Amorphous Silicon Thin Films Research Articles

On the characteristics of helium filled nano-pores in amorphous silicon thin films

On the characteristics of helium filled nano-pores in amorphous silicon thin films

Multifunctional Double Band Mesh Antenna with Solar Cell Integration for Communications Purposes

A dual band flexible antenna based on a circularly polarized modified meshed patch antenna design. This article focuses on some of the most pressing issues in small satellite applications. The antenna optimization and improvement of antenna performance, such as radiation efficiency. As is well known, circular polarization is immune to the Faraday rotation effect in the ionosphere and can thus prevent a 3-dB loss in geo-satellite communication. With the use of the software program Computer Simulation Technology (CST), the proposed circularly polarized modified meshed patch antenna has been created. Therefore, this article also presents a modified design of a circularly polarized meshed patch antenna to reduce the complexity of the antenna and decrease the size as much as it is capable. However, a meshed patch antenna can support a high communication data rate. The antenna architecture will theoretically be consistent with the installation of solar panels. The antenna utilizes a conductive copper as the core material and the substrate using flexible polyimide. The design antenna is very small, having an overall size of 30 * 30 mm when compared to other conventional non-transparent antenna operating at the same frequencies of 2.6, 3.5 GHz. The antenna that is proposed involves two meshed patch elements of same size but in various shapes. Finally, the proposed antenna is integrated into a solar cell by using the amorphous silicon thin film.

Broadband light absorption enhancement in a–Si:H ultrathin film solar cells with nanophotonic light trapping structures

Light trapping over a wide wavelength range is critical for applications such as thin-film solar cells (TFSCs). Therefore, in this paper, we report a plasmonic light trapping scheme as a solution to overcome the limited absorption of light in hydrogenated amorphous silicon (a-Si:H) thin film solar cells. Here we propose plasmonic nanostructures, which have periodic nanodisks added to the front surface of the cell. These structures combine a variety of photonic effects to reduce reflection, improve light trapping, and increase absorption over a broadband solar spectrum. Initially, to test whether the suggested plasmonic nanoparticles can enhance light-trapping within the absorber layers of the cell, we used the 3D finite difference time domain method to simulate the propagation of electromagnetic waves and the absorbed light in each layer of the cell. Additionally, the obtained optical properties after the FDTD simulation are used to design electrical model simulations using SCAPS software. The results show that the front surface of nanodisk-shaped solar cells with only a 100-nm-thick a-Si:H layer can absorb light at wavelengths ranging from 300 to 800 nm, which is greater than that of flat a-Si:H film devices. With optimized structural parameters, the short circuit current density Jsc could be enhanced by 98 % and 71 % with the addition of Au and Cu nanodisks, respectively. Additionally, the conversion efficiency is improved by 28 % and 26 % for Au and Cu, respectively. The proposed design of the light trapping structure can provide guidelines for ultra-TFSCs with high performance.

A Comparative Thermal and Lumen Performance Study of Thin-film Amorphous Silicon Dielectric Coating on Aluminum as an LED Packaging Substrate

A Comparative Thermal and Lumen Performance Study of Thin-film Amorphous Silicon Dielectric Coating on Aluminum as an LED Packaging Substrate

P‐32: Dual Gate Amorphous Silicon Thin Film Transistor Technology for High Brightness and High Frame Rate Outdoor Display Panels

In this paper, we present the development of a dual‐gate (DG) architecture for hydrogenated amorphous silicon thin film transistors (a‐Si:H TFTs). The aim is to address the challenges of low on‐state current (Ion) and light‐induced degradation in traditional single‐gate (SG) TFTs. The experimental results demonstrate that the DG‐TFT exhibits significantly higher Ion compared to the SG‐TFT, and the improvement depends on the thickness of the top gate insulator. Additionally, the threshold voltage (Vth) can be adjusted by applying the top gate voltage, allowing for a full‐ swing modulation coefficient of approximately 0.2. To ensure long‐term stability, a light‐blocking layer has been incorporated as the top gate electrode, enabling the DG‐ TFT to maintain its initial properties even under intense illumination conditions of up to 28,000 nits.

