Planar Silicon Research Articles

Ternary 14-electron XB2Be2 (X = Si, Ge, Sn, Pb) clusters: a planar tetracoordinate silicon (ptSi) system and its ptGe/Sn/Pb congeners.

A class of ternary 14-electron clusters, XB2Be2 (X = Si, Ge, Sn, Pb), have been computationally predicted with a planar tetracoordinate silicon (ptSi) unit, as well as its heavier ptGe/Sn/Pb congeners. These pentaatomic ptSi/Ge/Sn/Pb species are established as global-minimum structures via computer global searches, followed by electronic structure calculations at the PBE0-D3, B3LYP-D3, and single-point CCSD(T) levels. Molecular dynamics simulations indicate that they are also kinetically stable against isomerization or decomposition. Chemical bonding analyses show that the clusters have double 2π/2σ aromaticity. The latter concept underlies the stability of ptSi/Ge/Sn/Pb clusters, overriding the 14-electron count or its variants, such as the 18-electron rule. No sp3 hybridization occurs in these species, which naturally explains why they are ptSi/Ge/Sn/Pb (rather than traditional tetrahedral) systems.

Thermal grafting of aniline derivatives to silicon (1 1 1) hydride surfaces

Through a series of aniline derivatives with para-substituents possessing different electron donating/withdrawing characteristics, we examined the nature of thermal grafting of these nucleophilic anilines onto planar Silicon (111) surfaces via detailed XPS and AFM analysis. Based on our current results, para-positioned electron withdrawing group (4-Trifluoromethylaniline) would draw electron density away from the nucleophilic NH2 site which consequently reduces surface grafting. We also concluded that para-positioned halide (Cl and Br) may produce inductive effect that significantly reduces nucleophilic grafting of the NH2 to the silicon hydride while their bulky distal groups may further limited packing density on the surface. On the other hand, 1,3-diaminopropane (control) as well as Phenylenediamine were found to be highly reactive to the surface due to high electron density confinement at the NH2 groups. Furthermore, grafting of aromatic phenylenediamine was observed to have significantly lowered the underlying Si-Si back bonding lysis. Our results and proposed mechanisms were complemented by AFM surface interrogation, contact angle measurements, ATR-FTIR as well as DFT optimized electrostatic potential presentation. Herein, this study presents an in-depth view on molecular grafting through deliberate modulation of the electron density distribution around aromatic system and this may present an important insight towards producing useful bifunctional monolayers.

Dynamic Contact Angle Measurement on a Microscopic Area and Application to Wettability Characterization of a Single Fiber.

Dynamic contact angles on a microscopic area were measured using a specially developed system. Combining pulse injection equipment, a high-speed image capture system set on a microscope, and precise positioning stages, contact angles of typically 2 nL water droplets were measured at a repetition rate of 130 ms. Thereafter, measuring the series of the contact angles of a droplet on a planar silicon surface, contact angle hysteresis, defined as the difference between the advancing and receding contact angles, was measured, and the effect of droplet size was clarified. The system was then applied to characterize a single fiber wherein the contact angles of droplets suspended on a polypropylene fiber, typically 19 μm in diameter, were measured. Plasma treatment is often adopted to modify wettability and has directionality. By fixing a fiber while applying torsion and changing the measurement position along the fiber, the contact angles at different circumferential positions can be characterized. This effect was unraveled by comparing the contact angles on the treated side to its opposite side as well as the effect of fiber diameter.

A comparison of alpha-particle and gamma-ray spectrometry methods for determination of 235U, 238U and 226Ra activity concentration in samples of coal, slag and fly-ash

In order to compare alpha-particle and gamma-ray spectrometry, the activity concentrations of 235U, 238U and 226Ra in samples of coal, slag and fly-ash from the thermal power plant “Nikola Tesla A”, Serbia, were determined by these two methods. Methods were compared and discussed from the point of view of its precision, difficulty to apply and complexity. Gamma-ray spectrometry was performed with HPGe (High Purity Germanium) spectrometer, while alpha activity was measured by PIPS (Passivated Implanted Planar Silicon) detector. For the alpha-particle spectrometry, the chemical procedures applied were chromatographic resin extraction for uranium isotopes and micro-coprecipitation for 226Ra. Thin alpha sources were prepared by electrodeposition and filtration through polypropylene membrane filter for uranium determination, while filtration technique was performed for radium sources. For the evaluation of the statistical difference between individual measurement results obtained by application of two methods Z - test was used. In order to evaluate the difference between two methods used, paired samples t-test and F-test were applied. Results show that there is no statistical difference between two methods used and that gamma-ray spectrometry is a valid alternative to time consuming alpha spectrometry.

