Institute for Technical Physics and Materials Science

Budapest, Hungary

Institute for Technical Physics and Materials Science

Budapest, Hungary
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Szabo Z.,Institute for Technical Physics and Materials Science | Volk J.,Institute for Technical Physics and Materials Science | Volk J.,University of Pannonia | Fulop E.,Institute for Technical Physics and Materials Science | And 3 more authors.
Photonics and Nanostructures - Fundamentals and Applications | Year: 2013

Highly regular vertical ZnO nanopillar arrays were hydrothermally grown through a nucleation window pattern generated by nanosphere photolithography. The in-plane intensity modulation of the exposing ultraviolet light in the photoresist was performed by Stöber silica or polystyrene nanospheres in the masking Langmuir-Blodgett monolayer. By comparing six different nanosphere diameters in the 180-700 nm range only those with diameter above the exposure wavelength of 405 nm generate a pattern in the thin photoresist layer. The pattern quality is improving with increasing diameter, therefore, the masking for nanopillar growth was demonstrated with 700 nm polystyrene nanospheres. The results of the nanosphere photolithography were supported by finitedifference time-domain calculations. This growth approach was shown to have the potential for low-cost, low-temperature, large area fabrication of ZnO pillars or nanowires enabling a precise engineering of geometry. © 2012 Elsevier B.V. All rights reserved.

Fried M.,Institute for Technical Physics and Materials Science | Fried M.,University of Pannonia
Thin Solid Films | Year: 2014

Non-destructive analyzing tools are needed at all stages of thin film photovoltaic (PV) development, and on production lines. In thin film PV, layer thicknesses, micro-structure, composition, layer optical properties, and their uniformity (because each elementary cell is connected electrically in series within a big panel) serve as an important starting point in the evaluation of the performance of the cell or module. An important focus is to express the dielectric functions of each component material in terms of a handful of wavelength independent parameters whose variation can cover all process variants of that material. With the resulting database, spectroscopic ellipsometry coupled with multilayer analysis can be developed for on-line point-by-point mapping and on-line line-by-line imaging. This work tries to review the investigations of different types of PV-layers (anti-reflective coating, transparent-conductive oxide (TCO), multi-diode-structure, absorber and window layers) showing the existing dielectric function databases for the thin film components of CdTe, CuInGaSe2, thin Si, and TCO layers. Off-line point-by-point mapping can be effective for characterization of non-uniformities in full scale PV panels in developing labs but it is slow in the on-line mode when only 15 points can be obtained (within 1 min) as a 120 cm long panel moves by the mapping station. In the last years [M. Fried et al., Thin Solid Films 519, 2730 (2011)], instrumentation was developed that provides a line image of spectroscopic ellipsometry (wl = 350-1000 nm) data. Up to now a single 30 point line image can be collected in 10 s over a 15 cm width of PV material. This year we are building a 30 and a 60 cm width expanded beam ellipsometer the speed of which will be increased by 10 ×. Then 1800 points can be mapped in a 1 min traverse of a 60 ∗ 120 cm PV panel or flexible roll-to-roll substrate. © 2014 Elsevier B.V. All rights reserved.

Takacs M.,Institute for Technical Physics and Materials Science | Takacs M.,Budapest University of Technology and Economics | Ducso C.,Institute for Technical Physics and Materials Science | Pap A.E.,Institute for Technical Physics and Materials Science
Sensors and Actuators, B: Chemical | Year: 2015

Abstract The effect of WO3 nano-crystal characteristic size and layer morphology on gas sensitive properties was investigated in order to define the optimum preparation process. WO3 layers were synthesized by hydrothermal acidic precipitation method using different chemicals and reactive sputtering as reference. Micro-hotplate based conductivity type devices were fabricated and the sensitivity on NH3 up to 100 ppm was measured in the temperature range of 140-240°C. The measurements revealed that the characteristic size of the WO3 nano-crystal plays primary role, but layer morphology opens the way towards extended measuring range. The nano-rod structures operated at 220°C exhibit the best sensing characteristics in terms of sensitivity and stability over wide range of relative humidity. © 2015 Elsevier B.V.

