Ultrathin Silicon Research Articles

Thickness-Dependence of Surface Reconstruction on the (001) Surface of Ultrathin Silicon Nanosheets by Density Functional Tight Binding Simulations

The influences of the thickness of ultrathin Si nanosheets on the (001) surface morphologies and charge distribution were identified by using density functional tight binding (DFTB) simulations. The differences in structure and electronic properties were elucidated on the basis of bond lengths, bond angle distribution, and arrangement patterns in (001) surface atoms of Si nanosheets with their thickness decreasing from 1.5 nm to 0.4 nm. The surface atoms in some nanosheets present perfect zig-zag patterns in their dimers. The amounts of the trimers are far less than those of the dimers in the surface. The formation of the dimers lowers the surface energy of the nanosheets. Analysis of Mülliken gross populations indicates that there is the charge transfer from the inner part of the nanosheet to the surface. The moving distance and direction of the surface atoms can affect the charge distribution.

η-fiber microstructure and texture evolutions in ultra-thin silicon steel

0.08mm ultra-thin silicon steel is prepared with 0.30mm commercial grain-oriented silicon steel as raw material, and the evolutions of η-fiber microstructure and texture are investigated with emphasis. During rolling deformation, initial Goss orientation shows crystal rotation to {111 }<112> orientation. With the increase of rolling reduction, the retention of Goss orientation is reduced and more observed near the sheet surface. For initial deviated Goss oriented grains, {111}<112> and η-fiber oriented areas are also observed in 0.08mm rolled sheet, while the accuracy and concentration of these two components are decreased. During annealing, η-fiber nucleation superiority in γ-fiber deformed regions is significant, and thus contributes to strong η-fiber recrystallization texture. When the rolled sheets are heated at 800 °C for 15 min, strong η-fiber recrystallization texture and uniform microstructure is beneficial for the magnetic properties of ultrathin silicon steel sheets.

Photocurrent improvement of an ultra-thin silicon solar cell using cascaded cylindrical shape plasmonic nanoparticles

The main aim of this research work is to significantly improve the photocurrent of an ultra-thin silicon solar cell. Here, cylindrical shape cascaded plasmonic nanoparticles are used to design an ultra-thin silicon solar cell. The main idea is to manipulate the absorption spectra of a thin absorber by applying four cascaded cylindrical shape nanoparticles from different materials with different radii and heights. At first, a cell with one nanoparticle at the surface and another one with a nanoparticle at the bottom side are simulated, and their photocurrents are determined. Then, a cell with four cascaded Ag, Al, Ag-Al, and Al-Ag nanoparticles is simulated. The maximum photocurrent density and efficiency of 23.46 mA cm−2 and 13.95%, respectively, are obtained for a cell in which Ag and Al’s nanoparticles are used alternatively from top to bottom. The photocurrent density is 8.2 mA cm−2 for a cell without any nanoparticles. The simulated results show that cascaded nanoparticles significantly enhance the photocurrent. Finally, the generation rate is presented at different wavelengths.

Twinning Behavior in Cold-Rolling Ultra-Thin Grain-Oriented Silicon Steel

Twinning behaviors in grains during cold rolling have been systematically studied in preparing ultra-thin grain-oriented silicon steel (UTGO) using a commercial glassless grain-oriented silicon steel as raw material. It is found that the twinning system with the maximum Schmid factor and shear mechanical work would be activated. The area fraction of twins increased with the cold rolling reduction. The orientations of twins mainly appeared to be α-fiber (&lt;110&gt;//RD), most of which were {001}&lt;110&gt; orientation. Analysis via combining deformation orientation simulation and twinning orientation calculation suggested that {001}&lt;110&gt; oriented twinning occurred at 40–50% rolling reduction. The simulation also confirmed more {100} &lt;011&gt; oriented twins would be produced in the cold rolling process and their orientation also showed less deviation from ideal {001}&lt;110&gt; orientation when a raw material with a higher content of exact Goss oriented grains was used.

Tunnel nitride passivated contacts for silicon solar cells formed by catalytic CVD

An ultra-thin silicon nitride (SiN x ) layer formed by catalytic chemical vapor deposition (Cat-CVD) is used to replace the Si dioxide (SiO2) layer of a tunnel oxide passivated contact solar cell. The passivation quality of crystalline Si (c-Si) with a stack of the ultra-thin SiN x and n-type hydrogenated amorphous Si (a-Si:H) or microcrystalline Si (μc-Si:H), also formed by Cat-CVD, is significantly improved by annealing at 850 °C, probably due to the formation of a back surface field layer. Cat-CVD SiN x with thicknesses of up to 2.5 nm can have sufficient tunneling conduction. The ultra-thin SiN x having functions of surface passivation and carrier tunneling, and the unification of the formation method for the tunnel SiN x and conductive layers will lead to the realization of tunnel nitride passivated contact solar cells.

