Search

We present the memristive (memory resistive) behavior in two different pulsed laser deposited BaTiO3/Nb doped SrTiO3 junctions. The first junction is controlled by space charge limited current (SCLC) conduction while the post-annealed junction is dominated by Schottky emission. The latter junction displays better ferroelectric and memristive properties (with an order of magnitude higher OFF/ON resistance ratio) as compared to the former junction with SCLC conduction. We attribute the improved behavior of the latter junction to the reduction of oxygen vacancies due to post-annealing of the film.

Current transport through a unique structure design employing high quality GaN based heterostructure with sharp interfaces has been investigated. A novel approach of structure design has been adopted to enhance the current transport in GaN heterostructures with a specific number of barrier layers of AlN which includes Single Barrier Heterostructure (SBH) and Double Barrier Heterostructure (DBH) devices. The high band gap AlN can act as a barrier for current conduction between GaN layers and help in effectively enhancing the current transport in the device through tunneling phenomena. A highly enhanced current transport in comparison with No Barrier Heterostructure (NBH) has been observed in SBH and a further improvement is perceived in DBH. Moreover, the phenomenon of current conduction is explained through drift-diffusion model, in which current enhancement upon subsequent addition of high bandgap barrier layer has resulted in localized high electric field and thus charge carrier velocity overshoots. Further, this has also been explained via quantum model, by interference of transmitted and reflected electron wave at interfaces. UV photodetectors using such heterostructure designs with and without AlN barrier layers in metal-semiconductor-metal geometry have been fabricated. The UV photodetection device developed using DBH yields photoresponsivity 80 times higher as compared to NBH device under UV illumination (325 nm). Employment of such structures will enable scaling up the production of highly efficient optoelectronic devices.

CSIR-NPL is the custodian of National standards of electrical and electronic parameters. These include DC parameters such as voltage, current and resistance; low frequency and high frequency impedance related quantities such as capacitance, inductance and AC resistance; AC/DC high voltage and AC high current; AC power and energy; and quantum standard which includes quantum hall resistance (QHR), quantum current (QC) and quantum nanophotonics (QN). The metrological traceability of the electrical and electronics parameters to SI units is derived from Josephson Voltage Standard (JVS), Quantum Hall Resistance (QHR) standard and frequency (time) standards; all of them are being maintained at CSIR-NPL with metrological precision at par with international standards. The traceability of the aforementioned parameters is disseminated through an unbroken chain of apex level calibrations and testing at par with international level to the industries and strategic sectors of the country to improve the quality of life, which in turn will lead to the inclusive growth of the country and economic development. R&D efforts on the development of quantum standards is a constant endeavour and continues to be at the forefront. Specifically, CSIR-NPL focuses on the development of quantum standards related to the unit of current (ampere), the unit of resistance (ohm) and quantum nanophotonics which aims for detection of few photons (or even single photons) using the novel concept of superconducting nanowire single photon detectors (SNSPD). Among these the research on QC needs special mention, as this will lead to realisation of the SI unit of electric current (ampere), the only unit out of the seven base units of SI system. The quantum current standard (QCS) realisation is bifurcated into two approaches, (i) based on the single electron tunnelling effect (SET) observable in semiconductor quantum dot (QD) structures and (ii) the quantum phase slip phenomenon (QPS) observable in superconducting nanowires of cross-sectional area of the order of coherence length of the system. The realisation of the resistance unit (ohm) is based on the quantum hall effect observable in semiconductor 2DEG structures such as GaAs/AlGaAs systems. Recently there has been tremendous evidence emerging for the use of monolayer graphene for the use of QHR metrology. CSIR-NPL also started the growth of “epitaxial graphene anchored on SiC” and have obtained encouraging results. The nano-photonics measurement research is also taken up actively for its applications to realize quantum standards for optical radiation and device fabrication.

