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Evolution of structural and magnetic properties in a nickel/chromium (Ni/Cr) multilayer, as a function of different annealing temperatures was investigated. The Ni/Cr multilayer of nominal structure [Cr (50 Å)/Ni (50 Å)]×10/Cr (30 Å) was grown on a Si substrate by radio frequency ion beam sputtering at room temperature. X-ray diffraction, X-ray reflectometry, atomic force microscopy and crossectional scanning electron microscopy were employed for the complete structural characterization of the multilayer whereas superconducting quantum interference device vibration sample magnetometer was used for the bulk magnetisation study. The effect of in-situ and ex-situ annealing on overall structural property of the multilayer also reported in present work. From in-situ X-ray reflectometry (50–400 °C), 300 °C was detected as the optimum temperature for improved structural properties of the Ni/Cr multilayer. Initiation of alloying in the multilayer sample was noticed at 350 °C. The multilayer found to exhibit polycrystalline nature observed by X-ray diffraction. Total thickness of the multilayer system was confirmed by crossectional scanning electron microscopy and in well agreement with X-ray reflectivity results. The Ni/Cr sample found to exhibit soft ferromagnetic behaviour after annealing at 300 °C and 400 °C. However the net magnetic moment reduced upon annealing at higher temperature (400 °C).

We investigated the structural and optical properties of nanoparticle-assisted pulsed laser-deposited ZnO microrods and Au-coated ZnO microrods grown on Si substrate. Our present study indicates that Au-coated ZnO microrods exhibit whispering gallery modes (WGM) in the near band edge region with significant splitting into two branches. Moreover, the WGMs exhibited blue shift with decrease in rod size. We found that the modes are well split in Au coated ZnO rods when compared with as-grown rods, resulted from the plasmon enhancement of WGM modes. We also found that the Au-coated ZnO was stable in the ambient when compared with uncoated ZnO. WGM resonance from the exciton related emission, the enhancement in WGMs, and stability in the ambient condition of the Au-coated ZnO microrods suggest great potential for small-volume devices and microlasers.

Discovery of two-dimensional (2D) topological insulators (TIs) demonstrates tremendous potential in the field of thermoelectric since the last decade. Here, we have synthesized 2D TI, Sb2Te3 of various thicknesses in the range 65–400 nm using mechanical exfoliation and studied temperature coefficient in the range 100–300 K using micro-Raman spectroscopy. The temperature dependence of the peak position and line width of phonon modes have been analyzed to determine the temperature coefficient, which is found to be in the order of 10–2 cm−1/K, and it decreases with a decrease in Sb2Te3 thickness. Such low-temperature coefficient would favor to achieve a high figure of merit (ZT) and pave the way to use this material as an excellent candidate for thermoelectric materials. We have estimated the thermal conductivity of Sb2Te3 flake with the thickness of 115 nm supported on 300-nm SiO2/Si substrate which is found to be ~ 10 W/m–K. The slightly higher thermal conductivity value suggests that the supporting substrate significantly affects the heat dissipation of the Sb2Te3 flake.

With the 200 keV N+-ion implantation technique and a systematic variation of fluence, we report on the formation of highly conducting n-type diamond where insulator-to-metal transition (IMT) is observed above a certain fluence wherein the conductivity no longer obeys the hopping mechanism of transport rather, it obeys quantum corrections to Boltzmann conductivity at concentrations of nN ≥ 2 × 1020 cm−3. The conductivity for ultra-nanocrystalline diamond is found to be high, ∼650 Ω−1 cm−1 with thermal activation energy Ea ∼ 4 meV. Interestingly, with gradual increase in fluence, the conductivity in polycrystalline diamond films has been seen to progress from the hopping mechanism of transport in the case of low fluence implantation to a semiconducting nature with medium fluence and finally a semi-metallic conduction is observed where percolation occurs giving an insulator-to-metal transition. XANES confirms that the long-range order in diamond films remains intact when implanted with low and medium fluences; while implantation at sufficiently high fluences >5 × 1016 cm−2 leads to the formation of a disordered tetrahedral amorphous carbon network leading to metallic conduction resembling a metallic glass behaviour. XPS confirms that the sp2 fraction increases gradually with fluence starting from only 6% in the case of low fluence implantations and saturates at 40–50% for implantation at high fluences. A similar observation can be made for single crystal diamond when implanted at high fluence; it retains long-range order but percolative transport takes place through defects or semi-amorphized regions.

Substitution of alkali earth metal ion of Sr2+, in the Pb2+ site of Pb(Mg1/3Nb2/3)O3–PbTiO3 is expected to induce functional modulations in the system. Doping of 4 at.% of Sr2+ in 0.68PMN-0.32PT was carried out to lower the transition temperature, and to investigate the intended ferroelectric and dielectric variations. Excellent relaxor property was observed in the doped sample without appreciable reduction in remnant polarization. Doping with Sr2+ led to a reduction in transition temperature from 165 °C to 117 °C. Doped sample exhibited remnant polarization Pr = 16.2 μC/cm2, Squareness factor (Rsq) = 1.05 and Relaxor exponent (γ) around 2. Modulation in the functional response was exhibited by the doped composition, having low transition temperature, and its prospect in electrocaloric applications was analyzed.

