Structural optimization of silicon thin film for thermoelectric materials

The method to optimize nanostructures of silicon thin films as thermoelectric materials is developed. The simulated annealing method is utilized for predicting the optimized structure. The mean free path and thermal conductivity of thin films, which are the objective function of optimization, is evaluated by using phonon transport simulations and lattice dynamics calculations. In small systems composed of square lattices, the simulated annealing method successfully predicts optimized structure corroborated by an exhaustive search. This fact indicates that the simulated annealing method is an effective tool for optimizing nanostructured thin films as thermoelectric materials.

Estimating the uncertainty of measurements of thermal conductivity of thin films of thermoelectrics with the 3-omega method

Using the method of computer simulation, the uncertainty of measurements of the thermal conductivity of silicon, which is often used as substrates, and also thin films based on bismuth, is estimated. The influence of the application of an additional dielectric layer between the thermoelectric film and the resistive heater on the measurement results is shown.

Changes in the electrical conductivity of glass, quartz, Au, C, and MoS2 films under influence of continuous proton injection

Changes in the electrical conductivity of a wide range of materials with different crystal-chemical types and electrophysical properties (quartz, glass, molybdenum disulfide, graphite, gold) under continuous proton injection are studied. Film samples of layered MoS2 and graphite compounds were obtained on rough surfaces of glass or quartz by mechanical rubbing of powder. Gold films are formed on glass substrates by magnetron sputtering of a gold target. To create a continuous stream of protons injected into the test sample, a stationary ion source with a cold cathode and a magnetic field forming an ion beam of relatively low intensity was used. The current in the ion beam is up to 1.2 mA, the pressure of hydrogen in the chamber is ~10 – 2 Pa, the energy of hydrogen ions is from 1 to 4 keV. The experimental results indicate that under conditions of continuous proton injection, the electrical conductivity of thin films with a layered structure (MoS2 and graphite) increases sharply (by 4 – 5 orders of magnitude). This effect increases when the temperature decreases from ~ 293 to ~ 77 K, as well as when the number of charges supplied to the sample increases. In the case of continuous injection of protons into massive dielectrics (glass, quartz) and thin films of gold, no noticeable change in electrical conductivity was detected.

Measurement of Thermal Conductivities of Bi2Te3 and Sb2Te3 Nano-Powders at Extreme Temperature and Strain

The Raman optothermal technique has been the most successful method for measurement of thermal conductivity of two dimensional (2D) materials, and was used to measure the thin films for the first time in this work. In this technique, a laser is focused at the center of a thin film and used to measure the peak position of a Raman-active mode. As the laser power is increased, the sample is heated which enables red-shift Raman mode due to thermal softening. Another comparison experiment is conducted by placing the samples on a heating platform and monitor the change of Raman-active mode peak position shift. Combining these two sections of experiments provide us the thermal modeling can then be used to extract the thermal conductivity from the measured shift rate. We have used a refined version of the optothermal Raman technique to study thermal conductivity of thin films of Bi2Te3 and Sb2Te3, at extreme temperatures and mechanical strains. It is the first thermal measurement on these two materials by Raman optothermal technique. This work also addresses several important issues in the measurement of thermal conductivity of thin films using Raman spectroscopy.