Electronic energy loss and straggling in low energy H+ and H2 + interaction with silicon films

ABSTRACT The appearance of atomic structures of nanoscopic dimensions, with new and interesting physical properties, requires revisiting various aspects of particle interaction with solid matter. For this purpose in this work we present a study of electronic energy loss of H+ and protons (fragments) from the dissociation of H2 + ions interacting with ultra-thin amorphous silicon films for incident beam energies from 1 to 10 keV/u. We report measurements of energy distributions of transmitted protons and molecular fragments through these films, from which we derive the average energy losses and the energy loss straggling. Our experimental findings turn out to be in good agreement with nonlinear electronic stopping power models and some previous experimental data.

Enhanced light absorption of ultrathin crystalline silicon solar cells via the design of front nanostructured silicon nitride

Enhanced light absorption of ultrathin crystalline silicon solar cells via the design of front nanostructured silicon nitride

Electrical Unfolding of Cytochrome C During Translocation through a Nanopore Constriction

Many small proteins move across cellular compartments through narrow pores. In order to thread a protein through a constriction, free energy must be overcome to either deform or completely unfold the protein. In principle, the diameter of the pore, along with the effective driving force of transport, should be critical factors that govern whether protein translocation proceeds via squeezing, unfolding/threading, or both. To directly probe this, we studied the electric-field-driven translocation behavior of cytochrome c (cyt c) through ultrathin silicon nitride (SiNx) solid-state nanopores of diameters ranging from 1.5 to 5.5 nm. For a 2.5 nm diameter pore we find that in a threshold electric field regime of ∼30-100 MV/m cyt c is able to squeeze into the pore. Further, as electric fields inside the pore further increase the unfolded state of cyt c is stabilized, facilitating translocation. In contrast, for 1.5 nm and 2 nm diameter pores, translocation occurs only by threading of the fully unfolded protein after it transitions through a higher energy unfolding intermediate state at the mouth of the pore. The transition energies between the metastable, intermediate, and unfolded protein states are extracted by exploiting differences in the state-dependent electric dipole interactions with the applied electric field. These experiments also map the various modes of protein translocation through a constriction, which opens new avenues for exploring protein folding structures, internal contacts, and electric field-induced deformability.

Ultrathin Silicon Oxide Overlayers Enable Selective Oxygen Evolution from Acidic and Unbuffered pH-Neutral Seawater

Seawater electrolysis is an attractive approach for producing clean hydrogen fuel in scenarios where freshwater is scarce and renewable electricity is abundant. However, chloride ions (Cl-) in seawater can accelerate electrode corrosion and participate in the undesirable chlorine evolution reaction (CER). This problem is especially acute in acidic conditions that naturally arise at the anode as a result of the desired oxygen evolution reaction (OER). Herein, we demonstrate that ultrathin silicon oxide (SiOx) overlayers on model platinum anodes are highly effective at suppressing the CER in the presence of 0.6 M Cl- in both acidic and unbuffered pH-neutral electrolytes by blocking the transport of Cl- to the catalytically active buried interface while allowing the desired oxygen evolution reaction (OER) to occur there. The permeability of Cl- in SiOx overlayers is 3 orders of magnitude less than that of Cl- in a conventional salt-selective membrane used in reverse osmosis desalination. The overlayers also exhibit robust stability over 12 h in chronoamperometry tests at moderate overpotentials. SiOx overlayers demonstrate a promising step toward achieving selective and stable seawater electrolysis without the need to adjust the pH of the electrolyte.

Status and prospective of high-efficiency c-Si solar cells based on tunneling oxide passivation contacts

Current photovoltaic market is dominated by crystalline silicon (c-Si) solar modules and this status will last for next decades. Among all high-efficiency c-Si solar cells, the tunnel oxide passivated contact (TOPCon) solar cell has attracted much attention due to its excellent passivation and compatibility with the traditional c-Si solar cells. The so-called tunnel oxide passivated contact (TOPCon) consists of an ultra-thin silicon oxide layer less than 2 nm in thickness and a heavily doped poly-Si layer, which is used for implementing effective passivation and selective collection of carriers. This TOPCon solar cell has some advantages including no laser contact opening, no light-induced degradation and no elevated temperature-induced degradation because of N-type c-Si wafer, compatibility with high temperature sintering and technical scalability. This paper first introduces the basic structure and principles of TOPCon solar cells, then compares the existing methods of preparing ultra-thin silicon oxide layer and heavily doped poly-Si layer, and finally points out the future research direction of this cell based on the analysis of the current research status.

