arXiv subjects

A. Csik

Publications and source records attributed to A. Csik.

At least 19 recordsLinked to original sources

arXiv2023

Depth resolved study of annealing in IrMn/(Fe, Co, CoFe) exchange bias systems

Depth resolved study of structural and magnetic profiles of antiferromagnetic/ferromagnetic (AFM/FM) system upon annealing was performed in this work. We studied systems comprising of AFM IrMn and FM (Co, Fe, Co$_{70}$Fe$_{30}$) structures using polarized neutron and soft X-ray scattering, secondary neutral spectrometry, and magnetometry. Structural depth profiles obtained from neutron reflectometry indicate non-homogeneity of the AFM layer even before annealing, which is associated with the migration of manganese to the surface of the sample. Annealing of samples with CoFe and Co layers leads to a slight increase ($\sim$ 5 %) in the migration of manganese, which, however, does not lead to significant degradation of the exchange coupling at the AFM/FM interface. A significantly different picture was observed in the Fe/IrMn systems where a strong migration of iron into the AFM layer was observed upon annealing of the sample, leading to erosion of the magnetic profile, the formation of a non-magnetic alloy and degradation of the pinning strength. This study can be useful in the design of AF/FM systems in different spintronics devices, including HDD read heads, where thermal annealing is applied at different stages of the device manufacturing process.

cond-mat.mtrl-sci↗

arXiv2018

Magnetic and Superconducting Phase Diagram of Nb/Gd/Nb trilayers

We report on a study of the structural, magnetic and superconducting properties of Nb(25nm)/Gd($d_f$)/Nb(25nm) hybrid structures of a superconductor/ ferromagnet (S/F) type. The structural characterization of the samples, including careful determination of the layer thickness, was performed using neutron and X-ray scattering with the aid of depth sensitive mass-spectrometry. The magnetization of the samples was determined by SQUID magnetometry and polarized neutron reflectometry and the presence of magnetic ordering for all samples down to the thinnest Gd(0.8nm) layer was shown. The analysis of the neutron spin asymmetry allowed us to prove the absence of magnetically dead layers in junctions with Gd interlayer thickness larger than one monolayer. The measured dependence of the superconducting transition temperature $T_c(d_f)$ has a damped oscillatory behavior with well defined positions of the minimum at $d_f$=3nm and the following maximum at $d_f$=4nm; the behavior, which is in qualitative agreement with the prior work (J.S. Jiang et al, PRB 54, 6119). The analysis of the $T_c(d_f)$ dependence based on Usadel equations showed that the observed minimum at $d_f$=3nm can be described by the so called "$0$" to "$π$" phase transition of highly transparent S/F interfaces with the superconducting correlation length $ξ_f \approx 4$nm in Gd. This penetration length is several times higher than for strong ferromagnets like Fe, Co or Ni, simplifying thus preparation of S/F structures with $d_f \sim ξ_f$ which are of topical interest in superconducting spintronics.

cond-mat.supr-con↗

arXiv2017

Thermally activated processes of the phase composition and structure formation of the nanoscaled Co-Sb films

It is investigated the formation of the phase composition and structure in the nanoscaled CoSbx (30 nm) films deposited by the method of molecular-beam epitaxy on the substrates of the oxidated monocrystalline silicon at 200 C and following thermal treatment in vacuum in temperature range of 300-700 C. It is established that the films after the deposition are polycrystalline without texture. With increase in Sb content the formation of the phase composition in the films takes place in such sequence as this is provided by phase diagram for the bulky state of the Co-Sb system. At annealing in vacuum at temperature above 450-500 C a sublimation not only of the crystalline Sb phase but from the antimonides occurs.

cond-mat.mtrl-sci↗

arXiv2017

Oscillations and huge preferences of PbTe crystal surface sputtering under Secondary Neutral Mass Spectrometry conditions

Sputtering of PbTe crystals by Ar plasma with ion energies 50-550 eV is investigated. A dependence of sputter yields of the Te and Pb on the sputtering ion energy and sputtering time is measured. New phenomena: aperiodical oscillations of Pb and Te sputtering; a huge preference of Te sputtering reaching more than two orders of magnitude at the beginning of sputtering process; and a significant excess of Te integrated sputter yield over that of Pb for prolonged sputtering by low energy plasma at 50-160 eV, are observed. It is substantiated that these phenomena can be caused by the peculiarities of the charge states of the interstitial Pb and Te in PbTe crystal matrix and the processes of re-deposition of sputtered atoms on the sputtered surface

cond-mat.mtrl-sci↗

arXiv2017

Formation of Cu6Sn5 phase by cold homogenization in nanocrystalline Cu-Sn bilayers at room temperature

