Karel Hruska

Study of diamond film nucleation by ultrasonic seeding in different solutions

In this study we have investigated diamond nucleation on Si substrates by ultrasonic seeding with different liquid solutions of Ultradispersed Detonation Diamond (UDD) powder in a mixture of metal nano- or microparticles (Ni, Co, Y). The influence of different solutions on nucleation efficiency was investigated. For highlighting nucleation centers and better evaluation of the nucleation process the nucleated samples were moved into a Microwave Plasma Enhanced Chemical Vapor Deposition (MW CVD) reactor and a ”short-time” (10 min), then followed by a ”long-time” (+1 hour), diamond deposition was performed. The morphology of samples was characterized by Scanning Electron Microscopy (SEM) and the chemical composition of grown diamond layer was investigated by Raman Spectroscopy. From the measurements we found out that microsized metal particles positively influenced nucleation and the uniformity of the deposited diamond thin film. The lowest surface roughness was achieved in the case of nanodiamond powder mixed with Co and Y metal powder. The influence of Ni, Co and Y to the nucleation and early growth stage are discussed.

Nanostructuring of diamond films using self-assembled nanoparticles

We report the use of gold, nickel and diamond nanoparticles as a masking material for realization of diamond nano-structures by applying the dry plasma etching process. Applying low power plasma (100 W) in a gas mixture of CF4/O2 for 5 minutes results in a formation of three different types of diamond nanostructures, depending on the mask type material and particle size. Using of the Ni mask results in realization of diamond nano-rods, applying of the Au mask brings cauliflower-like structures, and using the diamond powder allows the production of irregular nano-structures. The main advance of the presented etching procedure is use of a self-assembly strategy where no lithographic steps are implemented.

Concept, design and coupled electro-thermal analysis of new hybrid drive vehicle for public transport

The paper deals with a study of new synchronous machine for use in hybrid vehicle. The synchronous machine is projected as permanent magnet synchronous motor with outer rotor embedded into rear rim of a bus. The main target of the study is design of an air self-cooled hub-wheel PMSM from electromagnetic point of view and using finite element analysis of electromagnetic field and thermal distribution. The analysis of losses in permanent magnets is also mentioned.

Design and FEM analyses of an electrically excited automotive synchronous motor

The paper deals with design of an electrically excited automotive synchronous motor and follow-up finite element method analyses. The machine is designed for water cooling of outer cover and enclosed inner air cooling circuit. The paper deals with complete design and analyses of the machine - calculation of losses, ventilation and cooling conditions.

Two-dimensional photonic crystal slab with embedded silicon nanocrystals: Efficient photoluminescence extraction

A two-dimensional photonic crystal (PhC) slab was fabricated from a luminescent planar waveguide, formed by a (800 nm thick) layer of silicon nanocrystals (SiNCs) embedded in a polished silica plate. Dimensions of the PhC were designed so that light emitted by SiNCs under excitation with an external UV source can, during its propagation in the layer, interact with the periodicity and be Bragg-diffracted into air. This approach leads to up to 8-fold vertical extraction enhancement of SiNCs luminescence from the PhC slab compared to the bare planar layer. Results of the experiment are supported by the computer simulation.

Enhanced Extraction of Silicon-Vacancy Centers Light Emission Using Bottom-Up Engineered Polycrystalline Diamond Photonic Crystal Slabs

Silicon vacancy (SiV) centers are optically active defects in diamond. The SiV centers, in contrast to nitrogen vacancy (NV) centers, possess narrow and efficient luminescence spectrum (centered at ≈738 nm) even at room temperature, which can be utilized for quantum photonics and sensing applications. However, most of light generated in diamond is trapped in the material due to the phenomenon of total internal reflection. In order to overcome this issue, we have prepared two-dimensional photonic crystal slabs from polycrystalline diamond thin layers with high density of SiV centers employing bottom-up growth on quartz templates. We have shown that the spectral overlap between the narrow light emission of the SiV centers and the leaky modes extracting the emission into almost vertical direction (where it can be easily detected) can be obtained by controlling the deposition time. More than 14-fold extraction enhancement of the SiV centers photoluminescence was achieved compared to an uncorrugated sample. Computer simulation confirmed that the extraction enhancement originates from the efficient light-matter interaction between light emitted from the SiV centers and the photonic crystal slab.

Gas sensing properties of nanocrystalline diamond at room temperature.

Summary This study describes an integrated NH3 sensor based on a hydrogenated nanocrystalline diamond (NCD)-sensitive layer coated on an interdigitated electrode structure. The gas sensing properties of the sensor structure were examined using a reducing gas (NH3) at room temperature and were found to be dependent on the electrode arrangement. A pronounced response of the sensor, which was comprised of dense electrode arrays (of 50 µm separation distance), was observed. The sensor functionality was explained by the surface transfer doping effect. Moreover, the three-dimensional model of the current density distribution of the hydrogenated NCD describes the transient flow of electrons between interdigitated electrodes and the hydrogenated NCD surface, that is, the formation of a closed current loop.

A comprehensive approach to calculation of the air gap magnetic flux density in induction machines with eccentrically placed rotor

This article presents a possible way of calculation of air gap magnetic flux density in induction machines with eccentrically placed rotor. In the text a method of analytical calculation is presented and results are compared with finite element analysis outputs.

Analysis of rotor's eccentricity influence on bearing load of induction machine

To ensure reliable drive with an induction machine requires deep insight in electro-mechanical dynamics during its operation. The flexible multibody modeling technique enables the simulation of dynamic loads on all drive components. This paper focuses on complex modeling of machines behavior in case of eccentrically placed rotor. The life time of machines bearing becomes very important issue of machines maintenance and reliability and is markedly influenced by any unbalanced forces acting on the rotor. The rotor eccentricity is one of the most significant aspects making machines bearing loaded by strong unbalanced magnetic pull. Only the complex flexible model of the rotor considering all unbalanced rotor forces can provide us the very detailed information about the bearing load. The methodology of determination of such loading is applied to the 11 kW squirrel-cage induction machine.

Basic operating characteristics of wireless power transfer system for small portable devices

Recent research in wireless power transfer using resonant inductive coupling has made a significant progress and reached very high efficiency (usually above 85 %) at large distances. This paper offers a methodology for the basic analysis and prediction of efficiency of the wireless power transfer system for small portable devices. It also gives an overview of operating characteristics of the system for different positions of transmitting and receiving elements. All presented theoretical presumptions are consequently verified by detailed measurement.