Tuning of superconducting phase transition temperature (Ts) and interfacial magnetism is of great technological importance for micro and nanoelectronics. To achieve the cherished goal, an ultra-thin layer (4 nm, 6 nm, 8 nm 10 nm) of ferroelectrics PbZr0.48Ti0.52O3 (PZT) on high-temperature superconductor YBa2Cu3O7-δ (YBCO) has deposited to tailor the magnetic and superconducting properties. The existence of Meissner effect confirmed the superconducting nature of YBCO in the heterostructures. However, its Ts significantly shifted to the lower temperature side with an increase in PZT capping layers' thickness. Nearly 10 K reduction in Ts was observed with an increase in the capping layer from 4 to 10 nm. A significant amount of magnetic moment was found in the heterostructures, which increases almost three times compared to the YBCO/LAO magnetic moment above Ts. We believe novel weak magnetic phases above the Ts may be due to the re-arrangement of oxygen anion near the ferroelectric-superconducting interface.

We report the temperature dependent current (I) – voltage (V) characteristics of Fe3O4 nanowires with varying width (w) of 132, 358, and 709 nm. While the widest nanowire (w=709 nm) shows ohmic I (V) curves for all temperatures, those for w=132 and 358 nm show nonlinearity, which can be expressed by a combination of linear (V) and cubic (V3) terms. The behaviour of conductance (linear bias component of current) and non-linearity in these nanowires is related to small polaron hopping related conduction. Moreover, we observed an anomalously large hopping lengths, which may be related to the size of percolation cluster and/or antiphase domain. Our study presents first experimental evidence for such non-linear polaronic conduction in magnetite nanowires.

We have synthesized graphene film by the filtered cathodic vacuum arc (FCVA) technique and determined the number of layers in graphene films by various techniques. Amorphous carbon (a-C) films of different thicknesses (1, 2, 3, 6, 10 and 18 nm) were synthesized by the FCVA technique on Si/SiO2/Ni substrate and then annealed in vacuum at 800°C and cooled down to room temperature naturally to obtain graphene. Prepared graphene films were transferred on different substrates and characterized by the Raman spectroscopy, UV-VIS-NIR spectroscopy, high-resolution transmission electron microscopy (HRTEM), optical microscopy, atomic force microscopy (AFM) and sheet resistance to determine the number of layers present in the graphene films. Raman spectra of the prepared graphene films exhibit that there is red shift in the position of D, G and 2 D peak. The value of I2D/IG varied from 0.18 to 0.51, ID/IG varied from 0.82 to 1.02 and full width at half maximum of 2 D peak varied from 101.2 to 128.0 cm−1, for ...

We report the growth and polarization switching properties of epitaxial ferroelectric–superconducting heterostructure PbZr0.52Ti0.48O3 (PZT) (100 nm)/YBa2Cu3O7−δ (YBCO) (100 nm) thin films for non-volatile ferroelectric random access memory elements. The epitaxial nature of the heterostructure is verified using the reciprocal space mapping data with the superconducting phase transition temperature (Tc) of nearly 25 K far below the Tc of as-grown YBCO under the same condition. The significant remanent polarization (Pr) ∼ 45 µC/cm2 at 1 kHz can switch from one state to another using 1 μs pulse. The devices meet the basic criteria of memory elements, such as high resistance ∼10 GΩ at 8 V, a butterfly-like capacitance–voltage (C/V) loop, significant polarization, a sharp change in the displacement current, long-time charge retention, and small fatigue at room temperature.

We present a low cost and scalable technique for the synthesis of graphene using solid carbon source. Filtered cathodic vacuum arc technique (FCVA) has been utilized to deposit amorphous carbon (a-C) films of thickness of 3 and 6 nm on nickel film grown on SiO2/Si substrate. Subsequently, a-C films were annealed at 750 and 800 degrees C in vacuum and cooled naturally to room temperature for transforming a-C films into graphene. These graphene films consist of regions of few layers. These films have been characterized using micro Raman spectroscopy, atomic force microscopy, optical microscopy, scanning electron microscopy, high resolution transmission electron microscopy, transmittance and sheet resistance. Field effect transistor (FET) has also been fabricated using graphene to calculate the mobility. Transmittance, sheet resistance and mobility of graphene films are in the range of 85.5-89.3%, 540-720 Omega/square and similar to 725 cm(2) V-1 s(-1), respectively. The graphene derived from a-C films of 3 nm thickness showed minimum sheet resistance, maximum transmittance accompanied with the high mobility of FET. This demonstrates that the FCVA technique has potential to grow better quality graphene.

