Si Samples Research Articles

Physical and electrochemical performances of novel tellurium composite films as anode applications in energy storage systems

Portable electronic devices and electric cars use lithium-ion batteries, but clumping lithium alloys limit their lifespan. Due to their strong electronic conductivity, volumetric capacity, and high energy density, researchers are conducting research on electrochemical metal cells utilizing tellurium for high-performance batteries. Theoretically, lithium-tellurium batteries can improve energy densities three times more than lithium-ion batteries. However, metal-tellurium faces challenges such as low rate capability, unclear redox reactions, intermediate dissolution, and electrode volume changes. This study explores the enhancement of the energy storage capacity of next-generation batteries by fabricating coated electrode films as novel anodes from tellurium, silicon, and graphene. Physical, thermal, and morphological analysis of composite material are investigated by XRD, TEM, TGA, DSC, SEM, UV, and XPS analyses, revealing its rigidity as well as durability through its crystal structure alignment and thermal stability. In electrochemical analysis (CV) at various scan rates, samples that exhibit consistent and high specific capacity (Cp) values at different scan speeds (25, 50, and 100 mV/s) indicate excellent ability to store and maintain charge. Decreasing Cp values with increasing scan rates indicate that the speed of cycling limits the charge transfer kinetics and electrode performance. In EIS, the charge transfer resistances (Rct) for the pure Te, Te + Gr, Te + Si + Gr, and Te + Si samples are 759.07 Ω, 4.21 Ω, 36.39 Ω, and 164.90 Ω, respectively. The Te + Gr sample has the lowest Rct, indicating the best charge transfer efficiency at the electrode contact, whereas the Te + Si + Gr sample has a comparatively lower Rct, indicating better charge transfer kinetics. The combined result exhibits the synergistic impact of tellurium, silicon, and graphene in enhancing the energy storage capacity of future batteries across the industry.

Theoretical and experimental study of plasmon oscillation dispersion in Si and Ge crystals

Plasma fluctuation dispersion has been theoretically and experimentally studied in monocrystal samples of Si (111) and Ge (111). It has been shown that the dispersion depends on crystallographic orientations of materials under study. In this work, the dispersion effects in the CLEE spectra, which manifest themselves in bulk samples of Si and Ge, have been studied. The loss energy electron was studied by the CLEE method upon their reflection from Si(111) and Ge(111) at different angles of incidence of the electron beam on the surface. Calculation of the total electron energy loss with formula (5) shows that the form of the CLEE spectrum of primary electrons depends on the nature and magnitude of the electron density in a given direction and is in satisfactory agreement with the experimental data. Thus, the theoretical and experimental results show that in the case of single-crystalline Si and Ge, with increasing k, the values of the bulk plasma oscillation increase by 2–3 eV.

Unlocking bioremediation potential: harnessing an indigenous bacterial consortium from effluent treatment plants for industrial wastewater treatment

Common Effluent Treatment Plant (CETP) wastewater poses significant environmental and health risks, necessitating advanced treatment technologies to meet discharge standards. This study focuses on the collection and characterisation of wastewater from CETP Vatva, Ahmedabad, to evaluate physicochemical parameters heavy metal concentrations, and identify indigenous bacterial species. Using Taguchi’s systematic orthogonal array, an effective indigenous bacterial consortium (EIBC) was created for bioreactor-based CETP wastewater treatment. The 16S rDNA analysis revealed the presence of various bacterial strains, including the newly reclassified bacteria Stutzerimonas stutzeri. The analysis of the SI sample indicated substantial reductions in the concentrations of total dissolved solids (1090 mg L−1), biological oxygen demand (28 mg l−1), chemical oxygen demand (180 mg l−1), and total phosphorus (1.4 mg l−1) compared to their initial values of 7504 mg l−1, 29 6 mg l−1, 58 8 mg l−1, and 3.04 mg l−1, respectively, with a similar trend observed in samples SII and SIII. While turbidity was significantly reduced from initial concentrations ranging between 36–42 NTU to 4 NTU in SI, 5 NTU in SII, and 3 NTU in SIII samples, resulting in clear water, odour remained a persistent concern throughout the study. Heavy metal concentrations were within permissible discharge limits, with notable removal rates for Cu, Fe, and Cd. The study concludes that integrating systematic design modelling with bioreactor-based remediation effectively mitigates water pollution and safeguards human well-being.

