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The galvanomagnetic properties (magnetoresistivity and Hall Effect) and resistivity at temperatures from 2 K to 300 K in magnetic fields of up to 9 T as well as optical characteristics (real and imaginary parts of the complex permittivity, optical conductivity, and reflectivity) at room temperature were studied. It was shown that the temperature dependence of the electrical resistivity has a “metallic” type and is quadratic at low temperatures (< 60 K) that can be caused by the “electron-phonon-surface” interference scattering mechanism in WTe2. Whereas an applied magnetic field induces a minimum in the temperature dependence of the resistivity at low temperatures, that shifts to higher temperature with increasing field, one of the possible explanation of which is the transition from high to weak effective magnetic fields. The magnetoresistivity increases with the magnetic field according to the quadratic law, reaching 1750% at 2 K, which is due to the compensation of charge carriers in WTe2. Hall Effect studies showed that the majority charge carriers are electrons with the concentration 1019 cm-3 and the mobility 7500 cm2/V•s at 2 K. At the same time optical investigations did not reveal the features characteristic of metals. The optical conductivity spectrum is a broad band centered at 3.4 eV, formed by interband transitions. The presence of peaks in the infrared region indicates the formation of low-energy gaps in the band spectrum of WTe2. The obtained data on the real and imaginary parts of the complex permittivity also evidence the absence of a contribution from free carriers up to 0.2 eV. The optical characteristics are shown to be in good agreement with the data on electronic transport properties. The revealed features are a manifestation of the topological nature of the material.

We report the growth and characterization of Sb2Se3/Bi2Se3 bilayer films fabricated by molecular beam epitaxy. High quality heterostructures are obtained as evidenced from the X-ray diffraction (XRD), atomic force microscopy and high-resolution transmission electron microscopic (HRTEM) analysis. Interestingly, Sb2Se3 grows as a (120) hexacrystal film in orthorhombic phase on rhombohedral Bi2Se3 (0001) plane, as verified by the out-of-plane and in-plane XRD scans. The cross-sectional TEM studies indicate a sharp interface between Sb2Se3 and Bi2Se3, which is important for the protection of surface states Bi2Se3. The ultraviolet photoelectron spectroscopy indicates that the Fermi level located 0.95 eV above the valence band maximum in Sb2Se3. The insulating nature of Sb2Se3 is confirmed by the nonlinear current-voltage curve via the vertical junction electrical measurement. By four point probe measurements, we confirm the charge transfer effect from Sb2Se3 into Bi2Se3, and such effect can be reduced in the Sb2Se3/(Bi0.7Sb0.3)2Se3 bilayer. This work opens a new avenue for the synthesis of multilayers consisting of topological insulators and ordinary insulator, which is important for harvesting of the multiple surface states for advanced electronic and spintronic applications.

Antimonene is a promising two-dimensional (2D) material that is calculated to have a significant fundamental bandgap usable for advanced applications such as field-effect transistors, photoelectric devices, and the quantum-spin Hall (QSH) state. Herein, we demonstrate a phenomenon termed topological proximity effect, which occurs between a 2D material and a three-dimensional (3D) topological insulator (TI). We provide strong evidence derived from hydrogen etching on Sb2Te3 that large-area and well-ordered antimonene presents a 2D topological state. Delicate analysis with a scanning tunneling microscope of the evolutionary intermediates reveals that hydrogen etching on Sb2Te3 resulted in the formation of a large area of antimonene with a buckled structure. A topological state formed in the antimonene/Sb2Te3 heterostructure was confirmed with angle-resolved photoemission spectra and density-functional theory calculations; in particular, the Dirac point was located almost at the Fermi level. The results reveal that Dirac fermions are indeed realized at the interface of a 2D normal insulator (NI) and a 3D TI as a result of strong hybridization between antimonene and Sb2Te3. Our work demonstrates that the position of the Dirac point and the shape of the Dirac surface state can be tuned by varying the energy position of the NI valence band, which modifies the direction of the spin texture of Sb-BL/Sb2Te3via varying the Fermi level. This topological phase in 2D-material engineering has generated a paradigm in that the topological proximity effect at the NI/TI interface has been realized, which demonstrates a way to create QSH systems in 2D-material TI heterostructures.

The enhancement of spin-to-charge conversion in Py/Cu/Bi2Se3 is achieved when increasing the Cu layer thickness up to 7nm. The conversion rate is studied using spin pumping technique. The inverse IEE length λIEE is found to increase up to ∼2.7nm when 7nm Cu layer is introduced. Interestingly, maximized λIEE is obtained when the effective spin mixing conductance (and thus Js) is decreased due to the Cu insertion. Monotonic increase of λIEE with decreasing Js suggests that IEE relaxation time τ is enhanced due to additional tunnelling barrier (Cu) that limits the interface transmission rate. The results have shown the importance of interface engineering in Py/TI magnetic heterostructure, which is the key factor for optimizing spin-to-charge conversion efficiency.

