Theoretical Methods for Calculating Electronic Properties of Semiconductor Superlattices

1985 ◽  
Vol 56 ◽  
Author(s):  
JOEL N. SCHULMAN
Keyword(s):  
Electronic Properties ◽  
Energy Levels ◽  
Tight Binding ◽  
Theoretical Models ◽  
Semiconductor Superlattices ◽  
Band Dispersion ◽  
Physical Effects ◽  
Relationship Of ◽  
The Relationship ◽  
Bulk Band

AbstractA variety of theoretical models have been used to calculate the electronic properties of semiconductor superlattices. The methods vary in their ease of implementation, number of empirical parameters, and ability to incorporate physical effects. There is no “best” method; the choice of model is made on the basis of the desired property under investigation, such as subband energy levels, energy band dispersion and effective mass, strain effects, or optical spectra. The strength and limitations of the Kronig- Penney, envelope function, and tight-binding models will be reviewed, including one-, two-, and multi-band versions. The relationship of superlattice to bulk band structure, and the issue of dispersion in the growth and in-plane directions will be illustrated with the examples of the CaAs-GaAlAs and HgTe-CdTe superlattices.

The 12 C(γ, 3α) reaction energy levels of 8 Be and 12 C

1955 ◽  
Vol 228 (1174) ◽  
pp. 376-396 ◽  
Keyword(s):  
Ground State ◽  
Energy Levels ◽  
Electric Quadrupole ◽  
Angular Distributions ◽  
Reaction Energy ◽  
Reaction Proceeds ◽  
Γ Ray ◽  
Relationship Of ◽  
The Relationship ◽  
Α Particles

The mechanism of the 12 C(γ, 3α) reaction, for γ-ray energies, E γ , up to about 40 MeV, has been determined from a study of over 2500 stars in nuclear emulsions. The study includes investigation of the angular distributions and correlations of the α-particles. The reaction is initiated mainly by electric-dipole and electric-quadrupole γ-ray interaction, the former being unexpectedly strong when E γ < 20 MeV. For E γ < 25 MeV the reaction proceeds mainly by transitions to the ground-state of 8 Be (spin J = 0), and to 2⋅95 ± 0⋅10 MeV ( J = 2) and 4⋅0 ± 0⋅1 MeV ( J = 2 or 4) levels of 8 Be. Transitions to levels near 6, 10 and 15 MeV (all J = 0, 2 or 4) become predominant when 25 MeV ≤ E γ <26 MeV. For E γ ≥ 26 MeV, most transitions lead to 16⋅8 ± 0⋅2 MeV ( J = 2) and 17⋅6 ± 0⋅2 MeV ( J = 2, possibly 0) levels, and possibly to a further 16⋅4 ± 0⋅2 MeV ( J = 0 or 2) level, levels which have not been detected in other reactions. The reaction mechanism is interpreted in terms of competing modes of decay of a compound nucleus, demonstrating the strong influence of the isotopic spins ( T ) of the levels of 12 C and 8 Be involved. For example, the 2 + levels of 12 C involved when 16 MeV ≤ E γ <20 MeV are (unexpectedly) found to have T = 1, and the 16⋅8 and 17⋅6 MeV levels of 8 Be are also found to have T = 1. The relationship of the 12 C (γ, 3α) reaction to other 12 C photodisintegration reactions (including some new reactions established during the present experiments) is discussed.

Dynamics at a Step on the Diamond (111) Surface

1994 ◽  
Vol 339 ◽  
Author(s):  
Brian N. Davidson ◽  
Warren E. Pickett
Keyword(s):  
Flat Surface ◽  
Tight Binding ◽  
Diamond Growth ◽  
Diamond Structure ◽  
Growth Mechanisms ◽  
Structure And Dynamics ◽  
Graphitic Layer ◽  
Tight Binding Method ◽  
Relationship Of ◽  
The Relationship

ABSTRACTUsing an accurate tight-binding method, we examine the structure and dynamics at a C(lll) step. We find the H vibration frequencies at a step are distinguishable from the flat surface. Removal of H from the surface creates an unstable bulk terminated diamond structure which relaxes to a graphitic layer and pulls away from the bulk. The explanation for these results can be given in terms of the relationship of the band structure to the relaxed geometries. The addition of H stabilizes this surface and reverts it back to sp3 bonding. The addition of CH3 near a step is also discussed. These results are important towards the understanding of possible diamond growth mechanisms that occur at a step.

