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In the present study, we have investigated the effect of magnetic Cr doping on the transport properties of a sputtered Bi2Se3 thin film on the SrTiO3 (110) substrate. The high-resolution x-ray diffraction and Raman spectroscopy measurements revealed the growth of rhombohedral Bi2Se3 thin films. Further electronic and compositional analysis was done by x-ray photoemission spectroscopy and Rutherford backscattering spectroscopy, and the x-value was estimated to be 0.18 in the Bi2−xCrxSe3 thin film. The variation in the resistivity with temperature (2–300 K) revealed the metallic nature in undoped Bi2Se3 up to 30 K and upturn resistivity below 30 K. The Cr-doped Bi2Se3 resistivity data show a traditional semiconducting nature up to 25 K and take an abrupt upturn resistivity below 25 K. The resistivity behavior of both samples was explained by adopting a model that consists of the total resistance, a combination of bulk and surface resistance in parallel. The bulk bandgap value determined by this method is obtained to be 256 meV in an undoped Bi2Se3 thin film. Magnetoconductance data of the undoped thin film revealed a weak anti-localization (WAL) effect, while the Cr-doped thin film showed a weak localization (WL) effect at low temperatures (<50 K). At low magnetic field and low temperature, a competing nature of WAL and WL effects was prominent in the Cr-doped film. A drastic increase in the electrical resistance suggests that Cr doping can significantly modify the electrical properties of Bi2Se3 thin films, which could have potential applications in futuristic devices. [ABSTRACT FROM AUTHOR]

Here, we have grown crystalline MoSe2 and WSe2 nanostructures on thin flexible Mo and W metal foils at growth temperature of 450–550°C by using the single-zone atmospheric pressure chemical vapour deposition (CVD) method. Raman spectroscopy measurements confirm the structural formation with low line widths for MoSe2 on Mo foil at 450°C and WSe2 on W foil at 550°C corresponding to their optical vibrational Raman modes. X-ray diffraction (XRD) patterns show the hexagonal 2H phase of grown MoSe2 and WSe2 nanostructures attributed to their distinguished XRD peaks. The field emission scanning electron microscopy revealed the granular-layered MoSe2 surface, whereas the nano-woolforest type surface of WSe2 film. Elemental analysis using energy-dispersive X-ray spectroscopy technique confirms the formation of nearly stoichiometry MoSe2 and WSe2 compounds. Chemical composition and binding energy values of deposited films were studied by using X-ray photoelectron spectroscopy. Growth of polycrystalline and large-area MoSe2 and WSe2 film on flexible metal foils using scalable and low-cost CVD system paves the way for the fabrication of futuristic flexible energy devices on metal foils. [ABSTRACT FROM AUTHOR]

Group 10 transition metal dichalcogenide PtSe2 has drawn considerable attention toward the search for an efficient visible light photocatalyst due to its strong light–matter interaction nature. Here we report PtSe2/TiO2 heterostructure for solar energy conversion through photoelectrochemical (PEC) water splitting. The PtSe2/TiO2 heterostructure was prepared by sputtered Pt film followed by the chemical vapor deposition method. Raman spectroscopy and X-ray diffraction analysis confirmed the growth of hexagonal phase PtSe2 and anatase TiO2 corresponding to their distinguished peak characteristics. The field-emission scanning electron microscopy and transmission electron microscopy studies reveal that TiO2 nanotubes were decorated with PtSe2 nanoflakes forming PtSe2/TiO2 heterostructure. The chemical composition of the prepared samples was studied by using the X-ray photoelectron spectroscopy and indicated the sole presence of PtSe2 and TiO2 compounds. The PEC measurements were taken in 0.5 M Na2SO4 electrolyte solution under simulated sunlight (AM = 1.5 G). The maximum photocurrent density of ~ 234.7 µA/cm2 at 1.4 V versus RHE was recorded for PtSe2/TiO2 heterostructure, which is 1.7 times higher than that of Pt/TiO2. The improved PEC performance of PtSe2/TiO2 as a result of efficient solar absorption over a wider spectrum and effective charge separation produced by type-II band alignment between PtSe2 and TiO2. [ABSTRACT FROM AUTHOR]