The continuous depletion of fossil fuels and the increasing demand for eco-friendly and sustainable energy sources have prompted researchers to look for alternative energy sources. The loss of thermal energy in heat engines (100 °C–350 °C), coal-based thermal plants (150 °C–700 °C), heated water pumping in the geothermal process (150 °C–700 °C), and burning of petrol in the automobiles (150 °C–250 °C) in form of untapped waste-heat can be directly and/or reversibly converted into usable electricity by means of charge carriers (electrons or holes) as moving fluids using thermoelectric (TE) technology, which works based on typical Seebeck effect. The enhancement in TE conversion efficiency has been a key challenge because of the coupled relation between thermal and electrical transport of charge carriers in a given material. In this review, we have deliberated the physical concepts governing the materials to device performance as well as key challenges for enhancing the TE performance. Moreover, the role of crystal structure in the form of chemical bonding, crystal symmetry, order–disorder and phase transition on charge carrier transport in the material has been explored. Further, this review has also emphasized some insights on various approaches employed recently to improve the TE performance, such as, (i) carrier engineering via band engineering, low dimensional effects, and energy filtering effects and (ii) phonon engineering via doping/alloying, nano-structuring, embedding secondary phases in the matrix and microstructural engineering. We have also briefed the importance of magnetic elements on thermoelectric properties of the selected materials and spin Seebeck effect. Furthermore, the design and fabrication of TE modules and their major challenges are also discussed. As, thermoelectric figure of merit, zT does not have any theoretical limitation, an ideal high performance thermoelectric device should consist of low-cost, eco-friendly, efficient, n- or p-type materials that operate at wide-temperature range and similar coefficients of thermal expansion, suitable contact materials, less electrical/thermal losses and constant source of thermal energy. Overall, this review provides the recent physical concepts adopted and fabrication procedures of TE materials and device so as to improve the fundamental understanding and to develop a promising TE device.

Here, we report the fabrication of ZnO/p-GaN based high responsivity ultraviolet (UV) photodetector. Hydrothermal technique has been followed to grow ZnO nanorods; where two different types of precursors (nitrate and chloride) were used for the growth of nanorods. Interestingly, it was found that the ZnO nanorods grown using nitrate precursor are less prone to defect emission in comparison to the ZnO nanorods prepared using chloride-based precursor which resulted in low dark current levels. The photo-responsivity and photo-detectivity values of the as-fabricated device were calculated to be 350 mA W−1 and 3.5 × 1011 Jones, respectively at 360 nm excitation wavelength and ∼1.79 µW cm−2 excitation intensity. The demonstration of high responsivity UV detectors (at low excitation intensity values) using ZnO nanorods/GaN can pave the way toward the development of high-performance next generation UV photodetectors.

We have made an attempt to fabricate free standing warpage free PZT thick films of 100 µm thickness by tape casting method. The poly crystalline nature and nanoscale polarization switching of free ...

We report on the fabrication of ZnO and Zn0.9Mg0.1O microrods using nanoparticle assisted pulsed laser deposition (NAPLD). Micro-photoluminescence studies reveal that Zn0.9Mg0.1O microrods exhibited a blue shift in the ultraviolet (UV) emission relative to unintentionally doped ZnO that was attributed to the increase in bandgap due to Mg doping. High-resolution micro-photoluminescence clearly indicated the presence of whispering gallery modes (WGMs) for both ZnO and Zn0.9Mg0.1O. Transverse electric (TE) and transverse magnetic (TM) optical WGMs were identified using the existing plane-wave model. The observation of lower order WGM modes in Zn0.9Mg0.1O microrods may be of great interest for future UV WGM lasing.

Machining of Al-SiC metal matrix composite (MMC) is still being a challenging task in the automotive and aerospace sector due to its frequent tool wear while processing this MMC. The hard Polycrystalline diamond tools (PCD) are used as a cutting tool in many sectors for machining of MMC. But the usage of PCD is commercially not viable due to its high cost involved in the fabrication. In this regard, low-cost diamond-coated tungsten carbide (WC-Co) tools are considered as an alternative to PCD. However, the diffusion of cobalt from WC-Co during diamond deposition promotes higher graphitization at the diamond-carbide interface. This induces coating delamination during MMC machining. This outward diffusion of cobalt can be hindered by doping boron in the diamond lattice to enhance adhesion strength of the coating. Hence in this work, the boron doped graded layer diamond coating (BDD/transition layer/NCD) on WC-Co was proposed to improve the machining performance of MMC. In this work, four different CVD diamond coated WC-Co tools such as microcrystalline diamond coating (MCD), nano-crystalline diamond coating (NCD), boron-doped diamond coating (BDD) were considered for comparison along with the proposed tools. The different phases (sp3 and sp2) in the diamond coating were analyzed through cross-sectional Raman mapping technique. The Rockwell indentation test confirms that the better adhesion strength obtained in BMTN coated tools. The wear behavior of these diamond coated tools was tested by machining of AA2124/25%SiCp material. In addition, performances of these tools were compared with widely accepted industrial grade PCD tools. The temperature at the cutting zone, chip morphology and surface roughness of the machined component were studied through an appropriate test method. The occurrence of edge chipping while machining was continuously monitored through acoustic emission (AE) signals. The machining results show that BMTN coated tool exhibits least tool wear (VB = 0.25 mm) in comparison with MCD (VB=0.47 mm), NCD (VB=0.57 mm), BDD (VB= 0.33 mm) coated tools and PCD (VB = 0.29 mm) tools respectively. In addition, the results of AE signals show that MCD, NCD coated tools and PCD tools undergone edge chipping whereas there was no edge chipping observed in BDD and BMTN tools. Thus Nano –Engineered BMTN tools observed to be a preferred cutting tool for efficient machining of Al-SiC MMC material.

Cubic silicon carbide (3C-SiC) films were grown by pulsed laser deposition (PLD) on magnesium oxide [MgO (100)] substrates at a substrate temperature of 800°C. Besides, p-type SiC was prepared by laser assisted doping of Al in the PLD grown intrinsic SiC film. The SiC phases, in the grown thin films, were confirmed by x-ray diffraction (XRD), Si–C bond structure is identified by Fourier-transform infrared spectroscopy spectrum analysis. Measurements based on the XRD and Raman scattering techniques confirmed improvement in crystallization of 3C-SiC thin films with the laser assisted doping. The studies on I–V characteristics by two probe technique, elemental analysis by energy dispersion spectrum, binding energy by x-ray photoelectron spectroscopy and carrier concentration by Hall effect, ensured Al doping in SiC thin film. From the UV–visible NIR spectroscopic analysis, the optical bandgap of the PLD grown 3C-SiC was obtained. Numerical analysis of temperature and carrier concentration distribution is simulated to understand the mechanism of laser assisted doping.

