Sn Bilayer Research Articles

Structural, optical, photoluminescence and electrical properties of p-CuO/n-ZnO:Sn and p-CuO/n-[formula omitted]-Fe2O3 efficient hetero-junctions for optoelectronic applications

p-CuO/n-ZnO:Sn and p-CuO/n-α-Fe2O3 novel hetero-junctions were synthesized by chemical spray pyrolysis (CSP) technique. These two bilayers were dealing with films deposited on top of each other. The substrate (ZnO:Sn/glass or α-Fe2O3/glass) effect on the physical properties of CuO thin layers was studied. X-ray diffraction (XRD), scanning electron microscopy (SEM), fluorescence spectrometer, spectrophotometer and impedance spectroscopy were used to investigate respectively, structural, morphological, photoluminescence, optical and electrical characteristics. The CuO films with crystallite size ranging from 36.32 to 39.14 nm were formed in good crystalline quality without detection of secondary phases. Principal optical studies revealed that the two hetero-junctions exhibited a high reflection in the near infrared field (between 27 and 47 %) but the p-CuO/n-ZnO:Sn hetero-junction presented a band gap energy (1.5 eV) larger than that of p-CuO/n-α-Fe2O3 one (1.2 eV). Moreover, these two hetero-junctions exhibited the same emission peaks at 403 nm (3.08 eV), 418 nm (2.96 eV) and 493 nm (1.55 eV) with accentuated intensity for the p-CuO/n-α-Fe2O3 bilayer but best electrical parameters were found for the p-CuO/n-ZnO:Sn one. The photo-catalytic degradation of methylene blue (MB) dye under sunlight irradiation was investigated for all grown hetero-junctions. The p-CuO/n-ZnO:Sn bilayer structure showed the highest efficiency around 97 % after 5 h of sunlight irradiation.

Voltage controllable superconducting state in the multiterminal superconductor–normal-metal bridge

We study voltage controllable superconducting state in multi-terminal bridge composed of the dirty superconductor/pure normal metal (SN) bilayer and pure normal metal. In the proposed system small control current $I_{ctrl}$ flows via normal bridge, creates voltage drop $V$ and modifies distribution function of electrons in connected SN bilayer. In case of long normal bridge the voltage induced nonequilibrium effects could be interpreted in terms of increased local electron temperature. In this limit we experimentally find large sensitivity of critical curent $I_c$ of Cu/MoN/Pt-Cu bridge to $I_{ctrl}$ and relatively large current gain which originate from steep dependence of $I_c$ on temperature and large $I_c$ (comparable with theoretical depairing current of superconducting bridge). In the short normal bridge deviation from equilibrium cannot be described by simple increase of local temperature but we also theoretically find large sensitivity of $I_c$ to control current/voltage. In this limit we predict existence at finite $V$ of so called in-plane Fulde-Ferrell state with spontaneous currents in SN bilayer. We argue that its appearance is connected with voltage induced paramagnetic response in N layer.

Approaching depairing current in dirty thin superconducting strip covered by low resistive normal metal

We experimentally demonstrate that a thin dirty superconducting (S) strip covered by low resistive normal metal (N) approaches closer to the depairing current than a single S strip, which makes its non-linear properties stronger. The obtained result comes from proximity-induced superconductivity in the N layer, its large contribution to the superconducting properties of the SN bilayer and larger sensitivity to the current than that of the host S layer. We argue that such an SN bilayer could be a promising system for different applications based on the current-dependent kinetic inductance. In addition, we also find that in the presence of the N layer the maximal vortex velocity in the resistive state considerably increases.

A Josephson junction based on a highly disordered superconductor/low-resistivity normal metal bilayer.

We calculate the current–phase relation (CPR) of a SN-S-SN Josephson junction based on a SN bilayer of variable thickness composed of a highly disordered superconductor (S) and a low-resistivity normal metal (N) with proximity-induced superconductivity. In such a junction, the N layer provides both a large concentration of phase in the weak link and good heat dissipation. We find that when the thickness of the S and the N layer and the length of the S constriction are about the superconducting coherence length the CPR is single-valued and can be close to a sinusoidal shape. The product IcRn can reach Δ(0)/2|e| (Ic is the critical current of the junction, Rn is its normal-state resistance, Δ(0) is the superconductor gap of a single S layer at zero temperature). Our calculations show, that the proper choice of the thickness of the N layer leads both to nonhysteretic current–voltage characteristics even at low temperatures and a relatively large product IcRn.