Electrical control of the g tensor of the first hole in a silicon MOS quantum dot

Single holes confined in semiconductor quantum dots are a promising platform for spin qubit technology, due to the electrical tunability of the $g$-factor of holes. However, the underlying mechanisms that enable electric spin control remain unclear due to the complexity of hole spin states. Here, we study the underlying hole spin physics of the first hole in a silicon planar MOS quantum dot. We show that non-uniform electrode-induced strain produces nanometre-scale variations in the HH-LH splitting. Importantly, we find that this \RR{non-uniform strain causes} the HH-LH splitting to vary by up to 50\% across the active region of the quantum dot. We show that local electric fields can be used to displace the hole relative to the non-uniform strain profile, allowing a new mechanism for electric modulation of the hole g-tensor. Using this mechanism we demonstrate tuning of the hole $g$-factor by up to 500\%. In addition, we observe a \RR{potential} sweet spot where d$g_{(1\overline{1}0)}$/d$V$ = 0, offering a configuration to suppress spin decoherence caused by electrical noise. These results open a path towards a previously unexplored technology: engineering of \RR{non-uniform} strains to optimise spin-based devices.

Polysilicon contact structures for silicon solar cells using atomic layer deposited oxides and nitrides as ultra‐thin dielectric interlayers

AbstractPolysilicon contact structures with ultra‐thin atomic layer deposited (ALD) oxide and nitride interlayers based on SiOx, SiNx, AlOx, AlNx, and TiOx either as part of an interlayer stack when applied on top of a conventional thermally‐grown SiOx or as a single interlayer were investigated. ALD SiOx single interlayers provided a very good passivation quality with high implied open‐circuit voltage and low‐specific contact resistivity when an optimal thickness and annealing temperature was applied. Also, ALD SiNx single interlayers showed a promising passivation quality, while AlOx and AlNx interlayers only allowed for a moderate and TiOx interlayers exhibited a very poor passivation quality. ALD SiOx interlayers on planar and textured silicon solar cells with poly‐Si(p) hole‐selective contacts and poly‐Si(n) electron‐selective contacts enabled a conversion efficiency of almost 21% as a proof‐of‐concept. These results are comparable with silicon solar cells with conventional thermally‐grown SiOx, showing that ALD SiOx interlayers are an alternative to conventional thermally‐grown SiOx in polysilicon contacts structures.

Influence of base doping level on the npn microstructure solar cell performance: A TCAD study

Silicon industry has a mature learning curve which is the driver for 90% share of the PV market. Yet, the cost/m 2 of the planar crystalline silicon solar cell is still high. To reduce the cost of silicon-based solar cells, heavily doped wafers can be used in a proposed npn microstructure in which photoexcited carries are vertically generated while the collection of carriers is accomplished in the lateral direction. In this work, we report on the influence of the heavily p + base doping concentration, N a , on the performance of the cell for different base widths. All simulations are performed by using SILVACO TCAD under AM1.5 illumination. The results show that for N a extending from 5 × 10 17 cm −3 to 2 × 10 19 cm −3 , the cell could achieve a competitive efficiency, from 15.4% to 9%, respectively. • Device simulation of proposed npn microstructure solar cell was comprehensively performed. • The impact of base high doping on the device performance was fully discussed. • The results show that for N B ranging from 5 × 10 17 cm −3 to 2 × 10 19 cm −3 , the cell could achieve a competitive efficiency, from 15.4% to 9%, respectively. • For base doping ranging from 5×10 17 cm -3 to 2×10 19 cm -3 , a competitive efficiency is 15.4% to 9%, respectively.

