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Fe-substituted NiO nanoparticles (Ni1−xFexO2) (x= 0.00, 0.03, 0.05, 0.07, and 0.09) were synthesised using ball-milling method followed by vacuum sintering and studied for their microstructural and magnetic properties. All the samples show a cubic structure with a crystallite size of 17–26 nm. Secondary phases related to Fe2O3 were identified from XRD, indicating that the observed ferromagnetism may be due to the dopants. The doping of Fe ions does not cause any significant variation in the crystal structure. The pure NiO nanoparticles were weak ferromagnetic in nature, and Fe-doped NiO nanoparticles exhibit room temperature ferromagnetism. The strength of magnetization increased from 0.57 to 0.94 emu/g with an increase of Fe concentration from 3 to 7 at.%, respectively. A high coercive field of 173 Oe was observed for the Ni1−xFexO2 nanoparticles at x= 0.09. The results and the process of development of ferromagnetism at room temperature in the Ni1−xFexO2 nanoparticles were presented and discussed in detail.

Nickel doped indium oxide thin films (In1−xNix)2O3 at x = 0.00, 0.03, 0.05 and 0.07 were deposited onto glass substrates by electron beam evaporation technique. The deposited thin films were subjected to annealing in air at 250 °C, 350 °C and 450 °C for 2 h using high temperature furnace. A set of films were vacuum annealed at 450 °C to study the role of oxygen on magnetic properties of the (In1−xNix)2O3 thin films. The thin films were subjected to different characterization techniques to study their structural, chemical, surface, optical and magnetic properties. All the synthesized air annealed and vacuum annealed films exhibit body centered cubic structure without any secondary phases. No significant change in the diffraction peak position, either to lower or higher diffraction angles has been observed. The band gap of the films decreased from 3.73 eV to 3.63 eV with increase of annealing temperature from 250 °C to 450 °C, in the presence of air. From a slight decrease in strength of magnetization to a complete disappearance of hysteresis loop has been observed in pure In2O3 thin films with increasing the annealing temperature from 250 °C to 450 °C, in the presence of air. The (In1−xNix)2O3 thin films annealed under vacuum follow a trend of enhancement in the strength of magnetization to increase in temperature from 250 °C to 450 °C. The hysteresis loop does not disappear at 450 °C in (In1−xNix)2O3 thin films, as observed in the case of pure In2O3 thin films.

An effort was made to develop semiconductor oxide-based room temperature dilute magnetic semiconductor (DMS) thin films based on wide band gap and transparent host lattice with transition metal substitution. The Sn $_{\mathrm {1}-x}$ Ni $_{x}\textit {O}_{\mathrm {2}}$ ( $x\,= \mathrm {0.00, 0.03, 0.05, 0.07, 0.10, and \,0.15}$ ) thin film samples were prepared on glass substrates by flash evaporation technique. All the samples were shown single phase crystalline rutile structure of host SnO $_{\mathrm {2}}$ with dominant (110) orientation. The Ni substitution promotes reduction of average crystallite size in SnO $_{\mathrm {2}}$ as evidenced from the reduction of crystallite size from 40 (SnO $_{\mathrm {2}}$ ) to 20 nm (Sn $_{\mathrm {0.85}}$ Ni $_{\mathrm {0.15}}\textit {O}_{\mathrm {2}}$ ). In the energy dispersive spectra as well as X-ray photoelectron spectra of all the samples show, the chemical compositions are close to stoichiometric with noticeable oxygen deficiency. The crystalline films were formed by coalescence of oval-shaped polycrystalline particles of 100 nm size as evidenced from the electron micrographs. The energy band gap of DMS films decreases from 4 (SnO $_{\mathrm {2}}$ ) to 3.8 eV (x $=$ 0.05) with increase of Ni content. The magnetic hysteresis loops of all the samples at room temperature show soft ferromagnetic nature except for SnO $_{\mathrm {2}}$ film. The SnO $_{\mathrm {2}}$ films show diamagnetic nature and it converts into ferromagnetic upon substitution of 3 % Sn $^{\mathrm {4+}}$ by Ni $^{\mathrm {2+}}$ . The robust intrinsic ferromagnetism (saturation magnetization, 21 emu/cm $^{\mathrm {3}}$ ). Further increase of Ni content weakens ferromagnetic strength due to Ni-O antiferromagnetic interactions among the nearest neighbour Ni ions via O $^{\mathrm {2-}}$ ions. The observed magnetic properties were best described by bound magnetic polarons model.

