In a very recent x-ray magnetic circular dichroism experiment concerning with Ru and Rh impurities and metal films on Ag(001) substrate, no local magnetic momen ts were displayed in direct contradiction with previous theoretical works. It is thought that there can be three main reasons for this inconsistency: relaxation, alloying and many-body effects. Some of the above-mentioned systems are studie d by using a first-principles method in which relaxation and alloying are taken into account, even so magnetism is still obtained. For low-coverage systems, hig h magnetic moments in both Ru ($\sim$ 2.49 $μ_{B}$) and Rh ($\sim$ 2.00 $μ_{B}$) are obtained. Naturally, as the coverage is increased the magnetic moments are approached to zero. Also, it is noticed that the relaxation distances are in creased by magnetism, which in turn is decreased by alloying. The behavior of th e magnetic properties is explained in terms of Stoner model.
Direct magnetization measurements of thin gold films are presented. These measurements integrate the signal from the thin film under study and the magnetic contribution of the film's interface with the substrate. The diamagnetic contribution to the signal from the bulk substrate is of the same order as the noise level. we find that thin gold films can exhibit positive magnetization. The character of their magnetic behavior is strongly substrate dependent.
The impact of growth conditions on the magnetic and electrical transport properties of oriented polycrystalline Sm0.55Sr0.45MnO3 thin films prepared on nearly lattice matching LSAT(100) single crystal substrates by nebulized spray pyrolysis has been studied.
It is shown that polycrystalline fullerene thin films on hydrogen passivated Si(111) substrates irradiated by 2 MeV protons displays ferromagnetic-like behavior at 5 K. At 300 K both the pristine and the irradiated film show diamagnetic behavior. Magnetization data in the temperature range 2 - 300 K, in 1 Tesla applied field, for the irradiated film shows much stronger temperature dependence compared to the pristine film. Possible origin of ferromagnetic-like signals in the irradiated films are discussed.
Nanocrystalline films of La-doped CaB$_6$ have been fabricated by using a rf-magnetron sputtering. Lattice expansion of up to 6% with respect to the bulk value was observed along the direction perpendicular to the film plane, which arises from the trapping of Ar gas into the film. Large ferromagnetic moment of 3 ~ 4 Bohr magneton per La has been observed in some La-doped films only when the lattice expansion rate is larger than 2.5%.
Magnetism of FeRh (001) films strongly depends on film thickness and surface terminations. While magnetic ground state of bulk FeRh is G-type antiferromagnetism, the Rh-terminated films exhibit ferromagnetism with strong perpendicular MCA whose energy +2.1 meV/$\Box$ is two orders of magnitude greater than 3$d$ magnetic metals, where $\Box$ is area of two-dimensional unit cell. While Goodenough-Kanamori-Anderson rule on the superexchange interaction is crucial in determining the magnetic ground phases of FeRh bulk and thin films, the magnetic phases are results of interplay and competition bet…
Thin films of orthorhombic TbMnO3, as well as other orthorhombic manganites, epitaxially grown on cubic SrTiO3 substrates display an induced magnetic moment that is absent in the bulk (antiferromagnetic) counterpart. Here we show that there is a clear correlation between the domain microstructure and the induced magnetic moment in TbMnO3 films on SrTiO3. In addition, the distinct dependence of the magnetization with the film thickness is not consistent with domain magnetism and indicates that the domain walls, rather than the domains, are the origin of the net magnetic moment. Since the orient…
The double perovskite La2NiMnO6 (LNMO) exhibits complex magnetism due to the competition of magnetic interactions that are strongly affected by structural and magnetic inhomogeneities. In this work, we study the effect of oxygen annealing on the structure and magnetism of epitaxial thin films grown by pulsed laser deposition. The key observations are that a longer annealing time leads to a reduction of saturation magnetization and an enhancement in the ferromagnetic transition temperature. We explain these results based upon epitaxial strain and oxygen defect engineering. The oxygen enrichment…
Quality of epitaxial films strongly depends on their structural and chemical match with the substrates: the more closely they match, the better the film quality is. Topological insulators (TI) such as Bi2Se3 thin films are of no exception. However, there do not exist commercial substrates that match with TI films both structurally and chemically, at the level commonly available for other electronic materials. Here, we introduce BiInSe3 bulk crystal as the best substrate for Bi2Se3 thin films. These films exhibit superior surface morphology, lower defect density and higher Hall mobility than th…