Stolarczyk J.K.,Ludwig Maximilians University of Munich | Deak A.,Institute for Technical Physics and Materials Science | Brougham D.F.,National Institute for Cellular Biotechnology | Brougham D.F.,University College Dublin
Advanced Materials | Year: 2016

The current state of the art in the use of colloidal methods to form nanoparticle assemblies, or clusters (NPCs) is reviewed. The focus is on the two-step approach, which exploits the advantages of bottom-up wet chemical NP synthesis procedures, with subsequent colloidal destabilization to trigger assembly in a controlled manner. Recent successes in the application of functional NPCs with enhanced emergent collective properties for a wide range of applications, including in biomedical detection, surface enhanced Raman scattering (SERS) enhancement, photocatalysis, and light harvesting, are highlighted. The role of the NP–NP interactions in the formation of monodisperse ordered clusters is described and the different assembly processes from a wide range of literature sources are classified according to the nature of the perturbation from the initial equilibrium state (dispersed NPs). Finally, the future for the field and the anticipated role of computational approaches in developing next-generation functional NPCs are briefly discussed. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Tapaszto L.,Institute for Technical Physics and Materials Science | Dumitrica T.,University of Minnesota | Kim S.J.,Korea Research Institute of Standards and Science | Nemes-Incze P.,Institute for Technical Physics and Materials Science | And 2 more authors.
Nature Physics | Year: 2012

Understanding how the mechanical behaviour of materials deviates at the nanoscale from the macroscopically established concepts is a key challenge of particular importance for graphene, given the complex interplay between its nanoscale morphology and electronic properties 1-5. In this work, the (sub)nanometre-wavelength periodic rippling of suspended graphene nanomembranes has been realized by thermal strain engineering and investigated using scanning tunnelling microscopy. This allows us to explore the rippling of a crystalline membrane with wavelengths comparable to its lattice constant. The observed nanorippling mode violates the predictions of the continuum model 6, and evidences the breakdown of the plate idealization of the graphene monolayer. Nevertheless, microscopic simulations based on a quantum mechanical description of the chemical binding accurately describe the observed rippling mode and elucidate the origin of the continuum model breakdown. Spatially resolved tunnelling spectroscopy measurements indicate a substantial influence of the nanoripples on the local electronic structure of graphene and reveal the formation of one-dimensional electronic superlattices. © 2012 Macmillan Publishers Limited.

Zambo D.,Institute for Technical Physics and Materials Science | Radnoczi G.Z.,Institute for Technical Physics and Materials Science | Deak A.,Institute for Technical Physics and Materials Science
Langmuir | Year: 2015

Low-molecular weight polyethylene glycol (PEG) has a lower critical solution temperature well outside the boiling point of water at ambient pressure, but it can be reduced at high ionic strengths. We extend this concept to trigger the clustering of gold nanoparticles through the control of colloidal interactions. At high ionic strengths, low-molecular weight (<2000 Da) mPEG-SH-modified gold nanoparticles show clustering with an increase in the solution temperature. The clustering temperature decreases with an increasing ionic strength. The clustering is attributed to the delicate interplay between the high ionic strength and elevated temperature and is interpreted in terms of chain collapse of the surface-grafted PEG molecules. The chain collapse results in a change in the steric interaction term, whereas the high ionic strength eliminates the double-layer repulsion between the particles. The observations are backed by nanoparticle interaction model calculations. We found that the intermediate attractive potential on the order of a few kT allows the experimental fabrication of compact nanoparticle clusters in agreement with theoretical predictions. The approach presented here has the potential to be extended on the externally triggered preparation of nanoparticle clusters with different types of nanoparticles. © 2015 American Chemical Society.

Sule P.,Institute for Technical Physics and Materials Science | Szendro M.,Eötvös Loránd University
Surface and Interface Analysis | Year: 2014

The accurate molecular dynamics simulation of weakly bound adhesive complexes, such as supported graphene (gr), is challenging because of the lack of an adequate interface potential. Instead of the widely used Lennard-Jones potential for weak and long-range interactions, we use a newly parameterized Tersoff potential for gr/Ru(0001) system. The new interfacial force field provides adequate moire superstructures in accordance with scanning tunneling microscopy images and with density functional theory (DFT) results. In particular, the corrugation of ξ ≈ 1.0 ± 0.2 Å is found that is somewhat smaller than found by DFT approaches (ξ ≈ 1.2 Å) and is close to scanning tunneling microscope measurements (ξ ≈ 0.8 ± 0.3 Å). The new potential could open the way toward large-scale simulations of supported gr with adequate moire supercells in many fields of gr research. Moreover, the new interface potential might provide a new strategy in general for obtaining accurate interaction potentials for weakly bound adhesion in large-scale systems in which atomic dynamics is inaccessible yet by accurate DFT calculations. Copyright © 2013 John Wiley & Sons, Ltd.

