Ákos Nemcsics

Localized Electroless Ag Plating at a Tip Apex for Scanning Kelvin Probe Microscopy

A typical probe for scanning Kelvin probe microscopy (SKPM) consists of an atomic force microscopy (AFM) probe with a metallic coating. Such probes result in a large sensing area and lead to poor spatial resolution due to the stray-field effect. With electroless Ag plating (EAP), we employed an AFM system to form a Ag nanodot (AND) at the apex of the probe tip, which reduces the sensing area of the SKPM probe, thereby suppressing the stray-field effect. It was revealed that the tip with an AND structure had improved the spatial resolution in SKPM. Our experimental results showed that the EAP process can be completed in a few seconds, implying that localized EAP is a simple and rapid process for preparing an AND structure at the tip apex in SKPM measurements.

Facetting of the self-assembled droplet epitaxial GaAs quantum dot

Abstract In this work, droplet epitaxially grown GaAs quantum dots on AlGaAs surface are studied. The quantum dots are investigated in situ with RHEED and ex situ with TEM method. The TEM picture shows that the quantum dot is perfectly crystalline and fits very well to the crystal structure of the substrate. Furthermore, the side of the quantum dot shows stepped facet shape. Here, we show, how the stepped side shape forms from the droplet during crystallization. The RHEED picture shows broadened chevron-tail, which can be explained by the shape of the quantum dot.

Fractal and structural entropy calculations on the epitaxially grown fulleren structures with the help of image processing

Molecular beam epitaxially grown fullerene layers are investigated with the help of image processing. The layered structures are studied in morphological respect. The individual layer morphologies are derived from the atomic force microscopy picture of the surface. The pattern morphology of the certain layers is analysed by box counting method. The surface morphology shows fractal behaviour. The pattern of each layer shows different dimension. The actual dimension depends on the actual distance of the layer from the substrate. The change of the dimension is attributed to the change of the binding behaviour. The topology of the surface is also studied using participation ratio and structural entropy calculations.

On the shape formation of the droplet epitaxial quantum dots

Abstract In this paper, the shape evolution kinetics of droplet epitaxially grown QDs is investigated. Here, the growth parameter dependent of two distinct QD shape regimes is discussed. We show that the QD shape is determined by the size and the contact angle of the initial droplet. Furthermore, the surface tension dependence on the droplet size is also discussed. Finally, the temporal course of the crystallization process is investigated.

Real time RHEED evaluation with the help of image processing

In this paper, the reflection high-energy electron diffraction (RHEED) pattern during the nano structure formation with the help of image processing is investigated. Nowadays, the growth of self-organised nano structures has been intensively investigated. It is very important to understand their growth process and the knowledge about their shape is particularly significant. The growth of these nano structures can be tracked in-situ manner with the help of RHEED. In-situ information about the stage of the process and the shape of the structure has been provided by RHEED. The temporal relation between the formation of the nano structure and the RHEED pattern is rather complicate. The image processing of the RHEED pattern help us to recognize and to interpret the metamorposis of the pattern during the growth process.

Ga metal nanoparticle-GaAs quantum molecule complexes for terahertz generation

A hybrid metal-semiconductor nanosystem for the generation of THz radiation, based on the fabrication of GaAs quantum molecules-Ga metal nanoparticles complexes through a self assembly approach, is proposed. The role of the growth parameters, the substrate temperature, the Ga and As flux during the quantum dot molecule (QDM) fabrication and the metal nanoparticle alignment are discussed. The tuning of the relative positioning of QDMs and metal nanoparticles is obtained through the careful control of Ga droplet nucleation sites via Ga surface diffusion. The electronic structure of a typical QDM was evaluated on the base of the morphological characterizations performed by atomic force microscopy and cross sectional scanning electron microscopy, and the predicted results confirmed by micro-photoluminescence experiments, showing that the Ga metal nanoparticle-GaAs quantum molecule complexes are suitable for terahertz generation from intraband transition.

Soft-computing based classification and design of quantum dot nanostructures on GaAs substrate

The parameters of the semiconductor devices can be improved by nanostructures significantly. For this reason, it is necessary to produce nanostructures with given parameters. The soft-computing design of the self-organized nanostructures and a new classification model will be discussed in this paper. These nanostructures are formed by droplet epitaxy on compound semiconductor substrate. The parameters of the nanostructures (type, size, distribution) depend on the applied technology. The key factors of the technology (substrate temperature, Ga flux, As pressure, annealing time and annealing temperature) will be determined as design parameters. These parameters are set in order to produce nanostructures with the desired property. The revised version of previously introduced nanostructure fuzzy-based classification model will be also discussed.

Fuzzy and Kohonen SOM based classification of different 0D nanostructures

In this paper, the clustering of the GaAs-based droplet epitaxially grown self-assembled nanostructures was investigated by soft-computing methods. The properties and the operation of these devices, depend on the type, the shape, the size, and their distribution of these 0 dimensional nanostructures. Because of this, it is very important to know, how and what kind of nanostructures can form, at the given technological parameters. Our goal is the classification of these nanostructures, in order to support the research and the production of these devices. Our solution is based on the shape factor calculation of the given nanostructure. In this work, two possible classification methods of nanostructures were introduced as well. First, the classification potential of the Kohonen Self-Organizing Mapping (SOM) was investigated. Second, the fuzzy inference system based classification was studied. In this case, the shape factor was determined by geometrical sizes of the nanostructures. In this paper the clustering was introduced, which supports many kinds of technology as well.

Nanostructure Growth Supported by In Situ RHEED Evaluation

The in-situ monitoring of the MBE grown nanostructures can be carried out using the RHEED method. During the droplet epitaxal growth, the observation of the nanostructure formation is very important to understand the growth kinetics. In the present work, a novel in-situ RHEED evaluation and further MBE related developments are introduced, with which the quality of the nanostructure preparation can be improved.

Study of urbanistical complexity on two Hungarian regions

In our present work, we study and compare two Hungarian regions, from the viewpoint of complexity and self-assembly. In the size-order log-log diagram, we can observe two linear sections. There are two types of linear sections, which are corresponds to the two types of driving forces. We study, how the talents of the two regions in the diagrams appear and what do they mean from the viewpoint of driving forces.