Thermal stability of hydrogenated amorphous Si/Ge multilayers has been investigated by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Small-Angle X-Ray Diffraction (SAXRD) techniques. Amorphous H-Si/Ge multilayers were prepared by RF sputtering with 1.5 and 6 ml/min H2 flow-rate. It is shown by Elastic Recoil Detection Analysis (ERDA) that the hydrogen concentration increased by increasing H2 flow-rate. Annealing of the samples was carried out at 400 and 450 oC for several hours. It has been observed that samples prepared with 6 ml/min flow-rate at both annealing temperatures underwent significant structural changes: the surface of the samples was visibly roughened, gas bubbles were formed and craters were created. The decay of the periodic structure of Si and Ge layers in these types of multilayers was faster than in non-hydrogenated samples. Samples prepared with 1.5 ml/min flow-rate have similar behaviour at 450 oC, but at 400 oC the decay of the first order SAXRD peaks was slower than in case of the non-hydrogenated multilayers. Qualitatively the observed behaviour can be explained by the fast desorption of the saturated hydrogen, leading to the formation of bubbles and craters at 450 oC, as well as, at 400oC in the sample with lower H-content, by the possible passivation of the dangling bonds resulting in a slowing down of the diffusion intermixing.
The thermally-induced structural evolution of silicon- and oxygen-containing hydrogenated amorphous carbon (a-C:H:Si:O) was investigated by X-ray photoelectron and absorption spectroscopy, as well as molecular dynamics (MD) simulations. The spectroscopic results indicate that the introduction of Si and O in hydrogenated amorphous carbon (a-C:H) increases the activation energy for the conversion of sp3- to sp2-bonded C. MD simulations indicate that the higher thermal stability of a-C:H:Si:O compared to a-C:H derives from the lower fraction of strained C-C sp3 bonds in a-C:H:Si:O.
We employ ab initio molecular dynamics to simulate the response of hydrogenated amorphous silicon to light exposure (Staebler-Wronski effect). We obtain improved microscopic understanding of PV operation, compute the motion of H atoms, and modes of light-induced degradation of photovoltaics. We clarify existing models of light-induced change in aSi:H and show that the Hydrogen collision model of Branz3 is correct in essentials.
Ferromagnetism above room temperature was observed in Cr-doped hydrogenated amorphous silicon films deposited by rf magnetron-sputtering. Structure analysis reveals that films are amorphous without any detectable precipitates up to the solubility limit 16 atomic percentages of Cr. Experimental results suggest that hydrogenation has a dramatic influence on magnetic properties, electrical conductivity and carrier concentration in the thin films. Pronounced anomalous Hall effect and magnetization curve both suggest the origin of the ferromagnetism may arises from percolation of magnetic polarons.
We present an ab initio calculation of the DC conductivity of amorphous silicon and hydrogenated amorphous silicon. The Kubo-Greenwood formula is used to obtain the DC conductivity, by thermal averaging over extended dynamical simulation. Its application to disordered solids is discussed. The conductivity is computed for a wide range of temperatures and doping is explored in a naive way by shifting the Fermi level. We observed the Meyer-Neldel rule for the electrical conductivity with E_MNR = 0.06 eV and a temperature coefficient of resistance, TCR ~ -2.0% K^-1 for a-Si:H. In general, experime…
The structural relaxation of pure amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) materials, that occurs during thermal annealing experiments, has been analysed by Raman spectroscopy and differential scanning calorimetry. Unlike a-Si, the heat evolved from a-Si:H cannot be explained by relaxation of the Si-Si network strain, but it reveals a derelaxation of the bond angle strain. Since the state of relaxation after annealing is very similar for pure and hydrogenated materials, our results give strong experimental support to the predicted configurational gap between a-Si an…
A study is presented of the structural changes occurring as a function of the annealing conditions in hydrogenated amorphous Si/Ge multilayers prepared by sputtering. Annealing changes the structure of the as-deposited multilayer except for the less severe conditions here applied (150 oC, time<22 h). For higher temperatures and/or times, the modifications consist of layer intermixing and surface degradation in the shape of bumps and craters. They are argued to be due to the formation of H bubbles upon heating. Hydrogen should be mostly released from the amorphous Ge layers.