Crystallization of Hydrogenated Amorphous Silicon Thin Films Using Combined Continuous Wave Laser and Thermal Annealing

Crystallization of Hydrogenated Amorphous Silicon Thin Films Using Combined Continuous Wave Laser and Thermal Annealing

Influence of Photonics and Plasmonics Effect on Ultrathin Amorphous Silicon Thin Film Solar Cell

Abstract Our recent surge in silicon derived materials has major demand in thin film photovoltaic (PV) modules and enhancing the significant numbers. The rigorous coupled wave analysis method is a simple and fast method also known as developed to determine the light absorption and cell efficiency. The optics of thin film solar cells (amorphous silicon) garnering crucial role in the photovoltaic market. In this work, an ultrathin thin film amorphous silicon solar cell PV performance investigated by periodically textured surfaces at the nanoscale level. This analysis of periodic textured substrate was deriving optimal surface textures. The nanogratings lead to light scattering mechanism with the higher order diffraction angle and enhanced the light absorption of the incidence spectrum. The influence of grating period and height, the collection of the charge carriers increased at various wavelengths from ultraviolet, visible and infrared spectral regions are discussed with the assistance of photonic and plasmonic modes. Finally, nanoscale engineering mechanism the optimized thin film amorphous silicon solar cell yielded the highest current densities (22.6 and 23.8 mA/cm2) in both polarization modes.

Nickel–silicon interfacial adhesion strength measured by laser spallation

Thin films of amorphous silicon (a-Si) coated on metals such as nickel (Ni) are one of the most promising anode architectures for high-energy-density lithium-ion (Li-ion) batteries. The performance and longevity of batteries with this type of electrode depend on the integrity of the Ni/a–Si interface. The integrity of the a-Si /Ni bonded interface during cycling is critical, but the experimental characterization of interfacial failure of this material system is highly challenging and there is a sparsity of interface strength data in the literature. Here, we describe a laser spallation (LS) technique to characterize the interfacial adhesion strength of Ni/a–Si multilayer films created by chemical vapor deposition (CVD). The LS technique enables the non-contact measurement of the tensile interfacial strength with high precision when compared to conventional methods for characterizing adhesion. Interferometric measurement combined with finite element analysis shows that the Ni/a–Si interface, created via the CVD of a-Si on Ni surfaces can withstand ≈46–72 MPa in tension before failure initiation. To ensure successful and precise characterization of interfacial adhesion strength using LS, we further develop a design criterion for multi-layer samples by analyzing the thin-film mechanics. Our study provides insights into the strength of the Ni/a–Si interface that governs the performance and durability of high-energy-density anodes and offers design guidelines for improving thin-film electrode integrity.

Gaussian grating for enhancing light absorption by amorphous silicon thin-film solar cells

In this study, a grating with a Gaussian distribution was used to increase the absorption of light by amorphous silicon thin film solar cells. A grating is an effective structure for trapping light inside the active layer of a cell, so a two-dimensional Gaussian grating with a rectangular structure was placed on the front surface of the cell. The results obtained by using the finite element method showed that the Gaussian grating significantly enhanced the absorption of light in the visible and near-infrared ranges by a cell with a thickness of 0.5 μm compared with a cell without gratings and a cell with normal gratings. The maximum average light absorption by the cell with a Gaussian grating was 84.8%, which was 90% higher compared with the reference cell. In addition, the short-circuit current density and efficiency were determined as 34.2 and 17.6 mA/cm2, respectively, which were 72% and 72.5% higher, respectively, compared with the reference cell. The proposed structure could be used in a cell to convert more light into electricity.

Fine-Tuning Intrinsic and Doped Hydrogenated Amorphous Silicon Thin-Film Anodes Deposited by PECVD to Enhance Capacity and Stability in Lithium-Ion Batteries.