Theories of the Classical Sound Film

2018 ◽  
Author(s):  
James Buhler
Keyword(s):  
Film Music ◽  
Theoretical Models ◽  
Conceptual Space ◽  
Sound Film ◽  
Siegfried Kracauer ◽  
Formal Relations ◽  
Relationship Of ◽  
The Relationship

Chapter 3 examines theories after the sound film had been codified. The characteristic forms of theory became the grammar and typology: the goal was to map the potential formal relations between image and sound. This chapter considers six theoretical models focusing on the treatment of music and the relationship of the soundtrack to narrative: Eisenstein’s concept of vertical montage and the modes of synchronization that he developed from the concept; Aaron Copland’s typology of functions for film music; Hanns Eisler and Theodor W. Adorno’s response to Eisenstein, their critique of Hollywood practice, and their list of “bad habits”; and the formal typologies offered by Raymond Spottiswoode, Siegfried Kracauer, and Roger Manvell and John Huntley, which all seek to map the conceptual space of the image–sound relationship in film.

scholarly journals Even–odd conductance effect in graphene nanoribbons induced by edge functionalization with aromatic molecules: basis for novel chemosensors

2020 ◽  
Vol 135 (8) ◽  
Author(s):  
Kristiāns Čerņevičs ◽  
Michele Pizzochero ◽  
Oleg V. Yazyev
Keyword(s):  
Density Functional ◽  
Nearest Neighbor ◽  
Graphene Nanoribbons ◽  
Energy Levels ◽  
Tight Binding ◽  
Density Functional Theory Calculations ◽  
Aromatic Rings ◽  
Functional Theory ◽  
Aromatic Molecules ◽  
Physical Effects

AbstractWe theoretically investigate the electron transport in armchair and zigzag graphene nanoribbons (GNRs) chemically functionalized with p-polyphenyl and polyacene groups of increasing length. Our nearest-neighbor tight-binding calculations indicate that, depending on whether the number of aromatic rings in the functional group is even or odd, the resulting conductance at energies matching the energy levels of the corresponding isolated molecule is either unaffected or reduced by exactly one quantum as compared to the pristine GNR, respectively. Such an even–odd effect is shown to originate from a subtle interplay between the electronic states of the guest molecule that are spatially localized on the binding sites and those of the host nanoribbon. We next generalize our findings by employing more accurate tight-binding Hamiltonians along with density-functional theory calculations and critically discuss the robustness of the observed physical effects against the level of theory adopted. Our work offers a comprehensive understanding of the influence of aromatic molecules bound to the edge of graphene nanoribbons on their electronic transport properties, an issue which is instrumental to the prospective realization of graphene-based chemosensors.

scholarly journals Proposing a theoretical framework to investigate the relationships between an organization and its environment

2007 ◽  
Vol 11 (1) ◽  
pp. 75-96 ◽  
Author(s):  
Ricardo Corrêa Gomes ◽  
Luciana de Oliveira Miranda Gomes
Keyword(s):  
Resource Dependence ◽  
Open Systems ◽  
Theoretical Models ◽  
Theoretical Framework ◽  
Extensive Literature ◽  
Theoretical Support ◽  
External Agents ◽  
And Performance ◽  
Relationship Of ◽  
The Relationship

This paper proposes a theoretical framework for investigating stakeholder theory in organizations. The organizations theory can be understood in three theoretical models: rationalist, natural and open systems. These models are presented to justify that organizations should be analyzed taking into account that social system aspects and the natural and open system models are employed. The applications of this paper rely upon the theoretical framework which is based on an extensive literature review comprising environment based theories. This paper would be of help to researchers examining the whole set of the relationship of organizations with their environment instead of only the relationships with external agents. Employing the theoretical basis presented in this analysis, the researcher will be able to identify both feasible theoretical sources for his/her studies and useful approaches for carrying on his/her investigations. The paper presents theories for explaining the organization's behavior and performance as being influenced by stakeholders who inhabit its environment. Resource dependence and institutional theory are employed to give theoretical support to the stakeholder. At the end of the paper, a diagram representing the theoretical framework is presented.

scholarly journals Subjective perception of social space: elements, centre and metric

2019 ◽  
pp. 45-50
Author(s):  
Kirill V. Zlokazov ◽  
Nikolay I. Leonov
Keyword(s):  
Social Psychology ◽  
Social Space ◽  
Space Perception ◽  
Theoretical Models ◽  
Subjective Perception ◽  
Theoretical Approaches ◽  
Space Objects ◽  
The Subject ◽  
Relationship Of ◽  
The Relationship

We discuss in the articles theoretical approaches in social psychology, used for describe representation of social space by subject. It is shown that different social sciences use original theoretical models of social space. In social psychology, these models are used to measure the relationship of the subject with physical (real) world. At the same time, research concepts do not always correspond to the subject's ideas about social space. As a result, image of subjective perception of space can be misrepresented. The decision is seen as a generalisation of the parameters used to explain the subject’s space perception in physical, phenomenological, social-interactional and topological approach.They are: elements of space (objects), centre and metric (as a way of organising elements of space, used for evaluate relations between them). In conclusion, need of empirical verification of assumptions made about inner components representation of social space is noted.

Hospital Capital Structure Decisions: Theory and Practice

1993 ◽  
Vol 6 (4) ◽  
pp. 237-247
Author(s):  
Louis C. Gapenski
Keyword(s):  
Capital Structure ◽  
Real World ◽  
Theoretical Models ◽  
Theory And Practice ◽  
Structure Theory ◽  
Chief Financial Officers ◽  
Hospital Sector ◽  
Relationship Of ◽  
The Relationship ◽  
Capital Structure Theory

The paper explores capitalisation decisions within the hospital sector. This is done theoretically by examining the appropriateness of capital structure theory of hospitals and also in a real world context of soliciting the views of hospital chief financial officers. The ways in which capital decisions are made is described and the relationship of practice to theoretical models discussed.

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