Pure Semiconductor Research Articles

Amplification of PEC hydrogen production through synergistic modification of Cu2O using cadmium as buffer layer and dopant

A facile single step electro-synthesis is applied to develop Cu/Cu2O/Cd(OH)2 thin films from the alkaline copper sulfate solution in presence of different levels of Cd2+. Cadmium implemented a synergistic effect, in the modification of Cu2O, through the diffusion into the bulk Cu2O and formation of Cd(OH)2 buffer layer. The photoelectrochemical (PEC) performances of the optimized Cu/Cu2O/Cd(OH)2, significantly enhance the H+ reduction photocurrent to −6.1 mA/cm2 (1.5 times than that of pure Cu/Cu2O) and the solar energy conversion efficiency also improve up to 5.8%, which is 2 fold higher than the pure semiconductor. Experimental evidences, including SEM-EDX, XRD, Raman, XPS and EIS confirm that Cd modifies Cu2O through lowering the particle size with better crystallinity (accretive working surface area), minimizing resistance, increasing carrier concentration and rapid transfer of photogenerated charge carrier, resulting in suppression in electron-hole recombination, which facilitates the improved PEC performances.

Hydrothermal synthesis of photo-catalyst and photo-luminescence polymer-CdS flexible nanocomposites

CdS nanoparticles are II-VI group semiconductor in nature with suitable band gap for photoluminescence and photo-catalyst applications. CdS nanostructures were synthesized via a facile precipitation method in the presence of green capping agents such as starch, glucose, gelatin, salicylic acid in the green solvent of water. The influence of concentration, surfactant, precipitating agent on the particle size and shape of the products were examined. Then for preparation of polymer based nanocomposites, cadmium sulphide nanoparticles were added to poly styrene, poly vinyl alcohol, cellulose acetate and acrylonitrile-butadiene-styrene polymers. The prepared samples were characterized by X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) spectroscopy. The photocatalytic behaviour of cadmium sulfide was evaluated using the degradation of three azo dyes (methyl orang, acid violet 49 and acid black 1) under ultraviolet and visible light irradiation. Our results confirm preparation of pure semiconductor nanoparticles and polymer-based thin film nanocomposite with both appropriate photo-luminescence and photocatalytic performance simultaneously. Interestingly outcomes show photocatalysts can photo-degrade toxic dyes in less than 15 min.

Evidence of Ferromagnetism in the Diluted Magnetic Semiconductor CuGa1-xMnxTe2

Diluted magnetic semiconductors (DMS) are alloys in which a magnetic ion is randomly distributed into the solid host and have been the subject of extensive experimental and theoretical work during the last decades [1-5]. The fundamental magnetic, electronic and optical properties of these systems are quite different from their pure semiconductor counterpart, and over the last years, it has been shown that these properties are greatly influenced by the presence of charged carriers and the localized magnetic moments of the ions, leading to strong magnetotransport and magnetooptical effects. These phenomena have been widely studied and understood in Mn-based DMS in which the magnetic moments of the Mn ions interact antiferromagnetically [6].

Integrated computational materials engineering for advanced materials: A brief review

After developing the simulation-based design approach of materials for decades, computational materials science/engineering present the power in accelerating the discoveries and the applications of novel advanced materials through a digital-twin design paradigm of integrated computational materials engineering (ICME). While the short goals of ICME are almost accomplished, those long goals are on the right way, highlighting the concept/strategy of materials by design. In this brief review, the recent frameworks of data-driven ICME in the last two years are discussed, presenting key aspects of principles, benchmarks, standards, databases, platforms and toolkits via various case studies. The author and his collaborators display a routine of data-driven ICME utilized in the investigations of Mg alloys through integrating the high-throughput first-principles calculations and the CALPHAD approach. It is highlighted that the bonding charge density could not only provide an atomic and electronic insight into the physical nature of chemical bond of pure elements, alloys, metal melts, oxides and semiconductors, surface and interfaces, but also reveal the fundamental solid-solution strengthening/embrittlement mechanism and the grain refinement mechanism, paving a path in accelerating the development of advanced materials. It is believed that the combinations of high-throughput multi-scale computations and fast experiments/manufacturing will build the advanced algorithms in the development of a promising digital fabricating approach to overcome the present and future challenges, illuminating the way toward the digital-twin intelligent manufacturing era.