MnxGa films with high perpendicular anisotropy, coercivity and energy product have great application potential in ultrahigh-density perpendicular recording, permanent magnets, spin-transfer-torque memory and oscillators, magneto-resistance sensors and ferromagnetic metal/semiconductor heterostructure devices. Here we present a comprehensive diagram of effective magnetism-tailoring of perpendicularly magnetized MnxGa films grown on III-V semiconductor GaAs by using molecular-beam epitaxy for the first time, by systematically investigating the wide-range composition and detailed post-growth anne…
We perform in-situ two-cycle thermal cycling and annealing studies for a transferred CVD-grown monolayer MoS2 on a SiO2/Si substrate, using spatially resolved micro-Raman and PL spectroscopy. After the thermal cycling and being annealed at 305 deg C twice, the film morphology and film-substrate bonding are significantly modified, which together with the removal of polymer residues cause major changes in the strain and doping distribution over the film, and thus the optical properties. Before annealing, the strain associated with ripples in the transferred film dominates the spatial distributio…
We have carried out the growth of h-RFeO3 (001) (R=Lu, Yb) thin films on Fe3O4 (111)/Al2O3 (001) substrates, and studied the effect of the h-RFeO3 (001)/Fe3O4 (111) interfaces on the epitaxy and magnetism. The observed epitaxial relations between h-RFeO3 and Fe3O4 indicates an unusual matching of Fe sub-lattices rather than a matching of O sub-lattices. The out-of-plane direction was found to be the easy magnetic axis for h-YbFeO3 (001) but the hard axis for Fe3O4 (111) in the h-YbFeO3 (001)/Fe3O4 (111)/Al2O3 (001) films, suggesting a perpendicular magnetic alignment at the h-YbFeO3 (001)/Fe3O…
Germanosilicide thin films are quite different from silicides and germanides. The germanium composition is not homogeneous, grains have a different shape, and the substrate is generally strained. This affects grain boundary grooving and favors agglomeration of germanosilicide films. Our thermodynamics model shows that the equilibrium Ge composition of germanosilicide films formed on strained substrates is inhomogeneous and these films are more likely to agglomerate than those formed on relaxed substrates, in agreement with experiments. Grain shape too can affect agglomeration: polygonal films,…
We employ x-ray spectroscopy to characterize the distribution and magnetism of particular alloy constituents in (Ga,Fe)N films grown by metal organic vapor phase epitaxy. Furthermore, photoelectron microscopy gives direct evidence for the aggregation of Fe ions, leading to the formation of Fe-rich nanoregions adjacent to the samples surface. A sizable x-ray magnetic circular dichroism (XMCD) signal at the Fe L-edges in remanence and at moderate magnetic fields at 300 K links the high temperature ferromagnetism with the Fe(3d) states. The XMCD response at the N K-edge highlights that the N(2p) …
Here we present a novel approach to control magnetic interactions in atomic-scale nanowires. Our ab initio calculations demonstrate the possibility to tune magnetic properties of Fe nanowires formed on vicinal Cu surfaces. Both intrawire and interwire magnetic exchange parameters are extracted from DFT calculations. This study suggests that the effective interwire magnetic exchange parameters exhibit Ruderman--Kittel--Kasuya--Yosida-like (RKKY) oscillations as a function of Fe interwire separation. The choice of vicinal Cu surface offers possibilities for controlling the magnetic coupling. Fur…
Ion irradiation of semiconductors is a well understood method to tune the carrier concentration in a controlled manner. We show that the ferromagnetism in GaMnAs films, known to be hole-mediated, can be modified by He ion irradiation. The coercivity can be increased by more than three times. The magnetization, Curie temperature and the saturation field along the out-of-plane hard axis all decrease as the fluence increases. The electrical and structural characterization of the irradiated GaMnAs layers indicates that the controlled tailoring of magnetism results from a compensation of holes by g…
We measured the chemical and magnetic depth profiles of a single crystalline (La$_{1-x}$Pr$_x$)$_{1-y}$Ca$_y$MnO$_{3-δ}$ (x = 0.52\pm0.05, y = 0.23\pm0.04, δ = 0.14\pm0.10) film grown on a NdGaO3 substrate using x-ray reflectometry, electron microscopy, electron energy-loss spectroscopy and polarized neutron reflectometry. Our data indicate that the film exhibits coexistence of different magnetic phases as a function of depth. The magnetic depth profile is correlated with a variation of chemical composition with depth. The thermal hysteresis of ferromagnetic order in the film suggests a first …