Safran G.,Institute for Technical Physics and Materials Science | Szasz N.,Institute for Technical Physics and Materials Science | Safran E.,Institute for Technical Physics and Materials Science
Microscopy Research and Technique | Year: 2015

Transmission electron microscopy (TEM) sample preparation requires special skills, it is time consuming and costly, hence, an increase of the efficiency is of primary importance. This article describes a method that duplicates the yield of the conventional mechanical and ion beam preparation of plan-view TEM samples. As a modification of the usual procedures, instead of one two different samples are comprised in a single specimen. The two pre-cut slabs, one from each samples, are embedded side by side in the window of a 3 mm dia Ti disk and the specimen is thinned mechanically and by ion milling until perforation that occurs at the interface of the two different slabs. That, with proper implementation, provides acceptable size thin area for the TEM study of both samples. The suitability of the two-in-one method has been confirmed through examples. © 2015 Wiley Periodicals, Inc.

Sule P.,Institute for Technical Physics and Materials Science | Szendro M.,Institute for Technical Physics and Materials Science | Hwang C.,Korea Research Institute of Standards and Science | Tapaszto L.,Institute for Technical Physics and Materials Science
Carbon | Year: 2014

Graphene on copper is a system of high technological relevance, as Cu is one of the most widely used substrates for the CVD growth of graphene. However, very little is known about the details of their interaction. One approach to gain such information is studying the superlattices emerging due to the mismatch of the two crystal lattices. However, graphene on copper is a low-corrugated system making both their experimental and theoretical study highly challenging. Here, we report the observation of a new rotational moiré superlattice of CVD graphene on Cu (1 1 1), characterized by a periodicity of (1.5±0.05) nm and corrugation of (0.15±0.05) Å, as measured by scanning tunneling microscopy (STM). To understand the observed superlattice we have developed a newly parameterized Abell-Tersoff potential for the graphene/Cu (1 1 1) interface fitted to nonlocal van der Waals density functional theory (DFT) calculations. The interfacial force field with time-lapsed classical molecular dynamics (CMD) provides superlattices in good quantitative agreement with the experimental results, for a misorientation angle of (10.4±0.5°), without any further parameter adjustment. Furthermore, the CMD simulations predict the existence of two non-equivalent high-symmetry directions of the moiré pattern that could also be identified in the experimental STM images. © 2014 Elsevier Ltd. All rights reserved.

Sule P.,Institute for Technical Physics and Materials Science | Szendro M.,Institute for Technical Physics and Materials Science | Magda G.Z.,Institute for Technical Physics and Materials Science | Hwang C.,Korea Research Institute of Standards and Science | Tapaszto L.,Institute for Technical Physics and Materials Science
Nano Letters | Year: 2015

The adherence of graphene to various crystalline substrates often leads to a periodic out-of-plane modulation of its atomic structure due to the lattice mismatch. While, in principle, convex (protrusion) and concave (depression) superlattice geometries are nearly equivalent, convex superlattices have predominantly been observed for graphene on various metal surfaces. Here we report the STM observation of a graphene superlattice with concave (nanomesh) morphology on Au(111). DFT and molecular dynamics simulations confirm the nanomesh nature of the graphene superlattice on Au(111) and also reveal its potential origin as a surface reconstruction, consisting of the imprinting of the nanomesh morphology into the Au(111) surface. This unusual surface reconstruction can be attributed to the particularly large mobility of the Au atoms on Au(111) surfaces and most probably plays an important role in stabilizing the concave graphene superlattice. We report the simultaneous observation of both convex and concave graphene superlattices on herringbone reconstructed Au(111) excluding the contrast inversion as the origin of the observed concave morphology. The observed graphene nanomesh superlattice can provide an intriguing nanoscale template for self-assembled structures and nanoparticles that cannot be stabilized on other surfaces. © 2015 American Chemical Society.

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