On Stiffness of Optical Self-Injection Locking

Spectrally pure semiconductor lasers produced via self-injection locking to high quality factor monolithic optical resonators demonstrate sub-kHz instantaneous linewidth. The lasers are used in photonic sensor systems and microwave photonic oscillators benefitting from the improved spectral purity, the stability and the reduced environmental sensitivity of the lasers. The laser frequency stability is defined by both the optical resonator and the optical path of the entire system comprising the laser, the resonator, and the miscellaneous optical components. The impacts of the various destabilization factors are usually convoluted, and it is hardly possible to separate them. In this paper, we report on an experimental study of an influence of the variations of the optical path on the laser frequency stability. We have created a whispering gallery mode optical resonator having the record small thermal sensitivity, on the order of 0.1 ppm/ ∘ C, and demonstrated a self-injection locked laser based on this resonator. The measured laser stability is characterized with 1 s Allan deviation of 10 − 12 , limited by the thermal sensitivity of the optical path between the laser and the resonator. The thermal stabilization on the order of 10 μ K at 1 s is achieved using a standard thermo-electric element. The long term drift of the laser frequency is determined by both the fluctuations of the atmospheric pressure in the laboratory impacting the monolithic resonator and by the optical path instability.

Stretchable and Degradable Semiconducting Block Copolymers.

This paper describes the synthesis and characterization of a class of highly stretchable and degradable semiconducting polymers. These materials are multi-block copolymers (BCPs) in which the semiconducting blocks are based on the diketopyrrolopyrrole (DPP) unit flanked by furan rings and the insulating blocks are poly(ε-caprolactone) (PCL). The combination of stiff conjugated segments with flexible aliphatic polyesters produces materials that can be stretched >100%. Remarkably, BCPs containing up to 90 wt% of insulating PCL have the same field-effect mobility as the pure semiconductor. Spectroscopic (ultraviolet-visible absorption) and morphological (atomic force microscopic) evidence suggests that the semiconducting blocks form aggregated and percolated structures with increasing content of the insulating PCL. Both PDPP and PCL segments in the BCPs degrade under simulated physiological conditions. Such materials could find use in wearable, implantable, and disposable electronic devices.

Band Dispersion and Hole Effective Mass of Methylammonium Lead Iodide Perovskite

Solar cells incorporating organic–inorganic perovskites, especially methylammonium lead iodide (CH3NH3PbI3), have recently shown remarkable performances and therefore attracted wide interest. For understanding the origin of the high performance, the effective charge carrier masses of CH3NH3PbI3 are critical. However, reliable experimental data on its electronic band structure, which determines the effective mass, is yet to be provided. Here, the electronic structure of CH3NH3PbI3 single crystals is studied by using angle‐resolved photoelectron spectroscopy on cleaved crystal surfaces after characterizing the surface structure by low‐energy electron diffraction. Coexisting cubic and tetragonal phases of CH3NH3PbI3 are found in diffraction patterns. Moreover, a clear band dispersion of the top valence band is observed along directions parallel to different high‐symmetry points of the cubic structure, in consistence with theoretical calculations. Based on these values, the effective hole mass is then estimated to be 0.24(±0.10)m0 around the M point and 0.35(±0.15)m0 around the X point, which are significantly lower than in organic semiconductors. These results reveal the physical origin of the high performance of solar cells incorporating perovskite materials compared to pure organic semiconductors.

The effect of C-doping on the properties and photocatalytic activity of ZrO2 prepared via sol-gel route

This work explored the synthesis and characterization of zirconium oxide/carbon xerogel composite, using the material as a photocatalyst in the photodegradation of methylene blue. The band gap energy of the samples was determined using diffuse reflectance spectroscopy. The crystallographic phase, morphology, elemental analysis, analysis of metal content and porosity of the samples was examined by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry and infrared spectrometry, respectively. The methylene blue concentration was determined using a UV–vis spectrophotometer. The analysis results confirm the formation of zirconium oxide in its monoclinic crystal structure in the pure oxide. The composite presented amorphous structure. The zirconium oxide/carbon xerogel composite presented a higher radiation absorption, in all wavelengths tested. The results regarding the degradation of methylene blue confirm the existence of photocatalytic activity of the materials when submitted to the UVC wavelength. The XZrC composite presented considerably superior photocatalytic efficiency, when compared to the pure semiconductor, as the degradation obtained with the composite was 67% higher than the one obtained with the ZrO2.

