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Quasi-2D thin film of TI material TlBiSe2, as well as TlBiSe2/GaN configuration, have been fabricated employing the thermal evaporation technique. Raman peaks of vibrational modes were analyzed in a TlBiSe2/GaN heterojunction showing a substrate-induced signal for the surface phonon mode (SPM). The study of ultrafast kinetics of charge carriers and transient absorption spectroscopy (TAS) gave excited-state spectrum characteristics and exciton dynamics in TlBiSe2/GaN heterojunction. The electrical characterization showed that the heterojunction device exhibited a good diode nature with an excellent rectification ratio of 160. The photodetection capabilities were examined by optical power varying from 2.37 µW to 3.78 µW in the ultraviolet to near-infrared region (300–900 nm). It demonstrated maximum photoresponse at 500 nm in forward and reverse bias. The current conduction mechanism and enhancement in current under light impact were explained using energy band modeling. The present work is important in regarding the development of photodetectors of succeeding generations with a topological insulator material. [ABSTRACT FROM AUTHOR]

The bulk carrier excitation influences the phonon dynamics, which can alter and modulate the surface charge density of topological insulators such as bismuth selenide (Bi2Se3). This work investigates the charge carrier and phonon dynamics in Bi2Se3 grown on various substrates. The orientation of the substrate, the size of the crystallites, and the misfit of the lattice affect the carrier and phonon dynamics. Bi2Se3 thin films are grown under the same growth conditions on SiO2, Si(111), and SiN. Bi2Se3 overlayers exhibit substrate- dependent charge carrier relaxation channels and phonon dynamics. It is evident from Raman spectroscopy and ultrafast transient absorption spectroscopy that the heterointerface interactions of all three samples affect the vibration modes of Bi2Se3 and coherent acoustic phonon oscillations in the NIR range. At 13.6, 41.2, and 34.4 GHz, the vibration modes of SiO2, Si(111), and SiN are equivalent. The propagation depth of phonon waves is shown by measuring the speed of sound in Bi2Se3 overlayers on SiO2, Si(111), and SiN. This study demonstrates that the surface and bulk-bound charge carriers of a topological insulator determine the frequency and velocity of the generated sound. [ABSTRACT FROM AUTHOR]

The effect of deposition temperature on surface morphology and write once read many times resistive switching properties of RF sputtered BaTiO3 (BTO) thin films has been demonstrated. A conventional sandwiched structure was used to fabricate the memory cell with FTO as bottom electrode and silver as top electrode. The devices exhibit switching from a high resistance state to a low resistance state with the conductive filament(s) formation through BTO active layer. The switching performances are investigated for different devices with different deposition temperatures, varying from room temperature (RT) to 450 °C. All the devices are characterized for a voltage sweep of − 1.5 V to 1.5 V with 12,000 pulses for retention and 300 write-read erase read cycles. Shifting in the switching voltage to a lower value from 1.31 to 0.49 V (450 °C) is recorded with the increased deposition temperature. We observe the highest on-off ratio of 5.9 × 106 for sample deposited at room temperature and 0.9 × 104 for sample deposited at 450 °C. The write read erase read characterizations for over 1000 cycles were carried out for all four devices to test the device reliability and observe the stable read current over the period irrespective of erase cycles. The fabricated devices show stable and reliable reading endurance and data retention characteristics for more than 12,000 s. [ABSTRACT FROM AUTHOR]

We report the ultrafast carrier dynamics of an SnSe2–SnSe composite thin film (∼150 nm thick) deposited using thermal evaporation of in-house synthesized SnSe2 powder. Raman and UV–visible spectroscopy supports the optical properties (direct and indirect bandgaps of 1.86 eV and 0.96 eV, respectively). Ultrafast transient spectroscopy is used to study the charge excited state dynamics in the SnSe2–SnSe composite thin film in the femtosecond to nanosecond interval. An energy model has been proposed based on the ultrafast transient absorption and the thin film's steady-state absorption studies. This article provides comprehensive knowledge about the excited carriers and their relaxations in 0.9 ps–31.1 ns via different trap states. [ABSTRACT FROM AUTHOR]

