scholarly journals A Simple Model of Ballistic Conduction in Multi-Lead Molecular Devices

2021 ◽  
Vol 11 (24) ◽  
pp. 11696
Author(s):  
Patrick W. Fowler ◽  
Barry T. Pickup
Keyword(s):  
Molecular Graph ◽  
Wide Band ◽  
Molecular Devices ◽  
Interference Effects ◽  
Selection Rules ◽  
Carbon Framework ◽  
Multiple Sink ◽  
Ballistic Conduction ◽  
Insight Into ◽  
Lead Device

A fully analytical model is presented for ballistic conduction in a multi-lead device that is based on a π-conjugated carbon framework attached to a single source lead and several sink leads. This source-and-multiple-sink potential (SMSP) model is rooted in the Ernzerhof source-and-sink potential (SSP) approach and specifies transmission in terms of combinations of structural polynomials based on the molecular graph. The simplicity of the model allows insight into many-lead devices in terms of constituent two-lead devices, description of conduction in the multi-lead device in terms of structural polynomials, molecular orbital channels, and selection rules for active and inert leads and orbitals. In the wide-band limit, transmission can be expressed entirely in terms of characteristic polynomials of vertex-deleted graphs. As limiting cases of maximum connection, complete symmetric devices (CSD) and complete bipartite symmetric devices (CBSD) are defined and solved analytically. These devices have vanishing lead-lead interference effects. Illustrative calculations of transmission curves for model small-molecule systems are presented and selection rules are identified.

A graph-theoretical model for ballistic conduction in single-molecule conductors

2011 ◽  
Vol 83 (8) ◽  
pp. 1515-1528 ◽  
Author(s):  
Patrick W. Fowler ◽  
Barry T. Pickup ◽  
Tsanka Z. Todorova
Keyword(s):  
Single Molecule ◽  
Molecular Graph ◽  
Tight Binding ◽  
Transmission Function ◽  
Kekulé Structure ◽  
Qualitative Description ◽  
Frontier Orbital ◽  
Conduction Behavior ◽  
Ballistic Conduction ◽  
Source And Sink

The tight-binding version of the source-and-sink potential (SSP) model of ballistic conduction can be cast in a graph-theoretical form where the transmission through a molecular wire depends on four characteristic polynomials: those of the molecular graph and the vertex-deleted subgraphs with one or both of the molecular vertices contacting the electrodes removed. This gives an explicit function for the dependence of transmission on energy, one that is well adapted for qualitative description of general classes of conductors and conduction behavior. It also leads directly to a selection-rule criterion for conduction in terms of counting zero roots of the polynomials, which for benzenoids and graphenes is shown to subsume literature approaches based on Kekulé structure counting, bond order, and frontier-orbital matching. As explicitly demonstrated here, the SSP transmission function agrees with that derived by the Green’s function (GF) method.

scholarly journals Optical selection rules and scattering processes in rocksalt wide band gap ZnO

2014 ◽  
Vol 211 (2) ◽  
pp. 435-439 ◽  
Author(s):  
H. W. Kunert ◽  
M. Govender ◽  
A. G. J. Machatine ◽  
B. W. Mwakikunga ◽  
P. Niyongabo
Keyword(s):  
Band Gap ◽  
Wide Band ◽  
Wide Band Gap ◽  
Selection Rules

Interference Effects in Two-Step Reaction Processes

1972 ◽  
Vol 50 (7) ◽  
pp. 700-702 ◽  
Author(s):  
D. G. Burke ◽  
J. C. Waddington
Keyword(s):  
Simple Expression ◽  
Single Step ◽  
Excitation Mechanism ◽  
Interference Effects ◽  
Reaction Paths ◽  
Reaction Processes ◽  
Insight Into

In reaction studies on even–even target nuclei, one is frequently interested in a state for which (a) the population by single-step processes is forbidden, (b) the dominant excitation mechanism is by two-step processes, and (c) two competing reaction paths are involved. A simple expression is given for such cases which offers some insight into the effects of interference between these two paths. A comparison of the predictions of this expression with several types of experiment is presented. In particular, an interpretation is presented for some recent (3He, α) reaction results which could not previously be explained.