International audience; We explored the time dependence of the nanoscale domain relaxation mechanism in epitaxial K0.5Na0.5NbO3 (KNN) thin films grown on La0.67Sr0.33MnO3/SrTiO3 (001) substrates over the thickness range 20− 80 nm using scanning probe microscopy. Kelvin probe force microscopy (KFM) and piezoresponse force microscopy were performed on pulsed-laser-deposition-deposited KNN thin films for studying the time evolution of trapped charges and polarized domains, respectively. The KFM data show that the magnitude and retention time of the surface potential are the maxima for 80 nm-thick film and reduce with the reduction in the film thickness. The charging and discharging of the samples reveal the easier and stronger electron trapping compared to hole trapping. This result further indicates the asymmetry between retention of the pulse-voltage-induced upward and downward domains. Furthermore, the time evolution of these ferroelectric nanodomains are found to obey stretched exponential behavior. The relaxation time (T) has been found to increase with increase in thickness; however, the corresponding stretched exponent (β) is reduced. Moreover, the written domain can retain for more than 2300 min in KNN thin films. An in-depth understanding of domain relaxation dynamics in Pb-free KNN thin films can bridge a path for future high-density memory applications.

Frustrated magnets based on oxide double perovskites offer a viable ground wherein competing magnetic interactions, macroscopic ground state degeneracy and complex interplay between emergent degrees of freedom can lead to correlated quantum phenomena with exotic excitations highly relevant for potential technological applications. By local-probe muon spin relaxation ($$\mu$$ μ SR) and complementary thermodynamic measurements accompanied by first-principles calculations, we here demonstrate novel electronic structure and magnetic phases of Ba$$_{2}$$ 2 MnTeO$$_{6}$$ 6 , where Mn$$^{2+}$$ 2 + ions with S = 5/2 spins constitute a perfect triangular lattice. Magnetization results evidence the presence of strong antiferromagnetic interactions between Mn$$^{2+}$$ 2 + spins and a phase transition at $$T_{N}$$ T N = 20 K. Below $$T_{N}$$ T N , the specific heat data show antiferromagnetic magnon excitations with a gap of 1.4 K, which is due to magnetic anisotropy. $$\mu$$ μ SR reveals the presence of static internal fields in the ordered state and short-range spin correlations high above $$T_{N}$$ T N . It further unveils critical slowing-down of spin dynamics at $$T_{N}$$ T N and the persistence of spin dynamics even in the magnetically ordered state. Theoretical studies infer that Heisenberg interactions govern the inter- and intra-layer spin-frustration in this compound. Our results establish that the combined effect of a weak third-nearest-neighbour ferromagnetic inter-layer interaction (owing to double-exchange) and intra-layer interactions stabilizes a three-dimensional magnetic ordering in this frustrated magnet.

Boron-doped diamond granular thin films are known to exhibit superconductivity with an optimal critical temperature of T c = 7.2 K. Here, we report the measured in-plane complex surface impedance of boron-doped diamond films in the microwave frequency range using a resonant technique. Experimentally measured inductance values are in good agreement with estimates obtained from the normal state sheet resistance of the material. The magnetic penetration depth temperature dependence is consistent with that of a fully gapped s-wave superconductor. Boron-doped diamond films should find application where high kinetic inductance is needed, such as microwave kinetic inductance detectors and quantum impedance devices.

Optoelectronic devices are becoming increasingly important due to their compatibility with CMOS fabrication technology and their superior performance in all dimensions compared to currently available devices. Numerous modern applications are formulated based on various aspects of optoelectronic materials and devices, such as artificial intelligence, optical memory, optoelectronic synapses, humanoid-photodetectors, holography, solar cells, charge storage devices, bio-electronic devices, and so on. Persistent photoconductivity (PPC), an optoelectronic phenomenon that has piqued the scientific community’s interest, is a novel approach to these modern applications. In this article, we highlighted the use of PPC in a variety of emerging optoelectronic applications. PPC is a light-induced mechanism that persists after light excitation is terminated, i.e. the response does not stop immediately but remains available for a period of time. In recent years, the time duration over which the response after turning off the illumination is available has been proposed for a variety of applications. PPC has primarily been explored from a theoretical point of view, with the application component being largely ignored. Very recently, the scientific community has started exploring the possible applications pertaining to PPC such as optoelectronic synapses, holography, optical memory, bioelectronics, and artificial intelligence. Depending on the nature of the material and the type of model used in the application, a variety of mechanisms can be used to modulate the charge trapping and de-trapping methodologies for a specific application. This topical review summarizes the origins of PPC, its control mechanism, and recent advances in a variety of materials such as metal oxides, superconductors, nanofibers, 2D-semiconductors, alloys, nitrides, organic materials, topological insulators, and so on. In addition, the paper has carefully explored the development of next-generation optoelectronic applications designed for industry 4.0 leveraging the PPC phenomenon.

Diamond due to its outstanding optical, electrical, mechanical and thermal properties finds an important place in electronic, opto-electronic and quantum technologies. Recent progresses showing superconductivity in diamond by boron doping has opened up many avenues including its applications in SQUID devices especially with polycrystalline diamond films. Granular boron doped diamond films find applications in quantum inductance devices where high surface inductance is required. Particularly important are the defect centers in diamond like nitrogen-vacancy (N-V), silicon vacancy (SiV) and other color centers which are ideal candidates for next generation quantum hardware systems. For efficient device applications, an indispensable need remains for a substitutional donor in diamond lattice that yields a lower thermal activation energy at room temperature. In this review, a comprehensive summary of research and the technological challenges has been reported including some of the results on nitrogen doping in polycrystalline diamond to understand the transport phenomenon emphasizing on its possible future applications.

