National Institute Of Materials Physics - Romania

Integrating two-dimensional transition-metal dichalcogenides with graphene is attractive for low-power memory and neuromorphic hardware, yet sequential wet transfer leaves polymer residues and high contact resistance. We demonstrate a complementary metal-oxide-semiconductor (CMOS)-compatible, transfer-free route in which an atomically thin amorphous MoS2 precursor is RF-sputtered directly onto chemical vapor-deposited few-layer graphene and crystallized by confined-space sulfurization at 800 degrees C. Grazing-incidence X-ray reflectivity, Raman spectroscopy, and X-ray photoelectron spectroscopy confirm the formation of residue-free, three-to-four-layer 2H-MoS2 (roughness: 0.8-0.9 nm) over 1.5 cm x 2 cm coupons. Lateral MoS2/graphene devices exhibit reproducible non-volatile resistive switching with a set transition (SET) near +6 V and an analogue ON/OFF approximate to 2.1, attributable to vacancy-induced Schottky-barrier modulation. The single-furnace magnetron sputtering + sulfurization sequence avoids toxic H2S, polymer transfer steps, and high-resistance contacts, offering a cost-effective pathway toward wafer-scale 2D memristors compatible with back-end CMOS temperatures.

Pnictogen chalcohalide semiconductors are emerging materials with broad potential in energy-related applications, including solar cells, photocatalysis, photodetectors, batteries, supercapacitors, thermoelectric and piezoelectric generators. Their compositional flexibility allows fine tuning of structural and optoelectronic properties. In this study, microcrystalline powders of Sb1-xBixSeI (x = 0-1) were synthesized from binary precursors by a solid-state method in evacuated quartz ampoules. Energy dispersive spectroscopy confirmed the successful substitution of Sb with Bi in Sb1-xBixSeI. The formation of solid solutions was also supported by Raman spectroscopy and X-ray diffraction (XRD). All materials exhibited needle-shaped crystal morphologies and orthorhombic crystal structure (Pnma), regardless of the Bi/Sb ratio. XRD patterns shifted toward smaller angles with increasing Bi content, indicating lattice expansion. Calculated lattice parameters (b and c) increased linearly with Bi incorporation, while the lattice parameter (a) remained constant. Raman spectra exhibited characteristic peaks at 182 cm- 1 for Bi-Se vibration and 209 cm- 1 for Sb-Se vibration, with intensity ratios reflecting Bi content. UV-Vis-NIR diffuse reflectance spectroscopy revealed a direct band gap that decreased from 1.7 eV (SbSeI) to 1.29 eV (BiSeI). Room-temperature photoluminescence measurements exhibited a single emission band, shifting from 1.75 eV to 1.41 eV with increasing Bi content. Ultraviolet photoelectron spectroscopy indicated a shift in the valence band maximum from 0.44 eV (SbSeI) to 1.1 eV (BiSeI). These findings highlight the tunability of Sb1-xBixSeI compounds, offering pathways for optimizing their properties for specific optoelectronic applications.

CuO is a p-type semiconductor that can be found useful in various applications, sensing, photocatalysis or photovoltaics. Better material performance can be achieved by doping. In our study the doping was done using Cr ions and implantation method. Thin film samples were characterised with X-ray photoelectron spectroscopy (XPS) technique to study chemical properties of the films' surface and to determine the in-depth compositional profile of the films before and after annealing of an implanted sample. Spectroscopic ellipsometry was used to extract the dielectric function of CuO thin films. Depolarization measurements are shown as a useful method to quickly study differences between similar samples. XPS measurements proved that before annealing there is a peak of Cr concentration in depth of the sample, which is no longer present after annealing. Measurement of film resistance as function of temperature in range of 150-300 degrees C resulted with 0.82 eV bandgap. Electronic structure obtained with density functional theory calculations (DFT) showed that with Cr doping the energy band gap narrows and the material should become metallic.

Superconducting bulk disks, of 20 mm in diameter and similar to 3.5-mm thickness of MgB2 were prepared by spark plasma sintering. Samples are co-added with 10 wt. % hexagonal BN (h-BN) or graphene (G) and other additives (B4C, Te, cubic BN, fullerene C-60, or Repa-C6H10O7Ge2 (GEP)), where h-BN and G are introduced in the composite to provide full machinability by chipping of the composite and the other additives to modify microstructure and superconducting characteristics. Measurements of trapped magnetic field B-tr for a fixed rate of the applied magnetic field decrease (0.00015 T/s) indicate that samples with G show less flux jumps, but a higher thermomagnetic stability is accompanied by lower values of B-tr than for samples with h-BN. The highest maximum B-tr at 12 K for samples added with h-BN or graphene was recorded for MgB2(Te)(0.01) + 10wt.% h-BN (3.48 T) and MgB2(B4C)(0.01) + 10wt.% G (2.73 T), respectively. These values of maximum trapped field were determined for an applied field of - 2.5 and - 1.8 T. Results suggest that machinable MgB2-based composites show potential for bulk superconducting magnet applications.

Electrochemical water splitting is regarded as a viable solution to future energy demands. Considering this, an innovative method to produce efficient oxygen evolution electrodes based on Co and Ni was proposed and successfully developed, where the metal atoms are intimately mixed before the calcination treatment. Electrochemical measurements demonstrated the high oxygen evolution activity and stability of the thus synthesized electrodes, EDX, and XPS revealing that the surface exhibits a remarkable oxidation resistance, allowing the active phase to better maintain its state when subjected to the aggressive positive potential required for oxygen evolution. Moreover, low electrical resistivity was recorded as a result of reduced thickness of the catalytic layer, further increasing the efficiency. These findings provide new insights into the design of durable and high-performance OER electrodes.