Mechanistic understanding of the discrete morphology formed by multi-cycle assembly of tannic acid with Poloxamer 188 on silicon using QMC-D

Formation of discrete microdome-shaped features on planar silicon surfaces through multi-cycles of alternate adsorption of tannic acid (TA) and Poloxamer 188 of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (P188) has been reported recently. To further our understanding of the underlying fundamentals, we turned to quartz crystal microbalance with dissipation (QCM-D) for non-invasive monitoring of the process using SiO 2 -coated quartz crystals. Different concentrations of TA and P188 solutions were used for the step-by-step assembly, and the corresponding QCM-D responses were investigated. Additional TA-P188 assemblies were prepared on silicon substrates using the same concentration settings and subjected to surface morphology characterizations before and after drying. The results showed that increasing the concentration of P188 causes increased restructuring of the constructs during the assembling process, and leads to the formation of well-hydrated but less spherically shaped morphology with more continuity in coverage. In contrast, increasing TA concentration helps the assembled discrete features grow in size without inducing drastic change in morphology, and the large dissipation shift recorded is most likely related to water trapped in between the features. Furthermore, the study revealed that, besides the amphiphilic nature of P188 and the right solution concentration of TA, the surface of the underlying silicon substrate being hydrophilic is also instrumental in achieving discrete features of TA-P188 assembly. Collectively, findings reported herein allow for further tailored design of functional surfaces using TA and P188 as building blocks.

Wafer-Scale Electroactive Nanoporous Silicon: Large and Fully Reversible Electrochemo-Mechanical Actuation in Aqueous Electrolytes.

Nanoporosity in silicon results in interface-dominated mechanics, fluidics, and photonics that are often superior to the ones of the bulk material. However, their active control, for example, by electronic stimuli, is challenging due to the absence of intrinsic piezoelectricity in the base material. Here, for large-scale nanoporous silicon cantilevers wetted by aqueous electrolytes, electrosorption-induced mechanical stress generation of up to 600 kPa that is reversible and adjustable at will by potential variations of ≈1 V is shown. Laser cantilever bending experiments in combination with in operando voltammetry and step coulombmetry allow this large electro-actuation to be traced to the concerted action of 100 billions of parallel nanopores per square centimeter cross-section and determination of the capacitive charge-stress coupling parameter upon ion adsorption and desorption as well as the intimately related stress actuation dynamics for perchloric and isotonic saline solutions. A comparison with planar silicon surfaces reveals mechanistic insights on the observed electrocapillarity (Hellmann-Feynman interactions) with respect to the importance of oxide formation and wall roughness on the single-nanopore scale. The observation of robust electrochemo-mechanical actuation in a mainstream semiconductor with wafer-scale, self-organized nanoporosity opens up novel opportunities for on-chip integrated stress generation and actuorics at exceptionally low operationvoltages.

Measurement of material isotopics and atom number ratio with [formula omitted]-particle spectroscopy for a NIFFTE fission Time Projection Chamber actinide target

We present the results of a measurement of isotopic concentrations and atomic number ratio of a double-sided actinide target using α-spectroscopy and mass spectrometry. The double-sided actinide target, with predominantly 239Pu on one side and 235U on the other, was used in the fission Time Projection Chamber (fissionTPC) for a measurement of the neutron-induced fission cross-section ratio between the two isotopes. The measured atomic number ratio is needed to extract an absolute measurement fission cross-section ratio. The 239Pu/235U atom number ratio was measured with a combination of mass spectrometry and α-spectroscopy with a planar silicon detector achieving uncertainties of less than 1%. Different strategies for estimating isotopic concentration from the α-spectrum are presented to demonstrate the potential of these methods for non-destructive target assay. We found that a combination of fitting spectra with constraints from mass spectrometry, and summing counts in a region of the spectrum provided the most consistent results with the lowest uncertainty.

Cononsolvency of Poly[2-(methacryloyloxy)ethyl phosphorylcholine] in Ethanol-Water Mixtures: A Neutron Reflectivity Study.