Silicon is a promising alternative to graphite as an anode material in lithium-ion batteries, thanks to its high theoretical lithium storage capacity. Despite these high expectations, silicon anodes still face significant challenges, such as premature battery failure caused by huge volume changes during charge-discharge processes. To solve this drawback, using amorphous silicon as a thin film offers several advantages: its amorphous nature allows for better stress mitigation and it can be directly grown on current collectors for material savings and improved Li-ion diffusion. Furthermore, its conductivity is easily increased through doping during its growth. In this work, we focused on a comprehensive study of the influence of both electrical and structural properties of intrinsic and doped hydrogenated amorphous silicon (aSi:H) thin-film anodes on the specific capacity and stability of lithium-ion batteries. This study allows us to establish that hydrogen distribution in the aSi:H material plays a pivotal role in enhancing battery capacity and longevity, possibly masking the significance of the conductivity in the case of doped electrodes. Our findings show that we were able to achieve high initial specific capacities (3070 mAhg-1 at the 10th cycle), which can be retained at values higher than those of graphite for a significant number of cycles (>120 cycles), depending on the structural properties of the aSi:H films. To our knowledge, this is the first comprehensive study of the influence of these properties of thin films with different doping levels and hydrogen distributions on their optimization and use as anodes in lithium-ion batteries.

Electrodeposition preparation and electrochemical properties of silicon anode

The theoretical capacity of silicon is about 4200 mA h g−1, so the silicon anode is the most attractive substitute for the graphite anode of lithium-ion battery. In this paper, amorphous silicon thin films is successfully prepared on the surface of 12 µm thick copper foil by pulsed electrodeposition, then the silicon anode is prepared and the electrochemical performance is tested. The research results show that the silicon anode exhibits higher reversible capacity (1200 mA h g−1) compared with the graphite anode, and there is no obvious capacity fade after 100 cycles at the current density of 200 mA g−1. The amorphous silicon can alleviate the cracking of silicon thin films, and form stable Solid Electrolyte Interphase, which can reduce lithium consumption and improve the coulombic efficiency of lithium-ion battery. In addition, the lithium-ion battery with silicon anode exhibits excellent cycle performance and rate capability.

Operando Nanomechanical Mapping of Amorphous Silicon Thin Film Electrodes in All-Solid-State Lithium-Ion Battery Configuration during Electrochemical Lithiation and Delithiation.

An operando bimodal atomic force microscopy system was constructed to perform nanomechanical mapping of an amorphous Si thin film electrode deposited on a Li6.6La3Zr1.6Ta0.4O12 solid electrolyte sheet during electrochemical lithiation/delithiation. The evolution of Young's modulus maps of the Si electrode was successfully tracked as a function of apparent Li content x in lithium silicide (LixSi) simultaneously with real-time surface topography observation. At the initial stage of lithiation, the average modulus steeply decreased due to the generation of LixSi from intrinsic Si, followed by a moderate modulus reduction until the electrode capacity reached 3300 mAh g-1 (Li content x = 3.46). In the following delithiation, the gradual recovery of the average modulus of LixSi was observed up to 1467 mAh g-1 (Li content x = 1.54) at which delithiation stopped due to the significant volume change induced by phase transformation of LixSi.

Multipole interference and optical sensing based on the bound states in the continuum formed in dimer metasurfaces

The all-dielectric metasurface supporting BIC based on dimer structures is proposed with the rectangular holes etched in amorphous silicon thin films. By introducing perturbations of the rotation angle of the rectangular hole as well as the difference in length and width, quasi-BIC modes in the near-infrared band can be created. Meanwhile, the research found that two different perturbations display different tuning abilities on the Fano resonance induced by the quasi-BIC. This paper reveals that the formation of the BIC mode originates from the interference between competing multipole moments, which ultimately leads to the emergence of a pair of reverse parallel electric dipoles. It explains the mismatch between the macroscopic response of the structure under the influence of competing multipole moments and the results of the multipole expansion. From the perspective of the influence of asymmetry on multipole moments, we explain the resulting radiation sources. The study demonstrates that the proposed dimer metasurface can support optical sensing under both x-polarization and circular polarization excitation, and it is observed that different perturbations have different abilities to modulate the sensitivity, which has great potential for device performance optimization and precise modulation.