We report first principles ab initio density functional calculations of hydrogen dynam- ics in hydrogenated amorphous silicon. Thermal motion of the host Si atoms drives H diffusion, as we demonstrate by direct simulation and explain with simple models. Si-Si bond centers and Si ring centers are local energy minima as expected. We also describe a new mechanism for break- ing Si-H bonds to release free atomic H into the network: a fluctuation bond center detachment (FBCD) assisted diffusion. H dynamics in a-Si:H is dominated by structural fluctuations intrinsic to the amorphous phase not presen…
The growth of thin amorphous hydrogenated carbon films (a-C:H) on diamond (111) surface from the bombardment of CH2 radicals is studied using molecular dynamics simulations. The structural analysis shows that the local structure (e.g., the first coordination number of C atoms) of a-C:H depends critically on the content of hydrogen. The increase of kinetic energy of incident radicals leads to the decrease of hydrogen content, which subsequently changes the ratio of sp3 bonded C atoms in a-C:H.
Surface resistivity of hydrogenated amorphous carbon films was measured as a function of the applied electrical field. The measured dependence shows a sharp ambipolar peak near zero gate voltage. Furthermore, we found that in some samples sheet resistance at the peak is as low as 7.5 kΩ/sq. This value is the same order of magnitude as the sheet resistance of a defect free graphene monolayer. Therefore a conclusion is made that an intrinsic graphene with dimensions of at least millimeters exist on the surface of amorphous carbon films. These results can open new perspectives not only for graphe…
The evolution is presented of infrared transmission spectra of hydrogenated and chlorinated amorphous silicon films versus the chlorine concentration and the annealing temperature. As the chlorine content increases, an increase of the 2100 cm-1 band intensity is observed. We associate this effect with the existence of SiH2CI2, mixed configurations. The Sic1 stretching band, located at 545 cm-1 in unannealed samples, shifts continuously up to 590 cm-1 as the annealing temperature increases. This displacement is attributed to a predominance of SiCI2, species around 500°C and their transformation…
We use accurate first principles methods to study the network dynamics of hydrogenated amorphous silicon, including the motion of hydrogen. In addition to studies of atomic dynamics in the electronic ground state, we also adopt a simple procedure to track the H dynamics in light-excited states. Consistent with recent experiments and computer simulations, we find that dihydride structures are formed for dynamics in the light-excited states, and we give explicit examples of pathways to these states. Our simulations appear to be consistent with aspects of the Staebler-Wronski effect, such as the …
The dynamics of charge carriers in amorphous semiconductors fundamentally differ from those in crystalline semiconductors due to the lack of long-range order and the high defect density. Despite intensive technology-driven research interests and the existence of well-established experimental techniques, such as photoconductivity time-of-flight and ultrafast optical measurements, many aspects of the dynamics of photo-excited charge carriers in amorphous semiconductors remain poorly understood. Here we demonstrate direct imaging of carrier dynamics in space and time after photo-excitation in hyd…
The resonant Raman scattering in N-IR - UV range from amorphous hydrogenated carbon (a-C:H) reveal inclusions of trans-polyacetylene (trans-(CH)x) chains with approximate length of up to 120 C=C units and inclusions of poly(p-phenylene vinylene) (PPV) polymer chains. The PPV is evidenced by a strong dispersive mode at ca. 1175 cm-1. It was found that the Raman response from core Ag trans-(CH)x modes incorporated into a-C:H to changing excitation energy is identical to of free-standing chains thus facilitating identification of trans-(CH)x in complex carbonaceous materials spectra.
