Zsolt Geretovszky

Improving InAs nanotree growth with composition-controlled Au–In nanoparticles

Au nanoparticles are commonly used as seeds for epitaxial growth of III-V semiconductor nanowires. However, the interaction between Au and In-containing III-V materials makes it difficult to control the growth of more complex nanowire structures in materials such as InAs. Here we report the growth of InAs nanowires and branched nanotrees using Au and Au-In nanoparticles. We show that the initial composition of the particle does not affect the morphology of the first-generation nanowires, nor does it affect the final composition of the particle after growth. However, when the Au-In particles were used to seed a second generation of nanowires, producing nanotrees, the branches exhibited a 2-3 times higher growth rate and more regular shape than those seeded by pure Au particles. This result is attributed to the decreased interaction between the seed particle and the trunk nanowires when Au-In particles are used. Thus the incorporation of In into the seed particle during particle production allows for modification of the particle-wire interaction.

Multi-pulse laser-induced plasma spectroscopy using a single laser source and a compact spectrometer

A portable laser induced breakdown spectrometer (LIBS), built around a microscope using a Q-switched Nd:GGG laser releasing multiple pulses and a non-intensified fiber optic spectrometer, was used to investigate the signal improvement of emission data achievable by the multiple-pulse approach. LIBS experiments were carried out in air and using Al, Cu, Si and Zn metallic targets. It was found that the use of 7 laser pulses, separated by ca. 25 μs time intervals, enhance line emissions by a factor of 2.5 to 129 with respect to the single-pulse case, and also decrease the relative standard deviation of the signal based on five consecutive measurements to 2–5%. Time-resolved emission data and the observation of ablation craters suggest that the signal enhancement is mainly attributable to the reheating of the plasma by multiple laser pulses.

Construction and characterization of a diode laser system for atomic spectrometric experiments

Construction and characterization of a simple but flexible, low cost diode laser system for atomic spectrometry is reported. Detailed electronic circuit layouts of the diode laser current controller, supplying maximum 1300 mA current with 1 mA resolution, and functional description of all other components (temperature controller, optics, mount, etc.) are given. The system features bi-directional computer control and full diode laser protection against voltage, current and temperature failure/overrun. Results of electronic and spectroscopic tests show that wavelength tuning with a precision of approximately 0.01 nm and current modulation frequency up to 10 kHz are possible with this system. Performance characteristics qualify the proposed instrumental setup for atomic fluorescence and absorption measurements in inductively coupled plasmas.

Thin film homogenization by inverse pulsed laser deposition

Recently we proposed a novel PLD arrangement, termed inverse pulsed laser deposition (IPLD). Being able to produce thin films of better surface morphology without any complex instrumentation, this method can represent an alternative to the traditional PLD technique while preserving versatility. Two configurations of this new target-substrate arrangement, namely static and co-rotating IPLD were developed. In the static IPLD configuration, the substrate is stationary with respect to the ablated spot; while in the co-rotating IPLD configuration the substrate is fixed to the target surface and rotates simultaneously with the target. Co-rotating IPLD proved to be capable of homogenizing the film thickness. Here we report a model calculation supported by experimental results to describe the radial growth rate variation of corotating IPLD films. To characterize the homogeneity of CNx, TiOx, and Ti co-rotating IPLD films, a thickness inhomogeneity index (TII) was introduced, which allows the comparison of thickness homogeneity between films of different lateral dimensions. The presented semi-analytical, semi-numerical model derives the radial variation of the growth rate of co-rotating IPLD films from the lateral growth rate distributions measured along the symmetry axes of the static IPLD films. The laterally averaged growth rate (LAGR) was used to describe how the ambient pressure affects thin film growth in the 0.5-50 Pa domain. As an example, the absolute error between the measured and calculated radial growth rate variation of CNx layers grown by co-rotating IPLD at 5 Pa, was less than 3%, while the LAGR was predicted with 20% accuracy.