National Institute Of Materials Physics - Romania

Self-powered near-infrared (NIR) photodetectors are essential for surveillance systems, sensing in IoT electronics, facial recognition, health monitoring, optical communication networks, night vision, and biomedical imaging. However, silicon commercial detectors need external power to operate and cooling to suppress large dark currents. This work demonstrates a new class of CMOS-compatible self-powered NIR photodetector based on ferroelectric 5-nm thick ZrO2 films which do not require cooling and therefore have two key advantages over Si, and at the same time have comparable performance metrics. At room-temperature, under 940 nm wavelength illumination (1.4 mW cm-2 power density, 10 Hz repetition rate), and without any power applied, fast rise and fall times of approximate to 2 and 4 mu s, respectively, are achieved in Al/Si/SiOx/ZrO2/ITO devices, along with responsivity, detectivity and sensitivity values of up to approximate to 3.4 A W-1, 1.2 x 1010 Jones and 4.2 x 103, respectively, far exceeding all other emerging self-powered systems. Furthermore, dual-band NIR detection is shown for different NIR wavelengths, proof-of-concept feasibility being demonstrated for the smart identification of NIR targets. Therefore, it is demonstrated, for the first time, that coupling together the pyroelectric effect, the photovoltaic effect, and the ferroelectric effect is a novel method to significantly enhance the performance of CMOS-compatible ZrO2-based self-powered photodetectors in the NIR region.

This study examines the impact of shale volume (Vsh) and clay mineral distribution on the petrophysical properties and reservoir quality of the Matulla Formation in the Gulf of Suez, a critical factor in global hydrocarbon exploration and production. Understanding how shale affects porosity, permeability, and fluid saturation enhances reservoir characterization, optimizing recovery techniques such as hydraulic fracturing and sustainable resource management. The evaluation process involved calculating shale volume using the neutron-density method, with values ranging from 1.9% to 11% across four wells (GS323-1, GS323-2A, GS323-3, GS323-4A). Clay minerals have been identified through Potassium-Thorium (K-Th) cross-plot include chlorite, illite, kaolinite, montmorillonite, and mixed-layer clays. Montmorillonite and chlorite negatively impact porosity and permeability, while kaolinite and illite improve hydrocarbon retention. Shale distribution analysis using the Thomas and Stieber model showed both laminated and dispersed forms, where laminated shales had minimal blockage, and dispersed clays significantly reduced the reservoir quality. Results reveal that wells with low Vsh (GS323-1 and GS323-4A) which ranges from 1.5 to 2% exhibit excellent reservoir quality, with high porosity (14%), high permeability (317-320.7 mD), and low water saturation (32-44%). Moderate Vsh wells (GS323-2A) show reduced porosity (13%), permeability (220 mD), and increased water saturation (46%), reflecting good but diminished quality. High Vsh well (GS323-3) display lower porosity (12%), permeability (140 mD), and moderate water saturation (37%), indicating challenges in fluid flow. This study highlights the need for tailored strategies to mitigate high shale content and swelling clays, offering valuable insights into optimizing hydrocarbon exploration and production in shale-influenced reservoirs worldwide.

Photoanodes based Ce-doped ZnO nanorods arrays were prepared by hydrothermal method in order to improve photoelectrochemical efficiency of ZnO photoanodes in water splitting process. Scanning electron microscopy investigation showed ZnO based nanorods with length of around 500 nm and different thicknesses and growth directions. Some morphological changes were noted following the thermal treatment. Energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy measurements proved the presence of cerium species both in bulk and on the surface of ZnO nanorods. A current density of 2.44 mA/cm(2) at 1.23 V against the reversible hydrogen electrode (0.265 V vs. Ag/AgCl) was obtained for Ce-doped ZnO sample, which is >162% increase over that of ZnO sample. The increased photocurrent value obtained for this sample was correlated with the passivation of surface defects evidenced by photoluminescence study and the increased concentration of Ce3+ on the surface. Also, the electrochemical impedance spectroscopy measurements suggested that Ce doping improves the charge transfer in bulk.