Molecular mechanisms underlying the cononsolvency, a re-entrant coil-to-globule-to-coil conformational transition of polymer chains in mixtures of two good solvents, of poly[2-(methacryloyloxy)ethyl phosphorylcholine] (PMPC) in ethanol-water binary mixtures were complementarily investigated. This was accomplished by following a statistical mechanical model for competitive hydrogen bonding combined with the cooperative solvation concept as well as neutron reflectivity (NR) experiments employing contrast variation in the cononsolvents. The experimental re-entrant aggregation of the PMPC chains in ethanol-water mixed solvents, obtained on the basis of turbidity was accurately reproduced by theoretical calculations. The calculation proved the relatively strong cooperativity of ethanol and the preferential interaction of water, while the total coverage of solvents was the lowest at an ethanol volume fraction (fethanol) of 0.90. At this level, the cononsolvency was the most significant, and the collapsed PMPC chains were solvated with more water than the bulk mixed solvent. The ethanol-water cononsolvency for the PMPC brushes on a planar silicon wafer was investigated by NR experiments, and the solvent composition involved in the collapsed PMPC brush was addressed according to the contrast variation study with mixed solvents of water, deuterium oxide, ethanol-d5, and ethanol-d6. The collapsed PMPC brushes at fethanol = 0.90 contained more water than the bulk solvent. The preferential distribution of water in the collapsed PMPC brush was consistent with the simulation results. Therefore, the molecular mechanism for the cononsolvency of PMPC in ethanol-water mixed solvents based on competitive hydrogen bonding coupled with cooperative solvation was experimentally rationalized.

The Role of Electrode-Site Placement in the Long-Term Stability of Intracortical Microstimulation.

Intracortical microelectrodes are neuroprosthetic devices used in brain-machine interfaces to both record and stimulate neural activity in the brain. These technologies have been improved by advances in microfabrication, which have led to the creation of subcellular and high-density microelectrodes. The greater number of independent stimulation channels in these devices allows for improved neuromodulation selectivity, compared to single-site microelectrodes. Elements of electrode design such as electrode-site placement can influence the long-term performance of neuroprostheses. Previous studies have shown that electrode-sites placed on the edge of a planar microelectrode have greater chronic recording functionality than sites placed in the center. However, the effect of electrode-site placement on long-term intracortical microstimulation (ICMS) is still unknown. Here, we show that, in rats chronically implanted with custom-made planar silicon microelectrodes, electrode-sites on the tip of the device outperformed those on both the edge and center in terms of the effect per charge delivered, though there is still a slight advantage to using edge sites over center sites for ICMS. Longitudinal analysis of ICMS detection thresholds over a 16-week period revealed that while all sites followed a similar trend over time, the tip and edge sites consistently elicited the behavioral response with less charge compared to center sites. Furthermore, we quantified channel activity over time and found that edge sites remained more active than center sites over time, though the rate of decay of active sites for center and edge sites was comparable. Our results demonstrate that electrode-site placement plays an important role in the long-term stability of intracortical microstimulation and could be a potential factor to consider in the design of future intracortical electrodes.

Исследование двухсторонних кремниевых солнечных элементов и модулей

The first description of the photoelectric effect in a vertical p-n transition in a silicon crystal dates back to 1941. The development of solar photovoltaic energy began in 1954 after the development of a single-sided planar silicon solar cell in the USA, in which the p-n junction is located parallel to the working illuminated surface. (Research purpose) The research purpose is in conducting an analytical review of the designs and electrophysical characteristics of double-sided solar cells and modules, justifying the leading role of Soviet and Russian scientists in its creation and assessing the prospects for the use of double-sided solar cells and modules in solar photovoltaic energy. (Materials and methods) The first double-sided planar solar cells made of silicon were developed in the USSR in 1969-1970 and were widely used for power supply of low-orbit spacecraft; the first double-sided matrix solar cells with a vertical p-n transition made of silicon were created in the USSR in 1967-1970 and were first used at the Venera-7 interplanetary station in 1970. (Results and discussion) As a result of studies of various types of double-sided matrix solar cells, the following limiting characteristics were obtained: voltage density is 100 volts per square centimeter; linear dependence of the current in the illumination range is up to 10 kilowatts per square centimeter; voltage of one module is of 1000 volts; efficiency at illumination of 10 kilowatts per square meter is of 25 percent; efficiency at monochromatic illumination of 950-1060 nanometers is of 36-42 percent; the maximum voltage of the solar battery is of 32 kilovolts. A global solar power system consisting of three solar power plants measuring 200 by 200 kilometers from double-sided solar modules installed in Australia, Africa and Latin America, and connected by an electric transmission line, will provide year-round and round-the-clock energy supply to the Earth in the amount of 26,000 terawatt-hours per year under the program of transition to carbon-free energy. (Conclusions) During the analysis of the design, manufacturing technologies and characteristics of silicon solar cells with one and two working surfaces, it was revealed that double-sided solar cells have the greatest prospects for development in the solar energy industry.