Specific heat measurements from 2 to 300 K of hydrogenated amorphous silicon prepared by hot-wire chemical vapor deposition show a large excess specific heat at low temperature, significantly larger than the Debye specific heat calculated from the sound velocity. The as-prepared films have a Schottky anomaly that is associated with metastable hydrogen in the amorphous network, as well as large linear and excess cubic term commonly associated with tunneling two-level systems in amorphous solids. Annealing at 200 °C, a temperature that enables hydrogen mobility but not evaporation, irreversibly …
Multilayers of hydrogenated ultrathin (3 nm) amorphous a-Si and a-Ge layers prepared by sputtering have been studied by atomic force microscopy (AFM) and transmission electron microscopy (TEM) to check the influence of annealing on their structural stability. The annealed multilayers exhibit surface and bulk degradation with formation of bumps and craters whose density and size increase with increasing hydrogen content and/or annealing temperature and time. Bumps are due to the formation of H2 bubbles in the multilayer. The craters are bumps blown up very likely because of too high a gas press…
We have extended our experimentally constrained molecular relaxation technique (P. Biswas {\it et al}, Phys. Rev. B {\bf 71} 54204 (2005)) to hydrogenated amorphous silicon: a 540-atom model with 7.4 % hydrogen and a 611-atom model with 22 % hydrogen were constructed. Starting from a random configuration, using physically relevant constraints, {\it ab initio} interactions and the experimental static structure factor, we construct realistic models of hydrogenated amorphous silicon. Our models confirm the presence of a high frequency localized band in the vibrational density of states due to Si-…
In this paper we discuss the application of current it ab initio computer simulation techniques to hydrogenated amorphous silicon (a-Si:H). We begin by discussing thermal fluctuation in the number of coordination defects in the material, and its temperature dependence. We connect this to the ``fluctuating bond center detachment" mechanism for liberating H bonded to Si atoms. Next, from extended thermal MD simulation, we illustrate various mechanisms of H motion. The dynamics of the lattice is then linked to the electrons, and we point out that the squared electron-lattice coupling (and the the…
Visible luminescence is observed from the composite of SiO2 with embedded silicon nanocrystallites produced by femtosecond laser irradiation of hydrogenated amorphous silicon (a-Si:H) film in air. The photoluminescence originates from the defect states at the interface between silicon crystallites and SiO2 matrix. The method could be used for fabrication of luminescent layers to increase energy conversion of a-Si:H solar cells.
We deposit intrinsic hydrogenated amorphous silicon (a-Si:H) thin films by reactive pulsed laser deposition, for various hydrogen pressures in the 0-20 Pa range, at a low deposition temperature of 120C, and investigate the hydrogen incorporation, structural, optical, and electrical properties of the films, as a function of the ambient hydrogen pressure. The film thickness decreases linearly as the hydrogen pressure increases. The hydrogen content of the films is determined by infrared spectroscopy and the optical bandgap from UV-Vis-NIR transmittance and reflectance measurements. Electric meas…
We have studied the effects of oxygen on hydrogenated amorphous/crystalline silicon films in terms of their structural and optical properties. Different hydrogenated silicon oxide (SiO:H) and silicon (Si:H) films are fabricated between microcrystalline and amorphous transition region. X-ray diffraction, Raman, FTIR and UV-Vis emission spectrometry have been used to characterize different films. A comparison of the results with those of different types of films like hydrogenated amorphous silicon oxide (a-SiO:H), hydrogenated amorphous silicon (a-Si:H) and microcrystalline silicon ($μ$c-Si:H) f…
The present work is essentially focused on the study of optical and structural properties of hydrogenated amorphous silicon thin films (a-Si:H) prepared by radio-frequency cathodic sputtering. We examine separately the influence of hydrogen partial pressure during film deposition, and the effect of post-deposition thermal annealings on the main optical characteristics of the layers such as refraction index, optical gap and Urbach energy. Using the grazing X-rays reflectometry technique, thin film structural properties are examined immediately after films deposition as well as after surface oxi…
