1,720,971 research outputs found
Top–down SiGe nanostructures on Ge membranes realized by e-beam lithography and wet etching
No full textSiGe nanostructures on Ge membranes have been fabricated by electron beam lithography and anisotropic wet chemical etching, starting from SiGe/Ge heterostructures epitaxially deposited on Si substrates. Two different top-down approaches have been studied in order to obtain the best freestanding structures. We find that the process in which the Ge membrane is suspended after the lithography of the SiGe nanostructures leads to high quality SiGe nanostructures without damage to either the SiGe nanostructures or the Ge membrane. The structures have been systematically analyzed at every step of the fabrication process, by scanning electron microscopy and by atomic force microscopy
Plasmon-enhanced Ge-based metal-semiconductor-metal photodetector at near-IR wavelengths
Full text linkWe demonstrate the use of plasmonic effects to boost the near-infrared sensitivity of metal-semiconductor-metal detectors. Plasmon-enhanced photodetection is achieved by properly optimizing Au interdigitated electrodes, micro-fabricated on Ge, a semiconductor that features a strong near IR absorption. Finite-difference time-domain simulations, photocurrent experiments and Fourier-transform IR spectroscopy are performed to validate how a relatively simple tuning of the contact geometry allows for an enhancement of the response of the device adapting it to the specific detection needs. A 2-fold gain factor in the Ge absorption characteristics is experimentally demonstrated at 1.4 µm, highlighting the potential of this approach for optoelectronic and sensing applications.QCD/Scappucci La
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Patterning of metastable epitaxial films of SiGe on Ge for direct band gap induction in Ge
No full textLAUREA MAGISTRALELo scopo di questo lavoro di tesi di laurea magistrale é quello di indurre uno strain tensile nel germanio, usando delle strisce di una lega silicio-germanio (SiGe) come stressori, con lo scopo di modidicarne la struttura a bande per ottenere la gap fondamentale diretta.
Spiegherò il percorso intrapreso per raggiungere lo scopo, il quale inizia con lo studio e la caratterizzazione dei film di SiGe e termina con il commento alle analisi strutturali sui campioni, passando per i processi di fabbricazione. Sono state eseguite delle analisi XRD (X-Ray Diffraction) sui film di SiGe per dedurne la composizione, lo spessore ed il rilassamento plastico. É stato utilizzato un modello numerico semplificato per poter descrivere i risultati sperimentali ottenuti, modello che é basato su quello di Fischer e Zaumseil, in quanto i valori degli spessori critici di equilibrio riportati in letteratura sono stati oltrepassati. Saranno illustrati i processi di fabbricazione, inclusi quelli di pulizia, sia quelli wet che di dry etching e quelli litografici. Inoltre, sono stati ottimizzati dei processi di etching chimico basato su di una soluzione di KOH (idrossido di potassio), per poter ottenere delle strutture SiGe/Ge che siano sospese. Strutture che devono presentare una elevata qualitá delle superfici, mentre la soluzione una elevata velocitá di attacco. Infine viene confermato l’ottenimento di un valore dello strain tensile nel Ge superiore al 4%, mediante analisi μRaman.The goal of this master’s thesis work is to induce a tensile strain in germanium using silicon-germanium alloy (SiGe) stripes as stressors, in order to modify the band structure in a way which leads to a direct fundamental gap.
I explain the path taken towards the goal, which starts from the sudy and characterization of SiGe films and passes through fabrication steps to ends with the comments on structural analysis of specimens. XRD (X-Ray Diffraction) analysis was performed on SiGe films to deduce composition, thickness and plastic relaxation. A simplified numerical model based on that of Fischer and Zaumseil was used to describe experimental results, because the equilibrium critical thickness reported in literature has been exceeded. Fabrication steps of stressors are illustrated, including cleaning, wet and dry etching and lithography steps. Furthermore, wet etching processes based on KOH (potassium hydroxide) solutions were tuned in order to obtain suspended SiGe/Ge structures with high quality surfaces at high etch rate. The achievement of over 4% uniaxial tensile strain in Ge is confirmed by μRaman analysis
Tensile strain in Ge membranes induced by SiGe nanostressors
Full text linkThe monolithic integration of photonic functionality into silicon microtechnology is widely advanced. Yet, there is no final solution for the realization of a light source compatible with the prevailing complementary metal-oxide-semiconductor technology. A lot of research effort focuses on germanium (Ge) on silicon (Si) heterostructures and tensile strain application to Ge is accepted as one feasible route to make Ge an efficient light emitter. Prior work has documented the special suitability of Ge membranes to reach the high tensile strain. We present a top-down approach for the creation of SiGe stressors on Ge micro-bridges and compare the obtained strain to the case of an attached bulk-like Ge layer. We could show that the Ge influenced by a SiGe stressor is under tensile strain; absolute strain values are of the order of 0.7% for both micro-bridge and bulk. The relative strain induced by the nanostructures in the micro-bridge is 1.3% due to the high sharing of elastic energy between nanostructures and bridges
Variations on the Author
Full text link“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
Full text linkWe 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
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