1,354,148 research outputs found
2D scaling behavior of nanotextured GaN surfaces: A case study of hillocked and terraced surfaces
No full textThe 2D scaling properties of GaN surfaces have been studied by means of the 2D height–height correlation function (HHCF). The GaN layers under investigation presented exemplar morphologies, generated by distinct growth methods: a molecular beam epitaxy (MBE) grown surface decorated by hillocks and a metal organic vapor phase epitaxy (MOVPE) grown surface with terraced structure. The 2D statistical analysis of these surfaces has allowed assessing quantitatively the degree of morphological variability along all the different directions across each surface, their corresponding roughness exponents and correlation lengths. A scaling anisotropy as well as correlation length anisotropy has been detected for both hillocked and terraced surfaces. Especially, a marked dependence of correlation length from the direction across the terraced surface has been observed. Additionally, the terraced surfaces showed the lower root mean square (RMS) roughness value and at the same time, the lower roughness exponent value. This could appear as a contradiction, given that a low RMS value is associated to a smooth surface, and usually the roughness exponent is interpreted as a “measure” of the smoothness of the surface, the smoother the surface, the higher (approaching the unity) is the roughness exponent. Our case study is an experimental demonstration in which the roughness exponent should be, more appropriately, interpreted as a quantification of how the roughness changes with length scale
TCAD Simulation Framework of Gas Desorption in CNT FET NO2Sensors
No full textA technology computer-aided design (TCAD) simulation framework of gas desorption induced by self-heating in carbon nanotube (CNT) field effect transistor (FET) gas sensors is presented. Its key feature is the use of temperature profiles extracted from electrothermal simulations to determine the change of the effective gas-induced doping concentration during the gas desorption phase. The approach allows to investigate the impact of geometrical and physical parameters, in particular the ones related to contacts, on the self-heating desorption process. The main conclusion is that, due to the nonuniform self-heating temperature profile, the near-threshold part of the IDS-VGS curves recover their pristine aspect faster than the rest of the characteristics
Electron mobility of strained InGaAs long-channel MOSFETs: From scattering rates to TCAD model
No full textTCAD modelling of InGaAs channel MOSFETs is a complex task due to the combined effect of quantization and interface or border traps, which affect the device electrostatics as well as the electron mobility through Coulomb scattering. In addition, trap distributions and mobility are strain-dependent. In this paper, we start from a microscopic physical approach, based on the use of Sentaurus SBand by Synopsys as 1D Schrödinger-Poisson solver and mobility calculator through the Kubo-Greenwood (KG) approach, to end up with a TCAD modelling framework that combines the Density Gradient (DG) model for quantum corrections with simple empirical expressions for the mobility model. Only the long-channel (or low-field) mobility is addressed. A distinctive feature of the paper is the use of experimental Hall electron density and mobility data as a reference for the calibration of interface traps and scattering rates in SBand. SBand simulation results for different strain levels and layer thicknesses are then used as the basis for the TCAD model calibration (DG and mobility). Our findings indicate that strain can increase mobility mainly through the reduction of Coulomb scattering with trapped charge
On the electron mobility of strained InGaAs channel MOSFETs
No full textA discussion over the microscopic electron mobility of strained InGaAs channels of metal-oxide-semiconductor field-effect transistors (MOSFETs) is presented. The theoretical model is validated against experimental results of strained InGaAs-on-Insulator (InGaAs-OI) MOSFETs. It accurately reproduces effective and Hall mobilities vs. charge density curves, once the calibration of interface trap density has been performed. Our findings are that 1) the interface trap distribution is decreased by strain, and this explains 2) the increase of Hall mobility with strain for low tensile strain values and 3) the insensitivity of Hall mobility to strain for higher tensile strain values. Finally, for the same reason 4) in ideal trap-free devices no strain-induced mobility enhancement is foreseen
Electron Beam Patterning of GaAs Nanowires: Tailoring the Morphology of Semiconductor Nanowire Arrays for a Bio-mimetic Functionalization Approach
No full textThe superior chemical and physical properties of natural surfaces are frequently related to the multi-scale design of micro- and nano-structures on them. Following this bio-mimetic approach, the geometrical tailoring of semiconductor nanowire (NW) arrays allows rising a novel nanofabrication concept, where the semiconductor properties and the boosting effect of quantum properties merge into morphology-based functionalities. This contribution presents the results of Molecular Beam Epitaxy grown GaAs NW arrays locally patterned by the electron beam-mediated bending and by their adhesion-induced bundling. We explain the self-assembly of NWs into clusters in the frame of adhesion properties of natural contact surfaces (“gecko effect”), by generalizing the concept of “lateral collapse of fibrils”. We demonstrate how a careful choice of material properties and geometrical design of semiconductor NW arrays may turn the scanning electron microscope into a new patterning tool with nanoscale fine-tuning of the structure of NW-decorated surfaces. Additionally, the NW bending by the electron beam has further advantages in respect to the traditional elastocapillary method. In fact it allows to implement NW aggregation under vacuum ambient, so as to avoid the contamination of the delicate NW surface by external substances (liquids). The potential applications of tailored NW arrays range from energy conversion to nanoelectronics, chemical and biological sensing, and bioengineering
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Defect level characterization of silicon nanowire arrays: Towards novel experimental paradigms
No full textThe huge amount of knowledge, and infrastructures, brought by silicon (Si) technology, make Si Nanowires (NWs) an ideal choice for nano-electronic Si-based devices. This, in turn, challenges the scientific research to adapt the technical and theoretical paradigms, at the base of established experimental techniques, in order to probe the properties of these systems. Metal-assisted wet-Chemical Etching (MaCE) [1, 2] is a promising fast, easy and cheap method to grow high aspect-ratio aligned Si NWs. Further, contrary to other fabrication methods, this method avoids the possible detrimental effects related to Au diffusion into NWs. We investigated the bandgap level diagram of MaCE Si NW arrays, phosphorous-doped, by means of Deep Level Transient Spectroscopy. The presence of both shallow and deep levels has been detected. The results have been examined in the light of the specificity of the MaCE growth. The study of the electronic levels in Si NWs is, of course, of capital importance in view of the integration of Si NW arrays as active layers in actual devices
Variations on the Author
No full text“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
Properties of Si nanowires as a function of their growth conditions
No full textSilicon nanowires physical properties strongly depend on their growth conditions, as already assessed.
We report on the electrical properties of nanowires (NWs) grown by the vapor–liquid–solid (VLS)
mechanism, one of the most established for NW growth, and by the more recent metal-assisted wet
chemical etching (MaCE).Wet etching growth process promises to be an industrial advantageous way for
growing Si NWs, because of its cheapness, fastness, relative easiness. The electronic level scheme in VLS
grown, boron (B)- and phosphorus (P)-doped NWs has been experimentally investigated. We have
demonstrated that the doping impurities induce the same shallow levels as in bulk silicon. The presence
of two donor levels in the lower half-bandgap is also revealed, which has been successfully related to VLS
growth details.
We report, also, on the first results on the physical properties of Si NW arrays grown by MaCE, and
compare them to those of VLS grown Si NWs
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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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