A topological semimetal PtSn4 single crystal is grown and the following properties are studied: its electrical resistivity in the temperature range from 4.2 to 300 K, galvanomagnetic properties at temperatures from 4.2 to 80 K and in magnetic fields of up to 100 kOe, and optical properties at room temperature. Theoretical calculations of the electronic structure are performed. It is shown that the residual resistivity is rather small: ρ0 = 0.47 μΩ cm, which is characteristic of a “good” metal. The ρ(T) dependence is of the metallic type, increasing monotonically with temperature. Analysis of the temperature dependences of the magnetoresistivity suggests that the Fermi surface of the PtSn4 compound may contain closed sheets. Studies of the Hall effect and the estimates made in the single-band model allowed us to conclude that the predominant type of current carriers are holes with concentration n = 6.8 × 1021 cm–3 and mobility μ ≈ 1950 cm2/(V s) at T = 4.2 K. It is shown that the optical properties of PtSn4 have features characteristic of “bad” metals. The calculation of the electronic structure of PtSn4 showed that, in general, this compound has a structure characteristic of metallic systems with a sufficiently large number of electronic states at the Fermi level, which is consistent with the experimental results on the electronic transport and optical properties of the PtSn4 single crystal.

Tuning the Fermi level (EF) in Bi2Te3 topological-insulator (TI) films is demonstrated on controlling the temperature of growth with molecular-beam epitaxy (MBE). Angle-resolved photoemission spectra (ARPES) reveal that EF of Bi2Te3 thin films shifts systematically with the growth temperature (Tg). The key role that a Bi-on-Te(1) (BiTe1) antisite defect plays in the electronic structure is identified through extended X-ray-absorption fine-structure (EXAFS) spectra at the Bi L3-edge. Calculations of electronic structure support the results of fitting the EXAFS, indicating that the variation of EF is due to the formation and suppression of BiTe1 that is tunable with the growth temperature. Our findings provide not only insight into the correlation between the defect structure and electronic properties but also a simple route to control the intrinsic topological surface states, which could be useful for applications in TI-based advanced electronic and spintronic devices.

Inorganic–organic hybrid perovskite solar cells (PSCs) are considered as one of the promising devices for green energy. Bifacial-illuminated solar cells have been studied for many practical applications such as in wearable electronics and building window devices. p-Type transparent conductive oxides (TCOs) are highly desired for efficient bifacial-illuminated solar cells. However, the preparation of p-type TCOs usually requires high power sputtering and high temperature processes, and the thus-prepared TCOs can hardly be applied to PSCs due to the vulnerability of perovskites. In this study, p-type Cu/Cu2O (CCO) composite films are developed for bifacial-illuminated PSCs. The p-type CCO composite films can be easily prepared by sputtering at room temperature and do not damage the underlying organic materials Spiro-OMeTAD and perovskites. With a reduced film thickness of about 12 nm, the p-type CCO films can be employed as transparent conductive films in PSCs. The power conversion efficiencies (PCEs) of 14.10% and 9.37% have been achieved for bifacial PSCs illuminated via the fluorine-doped tin oxide (FTO) and CCO sides, respectively. In addition, the CCO films are stable under ambient conditions and can serve as a protection layer for PSCs. Therefore, ultra-thin p-type CCO films are promising candidates for applications in bifacial-illuminated, efficient and stable PSCs under ambient conditions.

The electrical resistivity of thin films of topological insulator (TI) Bi2Se3 10 to 75 nm thick is measured in the temperature range of 4.2 to 300 K. A size effect is observed in the electrical conductivity of the Bi2Se3 films; i.e., there is a linear dependence of a film’s conductivity on its inverse thickness. It is assumed that a similar effect can be observed in other TIs and in systems with nonuniform distributions of current over the cross section of a sample.

Ultrathin bilayers (BLs) of bismuth have been predicated to be a two-dimensional (2D) topological insulator. Here we report on a new route to manufacture the high-quality Bi bilayers from a 3D topological insulator, a top-down approach to prepare large-area and well-ordered Bi(111) BL with deliberate hydrogen etching on epitaxial Bi2Se3 films. With scanning tunneling microscopy (STM) and X-ray photoelectron spectra (XPS) in situ, we confirm that the removal of Se from the top of a quintuple layer (QL) is the key factor, leading to a uniform formation of Bi(111) BL in the van der Waals gap between the first and second QL of Bi2Se3. The angle resolved photoemission spectroscopy (ARPES) in situ and complementary density functional theory (DFT) calculations show a giant Rashba splitting with a coupling constant of 4.5 eV A in the Bi(111) BL on Bi2Se3. Moreover, the thickness of Bi BLs can be tuned by the amount of hydrogen exposure. Our ARPES and DFT study indicated that the Bi hole-like bands increase with i...

