Journal of Physics D: Applied Physics

Sharif, Ayesha; Farid, Nazar; Wang, Mingqing; Vijayaraghavan, Rajani K; Choy, Kwang-Leong; McNally, Patrick J; O’Connor, Gerard M

doi: 10.1088/1361-6463/ac3e91pmid: N/A

It is challenging to crystalize a thin film of higher melting temperature when deposited on a substrate with comparatively lower melting point. Trading such disparities in thermal properties between a thin film and its substrate can significantly impede material processing. We report a novel solid-state crystallization process for annealing of high melting point molybdenum thin films. A systematic investigation of laser induced annealing from single pulse to high pulse overlapping is reported upon scanning at fluences lower than the threshold required for the damage/ablation of molybdenum thin films. The approach allows better control of the grain size by changing the applied laser fluence. Atomic force microscopy surface morphology and x-ray diffraction (XRD) analysis reveal significant improvements in the average polycrystalline grain size after laser annealing; the sheet resistance was reduced by 19% of the initial value measured by a Four-point probe system. XRD confirms the enlargement of the single crystal grain size. No melting was evident, although a change in the close packing, shape and size of nanoscale polycrystalline grains is observed. Ultrashort laser induced crystallinity greatly enhances the electrical properties; Hall measurements reinforced that the overall carrier concentration increases after scanning at different laser fluences. The proposed method, based on the aggregation and subsequent growth of polycrystalline and single crystal-grains, leading to enhanced crystallization, has potential to be applicable in thin film processing industry for their wide applications.

Buzdakov, A G; Skirdkov, P N; Zvezdin, K A

doi: 10.1088/1361-6463/ac3e93pmid: N/A

Spin-torque diodes (STDs) with interfacial perpendicular magnetic anisotropy (IPMA) in the free layer (FL) demonstrate outstanding microwave signal rectification performances. Large sensitivity values in such systems are usually associated with an easy-cone (EC) magnetic state, when the magnetization in the FL is tilted from the normal to the plane of the film. Here, we theoretically investigate the phase diagram for the EC state in an infinite FL of the magnetic tunnel junction (MTJ) considering both IPMA (of the first and of the second order) and magnetostatic interaction. We show that the increase of the magnetostatic field leads to the EC state phase expansion. For elliptical MTJ nanopillars we investigate the influence of the orientation of the nanopillar ellipticity on the obtained phase diagrams. And finally, we consider the dynamic properties and rectification efficiency of the STD under microwave current injection. Our results clarify the role of magnetostatic interaction for microwave rectification with the IPMA-based STDs and suggest approaches to the EC state effective rectification phase extension through the parameters optimization.

Challa, S R; Witte, H; Schmidt, G; Bläsing, J; Vega, N; Kristukat, C; Müller, N A; Debray, M E; Christen, J; Dadgar, A; Strittmatter, A

doi: 10.1088/1361-6463/ac40b8pmid: N/A

The characteristic energies of traps in InAlN/AlN/GaN high-electron mobility transistor structures on Si(111) substrates formed after irradiation with 75 MeV S-ions are studied by means of c-lattice parameter analysis, vertical IV-characteristics, micro-photoluminescence (µ-PL), photocurrent (PC) and thermally stimulated current (TSC) spectroscopy. From the lattice parameter analysis, point defect formation is concluded to be the dominant source of defects upon irradiation. A strong compensation effect manifests itself through enhanced resistivity of the devices as found in vertical IV-measurements. Defect formation is detected optically by an additional PL-band within the green spectral region, while defect states with threshold energies at 2.9 eV and 2.65 eV were observed by PC spectroscopy. The TSC spectra exhibit two defect-related emissions between 300 K and 400 K with thermal activation energies of 0.78–0.82 eV and 0.91–0.98 eV, respectively. The data further supports the formation of Ga vacancies (VGa) and related complexes acting mainly as acceptors compensating the originally undoped n-type GaN buffer layers after irradiation.