Inclusions of sp-hybridised, trans-polyacetylene [trans-(CH)x] and poly(p-phenylene vinylene) (PPV) chains are revealed using resonant Raman scattering (RRS) investigation of amorphous hydrogenated carbon (a-C:H) films in the near IR - UV range. The RRS spectra of trans-(CH)x core Ag modes and the PPV CC-H phenylene mode are found to transform and disperse as the laser excitation energy \hbarωL is increased from near IR through visible to UV, whereas sp-bonded inclusions only become evident in UV. This is attributed to \hbarωL probing of trans-(CH)x chain inhomogeneity and the distribution of …
We present a fast and simple way to determine the erosion rate and absorption coefficient of hydrogenated amorphous carbon films exposed to a hydrogen atomic source based on ex-situ Raman micro-spectroscopy. Results are compared to ellipsometry measurement. The method is applied to films eroded at different temperatures. A maximum of the erosion rate is found at ~ 450 {\degree}C in agreement with previous results. This technique is suitable for future quantitative studies on the erosion of thin carbonaceous films, especially of interest for plasma wall interactions occurring in thermonuclear f…
The nanostructure of hydrogenated amorphous silicon (a Si:H) is studied by a combination of small-angle X-ray (SAXS) and neutron scattering (SANS) with a spatial resolution of 0.8 nm. The a-Si:H materials were deposited using a range of widely varied conditions and are representative for this class of materials. We identify two different phases which are embedded in the a-Si:H matrix and quantified both according to their scattering cross-sections. First, 1.2 nm sized voids (multivacancies with more than 10 missing atoms) which form a superlattice with 1.6 nm void-to-void distance are detected…
Recent experiments on hydrogenated amorphous silicon using infrared absorption spectroscopy have indicated the presence of mono- and divacancy in samples for concentration of up to 14\% hydrogen. Motivated by this observation, we study the microstructure of hydrogen in two model networks of hydrogen-rich amorphous silicon with particular emphasis on the nature of the distribution (of hydrogen), the presence of defects, and the characteristic features of the nuclear magnetic resonance spectra at low and high concentration of hydrogen. Our study reveals the presence of vacancies, which are the b…
Historically, the design of hybrid solar photovoltaic thermal (PVT) systems has focused on cooling crystalline silicon (c-Si)-based photovoltaic (PV) devices to avoid temperature-related losses. This approach neglects the associated performance losses in the thermal system and leads to a decrease in the overall exergy of the system. Consequently, this paper explores the use of hydrogenated amorphous silicon (a-Si:H) as an absorber material for PVT in an effort to maintain higher and more favourable operating temperatures for the thermal system. Amorphous silicon not only has a smaller temperat…
Ultrananocrystalline diamond/hydrogenated amorphous carbon composite thin films synthesized via coaxial arc plasma possess a marked structural feature of diamond grains embedded in an amorphous carbon and a hydrogenated amorphous carbon matrix which are the largest constituents of the films. Since the amorphous nature yields much larger light absorption coefficients as well as a generation source of photo-induced carriers with UV rays, these films can be potential candidates for deep-UV photodetector applications. From some previous studies p-type conduction of the films has been realized by d…
Specific heat measurements of hydrogenated amorphous silicon prepared by hot-wire chemical vapor deposition show a large density of two-level systems at low temperature. Annealing at 200 °C, well below the growth temperature, does not significantly affect the already-low internal friction or the sound velocity, but irreversibly reduces the non-Debye specific heat by an order of magnitude at 2 K, indicating a large reduction of the density of two-level systems. Comparison of the specific heat to the internal friction suggests that the two-level systems are uncharacteristically decoupled from ac…
We present a novel approach for parameter-free modeling of the structural, dynamical and electronic properties of non-crystalline materials based on ab-initio Molecular Dynamics, improved signal processing technique and computer visualization. The method have been extensively tested by investigating hydrogen and silicon dynamics in hydrogenated amorphous silicon (a-Si:H). By comparing the theoretical and experimental vibrational spectra we demonstrate how to relate vibrational properties to the structural stability, bonding and hydrogen diffusion. We extracted microscopic characteristics that …
We describe a mechanism, which links the long-range potential fluctuations induced by charged defects to the low frequency resistance noise widely known as 1/f noise. This mechanism is amenable to the first principles microscopic calculation of the noise spectrum, which includes the absolute noise intensity. We have performed such a calculation for the thin films of hydrogenated amorphous silicon (a-Si:H) under the condition that current flows perpendicular to the plane of the films, and found a very good agreement between the theoretical noise intensity and the measured one. The mechanism des…
