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The present study reports a strong thickness-dependence and anomalously large enhancement in the values of the Seebeck coefficient and electrical conductivity in Bi2Te3 films at ultralow thickness. An opposite sign of the Hall coefficient (negative) and Seebeck coefficient (positive) is observed in an ultrathin Bi2Te3 film (65 nm) as compared to the normally observed identical sign in the case of Bi2Te3 thin films (520 nm). A simultaneous enhancement in the values of electrical conductivity and the Seebeck coefficient results in a giant enhancement in the value of power factor from 1.86 mW/m K2 to 18.0 mW/m K2 at 416 K, with a reduction in thickness. X-ray photoelectron spectroscopy investigation reveals the absence of any significant change in stoichiometry and chemical bonding upon reduction of thickness. Magnetoresistance vs magnetic field data show a sharp dip at the lower magnetic field values, indicating a weak antilocalization effect in the case of the ultrathin film sample suggesting the role of strong spin–orbit coupling toward the carrier filtering effect resulting in enhancement of thermoelectric properties. Observation of the large Seebeck coefficient and the power factor at lower thickness values and its relationship with spin–orbit coupling is an important result, both for practical applications and for better understanding of the thermoelectric properties. [ABSTRACT FROM AUTHOR]

Highly efficient broadband photodetectors based on 2D metal chalcogenides have enchanted immeasurable research curiosity due to their tunable bandgap and unique electrical properties suitable for applications in optoelectronic nanodevices. In the present study, we fabricated photodetectors based on heterojunctions composed of 2D nanoflakes of indium sulfide (In2S3) and ZnO with the aim to enhance the photodetection spectral range. The fabricated 2D–3D heterostructure exhibited superior photodetection performance in terms of a high responsivity (Rλ), specific detectivity, and external quantum efficiency with a broader spectral response extending from the UV to visible region. It displayed a high responsivity value of 440 mA W−1, specific detectivity of 10 × 1010 Jones, and external quantum efficiency of 330%. The experimentally measured optical absorption edge, work function, and valence band offset confirmed the formation of a type-II band alignment at the β-In2S3–ZnO interface, which promoted the charge-carrier separation. The present study presents a novel way of enhancing the photodetector properties by combining a well-known oxide semiconductor with a 2D material having tunable optical properties. [ABSTRACT FROM AUTHOR]

Square arrays of artificial spin ice (ASI) constituting weakly interacting NiFe nano-islands, with length ~312 nm, width ~125 nm, thickness ~20 nm, and lattice constant ~570 nm, were fabricated on Nb thin film and on thermally grown 300 nm SiO2 on silicon. Detailed investigations of magnetic force microscopy (MFM) at room temperature, and magnetization M(H) loops and relaxation of remanent magnetization (Mr) at various temperatures were carried out in two in-plane field geometries, namely, parallel ("P"-parallel to the square lattice) and diagonal ("D"- 45° to the square lattice). The magnetic response of the ASI samples shows striking difference for insulating (SiO2), metallic (Nb, T > 6.6 K) and superconducting (Nb, T < 6.6 K) bases, and the field geometry. For instance, with the Nb base in the normal metallic state (T > 6.6 K), (1) in "P" geometry the M(H) loops are found to be more "S" shaped in comparison with that for SiO2 base; (2) the ratio of magnetic vertex population of Type II to Type III vertices extracted from MFM studies in "P"("D") geometry is ~1:1.1(1.2:1) that changed for the SiO2 base to ~2.1:1 (4: 1). However, the NiFe-ASI on both metallic Nb and SiO2 bases exhibit a highly athermal decay of magnetization, and the % change in Mr in about two hours at T = 10 K (300 K) lies in a range of ~1.07-1.80 (0.25-0.62). With Nb base in superconducting state (T < 6.6 K), the M(H) loops not only look radically different from those with SiO2 and metallic Nb as bases but also show significant difference in "P" and "D" geometries. These results are discussed in terms of inter-island magnetostatic energy as influenced by field geometry, presence of metallic Nb base and competing vortex pinning energy of superconducting Nb base. [ABSTRACT FROM AUTHOR]

ZnS:Mn is produced in nanocrystalline form by a chemical method using polyvinylpyroledone as a chemical capping agent. The study shows that the prepared pure MnS samples did not show any photoluminescence at room temperature and concludes that the observed photoluminescence is Mn(super 2+) induced in nanocrystalline ZnS host.

Structural, optical, and surface potential properties of CdSe nanoparticles (NPs) prepared on ZnS thin-films have been investigated. CdSe NPs/ZnS thin-films with varying CdSe NPs diameters are synthesised by sequential radio frequency magnetron sputtering technique. A blue shift in the optical absorption edge and enhancement in the optical constants are observed with decrease in the nanoparticles size. CdSe NPs/ZnS thin-films show an absorption edge at about 3.5 eV corresponding to ZnS and another size dependent absorption edge in the energy range of 1.74-2.16 eV, corresponding to CdSe NPs. Decrease in photoluminescence (PL) intensity of ZnS film on incorporation of CdSe NPs is observed; however, no distinct emission peaks corresponding to NPs are seen. Multilayered CdSe NPs/ZnS thin-films comprising of six alternating layers show PL signature both due to ZnS and CdSe NPs. Kelvin probe force microscopy (KPFM) studies show that surface potential values of CdSe NPs/ZnS thin-films lie in between that of ZnS (209 meV) and CdSe/ZnS (-4 meV) thin-films, which confirms charge transfer between CdSe NPs and ZnS thin-films. The evolution of CdSe NPs/ZnS nanoscale heterojunction has been observed with shift in the surface potential values by varying size and coverage of CdSe NPs. [ABSTRACT FROM AUTHOR]