The spin-density wave (SDW) state in thin chromium films is well known to be strongly affected by proximity effects from neighboring layers. To date the main attention has been given to effects arising from exchange interactions at interfaces. In the present work we report on combined neutron and synchrotron scattering studies of proximity effects in Cr/V films where the boundary condition is due to the hybridization of Cr with paramagnetic V at the interface. We find that the V/Cr interface has a strong and long-range effect on the polarization, period, and the Néel temperature of the SDW in …
Interface effects on the ferroelectric behavior of PbTiO$_3$ ultrathin films deposited on SrTiO$_3$ substrate are investigated using an interatomic potential approach with parameters fitted to first-principles calculations. We find that the correlation of atomic displacements across the film/substrate interface is crucial for the stabilization of the ferroelectric state in films a few unit-cells thick. We show that the minimum film thickness for the appearance of a spontaneous polarized domain state is not an intrinsic property of the ferroelectric film but depends on the polarizability of the…
The strain tuned magnetism of YTiO$_3$ film grown on the LaAlO$_3$ ($110$) substrate is studied by the method of the first principles, and compared with that of the ($001$)-oriented one. The obtained magnetism is totally different, which is ferromagnetic for the film on the ($110$) substrate but A-type antiferromagnetic on the ($001$) one. This orientation-dependent magnetism is attributed to the subtle orbital ordering of YTiO$_3$ film. The $d_{xz}$/$d_{yz}$-type orbital ordering is predominant for the ($001$) one, but for the ($110$) case, the $d_{xy}$ orbital is mostly occupied plus a few c…
Thin epitaxial films of Tb metal were grown on a clean W(110) substrate in ultra-high vacuum and studied in-situ by low-energy electron microscopy. Annealed films present magnetic contrast in spin-polarized low-energy electron microscopy. The energy dependence of the electron reflectivity was determined and a maximum value of its spin asymmetry of about 1\% was measured. The magnetization direction of the Tb films is in-plane. Upon raising the temperature, no change in the domain distribution is observed, while the asymmetry in the electron reflectivity decreases when approaching the critical …
Indirect magnetoelectric effect has been studied in magnetostrictive-film/substrate/piezoelectric-actuator heterostructures. Two different substrates have been employed: a flexible substrate (Young's modulus of 4 GPa) and a rigid one (Young's modulus of 180 GPa). A clear optimization of the indirect magnetoelectric coupling, studied by micro-strip ferromagnetic resonance, has been highlighted when using the polymer substrate. However, in contrast to the rigid substrate, the flexible substrate also leads to an a priori undesirable and huge uniaxial anisotropy which seems to be related to a non …
The recent emergence of topological insulators (TI) has spurred intensive efforts to grow TI thin films on various substrates. However, little is known about how robust the topological surface states (TSS) are against disorders and other detrimental effects originating from the substrates. Here, we report observation of a well-defined TSS on Bi2Se3 films grown on amorphous SiO2 (a-SiO2) substrates and a large gating effect on these films using the underneath doped-Si substrate as the back gate. The films on a-SiO2 were composed of c-axis ordered but random in-plane domains. However, despite th…
We report on the magnetic and structural properties of ferromagnetic-insulating La$_2$CoMnO$_6$ thin films grown on top of (001) STO substrates by means of RF sputtering technique. Careful structural analysis, by using synchrotron X-ray diffraction, allows identifying two different crystallographic orientations that are closely related to oxygen stoichiometry and to the features (coercive fields and remanence) of the hysteresis loops. Both Curie temperature and magnetic hysteresis turn out to be dependent on the oxygen stoichiometry. In situ annealing conditions allow tailoring the oxygen cont…
We perform first-principles density functional calculations to explore the role of substrate proximity effects on the octahedral rotation patterns in perovskite oxide superlattices. With cubic perovskite SrFeO$_3$ as our model film and tetragonal SrTiO$_3$ as the substrate, we show that in most cases the substrate octahedral rotation patterns propagate into the film across the heterointerface. We also identify elastic boundary conditions for which the enforced structural coherence induces atomic displacement patterns that are not found in the bulk phase diagram of either individual constituent…
