Silicon Films Research Articles

Optical and Electron-Beam Initiation of Porous Silicon Films with Different Contents of Oxidizer and Graphene

Optical and Electron-Beam Initiation of Porous Silicon Films with Different Contents of Oxidizer and Graphene

A wireless triboelectric sensing system with polygonal synchronous driven by bipolar electromagnetic generators for wide wind speed monitoring

The change of wind speed has an important impact on the ecological balance in the wind-eroded grassland. Using the wind speed monitoring technology can promote the sustainable management of grasslands, but commercial wind speed sensors pose certain challenges to energy consumption. Here, a self-powered wide wind speed sensor (SWSS) is proposed, consisting of polygonal cam synchronous driven triboelectric nanogenerator and stereoscopic electromagnetic nanogenerator. The circumferential array cam drive mechanism and the double-optimized silicone film realize the synergistic enhancement effect of force-electric coupling, which makes the synchronous sensing unit output wind speed signals with high sensitivity and up to 0.991 linearity. In addition, at 8 m/s wind speed, the transducer unit with the three-dimensional magnetic field enhanced layout and the energy capture unit with the semi-cylindrical blade designed for installation angle jointly achieved a power output of 69.35 mW, and the energy conversion efficiency reached 6.91 %. Owing to the intermittency of wind energy, the energy closed loop is realized through solar-assisted energy supply and energy management technology. In short, the design, optimization and integration of SWSS provide an innovative strategy for wide wind speed monitoring and sustainable management of wind-eroded grassland.

Young's Modulus Characterization of Nano‐Level Silicon Nanomembrane

Silicon nanomembrane (SiNM) has drawn great attention for the application in nanoelectrical devices as it shows excellent flexibility and is compatible with the integrated circuit process. The mechanical property measurement of the SiNM with nanoscale thickness is critical. A suspended SiNM (40 nm thick) for mechanical measurements is fabricated by transferring a chemically etched ultrathin monocrystalline silicon film from silicon on insulator wafer to a substrate with a multi‐hole array. And then, the atomic force probe is utilized to load force on the free‐standing SiNM to obtain a force deflection curve, and then the Young's modulus of such floating SiNM can be directly calculated based on the large deflection plane model. It shows that the Young's modulus of such SiNM is basically consistent with that of the bulk silicon. However, the SiNMs’ floating area significantly affects the results, i.e., the Young's modulus varies with the ratio of the suspended area diameter (i.e., hole diameter) to the film thickness. The Young's modulus is independent of hole diameter when the ratio is greater than 425. According to this relationship, the variation of Young's modulus can be predicted for arbitrary thick SiNMs and any transferable nanofilms.

3D superhydrophobic lightweight foam concrete designed via in-situ foaming and self-assembled silicone microfilms

The poor durability of lightweight foam concrete, stemming from its highly porous and hydrophilic nature, is a major limitation for its wider application. Designing a superhydrophobic structure would be an effective approach to improving the durability of foam concrete. In this study, a facile strategy was developed to produce 3D superhydrophobic foam concrete using Poly(methyl hydrogen)siloxane (PMHS) by means of in-situ foaming and low surface energy characteristic. Results show that PMHS could be hydrolyzed and released hydrogen gas by reacting with the hydration product of Ca(OH)2. The resulting self-foaming lightweight concrete exhibits controllable average pore sizes ranging from 229 to 430 μm, with a density between 610 and 1177 kg/m3. The hydrolyzed PMHS self-assembles on the foam films, and the micrometer pores are carried with gel-like silicone microfilms through PMHS liquid–solid phase transition after 90℃ steam curing. With the synergetic effect of the dense silicone films and the particular pore frame, the superhydrophobic foam concrete demonstrates good fundamental properties, including thermal insulation and sound absorption, mechanical robustness, chemical durability, and weathering resistance. This study provides a practical solution for developing superhydrophobic lightweight concrete, which substantially enhances the durability of porous cement-based materials.