Superconducting resonators used in millimeter-submillimeter astronomy would greatly benefit from deposited dielectrics with a small dielectric loss. We deposited hydrogenated amorphous silicon films using plasma-enhanced chemical vapor deposition, at substrate temperatures of 100°C, 250°C and 350°C. The measured void volume fraction, hydrogen content, microstructure parameter, and bond-angle disorder are negatively correlated with the substrate temperature. All three films have a loss tangent below $10^{-5}$ for a resonator energy of $10^5$ photons, at 120 mK and 4-7 GHz. This makes these film…
We study the distribution of hydrogen and various hydride configurations in realistic models of a-Si:H for two different concentration generated via experimentally constrained molecular relaxation approach (ECMR) [1]. The microstructure corresponding to low (< 10%) and high (> 20%) concentration of H atoms are addressed and are compared to the experimental results with particular emphasis on the size of H clusters and local environment of H atoms.The linewidths of the nuclear magnetic resonance (NMR) spectrum for the model configurations are calculated in order to compare to the experimental N…
We have studied the effect of nitriding on the humidity sensing properties of hydrogenated amorphous carbon (a-C:H) films. The films were prepared in two stages combining the techniques of physical deposition in vapor phase evaporation (PAPVD) and plasma pulsed nitriding. By deconvolution of the Raman spectrum we identified two peaks corresponding to the D and G modes characteristic of a-C:H. After the N$_2$-H$_2$ plasma treating, the peaks narrowed and shifted to the right, which we associated with the incorporation of N into the structure. We compared the sensitivity to the relative humidity…
Ultranonocrystalline diamond/hydrogenated amorphous carbon composite thin films consist of three different components; ultrananocrystalline diamond crystallites, hydrogenated amorphous carbon, and grain boundaries between them. Since grain boundaries contain a lot of dangling bonds and unsaturated bonds, they would be a cause of carrier trap center degrading device performance in possible applications such as UV photo-detectors. We experimentally demonstrate hydrogen atoms preferentially incorporate at grain boundaries and terminate dangling bonds by means of several spectroscopic techniques. …
A structural model of hydrogenated amorphous silicon containing an isolated dangling bond is used to investigate the effects of electron interactions on the electronic level splittings, localization of charge and spin, and fluctuations in charge and spin. These properties are calculated with a recently developed density-matrix correlation-energy functional applied to a generalized Anderson Hamiltonian, consisting of tight-binding one-electron terms parametrizing hydrogenated amorphous silicon plus a local interaction term. The energy level splittings approach an asymptotic value for large valu…
Amorphous/crystalline multilayer structures of Fe-P alloys were deposited electrochemically using the single bath technique. Hall-Petch behavior of microhardness with respect to sublayer thickness was observed down to a sublayer thickness of 15 nm. For thinner sublayers, a hardness plateau was obtained. The transition at a sublayer thickness of 15 nm coincides with the loss of the multilayer structure as observed in transmission electron microscopy. The transition is a possible result of a change in the amorphous to crystalline sublayer thickness ratio and the interface roughness development d…
It is shown that the well-known blue-shift of the fundamental absorption edge in as-deposited compositionally modulated amorphous Si/Ge and As6Se94/Se80Te20 multilayers (with periods of 4-8 nm) is further enhanced due to the thermal or laser-induced intermixing of adjacent layers. The laser-induced intermixing process, as supported by experiments and model calculations, can be attributed to both the local heating and photo-effects in As6Se94/Se80Te20 multilayers, while only the thermal effects were observed for Si/Ge multilayers. Structural transformations, based on this enhanced interdiffusio…
Structural and superconducting transitions of layered van der Waals (vdW) hydrogenated germanene (GeH) were observed under high-pressure compression and decompression processes. GeH possesses a superconducting transition at critical temperature (Tc) of 5.41 K at 8.39 GPa. A crystalline to amorphous transition occurs at 16.80 GPa while superconductivity remains. An abnormally increased Tc up to 6.1 K has been observed in the decompression process while the GeH remained amorphous. Thorough in-situ high-pressure synchrotron X-ray diffraction and in-situ high-pressure Raman spectroscopy with the d…