The initial homoepitaxial growth of SrTiO3 on a (\surd13\times\surd13) - R33.7°SrTiO3(001) substrate surface, which can be prepared under oxide growth conditions, is atomically resolved by scanning tunneling microscopy. The identical (\surd13\times\surd13) atomic structure is clearly visualized on the deposited SrTiO3 film surface as well as on the substrate. This result indicates the transfer of the topmost Ti-rich (\surd13\times\surd13) structure to the film surface and atomic-scale coherent epitaxy at the film/substrate interface. Such atomically ordered SrTiO3 substrates can be applied to …
The prediction of ferromagnetism at room temperature in Co-ZnO thin films has generated a large interest in the community due to the possible applications. However, the results are controversial, going from ferromagnetism to non-ferromagnetism, leading to a large debate about its origin (secondary phase, Co clusters or not). By carefully studying the micro-structure of various Co-ZnO films, we show that the Co2+ partly substitutes the ZnO wurtzite matrix without forming Co clusters. Surprisingly, the ferromagnetism nature of the films disappears as the Co content increases. In addition, our re…
A theoretical study of the structural transition of impurity nanorod array in epitaxial YBCO films on vicinal STO substrates is presented. Two possible types of film/substrate interface were considered with one assuming a complete coherence while the other, defective as manifested in presence of anti-phase grain boundaries. Only in the former case, the increase of the vicinal angle of the substrate leads to a substantial change of the strain field in the film, resulting in a transition of the nanorod orientation from the normal to in-plane direction of the film. The calculation of the threshol…
We present SEM images of films thermally evaporated onto Anodic Aluminum Oxide substrates that are patterned with a hexagonal array of 34 and 80 nm diameter holes spaced by 100 nm. Over a range of film thicknesses, Pb and Sn films spontaneously self assemble into an array of nano-crystals in registry with the underlying hole lattice. The development of the arrays with thickness indicates that surface energies drive coalescing grains to move over the holes. Materials that wet the substrate or whose grains do not coalesce at these substrate temperatures do not form arrays. We discuss some potent…
BiFeO3 thin films have been deposited on Pt/sapphire and Pt/Ti/SiO2/Si substrates with pulsed laser deposition using the same growth conditions, respectively. Au was sputtered as the top electrode. The microscopic structure of the thin film varies by changing the underlying substrate. Thin films on Pt/sapphire are not resistively switchable due to the formation of Schottky contacts at both the top and the bottom interface. However, thin films on Pt/Ti/SiO2/Si exhibit an obvious resistive switching behavior under forward bias. The conduction mechanisms in BiFeO3 thin films on Pt/sapphire and Pt…
Liquid gas was used to produce DLC films on Cu, Al and steel substrates by DC plasma technique. The absorption in IR reflectance indicates, grown films are DLC. By deconvolution of room temperature UV-visible spectra of the films grown at 50 mtorr and 200${}^\circ$C, in addition to the spectra lines reported for CL, PL, PLC and ESR, some new spectra lines were obtained. We also, have seen exciton absorption line at room temperature.
We report the structural and transport properties of LaNiO3 thin films prepared by pulsed laser deposition technique. To understand the effects of film thickness, lattice mismatch and grain size on transport properties, various oriented substrates were used for deposition, including single-crystalline SrLaAlO4 (001), SrTiO3 (100) and LaAlO3 (100). To achieve a high quality LaNiO3 thin films, the vital parameters (such as laser fluence, substrate temperature, oxygen pressure, and deposition time) were optimized. The best quality films are found to be well textured samples with good crystalline …
Sol-gel derived thin films of Zn0.95Mn0.05O have been implanted with Ar9+ ions with doses viz. 5x10e14 ions/cm2 (low), 1x10e15 ions/cm2 (intermediate) and 1x10e16 ions/cm2 (high). Structural, morphological, optical and magnetic properties of the films have been investigated. Structural study confirmed single phase, wurtzite structure of the films. The absence of impurity phase has been confirmed from several measurements. Ion implantation induces a large concentration of point defects into the films as identified from optical study. All films exhibit well above room temperature (RT) intrinsic …
Thin epitaxial GaAs films, with thickness varying from 140 to 1000 nm and different Si doping levels, were grown at 650C by organometallic vapor phase epitaxy (OMVPE) on Ge substrates and extensively analyzed by low-temperature photoluminescence (PL) spectroscopy.