Electromotive Force of Spontaneously Polarized Semiconductors

Background: Spontaneously polarized finely dispersed semiconductors can be sources of direct electric current, similar to thermoelectric converters. Their power is low due to the low electrical conductivity of the powders. Objective: Theoretical description of the electromotive force of a spontaneously polarized homogeneous semiconductor film with ionized donor centers uniformly distributed over its two surfaces and free electrons in the volume. Establishment of technical characteristics and competitive advantages of using a film as a current source converts the received energy (heat or light) into the work of an electric field. Methods: The theory of semiconductors and the laws of thermodynamics are used. Results: Analytical expressions are obtained that describe the electronic processes in a metal-semiconductor-metal three-layer film and the technical characteristics of its use as a current source. Estimates are given on the example of a silicon film with arsenic-doped surfaces. Conclusion: The universal principles for creating homogeneous solids of macroscopic dimensions are substantiated, with the efficiency of converting heat into the work of an electric field, which is significantly (by an order of magnitude) higher than the efficiency of materials used to create thermo-EMF sources. The heat absorbed by the metal-semiconductor-metal three-layer film serves as an energy source for a direct current in a closed circuit generated by this structure with an efficiency of 100%. The power of the current source 10 - 105 W/m depends on the received heat flow. A semiconductor film with a built-in electric field is an analogue of a p - n junction and does not have its drawbacks.

A new approach towards extracorporeal gas exchange and first invitro results.

Extracorporeal life support (ECLS) pertains to therapeutic and prophylactic techniques utilized in a wide range of medical applications, with severe pulmonary diseases being the most prominent cases. Over the past decades, little progress has been made in advancing the basic principles and properties of gas exchangers. Here, in an unconventional approach, dialysis hollow fibers are handled with silicone to create a purely diffusive coating that prevents plasma leakage and promotes gas exchange. Commercial dialyzers of varying surface area and fiber diameter have been coated with silicone, to determine the impact of each parameter on performance. The impermeability of the silicone layer has been validated by pressurization and imaging methods. SEM images have revealed a homogeneous silicone film coating the lumen of the capillaries, while fluid dynamic investigations have confirmed its purely diffusive nature. The hemodynamic behavior and the gas exchange efficiency of the silicone-coated prototypes have been investigated invitro with porcine blood under various operating conditions. Their performance has been found to be similar to that of a commercial PMP oxygenator. This novel class of gas exchangers is characterized by high versatility and expeditious manufacturing. Intraoperability between conventional ECLS systems and dialysis machines broadens the range of application infinitely. Ultimately, long-term clinical applicability ought to be determined over invivo animal investigations.

A comprehensive calibration of integrated magnetron sputtering and plasma enhanced chemical vapor deposition for rare-earth doped thin films

A new integrated deposition system taking advantage of magnetron sputtering and electron cyclotron-plasma enhanced chemical vapour deposition (IMS ECR-PECVD) is presented that mitigates the drawbacks of each fabrication system. This tailor-made system provides users with highly homogeneous and pure thin films with less undesired hydrogen and well-controlled rare-earth concentration compared to existing methods of rare-earth doping, such as metalorganic powders, sputtering, and ion implantation. We established the first comprehensive report on the deposition parameters of argon flow and sputtering power to achieve desired rare-earth concentrations in a wide composition range of terbium (Tb) doped-silicon oxide (Tb:SiOx) matrices including silicon-rich (x < 2), oxygen-rich (x > 2), and stoichiometric silicon oxide (x = 2). The deposition parameters to fabricate crystalline structure (Tb2Si2O7) in oxygen-rich samples are reported where Tb ions are optically active. IMS ECR-PECVD pushes the solubility limit of the rare-earth dopant in silicon films to 17 at.% for the desired future nanophotonic devices.Graphical

Silicon oxide film formation by spraying tetraethyl orthosilicate onto substrate with simultaneous low-energy SiO+ ion-beam irradiation

We attempted to deposit silicon oxide films by spraying tetraethyl orthosilicate (TEOS) onto a substrate while the substrate was also irradiated with a low-energy SiO+ ion beam. The energy of the SiO+ ions was 55 eV, and the substrate temperature was 300 °C. Following this process, we were able to deposit a film on the substrate. X-ray photoelectron spectroscopy (XPS) measurements of the film showed that it was composed of silicon oxide. XPS analysis also showed that the oxygen-to-silicon atomic concentration ratio (O/Si ratio) for the film was 1.57. For comparison, an SiO+ ion beam was used to irradiate a substrate at room temperature with simultaneous spraying of TEOS. XPS analysis of the deposited film showed that it was silicon oxide with an O/Si ratio of 1.45. In this case, however, a relatively large number of carbon atoms (7 at. %) were incorporated into the film. In both the 300 °C and room-temperature cases, we confirmed that the film deposition rate was substantially improved by supplying TEOS during SiO+ ion-beam irradiation.