Enhanced plasma grating-induced breakdown spectroscopy for sensitive detection of heavy metal in solution

Plasma grating-induced breakdown spectroscopy (GIBS) has gained notable attention for its capacity in trace metal element detection. This study examined the utilization of plasma grating to create micropores and nanoparticles on a Si sample surface and explored their impact on GIBS. We found that the presence of these features resulted in a significant 2.4-fold enhancement in the spectral intensity of the Si plasma at a laser energy of 2.7 mJ, with micropores structures and nanoparticles promoting the plasma excitation. Furthermore, the effect of micropores structures and nanoparticles on the spectral intensities of Cr and Cd elements in water was investigated. Significantly, the spectral line intensity of heavy metal Cr and Cd in the etched area was about 4.5 and 2.6 times that of the unetched area, and the detection limit for trace levels of Cr and Cd in water was determined to be 6.40 mg/L and 75.0 mg/L, respectively. These findings highlight the promising potential of the enhanced GIBS as a more sensitive method for detecting trace metal elements in water.

High Optical Abropsion from Thin Film MoS2 Nano-Flakes

Due to their distinctive electronic and optical characteristics, transition metal dichalcogenides (TMDs) have become significant materials in optoelectronics. Molybdenum disulfide (MoS2) flakes have received significant interest due to their potential applications. The unique bandgap properties exhibited by MoS2 flakes render them highly appealing for applications in optoelectronic devices [1]. A direct bandgap in this material enables effective interactions between light and matter, which is significant for various applications, including transistors, photodetectors, and light-emitting diodes [2].In this work, we synthesized our MoS2 flakes by exfoliating MoS2 powder following [3]’s recipe. We disperse 500 mg of MoS2 powder into 50 mL of N-Methyl-2-pyrrolidone (NMP)and then use a probe sonicator for the exfoliation process that runs continuously for 6 hours while keeping the sample cooled by a 0 °C ice bath. We later centrifuged at 1500 rpm for 60 min to remove any unexfoliated particles and then centrifuged again at 7500 rpm for 30 min to remove soluble impurities. After removing NMP, the acquired MoS2 flakes dispersed in 50 mL isopropyl alcohol. To study the optical properties of these MoS2 flakes, we prepared 3 x 3 cm2 fused silica substrate rinsed with acetone and DI water, respectively. Before deposition, we sonicate our MoS2 solution for 60 minutes in a bath sonicator. A precise pipet is used to drop-cast 20 uL of MoS2 on the fused silica substrate and wait 120 seconds to let it spread and settle. Afterward, we spin the sample at a low 150 rpm for 40 seconds, ensuring no spillovers. The sample was then carried to a UV-Vis Lambda 1050 spectrometer tool to measure the transmittance and reflectance of the sample over a range of wavelengths 250 to 1200 nm. Subsequently, we calculated absorbance values from this data. We repeat this on the same sample in steps of 20 uL of MoS2, acquiring spectrometer data for 20 to 200 uL of MoS2 on fused silica. The absorbance data showed a slope increase of absorption around 830 nm wavelength, reaching a peak around 660 nm, and It continues to absorb to 250 nm wavelength of the UV range.Moreover, as we increased the MoS2 amount, the overall absorbance increased. At the same time, reflectance increased; however, the change slowed after 60 uL of MoS2. We suspect that the former is due to the increase in the overall thickness of the deposited material, which increases the chance of photons traversing the material to be absorbed. The latter effect could be attributed to texturing, as these deposited MoS2 flakes do not seem to fall flat and create a uniform film and additional reflection from the MoS2 surface. To study that, we prepared five other 3x3 cm2 MoS2 on silicon (Si) samples with 20-100 uL in steps of 20 uL using the same process described earlier. Looking at the morphology using an optical microscope and SEM images of MoS2 on Si, the images show random settlement of MoS2 flakes, leading to uneven coating and witnessing MoS2 flakes arranged and aggregated into islands similar to results reported by others [4]. Also, we found similar dips in reflectivity as reported by literature due to absorption of A and B excitons[5]. Additionally, we measured the electrical conductivity using a hall measurement system of 100 uL MoS2 sample and found that it exhibited n-type behavior with an average sheet resistance value of 2.91x102 Ω/sq. We aim to investigate further the properties and potential applications of these MoS2 flakes.[1] K. F. Mak, C. Lee, J. Hone, J. Shan, and T. F. Heinz, “Atomically Thin MoS2: A New Direct-Gap Semiconductor,” Phys. Rev. Lett., vol. 105, no. 13, p. 136805, Sep. 2010, doi: 10.1103/PhysRevLett.105.136805.[2] H. J. Jin, C. Park, H. H. Byun, S. H. Park, and S.-Y. Choi, “Electrically Modulated Single/Multicolor High Responsivity 2D MoTe2/MoS2 Photodetector for Broadband Detection,” ACS Photonics, vol. 10, no. 9, pp. 3027–3034, Sep. 2023, doi: 10.1021/acsphotonics.3c00143.[3] X. Yu et al., “Hybrid Heterojunctions of Solution-Processed Semiconducting 2D Transition Metal Dichalcogenides,” ACS Energy Lett., vol. 2, no. 2, pp. 524–531, Feb. 2017, doi: 10.1021/acsenergylett.6b00707.[4] N. Zebardastan et al., “2D MoS2 Heterostructures on Epitaxial and Self-Standing Graphene for Energy Storage: From Growth Mechanism to Application,” Advanced Materials Technologies, vol. 7, no. 4, p. 2100963, 2022, doi: 10.1002/admt.202100963.[5] “Layer-number dependent reflection spectra of MoS2 flakes on SiO2/Si substrate.” Accessed: Nov. 23, 2023. [Online]. Available: https://opg-optica-org.libconnect.ku.ac.ae/ome/fulltext.cfm?uri=ome-8-10-3082&id=398132 Figure 1