Domain structures of 320 nm thin epitaxial films of ferroelectric PbTiO3 grown by MOCVD technique in identical conditions on SmScO3 and TbScO3 perovskite sub- strates have been investigated by Raman spectroscopy and piezoresponse force microscopy techniques. Phonon frequency shifts and typical domain structure motifs are discussed. The results reveal strikingly different domain structure architecture: domain structures of the PbTiO3 film grown on SmScO3 have dominantly a-domain orientation while strongly preferential c-domain orientation was found in the PbTiO3 film grown on the TbScO3 substra…
The cobalt oxide system LaCoO$_3$ and its Sr-doped child compounds have been intensively studied for decades due to their intriguing magnetic and electronic properties. Preparing thin La$_{1-x}$Sr$_x$CoO$_3$ (LSCO) films on different substrates allows for studies with a new type of perturbation, as the films are subject to substrate-dependent epitaxial strain. By choosing a proper substrate for a thin film grow, not only compressing but also tensile strain can be applied. The consequences for the fundamental physical properties are dramatic: while compressed films are metallic, as the bulk mat…
Lead island films were obtained via vacuum vapor deposition on glass and ceramic substrates at 80 K. Electrical conductance was measured during vapor condensation and further annealing of the film up to room temperature. The resistance behavior during film formation and atomic force microscopy of annealed films were used as information sources about their structure. A model for the quenched growth, based on ballistic aggregation theory, was proposed. The nanostructure, responsible for chemiresistive properties of thin lead films and the mechanism of sensor response are discussed.
Barrium fluoride (BaF2) thin films were prepared by electron beam evaporation technique at room temperature, on glass, Silicon and Aluminum substrates having thickness of 20 nm each. Its structural property and surface morphology were studied using glancing angle X-ray diffraction (GAXRD) and atomic force microscopy (AFM) respectively. It was found that grain size, average surface roughness and interface width changes with different substrates. Higuchi algorithm is applied for the fractal measure on AFM images.It was observed found that the fractal dimension varied from substrate to substrate.
Growth of perovskite oxide thin films on Si in crystalline form has long been a critical obstacle for the integration of multifunctional oxides into Si-based technologies. In this study, we propose pulsed laser deposition of a crystalline SrTiO3 thin film on a Si using graphene substrate. The SrTiO3 thin film on graphene has a highly (00l)-oriented crystalline structure which results from the partial epitaxy. Moreover, graphene promotes a sharp interface by highly suppressing the chemical intermixing. The important role of graphene as a 2D substrate and diffusion barrier allows expansion of de…
The application of a substrate bias during rf magnetron sputtering alters the crystalline structure, grain morphology, lattice strain and composition of BaxSr1-xTiO3 thin films. As a result, the dielectric properties of Pt/BaxSr1-xTiO3/Pt parallel-plate capacitors change significantly. With increasing substrate bias we observe a clear shift of the ferroelectric to paraelectric phase transition towards higher temperature, an increase of the dielectric permittivity and tunability at room temperature, and a deterioration of the dielectric loss. To a large extent these changes correlate to a gradu…
Atomic-layer-deposited Al2O3 and HfO2 films on GaSb substrates were treated by in-situ ozone post deposition treatment (PDT). The effects of ozone PDT on the interfacial and electrical properties of Al2O3 and HfO2 gate dielectric films on GaSb substrates were investigated carefully. It is found that the dielectric quality and the interfacial properties of the Al2O3 and HfO2 films are improved by ozone PDT. After in-situ ozone PDT for 5 min, the Al2O3 and HfO2 films on GaSb substrates exhibit improved electrical and interfacial properties, such as reduced frequency dispersion, gate leakage curr…
The structural and ferroelectric domain variants of highly-strained BiFeO3 films grown on vicinal LaSrAlO4 substrates were studied by piezoelectric force microscopy and high-resolution X-ray reciprocal space mapping. Through symmetry breaking of the substrate surface, ferroelastic domain variants in the highly-strained MC phase BiFeO3 can be greatly reduced. Single-domain film can be obtained on substrates with large miscut angle, which is accompanied by the reduction of structural variants in the mixed-phase nanodomains. These findings lead to better understanding of the phase evolution and p…