ZnO nanowires (NWs) were directly grown on ductile zinc foil by thermal oxidation at 500 °C. The highly crystalline ZnO NWs exhibited bidirectional growth preferentially oriented in the [101] orientation. The ZnO NWs were highly resistant to hydroxyl groups and water compared with Zn foil that was oxidized naturally. The narrow excitonic photoluminescence (PL) peak combined with strongly suppressed visible emission demonstrated the high optical quality of the NWs. The binding energies of the donor bands and an acceptor band were obtained through temperature-dependent PL analysis. The NWs would be suitable for flexible planar UV device applications.

In this study, we investigate the proximity effect in topological insulator (TI) and magnetic insulator bilayer system. (Bi1−xSbx)2Se3/CoFe2O4 (CFO) heterostructure was fabricated using molecular beam epitaxy and pulsed laser deposition system respectively. As revealed from the magnetoresistance measurement, the weak anti-localization (WAL) is strongly suppressed by proximity effect in (Bi1−xSbx)2Se3/CFO interface. Modified Hikama-Larkin-Nagaoka equation was used to fit the WAL results so that the size of surface state gap can be extracted successfully. The temperature-dependent resistance of the heterostructures at small and large perpendicular magnetic fields were also measured and analyzed. The results indicate that the surface band gap can be induced in TI and continuously enlarged up to 9 T, indicating the gradual alignment of the magnetic moment in CFO under perpendicular magnetic field. The approaches and results accommodated in this work show that CFO can effectively magnetize (Bi1−xSbx)2Se3 and the heterostructures are promising for TI-based spintronic device applications.

Ultrathin three-dimensional topological insulator films are promising for use in field effect devices. (Bi1–xSbx)2Se3 ultrathin films were fabricated on SrTiO3 substrate, where large resistance changes of ∼25 000% could be achieved using the back gate voltage. We suggest that the large ON/OFF ratio was caused by the combined effect of Sb-doping and the reduction of film thickness down to the ultrathin regime. The crossover of different quantum transport under an electric field may form the basis for topological insulators (TI)-based spin transistors with large ON/OFF ratios in the future.

The Mn-doped PbPdO 2 nanograin film with many Pb vacancies was synthesized by using a sol-gel spin-coating method. The valence states for Pb, Pd and Mn ions were found to be 2 +, 2 + and the mixed one of 3 + and 4 +, respectively. The existence of Pb vacancies was believed to result in the increase of the Mn valence. The ferromagnetism and the antiferromagnetism were found to coexist in the formed Mn-doped PbPdO 2 nanograin film. The ferromagnetism which can be maintained to above the room temperature was proved to be intrinsic. The carrier-mediated mechanism bridged to bound magnetic polaron model was used to explain the coexistence of the antiferromagnetism and the ferromagnetism within the Mn-doped PbPdO 2 film.

ZnO nanowires (NWs) were directly grown on ductile zinc foils through a two-step process: (a) large, thin, and ductile Zn foils were fabricated from a mixture of Zn and ZnO powders; and (b) ZnO NWs were produced by thermal oxidation at temperatures of 300–600 °C. The ZnO NWs presented preferential growth in the [101] orientation. The highly crystalline NWs synthesized at 500 °C exhibited a bidirectional mode with an angle of approximately 60° between their longitudinal axes. On foils oxidized at 600 °C, the NWs evolved into nanotowers. The photoluminescence (PL) spectra showed strong peaks at approximately 368 nm and weaker peaks at approximately 374 nm in the UV region; moreover, a broad deep-level-related green emission peak was recorded at approximately 520 nm in the visible region. The PL green emission line was strongly suppressed for the samples produced at higher oxidation temperatures, which indicated good optical qualities. These good optical qualities, combined with the bidirectional mode and the ductility of the foil, are expected to be useful for flexible planar device applications. The electrical properties of a single ZnO NW were investigated. I–V measurements revealed the Schottky characteristics of the NWs and the resistivity of the ZnO NWs was measured to be ∼93 Ω cm.