In Plasma ion beam analysis of polymer layer and adsorbed H monolayer etching

We present two experiments where a layer is plasma-etched while monitoring its evolution by in plasma ion beam analysis. First, we etch a photoresist with a diffuse O2 plasma at low pressure. Using a 4.335 MeV He beam, Rutherford Backscattering Spectrometry and Elastic Recoil Detection spectra are acquired every minute during 8 h. Etching of most elements follows a linear trend, but H desorbs faster at the beginning of the plasma process, which we ascribe to the ion beam-induced desorption. In addition, we observe a thin Mo layer building up at the surface, likely due to the sputtering of an electrode in the plasma source. Secondly, we etch in HF a crystalline Si (c-Si) sample with <100> surface orientation, which should leave 14 H/nm2 bonded to the c-Si surface. The sample is then introduced in the chamber and exposed to a diffuse Ar plasma at low pressure. During plasma processing, the H surface concentration is monitored using a resonant nuclear reaction with a 15N beam at 6.385 MeV. The initial H concentration is 11.7±1.1 H/nm2, and it decreases over a 3-minute timescale to an equilibrium concentration of 6.0±0.8 H/nm2. Over the range of experimental conditions investigated, the diffuse Ar plasma is therefore not able to entirely sputter the H from the c-Si surface.

Process-induced microstructural variations in laser powder bed fusion of novel titanium alloys: A comprehensive study on volumetric energy density and alloying effects