Ünlü, Feray; Deo, Meenal; Mathur, Sanjay; Kirchartz, Thomas; Kulkarni, Ashish

doi: 10.1088/1361-6463/ac3033pmid: N/A

The efficiency of organic-inorganic hybrid lead halide perovskite solar cells (PSCs) has increased over 25% within a frame of ten years, which is phenomenal and indicative of the promising potential of perovskite materials in impacting the next generation solar cells. Despite high technology readiness of PSCs, the presence of lead has raised concerns about the adverse effect of lead on human health and the environment that may slow down or inhibit the commercialization of PSCs. Thus, there is a dire need to identify materials with lower toxicity profile and comparable optoelectronic properties in regard to lead-halide perovskites. In comparison to tin-, germanium-, and copper-based PSCs, which suffer from stability issues under ambient operation, bismuth-based perovskite and perovskite-inspired materials have gained attention because of their enhanced stability in ambient atmospheric conditions. In this topical review, we initially discuss the background of lead and various lead-free perovskite materials and further discuss the fundamental aspects of various bismuth-based perovskite and perovskite-inspired materials having a chemical formula of A3Bi2X9, A2B′BiX6, B′aBibXa+3b (A = Cs+, MA+ and bulky organic ligands; B′ = Ag+, Cu+; X = I−, Cl−, Br−) and bismuth triiodide (BiI3) semiconducting material particularly focusing on their structure, optoelectronic properties and the influence of compositional variation on the photovoltaic device performance and stability

Caram, Jorge; Senno, Maximiliano; Cencha, Luisa; Tinte, Silvia; Urteaga, Raúl; Arce, Roberto D

doi: 10.1088/1361-6463/ac3865pmid: N/A

Organo-inorganic perovskites (OIPs) have been intensively studied due to their potential application in low-cost, high-efficiency energy conversion in solar cells. Despite the great improvement in the quality of OIP films, wide dispersion in the same batch of perovskite-based devices remains an obstacle to obtaining highly reproducible results. For that reason, new and efficient strategies for testing deposition results is essential. Here we present a simple and efficient procedure for characterizing optical and morphological properties based on simultaneous reflectance and transmittance measurements under normal incidence over a methylammonium lead iodide film. The proposed method provides qualitative and quantitative morphological information associated with the film roughness as well as information about the position of the optical gap and possible contributions to optical dispersion in the structure that can be used as a simple diagnostic tool to optimize film deposition. Results are compared and validated with electronic and atomic force microscopy, as well as first-principles calculations.

Lei, Xinyu; Cheng, He; Nie, LanLan; Xian, YuBin; Lu, Xinpei

doi: 10.1088/1361-6463/ac3f0epmid: N/A

A novel three-level coupled rotating electrodes air plasma with nano-sized TiO2 photocatalysts is developed for plasma-catalytic NOxproduction. The effects of plasma catalysis on NOxproduction with different air flow rates, different N2 fractions and different humidity levels are evaluated. Final results show the exceptional synergistic effect between TiO2 and three-level coupled rotating electrodes air plasma significantly increases the NOxconcentration by 68.32% (from 4952 to 8335 ppm) and reduces the energy cost by 40.55% (from 2.91 to 1.73 MJ mol−1) at an air flow rate of 12 l min−1 and relative humidity level of 12%, which beats the ideal thermodynamic energy limit ∼2.5 MJ mol−1 for the thermal gas-phase process. A possible mechanism for enhanced NOxproduction with TiO2 is discussed: Highly energetic electrons in plasma contribute to the formations of the electron–hole pairs and oxygen vacancy (Vo) on the TiO2 catalyst surface, which may facilitate the dissociative adsorption of O2 molecules to form superoxide radical groups (like O2−), and H2O molecules to form surface hydroxyl groups (like OH·), and thus, improving energy efficiency.