In this study, a perovskite is integrated with an ultra-thin Cu/Cu

WTe2 and MoTe2 single crystals were grown, and their electrical resistivity in the temperature range from 80 K to 300 K, optical properties at room temperature in the spectral range of 0.17-5.0 eV were studied as well as theoretical calculations of the electronic structure were performed. It is shown that the temperature dependence of the electrical resistivity of orthorhombic WTe2 has a metallic type with resistivity value of (0.5-1) mOhmcm, while hexagonal MoTe2 has a semiconductor one and resistivity value (0.5-1) Ohmcm, which is three orders of magnitude larger than the resistivity of WTe2. Optical properties indicated that there is no contribution from free carriers in the entire spectral range studied. The calculated densities of the electronic states of MoTe2 and WTe2 showed the presence of a bunch of the molybdenum and tungsten electronic states in a wide energy interval with strong admixing of tellurium states. In the WTe2 compound, the larger number of the electronic states is located near the Fermi energy, characterizing a more metallic state in this compound as compared to MoTe2. © Published under licence by IOP Publishing Ltd. Government Council on Grants, Russian Federation: 02, 211 Russian Foundation for Basic Research, RFBR: 17-52-52008 Ministry of Education and Science of the Russian Federation, Minobrnauka: АААА-А18-118020190098-5 The research was carried out within the state assignment of Ministry of Education and Science of the Russian Federation (theme “Spin” No. АААА-А18-118020290104-2 and theme “Electron” No. АААА-А18-118020190098-5), supported in part by RFBR (Project No. 17-52-52008) and the Government of Russian Federation (Decree No. 211, Contract No. 02.A03.21.0006).

The single-phase body-centered-orthorhombic-structured Co-doped PbPdO 2 thin film was obtained using the sol–gel spin-coating method and an oxidation treatment. The film had a nanograin microstructure with an average grain size of about 56 nm and a thickness of about 150 nm. The adoption of a moderate calcination temperature of 650 °C was found to be very important for preparing the single-phase-PbPdO 2 -based film with a high crystalline quality. The magnetic studies exhibited that the ferromagnetism and the paramagnetism coexist within the formed Co-doped PbPdO 2 film and the ferromagnetism can be maintained above room temperature. The saturation magnetization of the ferromagnetism increasing with the temperature, as the peculiar characteristic of the spin gapless semiconductor, was found within the film. The investigation on the film's X-ray absorption near-edge structure revealed that the ferromagnetism of the Co-doped PbPdO 2 is intrinsic.

We have studied the magnetic origin and the effect of crystallinity of epitaxial semiconducting Co:ZnO films on ferromagnetism and magneto-transport properties by comparing signal-type domain (SD) and twin-type domain (TD) structure films grown in the same conditions. A higher saturation magnetization in TD films than that in SD films is observed, suggesting that bound charge carriers, produced mainly by defects in films, play a dominant role in ferromagnetism. A lower concentration of itinerant carriers in TD films than that in SD films is detected, which helps separate the effects of bound and itinerant carriers on ferromagnetism and magneto-transport. We hypothesize the interaction of the spin moments of itinerant carrier with the bound carrier mediated ferromagnetic domain results in the weaker strength of the anomalous Hall effect in TD films than that in SD films. It is likely that both itinerant and bound carriers are important for spintronic application in diluted magnetic oxides and could be modified by control of crystal structure.

Single-phase Co-doped PbPdO2 films with grain sizes ranging from 30 nm to 120 nm were synthesized using a sol–gel spin-coating method. The doped Co ions exhibit a mixed state of 2+ and 3+, which is caused by the existence of Pb vacancies and the low electronegativity of Co. Ferromagnetism, paramagnetism, antiferromagnetism and a charge ordering state were observed in all of the Co-doped PbPdO2 films. Additionally, the charge ordering signal determined by the surface state of the nanograins is gradually weakened with decreasing grain size. The carrier-mediated mechanism bridged to the bound magnetic polaron model was used to explain the coexistence of the ferromagnetism, paramagnetism and antiferromagnetism. For the ferromagnetism, the tendency of the saturation magnetization to increase with temperature was found in all the Co-doped PbPdO2 films with a nanograin structure. This abnormal magnetic behavior is believed to be one of the peculiar features of spin gapless semiconductors.

Long-range electronic interaction between Bismuth (Bi) adatoms on graphene formed on a 4H-SiC (0 0 0 1) substrate are clearly observed at room temperature (T = 300 K). Using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we have demonstrated that such oscillatory interaction results mainly from the mediation of graphene Dirac-like electrons and the effect of the corrugated surface of SiC substrate. These two factors cause the observed oscillatory interaction with characteristic distribution distances and linear arrangements of Bi adatoms. The present study sheds light on understanding and controlling the nucleation of adatoms and subsequent growth of nanostructures on graphene surface.

Cu/Cu2O films grown by ion beam sputtering were used as p-type modified layers to improve the efficiency and stability of perovskite solar cells (PSCs) with an n-i-p heterojunction structure. The ratio of Cu to Cu2O in the films can be tuned by the oxygen flow ratio (O2/(O2 + Ar)) during the sputtering of copper. Auger electron spectroscopy was performed to determine the elemental composition and chemical state of Cu in the films. Ultraviolet photoelectron spectroscopy and photoluminescence spectroscopy revealed that the valence band maximum of the p-type Cu/Cu2O matches well with the perovskite. The Cu/Cu2O film not only acts as a p-type modified layer but also plays the role of an electron blocking buffer layer. By introducing the p-type Cu/Cu2O films between the low-mobility hole transport material, spiro-OMeTAD, and the Ag electrode in the PSCs, the device durability and power conversion efficiency (PCE) were effectively improved as compared to the reference devices without the Cu/Cu2O interlayer. The enhanced PCE is mainly attributed to the high hole mobility of the p-type Cu/Cu2O film. Additionally, the Cu/Cu2O film serves as a protective layer against the penetration of humidity and Ag into the perovskite active layer.