Recent studies on twisted bilayer and multi-layer graphene have opened new avenues of research in condensed matter physics. These artificially made superlattices showed very intriguing electrical properties, including superconductivity at certain commensurate rotation angles between the stacked layers. Even though electrical properties are studied to some extent, the effect of rotation angle on the thermal properties has not received adequate attention. In particular, the thermal expansion of these systems is not well understood. In this direction, we have studied thermal expansion coefficient of few-layer graphene samples with rotational misorientation. These samples were synthesized using chemical vapor deposition technique from a solid carbon precursor. The Raman spectra of these samples indicated the presence of rotational stacking faults, which was confirmed by selected area electron diffraction measurements. Finally, the in-plane thermal expansion coefficient of this system was obtained using temperature dependent Raman spectroscopy for T = 4.5 to 300K. Thermal expansion coefficient was determined to be negative in this temperature range and the corresponding room temperature value was obtained to be ≈ -3.47 × 10-6 K-1. This value is comparable to that of few- layer graphene. We suggest that the thermal expansion of multilayer graphene with rotational stacking faults follows the thermal expansion of the individual few-layer crystallites rather than showing bulk graphitic behavior.

Understanding and tuning of metal–insulator transition (MIT) in oxide systems is an interesting and active research topics of condensed matter physics. We report thickness dependent MIT in Ga-doped ZnO (Ga:ZnO) thin films grown by pulsed laser deposition technique. From the electrical transport measurements, we find that while the thinnest film (6 nm) exhibits a resistivity of 0.05 Ω cm, lying in the insulating regime, the thickest (51 nm) has resistivity of 6.6 × 10−4 Ω cm which shows metallic type of conduction. Our analysis reveals that the Mott’s variable range hopping model governs the insulating behavior in the 6 nm film whereas the 2D weak localization (WL) phenomena is appropriate to explain the electron transport in the thicker Ga:ZnO films. Magnetoresistance study further confirms the presence of strong localization in 6 nm film while WL is observed in 20 nm and above thicker films. From the density functional calculations, it is found that due to surface reconstruction and Ga doping, strong crystalline disorder sets in very thin films to introduce localized states and thereby, restricts the donor electron mobility.

The local electrical conductivity and impurity band evolution in superconducting nanocrystalline boron doped diamond (BNCD) film are investigated using conducting atomic force microscopy (C-AFM) and X-ray absorption spectroscopy (XAS). C-AFM has been employed to investigate the local conductivity of superconducting BNCD with T c = 4.3 K and upper critical field H c 2 (0) = 5.2 T. A high local electrical heterogeneity of the BNCD film as evidenced from the C-AFM profile points to the uneven boron uptake during the process of doping. C-AFM also revealed that grain boundaries are the highly conducting regions, possibly, due to the presence of p-type trans-polyacetylene along with the C C and C H bonds in the grain boundaries. From the in-depth XPS profiling of the B 1s spectra we confirmed the macroscopic uniformity of the boron concentration across the depth of BNCD layers. X-ray absorption spectroscopy (XAS) measurements near B K-edge and C K-edge showed formation of in-gap states as a result of heavy boron doping. Near C K-edge, bandgap states at 282.8 eV and 284.1 eV are found which are responsible for superconductivity in the BNCD film. This work explores the non-uniform boron doping and its effect on the conduction band structure of a superconducting BNCD film.

Our work investigates the impurity band and the core excitonic level evolution of a series of systematically boron doped diamond (BDD) films using Raman and X-ray absorption (XAS) spectroscopies. The resistivity versus temperature data shows that Tc of the BDD films achieves a peak at a maximum gaseous phase boron to carbon ratio, [ B C ] max , beyond which Tc drops gradually as a result of excess defect formation, revealing a dome-shaped behaviour. Study of lattice expansion clearly shows the unambiguous presence of substitutional boron atoms beyond [ B C ] max . Direct probe of the impurity band using XAS show a systematic increase in the absorption intensity of the bandgap states which ultimately degrades as the limit of B C > [ B C ] max is exceeded. The binding energy of the BDD 1s core exciton reveal a shallow measured value of 0.11 eV. This is less than earlier found values of 0.19 - 1.2 eV, in various reports for intrinsic diamond.

A comparative study correlating structure and ferroelectricity in La-doped PbZr0.52Ti0.48O3 [PZT] for La = 0–4% has been carried out. Due to increase in tetragonality, 2% La doped PZT shows highest polarization. A modified low cost, but highly proficient method of Double Atmospheric Layer Protected Sintering (DALPS) has been developed to sinter pyrochlore free 2% La-doped PbZr0.52Ti0.48O3 prepared by a modified sol-gel synthesis. The DALPS method enhances the remnant polarization by 29% and dielectric constant by 23% with around 50% decrease in dielectric loss tangent. The effectiveness of DALPS in preventing lead loss is confirmed by EDS analysis. As a result of the employment of the modified sol-gel synthesis and DALPS, a remnant polarization value as high as 49.25 μC cm−2 with nearly ideal hysteresis loop is observed in bulk Pb0.97La0.02Zr0.52Ti0.48O3. The squareness factor of the P-E loop is 99.7% of an ideal value. The Positive Up Negative Down (PUND) measurement shows enhanced remnants with polarizations: the values of +dPr and –dPr are 112 and 117 μC cm−2 respectively. The dielectric loss is also sufficiently low and at room temperature and the value of tan δ is 0.016 with dielectric constant of 1369 at 1 kHz.

We find direct evidence of stain driven phase transition from face centered cubic (FCC) to body centered cubic (BCC) structure in radio frequency (RF) sputtered molybdenum (Mo) thin films as a function of deposition parameters. The structural, microstructural and electrical behavior of the Mo films are greatly influenced by the sputtering parameters i.e. RF power and argon (Ar) pressure. Although Mo is reported to be stable in BCC structure, our findings reveal that at certain deposition conditions, Mo films crystallize in FCC structure with good adherence to glass substrate; high resistance and strain (~214 Ω/□, ~3.43%). On varying sputtering parameters, strain releases and Mo films crystallize in mixed phase (FCC and BCC) which turns into pure BCC phase on further optimization. The stable BCC structured films have low resistance and strain (~1.29 Ω/□, ~−0.23%). We deposited bi-layer of Mo, where the bottom layer has strong adhesion to the substrate and top layer has low resistance (~0.81 Ω/□). The Mo film that crystallized in pure BCC form showed a strain value of −0.09% (compressive).