Cycloadditions with a Stable Charge-Separated Cyclobutadiene-Type Amido-Substituted Silicon Ring Compound.

Reductive debromination of {N(SiMe3)2}SiBr3 with Rieke magnesium results in the formation of the five‐vertex silicon cluster with one bromine substituent Si5{N(SiMe3)2}5Br, 1, and the cyclobutadiene analogue 2 in a 1:1 ratio. The latter features a planar four‐membered silicon ring with a charge‐separated electronic situation. Two silicon atoms in 2 are trigonal planar and the other two trigonal pyramidal. In cycloadditions with ethylene, diethylacetylene, 1,5‐cyclooctadiene, and 2,3‐dimethyl‐1,3‐butadiene cyclic unsaturated ring compounds (3–6) were formed at room temperature in quantitative reactions. Two of the products (3 and 6) show photochemical isomerization with LED light (λ=405 nm) to afford saturated ring compounds 4 e and 6′.

Simulation and characterization of planar high-efficiency back contact silicon solar cells

Short-circuit current, open-circuit voltage, and photoconversion efficiency of silicon high-efficiency solar cells with all back contact (BCSC) with planar surfaces have been calculated theoretically. In addition to the recombination channels usually considered in this kind of modeling, namely, radiative, Auger, Shockley–Read–Hall, and surface recombination, the model also takes into account the nonradiative trap-assisted exciton Auger recombination and recombination in the space charge region. It is ascertained that these two recombination mechanisms are essential in BCSCs in the maximum power operation regime. The model results are in good agreement with the experimental results from the literature.

Fabrication and Characterization of Inverted Silicon Pyramidal Arrays with Randomly Distributed Nanoholes

We report the fabrication, electromagnetic simulation and measurement of inverted silicon pyramidal arrays with randomly distributed nanoholes that act as an anti-reflectivity coating. The fabrication route combines the advantages of anisotropic wet etching and metal-assisted chemical etching. The former is employed to form inverted silicon pyramid arrays, while the latter is used to generate randomly distributed nanoholes on the surface and sidewalls of the generated inverted silicon pyramidal arrays. We demonstrate, numerically and experimentally, that such a structure facilitates the multiple reflection and absorption of photons. The resulting nanostructure can achieve the lowest reflectance of 0.45% at 700 nm and the highest reflectance of 5.86% at 2402 nm. The average reflectance in the UV region (250–400 nm), visible region (400–760 nm) and NIR region (760–2600 nm) are 1.11, 0.63 and 3.76%, respectively. The reflectance at broadband wavelength (250–2600 nm) is 14.4 and 3.4 times lower than silicon wafer and silicon pyramids. In particular, such a structure exhibits high hydrophobicity with a contact angle up to 132.4°. Our method is compatible with well-established silicon planar processes and is promising for practical applications of anti-reflectivity coating.

Development of a low-cost wireless data logging Pyrano-meter with inbuilt temperature and humidity monitoring system

A low cost photodiode-based pyrano-meter with an in-built temperature and humidity monitoring system, robust data-logging, long-range wireless interface to an indoor unit capable of measuring solar irradiance, instant temperature, and relative humidity was designed, developed and tested in this study. The work was carried out in Osun State University, Osogbo. The newly developed pyrano-meter comprises two sub-systems: Indoor Unit and Outdoor Unit. The Outdoor Unit is built around BPW21R- planar Silicon PN photodiode. The indoor unit uses PIC18F2550 as the central controller. The Solar radiation, Temperature, and Relative Humidity data received from the Outdoor unit were stored in an SD Card Memory, a reference for calibration and contrast, the SRS 100 pyrano-meter was used. A 73 ± 0.55 Wm−2 calibration constant was achieved. The stability of the systems built was comparable to the SRS 100 on an open day - a sky test that gave the device irradiances of 629 and 648 Wm−2 at 6 p.m. The pyrano-meter was tested with actual metrological standard value and it provides good results.