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.

Microstructure quantification of oblique angle sputtered porous a-Si thin films as a basis for structure-property relations of solid phase microextraction coatings

Understanding processing-structure-property (PSP) linkages of solid-phase microextraction (SPME) coating materials is crucial for the rational design and advancement of these new materials. As SPME is a diffusion-based extraction technique, analyzing the morphology of its coating materials is important for optimizing its performance. In this study, we assess the morphological evolution of micro/mesoporous amorphous silicon (a-Si) thin films sputtered at an oblique angle onto silicon, which serve as models for support materials in SPME devices. The contrast of scanning transmission electron microscopy (STEM) images is enhanced via ZnO infiltration by atomic layer deposition (ALD). Various metrics, including physical descriptors and two-point statistics methods, are employed to follow the films' evolution. Analysis of the two-point correlation function reveals a simple ellipse/spherical local pore geometry in contrast to the long-range irregular arrangement of pores identified by a range of traditional and novel metrics. Additionally, analyzing the internal structure of the pores through homology metrics aligns well with the theoretical understanding of morphological evolution in oblique sputtered films. These analyses show that the “average ratio of principal moment of inertia”, “Betti numbers”, and “two-point statistics” based metrics can capture valuable information during film growth.The morphological analysis approach proposed in this study can be applied to analyze any nanoporous medium as a first step towards developing structure-property relationships that tie back to a given preparation method. Ultimately, a more extensive experimental and/or simulation-based study should confirm the correlations between these metrics and actual diffusion properties as the basis for process-structure-properties relations for improved design and optimization of this film.

Electric-field-enhanced aluminum-induced crystallization of amorphous silicon thin film using decreasing stepwise current method

Electric-field-enhanced aluminum-induced crystallization (AIC) was applied to the crystallization of amorphous Si (a-Si) using a stepwise current method with two to four decreasing steps. In AIC, Si diffuses into an Al layer, which generates a layer exchange from an a-Si/Al layer to an Al/polycrystalline Si (p-Si) layer. This increases the electrical resistivity of the Al/p-Si layer. The stepwise decreasing current was an attempt to overcome the limitations of electric-field-enhanced AIC using a constant current. The samples were fabricated by depositing a 200 nm-thick a-Si layer and sputtering a 300 nm-thick Al layer onto an Eagle XG glass substrate. In-situ resistance and reflectivity were measured to monitor the AIC mechanism and layer exchange. The reflectivity measurements were compared with thin-film optics calculations on the a-Si/Al and Al/p-Si layers to indicate the growth of p-Si. The temperature variations during the heating process were supported by a numerical analysis. The crystallinity of produced polycrystalline silicon (p-Si) was verified by a Raman peak at around 519–520 cm−1. The stepwise current supply increased the crystallization time and improved the crystallinity of the produced p-Si compared to the constant current method.