Effect of Heat Treatment Conditions on the Structural Features of Porous Silicon Films Formed by Metal-Assisted Etching

Effect of Heat Treatment Conditions on the Structural Features of Porous Silicon Films Formed by Metal-Assisted Etching

ДОСЛІДЖЕННЯ П'ЄЗОРЕЗИСТИВНОГО ЕФЕКТУ В ПЛІВКАХ КРЕМНІЮ ТА РОЗРОБКА ВИМІРЮВАЛЬНИХ ПЕРЕТВОРЮВАЧІВ НА ЇХ ОСНОВІ

The piezoelectric effect in semiconductor materials is analyzed. The features of piezoresistance in silicon films on insulating substrates and the ratio of piezoresistance coefficients depending on the crystallographic orientation are considered. The desi

Light soaking effect on defect states distribution of Hydrogenated amorphous silicon investigated By means of constant photocurrent technique

In the present paper we have investigated, by using the constant photocurrent method in dc-mode (dc-CPM), the effect of the light soaking (LS) on the deep defect density (Nd) and the slope of the Urbach tail (E0) of a slightly phosphorus-doped hydrogenated amorphous silicon (a-Si:H) film prepared by Plasma-Enhanced Chemical Vapour Deposition (PECVD). By applying the derivative method, we have converted the measured data into a density of states (DOS) distribution in the lower part of the energy gap. The evolution of the sub-band-gap absorption coefficient and the CPMdetermined density of gap-states distribution within the gap versus the illumination time leads to: (i) an increase in the deep defect absorption without any significant changes in the Urbach tail (exponential part), (ii) a presence of more charged than neutral defects as predicted by the defect pool model, and (iii) a saturation point of the degradation of both optical absorption coefficient and density of deep states of slightly P-doped sample measured by dc-CPM. The constant photocurrent technique in dc-mode as a spectroscopy method for the defect distribution determination is, therefore, most reliable to study the light soaking effect on the stability of hydrogenated amorphous silicon layers used in solar cells manufacturing.

Microstructural evolution and properties of He-charged a-Si coatings prepared by magnetron sputtering

The introduction of porosity in nanomaterials via magnetron sputtering in helium atmospheres is an interesting strategy for the design of functional materials. Amorphous silicon coatings, with high concentration of He incorporated in the form of overpressurized nano-bubbles, present modified optical properties in comparison with dense coatings of similar composition.In this work, annealing process in He atmosphere from 300 °C up to 1200 °C is performed to evaluate stability after the release of He from the a-Si:He coatings (thickness ∼1700 nm) and to favor matrix crystallization and defect evolution. The work is focused on these effects on the silicon film and its properties. The composition and microstructural evolution of the coatings annealed to temperatures as high as 1200° were investigated by electron microscopy and X-Ray diffraction. Annealing effects on the optical properties and bandgap of the silicon coatings were evaluated by ellipsometry and UV–Vis spectrometry. Helium release from the coating, densification, defects evolution and ordering due to crystallization have a small effect on the refractive index, but cause a significant change in the material band gap from 1.37 eV to 1.80 eV.

Impact of relative humidity and deposition parameters on the tribological behavior of soft DLC coatings

When diamond-like carbon coatings are produced with plasma-assisted CVD, a softer but thicker DLC variant with excellent tribological behavior can be achieved. Due to great adhesion and load-bearing capacity, they can be deposited on low-alloy steels, commonly used in mechanical engineering, to reduce energy consumption and extend the lifespan of machine components.In this work, soft a-C:H coatings were deposited over AISI 4140 steel using a modified commercial PA-CVD system, with acetylene as carbon precursor. Two kind of coatings were deposited: Si free (a-C:H) and Si doped (a-C:H:Si). Adhesion, mechanical properties, and film structure were analyzed. Tribological behavior was evaluated with Pin-on-Disk tests using an alumina ball as counterpart and 12 N normal load. At constant room temperature, three different relative humidity conditions were tested: dry, room and wet. The frictional force was registered and the wear scars in the sample and in the counterpart were measured and evaluated by means of confocal, optical, and scanning electron microscopy with EDS.Si-doped coatings showed up to 60 times more wear than Si-free samples, with the later displaying a friction coefficient as low as 0.05, while for the Si-DLC was μ ~ 0.2. This can be caused by a change in the composition of the graphite-like transfer layer produced by the DLC when doping with Si. Both friction coefficient and wear volume increased along with the humidity level for the Si-free DLC, and the opposite trend was observed for the Si-DLC. This can be explained by the oxidation of the DLC in the case of a-C:H and by the stability of a silicon oxide film that is formed and regenerated in accordance with the environment's humidity in the case of a-C:H:Si.

Electrode Impact on the Electrical Breakdown of Dielectric Elastomer Thin Films.

