension plus fine des propriétés électroniques de nanostructures semi-conductrices considérées comme de potentiels éléments actifs dans des dispositifs futurs. Au cours de cette thèse, deux types de structures dont la géométrie s’apparente plus ou moins à un système uni-dimensionnel ont été considérés: des nanofils semi-conducteurs III-V fabriqués par croissance épitaxiale en ultravide et des nanoplatelets semi-conducteurs II-VI synthétisés chimiquement.Dans le premier cas, l’épitaxie par jets moléculaires sélective de nanofils planaires composés d’InGaAs permet d’élaborer des nano-cristaux localisés précisément à la surface d’un substrat d’InP grâce à l’utilisation d’un masque diélectrique. L’analyse de la morphologie de ces nanofils par microscopie à champ proche a révélé une anisotropie de forme en fonction de l’orientation des nanofils. En modélisant la cinétique de croissance, nous avons montré que cette variation de forme s’explique par une différence de diffusion des adatomes liée à la reconstruction (2x4) de la surface (001) des nanofils. Les propriétés de transport dans ces hétérostructures uni-dimensionelles In0.53Ga0.46As/InP ont ensuite été caractérisées par microscopie à effet tunnel à pointes multiples. Deux approches expérimentales basées l’une sur la spectroscopie tunnel à deux contacts, l’autre sur des mesures à quatre pointes en contact ont été conçues pour remonter à la mesure des discontinuités de bande entre le substrat d’InP et les nanofils d’InGaAs. L’obtention des discontinuités de bande est directe et ne requiert ni fabrication d’électrodes, ni modélisation des caractéristiques I(V), contrairement aux techniques électriques conventionnelles.Dans un second temps, nous avons considéré des nanoplaquettes de CdSe, qui s’apparentent à des puits quantiques colloïdaux d’épaisseur limitée à quelques plans atomiques pour des dimensions latérales comprises entre plusieurs nanomètres et quelques dizaines de nanomètres. Bien que les propriétés excitoniques des nanoplaquettes aient fait l’objet de nombreuses études, le rôle du confinement quantique latérale sur la localisation des porteurs de charge est encore mal connu. En utilisant la microscopie à effet tunnel, nous avons caractérisé des nanoplaquettes individuelles et des nanoplaquettes assemblées en paquet pour déterminer la densité d’états en bande de conduction. Les mesures spectroscopiques montrent l’existence, d’une part, de singularités superposées à une oscillation de la densité d’états, en bon accord avec la densité d’états calculée par la méthode des liaisons fortes et, d’autre part, la présence de piège sur les parois latérales des plaquettes. Contrairement à l’exciton dont le confinement est plus important, la délocalisation de l’électron est fortement influencée par le confinement latéral et la présence de piège. A cet effet, des travaux préliminaires par spectroscopie optique de nanoplaquettes cœur-coquille permet d’entrevoir l’intérêt d’une couronne pour mieux contrôler le confinement des porteurs de charge dans ces objets
Densité d'états, alignement de bande et injection de charges dans des nanostructures semiconductrices uni-dimensionnelles étudiées par microscopie à effet tunnel à pointes multiples
No full textThe traditional transistor miniaturization is resulting in devices experiencing quantum effects. Rather than fighting these effect by developing new architectures of conventional silicon-based devices, the long-term solution might be in revisiting existing knowledge of these fundamental concepts and studying them in a well-controlled and methodological manner. Consequently, the newly emergent insights could be applied to the keystones of modern-day electronic devices, such as one-dimensional shape and the presence of heterointerface, but on different materials. This, in fact, has a potential to yield an alternative approach to information processing and computation.Nowadays, it is possible to obtain nanostructures of any shape and size due to recent breakthroughs in nanofabrication. This thesis aims to exploit such possibilities to simulate an experimental environment in which quantum confinement effect can be studied in a controlled manner on different one-dimensional semiconductor nano-heterostructures. At first, a reliable methodology will be developed to accurately determine the band alignment between two dissimilar semiconductors comprising a heterointerface. This will be achieved on planar one-dimensional InGaAs nanostructures grown on InP by selective area molecular beam epitaxy, a nanofabrication method which, to date, offers the best control of nanostructure shape, size, position, and orientation in ultrahigh vacuum. The surface reconstruction, as well as the entire structure morphology will be investigated in great detail by means of atomic force microscopy and scanning tunneling microscopy, while the aforementioned growth will be described