1D metallic MoO2-C as co-catalyst on 2D g-C3N4 semiconductor to promote photocatlaytic hydrogen production

The surface carrier density and hydrogen activation ability are crucial in photocatalytic hydrogen evolution reaction (HER), which can be improved by introducing noble-metal co-catalyst such as Pt into the system. However, the noble-metals suffer from high cost in terms of upscaling, thereby the exploration of low-cost HER co-catalysts is highly demanded. In this work, we report that one-dimensional (1D) metallic MoO2-C nanowire clusters can serve as a co-catalyst in assisting the photocatalytic hydrogen production over 2D g-C3N4. The multiple merits of MoO2-C are demonstrated: (i) noble-metal-free; (ii) highly effective transfer ability of the photogenerated electrons; (iii) high-density adsorption and active sites for hydrogen evolution. As demonstrated in photocatalytic hydrogen production, MoO2-C/2D g-C3N4 exhibits significant enhancement in comparison with pure 2D g-C3N4 semiconductor. The optimal hydrogen evolution rate achieving 1071.0 μmol g−1 h−1, almost 157.5 times higher than that of pure 2D g-C3N4.

First-Principles Investigation of Electronic, Half-Metallic, and Optical Properties of Ti-Doped MgTe Semiconductors with Various Concentrations of Dopant

The electronic, magnetic, and optical properties of Ti-doped semiconductors Mg1−xTi x Te at concentrations of x = 0.25, 0.50, and 0.75 have been investigated in the framework of density functional theory. Spin-polarized calculations of the electronic structure of Mg1−xTi x Te revealed that these compounds are half-metallic ferromagnetic materials with 100% spin polarization at the Fermi level. Large half-metallic gaps of 1.69 eV, 1.18 eV, and 0.98 eV were obtained for these compounds with Ti concentration of 0.25, 0.50, and 0.75, respectively. In addition, the origin of the half-metallic gap in Mg1−xTi x Te is discussed based on the partial density of states. It is found that hybridization between Ti-3d and Te-5p states and the large exchange splitting of the Ti-3d states are responsible for the half-metallic property of Mg1−xTi x Te compounds. The Curie temperatures of Mg0.5Ti0.5Te and Mg0.25Ti0.75Te were predicted to be 572 K and 959 K, respectively, within the mean field approximation. The appropriate half-metallic properties of Mg1−xTi x Te (x = 0.50 and 0.75) make them appropriate electronic materials for use in spintronics applications. The optical properties of pure and Ti-doped MgTe semiconductors, such as the dielectric function, extinction coefficient, absorption coefficient, reflectivity, and optical conductivity, were also considered. It was found that Ti doping considerably changed the optical properties of the MgTe semiconductors, especially at lower frequencies, such that these materials can be used in optical devices such as photodetectors and solar cells over wider ranges of frequency than corresponding undoped material.

Collective thermal transport in pure and alloy semiconductors

Conventional models for predicting thermal conductivity of alloys usually assume a pure kinetic regime as alloy scattering dominates normal processes. However, some discrepancies between these models and experiments at very small alloy concentrations have been reported. In this work, we use the full first principles kinetic collective model (KCM) to calculate the thermal conductivity of Si1-xGex and InxGa1-xAs alloys. The calculated thermal conductivities match well with the experimental data for all alloy concentrations. The model shows that the collective contribution must be taken into account at very low impurity concentrations. For higher concentrations, the collective contribution is suppressed, but normal collisions have the effect of significantly reducing the kinetic contribution. The study thus shows the importance of the proper inclusion of normal processes even for alloys for accurate modeling of thermal transport. Furthermore, the phonon spectral distribution of the thermal conductivity is studied in the framework of KCM, providing insights to interpret the superdiffusive regime introduced in the truncated Lévy flight framework.

Thermal conductivity of silicon doped by phosphorus: ab initio study

AbstractAn original approach to the theoretical calculations of the heat conductivity of crystals based on the first principles molecular dynamics has been proposed. The proposed approach exploits the kinetic theory of phonon heat conductivity and permits calculating several material properties at certain temperature: specific heat, elastic constant, acoustic velocity, mean phonon scattering time and coefficient of thermal conductivity. The method has been applied to silicon and phosphorus doped silicon crystals and the obtained results have been found to be in satisfactory agreement with corresponding experimental data. The proposed computation technique may be applied to the calculations of heat conductivity of pure and doped semiconductors and isolators.