The Monte Carlo method in the canonical ensemble is used to investigate magnetization reversal in amorphous transition metal - rare earth multilayers. Our study is based on a model containing diluted clusters which exhibit an effective uniaxial anisotropy in competition with random magnetic anisotropy in the matrix. We simulate hysteresis loops for an abrupt profile and a diffuse one obtained from atom probe tomography analyses. Our results evidence that the atom probe tomography profile favors perpendicular magnetic anisotropy in agreement with magnetic measurements. Moreover, the hysteresis …
Low-loss deposited dielectrics will benefit superconducting devices such as integrated superconducting spectrometers, superconducting qubits and kinetic inductance parametric amplifiers. Compared with planar structures, multi-layer structures such as microstrips are more compact and eliminate radiation loss at high frequencies. Multi-layer structures are most easily fabricated with deposited dielectrics, which typically exhibit higher dielectric loss than crystalline dielectrics. We measured the sub-kelvin and low-power microwave and mm-submm wave dielectric loss of hydrogenated amorphous sili…
The thickness dependence of the magnetic properties of amorphous Fe90Zr10 layers has been explored using Fe90Zr10/Al75Zr25 multilayers. The Al75Zr25 layer thickness is kept at 40 Å, while the thickness of the Fe90Zr10 layers is varied between 5 and 20 Å. The thickness of the Al75Zr25 layers is sufficiently large to suppress any significant interlayer coupling. Both the Curie temperature and the spontaneous magnetization decrease non-linearly with decreasing thickness of the Fe90Zr10 layers. No ferromagnetic order is observed in the multilayer with 5 Å Fe90Zr10 layers. The variation of the Curi…
In the paper a theoretical study of critical (Curie) temperature of diluted ferromagnet based on multilayer graphene (or graphite) with hydrogen adatoms deposited over carbon atoms belonging to single sublattice is presented. The calculations are performed within Pair Approximation (PA) for diluted ferromagnetic system with long-range interactions. The method is able to take into account the spin-space anisotropy of coupling. The results obtained within Mean Field Approximation (MFA) are also presented for comparison. The assumed interaction between hydrogen adatom spins is inversely proportio…
We report on the preparation of hydrogenated amorphous carbon nano-particles whose spectral characteristics include an absorption band at 217.5 nm with the profile and characteristics of the interstellar 217.5 nm feature. Vibrational spectra of these particles also contain the features commonly observed in absorption and emission from dust in the diffuse interstellar medium. These materials are produced under slow deposition conditions by minimizing the flux of incident carbon atoms and by reducing surface mobility. The initial chemistry leads to the formation of carbon chains, together with a…
We investigate the magnetic properties of a Heisenberg ferrimagnetic multilayer by using Monte Carlo simulations. The aim of this work is to study the local structural anisotropy model which is a possible origin of the perpendicular magnetic anisotropy in transition metal/rare earth amorphous multilayers. We have considered a face centered cubic lattice where each site is occupied by a classical Heisenberg spin. We have introduced in our model of amorphous multilayers a small fraction of crystallized Fe-Dy nanoclusters with a mean anisotropy axis along the deposition direction. We show that a …
The transport response of dipole skyrmions in amorphous centrosymmetric Fe/Gd multilayer is investigated by temperature and field-dependent resistivity measurements collected in three current and magnetic field configurations. It is shown that a dipole skyrmion lattice phase may form at certain temperatures leading to a unique signature of the polar longitudinal resistivity. This signature differs from the conventional field-varying parabolic response associated with stripe phases, which transition to a disordered skyrmion phase under applied fields. Transport measurements under different fiel…
We measure charge transport in hydrogenated amorphous silicon (a-Si:H) using a nanometer scale silicon MOSFET as a charge sensor. This charge detection technique makes possible the measurement of extremely large resistances. At high temperatures, where the a-Si:H resistance is not too large, the charge detection measurement agrees with a direct measurement of current. The device geometry allows us to probe both the field effect and dispersive transport in the a-Si:H using charge sensing and to extract the density of states near the Fermi energy.