BaTi1-xSnxO3 of compositions x = 0.07, 0.08, 0.09, 0.10 and 0.11 are synthesized to study their piezoelectric and impedance characteristics. The studies revealed that the composition x = 0.08 exhibits the maximum piezoelectric coefficient (d33 = 296 pC/N) and remnant polarization (Pr = 6.92 μC/cm2) values. The impedance analysis showed that the depressed semi-circular arc observed in the Nyquist’s plots gave evidence for the existence of non-Debye type relaxation behavior in the compounds. The impedance studies suggested a possible correlation between the d33 and microstructural properties. The activation energies extracted from ac conductivity plots strongly indicate the existence of defect dipole assisted conductivity mechanism in the samples. Notably, the samples displayed positive temperature coefficient of resistance (PTCR) just above their ferroelectric transition. The frequency dependent ac conductivity follows the Jonscher’s universal power law. The dominant conduction mechanism in the samples is determined to be the small polaron hopping mechanism.

Asymmetric supercapacitors based on aqueous and solid-state electrolytes are useful for a variety of applications. The birnessite δ-MnO2 is one of the efficient materials from the MnOx family characterized by large interlayer distance (∼7.3 A) and high theoretical specific capacitance (∼1370 F g−1). However the main concern which hinders its usage for practical applications is its low electronic conductivity (∼10−6 S cm−1). There are different means to enhance the conductivity and in the present studies, two simultaneous methods viz; a method of synthesis of nano-flakes along with Zn-doping in δ-MnO2 is implemented. A specific capacitance of ∼466 F g−1 at a current density of 0.5 A g−1 is obtained for an optimum Zn doping concentration of 1 mol% which is almost two times more than the corresponding pristine one. Both aqueous and solid-state asymmetric supercapacitor devices are fabricated using Zn doped δ-MnO2 as electrode material which can be easily scalable to industrial level. A lab-scale demonstration prototype is constructed which essentially validated the charging of solid-state supercapacitor using battery and allowing the supercapacitor to discharge through a red-LED by means of a two-way switch.

Pulsed laser deposited MgxZn1 − xO films grown on sapphire substrates exhibited wurtzite hexagonal structure at lower Mg concentrations (x

We fabricated MgB2 samples with Ag additions using in situ solid-state reaction via a single-step sintering to study the effect of Ag on the structural, vibration, and superconducting properties of MgB2 samples. Ag addition to MgB2 resulted in a significant improvement in J c although no appreciable effect was observed in the lattice parameters and the superconducting transition temperature T c. Dramatic increase in the grain size was observed with Ag addition and topographic measurements with atomic force microscopy revealed the formation of Ag–Mg nanoparticles 5–20 nm in size at 2 and 4 wt% Ag additions. The fact that these samples showed high J c values suggests that the nanoparticles formed as a result of Ag addition are responsible for enhanced flux pinning. Raman spectroscopy measurements showed that Ag additions also increased disorder in the system and thereby affected the line width of the Raman active E 2g mode.

In this paper, tribological performance of boron doped diamond (BDD) films and boron doped graded layer diamond thin films (BDD/transition layer/NCD) were studied in detail. The widely used cemented tungsten carbide (WC-6 wt%Co) was selected as a substrate material for diamond coating. Diamond films were deposited on WC-Co by Hot-filament CVD reactor (HFCVD) setup. Tribology experiment was conducted using a reciprocating tribometer with a normal load of 30 N and a sliding velocity of 10 mm/s for a constant stroke length of 3 mm. Silicon nitride (Si3N4) ball was used as a counterpart to study the friction and wear behaviour of diamond films. The surface morphology, topography & roughness of the diamond films were analysed using scanning electron microscope and atomic force microscope respectively. The hardness of the thin diamond films was measured by using Berkovich nano indentation test method. In MCD coating (sp3 C-C) the wear rate increases with increase in hardness. On the contrary for NCD (sp2 graphite), wear rate decreases with decrease in hardness because of the corresponding phases. The test results found that BDD and boron doped graded layer shows a stable lowest friction coefficient values of 0.004 and 0.003 compared with conventional microcrystalline diamond films (0.007). On the other hand, the wear diameter of the silicon nitride ball for BDD and boron doped graded layer are found to be 620 μm and 785 μm, relatively lower in comparison with microcrystalline diamond films (897 μm). The wear track width was measured by scanning electron microscope and shows that BDD and boron doped graded layer indicates lower wear track width 564 μm and 596 μm compared with microcrystalline diamond films (712 μm). Raman mapping was conducted on the wear track of the diamond films to know about the phase pure diamond (sp3) and partly graphite phases (sp2) which in turn contributes for the distinct residual stresses in thin films. The obtained lower friction coefficient for BDD on WC-Co cutting tool can be suitable for machining of aluminium based metal matrix composites effectively.

In this study, the effect of annealing ambient on SnO 2 thin film transistors (TFTs) is presented. Phase pure SnO 2 films have been deposited using solution processed spin coating technique with SnCl 2 as the precursor material. The films are annealed at 500 °C for 1 h in different annealing ambient conditions with varying N 2 :O 2 ratio. Top gate, bottom contact TFTs have been fabricated with SnO 2 as the channel layer, silicon as the gate, silicon dioxide as the dielectric and gold as the contact material. XRD patterns reveal the amorphous nature of films. AFM image shows that the spin coated films are pin-hole free with extremely smooth surface morphology. PL and XPS measurements reveal that with increase in N 2 % during annealing, the defects in the films increase. However, with increase in nitrogen concentration, the device performance improves, the threshold voltage shifts towards lower values and mobility increases, but very high N 2 % is not suitable for device operation, a 70% N 2 + 30% O 2 annealing ambient is found to be suitable with devices showing saturation mobility of 0.23 cm 2 V −1 s −1 and threshold voltage of 6.8 V and on/off ratio of 10 6 .