Ti-based bulk metallic glass (BMGs) and their bimodal composites are linked with the pronounced strain hardening after yielding but with much low value of strength. Therefore, developing Ti-based alloys with high yield strength and high plasticity is the current challenge. Here, we report the synthesis of ultra-fine grained bulk (UFG) (Ti 0.705 Fe 0.295 ) 100− x Ga x (0 ⩽ x ⩽ 2) bimodal eutectic composites with not only high strength and larger plasticity but also with high yield strength which is one of the important mechanical property for structural application. Reasonably high strength, high yield strength, strain to failure ratio, and enhanced plasticity of ∼7 ± 0.8% was observed in (Ti 70.5 Fe 29.5 ) 98 Ga 2 composite which is superior than Ti-based BMGs and bimodal composites. Modification of degree of eutectic structure refinement and volume fraction of constituent phases with the addition of Ga are the crucial factors in enhancing the mechanical properties of Ti–Fi–(Ga) composites.

We report formation of aligned nanostructures on epitaxially grown polar and nonpolar GaN films via wet chemical (hot H3PO4 and KOH) etching. The morphological evolution exhibited stress relaxed faceted nanopyramids, flat/trigonal nanorods and porous structures with high hydrophilicity and reduced wettability. The nanostructured films divulged significant suppression of defects and displayed an enhanced intensity ratio of the near band edge emission to the defect band. Extensive photoemission analysis revealed variation in oxidation state along with elimination of OH− and adsorbed H2O molecules from the chemically modified surfaces. Fermi level pinning, and alteration in the surface polarity with substantial changes in the electron affinities were also perceived. The temperature dependent current–voltage analysis of the nanostructured surfaces displayed enhancement in current conduction. The in-depth analysis demonstrates that the chemically etched samples could potentially be utilized as templates in the design/growth of III-nitride based high performance devices.

We discuss the design and development of a cryogenic set-up down to ~1.8 K for carrying out measurements on superconducting nanowire single-photon detectors. The set-up consists of two separate low-temperature inserts, one for electrical characterization and the other for optical measurements and characterization of single-photon detectors. A sample holder with necessary arrangements for precise alignment of laser light with the active area of the device to enhance optical coupling efficiency has been designed for the optical probe. The invar alloy has been used for the sample holder to ensure that the alignment is not disturbed at low temperature. Single-mode fibres due to their high transmission rate, minimum attenuation and least distortion have been used to shine light on the samples. The sample holder with 20-pin LCC socket and matching chip carrier provides convenient and fast sample mounting in the electrical insert. Mumetal has been employed to cover the sample space in both the inserts in order to attenuate any electromagnetic interference. Temperature stability with the passage of time has been monitored. It has been found that variation in temperature is less than 10 mK at the lowest operating temperature. Another important advantage of the system is its low enough liquid helium loss rate (~100 ml/h) with all inserts, which allows uninterrupted measurements for several days without any refilling of liquid helium.