The introduction of ferromagnetism at the surface of a topological insulator (TI) produces fascinating spin-charge phenomena. It has been assumed that these fascinating effects are associated with a homogeneous ferromagnetic (FM) layer possessing a single type of magnetic phase. However, we obtained phase separation within the FM layer of a Ni80Fe20/Bi2Se3 heterostructure. This phase separation was caused by the diffusion of Ni into Bi2Se3, forming a ternary magnetic phase of Ni:Bi2Se3. The inward diffusion of Ni led to the formation of an FeSe phase outward, transforming the original Ni80Fe20/Bi2Se3 into a sandwich structure comprising FeSe/Ni:Bi2Se3/Bi2Se3 with dual-phase magnetic characteristics similar to that driven by the proximity effect. Such a phenomenon might have been overlooked in previous studies with a strong focus on the proximity effect. X-ray magnetic spectroscopy revealed that FeSe and Ni:Bi2Se3 possess horizontal and perpendicular magnetic anisotropy, respectively. The overall magnetic order of the heterostructure can be easily tuned by adjusting the thickness of the Bi2Se3 as it compromises the magnetic orders of the two magnetic phases. This discovery is essential to the quantification of spin-charge phenomena in similar material combinations where the FM layer is composed of multiple elements.

Thin films of a topological insulator (TI) Bi 2 Se 3 of various thicknesses from 20 nm to 75 nm were obtained. The resistivity measurements were carried out according to the conventional 4-contact DC technique. This allows to "separate" the bulk and surface conductivities at different temperatures and magnetic fields. It was suggested that similar effects should be observed in other TIs and systems with inhomogeneous distribution of dc-current on sample cross section. © 2018 The Authors, published by EDP Sciences. This work was partly supported by the state assignment of FASO of Russia (theme “Spin” No. ȺȺȺȺ Ⱥ 4 ), by the RFBR (project No. 17-52-52008), by the Government of the Russian Federation (state contract No. 02.A03.21.0006), and by grant of Russian Ministry of Education and Science No 14.Z50.31.0025.

Interaction between magnetization dynamics and spin polarized electronic transport has been studied for ferromagnet nanodisk situated upon a 3D topological insulator (TI) film. Resonant magnetization dynamics leads to generation of spin current, which flows into the topological insulator, where spin to charge conversion occurs. Using micromagnetic simulations for magnetization dynamics we estimate the dc voltage, which is created due to this process in topological insulator. Contribution from different modes, which are characteristic for nanodisks, to the voltage was calculated.

The results of the nuclear magnetic resonance (NMR) study of a grown high-quality Bi2Te3 semiconductor single crystal have been presented. Signals from the 125Te isotope were detected by the spin echo method in the range from 10 K to room temperature. It was found that the NMR spectrum consists of two lines. The line with a positive shift of the resonance frequency corresponded to the bulk of the sample. The line with a negative shift was interpreted as a signal from the surface of the single crystal. The temperature and orientational dependences of the positions of the NMR line of nuclei in the bulk of the crystal were studied. It was shown that the shifts are mainly determined by the Knight shift due to the interaction with mobile charge carriers. The thermoactivation character of the concentration of mobile charges in the crystal under study, which corresponds to the intrinsic conductance, was proved, and the energy parameters of the thermoactivation processes were calculated.

This work investigates that the applied electric field modulates the line shapes of magnetoconductance ( MC ) responses in pentacene:fullerene diodes under illumination. We attribute the line shape of MC curves herein is correlated with the strength of the exchange interaction in pentacene:fullerene charge transfer (CT) complex states. Applying the reversed bias increases the built-in electric field ( E built-in ) of the diodes to offset the exchange interaction of CT complex states and narrows the line shapes of MC responses. The saturation field of MC curves in the pentacene:fullerene bulk heterojunction device is 752 Oe when the device is biased at 0.4 V and decreases to 212 Oe at a reversed bias of −1.0 V. The line shape of MC curves for the diode made of pristine pentacene or fullerene as the active layer does not change with the applied bias voltage. Our results indicate the correlations of MC responses with the exchange interaction of CT complexes as modulated by the applied electric field.