This study explores the effect of in-situ alloying and volumetric energy density (VED) on the microstructure of Laser Powder Bed Fusion (L-PBF) fabricated Ti alloys. Pure Ti, Ti–5Cu, and Ti–5Cu–1Si (wt%) samples were printed using elemental powders with varying VEDs. This study investigates the influence of VED and Cu/Si additions on the growth restriction factor (Q) and columnar-to-equiaxed transition of the β phase. Pure Ti samples exhibited coarse, prior columnar β grains with an average diameter of 106 μm, and a grain shape factor greater than 3.0. In contrast, both Ti–Cu and Ti–Cu–Si samples displayed a significant fraction of equiaxed prior β grains with a near-spherical morphology. Additionally, Cu/Si addition refined the prior β columnar grains, reducing their average diameter to 37 μm and 25 μm in Ti–Cu and Ti–Cu–Si, respectively. Furthermore, the study reveals a strong dependence of microstructure on VED in the Ti–5Cu–1Si alloy. Higher VED promotes a more uniform distribution of solute elements and a lower thermal gradient, resulting in finer equiaxed β grains with an average diameter of 4.9 μm, compared to samples printed at lower VEDs. The addition of Cu and Si also significantly refined the lath-like α phase and decreased the c/a ratio of the Ti HCP lattice, introducing lattice microstrains in the Ti–Cu and Ti–Cu–Si alloys. These findings demonstrate the potential of in-situ alloying and VED optimization for tailoring microstructures in novel Ti alloys fabricated via L-PBF, paving the way for achieving superior mechanical properties.

Shallow Hydrogen‐Related Donors after a DC H Plasma Treatment in Si

Different donor‐like defects at a depth of several microns below the surface in n‐type Si samples are observed after subjecting them to DC hydrogen plasma treatment, conducted with and without broadband illumination. These defects cannot be correlated with vacancies or interstitials, likely due to the low energy of H ions or hydrogen platelets typically reported after RF H plasma treatment in various studies. It is found that the concentration of these donor‐like defects is highest near the surface and is significantly influenced by the oxygen or oxygen and carbon concentration in the Si samples. Several of these defects can be attributed to shallow donors, whereas other are likely to be correlated with deep‐level defects. The origin of these defects will be discussed.

Enhanced thermoelectric properties of nanostructured Si by excess P-doping

In this study, nanostructures were introduced into bulk Si, and the P content in Si was increased. Arc melting, ball milling, and spark plasma sintering were used to prepare excess P-doped Si samples (Si1−xPx, x = 0.01, 0.03, 0.06, 0.09, and 0.12). In Si0.94P0.06, thermal conductivity decreased to 18 W m−1 K−1 at room temperature, which is about 10% of that of bulk Si. Transmission electron microscopy observation of Si0.94P0.06 revealed a linearly localized alignment, in addition to the nanostructures observed in the previous studies of P-doped Si samples. Linear alignments were composed of Si-P nanoprecipitates and defects linearly localized around dislocations. These sub-microstructures can reduce thermal conductivity; as a result, ZT at 973 K increased to 0.43, which is approximately three times higher than that of single-crystal Si.

Optimizing the Sintering Conditions of (Fe,Co)1.95(P,Si) Compounds for Permanent Magnet Applications.

(Fe,Co)2(P,Si) quaternary compounds combine large uniaxial magnetocrystalline anisotropy, significant saturation magnetization and tunable Curie temperature, making them attractive for permanent magnet applications. Single crystals or conventionally prepared bulk polycrystalline (Fe,Co)2(P,Si) samples do not, however, show a significant coercivity. Here, after a ball-milling stage of elemental precursors, we optimize the sintering temperature and duration during the solid-state synthesis of bulk Fe1.85Co0.1P0.8Si0.2 compounds so as to obtain coercivity in bulk samples. We pay special attention to shortening the heat treatment in order to limit grain growth. Powder X-ray diffraction experiments demonstrate that a sintering of a few minutes is sufficient to form the desired Fe2P-type hexagonal structure with limited secondary-phase content (~5 wt.%). Coercivity is achieved in bulk Fe1.85Co0.1P0.8Si0.2 quaternary compounds by shortening the heat treatment. Surprisingly, the largest coercivities are observed in the samples presenting large amounts of secondary-phase content (>5 wt.%). In addition to the shape of the virgin magnetization curve, this may indicate a dominant wall-pining coercivity mechanism. Despite a tenfold improvement of the coercive fields for bulk samples, the achieved performances remain modest (HC ≈ 0.6 kOe at room temperature). These results nonetheless establish a benchmark for future developments of (Fe,Co)2(P,Si) compounds as permanent magnets.