Study of nanosized copper-doped ZnO dilute magnetic semiconductor thick films for spintronic device applications

Screen-printed pure and copper-doped ZnO dilute magnetic semiconductor thick films were casted from chemically co-precipitated zinc oxide and copper-doped zinc oxide nanoparticles followed by sintering at 550 °C to obtain desired stoichiometry in spintronic device applications. These thick films were characterized by different analytical techniques to reveal their structure, surface morphology, optical, magnetic and electrical characteristics. The diffraction peaks pertaining to wurtzite structure are observed in XRD patterns of these films, while SEM images show smooth and dense morphology. Infrared transmission and Raman spectra exhibit vibrational bands pertaining to Zn–O-stretching modes and E 2 (high) phonon mode, respectively, in 4000–400 cm−1 region. The direct bandgap energy of these films derived from diffused reflectance spectroscopy varies in 3.21–3.13 eV range and is supported by PL spectroscopy study. The semiconducting behaviour and activation energy of these thick films has been confirmed by DC conductivity measurements. Electron paramagnetic resonance spectra showed derivative signal of g value 2.0018 in pure ZnO due to oxygen vacancies produced during synthesis and 2.0704 in copper-doped ZnO dilute magnetic semiconductor films.

Substitutional Ta-doping in Y2O3 semiconductor by sol-gel synthesis: experimental and theoretical studies

The Pechini sol-gel method has been employed for the synthesis of pure and (181Hf→)181Ta-doped Y2O3 nanopowders. We performed a structural characterization from the micro to the subnanoscopic scale by means of scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, and time-differential perturbed γ–γ angular correlation (PAC) spectroscopy. The results show the formation of the cubic bixbyite structure after a thermal treatment at 1473 K. For the synthesized 181Ta-doped Y2O3, the PAC experiments demonstrate that the impurities are mainly located at both substitutional cationic sites of the bixbyite structure. The experimental investigation was complemented by performing first-principles electronic structure calculations for Ta atoms localized at the two cationic sites of the Y2O3 semiconductor structure, which allow the study of the structural and electronic modifications induced in the host system when the impurities are introduced. These calculations confirm that the measured electric-field gradients for the synthesized 181Ta-doped Y2O3 correspond to double-ionized impurities located at substitutional defect-free cationic sites of the bixbyite host structure and indicate the site occupancy preference for 181Hf(→181Ta) doping. The behaviour of the site preference of 181Ta impurities with temperature is also discussed. In addition to an extensive structural and electronic characterization of pure and Ta-doped Y2O3 semiconductor, our results demonstrate that the Pechini sol-gel process is an affordable and effective way to successfully synthesize these PAC substitutional doped samples.

One-step synthesis of Ceria/Ti3C2 nanocomposites with enhanced photocatalytic activity

In this study, CeO2/Ti3C2 nanocomposites were successfully synthesized by a one-step hydrothermal method with well-dispersed CeO2 nano-rods on Ti3C2 sheets. The synthetic strategy is based on the electrostatic attraction. The structure and morphology of as-prepared samples were characterized by XRD, TEM and SEM. The photocatalytic results showed that nanocomposites exhibited enhanced photocatalytic activity for the photodegradation of Rhodamine B under UV-light irradiation compared with pure CeO2 semiconductors and Ti3C2. The enhancement of photocatalytic activity can be attributed to the enhanced utilization of solar energy.

Photochemical Degradation of Fluocinolone Acetonidin Drug in Aqueous Solutions Using Nanophotocatalyst ZnO Doped by C, N, and S

It has been shown that the photocatalytic activity of doped semiconductor with some nonmetals is higher than a pure semiconductor. Hence, with an attempt to achieve higher photocatalytic activity, doped ZnO with C, N, and S was prepared by a sedimentary process and used for the photocatalytic degradation of Fluocinolone Acetonidin as a drug in aqueous solutions. X-Ray Diffraction (XRD), Energy Dispersion X-ray (EDX), X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM) were used to characterize the microstructure and morphology of the precursor and the products. The photocatalytic degradation of the drug was investigated using supported ZnO/C, N, and S photocatalyst under UV light irradiation. We also studied the influence of the basic photocatalytic parameters as well as irradiation time, the initial concentration of the drug, pH of the solution, amount of nanoparticles and addition of oxidant on the reaction. The optimum conditions of degradation were obtained accordingly: concentration of Fluocinolone Acetonidin, 20 ppm; the amount of photocatalyst, 7 mg; oxidant (K2S2O8), 5 mM; irradiation time, 6 h in pH=9. Kinetic analysis demonstrated that the amount of Fluocinolone Acetonidin photocatalytic degradation can be fitted by a pseudo-first-order model.