We report the tunneling current behavior of magnetic-ferroelectric-superconducting heterostructures for multistates non-volatile random access memory (NVRAM) elements. A heterostructure of La0.67 Sr0.33 MnO3 (LSMO) (50 nm)/PbZr0.52 Ti0.48 O3 (PZT) (5 nm)/Bi-Sr-Ca-Cu2 -OX (BSCCO) (100 nm)/LaAlO3 (LAO) architecture was fabricated by pulsed laser deposition technique. The tunneling effects were investigated well above and below the superconducting phase transition temperature of the BSCCO bottom electrode. A divergent current and conductance paths were observed for polarization up and down direction above the coercive field of the ferroelectric tunnel barrier. This behaviour was significant below T s where the moderate effect of the external magnetic field was also observed on the tunneling current. The dynamic conductance G (V ) data fitted well with Brinkman's model for both polarizations up and polarization down states which suggest the presence of large tunnel electro-resistance.

Fabrication of niobium nitride (NbN) superconducting nanowires based on focused ion beam (FIB) milling and electron beam lithography (EBL) is presented. The NbN films were deposited using reactive magnetron sputtering. Argon-to-nitrogen ratio turned out to be a crucial factor in synthesizing high quality superconducting NbN. Critical temperatures (T c ) of around 15.5 K were measured for films with a thickness of around 10 nm. Zero-field-cooled magnetization was measured to optimize the superconducting properties of ultra thin NbN films. The transport behaviour was studied using conventional resistance vs temperature and current-voltage characteristics down to 2 K. Effect of gallium contamination on superconducting properties has been discussed. Whereas the various processing steps of standard EBL route do not have any significant impact on the superconducting transition temperature as well as on the transition width of nanowires, there is significant degradation of superconducting properties of nanowires prepared using FIB. This has been attributed to gallium ion implantation across the superconducting channel. Although the effect of gallium implantation may have technological limitations in designing fascinating single photon detector architectures, it provides some interesting low-dimensional superconducting properties.

We report the structural and electrical transport studies on CrN1-x (CrN) thin films with varying of N2 flow (5 – 25 SCCM) in an Argon environment of 25 SCCM. CrN thin films were grown at 600°C, in a multi chamber vacuum system at working pressure of 1×10−2 Torr, under the base pressure of 1×10−7 Torr. Structural and electrical transport measurements were carried out using X-ray diffraction (XRD), atomic force microscopy (AFM) and SQUID magnetometer, respectively. XRD (θ-2θ, ω-2θ, and ω) patterns on CrN thin films revealed a structural phase transition which is associated with the lattice parameter variation from 4.136 to 4.168 A. The temperature dependent resistivity measurements on CrN/MgO(001) showed a clear change in slope at ≈280 K which confirms the magneto-structural transition of CrN from paramagnetic rock salt face-centered-cubic (FCC) to antiferromagnetic orthorhombic structure.

Oxidation characteristics of colloidal silver nanoparticles produced by pulsed laser ablation in pure and chemically treated water are studied as a function of the degree of ozonization. The bright yellow colloidal solution of silver characterized by a sharp surface plasmon mode at ~400 nm, becomes colorless in the initial stages of O 3 flow, and then acquires a brown hue with a broad plasmon peak centered at ~440 to ~450 nm on further ozonization. The solution again becomes colorless in a few days once the O 3 flow is stopped. We present a qualitative model for the reaction dynamics and analyze the optical absorption in the framework of an effective medium theory. The aqueous phase laser ablation chemistry described here provides a unique means to produce ionic silver for enhanced antimicrobial effects.

Nanoparticles of a cobalt-platinum (CoPt) alloy near equiatomic composition, dispersed in a surfactant-polymer matrix, are synthesized using aqueous phase laser ablation. The magnetization dynamics of these particles is examined in the framework of the superparamagnetic blocking phenomenon based on a log-normal size distribution. Our analysis reveals, in accordance with electron microscopy results, two size distributions which peak at 1.3 and 5.9 nm. The magnetic anisotropy energy of these particles is 0.9 × 10 6 J m -3 and 0.1 × 10 6 J m -3 , respectively.