In this study, we integrated bilayer structure of covered Pt on nickel zinc ferrite (NZFO) and CoFe/Pt/NZFO tri-layer structure by pulsed laser deposition system for a spin Hall magnetoresistance (SMR) study. In the bilayer structure, the angular-dependent magnetoresistance (MR) results indicate that Pt/NZFO has a well-defined SMR behavior. Moreover, the spin Hall angle and the spin diffusion length, which were 0.0648 and 1.31 nm, respectively, can be fitted by changing the Pt thickness in the longitudinal SMR function. Particularly, the MR ratio of the bilayer structure (Pt/NZFO) has the highest changing ratio (about 0.135%), compared to the prototype structure Pt/Y3Fe5O12 (YIG) because the NZFO has higher magnetization. Meanwhile, the tri-layer samples (CoFe/Pt/NZFO) indicate that the MR behavior is related with CoFe thickness as revealed in angular-dependent MR measurement. Additionally, comparison between the tri-layer structure with Pt/NZFO and CoFe/Pt bilayer systems suggests that the SMR ratio can be enhanced by more than 70%, indicating that additional spin current should be injected into Pt layer.

Ultrathin three-dimensional topological insulator films are promising for use in field effect devices. (Bi

Mn-doped ZnTe nanoparticles with various degrees of Mn-doping from 3 at.% to 18 at.% were synthesized by a hydrothermal method. A single-phase zinc-blende-structured sample was obtained only at the Mn-doping level of 3 at.%, while the impurity phase of MnO was present in the samples with higher degrees of Mn-doping. In all of the samples, the Mn valence states were lower than 2+. All samples exhibited both ferromagnetism and paramagnetism. The ferromagnetism is mainly attributable to the overlapping of the bound magnetic polarons and the paramagnetism is mainly caused by the isolated polarons and Mn ions. Samples that were doped with 3 at.% and 6 at.% Mn also exhibited superparamagnetism and antiferromagnetism. The superparamagnetism may have arisen from the presence of some tiny ferromagnetic nanoparticles. The antiferromagnetism is believed to have arisen mainly from the carrier-mediated interaction among Mn ions.

In this study, In2O3 films were prepared by three methods and resulted in three different film structures. We firstly produced In2O3 polycrystal films by the evaporation of In source under oxygen ambient. In the second attempt, In2O3(111) films were fabricated by oxidation of In films. The surface scattering contributed to the resistivity of the oxidized In film and resulted a poor conductivity. As the third approach, a combination of the first and the second way, we prepared an ultrathin In film, oxidized it, and made it served as a seeding layer in the evaporation of In source under oxygen ambient. Due to the specific fabrication, we obtained the In2O3(111) films, in which a better conductivity and a smooth surface were observed in the In2O3(111) film through the third approach.

In this study, a perovskite is integrated with an ultra-thin Cu/Cu2O (CCO) composite film, a transparent material with high mobility, to achieve a double-side and low-voltage operable photodetector. Compared to photodetectors that utilize metal electrode with perovskite, the use of CCO significantly enhances the photocurrent (from nA up to mA). It acts as a large-scale hole transport layer. The photodetector exhibits high responsivities of 6.79 AW-1 [illuminated via the fluorine-doped tin oxide (FTO) side] and 10.23 AW-1 (illuminated via CCO side). The detectivities obtained at both illuminated sides are as high as over 1011 Jones. Additionally, the Cu/Cu2O-covered perovskite effectively prevents the reaction of perovskite in the interface. This work reveals that the perovskite/CCO heterojunction photodetector can be considered a promising candidate for applications in bifacial-illuminated and flexible/wearable optoelectronic technologies.

In this study, we investigate the proximity effect in topological insulator (TI) and magnetic insulator bilayer system. (Bi1−xSbx)2Se3/CoFe2O4 (CFO) heterostructure was fabricated using molecular beam epitaxy and pulsed laser deposition system respectively. As revealed from the magnetoresistance measurement, the weak anti-localization (WAL) is strongly suppressed by proximity effect in (Bi1−xSbx)2Se3/CFO interface. Modified Hikama-Larkin-Nagaoka equation was used to fit the WAL results so that the size of surface state gap can be extracted successfully. The temperature-dependent resistance of the heterostructures at small and large perpendicular magnetic fields were also measured and analyzed. The results indicate that the surface band gap can be induced in TI and continuously enlarged up to 9 T, indicating the gradual alignment of the magnetic moment in CFO under perpendicular magnetic field. The approaches and results accommodated in this work show that CFO can effectively magnetize (Bi1−xSbx)2Se3 and the heterostructures are promising for TI-based spintronic device applications.