The Proximity and Josephson Effects in Niobium Nitride–Aluminum Bilayers

Highly disordered thin films of niobium nitride and the specific features of the proximity effect in NbN (S)–aluminum (N) bilayers with a large resistivity ratio, ρNbN/ρAl $$ \gg $$ 1, are studied. It is shown that magnetic screening and the critical current Ic of such SN structures significantly increase compared to the S layer. The observed effect is associated with the induced superconductivity in the N layer due to the proximity effect. The Josephson effect is demonstrated in NbN/Al–NbN–NbN/Al variable thickness bridges made of such SN bilayers.

Эффекты близости и Джозефсона в бислоях из нитрида ниобия и алюминия

The highly disordered thin films of niobium nitride and features of the manifestation of the proximity effect in the NbN (S) –Aluminium (N) bilayers with a high ratio of their specific resistances NbN / Al >> 1were investigated. It was shown that the magnetic screening and critical current Ic of such SN structures significantly increase compared with the S layer. The observed effect is associated with the appearance of induced superconductivity in the N layer due to the proximity effect. The Josephson effect was demonstrated in the variable thickness bridges NbN / Al - NbN - NbN / Al made from such SN bilayers.

Peculiar superconducting properties of a thin film superconductor–normal metal bilayer with large ratio of resistivities

Developing the earlier results of Aslamazov et al (1986 Sov. Phys. JETP 64 1051) we perform a detailed study of the superconducting properties of a bilayer consisting of highly disordered superconducting (S) and low-resistive normal metal (N) films. We demonstrate theoretically and experimentally that the screening and transport properties of such a SN bilayer can be considerably enhanced compared with the single S film. Such modification originates from the proximity-induced superconductivity in the N film and it is not related to enhanced vortex pinning in the SN hybrid. In particular, the coverage of superconducting NbN and MoN films by a thin Ag or Al layer is responsible for enhancing the diamagnetic response and the critical current Ic of the SN microbridge by several times and the appearance of the diode effect in a parallel magnetic field. Due to peculiar temperature dependence of Ic and the magnetic field penetration depth, such SN bilayers can be of potential interest for designing different types of superconducting bolometers and detectors.

Fabrication of p-type BaCuSF and n-type In2O3:Sn bilayer films and their applications to the back contact of CdS/CdTe solar cells

For applications to polycrystalline thin-film tandem solar cells, we studied p-type conductive BaCuSF single layer and p-type BaCuSF and n-type In2O3:Sn (ITO) bilayer films. The BaCuSF films were prepared by pulsed laser deposition (PLD), and the ITO films were prepared by RF sputtering. The bilayer film showed ohmic current–voltage characteristic. A tunnel junction between these two layers was successfully fabricated, because p-type BaCuSF and n-type ITO layers had sufficiently high carrier concentrations. The BaCuSF/ITO bilayer films were employed as the back electrodes of CdS/CdTe solar cells. A CdTe solar cell with a 20-nm-thick BaCuSF/a 300-nm-thick ITO bilayer back contact showed a high conversion efficiency of 13.9% (VOC = 818 mV, JSC = 25.2 mA/cm2, and FF = 0.675), which was higher than that of a CdTe solar cell with a BaCuSF single-layer back contact (11.1%). The efficiency is comparable to that of a CdTe solar cell with a SrCuSeF/ITO bilayer back contact (14.3%).

Fabrication of p-type SrCuSeF/n-type In2O3:Sn bilayer ohmic tunnel junction and its application to the back contact of CdS/CdTe solar cells

To develop polycrystalline thin-film tandem solar cells, a SrCuSeF/In2O3:Sn (ITO) bilayer film was studied. The transparent p-type conductive SrCuSeF layer was deposited by pulsed laser deposition (PLD), and the n-type conductive ITO layer was deposited by RF sputtering. The SrCuSeF/ITO bilayer film showed ohmic I–V characteristics. A tunnel junction between the p-type SrCuSeF and n-type ITO layers was successfully formed because the p-type SrCuSeF and the n-type ITO layers had sufficiently high carrier concentrations. The SrCuSeF/ITO bilayer film was applied as the back contact of a CdS/CdTe solar cell. The photovoltaic performance of the CdS/CdTe solar cell depends considerably on the thickness of the SrCuSeF layer. The CdTe solar cell with a back contact of the SrCuSeF layer with a thickness of 34 nm and the ITO layer with a thickness of 200 nm showed a high conversion efficiency of 14.3% (VOC = 804 mV, JSC = 27.5 mA/cm2, and FF = 0.65). The conversion efficiency was much higher than that of the CdTe solar cell with the SrCuSeF single-layer back contact (11.6%) and that of the CdTe cell with the ITO single-layer back contact (2.75%).