We report on the growth of ZnO nanostructures in different gas ambient (Ar and N 2 ) using pulsed laser deposition technique. Despite the similar growth temperature, use of N 2 ambient gas resulted in well-aligned nanorods with flat surface at the tip, whereas, nanorods grown with Ar ambient exhibited tapered tips. The Nanorods grown under N 2 ambient exhibited additional Raman modes corresponding to N induced zinc interstitials. The nanorods are c-axis oriented and highly epitaxial in nature. Photoluminescence spectroscopy reveals that the UV emission can be significantly enhanced by 10 times for the nanorods grown under Ar ambient. The enhanced UV emission is attributed to the reduction in polarization electric field along the c-axis. n -ZnO nanorods/p-Si heterojunction showed rectifying I–V characteristics with a turn of voltage of 3.4 V.

In this study we made an attempt to fabricate magnetoelectric composite of magnetostrictive NZFO layer on piezoelectric PSLZT multilayer by co-sintering them directly. Microstructural analyses of t...

Here we report on the tunable supercapacitance of the Mn3O4 beaded chains synthesized by a simple and low cost electro-spinning process. Tuning is achieved by controlled phase transformation of surface spinel Mn3O4 beaded chains to layered-birnessite MnO2 nanoflakes through galvanostatic charge-discharge cycling. Phase transformation rate is optimized to get maximum capacitance by controlling the parameters such as applied specific current value, number of galvanostatic charge-discharge cycles, micro-structure of working electrode material and the selection of potential range. A maximum specific capacitance of ∼445 F g−1 and areal capacitance of ∼495 mF cm−2 are obtained at current densities of 0.5 A g−1 and 0.125 mA cm−2 respectively. The superior performance in case of layered-spinel composites among similar nanostructures is due to high surface to volume ratio of the MnO2 nanoflakes formed from the Mn3O4 beaded chains which in turn give rise to large number of surface active sites for the redox reaction to take place. About 100% of capacity retention and coulombic efficiency are observed for ∼1000 cycles even at a higher current density of 7 A g−1. Morphological dependence of the phase transformation rate is investigated by preparing two different morphologies of Mn3O4 viz., octahedrons and spherical nanoparticles.

We have synthesized polycrystalline bulk FeSe materials with various Ag concentrations through double-sintering solid-state reaction. All the samples exhibited similar onset critical temperature of around 8 K. Atomic force microscopic observation revealed that the grain connectivity was improved through Ag addition. Raman spectroscopic studies confirmed that pristine and Ag-doped FeSe compounds have superconducting tetragonal structure with high crystalline quality. There was a clear red shift and peak broadening in Fe-related Raman modes when the Ag concentration is increased, which might be ascribed to the incorporation of Ag+ ions into the FeSe lattice. The critical current density decreased with Ag addition, although onset critical temperature remained constant.

We demonstrate reversible p -type nature of pulsed laser deposited (P, N) codoped ZnO thin films using rapid thermal annealing process. As grown thin films exhibited change in conductivity from p to n -type over a span of 120 days. Non-annealed n -type thin films contain unintentional donor impurities such as hydrogen and carbon. X-ray photoelectron spectroscopy and Raman measurements conclusively show that hydrogen passivates nitrogen acceptors by forming N H complex. Carbon can be annealed out at 600 °C, whereas, the dissociation of N H complex takes place at 800 °C. The films revert its p -type nature at an annealing temperature of 800 °C.

Tailoring spin-orbit interactions and Coulomb repulsion are the key features to observe exotic physical phenomena such as magnetic anisotropy and topological spin texture at oxide interfaces. Our study proposes a novel platform for engineering the magnetism and spin-orbit coupling at LaMnO3/SrIrO3 (3d-5d oxide) interfaces by tuning the LaMnO3 growth conditions which controls the lattice displacement and spin-correlated interfacial coupling through charge transfer. We report on a tunable and enhanced interface-induced Rashba spin-orbit coupling and Elliot-Yafet spin relaxation mechanism in LaMnO3/SrIrO3 bilayer with change in the underlying magnetic order of LaMnO3. We also observed enhanced spin-orbit coupling strength in LaMnO3/SrIrO3 compared to previously reported SrIrO3 layers. The X-Ray spectroscopy measurement reveals the quantitative valence of Mn and their impact on charge transfer. Further, we performed angle-dependent magnetoresistance measurements, which show signatures of magnetic proximity effect in SrIrO3 while reflecting the magnetic order of LaMnO3. Our work thus demonstrates a new route to engineer the interface induced Rashba spin-orbit coupling and magnetic proximity effect in 3d-5d oxide interfaces which makes SrIrO3 an ideal candidate for spintronics applications., Comment: 10 Pages, 4 Figures

Strain engineering is an important issue in oxide thin films to explore new functionalities. Here a series of high quality epitaxial ${\mathrm{PrVO}}_{3}$ (PVO) thin films were grown, by pulsed laser deposition (PLD) technique, as a function of thickness on (La,Sr)(Al,Ta)${\mathrm{O}}_{3}$ (100) [LSAT (100)] and ${\mathrm{LaAlO}}_{3}$ (100) [LAO (100)] substrates with a nominal lattice mismatch of $\ensuremath{-}0.8$% and $\ensuremath{-}2.9$%, respectively. X-ray diffraction revealed a constant out-of-plane lattice parameter of PVO/LSAT with an increase in film thickness, and a rather continuous decrease for PVO/LAO films. Whereas thicker PVO films show a ferromagneticlike behavior, at low thickness a surprising decrease of coercivity (${H}_{c}$) and increase of saturation magnetization (${M}_{s}$) is observed. This behavior is described by using a model of a ``dead layer'' which possesses a strong paramagnetic susceptibility. Our XPS investigations further reveal the formation of ${\mathrm{V}}^{4+}$ at the surface of the film to be responsible for this paramagnetic dead layer, which is reduced by adding a capping layer on top of the PVO film. Finally, the N\'eel temperature (${T}_{N}$) is examined as a function of film thickness, and found to vary between 25 and 30 K for LSAT and LAO, respectively. These results pave the way for the use of vanadate in thin film devices.