The influence of Ir1-xMnx composition and post-annealing on structure and exchange bias of epitaxial Ir1-xMnx(~10 nm)/Ni80Fe20(7 nm) films were studied. The Ir1-xMnx layer was prepared by MBE growth of [Mn(0.4 nm

Thin films of the zinc nickel ferrite, Zn0.7Ni0.3Fe2O4 (ZNFO), were deposited by the RF magnetron sputtering on a number of substrates, including (001) oriented single crystals of LaAlO3 (LAO) and SrTiO3 (STO), polycrystalline Pt/Si, and epitaxial films of BiFeO3 (BFO) and LaNiO3 (LNO). Except for the films on Pt/Si, the ZNFO films grown on other substrates were epitaxial and their magnetic properties were affected by the heteroepitaxy induced strains. Typically, the coercivity (Hc) was increased with the strain, i.e. Hc varied from 31 Oe for the 150 nm thick polycrystalline films grown on Pt/Si, to 55 Oe and 155 Oe for the 20 nm thick epitaxial films grown on BFO and LAO, respectively. The saturation magnetization of the epitaxial films was reduced accordingly to about 470 emu/cm3 from 986 emu/cm3 in the polycrystalline films. The all-oxide architecture allowed field-annealing to perform at the temperature above the Neel temperature of BFO (~ 370 °C), after which clear exchange bias was observed.

We present the surface electronic and magnetic properties of half-metal La0.6Sr0.4MnO3 (LSMO) thin film modified by a simple cleaning procedure, the so-called SC1 (5 H2O, 1 NH4OH, 1 H2O2), at 85 °C...

A new method to grow a well-ordered epitaxial ZnFe 2 O 4 thin film on Al 2 O 3 (0001) substrate is described in this work. The samples were made by annealing the ZnO/Fe 3 O 4 multilayer which was grown with low energy ion beam sputtering deposition. Both the Fe 3 O 4 and ZnO layers were found grown epitaxially at low temperature and an epitaxial ZnFe 2 O 4 thin film was formed after annealing at 1000 °C. X-ray diffraction shows the ZnFe 2 O 4 film is grown with an orientation of ZnFe 2 O 4 (111)//Al 2 O 3 (0001) and ZnFe 2 O 4 (1–10)//Al 2 O 3 (11–20). X-ray absorption spectroscopy studies show that Zn 2+ atoms replace the tetrahedral Fe 2+ atoms in Fe 3 O 4 during the annealing. The magnetic properties measured by vibrating sample magnetometer show that the saturation magnetization of ZnFe 2 O 4 grown from ZnO/Fe 3 O 4 multilayer reaches the bulk value after the annealing process.

A systematic investigation of structural, magnetic and electrical properties of nanocrystalline La 0.67 Ba 0.33 MnO 3 materials, prepared by citrate gel method has been undertaken. The temperature-dependant low-temperature resistivity in ferromagnetic metallic (∼50 K) phase shows upturn behavior and is suppressed with applied magnetic field. The experimental data ( T T P ) has been fitted with grain/domain boundary, electron–electron and magnon scattering mechanisms, while the insulating region ( T > T P ) of resistivity data has been explained based on adiabatic small polaron hopping mechanism.

Multiferroic BiFeO 3 films have been deposited on a number of substrates by RF magnetron sputtering. Two routes were adopted in order to obtain the films of high phase purity and accurate stoichiometry. The first was to sputter films at room temperature and then the BiFeO 3 phase was formed after sintering at various temperatures under controlled ambient atmosphere. The second was to grow BiFeO 3 in-situ at high temperature during sputtering. Although the sintered films grown on SrTiO 3 substrates were epitaxial and showed better texture than the in-situ films, they had much poorer ferroelectric properties, due to the residual traces of intermediate phases formed during heating. Under right growth parameters, the in-situ films grown on the LaNiO 3− x buffered SrTiO 3 showed fully saturated ferroelectric hysteresis loops with large remanent polarisation of 64 μC/cm 2 . Piezoresponse force microscopy (PFM) was used to examine the ferroelectric domain structures. When scanned without DC bias, fine spontaneous domains were observed. Under ±10 V DC bias, PFM confirmed that the domains could be poled and switched.

Multiferroic BiFeO 3 films of smooth surface and fully-saturated ferroelectric hysteresis loops have been grown by RF magnetron sputtering. The (001)-oriented epitaxial films showed a large remanent polarisation of 61 µC/cm 2 . A strategy to grow BiFeO 3 films of good ferroelectric property was demonstrated, that was using fast growth rate to achieve accurate stoichiometry for the BiFeO 3 phase and at the same time to avoid the formation of impurity phases associated with the fast growth by accurate control of thermodynamic parameters such as oxygen partial pressure and temperature, as well as proper selection of substrates. Piezoresponse force microscopy revealed fine spontaneous domains for highly resistive epitaxial films, which were switchable under DC biases. For the polycrystalline films of increased density of free carriers, single-domain grains of about 200 nm in diameter were observed due to effective compensation of depolarisation field by free carriers and therefore allowing larger domains.