Solid state reaction between nanocrystalline Cu and Sn films was investigated at room temperature by depth profiling with secondary neutral mass spectrometry and by X-ray diffraction. A rapid diffusion intermixing was observed leading to the formation of homogeneous Cu 6Sn5 layer. There is no indication of the appearance of the Cu3Sn phase. This offers a way for solid phase soldering at low temperatures, i.e. to produce homogeneous Cu6Sn5 intermediate layer of several tens of nanometers during reasonable time (in the order of hours or less). From the detailed analysis of the growth of the planar reaction layer, formed at the initial interface in Sn(100 nm)/Cu(50 nm) system, the value of the parabolic growth rate coefficient at room temperature is 2.3 x 10-15 cm2/s. In addition, the overall increase of the composition near to the substrate inside the Cu film was interpreted by grain boundary diffusion induced solid state reaction: the new phase formed along the grain boundaries and grew perpendicular to the boundary planes. From the initial slope of the composition versus time function, the interface velocity during this reaction was estimated to be about 0.5 nm/h.

cond-mat.mtrl-sci↗

arXiv2017

Quantitative depth profiling of Si1-xGex structures by time-of-flight secondary ion mass spectrometry and secondary neutral mass spectrometry

Quantification of Ge in Si1-xGex structures (0.092 0.9997) of intensity ratios of GeCs2+/SiCs2+ and 74Ge-/30Si- secondary ions and post-ionized 70Ge+/28Si+ sputtered neutrals with Ge concentration was obtained. The calibration data were used for quantitative depth profiling of [10x(12.3 nm Si0.63Ge0.37/34 nm Si)] structures on Si. Satisfactory compliance of the quantified Ge concentration in SiGe layers with the data measured by high-resolution X-ray diffraction was obtained for both techniques. Both SIMS and SNMS experimental profiles were fitted using the Hofmann mixing-roughness-information depth (MRI) model. In case of TOF-SIMS the quality of the reconstruction was higher than for SNMS since not only the progressing roughening, but also crater effect and other processes unaccounted in the MRI simulation could have significant impact on plasma sputter depth profiling.

cond-mat.mtrl-sci↗

arXiv2017

Preliminary studies of creation of gold nanoparticles on titanium surface towards biomedical applications

This paper is devoted to present the results of creation of gold nanoparticles on titanium surface. We focused on the problem how to create gold nanoparticles on the titanium surface with defined particle size and distribution, which could be interesting for several applications (e.g. providing well-defined substrates for biomedical research, etc.). To do that the sample is affected by the complex physical rout of gold nanoparticles formation: by gold ion implantation, thin Au layer deposition and thermal annealing. The effect of the technology, influence on the surface structure and its parameters were investigated by the X-ray diffraction, Scanning Electron and Atomic Force Microscopy, as well as by Secondary Neutral Mass Spectrometry methods.

cond-mat.mtrl-sci↗

arXiv2017

Morphology of PbTe crystal surface sputtered by argon plasma under Secondary Neutral Mass Spectrometry conditions

We have investigated morphology of the lateral surfaces of PbTe crystal samples grown from melt by the Bridgman method sputtered by Ar+ plasma with ion energy of 50-550 eV for 5-50 minutes under Secondary Neutral Mass Spectrometry (SNMS) conditions. The sputtered PbTe crystal surface was found to be simultaneously both the source of sputtered material and the efficient substrate for re-deposition of the sputtered material during the depth profiling. During sputtering PbTe crystal surface is forming the dimple relief. To be redeposited the sputtered Pb and Te form arrays of the microscopic surface structures in the shapes of hillocks, pyramids, cones and others on the PbTe crystal sputtered surface. Correlation between the density of re-deposited microscopic surface structures, their shape, and average size, on the one hand, and the energy and duration of sputtering, on the other, is revealed.

cond-mat.mtrl-sci↗

arXiv2015

Nanoscale characterization of thin immersion silver coatings on copper substrates

Microelectronic-grade copper foils were immersion silver plated in a home-made non-cyanide alkaline silver nitrate - thiosulfate solution and in two commercially available industrial baths via contact reductive precipitation. The concentration depth profiles of the freshly deposited silver layers were afterwards analyzed at nanoscale resolution by means of Secondary Neutral Mass Spectrometry (SNMS) and Glow Discharge Optical Emission Spectroscopy (GDOES). The thickness of deposited silver layers obtained with 30-60 s immersion time were in the range of 50-150 nm, depending on the parameters of the immersion procedure. Slight contamination of sulfur from the thiosulfate bath was detectable. Traces of Cr and Na could be observed as well around the interface between the copper substrate and silver deposit. Results also indicate that storage for longer time in air especially at higher than ambient temperatures induces a kind of ageing effect in the deposited layer, changing its composition. In case of samples prepared from home-made solution increasing amounts of copper together with its corrosion products became detectable.

