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41 results on '"Vértesy, Gábor"'

2. The structure and properties of graphene supported on gold nanoparticles

Author

Osváth, Zoltán, Deák, András, Kertész, Krisztián, Molnár, György, Vértesy, Gábor, Zámbó, Dániel, Hwang, Chanyong, and Biró, László P.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Optics
Abstract

Graphene covered metal nanoparticles constitute a novel type of hybrid materials, which provide a unique platform to study plasmonic effects, surface-enhanced Raman scattering (SERS), and metal-graphene interactions at the nanoscale. Such a hybrid material is fabricated by transferring graphene grown by chemical vapor deposition onto closely spaced gold nanoparticles produced on a silica wafer. The morphology and physical properties of nanoparticle-supported graphene is investigated by atomic force microscopy, optical reflectance spectroscopy, scanning tunneling microscopy and spectroscopy (STM/STS), and confocal Raman spectroscopy. This study shows that the graphene Raman peaks are enhanced by a factor which depends on the excitation wavelength, in accordance with the surface plasmon resonance of the gold nanoparticles, and also on the graphene-nanoparticle distance which is tuned by annealing at moderate temperatures. The observed SERS activity is correlated to the nanoscale corrugation of graphene. STM and STS measurements show that the local density of electronic states in graphene is modulated by the underlying gold nanoparticles.

Published
2015
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5. Tuning the electronic structure of graphene by ion irradiation

Author

Tapaszto, Levente, Dobrik, Gergely, Nemes-Incze, Peter, Vertesy, Gabor, Lambin, Philippe, and Biro, Laszlo P

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Mechanically exfoliated graphene layers deposited on SiO2 substrate were irradiated with Ar+ ions in order to experimentally study the effect of atomic scale defects and disorder on the low-energy electronic structure of graphene. The irradiated samples were investigated by scanning tunneling microscopy and spectroscopy measurements, which reveal that defect sites, besides acting as scattering centers for electrons through local modification of the on-site potential, also induce disorder in the hopping amplitudes. The most important consequence of the induced disorder is the substantial reduction in the Fermi velocity, revealed by bias-dependent imaging of electron-density oscillations observed near defect sites.

Published
2009
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8. Dipolar random field Ising model: an application to garnet films

Author

Magni, Alessandro and Vertesy, Gabor

Subjects
Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Materials Science
Abstract

The dipolar-random field Ising model (DRFIM) recently introduced displays a behaviour that can be connected to the magnetization of bidimensional magnetic media. Epitaxial magnetic garnet films seem to be the ideal test material for such a model. In this work the results of the measurements performed on garnet samples are presented, as well as the comparisons with simulation results obtained by the DRFIM. The results prove that a variety of hysteresis loops are well described by the DRFIM. This capability does not derive from the fine tuning of a great number of parameters, but by the interplay of exchange and dipolar interactions., Comment: HTML paper, GIF images. To appear on Phys.Rev.B (Brief Reports). Application of the model published on Phys.Rev.B 59 (1999) 985, cond-mat/9907074

Published
1999
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16. Investigation of Potential Material Inhomogeneity in the Magnetically Detected Neutron-Irradiation-Generated Structural Degradation of Nuclear Reactor Pressure Vessel Steel.

Author

Vértesy, Gábor, Gasparics, Antal, and Szenthe, Ildikó

Subjects
NUCLEAR pressure vessels, NUCLEAR reactors, RESEARCH reactors, MECHANICAL behavior of materials, TRANSITION temperature, VICKERS hardness, ADAPTIVE testing, EMBRITTLEMENT
Abstract

A novel nondestructive method called magnetic adaptive testing has been previously applied to detect the neutron-irradiation-generated structural changes in reactor pressure vessel steel material. This method has been found to be a useful tool for this purpose, and good correlation—as a tendency—has been found between the estimated ductile-to-brittle transition temperature and magnetic parameters. However, a significant scattering of measured points was also observed for the investigated set of Charpy specimens. The main result of the work was that by magnetic selection of samples, the scatter can be notably reduced. As a conclusion, the magnetically measured parameters seemed to be precise and reliable for the detection of embrittlement of the reactor pressure vessel steel, with lower scattering of points than in the conventionally used destructive mechanical characteristics (ductile-to-brittle transition temperature). This result is surprising and needs further verification. The purpose of the present work is to repeat the measurement on irradiated reactor steel blocks. In this work, instead of the DBTT transition temperature, individually measured Vickers hardness (VH) data were used to help characterize the mechanical properties of the material. The so-called "property transformation" is a known and applied technique in the nuclear industry. The mechanical property characterized by the transition temperature cannot be determined individually for each specimen; instead, it can be obtained only on a set of samples by statistical fitting. Therefore, the individually measured Vickers hardness values can be utilized in order to predict the individual transition temperature values by the help of the property transformation technique. In this paper, however, not these derived transition temperature values, but their origins, the Vickers hardness values, are studied in a direct manner. The same behavior of blocks was observed as in the case of Charpy specimens, which is considered to validate the previously published results. As a possible reason for the scattering of points, large magnetic inhomogeneity of samples cut even from the same block was also proved. The magnetic parameters and Vickers hardness correlate well with each other. This result justifies the potential future application of magnetic techniques in practice aimed at the regular inspection of nuclear reactors. [ABSTRACT FROM AUTHOR]

Published
2022
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32. Correlation between ultrasonic velocity and magnetic adaptive testing in flake graphite cast iron

Author

Vértesy, Gábor, Uchimoto, Tetsuya, Takagi, Toshiyuki, and Tomáš, Ivan

Subjects
magnetic NDE, magnetic adaptive testing, flake graphite cast iron, ultrasonic velocity
Abstract

A recently developed nondestructive method, called Magnetic Adaptive Testing was applied for investigation of flake graphite cast iron samples having various metallic matrices and graphite structures. MAT is typical by its low required magnetization of samples, because it is based on measurement of families of minor magnetic hysteresis loops. The flat samples were magnetized by an attached yoke and sensitive descriptors of their magnetic/structural state were obtained from evaluation of the measured data. Ultrasonic velocity measurements were performed and results of the non-destructive magnetic tests were compared with these data. A very good correlation was found between the magnetic descriptors and ultrasonic velocity. Web of Science 66 7s 177 174

Published
2015

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