Hole and positron interaction with vacancies and p-type dopants in epitaxially grown silicon

The concentration of vacancies and impurities in semiconductors plays a crucial role in determining their electrical, optical, and thermal properties. This study aims to clarify the nature of the interaction between positrons and ionized p-type impurities, emphasizing the similarities they share with the interaction between holes and this type of impurity. An overall strategy for investigating defects in semiconductor crystals that exhibit a combination of vacancies and p-type impurities is presented. By using positron annihilation spectroscopy, in particular, Doppler broadening of the annihilation radiation, we quantify the concentration of vacancies in epitaxial Si crystals grown by low-energy plasma-enhanced chemical vapor deposition. The vacancy number densities that we find are (1.2 ± 1.0) × 1017 cm−3 and (3.2 ± 1.5) × 1020 cm−3 for growth rates of 0.27 and 4.9 nm/s, respectively. Subsequent extended annealing of the Si samples effectively reduces the vacancy density below the sensitivity threshold of the positron technique. Secondary ion mass spectrometry indicates that the boron doping remains unaffected during the annealing treatment intended for vacancy removal. This study provides valuable insights into the intricate interplay between vacancies and ionized impurities with positrons in semiconductor crystals. The obtained results contribute to advance the control and understanding of material properties in heterostructures by emphasizing the significance of managing vacancy and dopant concentrations.

Deposition of silica in sorghum root endodermis modifies the chemistry of associated lignin.

Silica aggregates at the endodermis of sorghum roots. Aggregation follows a spotted pattern of locally deposited lignin at the inner tangential cell walls. Autofluorescence microscopy suggests that non-silicified (-Si) lignin spots are composed of two distinct concentric regions of varied composition. To highlight variations in lignin chemistry, we used Raman microspectroscopy to map the endodermal cell wall and silica aggregation sites in sorghum roots grown hydroponically with or without Si amendment. In +Si samples, the aggregate center was characterized by typical lignin monomer bands surrounded by lignin with a low level of polymerization. Farther from the spot, polysaccharide concentration increased and soluble silicic acid was detected in addition to silica bands. In -Si samples, the main band at the spot center was assigned to lignin radicals and highly polymerized lignin. Both +Si and -Si loci were enriched by aromatic carbonyls. We propose that at silica aggregation sites, carbonyl rich lignin monomers are locally exported to the apoplast. These monomers are radicalized and polymerized into short lignin polymers. In the presence of silicic acid, bonds typically involved in lignin extension, bind to silanols and nucleate silica aggregates near the monomer extrusion loci. This process inhibits further polymerization of lignin. In -Si samples, the monomers diffuse farther in the wall and crosslink with cell wall polymers, forming a ring of dense lignified cell wall around their export sites.

Dynamical Nonlinear Inversion of the Surface Photovoltage at Si(100).

A surface photovoltage (SPV) is observed whenever a doped semiconductor with non-negligible band bending is illuminated by light and charge carriers are excited across the band gap. The sign of the SPV depends on the nature of the doping, the amplitude of the SPV increases with the fluence of the light illumination up to a saturation value, which is determined by the doping concentration. We have investigated Si(100) samples with well-characterized doping levels over a wide range of illumination fluences. Surprisingly, the sign of the SPV upon illumination with 532nm photons reverses for some p-doping concentrations at high fluences. This is a new effect associated with a crossover between electronic excitations in the bulk and at the surface of the semiconductor.

Compact homogeneous Si/SiC/C in-situ nanocomposite microspheres as anode materials for lithium-ion batteries

Compact homogeneous Si/SiC/C in-situ nanocomposite microspheres are synthesized by a procedure consisted of sol-gel, air calcination and magnesiothermic reduction processes. The components of Si, C, and SiC are all generated in situ and have the advantages of high dispersion and uniform distribution at the nanoscale level, which can maximize the conductivity and structural stability of nanocomposite microspheres when used as the anode materials for lithium-ion batteries. A series of samples with different compositions and morphologies are obtained by controlling the temperature in the air calcination step. Electrochemical tests reveal that the sample with the best comprehensive performance delivers an initial coulombic efficiency of 79.1 %, a reversible specific capacity of 1513 mAh g−1, and a capacity retention of 87.8 % after 200 cycles. The significantly enhanced electrochemical performance relative to the pure Si sample composed of irregular nanoparticles confirms that the method of synthesizing compact homogeneous materials through in-situ means is highly effective and promising for the fabrication of high-performance electrode materials.

