Quantum transport of a nanowire field-effect transistor with complex phonon self–energy http://dx.doi.org/10.1063/1.4894066 by Valin, R.; Aldegunde, M.; Martinez, A. (Electronic Systems Design Centre, College
of Engineering, Swansea University, SA2 8PP (United Kingdom)); Barker, J. R. (School
of Engineering, University of Glasgow, G12 8LT (United Kingdom)), E-mail: r.valinferreiro@swansea.ac.uk,
E-mail: m.a.aldegunderodriguez@swansea.ac.uk, E-mail: a.e.Martinez@swansea.ac.uk,
E-mail: john.barker@glasgow.ac.uk Read MoreCollapse
[en]
In this work, the impact of the real part of the phonon self-energy on the transfer
characteristics of a silicon nanowire transistor is investigated. The physical effects
of the real part of the self-energy are to create a broadening and a shift on the
density of states. This increases the drain current in the sub–threshold region and
decreases it in the above–the–threshold region. In the first region, the current is
increased as a result of an increase of charge in the middle of the channel. In the
second one, the electrostatic self–consistency or the enforcement of charge neutrality
in the channel reduces the current because a substantial amount of electrons are under
the first subband and have imaginary wave vectors. The change in the phonon–limited
mobility due to the real part of self–energy is evaluated for a nanowire transistor
and a nanowire in which there is not source to drain barrier. We also assess the validity
of Mathiessen's rule using the self–consistent NEGF simulations and the Kubo–Greenwood
formalism$$$$
The enhancement of breakdown threshold is of benefit to the high power microwave transmission.
We propose a magnetic field in the transverse direction to the electric field to enhance
the breakdown threshold. A theory of electric field threshold with crossed magnetic
field for short pulse is developed, and verified by particle-in-cell/Monte Carlo collision
(PIC/MCC) simulations. The result shows that the crossed magnetic field can enhance
the breakdown threshold significantly.$$$$
Some mathematical problems connected with the numerical solving of equations of motion
for charged particles in inhomogeneous magnetic fields are considered. The three-dimensional
spline approximation of the magnetic field is proposed. This allows one to use high-accuracy
numerical methods to evaluate the trajectory of the moving charged particle in inhomogeneous
magnetic field. On the base of multidimensional approximation the fast algorithms
for the description of equations of motion solution and its derivatives with respect
to initial data are proposed. The application of the considered methods for ALICE
experiment are demonstrated. (author)$$$$
We experimentally demonstrate a novel nanoscale temperature sensing technique that
is based on single atomic defects in diamonds, namely nitrogen vacancy color centers.
Sample sizes range from millimeter down to a few tens of nanometers. In particular
nanodiamonds were used as dispersed probes to acquire spatially resolved temperature
profiles utilizing the sensitivity of the optically accessible electron spin level
structure we achieve a temperature noise floor of 5mK/Mhz for bulk diamond and 130mK/Mhz
for nanodiamonds and accuracies of 1mK. To this end we have developed a new decoupling
technique in order to suppress to otherwise limiting effect of magnetic field fluctuations.
In addition, high purity isotopically enriched 12C artificial diamonds is used. The
high sensitivity to temperature changes adds to the well studied sensitivities to
magnetic and electric fields and makes NV diamond a multipurpose nanoprobe. (author)$$$$
Soliton self-frequency shift in a highly nonlinear photonic-crystal fiber is shown
to enable an efficient wavelength conversion of 100-fs 70-MHz output of a solid-state
ytterbium laser, allowing the generation of sub-100-fs laser pulses with a central
wavelength tunable from 1060 to 1400 nm. In the single-soliton regime, laser pulses
are efficiently converted into isolated wavelength-tunable bands, with a photon-number
conversion efficiency of 82% achieved for ytterbium-laser pulses converted to a spectral
band at 1125 nm supporting 35-fs transform-limited pulses. For high input powers,
the ytterbium-laser pulses are coupled to multiple solitons inside the fiber, enabling
efficient supercontinuum generation through involved soliton dynamics$$$$
Recent developments in the theory of plasma-based collisionally excited x-ray lasers
(XRL) have shown an optimization potential based on the dependence of the absorption
region of the pumping laser on its angle of incidence on the plasma. For the experimental
proof of this idea, a number of diagnostic schemes were developed, tested, qualified
and applied. A high-resolution imaging system, yielding the keV emission profile perpendicular
to the target surface, provided positions of the hottest plasma regions, interesting
for the benchmarking of plasma simulation codes. The implementation of a highly efficient
spectrometer for the plasma emission made it possible to gain information about the
abundance of the ionization states necessary for the laser action in the plasma. The
intensity distribution and deflection angle of the pump laser beam could be imaged
for single XRL shots, giving access to its refraction process within the plasma. During
a European collaboration campaign at the Lund Laser Center, Sweden, the optimization
of the pumping laser incidence angle resulted in a reduction of the required pumping
energy for a Ni-like Mo XRL, which enabled the operation at a repetition rate of 10
Hz. Using the experiences gained there, the XRL performance at the PHELIX facility,
GSI Darmstadt with respect to achievable repetition rate and at wavelengths below
20 nm was significantly improved, and also important information for the development
towards multi-100 eV plasma XRLs was acquired. Due to the setup improvements achieved
during the work for this thesis, the PHELIX XRL system now has reached a degree of
reproducibility and versatility which is sufficient for demanding applications like
the XRL spectroscopy of heavy ions. In addition, a European research campaign, aiming
towards plasma XRLs approaching the water-window (wavelengths below 5 nm) was initiated.