Dielectric Elastomer Actuators (DEAs) enable the realization of energy-efficient and compact actuator systems. DEAs operate at the kilovolt range with typically microampere-level currents and hence minimize thermal losses in comparison to low voltage/high current actuators such as shape memory alloys or solenoids. The main limiting factor for reaching high energy density in high voltage applications is dielectric breakdown. In previous investigations on silicone-based thin films, we reported that not only do environmental conditions and film parameters such as pre-stretch play an important role but that electrode composition also has a significant impact on the breakdown behavior. In this paper, we present a comprehensive study of electrical breakdown on thin silicone films coated with electrodes manufactured by five different methods: screen printing, inkjet printing, pad printing, gold sputtering, and nickel sputtering. For each method, breakdown was studied under environmental conditions ranging from 1 °C to 80 °C and 10% to 90% relative humidity. The effect of different manufacturing methods was analyzed as was the influence of parameters such as solvents, silicone content, and the particle processing method. The breakdown field increases with increasing temperature and decreases with increasing humidity for all electrode types. The stiffer metal electrodes have a higher breakdown field than the carbon-based electrodes, for which particle size also plays a large role.

Effects of LPCVD-deposited thin intrinsic silicon films on the performance of boron-doped polycrystalline silicon passivating contacts

Highly efficient n-type tunnelling oxide passivated contact solar cells can be realized by integrating p-type polycrystalline silicon (p+ poly-Si) boron (B) diffusion technology. In this study, the intrinsic silicon (i-Si) film was prepared with varying crystalline states, by precisely controlling the deposition temperature using low-pressure chemical vapor deposition (LPCVD). The i-Si films transitioned from amorphous to polycrystalline when the deposition temperature was increased from 560 °C to 590 °C, with the crystallization rate increasing from 0 % to 81.5 %. An inverse correlation was observed between the electrical properties of B-diffused p+ poly-Si and the crystallization rate of i-Si thin films. The crystal structure of p+ poly-Si contained an amorphous phase, even after high-temperature B diffusion (>900 °C).The defect density and grain boundary potential barriers within the crystal were increased, which resulted in enhanced carrier scattering probability and deteriorated material performance. Amorphous silicon film deposited at lower temperatures can achieve low contact resistivity (ρc = 0.81 mΩ·cm2) and improved passivation performance (Δi-Voc > 10 mV) after B diffusion. These results have significant implications for the development of highly efficient passivated contact solar cells with excellent passivation performance and low contact resistance hole-selective contacts.

Preparation of pure hydrogenated amorphous silicon film via PECVD method as anode materials for high-performance lithium-ion batteries

In this paper, plasma-enhanced chemical vapor deposition (PECVD) is used to prepare a nano-scale pure hydrogenated amorphous silicon thin film anode, which improves the problem of large volume effect of traditional silicon-based anode materials during the charge and discharge process of lithium-ion batteries. Among them, the thinnest 120 nm pure silicon film still has a high specific capacity of 1254.6 mAh g−1 after 200 cycles at 0.5C (1C = 4.2 A g−1), and also has an excellent performance of 848.2 mAh g−1 after a large rate of charge and discharge of 5C. To give consideration to the performance and obtain a certain mass load at the same time, 170 nm pure silicon film was selected for vacuum annealing treatment at different temperatures to release the non-uniform compression stress during the deposition of hydrogenated amorphous silicon, and a more stable film structure was constructed, which further improved the performance of silicon film. Among them, the best performance is held at 100 °C for 5 h, and the reversible specific capacity of 1172.7 mAh g−1 is still maintained at 200 cycles at 0.5C, and the reversible specific capacity of 1131.6 mAh g−1 is also available at a super high rate of 10C.

Enhancing the Selectivity and Transparency of the Electron Contact in Silicon Heterojunction Solar Cells by Phosphorus Catalytic Doping

AbstractAn intrinsic hydrogenated amorphous silicon (a‐Si:H(i)) film and a doped silicon film are usually combined in the heterojunction contacts of silicon heterojunction (SHJ) solar cells. In this work, a post‐doping process called catalytic doping (Cat‐doping) on a‐Si:H(i) is performed on the electron selective side of SHJ solar cells, which enables a device architecture that eliminates the additional deposition of the doped silicon layer. Thus, a single phosphorus Cat‐doping layer combines the functions of two other layers by enabling excellent interface passivation and high carrier selectivity. The overall thinner layer on the window side results in higher spectral response at short wavelengths, leading to an improved short‐circuit current density of 40.31 mA cm−2 and an efficiency of 23.65% (certified). The cell efficiency is currently limited by sputter damage from the subsequent transparent conductive oxide fabrication and low carrier activation in the a‐Si:H(i) with Cat‐doping. Numerical device simulations show that the a‐Si:H(i) with Cat‐doping can provide sufficient field effect passivation even at lower active carrier concentrations compared to the as‐deposited doped layer, due to the lower defect density.