Cerium dioxide (CeO2) thin films were deposited by atomic layer deposition (ALD) on both Si and TiN substrates. The ALD growth produces CeO2 cubic polycrystalline films on both substrates. However, the films show a preferential orientation along <200> crystallographic direction for CeO2/Si or <111> for CeO2/TiN. In correspondence, we measure a relative concentration of Ce3+ equals to 22.0% in CeO2/Si and around 18% in CeO2/TiN, by X-ray photoelectron spectroscopy. Such values indicate the presence of oxygen vacancies in the films. Our results extend the knowledge on the structural and chemical…
The dewetting dynamics of an ultrathin film is studied in the presence of evaporation - or reaction - of adatoms on the substrate. KMC simulations are in good agreement with an analytical model with diffusion, rim facetting, and substrate sublimation. As sublimation is increased, we find a transition from the usual dewetting regime where the front slows down with time, to a sublimation-controlled regime where the front velocity is approximately constant. The rim width exhibits an unexpected non-monotonous behavior, with a maximum in time.
Here we demonstrate the controlled growth of Bi(110) and Bi(111) films on an (insulating) $α$-Al$_2$O$_3$(0001) substrate by surface X-ray diffraction and X-ray reflectivity using synchrotron radiation. At temperatures as low as 40 K, unanticipated pseudo-cubic Bi(110) films are grown having a thickness ranging from a few to tens of nanometers. The roughness at the film-vacuum as well as at the film-substrate interface, can be reduced by mild heating, where a crystallographic orientation transition of Bi(110) towards Bi(111) is observed at 400 K. From 450 K onwards high quality and ultrasmooth…
In this paper we report the results about the synthesis and characterization of optimally doped La1-xNaxMnO3 thin films grown onto SrTiO3 (100), NdGaO3 (100) and NdGaO3 (110) for thickness ranging from 11 to 82 nm. The effect of substrate nature and orientation, film thickness and annealing procedure was investigated in order to optimize their magnetoresistance (MR). We obtained very smooth films displaying MR values greater than 70%, near to room temperature.
Diamond Like Carbon (DLC) films were deposited on quartz substrates using Dense Plasma Focus (DPF) method. The formation of ${\rm sp^3}$ bonds as is it's content in the film strongly depends on the substrate and it seems quartz is not a suitable substrate. However, we report here the formation of DLC films on quartz substrates that were maintained at elevated temperatures and show the content of carbon atoms with ${\rm sp^3}$ bonds in the film is directly proportional to the substrate's temperature. Not only does this give good control of film fabrication, but also shows how to take advantage …
Experimental results for adhesive contacts on substrates coated with elastomeric thin films have recently been obtained by C. Tardivat and L. Léger (J. Adhesion Sci. Technol. 15 1055-1078 (2001)) by the so-called JKR test, which provides both adhesion energy and elastic modulus. These data show that on substrates coated with thin films the adhesion and effective elastic modulus of the sphere depend upon the film thickness. In keeping with the experimental conditions, we try to interpret these data using a simple model (E. Barthel and A. Perriot, J. Phys. D 40, 1059-1067 (2007)) in the thin fil…
Diamond-like carbon (DLC) films are synthesized on Si using plasma enhanced chemical vapor deposition. The role of substrate bias and nitrogen doping on the structural evolution and local elastic modulus of DLC films are systematically investigated. Raman spectroscopic studies reveal that the amount of graphitic C=C sp2 bonding increases with substrate bias and nitrogen doping. The density and hydrogen concentration in the films are found to vary from 0.7 to 2.2 g/cm3 and 16 to 38 atomic %, respectively, depending upon the substrate bias and nitrogen concentration in the DLC films. Atomic forc…