In this paper we introduce a novel method for fabricating MgB$_2$/MgO multilayers and demonstrate the potential for using them as a new model for disordered superconductors. In this approach we control the annealing of the MgB$_2$ to yield an interesting new class of disordered (amorphous) superconductors with relatively high transition temperatures. The multilayers appear to exhibit quasi-two-dimensional superconductivity with controlled anisotropy. We discuss the properties of the multilayers as the thickness of the components of the bilayers vary.
We discuss an inverse approach for atomistic modeling of glassy materials. The focus is on structural modeling and electronic properties of hydrogenated amorphous silicon and glassy GeSe2 alloy. The work is based upon a new approach "experimentally constrained molecular relaxation (ECMR)". Unlike conventional approaches (such as molecular dynamics (MD) and Monte Carlo simulations(MC), where a potential function is specified and the system evolves either deterministically (MD) or stochastically (MC), we develop a novel scheme to model structural configurations using experimental data in associa…
Annealing of crystalline multilayers composed of two miscible elements usually causes interfacial mixing of the constituent atoms, possibly leading to the formation of binary alloys at the interfaces. Magnetron sputtered c-Ni/a-Zr multilayers deposited at room temperature were vacuum annealed isochronally at 200degC and 400degC to observe thermal stability of the interfaces constituting the crystalline/amorphous multilayers. Control over the interfacial behaviour can aid the formation of materials with novel properties. The resultant changes in structural and magnetic properties of the multila…
The dynamic response of dipole skyrmions in Fe/Gd multilayer films is investigated by ferromagnetic resonance measurements and compared to micromagnetic simulations. We detail thickness and temperature dependent studies of the observed modes as well as the effects of magnetic field history on the resonant spectra. Correlation between the modes and the magnetic phase maps constructed from real-space imaging and scattering patterns allows us to conclude the resonant modes arise from local topological features such as dipole skyrmions but does not depend on the collective response of a closed pac…
The amorphous-to-crystalline transition in Al(1.0%wtSi)/Zr and Al(Pure)/Zr multilayers grown by direct-current magnetron sputtering system has been characterized over a range of Al layer thicknesses (1.0-5.0 nm) by using a series of complementary measurements including grazing incidence X-ray reflectometry, atomic force microscopy, X-ray diffraction and high-resolution transmission electron microscopy. The Al layer thickness transition exhibits the Si doped in Al could not only disfavor the crystallization of Al, but also influence the changing trends of surface roughness and diffraction peak …
We examine the atomic intermixing phenomenon in three distinct amorphous CoB-based multilayer thin film platforms - Pt/CoB/Ir, Ir/CoB/Pt and Pt/CoB/MgO - which are shown to stabilise room-temperature chiral magnetic textures. Intermixing occurs predominantly between adjacent metallic layers. Notably, it is stack-order dependent, and particularly extensive when Ir sits atop CoB. Intermixing induced variations in magnetic properties are ascribed to the formation of magnetic dead layer arising from CoIr alloying in the metallic stacks. It also produces systematic variations in saturation magnetiz…
Hyperbolic metamaterials show exceptional optical properties, such as near-perfect broadband absorption, due to their geometrically-engineered optical anisotropy. Many of their proposed applications, such as thermophotovoltaics or radiative cooling, require high-temperature stability. In this work we examine Ag/a-Si multilayers as a model system for the thermal stability of hyperbolic metamaterials. Using a combination of nanotomography, finite element simulations and optical spectroscopy, we map the thermal and optical instability of the metamaterials. Although the thermal instability initiat…