Quantum phase transitions in Sn bilayer based interfacial systems by an external strain.

Using first-principle calculations, we report for the first time, the changes in electronic structures of a single bilayer Sn stacked on a single bilayer Sb(Bi) and on a single quintuple layer Sb2Te3 induced by both interface polarization and strain. With BL Bi and QL Sb2Te3 substrates, the stanene tends to have a low-buckled configuration, whereas with BL Sb substrate, the stanene prefers to form high-buckled configurations. For strained Sn/Sb(Bi) system, we find that the Dirac cone state is not present in the band gap, whereas in strained Sn/Sb2Te3 system, spin-polarized Dirac cone can be introduced into the band gap. We discuss why tensile strain can result in the Dirac cone emerging at the K point based on a tight-binding lattice model. This theoretical study implies the feasibility of realizing quantum phase transitions for Sn thin films on suitable substrates. Our findings provide an effective manner in manipulating electronic structures and topological states in interfacial systems by using interface polarization and strain, which opens a new route for realizing atomically thin spintronic devices.

Dependence of intermetallic compound formation on the sublayer stacking sequence in Ag–Sn bilayer thin films

Intermetallic compound (IMC) formation in thermally-evaporated Ag–Sn bilayer thin films has been investigated employing especially X-ray diffraction (XRD) and (S)TEM methods. The specific IMCs that are present in the as-deposited state depend sensitively on the stacking sequence of the sublayers. In case of Sn on top of Ag, predominantly Ag3Sn is formed, whereas Ag4Sn is predominantly present in the as-deposited state for Ag on top of Sn. In the latter case this is accompanied by an extremely fast uptake of a large amount of Sn by the Ag sublayer, leaving behind macroscopic voids in the Sn sublayer. The results are discussed on the basis of the thermodynamics and kinetics of (IMC) product-layer growth in thin films. It is shown that both thermodynamic and kinetic arguments explain the contrasting phenomena observed.

Effects of deposition method on the microstructure and intermetallic compound formation in Ag–Sn bilayers

Abstract Thermal evaporation and magnetron sputtering were used for the deposition of bilayers of Ag and Sn with different stacking sequences of the sublayers, Ag on Sn (Ag/Sn) or Sn on Ag (Sn/Ag). The deposition method used significantly affects the intermetallic compound (IMC) formation in these thin films already during film deposition. Comparison of the corresponding microstructures and textures indicates that the observed, striking differences in IMC formation for the case of Ag/Sn bilayers can be related to the interplay of Sn upward diffusion, surface energy and interfacial intermixing for the two deposition methods.

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 Cu6Sn5 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(100nm)/Cu(50nm) system, the value of the parabolic growth rate coefficient at room temperature is 2.3×10−15cm2/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 0.5nm/h.

Interplay of strain and interdiffusion in Heusler alloy bilayers

Combining conventional and inverse magnetocaloric materials promises to enhance solid state refrigeration. As a first step here we present epitaxial Ni–Mn–Ga/Ni–Mn–Sn bilayer films. We examine the dependence of the lateral and normal lattice constants on the deposition sequence by combining experimental and ab initio techniques. Structural properties are determined with X‐ray diffraction as well as highresolution transmission electron microscopy, while ab initio calculations explain the interplay of strain, local relaxations and the interdiffusion of atoms. The latter is confirmed by Auger electron spectroscopy and is expected to have a noticeable impact on the functional properties of the Heusler materials. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Separation Characteristics of an LMPA-Polymer Mixture for the Encapsulation of Organic Light-Emitting Diode

An encapsulation method using the separation of low melting point alloy (LMPA) and a polymer from an LMPA-polymer mixture is proposed. Sn-Bi alloy and epoxy were used for the mixture. Separation was conducted using a two-step heat treatment of 160 °C for 5 min and 180 °C for 5 min. We found that the flux contained in the Sn-Bi solder played an important role in the separation process. A Cu sacrificial layer was introduced using the sputtering method under the Sn-Bi layer with thickness variations of 1500, 3000, and 6000 A. Using the 6000-A-thick Cu layer, the LMPA formed a well-separated and continuous sealing line. This double-line structure shows good potential for use as a sealing line for organic light-emitting diode encapsulation.