A comparative study of the superconducting transition temperature (Tc), crystallographic structure, and 2 MeV He+ ion channeling in La1.85Sr0.15CuO4 films deposited on SrLaAlO4 single crystals, and SrLaAlO4 and CaNdAlO4 buffer layers is presented. Rutherford backscattering (RBS) and ion channeling experiments suggest a non-zero misalignment in the growth directions of the LSCO and the buffer layer. The Tc of the films on buffer layers is lower by 8–10 K compared to the Tc of the films on SLAO crystals. However, annealing of these films in ozone leads to a distinct enhancement in the critical temperature.

Magnetic and electric field dependent charge transport in epitaxial films of La 0.7 Ca 0.3 MnO 3 deposited on (001) SrTiO 3 and LaAlO 3 substrates is compared as a function of the film thickness. A hysteretic and history dependent insulating behaviour and a strongly field dependent resistivity observed at small thicknesses suggest coexistence of charge ordered and ferromagnetically ordered regions in these films. This inhomogeneous film growth is presumably due to the lattice mismatch induced strain and atomic scale roughness of the substrates. It is shown that on SrTiO 3 substrates treated to obtain atomically flat TiO 2 terminated surfaces, films retain the metallic character of bulk La 0.7 Ca 0.3 MnO 3 down to 60 A thickness.

Filtered cathodic vacuum arc technique has been used to deposit amorphous carbon films of varying thickness on catalytic nickel thin film grown on SiO2/Si substrates. Subsequently these a-C films were annealed in vacuum at 650 °C. Raman spectroscopy together with optical microscopy and scanning electron microscopy has revealed multilayer graphene formation.

We report the Josephson coupling between optimally doped superconducting La1.85Sr0.15CuO4 through the normal metal barrier of La1.85Sr0.15Cu0.97Co0.03O4 (LSCCO). The critical current (Ic) across the junction exists even up to a barrier thickness of 50 nm. The barrier thickness dependence study of Ic yields a large coherence length in LSCCO of (15.2±1.4) nm at 5 K, which indicates the presence of giant proximity effect in such systems.

The multilayers of [Fe(5A)/Pt(25 A)]×15 were prepared by dc magnetron sputtering on 50 A Pt-buffered MgO substrates. The structural characterization of the multilayers was carried out using X-ray diffraction, X-ray reflectivity. The Secondary ion mass spectroscopy measurement reveals the depth profile and compositional modulations of the multilayer films as per our design specifications. Room temperature magnetic measurements were carried out by using SQUID both in-plane and out-of-plane sample geometry. Magnetization measurements show similar M-H loops for both in-plane and out-of-plane directions of external magnetic field with a coercivity of 190 Oe. These measurements indicate that our samples are magnetically soft and have multifunctional character which is important for making magnetic tunnel junctions.

Memristors are one of the most promising candidates for future information and communications technology (ICT) architectures. Two experimental proofs of concept are presented based on the intermixing of spintronic and memristive effects into a single device, a magnetically enhanced memristor (MEM). By exploiting the interaction between the memristance and the giant magnetoresistance (GMR), a universal implication (IMP) logic gate based on a single MEM device is realized.

We report on Boron diffusion and subsequent crystallization of Co$_{40}$Fe$_{40}$B$_{20}$ (CoFeB) thin films on SiO$_2$/Si(001) substrate using pulsed laser deposition. Secondary ion mass spectroscopy reveals Boron diffusion at the interface in both amorphous and crystalline phase of CoFeB. High-resolution transmission electron microscopy reveals a small fraction of nano-crystallites embedded in the amorphous matrix of CoFeB. However, annealing at 400$^\circ$C results in crystallization of CoFe with \textit{bcc} structure along (110) orientation. As-deposited films are non-metallic in nature with the coercivity (H$_c$) of 5Oe while the films annealed at 400$^\circ$C are metallic with a H$_c$ of 135Oe., Comment: 16 pages, 6 figures

