294 research outputs found
Sputtering phenomena in ion thrusters
Sputtering effects in discharge chambers of ion thrusters are lifetime limiting in basically two ways: (1) ion bombardment of critical thruster components at energies sufficient to cause sputtering removes significant quantities of material; enough to degrade operation through adverse dimensional changes or possibly lead to complete component failure, and (2) metals sputtered from these intensely bombarded components are deposited in other locations as thin films and subsequently flake or peel off; the flakes then lodge elsewhere in the discharge chamber with the possibility of providing conductive paths for short circuiting of thruster components such as the ion optics. This experimental work has concentrated in two areas. The first has been to operate thrusters for multi-hour periods and to observe and measure the films found inside the thruster. The second was to simulate the environment inside the discharge chamber of the thruster by means of a dual ion beam system. Here, films were sputter deposited in the presence of a second low energy bombarding beam to simulate film deposition on thruster interior surfaces that undergo simultaneous sputtering and deposition. Mo presents serious problems for use in a thruster as far as film deposition is concerned. Mo films were found to be in high stress, making them more likely to peel and flake
Across-wafer nonuniformity of long throw sputter deposition
A. A. Mayo et al., Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena 15, 1788 (1997) https://doi.org/10.1116/1.58952
Thin, high atomic weight refractory film deposition for diffusion barrier, adhesion layer, and seed layer applications
Thin, nearly conformal films are required for semiconductor applications to function as diffusion barriers, adhesion layers and seed layers within trenches and vias. The deposition of high mass refractory films with conventional, noncollimated magnetron sputtering at low pressures shows better-than-expected conformality which is dependent on the degree of directionality of the depositing atoms: the conformality increases as the directionality increases. The primary cause appears to be a strongly angle-dependent reflection coefficient for the depositing metal atoms. As the deposition is made more directional by increasing the cathode-to-sample distance, the depositing atoms are more likely to reflect from the steep sidewalls, leading to better conformality as well as a less columnar film structure. © 1996 American Vacuum Society.S. M. Rossnagel et al., Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena 14, 1819 (1996) https://doi.org/10.1116/1.58856
Time- and angle-resolved photoemission spectroscopy with optimized high-harmonic pulses using frequency-doubled Ti:Sapphire lasers
Time- and angle-resolved photoemission spectroscopy (trARPES) using femtosecond extreme ultraviolet high harmonics has recently emerged as a powerful tool for investigating ultrafast quasiparticle dynamics in correlated-electron materials. However, the full potential of this approach has not yet been achieved because, to date, high harmonics generated by 800 nm wavelength Ti:Sapphire lasers required a trade-off between photon flux, energy and time resolution. Photoemission spectroscopy requires a quasi-monochromatic output, but dispersive optical elements that select a single harmonic can significantly reduce the photon flux and time resolution. Here we show that 400 nm driven high harmonic extreme-ultraviolet trARPES is superior to using 800 nm laser drivers since it eliminates the need for any spectral selection, thereby increasing photon flux and energy resolution to < 150 meV while preserving excellent time resolution of about 30 fs. © 2014 The Authors
Self-amplified photo-induced gap quenching in a correlated electron material.
Capturing the dynamic electronic band structure of a correlated material presents a powerful capability for uncovering the complex couplings between the electronic and structural degrees of freedom. When combined with ultrafast laser excitation, new phases of matter can result, since far-from-equilibrium excited states are instantaneously populated. Here, we elucidate a general relation between ultrafast non-equilibrium electron dynamics and the size of the characteristic energy gap in a correlated electron material. We show that carrier multiplication via impact ionization can be one of the most important processes in a gapped material, and that the speed of carrier multiplication critically depends on the size of the energy gap. In the case of the charge-density wave material 1T-TiSe2, our data indicate that carrier multiplication and gap dynamics mutually amplify each other, which explains-on a microscopic level-the extremely fast response of this material to ultrafast optical excitation
Resonant photoemission at the absorption edge of Mn and Ti and electronic structure of 1T-MnTiSe
Resonant valence-band X-ray photoelectron spectra (ResPES) excited near
2p core level energies, 2p X-ray photoelectron spectra (XPS) and
L X-ray absorption spectra (XAS) of Ti and Mn in single crystal of
1T-MnTiSe were studied for the first time. The ionic-covalent character
of bonds formed by Mn atoms with the neighboring Se atoms in the octahedral
coordination is established. From the XPS and XAS measurements compared with
results of atomic multiplet calculations of Ti and Mn L XAS it is found
that Ti atoms are in ionic state of 4+ and Mn atoms are in the state of 2+. In
ResPES of MnTiSe excited near Ti 2p and Mn 2p
absorption edges the Ti 3d and Mn 3d bands at binding energies just below the
Fermi level are observed. According to band structure calculations
E the Ti 3d states are localized in the vicinity of
point and the Mn 3d states are localized along the direction
K--M in the Brillouin zone of the crystal.Comment: 18 pages (preprint), 9 figure
Pathway to the PiezoElectronic Transduction Logic Device
The information age challenges computer technology to process an
exponentially increasing computational load on a limited energy budget - a
requirement that demands an exponential reduction in energy per operation. In
digital logic circuits, the switching energy of present FET devices is
intimately connected with the switching voltage, and can no longer be lowered
sufficiently, limiting the ability of current technology to address the
challenge. Quantum computing offers a leap forward in capability, but a clear
advantage requires algorithms presently developed for only a small set of
applications. Therefore, a new, general purpose, classical technology based on
a different paradigm is needed to meet the ever increasing demand for data
processing.Comment: in Nano Letters (2015
Orbital textures and charge density waves in transition metal dichalcogenides
Low-dimensional electron systems, as realized naturally in graphene or
created artificially at the interfaces of heterostructures, exhibit a variety
of fascinating quantum phenomena with great prospects for future applications.
Once electrons are confined to low dimensions, they also tend to spontaneously
break the symmetry of the underlying nuclear lattice by forming so-called
density waves; a state of matter that currently attracts enormous attention
because of its relation to various unconventional electronic properties. In
this study we reveal a remarkable and surprising feature of charge density
waves (CDWs), namely their intimate relation to orbital order. For the
prototypical material 1T-TaS2 we not only show that the CDW within the
two-dimensional TaS2-layers involves previously unidentified orbital textures
of great complexity. We also demonstrate that two metastable stackings of the
orbitally ordered layers allow to manipulate salient features of the electronic
structure. Indeed, these orbital effects enable to switch the properties of
1T-TaS2 nanostructures from metallic to semiconducting with technologically
pertinent gaps of the order of 200 meV. This new type of orbitronics is
especially relevant for the ongoing development of novel, miniaturized and
ultra-fast devices based on layered transition metal dichalcogenides
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