(orig.)$$$$
The present doctoral thesis describes experimentally measured properties of the resonance
spectra of flat microwave billiards with partially broken timereversal invariance
induced by an embedded magnetized ferrite. A vector network analyzer determines the
complex scattering matrix elements. The data is interpreted in terms of the scattering
formalism developed in nuclear physics. At low excitation frequencies the scattering
matrix displays isolated resonances. At these the effect of the ferrite on isolated
resonances (singlets) and pairs of nearly degenerate resonances (doublets) is investigated.
The hallmark of time-reversal symmetry breaking is the violation of reciprocity, i.e.
of the symmetry of the scattering matrix. One finds that reciprocity holds in singlets;
it is violated in doublets. This is modeled by an effective Hamiltonian of the resonator.
A comparison of the model to the data yields time-reversal symmetry breaking matrix
elements in the order of the level spacing. Their dependence on the magnetization
of the ferrite is understood in terms of its magnetic properties. At higher excitation
frequencies the resonances overlap and the scattering matrix elements fluctuate irregularly
(Ericson fluctuations). They are analyzed in terms of correlation functions. The data
are compared to three models based on random matrix theory. The model by Verbaarschot,
Weidenmueller and Zirnbauer describes time-reversal invariant scattering processes.
The one by Fyodorov, Savin and Sommers achieves the same for systems with complete
time-reversal symmetry breaking. An extended model has been developed that accounts
for partial breaking of time-reversal invariance. This extended model is in general
agreement with the data, while the applicability of the other two models is limited.
The cross-correlation function between forward and backward reactions determines the
time-reversal symmetry breaking matrix elements of the Hamiltonian to up to 0.3 mean
level spacings. Finally the sensitivity of the elastic enhancement factor to time-reversal
symmetry breaking is studied. Based on the data elastic enhancement factors below
2 are found which is consistent with breaking of time-reversal invariance in the regime
of overlapping resonances. The present work provides the framework to probe for broken
time-reversal invariance in any scattering data by a multitude of methods in the whole
range between isolated and overlapping resonances. (orig.)$$$$
Molecular dynamics for fermions by Feldmeier, H. (Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany)); Schnack,
J. (Osnabrueck Univ. (Germany). Fachbereich Physik); Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany) Read MoreCollapse
[en]
The time-dependent variational principle for many-body trial states is used to discuss
the relation between the approaches of different molecular dynamics models to describe
indistinguishable fermions. Early attempts to include effects of the Pauli principle
by means of nonlocal potentials as well as more recent models which work with antisymmetrized
many-body states are reviewed under these premises. (orig.)$$$$
The time evolution of plasma potential has been measured with a retarding field analyzer
in pulsed operation mode with electron cyclotron resonance ion sources at JYFL and
RIKEN. Three different ion sources with microwave frequencies ranging from 6.4 to
18 GHz were employed for the experiments. The plasma potential was observed to increase
10-75 % during the Pre-glow and 10-30 % during the afterglow compared to steady state.
The paper is followed by the slides of the presentation. (authors)$$$$
New insights into self-heating in double-gate transistors by solving Boltzmann transport
equations http://dx.doi.org/10.1063/1.4893646 by Thu Trang Nghiêm, T. (Institute of Fundamental Electronics, UMR 8622, CNRS-University
of Paris-Sud, Orsay (France); The Center for Thermal Sciences of Lyon, UMR 5008, CNRS–INSA–University
of Lyon 1, Villeurbanne (France)); Saint-Martin, J.; Dollfus, P. (Institute of Fundamental
Electronics, UMR 8622, CNRS-University of Paris-Sud, Orsay (France)), E-mail: tthutrang.nghiem@gmail.com Read MoreCollapse
[en]
Electro-thermal effects become one of the most critical issues for continuing the
downscaling of electron devices. To study this problem, a new efficient self-consistent
electron-phonon transport model has been developed. Our model of phonon Boltzmann
transport equation (pBTE) includes the decay of optical phonons into acoustic modes
and a generation term given by electron-Monte Carlo simulation. The solution of pBTE
uses an analytic phonon dispersion and the relaxation time approximation for acoustic
and optical phonons. This coupled simulation is applied to investigate the self-heating
effects in a 20 nm-long double gate MOSFET. The temperature profile per mode and the
comparison between Fourier temperature and the effective temperature are discussed.
Some significant differences occur mainly in the hot spot region. It is shown that
under the influence of self-heating effects, the potential profile is modified and
both the drain current and the electron ballisticity are reduced because of enhanced
electron-phonon scattering rates$$$$