Evaluation of the Effective Microstructure Parameter of the Microwave Emission Model of Layered Snowpack for Multiple-Layer Snow

Natural snow, one of the most important components of the cryosphere, is fundamentally a layered medium. In forward simulation and retrieval, a single-layer effective microstructure parameter is widely used to represent the emission of multiple-layer snowpacks. However, in most cases, this parameter is fitted instead of calculated based on a physical theory. The uncertainty under different frequencies, polarizations, and snow conditions is uncertain. In this study, we explored different methods to reduce the layered snow properties to a set of single-layer values that can reproduce the same brightness temperature (TB) signal. A validated microwave emission model of layered snowpack (MEMLS) was used as the modelling tool. Multiple-layer snow TB from the snow’s surface was compared with the bulk TB of single-layer snow. The methods were tested using snow profile samples from the locally validated and global snow process model simulations, which follow the natural snow’s characteristics. The results showed that there are two factors that play critical roles in the stability of the bulk TB error, the single-layer effective microstructure parameter, and the reflectivity at the air–snow and snow–soil boundaries. It is important to use the same boundary reflectivity as the multiple-layer snow case calculated using the snow density at the topmost and bottommost layers instead of the average density. Afterwards, a mass-weighted average snow microstructure parameter can be used to calculate the volume scattering coefficient at 10.65 to 23.8 GHz. At 36.5 and 89 GHz, the effective microstructure parameter needs to be retrieved based on the product of the snow layer transmissivity. For thick snow, a cut-off threshold of 1/e is suggested to be used to include only the surface layers within the microwave penetration depth. The optimal method provides a root mean squared error of bulk TB of less than 5 K at 10.65 to 36.5 GHz and less than 10 K at 89 GHz for snow depths up to 130 cm.

Effect of microstructure parameter on the energy product in two-phase permanent magnetic materials

Two-phase permanent magnets with soft and hard magnetic phases are suitable candidates for high energy product permanent magnets. To obtain enhanced energy product, the microstructure has to be optimum and the magnetization and nucleation field has to be as large as possible. The present studies suggest suitable combinations of soft–hard composites that could result in higher energy product. The role of microstructural parameter on the energy product is also presented.

Hydrogen Injection in ETP Plasma Jet for Fast-Deposition of High-Quality a-Si:H

ABSTRACTWe have used a cascaded-arc expanding thermal plasma (ETP) to produce thin films of amorphous silicon at high growth rates (> 3 nm/s). Here, we present a study of the effect on material properties of hydrogen injection in the nozzle, i.e., at the exit of the arc where the plasma expands into the reactor chamber. The advantage of using extra H2 in the nozzle is that the plasma chemistry and pressure in the arc remain unchanged, whilst higher growth rates and a material with low defect densities can be obtained.We observe that with an increase of substrate temperature the growth rate decreases due to densification of the material. This densification is accompanied by a reduction of the hydrogen content and of the microstructure parameter. Further we observe that hydrogen content decreases with higher growth rate. A strong relation is found between the light conductivity and the microstructure parameter indicating a large void fraction in samples grown at low temperature.We have been able to grow a-Si:H material, with H2 in the nozzle, at 350°C and 3 nm/s with a light conductivity of 1.2 × 10−5 Ω1cm−1, which can be suitable for solar-cell application.

Effects of Excitation Frequency and H2 Dilution on Cluster Generation in Silane High-Frequency Discharges

Reduction of cluster amount in silane discharges is the key to decreasing microstructure parameter Rα of a-Si:H films deposited with the discharges. The cluster amount is found to be reduced more than one order of magnitude using 60 MHz discharges instead of 28 MHz ones or using H2 dilution of an H2/SiH4 ratio of 5. The cluster-suppressed plasma CVD using 60 MHz discharges realizes deposition of a-Si:H films of Rα~ 0 at a fairly high rate of 0.55 nm/s. Moreover, a downstream cluster collection method of high sensitivity has been developed for detecting a small amount of clusters formed under deposition conditions of Rα < 0.01.