The interface of two-dimensional transition metal dichalcogenides hosts collective interactions between the electronic structures that tune the charge density wave (CDW) states and the photoelectrochemical (PEC) properties of heterostructures. This work reports the influence of the interface on the CDW and PEC of a sputtered Bi2Se3/TiSe2 heterostructure on Ti metal foils. The hexagonal nanoflakes on the spiral-pyramid-like surface morphology of pristine TiSe2 confirm the Bi2Se3 decoration on the TiSe2 sample. The stoichiometric growth of TiSe2 and Bi2Se3 was revealed from X-ray photoelectron spectroscopy and Raman spectroscopy. The temperature-dependent Raman spectroscopy demonstrates the evolution of EgCDW and A1gCDW optical phonon modes with increased CDW phase transition temperature for the Bi2Se3/TiSe2 heterostructure. The enhancement of photoresponsive properties of the Bi2Se3/TiSe2 heterostructure under a solar light intensity of 100 mW/cm2 (AM = 1.5 G) in 0.5 M Na2SO4 electrolyte solution toward suitable water splitting was validated from the PEC measurements. This engineered heterostructure can pave the futuristic path to studying light-active electrodes with tunable CDW properties of pristine TiSe2 and Bi2Se3/TiSe2 heterostructures grown on flexible Ti substrates. [ABSTRACT FROM AUTHOR]

In the realm of optoelectronic applications, the incorporation of a metal interlayer between layers of a topological material holds significant potential. The interlayer introduces benefits such as improved charge transfer efficiency, tunable band alignment, plasmonics effect, and enhanced light‐matter interactions, paving the way for more efficient and versatile optoelectronic devices. This work explores the incorporation of gold between Bi2Se3, resulting in an enhancement in the response time of photoresponse of interlayered systems (Bi2Se3‐Au‐Bi2Se3). The introduction of a gold interlayer between Bi2Se3 significantly influences the overlayer structure, crystallinity, crystallite size, and even phonon behavior. Moreover, the responsivity of the interlayered device at a bias (2 V) is found to have high responsivity with fast response and decay time (τr = 0.1 ms, and τd = 24 ms of interlayered systems) as compared to intrinsic Bi2Se3(τr = 0.6 ms, and τd = 28 ms). This change is attributed to the bandgap alteration of the Bi2Se3/Au interface, which is monitored through transient spectroscopy performed at different electric biases. This study suggests that incorporating a gold interlayer holds potential benefits for various optoelectronic applications. [ABSTRACT FROM AUTHOR]

In recent years, p–n junction devices formed by wide-bandgap semiconductors and layered transition metal dichalcogenides have been promising candidates for applications in broadband photodetection. In this work, we have deposited MoSe2 thin films on GaN by magnetron sputtering technique. Raman spectroscopy and high-resolution x-ray diffraction studies disclosed the formation of 2H-MoSe2 whereas x-ray photoelectron spectroscopy confirmed the composition of MoSe2 thin films grown on p-type GaN/sapphire (0001) substrate. The worm-type granular MoSe2 thin film was grown on the GaN surface. The metal–semiconductor-metal-based photodetectors (PDs) were fabricated on MoSe2/p-GaN heterojunction using gold electrodes with a spacing of 20 µm. Fabricated device shows a high photoresponsivity of ~ 5.12 A/W and detectivity of ~ 3.7 × 108 Jones in the ultra-violet (355 nm) region, and a photoresponsivity of ~ 1.5 A/W with a detectivity of ~ 2.23 × 108 Jones in the near-infra-red (1064 nm) region at 5 V. Our results demonstrate that large area sputtered MoSe2/p-GaN PDs devices are beneficial for enhancing photodetector performance. [ABSTRACT FROM AUTHOR]

