The absolute densities of H atoms produced in catalytic chemical vapor deposition (Cat-CVD or hot-wire CVD) processes were determined by employing two-photon laser-induced fluorescence and vacuum ultraviolet absorption techniques. The H-atom density in the gas phase increases exponentially with increases in the catalyzer temperature in the presence of pure H2. When the catalyzer temperature was 2200 K, the absolute density in the presence of 5.6 Pa of H2 (150 sccm in flow rate) was as high as 1.5×1014 cm−3 at a point 10 cm from the catalyzer. This density is one or two orders of magnitude higher than those observed in typical plasma-enhanced chemical vapor-deposition processes. The H-atom density decreases sharply with the addition of SiH4. When 0.1 Pa of SiH4 was added, the steady-state density decreased to 7×1012 cm−3. This sharp decrease can primarily be ascribed to the loss processes on chamber walls.
The catalytic decomposition processes of NH 3 on heated W surfaces were examined by employing laser spectroscopic techniques. H atoms and NH 2 radicals were identified as primary decomposition products on the catalyzer surfaces. The effective enthalpies for the production of these species were both determined to be 150 kJ/mol. NH radicals were also identified, but the production of this species is ascribed to secondary processes. N atoms are minor products in both the primary and secondary processes. The absolute density measurements show that the decomposition efficiency of NH 3 is comparable to that of H 2 . The steady-state densities of NH 3 and the stable products, H 2 and N 2 , were also measured by mass spectrometry. When the catalyzer temperature is over 2000 K, the H 2 density is comparable to that of residual NH 3 . H atoms are produced not only by the direct decomposition of NH 3 but also by the decomposition of H 2 .
Magnetic skyrmions are versatile
topological excitations that can
be used as nonvolatile information carriers. The confinement of skyrmions
in channels is fundamental for any application based on the accumulation
and transport of skyrmions. Here, we report a method that allows effective
position control of skyrmions in designed channels by engineered energy
barriers and wells, which is realized in a magnetic multilayer film
by harnessing the boundaries of patterns with modified magnetic properties.
We experimentally and computationally demonstrate that skyrmions can
be attracted or repelled by the boundaries of areas with modified
perpendicular magnetic anisotropy and Dzyaloshinskii–Moriya
interaction. By fabricating square and stripe patterns with modified
magnetic properties, we show the possibility of building reliable
channels for confinement, accumulation, and transport of skyrmions,
which effectively protect skyrmions from being destroyed at the device
edges. Our results are useful for the design of spintronic applications
using either static or dynamic skyrmions.
Skyrmions and bimerons are versatile topological spin textures that can be used as information bits for both classical and quantum computing. The transformation between isolated skyrmions and bimerons is an essential operation for computing architecture based on multiple different topological bits. Here we report the creation of isolated skyrmions and their subsequent transformation to bimerons by harnessing the electric currentinduced Oersted field and temperature-induced perpendicular magnetic anisotropy variation. The transformation between skyrmions and bimerons is reversible, which is controlled by the current amplitude and scanning direction. Both skyrmions and bimerons can be created in the same system through the skyrmion-bimeron transformation and magnetization switching. Deformed skyrmion bubbles and chiral labyrinth domains are found as nontrivial intermediate transition states. Our results may provide a unique way for building advanced information-processing devices using different types of topological spin textures in the same system.
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