a-axis (100) oriented Aluminium Nitride (AlN) favours transverse acoustic wave applications. We have been able to realize preferential (100) oriented AlN films on Molybdenum (Mo) coated Si substrate using reactive RF magnetron sputtering. X-ray diffraction and Fourier-transform infrared spectroscopy studies reveal the crystallinity, preferred orientation and bond formation between Al and N2. Al 2p subpeak at 73.8 eV and N 1s subpeak at 396.6 eV from X-ray photoelectron spectroscopy studies confirm the Al-N and N-Al formation in wurtzite hexagonal phase. From the fabricated Mo-AlN-Mo capacitors, the measured dielectric constant and electrical resistivity were ( ~ 18) and ( ~ 7.5 × 106 Ω .m) respectively. The piezoelectric coefficient d 33 ( eff ) of AlN film was ( ~ 4.5) pmV−1. These excellent properties of preferential (100) AlN/Mo films will be very useful for high frequency resonator and energy harvesting applications.

No, defects are not always bad. Vacancies, antisites, or impurities are in general trapped at the grain boundaries and contribute to scattering (of charge carriers). In general, grain boundaries reduce the performance (efficiency of the solar cell). However, there are certain materials where the defects enhance performance. CdTe, CuInSe2 (CIS), Cu2ZnSnS4 (CZTS) are a few examples. The present work involves CAFM studies on CZTS films deposited to Si and soda-lime glass substrate to explore the underlying physics behind unique grain boundary physics in CZTS. Discussions are made in the light of the reactions that take place on CZTS surface and corresponding energy band diagrams are drawn

The present study is investigating the effect of high temperature sintering combined with ball milled powders for the preparation of FeSe material via solid state sintering technique. The commercial powders of Fe (99.9% purity) and Se (99.9% purity) were mixed in a nominal ratio Fe:Se = 1:1 and thoroughly ground and ball-milled in a glove box during 6 h. Then, the powder mixture was pressed into pellets of 5 mm in diameter and 2 mm thickness using an uniaxial pressure of 100 MPa. The samples were sealed in quartz tubes and sintered at 600 °C for 24 h. Then, the pellets were again thoroughly ground and ball-milled in the glove box and pressed into pellets, and the final sintering was performed at two different temperatures, namely at 900 °C for 24 h and at 950 °C for 24 h. X-ray diffraction results confirmed that both samples showed mainly of the β-FeSe with tetragonal structure. The temperature dependence of magnetization (M-T) curves revealed a sharp superconducting transition Tc, onset = 8.16 K for the sample sintered at 900 °C. Further, scanning electron microscopy observations proved that samples sintered at 900 °C show a platelike grain structure with high density. As a result, improved irreversibility fields around 5 T and the critical current density (Jc) values of 6252 A cm−2 at 5 K and self-field are obtained. Furthermore, the normalized volume pinning force versus the reduced field plots indicated a peak position at 0.4 for the sample sintered at 900 °C. Improved flux pinning and the high Jc values are attributed to the textured microstructure of the material, produced by a combination of high temperature sintering and ball milling.

In this report, we have evolved a new method to synthesize nanocrystalline calcium sulfate dihydrate (gypsum) via electrochemical oxidation. This method provides a facile, direct way of synthesizing nanocrystalline gypsum at room temperature. Field-emission scanning electron microscopy micrographs present an interesting phenomenon of formation of microcracks in the nano-CaFeO2.5 pellet during electrochemical oxidation leading to nucleation of gypsum within the cracks. A known theoretical model has been invoked to explain the gypsum growth within the cracks. Transmission electron microscopy studies indicate electron beam-induced phase transformation of single-crystalline calcium sulfate dihydrate to polycrystalline CaO nanoparticles. The hardness was found to be improved (63% higher) by the addition of a mere 5 wt % of nano-gypsum to commercial gypsum, which is almost 200% higher than nano-gypsum synthesized earlier via an indirect route of flame synthesis and hydration. Moreover, the compressive strength ...

Formation of ordered defect compounds and anomalous grain boundary physics are unique to Cu chalcogenides CuInX 2 (S/Se) and its alloys. X-ray photoelectron spectroscopy (XPS) studies were carried on Cu 2-x Zn 1.3 SnS 4 (x = 0.0, 0.3, 0.5 and 0.7) to determine the position of valence band edge and explore the formation of ordered vacancy compounds along with absorption studies. Conductive atomic force microscopy (C-AFM) studies were carried out Cu 2 ZnSnS 4 (CZTS) film deposited on Si and sodalime glass substrates to understand grain boundary physics.

The electrocaloric effect (ECE) is investigated in both relaxor as well as morphotropic composition of (1 − x)Pb(In1/2Nb1/2)O3-xPbTiO3 system. The ECE is analyzed by evaluating the electrocaloric temperature change (ΔT) using thermodynamic Maxwell equation. The relaxor phase (x = 0.15) show an anomalous broadening in ECE and the maximum of ΔT is found to shift from the proximity of depolarization temperature (Td) to around T′m with increase in electric field. However, for morphotropic composition (x = 0.33) a region with negative ΔT is observed below Td along with anomalous broadening in positive ΔT in the proximity of TRT. The maximum value of ΔT obtained for relaxor phase is 0.37 K whereas 0.12 K is observed for morphotropic composition at 225C. The electrocaloric responsivity ξmax is 0.21 mmK/kV for relaxor phase whereas 0.06 mmK/kV is obtained for the morphotropic composition at 18 kV/cm electric field.

