149 research outputs found
Crucible-free Pulling of Germanium Crystals
Commonly, germanium crystals are grown after the Czochralski (CZ) method. The
crucible-free pedestal and floating zone (FZ) methods, which are widely used
for silicon growth, are hardly known to be investigated for germanium. The
germanium melt is more than twice as dense as liquid silicon, which could
destabilize a floating zone. Additionally, the lower melting point and the
related lower radiative heat loss is shown to reduce the stability especially
of the FZ process with the consequence of a screw-like crystal growth. We found
that the lower heat radiation of Ge can be compensated by the increased
convective cooling of a helium atmosphere instead of the argon ambient. Under
these conditions, the screw-like growth could be avoided. Unfortunately, the
helium cooling deteriorates the melting behavior of the feed rod. Spikes appear
along the open melt front, which touch on the induction coil. In order to
improve the melting behavior, we used a lamp as a second energy source as well
as a mixture of Ar and He. With this, we found a final solution for growing
stable crystals from germanium by using both gases in different parts of the
furnace. The experimental work is accompanied by the simulation of the
stationary temperature field. The commercially available software FEMAG-FZ is
used for axisymmetric calculations. Another tool for process development is the
lateral photo-voltage scanning (LPS), which can determine the shape of the
solid-liquid phase boundary by analyzing the growth striations in a lateral cut
of a grown crystal. In addition to improvements of the process, these
measurements can be compared with the calculated results and, hence, conduce to
validate the calculation.Comment: 4 pages, 10 figures, ICCG-1
A theoretical model of conformational transitions in biomolecules based on single-molecule Förster resonance electron transfer measurements
Performance boost of time-delay reservoir computing by non-resonant clock cycle
The time-delay-based reservoir computing setup has seen tremendous success in
both experiment and simulation. It allows for the construction of large
neuromorphic computing systems with only few components. However, until now the
interplay of the different timescales has not been investigated thoroughly. In
this manuscript, we investigate the effects of a mismatch between the
time-delay and the clock cycle for a general model. Typically, these two time
scales are considered to be equal. Here we show that the case of equal or
resonant time-delay and clock cycle could be actively detrimental and leads to
an increase of the approximation error of the reservoir. In particular, we can
show that non-resonant ratios of these time scales have maximal memory
capacities. We achieve this by translating the periodically driven
delay-dynamical system into an equivalent network. Networks that originate from
a system with resonant delay-times and clock cycles fail to utilize all of
their degrees of freedom, which causes the degradation of their performance
Connecting reservoir computing with statistical forecasting and deep neural networks
Among the existing machine learning frameworks, reservoir computing demonstrates fast and low-cost training, and its suitability for implementation in various physical systems. This Comment reports on how aspects of reservoir computing can be applied to classical forecasting methods to accelerate the learning process, and highlights a new approach that makes the hardware implementation of traditional machine learning algorithms practicable in electronic and photonic systems
Growth Angle and Melt Meniscus of the RF-heated Floating Zone in Silicon Crystal Growth
This article presents a direct measurement of the growth angle during the
growth of a cylindrical 2" silicon crystal using a radio-frequency heated
floating zone process. From the high-resolution pictures taken during the
process, this growth angle was evaluated to be 11{\deg}{\pm}2{\deg}.
Furthermore, the free surface of the melt was modeled using the Laplace-Young
equation. This model has to include the electromagnetic pressure calculated by
the surface ring currents approximation. The results were compared to the
experimental free surface derived from video frames. It could be shown that the
calculated free surface will only fit the experimentally determined one if the
right growth angle is considered
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