Heavy metal concentrations and water quality assessment of different types of drinking water wells in the Erdenet Cu–Mo mining area

The Erdenet mine (Erdenet, Mongolia) is a copper–molybdenum open pit mine with a huge tailing pond and is located next to a residential area. As the sources of drinking water in this area rely on groundwater and can be categorized into public or private wells, we aimed to assess the groundwater quality of the different types of drinking water wells. To accomplish our goal, we analyzed 18 trace metals (As, Ba, Bi, Cd, Co, Cr, Cs, Cu, Ga, Mo, Ni, Pb, Se, Sr, Th, U, V, Zn) and 8 major metals (Al, Ca, Fe, K, Mg, Mn, Na, Si) samples using ICP-MS and ICP-OES, and the heavy metal pollution index, heavy metal evaluation index, and degree of contamination were calculated. The most concerning point is that the Mo concentration of waste water in the Erdenet mine tailing pond and at a natural spring located 300 m from the tailing pond was 1100 μg/L, which greatly exceeds the WHO permissible concentration for Mo of 70 μg/L. Furthermore, high Ca and Mg concentrations at all private wells indicated that consumers of these wells are more vulnerable to any type of water pollution, as these wells are not built with any disinfection or treatment system. A modified categorization of the water quality indices showed that the public and private wells have low–medium contamination and that the tailing pond seepage water, along with its nearest spring, have a high degree of contamination. Because many private wells are located along the tailing pond and used directly without any treatment, we suggest a continuous evaluation and monitoring of the groundwater quality in this area.

Nanoscale morphology, optical dynamics and gas sensor of porous silicon

We investigated the multifaceted gas sensing properties of porous silicon thin films electrodeposited onto (100) oriented P-type silicon wafers substrates. Our investigation delves into morphological, optical properties, and sensing capabilities, aiming to optimize their use as efficient gas sensors. Morphological analysis revealed the development of unique surfaces with distinct characteristics compared to untreated sample, yielding substantially rougher yet flat surfaces, corroborated by Minkowski Functionals analysis. Fractal mathematics exploration emphasized that despite increased roughness, HF/ethanol-treated surfaces exhibit flatter attributes compared to untreated Si sample. Optical approaches established a correlation between increased porosity and elevated localized states and defects, influencing the Urbach energy value. This contributed to a reduction in steepness values, attributed to heightened dislocations and structural disturbances, while the transconductance parameter decreases. Simultaneously, porosity enhances the strength of electron‒phonon interaction. The porous silicon thin films were further tested as effective gas sensors for CO2 and O2 vapors at room temperature, displaying notable changes in electrical resistance with varying concentrations. These findings bring a comprehensive exploration of some important characteristics of porous silicon surfaces and established their potential for advanced industrial applications.

Non-drude-like behavior of the photoinduced dielectric permittivity of GaAs and Si in the gigahertz range frequencies

A non-drude-like behavior of the real part of the photoinduced permittivity ReåP of GaAs and Si samples in the gigahertz range was detected by direct resonator measurements under conditions of fiber-optic irradiation at a wavelength of ë = 0.97 microns with power changes P in the range of 0÷1 W. It is shown that, in accordance with the hypothesis of the exciton mechanism of the photoinduced microwave dielectric permittivity, ReåP increases with increasing P (approaching saturation above P = 200 mW) instead of decreasing within the framework of free charge carriers by Drude. The generality of the behavior of the real parts of the photoinduced permittivity observed in semiconductors of different types (straight-band GaAs and non-straight-band Si) in different electrodynamic systems (waveguides, resonators, metastructures) testifying to the universality of the exciton mechanism is demonstrated. Optically controlled metastructures in the GHz band containing resonant electrically conductive elements loaded with GaAs and Si samples are proposed for the first time: a metastructure based on linear dipoles and a half-wave electric dipole based on a multi-pass spiral. Gigahertz responses of metastructures and the transformation of responses associated with changes in the dielectric permittivity of Si and GaAs during photoexcitation were measured for the first time. Based on the hypothesis put forward about the effect of excitons on photoexcitation, the observed saturation effect of gigahertz photoinduced permittivity is discussed.