A dynamically switchable multifunctional meta-device in terahertz based on vanadium dioxide and photosensitive silicon

In this study, we propose a dynamically switchable multifunctional device operating in the terahertz range. The device is designed by employing a multilayered planar structure that incorporates vanadium dioxide and photosensitive silicon films. We analyze the transmission characteristics and multifunctional attributes of the device. The device exhibits the capacity to transition among diverse functionalities, including linear polarization conversion, field intensity modulation, frequency selection, and wave absorption. The polarization conversion ratio exceeds 90%, and precise control over the amplitude ratio between cross-polarized and co-polarized fields is achievable. Field intensity modulation can be realized through any of three distinct methods. Upon activation of the frequency selection function, the device can effectively operate as a band-stop filter, yielding a -20dB bandwidth of 0.57 THz. Furthermore, in absorber mode, the device demonstrates a peak absorption efficiency of 90%.

Application of the Thermal Diffusivity Standard for the Heat Transfer Parameter Control in Absorbing Materials

Metrological support creation and use of heat transfer etalons are important stages in the development of modern materials science. This is especially concerned to the emergence of new materials in the world with previously unattainable thermophysical parameters. The purpose of this work was to develop and experimentally verify the idea of joint application of the transient gratings method which is well-known in nonlinear optics and the single thermal diffusivity etalon of conventional type for the heat transfer metrological control in materials of a wide values range. The method proposed is based on thermal diffusivity etalon application as a source of calibrated optical signals that are excited in it by short laser pulses. Their lifetime is formed by the etalon thermal diffusivity and on the transient grating spatial period. The etalon linear graph of gratings lifetimes as a function of the gratings periods squared and grating lifetime of the material under study are used for the thermal diffusivity calculation. Thermal diffusivity of thin sub-surface layers of the samples under study – duraluminium, monocrystalline silicon and thermoelectric lead telluride film was measured. The results obtained are in close agreement with the reference values.

Commissioning Intracranial Stereotactic Radiosurgery for a Magnetic Resonance-Guided Radiation Therapy (MRgRT) System: MR-RT Localization and Dosimetric End-to-End Validation

This is the first reporting of the MRIdian A3iTM intracranial package (BrainTxTM) and benchmarks the end-to-end localization and dosimetric accuracy for commissioning an magnetic resonace (MR)-guided stereotactic radiosurgery program. We characterized the localization accuracy between MR and radiation (RT) isocenter through an end-to-end hidden target test, relative dose profile intercomparison, and absolute dose validation. BrainTx consists of a dedicated head coil, integrated mask immobilization system, and high-resolution MR sequences. Coil and baseplate attenuation was quantified. An in-house phantom (Cranial phantOm foR magNetic rEsonance Localization of a stereotactIc radiosUrgery doSimeter, CORNELIUS) was developed from a mannequin head filled with silicone gel, film, and MR BB with pinprick. A hidden target test evaluated MR-RT localization of the 1×1×1 mm3 TrueFISP MR and relative dose accuracy in film for a 1 cm diameter (International Electrotechnical Commission (IEC)-X/IEC-Y) and 1.5 cm diameter (IEC-Y/IEC-Z) spherical target. Two clinical cases (irregular-shaped target and target abutting brainstem) were mapped to the CORNELIUS phantom for feasibility assessment. A 2-dimensional (2D)-gamma compared calculated and measured dose for spherical and clinical targets with 1 mm/1% and 2 mm/2% criteria, respectively. A small-field chamber (A26MR) measured end-to-end absolute dose for a 1 cm diameter target. Coil and baseplate attenuation were 0.7% and 2.7%, respectively. The displacement of MR to RT localization as defined through the pinprick was 0.49 mm (IEC-X), 0.27 mm (IEC-Y), and 0.51 mm (IEC-Z) (root mean square 0.76 mm). The reproducibility across IEC-Y demonstrated high fidelity (<0.02 mm). Gamma pass rates were 97.1% and 95.4% for 1 cm and 1.5 cm targets, respectively. Dose profiles for an irregular-shaped target and abutting organ-at-risk-target demonstrated pass rates of 99.0% and 92.9%, respectively. The absolute end-to-end dose difference was <1%. All localization and dosimetric evaluation demonstrated submillimeter accuracy, per the TG-142, TG-101, MPPG 9.a. criteria for SRS/SRT systems, indicating acceptable delivery capabilities with a 1 mm setup margin.