Cyclic‐di‐nucleotide‐based secondary messengers regulate various physiological functions, including stress responses in bacteria. Cyclic diadenosine monophosphate (c‐di‐AMP) has recently emerged as a crucial second messenger with implications in processes including osmoregulation, antibiotic resistance, biofilm formation, virulence, DNA repair, ion homeostasis, and sporulation, and has potential therapeutic applications. The contrasting activities of the enzymes diadenylate cyclase (DAC) and phosphodiesterase (PDE) determine the equilibrium levels of c‐di‐AMP. Although c‐di‐AMP is suspected of playing an essential role in the pathophysiology of bacterial infections and in regulating host‐pathogen interactions, the mechanisms of its regulation remain relatively unexplored in mycobacteria. In this report, we biochemically and structurally characterize the c‐di‐AMP synthase (MsDisA) from Mycobacterium smegmatis. The enzyme activity is regulated by pH and substrate concentration; conditions of significance in the homoeostasis of c‐di‐AMP levels. Substrate binding stimulates conformational changes in the protein, and pApA and ppApA are synthetic intermediates detectable when enzyme efficiency is low. Unlike the orthologous Bacillus subtilis enzyme, MsDisA does not bind to, and its activity is not influenced in the presence of DNA. Furthermore, we have determined the cryo‐EM structure of MsDisA, revealing asymmetry in its structure in contrast to the symmetric crystal structure of Thermotoga maritima DisA. We also demonstrate that the N‐terminal minimal region alone is sufficient and essential for oligomerization and catalytic activity. Our data shed light on the regulation of mycobacterial DisA and possible future directions to pursue. PDB Code(s): EMDB-33540;PDB-7Y0D [ABSTRACT FROM AUTHOR]

We report a low-temperature magneto transport study of Bi2Se3 thin films of different thicknesses (40, 80 and 160 nm), deposited on sapphire (0001) substrates, using radio frequency magnetron sputtering technique. The high-resolution x-ray diffraction measurements revealed the growth of rhombohedral c-axis {0003n} oriented Bi2Se3 films on sapphire (0001). Vibrational modes of Bi2Se3 thin films were obtained in the low wavenumber region using Raman spectroscopy. The surface roughness of sputtered Bi2Se3 thin films on sapphire (0001) substrates were obtained to be ~ 2.26–6.45 nm. The chemical and electronic state of the deposited Bi2Se3 was confirmed by X-ray photoelectron spectroscopy and it showed the formation of Bi2Se3 compound. Resistivity versus temperature measurements show the metallic nature of Bi2Se3 films and a slight up-turn transition in resistivity at lower temperatures < 25 K. The positive magneto-resistance value of Bi2Se3 films measured at low temperatures (2–100 K) confirmed the gapless topological surface states in Bi2Se3 thin films. The quantum correction to the magnetoconductivity of thin films in low magnetic field is done by employing Hikami–Larkin–Nagaoka theory and the calculated value of coefficient 'α' (defining number of conduction channels) was found to be 0.65, 0.83 and 1.56 for film thickness of 40, 80 and 160 nm, respectively. These observations indicate that the top and bottom surface states are coupled with the bulk states and the conduction mechanism in Bi2Se3 thin films varied with the film thicknesses. [ABSTRACT FROM AUTHOR]

Optoelectronic properties of GaN are underexplored on good lattice matching SrTiO3 (STO) due to STO's instability at the high GaN growth temperatures (800–1100 °C) required by traditional techniques. Here, GaN is grown on STO (100) at lower temperatures (500, 600, and 700 °C) using the laser‐assisted molecular beam epitaxy (LMBE) technique, and their morphological, crystalline, optical, and photodetection properties are analyzed. Further, heterojunction of Bi2Se3 thin film (bandgap of 0.3 eV) is formed on the highest photo‐responsive LMBE‐GaN/STO to fabricate a self‐powered broadband photodetector. The fabricated self‐powered heterojunction photodetectors device exhibits a high responsivity of 2.93 × 102 mAW−1 in ultraviolet region and a notable responsivity of 2.3 and 12 mAW−1 in visible and near‐infrared spectral regions, respectively. In addition, photoresponse properties of fabricated devices on bare LMBE‐GaN and its heterojunction are compared under UV light illumination. The photoresponsivity of heterojunction in UV region is estimated to be 3.05 × 104 mAW−1, which is enhanced by 100% compared to bare LMBE‐GaN. Combining the unique optoelectronic properties of GaN and rigidity of STO, epitaxy of GaN on STO enables construction of robust photodetector devices. Further, Bi2Se3‐functionalized GaN can provide self‐sufficient and high‐quality futuristic optoelectronics devices. [ABSTRACT FROM AUTHOR]