Performance evaluation of MoM-based wide-band EM simulation with adaptive frequency sampling and Stöer-Bulirsch algorithm

2017 ◽  
Vol 36 (4) ◽  
pp. 859-870
Author(s):  
Andrzej Karwowski
Keyword(s):  
Wide Band ◽  
Convergence Criterion ◽  
Test Problems ◽  
Frequency Domain Method ◽  
Content Type ◽  
Uniform Sampling ◽  
Frequency Sampling ◽  
Data Points ◽  
Insight Into ◽  
Study Offer

Purpose The purpose of this paper is to examine the convergence, offered accuracy and efficiency of the bisectional adaptive frequency sampling (AFS) scheme combined with the Stöer-Bulirsch (SB) algorithm as a tool for supporting frequency-domain method-of-moments (MoM) in broadband electromagnetic (EM) simulations. Design/methodology/approach The AFS and SB procedures have been interfaced with the MoM code, and then, an extensive parametric study has been carried out to explore the performance of the numerical solution for the test problems of reconstructing frequency responses of the wire radiator and scatterer, respectively, over at least a decade bandwidth. Findings The results give evidence for the efficiency of the overall approach and its capability of constructing the approximation of multi-resonant responses with sharp resonant peaks from a substantially reduced number of EM samples (data points) compared to that of conventional uniform sampling. Originality/value Results of the study offer thorough insight into the performance of the AFS-SB technique, and the data given in this paper may be helpful in selecting the convergence criterion and the tolerance for the AFS-SB algorithm to achieve a possibly economical broadband simulation technique.

scholarly journals Abundances of sulphur molecules in the Horsehead nebula

2019 ◽  
Vol 628 ◽  
pp. A16 ◽  
Author(s):  
P. Rivière-Marichalar ◽  
A. Fuente ◽  
J. R. Goicoechea ◽  
J. Pety ◽  
R. Le Gal ◽  
...  
Keyword(s):  
Wide Band ◽  
Physical Conditions ◽  
The Core ◽  
Complete Study ◽  
Chemical Behaviour ◽  
Molecular Excitation ◽  
Molecular Abundances ◽  
The Universe ◽  
Sulphur Species ◽  
Insight Into

Context. Sulphur is one of the most abundant elements in the Universe (S/H ~ 1.3 × 10−5) and plays a crucial role in biological systems on Earth. The understanding of its chemistry is therefore of major importance. Aims. Our goal is to complete the inventory of S-bearing molecules and their abundances in the prototypical photodissociation region (PDR) the Horsehead nebula to gain insight into sulphur chemistry in UV irradiated regions. Based on the WHISPER (Wide-band High-resolution Iram-30 m Surveys at two positions with Emir Receivers) millimeter (mm) line survey, our goal is to provide an improved and more accurate description of sulphur species and their abundances towards the core and PDR positions in the Horsehead. Methods. The Monte Carlo Markov chain (MCMC) methodology and the molecular excitation and radiative transfer code RADEX were used to explore the parameter space and determine physical conditions and beam-averaged molecular abundances. Results. A total of 13 S-bearing species (CS, SO, SO2, OCS, H2CS – both ortho and para – HDCS, C2S, HCS+, SO+, H2S, S2H, NS and NS+) have been detected in the two targeted positions. This is the first detection of SO+ in the Horsehead and the first detection of NS+ in any PDR. We find a differentiated chemical behaviour between C–S and O–S bearing species within the nebula. The C–S bearing species C2S and o-H2CS present fractional abundances a factor of > two higher in the core than in the PDR. In contrast, the O–S bearing molecules SO, SO2, and OCS present similar abundances towards both positions. A few molecules, SO+, NS, and NS+, are more abundant towards the PDR than towards the core, and could be considered as PDR tracers. Conclusions. This is the first complete study of S-bearing species towards a PDR. Our study shows that CS, SO, and H2S are the most abundant S-bearing molecules in the PDR with abundances of approximately a few 10−9. We recall that SH, SH+, S, and S+ are not observable at the wavelengths covered by the WHISPER survey. At the spatial scale of our observations, the total abundance of S atoms locked in the detected species is <10−8, only ~0.1% of the cosmic sulphur abundance.

Ballistic Effect and Application in Circuit Design of Wide Band-Gap Semiconductor

2014 ◽  
Vol 644-650 ◽  
pp. 3597-3600
Author(s):  
Xin Xiang Liang ◽  
Zhi Qun Cheng ◽  
Min Shi Jia
Keyword(s):  
Semiconductor Devices ◽  
Electronic Devices ◽  
Ballistic Transport ◽  
Wide Band ◽  
Mean Free Path ◽  
Molecular Devices ◽  
Wide Band Gap ◽  
Transport Distance ◽  
The Mean ◽  
Crystal Interfaces

With manufacturing technology innovation and progress of electronic devices of semiconductors, dimensions of electronic devices get smaller nowadays. There has been processing of 90nm and 20nm in production. With in-depth research, scientists are more and more interested in molecular devices. Since the size of molecular devices is small, electrons transfer by ballistic transport. In semiconductor devices, when the transport distance is at micrometer or smaller sizes, the ballistic transport phenomena of electrons and holes of carriers occur. This transfer form is not affected by lattice defects, doping, and interaction of crystal interfaces. Since there is no interference of these interactions, carrier’s velocity can be faster several times than common electronic devices, resulting in the doubled operating speed of these devices. Although it is difficult to achieve pure ballistic transport, when the size of semiconductor devices is close to the mean free path of carriers, the speed of carriers will still be greatly improved.

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