Hysteretic magnetoresistance (MR) is often used as a signature of ferromagnetism in conducting oxide thin films and heterostructures. Here, magnetotransport is investigated in a non-magnetic uniformly La-doped SrSnO3 film grown using hybrid molecular beam epitaxy. A 12 nm La:SrSnO3/2 nm SrSnO3/GdScO3 (110) film with insulating behavior exhibited a robust hysteresis loop in the MR at T < 5 K accompanied by an anomaly at ~ +/- 3 T at T < 2.5 K. Furthermore, MR with the field in-plane yielded a value exceeded 100% at 1.8 K. Using detailed temperature-, angle- and magnetic field-dependent resistan…
We have investigated random submonolayer films of 3d transition metals on W(001). The tight-binding linear muffin-tin orbital method combined with the coherent potential approximation was employed to calculate the electronic structure of the films. We have estimated local magnetic moments and the stability of different magnetic structures, namely the ferromagnetic order, the disordered local moments and the non-magnetic state, by comparing the total energies of the corresponding systems. It has been found that the magnetic moments of V and Cr decrease and eventually disappear with decreasing c…
In this paper we used Raman spectroscopy to investigate the optical properties of vanadium dioxide (VO2) thin films during the thermally induced insulating to metallic phase transition. We observed a significant difference in transition temperature in similar VO2 films grown on quartz and sapphire substrates: the film grown on quartz displayed the phase transition at a lower temperature (Tc=50C) compared a film grown on sapphire (Tc=68C). We also investigated differences in the detected Raman signal for different wavelengths and polarizations of the excitation laser. We found that for either s…
We investigated the ferroelectric properties of strontium titanate (STO) thin films deposited on SrTiO3 (001) substrate with SrRuO3 electrodes. The STO layer was grown coherently on the SrTiO3 substrate without in-plane lattice relaxation, but its out-of-plane lattice constant increased with a decrease in the oxygen pressure during deposition. Using piezoresponse force microscopy and P-V measurements, we showed that our tetragonal STO films possess room-temperature ferroelectricity. We discuss the possible origins of the observed ferroelectricity.
How to transfer MoS2 films from growth substrates onto target substrates is a critical issue for its practical applications. However, it remains a great challenge to avoid the sample degradation and substrate destruction, since current transfer method inevitably employs a wet chemical etching process. Herein, we develop an etching-free transfer method for transferring wafer-scale MoS2 films onto arbitrary substrates by using ultrasonication. Briefly, the collapse of ultrasonication-generated microbubbles at the interface between polymer-coated MoS2 film and substrates induce sufficient force t…
In ferromagnetic thin films, the Curie temperature variation with the thickness is always considered as continuous when the thickness is varied from $n$ to $n+1$ atomic planes. We show that it is not the case for Fe in Fe/Ir superlattices. For an integer number of atomic planes, a unique magnetic transition is observed by susceptibility measurements, whereas two magnetic transitions are observed for fractional numbers of planes. This behavior is attributed to successive transitions of areas with $n$ and $n+1$ atomic planes, for which the $T_c$'s are not the same. Indeed, the magnetic correlati…
The sensitivity of materials properties, particularly those of perovskite oxides, to epitaxial strain has been exploited to great advantage to create materials with new or enhanced properties. Although it has certainly been recognized that mismatch in the thermal expansion coefficients of the bulk and substrate material will contribute to the misfit strain, the significance of this contribution for ferroelectric perovskite thin-films has not been systematically explored. We use first-principles density functional theory and the example of ferroelectric PbTiO$_3$ thin-films on various substrate…
An evolution partial differential equation for the surface of a non-wetting single-crystal film in an attractive substrate potential is derived and used to study the dynamics of a pinhole for the varying initial depth of a pinhole and the strengths of the potential and the surface energy anisotropy. The results of the simulations demonstrate how the corresponding parameters may lead to complete or partial dewetting of the film. Anisotropy of the surface energy, through faceting of the pinhole walls, is found to most drastically affect the time to film rupture. In particular, the similations su…