Environment-friendly solid-state cooling technology necessitates the search for energy-efficient electrocaloric (EC) materials. In this regard, the EC effect and energy storage performance have been investigated on a site-engineered lead-free Ba1-x (Bi0.5Li0.5) x TiO3 (x = 0.0, 0.10, 0.125, 0.15 and 0.175) system from the perspective of its enhanced characteristic parameters. The ferroelectric and dielectric studies reveal the tunable polarization and Curie temperature as a function of composition. The EC measurements on these samples display superior EC parameters compared to the values reported for other polycrystalline ferroelectric systems. The observed EC parameters for the x = 0.10 sample, such as the change in entropy (ΔS), adiabatic temperature change (ΔT) and EC coefficient are 2.63 J kg−1 K, 2.03 K and 0.68 K mm−1 kV, respectively. Notably, the x = 0.15 sample displays near room-temperature (307 K) EC response with ΔT ≥ 0.30 K over a broad 24 K temperature range. In addition, the energy storage performance studies elucidate that the Ba1-x (Bi0.5Li0.5) x TiO3 compound with x = 0.175 displays large energy storage efficiency (96.7%) with 144 mJ cm−3 as the storage density. The tunable EC characteristics and high energy storage efficiency demonstrated in this work illustrate the application potential of site-engineered BaTiO3 samples in efficient cooling and storage devices.

Lead zirconate titanate {[Pb(Zrx, Ti1-x)O3], PZT)} (x = 0.40), synthesized by solid state route, is embedded in the polymer matrix (PMMA) (Poly(methylmethacrylate)) using solvent evaporation technique. Polymer based composite films are prepared by different weight percentage (0.1 wt%, to 2.0 wt%) of the PZT particles. X-ray diffraction (XRD) confirmed that the polymer induced a decrease in the average crystallite size (61 ± 2 nm). Raman spectra of the higher PZT concentration (2.0 wt%) in the matrix revealed the presence of tensile strain in the polymer. The morphology of the PZT particles is found as cubic and the particle size in the range 0.3 μm–4.5 μm. On poling for 1 h, remnant polarization (Pr) (1.33 μC/cm2) of the composite film (2 wt%) is found to exhibit a low leakage current density of 8.12 × 10−10 A/cm2 at 5 kV/cm. The realized properties enable the composites to be employed as potential candidates in sensors, actuators and in energy harvesting applications as well.

We have probed the changes in the phonon and magnon modes of BiFeO3 on substitution of Ba and Ca at the A-site using infrared reflectance spectroscopy. The systematic hardening of the phonon modes in the doped samples is seen to correlate well with the volume reduction of the unit cell observed from the Rietveld measurements. This is attributed to the generation of chemical pressure in these samples on account of substitution of the dopants. In addition, a near-complete suppression accompanied by a complete lifting of the degeneracy of the magnon modes as compared to the pristine BiFeO3 is detected for the Ca-doped samples. These results suggest that aliovalent doping at A-site affects the crystal field of FeO6 octahedra of BiFeO3, which eventually modifies its magnetic nature. These doping-induced modifications are mainly responsible for the improved magnetic and magnetoelectric properties of the Ca-doped BiFeO3 samples.

We carried out temperature and magnetic field-dependent magnetic measurements to understand the evolution of magnetic non-collinearity near the antiferromagnetic phase transition in conjunction with the onset of significant change in magnetic entropy. We observed the maximum magnetic entropy change just before the magnetic ordering of Cr3+ in YCrO3 with the maximum change in magnetic entropy of ~ −0.38 Jkg−1K−1 at 8 T external field. Thought the magnetization is linear in higher fields (3 T–8 T), a significant deviation is observed in lower fields, substantiating the presence of weak ferromagnetism in YCrO3 with the antiferromagnetic ground state.

SrIrO 3 with its large spin–orbit coupling and low charge conductivity has emerged as a potential candidate for efficient spin–orbit torque magnetization control in spintronic devices. Here we report on the influence of an interfacial oxide layer on spin pumping experiments in Ni 80Fe 20 (NiFe)/SrIrO 3 bilayer heterostructures. To investigate this scenario, we have carried out broadband ferromagnetic resonance (BBFMR) measurements, which indicate the presence of an interfacial antiferromagnetic oxide layer. We performed in-plane BBFMR experiments at cryogenic temperatures, which allowed us to simultaneously study dynamic spin pumping properties (Gilbert damping) and static magnetic properties (such as the effective magnetization and magnetic anisotropy). The results for NiFe/SrIrO 3 bilayer thin films were analyzed and compared to those from a NiFe/NbN/SrIrO 3 trilayer reference sample, where a spin-transparent, ultra-thin NbN layer was inserted to prevent the oxidation of NiFe. At low temperatures, we observe substantial differences in the magnetization dynamics parameters of these samples. In particular, the Gilbert damping in the NiFe/SrIrO 3 bilayer sample drastically increases below 50 K, which can be well explained by enhanced spin fluctuations at the antiferromagnetic ordering temperature of the interfacial oxide layer. Our results emphasize that this interfacial oxide layer plays an important role for the spin current transport across the NiFe/SrIrO 3 interface.

We have studied the low-temperature magnetic and infrared data of the BiFeO3 ceramic sample to investigate the behavior of phonons and magnon-phonon coupling below 300 K. From the magnetic study, we noticed two magnetic transitions near 150 and 257 K due to the spin-reorientation. Besides, this sample is found to be a mean-field system rather than a glassy system. In our assignment of the infrared modes, all the 13 allowed phonon modes are accounted for rhombohedral BiFeO3 at room temperature itself. Almost all the modes show anomalous behavior in their frequency dependence, close to the observed magnetic transitions. In addition, the emergence of two-magnon modes at 106 and 111 cm−1 below 160 K is observed due to a modification in the noncollinear spin structure. These results indicate the presence of magnon-phonon coupling in multiferroic BiFeO3 below room temperature.