by modeling the diffusion dynamics. A combination of low-temperature two-probe scanning tunneling spectroscopy and room-temperature four-probe contact measurements will be utilized to obtain accurate information about the band alignment and charge transport of the heterosystem.Once proven successful, the approach will be employed to study nanostructures of much smaller dimensions, where quantum size effect is ever-present: colloidal CdSe nanoplatelets, which imitate the typical optical characteristics of epitaxial quantum wells, but, due to anisotropic lateral dimensions, make the understanding of the impact of finite lateral confinement on the behavior of the free charge carriers more complex. In addition to the study of the morphology of the nanoplatelets and of their optical transitions, low-temperature scanning tunneling microscopy and spectroscopy investigations will be performed. Once drop-casted onto a gold substrate, the density of states of the nanoplatelets will be directly probed in order to accurately determine the extent of quantum confinement experienced by the carriers as a function of the nanoplatelets thickness, temperature and spatial configuration. The results which are, on one hand, inconsistent with foregoing quantum well-like perception found in literature, while on the other, perfectly in line with our tight binding calculations, will establish a solid baseline for the follow-up study of CdSe/CdS core-crown nanoplatelets.La miniaturisation continue des composants électroniques a atteint un seuil au-delà duquel les effets quantiques deviendront prépondérants. Plutôt que de vouloir supprimer ces effets, il peut être intéressant de les mettre à profit. Mais ce changement de perspective nécessite d’avoir une compréhension plus fine des propriétés électroniques de nanostructures semi-conductrices considérées comme de potentiels éléments actifs dans des dispositifs futurs. Au cours de cette thèse, deux types de structures dont la géométrie s’apparente plus ou moins à un système uni-dimensionnel ont été considérés: des nanofils semi-conducteurs III-V fabriqués par croissance épitaxiale en ultravide et des nanoplatelets semi-conducteurs II-VI synthétisés chimiquement.Dans le premier cas, l’épitaxie par jets moléculaires sélective de nanofils planaires composés d’InGaAs permet d’élaborer des nano-cristaux localisés précisément à la surface d’un substrat d’InP grâce à l’utilisation d’un masque diélectrique. L’analyse de la morphologie de ces nanofils par microscopie à champ proche a révélé une anisotropie de forme en fonction de l’orientation des nanofils. En modélisant la cinétique de croissance, nous avons montré que cette variation de forme s’explique par une différence de diffusion des adatomes liée à la reconstruction (2x4) de la surface (001) des nanofils. Les propriétés de transport dans ces hétérostructures uni-dimensionelles In0.53Ga0.46As/InP ont ensuite été caractérisées par microscopie à effet tunnel à pointes multiples. Deux approches expérimentales basées l’une sur la spectroscopie tunnel à deux contacts, l’autre sur des mesures à quatre pointes en contact ont été conçues pour remonter à la mesure des discontinuités de bande entre le substrat d’InP et les nanofils d’InGaAs. L’obtention des discontinuités de bande est directe et ne requiert ni fabrication d’électrodes, ni modélisation des caractéristiques I(V), contrairement aux techniques électriques conventionnelles.Dans un second temps, nous avons considéré des nanoplaquettes de CdSe, qui s’apparentent à des puits quantiques colloïdaux d’épaisseur limitée à quelques plans atomiques pour des dimensions latérales comprises entre plusieurs nanomètres et quelques dizaines de nanomètres. Bien que les propriétés excitoniques des nanoplaquettes aient fait l’objet de nombreuses études, le rôle du confinement quantique latérale sur la localisation des porteurs de charge est encore mal connu. En utilisant la microscopie à effet tunnel, nous avons caractérisé des nanoplaquettes individuelles et des nanoplaquettes assemblées en paquet pour déterminer la densité d’états en bande de conduction. Les mesures spectroscopiques montrent l’existence, d’une part, de singularités superposées à une oscillation de la densité d’états, en bon accord avec la densité d’états calculée par la méthode des liaisons fortes et, d’autre part, la présence de piège sur les parois latérales des plaquettes. Contrairement à l’exciton dont le confinement est plus important, la délocalisation de l’électron est fortement influencée par le confinement latéral et la présence de piège. A cet effet, des travaux préliminaires par spectroscopie optique de nanoplaquettes cœur-coquille permet d’entrevoir l’intérêt d’une couronne pour mieux contrôler le confinement des porteurs de charge dans ces objets
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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