Here, an ultrafast direct laser patterning technique to fabricate a low-cost microsensor and its application for formaldehyde detection are reported. The patterns of microheater and interdigitated electrodes (IDEs) were realized using laser micromachining techniques by ablation of gold thin film on alumina substrate. The thin film of gold microheater showed good stability up to 300 °C with a fast response time of 80 s and temperature coefficient of resistance (TCR) was calculated as 1.37 × 10−3/°C. Moreover, gold microheater exhibited long-term reliability under self-heating mode with a negligible resistance drift < 0.5% over a period of 330 h at 250 °C through consuming low power with a heating efficiency of 0.23 °C/mW. Thermal imaging camera revealed the uniform temperature distribution with negligible heat gradient profile over the whole microsensor platform. To state-of-the-art gas sensing application of this coplanar sensing platform, a nanostructured SnO2 was deposited on IDE, which exhibited high sensitivity (13.96% ppm−1) to formaldehyde even to detect sub-ppm concentrations with fast response (32 s) and recovery kinetics (72 s). Moreover, the microsensor was also used on-site rapid screening for the detection and quantification of formaldehyde concentration in formalin-treated fish sample. [ABSTRACT FROM AUTHOR]

We have developed a highly tunable film bulk acoustic wave resonator (TFBAR) using magnetostrictive (MS) Fe65Co35 thin films in acoustic layer stack. The resonator acoustic layer stack consists of Pt/ZnO/Fe65Co35 layers to tune the devices. Due to $\Delta {E}$ effect, TFBAR resonance frequency was up-shifted ~106.9 MHz (4.91%) in the presence of 2-kOe magnetic field. From experimental measurement, $\Delta {E}$ enhancement was estimated to be ~35 GPa. Further, it is observed that return loss (${S}_{{11}}$), phase response, and quality factor were improved in the presence of magnetic field. This improvement is due to the field-induced stiffness in the magnetic layer. Equivalent-modified Butterworth–Van Dyke (mBVD) circuit model was developed and fit with the experimental data, and circuit parameters were extracted. The proposed resonator is compact, low loss, power efficient, and highly tunable. This method also facilitates a new method of tuning FBAR devices using MS thin films. [ABSTRACT FROM AUTHOR]

ZnO thick Stress relaxed films were deposited by reactive magnetron sputtering on 2"-wafer of SiO2/Si at room temperature. The residual stress of ZnO films was measured by measuring the curvature of wafer using laser scanning method and found in the range of 0.18 x 109 × 11.28 x 109 dyne/cm2 with compressive in nature. Sputter pressure changes the deposition rates, which strongly affects the residual stress and surface morphologies of ZnO films. The crystalline wurtzite structure of ZnO films were confirmed by X-ray diffraction and a shift in (0002) diffraction peak of ZnO towards lower 2θ angle was observed with increasing the compressive stress in the films. The band gap of ZnO films shows a red shift from ~3.275 eV to ~3.23 eV as compressive stress is increased, unlike the stress for III-nitride materials. A relationship between stress and band gap of ZnO was derived and proposed. The stress-free growth of piezoelectric films is very important for functional devices applications. [ABSTRACT FROM AUTHOR]

Abstract: During AES and EELS investigations of thermal stability of Mg and Mg2Si films it was found that metallic Mg desorbs from the surface at temperatures higher than 80 °C, but the bulk-like Mg2Si film shows a thermal stability up to 180 °C. The maximal thermal stability up to 230 °C was observed for a two-dimensional magnesium silicide with structure (2/3√3×2/3√3)-R30°. A model of its thermal stability based on the peculiarities of the electronic structure of a two-dimensional magnesium silicide with structure (2/3√3×2/3√3)-R30° and on the continuity of 2D film was proposed. [Copyright &y& Elsevier]

This paper reports the deposition and characterization of nanocrystalline carbon thin films by filtered cathodic jet carbon arc technique assisted with three different gaseous environments of helium, nitrogen and hydrogen. All the films are nanocrystalline in nature as observed from the high resolution transmission electron microscopic (HRTEM) measurements, which suggests that the nanocrystallites of size ∼10–50 nm are embedded though out the amorphous matrix. X-ray photoelectron spectroscopic studies suggest that the film deposited under the nitrogen gaseous environment has the highest sp 3 /sp 2 ratio accompanied with the highest hardness of ∼18.34 GPa observed from the nanoindentation technique. The film deposited under the helium gaseous environment has the highest ratio of the area under the Raman D peak to G peak ( A D / A G ) and the highest conductivity (∼2.23 S/cm) at room temperature, whereas, the film deposited under the hydrogen environment has the lowest conductivity value (2.27 × 10 −7 S/cm). The temperature dependent dc conduction behavior of all the nanocrystalline carbon thin films has been analyzed in the light of Mott’s variable range hopping (VRH) conduction mechanism and observed that all the films obey three dimension VRH conduction mechanism for the charge transport. [ABSTRACT FROM AUTHOR]