Nanwani, Alisha; Pokharia, Ravindra Singh; Schmidt, Jan; Osten, H J; Mahapatra, Suddhasatta

doi: 10.1088/1361-6463/ac3f0dpmid: N/A

The role of post-growth cyclic annealing (PGCA) and subsequent regrowth, on the improvement of crystal quality and surface morphology of (111)-oriented Ge epitaxial layers, grown by low temperature (300 °C) molecular beam epitaxy on epi-Gd2O3/Si(111) substrates, is reported. We demonstrate that PGCA is efficient in suppressing rotational twins, reflection microtwins and stacking faults, the predominant planar defect types in Ge(111) epilayers. Continuing Ge growth after PGCA, both at low (300 °C) and high (500 °C) temperatures, does not degrade the crystal quality any further. By promoting adatom down-climb, PGCA is observed to also heal the surface morphology, which is further improved on Ge re-growth. These results are promising for development of high-quality Ge(111) epitaxial layers for photonic and electronic applications.

Lu, Yi; Chen, Juan; Li, Jianxing

doi: 10.1088/1361-6463/ac3bf5pmid: N/A

In this paper, an all-dielectric water-based transparent absorber is proposed. It is composed of transparent resin material filled with water, thus achieving the characteristics of being all-dielectric and transparent. The simulation results show that the proposed absorber can achieve absorptivity of more than 90% in the frequency band of 7.28–28.22 GHz, and has good thermal stability and oblique incidence angular stability. The thickness of the absorber is only 6.5 mm, corresponding to 0.16λmax∼0.61λmin. The test results are in good agreement with the simulation results, which proves that the water-based absorber has good performance. It can be applied in the field of electromagnetic (EM) stealth, EM energy harvesting and EM shielding.

Luo, Wenyao; Gao, Naikun; Li, Yanyan; Zhao, Zhixin; Liu, Duo

doi: 10.1088/1361-6463/ac3e2dpmid: N/A

Mechanical resonators, such as microcantilevers, demonstrate significant potential for use in information technology. Cantilevered beams of various geometries clamped at one end form the most ubiquitous structures in microelectromechanical systems that support multimode vibration for the detection, conversion, and processing of small signals. In this study, we demonstrate that the potential of these devices can be further extended by utilizing a strategy based on mode coupling and locking induced by asymmetric photothermal modulation. A cantilever was designed to have a Π-shape with a specific geometry such that the resonant frequencies of the two orthogonal modes are close to one another. Additionally, we show that mode coupling between the two modes, which are originally orthogonal to one another, can be achieved through laser-induced photothermal modulation. In particular, the two modes can be parametrically tuned to become degenerate through mode coupling with a significant increase in the quality factor from 112 to 839. This approach is universal and can be extended to improve the detection limits of microresonators in high-dissipation environments with enhanced signal-to-noise ratios.

Guthikonda, Nagaraju; Sai Shiva, S; Manikanta, Elle; Kameswari, D P S L; Ikkurthi, V R; Sijoy, C D; Prem Kiran, P

doi: 10.1088/1361-6463/ac3d5fpmid: N/A

We present results on the dynamics of laser-induced blow-off shockwave generation from the rear side of 20 µm thick aluminum and copper foil confined with a glass (BK7) substrate. These foils are irradiated by 10 ns, 532 nm laser pulses of energy 25–200 mJ corresponding to the intensity range 0.2–10 GW cm−2. The plasma temperature at the glass-foil interface is observed to play an important role in the coupling of laser energy to the foil. From our experiments and 1D hydrodynamic simulations, we confirm that moving the glass-foil interface away from the focal plane led to (a) enhanced absorption of the laser beam by the foil resulting in ∼30% higher blow-off shock velocities (b) significant changes in the material ejection in terms of increased blow-off mass of the foil (c) lower plasma density and temperatures. The material ejection as well as blow-off shock velocity is higher for Al compared to Cu. The simulated shock evolution in ambient air shows a reasonably good agreement with the experimental results.