Hybrid nanowire-hyperbolic metamaterial based broadband absorber for the visible and near-infrared regions

In this work, spectral absorbance of hybrid nanowire-hyperbolic metamaterial was investigated numerically by using transfer-matrix method. The hybrid nanowire-hyperbolic metamaterial is consisted of two-dimensional periodically arranged arrays of subwavelength-sized hybrid nanowires (with circular cross-section) embedded in silicon dioxide host matrix. Each hybrid nanowire is made by core-shell structure used silicon as a core and gold as a shell. The hybrid nanowire-hyperbolic metamaterial is used as a top layer of a broadband absorber. The top layer is over on a planar silicon dioxide layer, which is backed by a nano-sized layer of gold as a perfect reflector for guaranteeing high absorbance. When electromagnetic waves in the range of 400–1600 nm wavelength are obliquely incident on the top hybrid nanowire-hyperbolic metamaterial surface, the absorption spectra of the designed absorber structure are analyzed for different incident angles, and radii of hybrid nanowire components or fill-factor of the hyperbolic metamaterial layer. The multiple absorption peaks, which are continuously generated from multiple longitudinal and transverse surface plasmon modes and are supported by the hybrid nanowires, are observed directly. The absorption feature can be also tuned by various operational conditions. The proposed structure is made by in-complex nano-fabricating techniques comparing with the another and it provides acceptable broadband absorptivity.

CuS-Decorated GaN Nanowires on Silicon Photocathodes for Converting CO2 Mixture Gas to HCOOH.

Hybrid materials consisting of semiconductors and cocatalysts have been widely used for photoelectrochemical (PEC) conversion of CO2 gas to value-added chemicals such as formic acid (HCOOH). To date, however, the rational design of catalytic architecture enabling the reduction of real CO2 gas to chemical has remained a grand challenge. Here, we report a unique photocathode consisting of CuS-decorated GaN nanowires (NWs) integrated on planar silicon (Si) for the conversion of H2S-containing CO2 mixture gas to HCOOH. It was discovered that H2S impurity in the modeled industrial CO2 gas could lead to the spontaneous transformation of Cu to CuS NPs, which resulted in significantly increased faradaic efficiency of HCOOH generation. The CuS/GaN/Si photocathode exhibited superior faradaic efficiency of HCOOH = 70.2% and partial current density = 7.07 mA/cm2 at -1.0 VRHE under AM1.5G 1 sun illumination. To our knowledge, this is the first demonstration that impurity mixed in the CO2 gas can enhance, rather than degrade, the performance of the PEC CO2 reduction reaction.

Copper-assisted catalyzed etching for nanotextured black silicon with enhanced photoelectric-conversion properties.

Black silicon contains high-aspect-ratio micro/nanostructures with greatly suppressed front-surface reflection, thus possessing superior property in photoelectric devices. In this report, by a two-step copper-assisted chemical etching method, we have fabricated pyramid n+p-black silicon with optimized morphology and anti-reflectance capability, through systematically tuning the concentration of both copper ions and reducing agents, as well as the etching time. The improved optical absorption and superior charge transfer kinetics validate n+p-black silicon as a highly active photocathode in photoelectrochemical cells. The onset potential of 0.21 V vs. RHE and the saturation photocurrent density of 32.56 mA/cm2 are achieved in the optimal n+p-black silicon. In addition, the nanoporous structure with lower reflectance is also achieved in planar p-silicon via the same etching method. Moreover, the photodetectors based on planar p-black silicon show significantly enhanced photoresponsivity over a broad spectral range. This study offers a low-cost and scalable strategy to improve the photoelectric-conversion efficiency in silicon-based devices.