We report large-scale synthesis of monolayer WS2 films obtained by sulfurization of oxidized magnetron sputtered monolayer W precursors. Literature routes typically require similar to 800 degrees C, well above the 400 degrees C limit imposed by back-end-of-line (BEOL) integration. Here, using an enhanced chemical vapor deposition (CVD) approach, the magnetron sputtered ultrathin W precursor (a W monolayer film, 0.27 nm thick, which in ambient air becomes a WOx monolayer) is sulfurized at the lowest possible temperature (450 degrees C) within a microreactor, which consists of a sandwich-like structure formed by the precursor and a clean Si substrate. The obtained WS2 material has a good crystallinity and uniform morphology across the entire growth substrate, as confirmed by detailed characterization. These results highlight the versatility of the method combining magnetron sputtering and microreactor-CVD, facilitating its applications to wafer-scale synthesis of monolayer WS2, heterogeneously integrated into electronic circuits (a major objective for next-generation electronics and optoelectronics). Additionally, we investigate in detail the properties of WS2 films synthesized from a bilayer W precursor (0.43 nm thick), under the same conditions, and we calculated the frequencies of the second-order Raman scattering modes. For electrical measurements, we fabricated WS2/few-layer-graphene heterostructures, whose atomically clean interface yields reliable, low-resistance contacts. These devices exhibit resistive switching behavior, likely governed by vacancy migration, making it a promising candidate for memristive applications. Our results demonstrate that electronics-grade monolayer WS2 can be synthesized at 450 degrees C, approaching the BEOL requirement of 400 degrees C.

Ferroelectric-ferromagnetic heterostructures with well-defined polarization orientation are the focus of many research studies owing to their interesting interface-driven phenomena such as magnetoelectric coupling. In most practical electronic applications, capacitor geometry is often used, and in the case of ferroelectric-ferromagnetic heterostructures this can bring additional challenges regarding the overall functionality due to the physical phenomena from the ferroelectric-electrode interface. In this study, it is presented the influence of the top and bottom electrode on the electrical properties of Pb(Zr0,2Ti0,8)O3-La1-xSrxMnO3/SrTiO3(001) epitaxial heterostructures. This was done by growing the thin films with different layer stacking sequences by changing the Sr doping level from the bottom electrode. It was found that both the ferroelectric polarization orientation and tetragonality of the PZT films were significantly affected by the layer stacking sequence and Sr doping level of the bottom electrode. The ferroelectric polarization was oriented either towards or away from the Pb(Zr0,2Ti0,8)O3-La1-xSrxMnO3 interface depending on the layer stacking sequence, and the tetragonality increased when the Sr doping increases from x = 0.3 to x = 0.33. The materials used as the top electrode were Pt and Au/SrRuO3. Electric measurements performed in capacitor geometry show that the hysteresis curves start to be affected by leakage currents, which have a direct impact on the estimation of the ferroelectric polarization values and on the internal built in field. The most severely affected were the measurements performed with top Pt electrodes. The conduction mechanisms and leakage current values obtained by using the top Au/SrRuO3 electrode were found to be dependent on the Sr doping level, despite the fact that the electrical resistivity values and microstructures of the individual La1-xSrxMnO3 films were similar.

This study presents a systematic approach to engineering the electron transport layer (ETL) in perovskite solar cells using a spray deposition technique to fabricate sequentially compact and mesoporous titanium dioxide (c-TiO2, m-TiO2) films. The spray coating method leads to the development of a distinct reticulated morphology characterized by well-defined wavy-like surface features and significantly increased roughness-at least twice that of spin-coated mesoporous films. The increased interfacial area between the mesoporous TiO2 and the perovskite layer facilitates more efficient charge transfer, contributing to higher device performance. By optimizing the deposition parameters, particularly the number of spray cycles for the m-TiO2 layer, we achieve a significant enhancement in device performance, with improvements in power conversion efficiency (PCE), reduced series resistance, and minimized hysteresis. Our results demonstrate that an optimal film thickness promotes better perovskite anchoring, while excessive deposition impedes light transmission and increases sheet resistance. These findings advance the practical fabrication of high-performance perovskite solar cells using simple solution-processing techniques and highlights the potential of scalable spray deposition methods for industrial-scale fabrication.

In the present work, an essential advance in the preparation of novel nanocomposites based on functionalized V2O5 nanostructures with reduced graphene oxide by hydrothermal method, which has great potential for use in photocatalytic processes related to environmental remediation. XRD analysis confirmed V2O5 in an orthorhombic structure. SEM images showed transparent RGO layers well anchored onto the surface of the V2O5 with a homogeneous distribution. Raman spectroscopy further explained the hybridization and interaction between the components. The photocatalytic activity of Rhodamine-B in aqueous solutions has been studied upon irradiation with visible light. A high RhB degradation was obtained using the V2O5/RGO photocatalyst (82 %), compared to the degradation obtained with only V2O5 (60 %). First-principles Density Functional Theory (DFT) simulations reveal a strong interaction between V2O5 molecules and graphene surfaces, with an adsorption energy of -1.673 eV and a significant charge transfer of 0.367 e- to RGO. This interaction modifies the electronic structure, creating semi-metallic behavior near the Fermi level and enhancing catalytic activity through improved charge carrier dynamics and active sites for photocatalytic applications.