The field of newly developed two-dimensional (2D) materials with low symmetry and structural in-plane anisotropic properties has grown rapidly in recent years. The phosphorene analog of group IV monochalcogenides is a prominent subset of this group that has attracted a lot of attention because of its unique in-plane anisotropic electronic and optical properties, crystalline symmetries, abundance in the earth's crust, and environmental friendliness. This article presents a review of the latest research advancements concerning 2D group IV monochalcogenides. It begins with an exploration of the crystal structures of these materials, alongside their optical and electronic properties. The review continues by discussing the various techniques employed for the synthesis of layered group IV monochalcogenides, including both bottom-up methods such as vapor-phase deposition and top-down techniques like mechanical and/or liquid-phase exfoliation. In the final part, the article emphasizes the application of 2D group IV monochalcogenides, particularly in the fields of photocatalysis, photodetectors, nonlinear optics, sensors, batteries, and photovoltaic cells.

This article describes a new synthesis of nanoscaled Y2O3 that is bioinspired. It has been confirmed that Callistemon viminalis flower extract works well as a chelator when used to bioengineer high-shape anisotropy nanorods of single-phase Y2O3 . X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, fourier transform infrared spectroscopy and photoluminescence spectroscopy were used to analyse the structural, morphological, surface and optical features. The photoluminescent spectra of the bio-engineered nanorods show blue emissions. As the annealing temperature was increased from 300 to 500 degrees C, the blue colour purity values of the synthesized Y2O3 nanorods were 58.1, 80.7 and 77.0% at 300, 400 and 500 degrees C respectively. The chromaticity coordinates (0.2020, 0.1931), (0.1660, 0.1082) and (0.1714, 0.1226) from the photoluminescence spectra of the biosynthesized Y2O3 nanorods were used to determine these values. The CIE y-component coordinate values of the bioengineered blue-emitting nanophosphors suggest their potential for applications in display technology and white light-emitting diodes.

In recent decades, magnetic hyperthermia (MH) has gained considerable scientific interest in cancer treatment due to its ability to heat tumor tissues deeply localized inside the body. Functionalizing magnetic nanoparticles (MNPs) with vector molecules via specific organic molecules that coat the particle surface has enabled targeting particular tissues, thereby increasing the specificity of MH. MH relies on applying radiofrequency (RF) magnetic fields to a magnetic nanoparticle distribution injected in a tumor tissue. The RF field energy is converted into thermal energy through specific relaxation mechanisms and magnetic hysteresis-driven processes. This increases the tumor tissue temperature over the physiological threshold, triggering a series of cellular apoptosis processes. Additionally, the mechanical effects of low-frequency AC fields on anisotropic MNPs have been shown to be highly effective in disrupting the functional cellular components. From the macroscopic perspective, a crucial parameter measuring the efficiency of magnetic nanoparticle systems in MH is the specific absorption rate (SAR). This parameter is experimentally evaluated by different calorimetric and magnetic techniques and methodologies, which have specific drawbacks and may induce significant errors. From a microscopic perspective, MH relies on localized thermal and kinetic effects in the nanoparticle proximity environment. Studying MH at the cellular level has become a focused research topic in the last decade. In the context of these two perspectives, inevitable questions arise: could the thermal and kinetic effects exhibited at the cellular scale be linked by the macroscopic SAR parameter, or should we find new formulas for quantifying them? The present work offers a general perspective of MH, highlighting the experimental pitfalls encountered in SAR evaluation and motivating the necessity of standardizing the devices and protocols involved. It also discusses the challenges that arise in MH performance evaluation at the cellular level.

We report on the increase of luminescence of ZnS:Ag after exposure to a radio-frequency (RF) argon plasma at low powers ranging from 5W to 50W. The best luminescence enhancement was achieved at 5W RF power, when the increase was approximately 57.02 % over a 35-min exposure. The luminescence is measured in-situ by excitation with an electron beam with energy 13 keV and a fiber coupled to a spectrometer. The increase in luminescence is attributed to the cleaning effect of surface defects of the crystal caused by argon ions accelerated in the plasma sheath. Surface impurities were highlighted by TEM and XPS analysis. Zn2p(3/2), Zn2p(1/2) and S2p(3/2) peaks show initially high oxidation state and after plasma treatment they shifted to lower value which indicated a decontamination of trapped oxygen. At higher RF powers up to 50W, the trend of increased luminescence continues, but it is mitigated by the thermal quenching effect and sulfur depletion observed in EDS analysis. Calculations based on power deposition indicate a thermoquenching point of approximately 130-150 degrees C.