Magnetotransport measurements are performed over a broad range of temperature (T) and magnetic field (H) on highly degenerate n-type Zn(1-x)Co(x)O [Formula: see text] epitaxial films. The cobalt-free samples are characterized by a metallic resistivity ρ(T) down to 2 K, a negative and predominantly isotropic magnetoresistance (MR) and optical transmission above 85% in the visible range of the electromagnetic spectrum. X-ray diffraction measurements show that while for [Formula: see text], all cobalt atoms occupy the tetrahedral sites of the wurtzite structure of ZnO, a phase separation into CoO is seen for x0.2. In the solution phase, we do not observe any signatures of a spontaneous ordering of the cobalt spins despite a large concentration of mobile electrons (10(20) cm(-3)). The absence of anomalous Hall resistance is consistent with this observation. The carrier concentration (n) over the entire range of x remains above the Mott limit for the insulator-to-metal transition in a doped semiconductor. However, while the Co-free samples are metallic (T2 K), we see a resistivity (ρ) minimum followed by lnT divergence of ρ(T) at low temperatures with increasing x. The magnetoresistance of these samples is negative and predominantly isotropic. Moreover, the MR tends to follow a logH behaviour at high fields. These observations, including the Kondo-like minimum in the resistivity, suggest s-d exchange dominated transport in these dilute magnetic semiconductors.

The effect of strain due to lattice mismatch and of ferromagnetic (FM) exchange field on superconductivity (SC) in NbN-CoPt bilayers is investigated. Two different bilayer systems with reversed deposition sequence are grown on MgO (001) single crystals. While robust superconductivity with high critical temperature (T_c ~ 15.3 K) and narrow transition width DelT_c ~ 0.4 K) is seen in two types of CoPt-NbN/MgO heterostructures where the magnetic anisotropy of CoPt is in-plane in one case and out-of-plane in the other, the NbN-CoPt/MgO system shows markedly suppressed SC response. The reduced SC order parameter of this system, which manifests itself in Tc, temperature dependence of critical current density J_c (T), and angular (Phi) variation of flux-flow resistivity Rho_f is shown to be a signature of the structure of NbN film and not a result of the exchange field of CoPt. The Rho_f (H,T,Phi) data further suggest that the domain walls in the CoPt film are of the Neel type and hence do not cause any flux in the superconducting layer. A small, but distinct increase in the low-field critical current of the CoPt-NbN couple is seen when the magnetic layer has perpendicular anisotropy., 9 figures

The effects of growth rate (G_r), deposition temperature (T_d), film thickness (t_F), and substrate induced strain (epsilon) on morphological, crystallographic and magnetic characteristics of equiatomic CoPt epitaxial films synthesized with PLD are investigated. The (001) substrates of MgO, STO and LAO provide different degree of epitaxial strain for growth of the disordered face centered cubic (fcc) and ordered face centered tetragonal (L1_0) phases of CoPt. The films deposited at T_d~600 ^0C on all three substrates are fcc with in-plane magnetization and a narrow hysteresis loop of width~200 Oe. The L1_0 phase, stabilized only at T_d~700 ^0C becomes predominantly c-axis oriented as T_d is increased to 800 ^0C. While the crystallographic structure of the films depends solely on the T_d, their microstructure and magnetization characteristics are decided by the growth rate. At the higher G_r (~1A/sec) the L1_0 films have a maze-like structure which converts to a continuous film as the t_F is increased from 20 to 50 nm. The H_c of these films increases as the L1_0 phase fraction grows with T_d and its orientation becomes out of the film plane. The evolution of microstructure with T_d is remarkably different at lower growth rate (~0.4A /sec). Here the structure changes from a self-similar fractal pattern to an assembly of nano-dots as the T_d is raised from 700 to 800 ^0C, and is understood in terms of the imbalance between strain and interfacial energies. MFM of such films reveals no distinct domain walls within the nano-islands while a clear contrast is seen between the islands of reversed magnetization. The simple picture of coherent rotation of moment appears incompatible with the time dependence of the remanent magnetization in these films., 10 figures