In this study, the effect of the presence of secondary phases on the structural, electrical, and thermoelectric properties of nanocomposite Bi2Te3 films prepared by co-sputtering of silicon and carbon with Bi2Te3 has been investigated. Growth temperature and the presence of Si and C phase are observed to have a strong effect on the topography and orientation of crystallites. X-ray diffraction study demonstrates that Bi2Te3 and Bi2Te3:C samples have preferred (0 0 15) orientation in comparison to Bi2Te3:Si sample, which have randomly oriented crystallites. Atomic force, conducting atomic force, and scanning thermal microscopy analysis show significant differences in topographical, electrical, and thermal conductivity contrasts in Bi2Te3:Si and Bi2Te3:C samples. Due to the randomly oriented crystallites and the presence of Si along the crystallite boundaries, appreciable Seebeck coefficient, higher electrical conductivity, and lower thermal conductivity is achieved resulting in relatively higher value of power factor (3.71 mW K-2 m-1) for Bi2Te3:Si sample. This study shows that by incorporating a secondary phase along crystallite boundaries, microstructural, electrical, and thermoelectric properties of the composite samples can be modified. [ABSTRACT FROM AUTHOR]

The dynamics of magnetization (M) reversal and relaxation as a function of temperature (T) are reported in three non-interacting NiFe ring arrays having fixed ring outer diameter and varying widths. Additionally, the dependence of M(H) loop on the angle (ϑ) between magnetic field (H) and the plane of the rings is addressed. The M(H) loops show a double step transition from onion state (OS) to vortex state (VS) at all temperatures (T=3 to 300 K) and angles (ϑ=0 to 90°). The critical reversal fields HC1 (OS to VS) and HC2 (VS to OS) show a pronounced dependence on T, ring width, and ϑ. Estimation of the transverse and vortex domain wall energies reveals that the latter is favored in the OS. The OS is also the remanent state in the smallest rings and decays with the effective energy scale (U0/T) of 50 and 32 meV/K at 10 and 300 K, respectively. The robust in-plane anisotropy of magnetization of ring assemblies is established by scaling the M(H) with ϑ. [ABSTRACT FROM AUTHOR]

In this report, X-ray photoelectron spectroscopy studies have been carried out on Pd, Ag, Cu, Pd-Ag, and Pd-Cu nanoparticles having identical sizes corresponding to mobility equivalent diameters of 60, 40, and 20 nm. The nanoparticles were prepared by the gas phase synthesis method. The effect of size on valence and core levels in metal and alloy nanoparticles has been studied by comparing the values to those with the 60 nm nanoparticles. The effect of alloying has been investigated by comparing the valence and core level binding energies of Pd-Cu and Pd-Ag alloy nanoparticles with the corresponding values for Pd, Ag, and Cu nanoparticles of identical sizes. These effects have been explained in terms of size induced lattice contractions, alloying induced charge transfer, and hybridization effects. The observation of alloying and size induced binding energy shifts in bimetallic nanoparticles is important from the point of view of hydrogen reactivity. [ABSTRACT FROM AUTHOR]

In this study, in-situ X-ray diffraction has been carried out to investigate the effect of temperature and pressure on hydrogen induced lattice parameter variation in size selected Pd-Ag and Pd-Cu alloy nanoparticles. The nanoparticles of three different mobility equivalent diameters (20, 40, and 60 nm) having a narrow size distribution were prepared by gas phase synthesis method. In the present range of temperature (350K to 250 K) and pressure (10-4 to 100 millibars), no α (H/Pd≤0.03) ↔ β (H/Pd≥0.54) phase transition is observed. At temperature higher than 300 °C or pressure lower than 25 millibars, there is a large difference in the rate at which lattice constant varies as a function of pressure and temperature. Further, the lattice variation with temperature and pressure is also observed to depend upon the nanoparticle size. At lower temperature or higher pressure, size of the nanoparticle seems to be relatively less important. These results are explained on the basis of the relative dominance of physical absorption and diffusion of H in Pd alloy nanoparticles at different temperature and pressure. In the present study, absence of a α ↔ β phase transition points towards the advantage of using Pd-alloy nanoparticles in applications requiring long term and repeated hydrogen cycling. [ABSTRACT FROM AUTHOR]

This study reports the change in the structural and junction properties of Ti-CuO-Cu structure on incorporation of a 2-dimensional (2D) organic layer comprising of n-type hexafluoro-hexa-peri-hexabenzocoronene (6F-HBC). A bipolar resistive switching is observed in the device having interface between sputter deposited copper oxide (CuO) and vacuum sublimated 6F-HBC hybrid interface. The CuO/6F-HBC hybrid interface exhibits rectifying I-V characteristics in complete contrast to the ohmic and rectifying characteristics of junctions based on individual 6F-HBC and CuO layers. Large change in resistive switching property from unipolar resistive switching in CuO/HBC to bipolar resistive switching in CuO/6F-HBC interface was observed. At the CuO/6F-HBC interface, C1s peak corresponding to fluorinated carbon is shifted by 0.68 eV towards higher binding energy (BE) side and O1s peak due to non-lattice oxygen is shifted by 0.6 eV towards lower BE, confirming the interaction of O2- ion in CuO with fluorinated carbon atoms in 6F-HBC at the hybrid interface. Correlation between conductive atomic force microscopy images and atomic force microscopy topography images, I-V characteristics in conducting, non-conducting, and pristine regions along with x-ray photoelectron spectroscopy results establishes the important role of hybrid interface to determining the resistive switching properties. This study demonstrates that the resistive switching and interface properties of a hybrid device based on inorganic and organic 2D materials can be modified by changing the electronic properties of organic layer by attaching suitable functional groups. [ABSTRACT FROM AUTHOR]