This study explores the development of highly sensitive hydrogen sulfide (H2S) gas sensors employing hierarchical aluminum-doped zinc oxide (AZO) nanostructures. Vertically oriented AZO nanoplatelets with Al/ZnO molar ratios of 4% and 6% were successfully synthesized using an automated successive ionic layer adsorption and reaction (SILAR) technique. The morphological features of the AZO films significantly changed with the Al content. The AZO thin films exhibited a polycrystalline wurtzite structure and an increase in crystallite size with increasing Al concentrations. This work demonstrates that our AZO sensor structures achieved a maximum response at 150 ppm H2S and 573 K of 23.3%, being characterized by fast response and recovery times of 28 and 464 s, respectively. Notably, the 6% AZO samples exhibited an augmented selective sensitivity to H2S, demonstrating stable detection performance. Additionally, the significant improvement in detection capabilities can be attributed to the synergistic effects of electronic and chemical sensitization. These effects enhance the formation of active sites and create doping-induced defects while providing shorter and more efficient diffusion paths for the electrons, significantly improving the sensor's sensitivity and response speed.

We model a change of the spin configuration in a two-dimensional square array, or a lateral superlattice, of quantum rings in an external perpendicular homogeneous magnetic field. The electron system is placed in a circular cylindrical far-infrared photon cavity with a single circularly symmetric photon mode. Our numerical results reveal that the spin ordering of the two-dimensional electron gas in each quantum ring can be influenced or controlled by the electron-photon coupling strength and the energy of the photons. The Coulomb interaction between the electrons is described by a spin-density functional approach, but the para- and diamagnetic electron-photon interactions are modeled via a configuration interaction formalism in a truncated many-body Fock-space, which is updated in each iteration step of the density functional approach. In the absence of external electromagnetic pulses this reordering of the spin configuration is replicated in the orbital magnetization of the rings. The change in the spin configuration can be suppressed by a strong electron-photon interaction. In addition, fluctuations in the spin configuration are found in dynamical calculations, where the system is excited by a time-dependent coupling scheme to a cylindrical cavity mode for emphasizing the diamagnetic electron-photon interaction not leading to simple electrical dipole oscillations. The diamagnetic interaction is enhanced by the rotational electric field of the particular cavity mode.

Herein, alpha-MoO3 micro- and nanoparticles were synthesized by a modified Pechini method, and the impact of the crystal structure and crystal growth orientation on the formation of ionic defects and, consequently, on the catalytic performance of the materials in the ethylic transesterification reaction for biodiesel production was investigated. Structural refinements from X-ray diffraction data and Raman spectra revealed the formation of alpha-MoO3 in a Pbnm orthorhombic phase, with nanoplate-like morphology at 500 degrees C (thickness between 100 and 260 nm) or ribbon-like morphology at 700 degrees C (thickness between 400 and 900 nm). An anisotropic crystal orientation along the [010] direction was observed with an increase of the calcination temperature. We emphasize the dependence of the orientation change with the elimination of ionic-type defects (oxygen vacancies and reduced Mo5+ centers) by the temperature using complementary techniques such as X-ray photoelectron and electron paramagnetic resonance spectroscopies. The catalytic activity of the samples depends on the orientation process and the presence of defects that act as acid-active sites on the catalyst surface and therefore play an important role in biodiesel production. This effect was confirmed by surface stability and reactivity simulated by density functional theory calculations, suggesting that the Mo and O surface terminals greatly impacted the interface catalytic reaction. The highest catalytic performance toward the biodiesel conversion (89% of conversion at 150 degrees C for 2 h) was achieved for the polycrystalline catalyst calcined at 500 degrees C, which was correlated with random crystal orientation and the presence of reduced Mo5+ and oxygen vacancy centers on the different facets exposed on the surface. The biodiesel production was confirmed by H-1 and C-13 NMR spectroscopy and gas chromatography analysis.