On the oscillatory hydrodynamic modes in liquid metal layers with an obstruction located on the bottom

Hydrodynamic disturbances represent the preferred mode of instability of thermogravitational flow for a relatively wide range of substances and conditions (essentially pure or compound semiconductor and superconductor materials in liquid state). As nowadays almost all modern technologies rely greatly on such crystallized materials, targeting an improved understanding of the convective phenomena which occur in the melt has become a subject of great importance. Here an “ad hoc” model is developed to inquire specifically about the role played in such a context by geometrical “irregularities” affecting the melt container. More precisely, results are presented for the case of a fluid with Pr = 0.01 (silicon) filling an open cavity with a single backward-facing or forward-facing step on the bottom wall or with an obstruction located in the centre. It is shown that the presence of sudden changes in the considered geometry can lead to a variety of scenarios with a significant departure from classical situations examined in the past. These configurations have different spatial symmetries and show different dynamics, including rhythmic roll expansions and contractions along the vertical and horizontal directions at different locations, roll nucleation, deformation, transport and merging phenomena. In some circumstances a travelling wave with front perpendicular to the imposed temperature gradient emerges, which has never been reported in the literature. A frequency spectrum analysis is used to support the identification of the multiple convective phenomena enabled by the new geometric features.

Structural, dielectric and ferromagnetic properties of nano-crystalline Co-doped SnS

Doping-induced tuning of host semiconductors properties offers an efficient way to realize the desired physical properties. In this study, we have synthesized pure and Co-doped SnS-diluted magnetic semiconductors with x Co = 0.00–0.10, by employing a very simple and low-cost chemical co-precipitation technique. The structural properties, determined through X-ray diffraction, have confirmed single-phase orthorhombic structure and have depicted nano-crystallites. Near-edge X-ray absorption fine structure spectroscopy has revealed a Co-doping-induced shift in the absorption edge towards lower energy, indicating a change in the Co oxidation state. Surface morphology observed through scanning electron microscopy indicates nano-structured surface. Dielectric properties measured by impedance analyzer (LCR meter) in the frequency range 1 kHz–20 MHz depict that grown materials respond to the electromagnetic radiations suggesting potential device applications. Complex impedance spectroscopy illustrates the dominance of grain resistance. The magnetic properties observed by vibrating sample magnetometer reveal room temperature ferromagnetism, and Co ions inducing tuning of the ferromagnetism suggests potential applications in the data storage devices.

Surface-Electronic-State-Modulated, Single-Crystalline (001) TiO2 Nanosheets for Sensitive Electrochemical Sensing of Heavy-Metal Ions.

Intrinsically low conductivity and poor reactivity restrict many semiconductors from electrochemical detection. Usually, metal- and carbon-based modifications of semiconductors are necessary, making them complex, expensive, and unstable. Here, for the first time, we present a surface-electronic-state-modulation-based concept applied to semiconductors. This concept enables pure semiconductors to be directly available for ultrasensitive electrochemical detection of heavy-metal ions without any modifications. As an example, a defective single-crystalline (001) TiO2 nanosheet exhibits high electrochemical performance toward Hg(II), including a sensitivity of 270.83 μA μM-1 cm-2 and a detection limit of 0.017 μM, which is lower than the safety standard (0.03 μM) of drinking water established by the World Health Organization (WHO). It has been confirmed that the surface oxygen vacancy adsorbs an O2 molecule while the Ti3+ donates an electron, forming the O2•- species that facilitate adsorption of Hg(II) and serve as active sites for electron transfer. These findings not only extend the electrochemical sensing applications of pure semiconductors but also stimulate new opportunities for investigating atom-level electrochemical behaviors of semiconductors by surface electronic-state modulation.

Electronically Pure Single Chirality Semiconducting Single-Walled Carbon Nanotube for Large Scale Electronic Devices

Abstract Carbon nanotube thin film transistors (TFTs) with characteristics resembling those of TFTs constructed on amorphous silicon, low-temperature polycrystalline silicon and metal oxides were fabricated on (6,5) single chirality single-walled carbon nanotube (SWCNT) thin film deposited from electronically pure semiconducting (6,5) single chirality single-walled carbon nanotube (SWCNT) ink. This ink was extracted in industrial scale from raw SWCNTs produced using high pressure carbon monoxide conversion, and deposited on pretreated substrates to form uniform and consistent (6,5) HiPCO SWCNT thin film using solution process. The (6,5) HiPCO SWCNT thin films were characterized as pure semiconductor without metallic impurities showing classic nonlinear current-bias curves in Schottky-type diodes. Both N-type and P-type (6,5) HiPCO SWCNT TFTs were fabricated with femto Ampere off-current and ION/IOFF ratio of 108 by depositing SiNx and HfO2 dielectrics on the top of (6,5) HiPCO SWCNT thin films, respectively. The (6,5) HiPCO SWCNT inverter with voltage gain of 52 was also demonstrated by wire-bonding one P-type HiPCO SWCNT TFT to one N-type HiPCO SWCNT TFT.