1,721,296 research outputs found
Simulation of XSTS imaging of Self-Assembled quantum dot electronic states
No full textRecently, STM measurements of cleaved, self assembled quantum dots (SAQDs) have provided important information on the morphology and composition of these buried semiconductor islands. It is also now becoming possible to use STM techniques to image the electronic charge density within the SAQDs. At low bias voltages, the tunnelling current measured during crosssectional scanning tunnelling spectroscopy (XSTS) experiments contains direct information on the 0D bound electronic states of the cleaved quantum dots. In this paper we present a numerical simulation of an XSTS experiment. The calculated tunnelling currents between an STM tip and the bound states inside a physically realistic model of a cleaved SAQD are compared to experimental results and qualitative agreement is found. The calculation of the tunnelling current is split into two stages. First the bound electron states of the cleaved quantum dot are calculated by exact diagonalisation of the Hamiltonian in a simple harmonic oscillator basis set. The calculation is performed within the single-band effective mass approximation including the position dependence of the effective mass and, most crucially, the effect of the deformations of the cleaved dot structure and the strain field within the system. The strains and deformations of the heterostructure are found with a continuum, finite element model. The calculation method is completely general, however, in this paper we apply it to the InGaAs dot structure reported by Bruls et al [1]. Second, the Tersoff-Hamann approximation [2] is used to calculate the tunnelling probability between the bound electronic states and the STMtip at different tip positions and bias voltages. The calculated STM signal is compared to experimental data and reasonable agreement is obtained. The method may be used to obtain additional physical information about the buried SAQDs, for example, details on the lateral variations in the composition
Simulation of XSTS imaging of Self-Assembled quantum dot electronic states
No full textRecently, STM measurements of cleaved, self assembled quantum dots (SAQDs) have provided important information on the morphology and composition of these buried semiconductor islands. It is also now becoming possible to use STM techniques to image the electronic charge density within the SAQDs. At low bias voltages, the tunnelling current measured during crosssectional scanning tunnelling spectroscopy (XSTS) experiments contains direct information on the 0D bound electronic states of the cleaved quantum dots. In this paper we present a numerical simulation of an XSTS experiment. The calculated tunnelling currents between an STM tip and the bound states inside a physically realistic model of a cleaved SAQD are compared to experimental results and qualitative agreement is found. The calculation of the tunnelling current is split into two stages. First the bound electron states of the cleaved quantum dot are calculated by exact diagonalisation of the Hamiltonian in a simple harmonic oscillator basis set. The calculation is performed within the single-band effective mass approximation including the position dependence of the effective mass and, most crucially, the effect of the deformations of the cleaved dot structure and the strain field within the system. The strains and deformations of the heterostructure are found with a continuum, finite element model. The calculation method is completely general, however, in this paper we apply it to the InGaAs dot structure reported by Bruls et al [1]. Second, the Tersoff-Hamann approximation [2] is used to calculate the tunnelling probability between the bound electronic states and the STMtip at different tip positions and bias voltages. The calculated STM signal is compared to experimental data and reasonable agreement is obtained. The method may be used to obtain additional physical information about the buried SAQDs, for example, details on the lateral variations in the composition
Digital alloy InGaAs/InAlAs laser structures studied by cross-sectional scanning tunneling microscopy
No full textWe have studied digital alloy InAlAs/InGaAs quantum well and quantum cascade laser structures with cross-sectional scanning tunneling microscopy.We show the effect of rapid thermal annealing on structural properties of a digital alloy quantum well structure. Further, we compare a quantum cascade laser structure with digital alloy graded barriers to a structure with abrupt interfaces. We show that due to alloy fluctations, softening of the barriers occurs even without the digital alloy grading
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
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
STM, scanning tunneling microscopy/spectroscopy and related techniques : 12th international conference, Eindhoven University of Technology, Eindhoven, July 21-25, 2003
No full textSTM, scanning tunneling microscopy/spectroscopy and related techniques : 12th international conference, Eindhoven University of Technology, Eindhoven, July 21-25, 2003
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