Determination of Gallium Concentration in Silicon from Low‐Temperature Photoluminescence Analysis

Increasing the understanding of the electronic properties of gallium (Ga) in silicon (Si) used nowadays to manufacture p‐type Si solar cells is of key technological importance. In this contribution, the results of the effect of Ga concentration on the low‐temperature photoluminescence (PL) spectra in crystalline Si are reported. The Ga‐doped Si samples studied have negligible boron concentrations, which can complicate spectral analysis of the bound exciton (BE) lines. The split Ga BE ground state at T = 10 K is analyzed and the PL intensity ratios for the BE to free exciton peaks are compared. By comparing these to known Ga concentrations, derived from capacitance–voltage measurements, an all‐optical (PL) calibration curve for the quantification of Ga concentration in Si is established. The effects of both temperature and excitation power on the PL intensity ratios are also studied. By combining the temperature‐induced changes in the PL intensity ratios with the calibration curve at 10 K, a calibration function has been determined. It is found that the decay rates of the PL intensity ratios as a function of excitation power are independent of the chosen (split) BE peak. The major benefits of this method and its limitations are discussed.

Direct Fabrication of Te-Doped Black Si with an Enhanced Photoelectric Performance by Femtosecond Laser Irradiation under Water.

Tellurium (Te)-doped black silicon (Si) with enhanced absorption and photoelectric performance over a broad wavelength range of 0.2-2.5 μm was obtained using femtosecond (fs) laser irradiation in liquid water. Prior to laser irradiation, the Si sample was covered with a Te thin film (thickness 200 nm) over an adhesion layer of Cr (thickness 5 nm). Surface analyses by scanning electron microscopy and three-dimensional confocal microscopy evidence the presence of hierarchical surface structures combining quasi-periodic stripes with a spatial period of about 5 μm and subwavelength laser-induced periodic surface structures directed in directions parallel and perpendicular to the direction of the laser polarization, respectively. Moreover, the incorporation of Te generates intermediate levels within the Si bandgap. The Te-doped black Si shows a significant enhancement of the absorption, which reaches values of about 48% in the UV and visible (0.2-1.1 μm) and 70% in the near-infrared (1.1-2.5 μm) spectral ranges, respectively, due to the synergistic effects of multiscale surface structures and Te incorporation. Moreover, the surface reflectance is reduced to almost zero across the entire spectrum. The Te-doped black Si sample is used to realize a photodetector which displays an impressive photoelectric capability, being characterized by a responsivity of 328 mA/W, and an external quantum efficiency of 49.27% at a voltage bias of -10 V for 1064 nm light illumination, with rising and falling times of 55 and 67 ms, respectively. These figures remarkably outperform the response of unprocessed Si under the same experimental conditions.

Foam stability and thermo-mechanical properties of micro/nano filler loaded castor oil based flexible polyurethane foam

Use of fillers in polymers is to improve thermo-mechanical properties of the resulting material. Fillers are also used in polymeric foam as cell openers. Flexible polyurethane (PU) foams undergo major loss in structural stability when synthetic polyol is replaced with castor oil in the formulation as an alternate polyol. This study probes the effect of various micro and nano-fillers on PU foams prepared using blend polyol containing castor oil and synthetic polyol at a ratio of 1:1. Physical and cellular properties such as foam height, cell diameter, strut thickness and cell number density were evaluated to probe the structural stability of the foam. All foams prepared were found stable while it was found that the densities of the PU foams synthesized were greater than that of the conventional PU foams. Addition of fillers found to enhance thermal and mechanical properties of the foam. Moreover, all foam samples were found to observe thermal stability over and above 258 °C. Minimum glass transition temperature was recorded for 15% HG samples (i.e., −35.5 °C). Highest tensile strength was observed for 15% Si samples whereas, highest elongation was observed for 10% NC.