Room temperature diluted ferromagnetic semiconductor is a very promising candidate for spintronics applications. In this work, we present the cobalt ion implanted ZnO epitaxial thin film under controlled annealing temperature to investigate the origin of ferromagnetism in this system. For the as-implanted sample a metallic cobalt cluster was observed. After annealing at 700degC, the Co atoms were to substitute the Zn sites of the ZnO matrix and exhibited a spontaneous room temperature ferromagnetism. However the XMCD measurements on the annealed samples show the cobalt element is almost paramagnetism at 26 K. The result might indicate oxygen vacancies caused ferromagnetism of intrinsic dilute magnetic semiconductors in the sample of the Co-implanted ZnO.

Spin-casting or thermal evaporation in vacuum of a salt-free, neutral, organic-oxide ultra-thin film as a buffer layer with an aluminum (Al) cathode has become an alternative approach for fabricating high-performance organic and polymer light-emitting diodes (O/PLEDS). [Guo et al., Appl. Phys. Lett. 2006, 88, 113501 and Appl. Phys. Lett. 2006, 89, 053507] The electroluminescence efficiency of phenyl-substituted poly(para-phenylene vinylene) copolymer-based PLEDs is 0.16 cd A -1 when Al is used as the device cathode, but is approximately two orders of magnitude higher, 14.53 cd A -1 , when an organic oxide/A 1 composite cathode is used. The polymer/metal junction in PLEDs with and without depositing an ultra-thin organic oxide interlayer is studied by X-ray photoelectron spectroscopy. Experimental results indicate that the deposition of an Al electrode causes the oxidation at the surface of the light-emissive polymer layer. Introducing an organic-oxide cathode buffer layer suppresses the oxidation and the diffusion of the Al atoms into the functional polymer layer. The formation of a carbide-like (negative carbon) thin layer, which accompanies interfacial interactions, is critical to the injection of electrons through the Al cathode. The balanced charge injection is responsible for the substantially improved device performance. This process is specific to the organic oxide/A1 interface, as revealed by a comparison with similar device configurations that have Ag as the electrode, in which no significant interaction in the interface is observed.

Epitaxial Ni80Fe20(5 nm)/Ru(x nm)/Ni80Fe20(5 nm) trilayers with thickness x = 0.5–3.0 were prepared on Al2O3 ( 1 1 2 ¯ 0 ) substrate. The structure, magnetic properties and magnetic depth profiles of the epitaxial Ni80Fe20(1 1 1)/Ru(0 0 0 1) multilayers were studied by X-ray diffraction, X-ray magnetic circular dichroism and polarized neutron reflectivity. A strongly enhanced orbital moment of Fe in the permalloy layer was observed at the Ru thickness of the first anti-ferromagnetic coupling, which might be due to an interference between two interfaces. At this Ru thickness, the neutron reflectivity data show a 0.8 nm layer at the interface with the magnetic moment perpendicular to the surface plane, which might be due to the enhanced spin-orbital coupling at interface.

To improve graphene-based multifunctional devices at nanoscale, a stepwise and controllable fabrication procedure must be elucidated. Here, a series of structural transition of bismuth (Bi) adatoms, adsorbed on monolayer epitaxial graphene (MEG), is explored at room temperature. Bi adatoms undergo a structural transition from one-dimensional (1D) linear structures to two-dimensional (2D) triangular islands and such 2D growth mode is affected by the corrugated substrate. Upon Bi deposition, a little charge transfer occurs and a characteristic peak can be observed in the tunneling spectrum, reflecting the distinctive electronic structure of the Bi adatoms. When annealed to ~500 K, 2D triangular Bi islands aggregate into Bi nanoclusters (NCs) of uniform size. A well-controlled fabrication method is thus demonstrated. The approaches adopted herein provide perspectives for fabricating and characterizing periodic networks on MEG and related systems, which are useful in realizing graphene-based electronic, energy, sensor and spintronic devices.

The geometric and electronic properties of Bi-adsorbed monolayer graphene, enriched by the strong effect of substrate, are investigated by first-principles calculations. The six-layered substrate, corrugated buffer layer, and slightly deformed monolayer graphene are all simulated. Adatom arrangements are thoroughly studied by analyzing the ground-state energies, bismuth adsorption energies, and Bi-Bi interaction energies of different adatom heights, inter-adatom distance, adsorption sites, and hexagonal positions. A hexagonal array of Bi atoms is dominated by the interactions between the buffer layer and the monolayer graphene. An increase in temperature can overcome a $\sim 50$ meV energy barrier and induce triangular and rectangular nanoclusters. The most stable and metastable structures agree with the scanning tunneling microscopy measurements. The density of states exhibits a finite value at the Fermi level, a dip at $\sim -0.2$ eV, and a peak at $\sim -0.6$ eV, as observed in the experimental measurements of the tunneling conductance.