Iron doped tin oxide thin films (Sn1−xFexO2) at x = 0.00, 0.03, 0.05, 0.07,0.10 and 0.15 were prepared onto Corning 7059 substrates using flash evaporation technique and studied the effect of iron (Fe) doping concentration on structural, optical and magnetic properties of the prepared thin films. From the X-ray diffraction patterns, it was found that the Sn1−xFexO2 thin films were polycrystalline with tetragonal structure. The crystallite sizes of the films were calculated using Scherrer’s relation and found that it was about 25 nm. The chemical composition and oxidation states of the elements were found using energy dispersive analysis of X-rays and X-ray photoelectron spectroscopy. From this it was confirmed that the Fe was substituted Sn sites and is in Fe+3states. The optical band gap of the films decreased from 3.98 to 3.76 eV with increase of Fe doping concentration. The pure SnO2 thin films exhibited diamagnetism whereas Sn1−xFexO2 thin films exhibited ferromagnetism at room temperature. A magnetic (Ms), coercivity (Hci) and retentivity (Mr) were found to be 13.062 emu/cm3, 114.98 G, 7.487 × 10−6 emu/cm3, respectively Sn1−xFexO2 thin films at x = 0.07.

Large-area and highly crystalline CVD-grown multilayer MoSe2 films exhibit a well-defined crystal structure (2H phase) and large grains reaching several hundred micrometers. Multilayer MoSe2 transistors exhibit high mobility up to 121 cm(2) V(-1) s(-1) and excellent mechanical stability. These results suggest that high mobility materials will be indispensable for various future applications such as high-resolution displays and human-centric soft electronics.

Thin-film transistors (TFTs) based on multilayer molybdenum diselenide (MoSe2 ) synthesized by modified atmospheric pressure chemical vapor deposition (APCVD) exhibit outstanding photoresponsivity (103.1 A W-1 ), while it is generally believed that optical response of multilayer transition metal dichalcogenides (TMDs) is significantly limited due to their indirect bandgap and inefficient photoexcitation process. Here, the fundamental origin of such a high photoresponsivity in the synthesized multilayer MoSe2 TFTs is sought. A unique structural characteristic of the APCVD-grown MoSe2 is observed, in which interstitial Mo atoms exist between basal planes, unlike usual 2H phase TMDs. Density functional theory calculations and photoinduced transfer characteristics reveal that such interstitial Mo atoms form photoreactive electronic states in the bandgap. Models indicate that huge photoamplification is attributed to trapped holes in subgap states, resulting in a significant photovoltaic effect. In this study, the fundamental origin of high responsivity with synthetic MoSe2 phototransistors is identified, suggesting a novel route to high-performance, multifunctional 2D material devices for future wearable sensor applications.

Layered semiconductors with atomic thicknesses are becoming increasingly important as active elements in high-performance electronic devices owing to their high carrier mobilities, large surface-to-volume ratios, and rapid electrical responses to their surrounding environments. Here, we report the first implementation of a highly sensitive chemical-vapor-deposition-grown multilayer MoSe2 field-effect transistor (FET) in a NO2 gas sensor. This sensor exhibited ultra-high sensitivity (S = ca. 1,907 for NO2 at 300 ppm), real-time response, and rapid on–off switching. The high sensitivity of our MoSe2 gas sensor is attributed to changes in the gap states near the valence band induced by the NO2 gas absorbed in the MoSe2, which leads to a significant increase in hole current in the off-state regime. Device modeling and quantum transport simulations revealed that the variation of gap states with NO2 concentration is the key mechanism in a MoSe2 FET-based NO2 gas sensor. This comprehensive study, which addresses material growth, device fabrication, characterization, and device simulations, not only indicates the utility of MoSe2 FETs for high-performance chemical sensors, but also establishes a fundamental understanding of how surface chemistry influences carrier transport in layered semiconductor devices.

We used high-resolution Kelvin probe force microscopy (KPFM) to investigate the immobilization of a prostate specific antigen (PSA) antibody by measuring the surface potential (SP) on a MoS2 surface over an extensive concentration range (1 pg/ml–100 μg/ml). After PSA antibody immobilization, we demonstrated that the SP on the MoS2 surface characterized by KPFM strongly correlated to the electrical signal of a MoS2 bioFET. This demonstration can not only be used to optimize the immobilization conditions for captured molecules, but can also be applied as a diagnostic tool to complement the electrical detection of a MoS2 FET biosensor.

Various strategies and mechanisms have been suggested for investigating a Schottky contact behavior in molybdenum disulfide (MoS2) thin-film transistor (TFT), which are still in much debate and controversy. As one of promising breakthrough for transparent electronics with a high device performance, we have realized MoS2 TFTs with source/drain electrodes consisting of transparent bi-layers of a conducting oxide over a thin film of low work function metal. Intercalation of a low work function metal layer, such as aluminum, between MoS2 and transparent source/drain electrodes makes it possible to optimize the Schottky contact characteristics, resulting in about 24-fold and 3 orders of magnitude enhancement of the field-effect mobility and on-off current ratio, respectively, as well as transmittance of 87.4 % in the visible wavelength range.