cond-mat.mtrl-sci↗

arXiv2015

Light-induced mass transport in amorphous chalcogenides: Towards surface plasmon-assisted nanolithography and near-field nanoimaging

Two types of amorphous functional materials, based on lightsensitive inorganic compounds like Se and As20Se80 chalcogenide glass (ChG) were investigated with the aim to establish the influence of plasmonic fields, excited by the band-gap light in nanocomposite layers made of these compounds and gold nanoparticles on their photomechanical response. Both these basic materials are characterized by pronounced photoplastic effect and used for real-time optical recording of optoelectronic elements (based mainly on surface relief gratings) due to high photofluidity and polarization-dependent masstransport. We established that mass-transport processes in these ChG can be enhanced in the presence of localized plasmonic fields generated by light if the condition of surface plasmon resonance (SPR) is fulfilled. The subjects of special interest are the mass-transport processes at the nano-scale stimulated in the nano-copmosite layers of either by the uniform or periodically distributed optical fields. It was found that irradiation by light with SPR really enhance the efficiency of masstransport and produce surface nanostructurizations. The variation in the topography follows closely and permanently the underlying near field intensity pattern.

cond-mat.mtrl-sci↗

arXiv2015

Ion beam effect on Ge-Se chalcogenide glass films: Non-volatile memory array formation, structural changes and device performance

The conductive bridge non-volatile memory technology is an emerging way to replace traditional charge based memory devices for future neural networks and configurable logic applications. An array of the memory devices that fulfills logic operations must be developed for implementing such architectures. A scheme to fabricate these arrays, using ion bombardment through a mask, has been suggested and advanced by us. Performance of the memory devices is studied, based on the formation of vias and damage accumulation due to the interactions of Ar+ ions with GexSe1-x (x=0.2, 0.3 and 0.4) chalcogenide glasses as a function of the ion energy and dose dependence. Blanket films and devices were created to study the structural changes, surface roughness, and device performance. Raman Spectroscopy, Atomic Force Microscopy (AFM), Energy Dispersive X-Ray Spectroscopy (EDS) and electrical measurements expound the Ar+ ions behavior on thin films of GexSe1-x system. Raman studies show that there is a decrease in area ratio between edge-shared to corner-shared structural units, revealing occurrence of structural reorganization within the system as a result of ion/film interaction. AFM results demonstrate a tendency in surface roughness improvement with increased Ge concentration, after ion bombardment. EDS results reveal a compositional change in the vias, with a clear tendency of greater interaction between ions and the Ge atoms, as evidenced by greater compositional changes in the Ge rich films.

cond-mat.mtrl-sci↗

arXiv2014

X-ray and neutron reflectometry study of copper surface reconstruction caused by implantation of high-energy oxygen ions

Combination of neutron and X-ray reflectometry was used to study the vertical structure of 100 nm-thin copper films with implanted oxygen ions of energy E = [10-30] keV and doses D=[0.2-5.4]x$10^{16}$ $cm^{-2}$. The study shows that oxygen ion implantation with an energy of E = 30 keV leads to the formation of a 3 nm thick layer on the surface. Density and copper/oxygen stoichiometry of the observed surface layer are close to $Cu_2O$ oxide. We attribute the $Cu_2O$ oxide formation to highly mobilized copper atoms generated by stimulated ion implantation.

cond-mat.mtrl-sci↗

arXiv2014

Structural, magnetic and superconducting characterization of the CuNi/Nb bilayers of the S/F type using Polarized Neutron Reflectometry and complementary techniques

Structural, magnetic, and superconducting properties of S/F bilayers Nb/Cu40Ni60 deposited on silicon substrate have been characterized using Polarized Neutron Reflectometry and complementary techniques. The study allowed to determine real thicknesses of the S and F layers as well as the r.m.s. roughness of the S/F interfaces. The latter does not exceed 1 nm, showing the high quality of the S/F interface. Using SQUID and a mutual inductance setup we determined the superconducting transition temperatures of the samples, which are in agreement with the literature data. Using of PNR for the single S layer allowed to determine the screening length lambda of the superconducting layer, lambda = 120 nm. This value is higher than the London penetration depth for pure niobium which may indicate that the superconductor is in the dirty limit. PNR and SQUID studies of magnetic properties of the CuNi layer have shown the presence of ferromagnetism in all investigated samples.

cond-mat.str-el↗

arXiv2014

Segregation of the Eu impurity as function of its concentration in the melt for growing of the lead telluride doped crystals by the Bridgman method