Thin film heterostructures provide a powerful means to study the antagonism between superconductivity (SC) and ferromagnetism (FM). One interesting issue in FM-SC hybrids which defies the notion of antagonistic orders is the observation of magnetic field induced superconductivity (FIS). Here we show that in systems where the FM domains/islands produce spatial inhomogeneities of the SC order parameter, the FIS can derive significant contribution from different mobilities of the magnetic flux identified by two distinct critical states in the inhomogeneous superconductor. Our experiments on nanoengineered bilayers of ferromagnetic CoPt and superconducting NbN where CoPt/NbN islands are separated by a granular NbN, lend support to this alternative explanation of FIS in certain class of FM-SC hybrids., Comment: 5 figures

The authors present a viable process to grow the high quality graphene films with control over number of layers by the filtered cathodic vacuum arc (FCVA) technique. In the FCVA process, the different carbon concentrations can be controlled by precisely tuning the arc time (1–4 s). The arc generated carbon was deposited on the nickel catalyst at 800 °C, annealed for 10 min, and cooled down to room temperature in the presence of hydrogen gas, resulting in the graphene films with control over number of layers. Prior to arcing, hydrogen etching of nickel was carried out to clean the surface of the substrate. A growth model to prepare the high quality graphene has also been proposed. The as-grown graphene films were transferred to different substrates and are characterized by Raman spectroscopy, optical microscopy, high resolution transmission electron microscopy, and atomic force microscopy to determine the number of layers present in these films. Raman spectra of the prepared graphene films exhibit change i...

The temperature dependent resistance R(T) of polycrystalline ferromagnetic CoFeB thin films of varying thicknesses are analyzed considering various electrical scattering processes. We observe a resistance minimum in R(T) curves below similar or equal to 29 K, which can be explained as an effect of the intergranular Coulomb interaction in a granular system. The structural and Coulomb interaction related scattering processes contribute more as the film thickness decreases implying the role of disorder and granularity. Although the magnetic contribution to the resistance is the weakest compared to these two, it is the only thickness independent process. On the contrary, the negative coefficient of resistance can be explained by the electron interaction effect in disordered amorphous films.

We have investigated the effect of ferroelectric barium titanate (BaTiO3) film thickness on the charge transport mechanism in pulsed laser deposited epitaxial metal–ferroelectric semiconductor junctions. The current (I)–voltage (V) measurements across the junctions comprising of 20–500 nm thick BaTiO3 and conducting bottom electrode (Nb: SrTiO3 substrate or La2/3Ca1/3MnO3 buffer layer) demonstrate the space charge limited conduction. Further analysis indicates a reduction in the ratio of free to trapped carriers with increasing thickness in spite of decreasing trap density. Such behaviour arises the deepening of the shallow trap levels (

The effect of temperature on the nature of metal-semiconductor system in a Au contact deposited on c-plane and a-plane GaN film was investigated by current–voltage (I–V) measurements. The I–V measurements have been obtained systematically at different temperatures ranging from room temperature (300 K) to low temperature (78 K). Photoluminescence measurements were obtained to investigate correlation between the growth conditions, the substrate used for the growth of GaN film, and the presence of deep level defects therein by equating with the yellow band luminescence. The resistance–voltage–temperature analysis indicates that a gradual shift of the nature of contact towards Schottky behavior takes place while moving from room temperature to low temperature. Additionally, memory effect like aberration is present at low temperature, which can be attributed to the presence of deep-level defects and carrier recombination therein.

High coercivity nanoscale structures of CoPt are grown on (001) SiTiO3 with pulsed laser ablation. At low growth rate (≃0.4A∕s), the film morphology changes from a self-similar fractal to nanodots as the deposition temperature is raised from 700to800°C. While the nanodots are L10 ordered phase with out-of-plane c axis and coercivity Hc⊥≃30kOe, the fractals have a nonzero, in-plane c-axis component of the L10 phase. The large lattice mismatch between (001) SrTiO3 and the ac∕bc plane of L10 imparts tensile strain to the films whose morphological manifestations can be suppressed at high growth rates.