Gas Immersion Laser Doping for superconducting nanodevices

We have conceived and fabricated Superconductor/Normal metal/Superconductor Josephson junctions made entirely of boron doped Silicon. We have used Gas Immersion Laser Doping to fabricate SN bilayers with good ohmic interfaces and well controlled concentration and doping depth. Standard fabrication processes, optimised for silicon, were employed to nanostructure the bilayers without affecting their transport properties. The junctions thus fabricated are proximity superconducting and show well understood I–V characteristics. This research opens the road to all-silicon, non-dissipative, Josephson Field Effect Transistors.

SN@silicate: an anionic dye sorbent and its reuse

It is difficult for dye-synthesizing wastewater to be treated efficiently together with eco-friendly disposal of dye sludge. Octadecyl dimethyl hydroxyethyl quaternary ammonium (SN) was hybridized with magnesium silicate, and then characterized by various techniques. The SN bilayer stacking via hydrophobic interactions intercalated into the magnesium silicate sheets and caused an interlayer increase to 4.9 nm. More than 40% SN was embedded so that the hybrid contained a large number of positive charges and hydrophobic areas. It exhibited a faster adsorption to anionic dyes with higher capacities from 108 to 553 mg g−1 than for conventional sorbents. In addition, it captured microcystin-LR from water according to the lipid-water partition model. The resultant dye sludge was added into epoxy top coating and paint to fabricate colored films with an electric resistance decrease to 0.75 × 107 Ω. The facile preparation of such a functional material provided a “killing two birds with one stone” approach, from treatment of dye wastewater to disposal of the dye sludge, turning it to an antistatic colorant.

Proximity effect inNb∕Cu∕CoFetrilayers

We have fabricated $\mathrm{Nb}∕\mathrm{Cu}∕\mathrm{CoFe}$ trilayers, varying the thickness of the Cu or $\mathrm{CoFe}$ layer in order to control the coupling between the superconductivity and the ferromagnetism. The ${T}_{c}$ behavior of the $\mathrm{Nb}∕\mathrm{Cu}$ bilayer exhibits the well-known proximity effect of an SN bilayer. In a $\mathrm{Nb}∕\mathrm{Cu}∕\mathrm{CoFe}$ trilayer with the thicknesses of the Nb and $\mathrm{CoFe}$ layers fixed, the ${T}_{c}$ values increase on two different scales of length as the thickness of the Cu layer increases: one with a length scale of about $2\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ when the Cu layer is less than $5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in thickness and the other with a length scale of about $68\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, the normal coherence length of Cu, when the Cu layer is larger than $5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in thickness. Furthermore, in a similar manner to the case of $\mathrm{Nb}∕\mathrm{CoFe}$, the ${T}_{c}$ behavior of a $\mathrm{Nb}∕\mathrm{Cu}∕\mathrm{CoFe}$ trilayer as a function of $\mathrm{CoFe}$ thickness shows a small dip structure. By employing Usadel formalism, we deduced all the relevant parameters that can explain our data in a consistent manner. In spite of the better interfaces in the $\mathrm{Nb}∕\mathrm{Cu}∕\mathrm{CoFe}$ system, no ${T}_{c}$ oscillation as a function of the Cu thickness was observed, in contrast to the $\mathrm{Nb}∕\mathrm{Au}∕\mathrm{CoFe}$ system. We will discuss the difference and similarity between the $\mathrm{Nb}∕\mathrm{Cu}∕\mathrm{CoFe}$ and $\mathrm{Nb}∕\mathrm{Au}∕\mathrm{CoFe}$ systems.

Abrikosov vortex core structure in a proximity-effect multilayer

The core structure of the Abrikosov vortex perpendicular to the layers of a proximity effect SN multilayer is discussed. We assume that the superconducting correlations are induced in N via the proximity effect and the dirty limit conditions are fulfilled. The approach for calculation of the local densities of states in N and S layers is developed in the framework of the quasiclassical Usadel equations. For the practically interesting case of SN bilayer, relevant to the STM spectroscopy, the densities of states and apparent STM vortex-core radius, related to the energy-dependent coherence length in N, are calculated.