Effect of Stress on the Electrochemical Response of Amorphous Silicon Electrodes

Silicon electrodes for lithium-ion batteries exhibit a theoretical capacity ten times higher than that of the graphite electrodes currently used in commercial systems. When lithiated/delithiated, silicon experiences stresses on the order of one GPa, inducing the damage of the material, which results in poor cyclability. Concurrently, irreversible continuum thermodynamics predicts that these stresses affect the lithiation itself in different ways for monophasic and biphasic lithiation (progressive invasion of the electrode by a lithiated phase of given composition) [1,2]. When lithiation takes place homogeneously (without phase transformation), mechanical stresses affect lithiation through their effect on the chemical potential of diffusing lithium (Larché-Cahn theory). On the other hand, when lithiation is biphasic, mechanical stresses affect lithiation through an effect on both chemical potential of lithium and thermodynamic driving force acting on the phase boundary. This coupling has first been probed experimentally in homogeneous lithiation using a method where the stress state of silicon is modified indirectly through incremental delithiation [3].In this work, we investigate the interplay between the electrochemical state (electrode potential and current density) of an amorphous silicon electrode and its stress state. The electrochemical response of the amorphous silicon thin film deposited on a stainless steel substrate has been recorded under varying mechanical loading during lithiation and delithiation cycles. The mechanical loading is applied by deforming elastically the steel substrate of the amorphous silicon thin film, which allows us to directly probe the contribution of mechanics to the lithiation/delithiation processes. When carried out under galvanostatic conditions, incremental changes in stress lead to instantaneous change in the electrode potential. Experimental results from uniaxial tensile tests show that an applied strain of 0.3%, resulting in changes in stress in silicon of ~ 200-300 MPa, induces a potential variation on the order of 2.5 mV. Stress-induced changes in the potential are measured for the biphasic first lithiation, as well as subsequent monophasic lithiation and delithiation sequences at different states of charge. These results are discussed within the context of continuum thermodynamic theories of the coupling between transport of chemical species and mechanical stress.[1] A. F. Bower, E. Chason, P. R. Guduru, B. W. Sheldon, Acta Mater. 98 (2015) 229-241.[2] A. F. Bower, P. R. Guduru, E. Chason, Int. J. Solids Struct. 69 (2015) 328-342.[3] V. A. Sethuraman, V. Srinivasan, A. F. Bower, P. R. Guduru, J. Electrochem. Soc. 157 (2010) A1253.

Efficiency improvement in thin-film amorphous silicon solar cells based on PbS quantum dots

Efficiency improvement in thin-film amorphous silicon solar cells based on PbS quantum dots

Lifetime Optimization of Amorphous Silicon Thin-Film Anodes for Lithium-Ion Batteries

Lifetime Optimization of Amorphous Silicon Thin-Film Anodes for Lithium-Ion Batteries

Perpendicular magnetic anisotropy at room-temperature in sputtered a-Si/Ni/a-Si layered structure with thick Ni (nickel) layers

In the literature, a magnetic “easy” axis perpendicular to the film plane at room temperature (i.e., perpendicular magnetic anisotropy - PMA) has been reported in Ni (nickel) layers with thicknesses below ≈15 nm. In this work, we observed room-temperature PMA in a-Si/Ni/a-Si (where a-Si denotes amorphous silicon) thin film structures with nickel layer thicker than 15 nm. Two layered structures were prepared by DC/RF triode sputtering: [a-Si/Ni/a-Si] sandwich structure and [a-Si/Ni/a-Si]5 multilayer structure. The cross sectional STEM revealed uniform Ni layers with thicknesses of ≈17 nm in [a-Si/Ni/a-Si]5 – multilayer and ≈28 nm in [a-Si/Ni/a-Si] – single-layer whereas amorphous Si layers were ≈15 nm and 170 nm thick, respectively. An amorphous Ni–Si interphase was also observed in the layered structures. The XRD showed patterns for fcc-Ni with dominant (111) orientation. No other crystalline phases were observed in the XRD patterns. To our knowledge, there are no literature reports of easy magnetization direction perpendicular to the film plane at room temperature for Ni layers with thickness of ≈28 nm as presented in this work. The origin of PMA in a-Si/Ni/a-Si films may be mainly attributed to the magnetoelastic anisotropy whereas the secondary source of PMA is believed to be the surface anisotropy and magnetocrystalline anisotropy of [111] columnar grains. Amorphous silicon layers (substrate) do not have a well-defined lattice structure like crystalline substrates. Therefore, they do not induce strains in the nickel layers through lattice mismatch as in the case of epitaxy. The strains can be caused by other factors such as diffusion-induced strain, thermal expansion mismatch or intrinsic stresses during the growth process. These results could be important for applications in memory devices, sensors, logic chips, magneto-optic, magneto-electronic and spintronic devices and in fundamental research, as well as first step toward preparation and understanding of the PMA in thick nickel layers.