Behaviour of a rare earth impurity of Eu in the PbTe single crystals grown by the Bridgman method from the melt with different initial concentrations of impurity N about 1*10+19 cm-3 and less is investigated with X-ray fluorescent element analysis, Secondary Neutral Mass Spectroscopy (SNMS), and magnetic measurements. The impurity distributions along and across the doped ingots are established. It is revealed that doping impurity enters into the bulk of doped crystals only if its initial concentration in the melt is high enough, approximately 1*10+20 cm-3. If this concentration is lower, about 1*10+19 cm-3 and less, the doping Eu impurity is pushed out onto the surface of doped ingot. The thickness of the doped surface layer is estimated to be in the order of several microns or somewhat more. The longitudinal distributions of Eu impurity along the axis of doped ingot for N=1*10+20 cm-3, as well as the transverse one in the surface layer where entire doping impurity is pushed out for N=1*10+19 cm-3, are strongly non-monotonic. Possible reasons for this unusual behaviour of Eu doping impurity during the growth of PbTe:Eu crystals from the melt are analyzed.

cond-mat.mtrl-sci↗

arXiv2013

On the feasibility to study inverse proximity effect in a single S/F bilayer by Polarized Neutron Reflectometry

Here we report on a feasibility study aiming to explore the potential of Polarized Neutron Reflectometry (PNR) for detecting the inverse proximity effect in a single superconducting/ferromagnetic bilayer. Experiments, conducted on the V(40nm)/Fe(1nm) S/F bilayer, have shown that experimental spin asymmetry measured at T = 0.5TC is shifted towards higher Q values compared to the curve measured at T = 1.5TC. Such a shift can be described by the appearance in superconducting vanadium of magnetic sub-layer with thickness of 7 nm and magnetization of +0.8 kG.

cond-mat.str-el↗

arXiv2009

Investigation of Sb diffusion in amorphous silicon

Amorphous silicon materials and its alloys become extensively used in some technical applications involving large area of the microelectronic and optoelectronic devices. However, the amorphous-crystalline transition, segregation and diffusion processes still have numerous unanswered questions. In this work we study the Sb diffusion into an amorphous Si film by means of Secondary Neutral Mass Spectrometry (SNMS). Amorphous Si/Si1-xSbx/Si tri-layer samples with 5 at% antimony concentration were prepared by DC magnetron sputtering onto Si substrate at room temperature. Annealing of the samples were performed at different temperature in vacuum (p<10-7 mbar) and 100 bar high purity (99.999%) Ar pressure. During annealing a rather slow mixing between the Sb-alloyed and the amorphous Si layers was observed. Supposing concentration independent diffusion, the evaluated diffusion coefficients are in the range of ~10-21 m2s-1 at 823 K.

cond-mat.mtrl-sci↗

arXiv2009

Pattern formation in SiSb system

Thermal annealing of Si/Si1-xSbx/Si amorphous thin film tri-layer samples (x=18 and 24 at%Sb) under 100 bar Ar pressure results in an interesting pattern formation. In pictures, taken by means of cross-sectional transmission electron microscopy (TEM), stripe-shaped contrast, with three maxima, parallel with the interfaces can be seen. Secondary neutral mass spectrometer (SNMS) measurements revealed that the regions with different contrasts correspond to Sb-rich and Sb-depleted regions. Furthermore, the Sb concentration peaks in the Sb-rich regions, especially at longer annealing times, are different: the peak developed at the Si/SiSb interface closer to the free surface decays faster than that of the inner one closer to the substrate. The pattern formation is interpreted by segregation-initiated spinodal-like decomposition, while the difference of the Sb concentration peaks is explained by the resultant Sb transport to and evaporation from the free surface. The possible role of formation of nanocrystalline grains, in the explanation of the fast transport under pressure as compared to vacuum is also discussed.

cond-mat.mtrl-sci↗

arXiv2009

Degradation of Ag/Si multilayers during heat treatments

Microstructure changes during annealing of nano-crystalline silver and amorphous silicon multilayers (Ag/a-Si) have been studied by X-ray diffraction and transmission electron microscopy. The dc-magnetron sputtered Ag/a-Si multilayers remained stable even after annealing at 523K for 10h, and microstructural changes occurred only above 600K. The degradation of Ag/a-Si multilayers can be described by the increase of size of Ag grains, formation of grooves and pinholes at Ag grain boundaries and by the diffusion of silicon atoms through the silver grain boundaries and along the Ag/a-Si interfaces. This results in thinning of a-Si layers, and in formation of Ag granulates after longer annealing times.

cond-mat.mtrl-sci↗