294 research outputs found
Spin-dependent Klein tunneling in graphene: Role of Rashba spin-orbit coupling
Within an effective Dirac theory the low-energy dispersions of monolayer
graphene in the presence of Rashba spin-orbit coupling and spin-degenerate
bilayer graphene are described by formally identical expressions. We explore
implications of this correspondence for transport by choosing chiral tunneling
through pn and pnp junctions as a concrete example. A real-space Green's
function formalism based on a tight-binding model is adopted to perform the
ballistic transport calculations, which cover and confirm previous theoretical
results based on the Dirac theory. Chiral tunneling in monolayer graphene in
the presence of Rashba coupling is shown to indeed behave like in bilayer
graphene. Combined effects of a forbidden normal transmission and spin
separation are observed within the single-band n to p transmission regime. The
former comes from real-spin conservation, in analogy with pseudospin
conservation in bilayer graphene, while the latter arises from the intrinsic
spin-Hall mechanism of the Rashba coupling.Comment: 10 pages, 10 figure
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Automatic spike correction using UNIFIT 2020
The improvement of the software UNIFIT 2020 from an analysis processing software for photoelectron spectroscopy (XPS) only to a powerful tool for XPS, Auger electron spectroscopy (AES), X-ray absorption spectroscopy (XAS), and Raman spectroscopy requires new additional programme routines. Particularly, the implementation of the analysis of Raman spectra needs a well-working automatic spike correction. The application of the modified discrete Laplace operator method allows for a perfect localization and correction of the spikes and finally a successful peak fit of the spectra. The theoretical basis is described. Test spectra allow for the evaluation of the presented method. A comparison of the original and spike-corrected real measurements demonstrates the high quality of the method used
Edge state effects in junctions with graphene electrodes
We consider plane junctions with graphene electrodes, which are formed by a
single-level system ("molecule") placed between the edges of two single-layer
graphene half planes. We calculate the edge Green functions of the electrodes
and the corresponding lead self-energies for the molecular levels in the cases
of semi-infinite single-layer electrodes with armchair and zigzag edges. We
show two main effects: first, a peculiar energy-dependent level broadening,
reflecting at low energies the linear energy dependence of the bulk density of
states in graphene, and, second, the shift and splitting of the molecular level
energy, especially pronounced in the case of the zigzag edges due to the
influence of the edge states. These effects give rise to peculiar conductance
features at finite bias and gate voltages.Comment: 8 pages, 8 figures, submitted to PR
Ion beam sputtering of silicon: Energy distributions of sputtered and scattered ions
The properties of sputtered and scattered ions are studied for ion beam sputtering of Si by bombardment with noble gas ions. The energy distributions in dependence on ion beam parameters (ion energy: 0.5-1 keV; ion species: Ne, Ar, Xe) and geometrical parameters (ion incidence angle, polar emission angle, and scattering angle) are measured by means of energy-selective mass spectrometry. The presence of anisotropic effects due to direct sputtering and scattering is discussed and correlated with process parameters. The experimental results are compared to calculations based on a simple elastic binary collision model and to simulations using the Monte-Carlo code sdtrimsp. The influence of the contribution of implanted primary ions on energy distributions of sputtered and scattered particles is studied in simulations. It is found that a 10% variation of the target composition leads to detectable but small differences in the energy distributions of scattered ions. Comparison with previously reported data for other ion/target configurations confirms the presence of similar trends and anisotropic effects: The number of high-energy sputtered ions increases with increasing energy of incident ions and decreasing scattering angle. The effect of the ion/target mass ratio is additionally investigated. Small differences are observed with the change of the primary ion species: The closer the mass ratio to unity, the higher the average energy of sputtered ions. The presence of peaks, assigned to different mechanisms of direct scattering, strongly depends on the ion/target mass ratio
Phase Coherent Transport in Graphene Nanoribbons and Graphene Nanoribbon Arrays
We have experimentally investigated quantum interference corrections to the
conductivity of graphene nanoribbons at temperatures down to 20 mK studying
both weak localization (WL) and universal conductance fluctuations (UCF). Since
in individual nanoribbons at millikelvin temperatures the UCFs strongly mask
the weak localization feature we employ both gate averaging and ensemble
averaging to suppress the UCFs. This allows us to extract the phase coherence
length from both WL and UCF at all temperatures. Above 1 K, the phase coherence
length is suppressed due to Nyquist scattering whereas at low temperatures we
observe a saturation of the phase coherence length at a few hundred nanometers,
which exceeds the ribbon width, but stays below values typically found in bulk
graphene. To better describe the experiments at elevated temperatures, we
extend the formula for 1D weak localization in graphene, which was derived in
the limit of strong intervalley scattering, to include all elastic scattering
rates.Comment: 8 pages, 6 figures, accepted by PR
Dielectric constants and phonon modes of amorphous hafnium aluminate deposited by metal organic chemical vapor deposition
Dielectric constants and long-wavelength optical phonon modes of amorphous hafnium aluminate films with a maximum aluminum content of 19 at. % are studied by infrared spectroscopic ellipsometry (IRSE). The hafnium aluminate films were prepared by metal organic chemical vapor deposition on silicon substrates. IRSE revealed one polar lattice mode and one impurity-type mode, which show all a systematic shift in frequency with varying Al content. The static dielectric constant decreases from 10.1 for 4.6 at. % Al to 8.1 for 19 at. % Al. The absolute values were found to be between 50% and 70% smaller than the values obtained from electrical measurements
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Modelling of a radio frequency plasma bridge neutralizer (RFPBN)
A performance model of a radio frequency plasma bridge neutralizer was developed to calculate the electrical parameters and optimize the neutralizer design. Minimization of power losses and gas consumption, and a maximization of the neutralizer lifetime and the reliability of the system are requirements of all electric propulsion concepts and strongly determine their future application. The requirements of the neutralizer depend on mission profiles
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