Constructive and destructive interference of Kerker-type scattering in an ultrathin silicon Huygens metasurface

High refractive index dielectric nanoparticles have provided a new platform for exotic light manipulation through the interference of multipole modes. The Kerker effect is one example of a Huygens source design. Rather than exploiting interference between the electric dipole and magnetic dipole, as in many conventional Huygens source designs, we explore Kerker-type suppressed backward scattering mediated by the dominant electric dipole, toroidal dipole and magnetic quadrupole. These modes are provided by a designed and fabricated CMOS compatible ultra-thin Silicon nanodisk metasurface with a suppressed magnetic dipole contribution, and verified through multipole decomposition. The non-trivial substrate effect is considered using a semi-analytical transfer matrix model. The model successfully predicts the observed reflection dip. By applying a general criterion for constructive and destructive interference, it is shown that while constructive interference occurs between the electric and toroidal dipole contributions, the experimentally observed suppressed backward Kerker-type scattering arises from the destructive interference between backward scattered contributions due to the total electric dipole and the magnetic quadrupole. Our study paves the way towards new types of Huygens sources or metasurface design, such as for peculiar transverse Kerker scattering.

High-performing silicon-based germanium Schottky photodetector with ITO transparent electrode* *Project supported by the National Key Research and Development Program of China (Grant No. 2018YFB2200103), the National Natural Science Foundation of China (Grant No. 61474094), and Principal Fund of Minnan Normal University (Grant No. KJ2020006).

A near-infrared germanium (Ge) Schottky photodetector (PD) with an ultrathin silicon (Si) barrier enhancement layer between the indium-doped tin oxide (ITO) electrode and Ge epilayer on Si or silicon-on-insulator (SOI) is proposed and fabricated. The well-behaved ITO/Si cap/Ge Schottky junctions without intentional doping process for the Ge epilayer are formed on the Si and SOI substrates. The Si- and SOI-based ITO/Si cap/Ge Schottky PDs exhibit low dark current densities of 33 mA/cm2 and 44 mA/cm2, respectively. Benefited from the high transmissivity of ITO electrode and the reflectivity of SOI substrate, an optical responsivity of 0.19 A/W at 1550 nm wavelength is obtained for the SOI-based ITO/Si cap/Ge Schottky PD. These complementary metal–oxide–semiconductor (CMOS) compatible Si (or SOI)-based ITO/Si cap/Ge Schottky PDs are quite useful for detecting near-infrared wavelengths with high efficiency.

Transfer of an ultrathin single-crystal silicon film from a silicon-on-insulator to a polymer

This study reports the manufacturing of silicon-on-polymer (SOP). It describes the transfer of a 200 mm diameter silicon thin film from a silicon-on-insulator (SOI) substrate to a flexible polymer. The thickness of the single-crystal silicon film was less than 200 nm, and the transfer was achieved by bonding the SOI wafer to a temporary silicon carrier with an adhesive polymer. Various parameters of the transfer were investigated: adherence of the stack, temperature of bonding, temporary carrier, and Si film thickness. The substrate and the SOI buried oxide were removed by mechanical grinding and chemical etching. The Si thin film was held on a flexible tape, and the temporary carrier was dismounted. SOPs consisting of 20–205-nm thin Si films on a flexible polymer (230 μm) were successfully obtained. Full wafers or patterned wafers of 200-mm diameter could be transferred.

Fabrication of spectrally sharp Si-based dielectric resonators: combining etaloning with Mie resonances.

We use low-resolution optical lithography joined with solid state dewetting of crystalline, ultra-thin silicon on insulator (c-UT-SOI) to form monocrystalline, atomically smooth, silicon-based Mie resonators in well-controlled large periodic arrays. The dewetted islands have a typical size in the 100 nm range, about one order of magnitude smaller than the etching resolution. Exploiting a 2 µm thick SiO2 layer separating the islands and the underlying bulk silicon wafer, we combine the resonant modes of the antennas with the etalon effect. This approach sets the resonance spectral position and improves the structural colorization and the contrast between scattering maxima and minima of individual resonant antennas. Our results demonstrate that templated dewetting enables the formation of defect-free, faceted islands that are much smaller than the nominal etching resolution and that an appropriate engineering of the substrate improves their scattering properties. These results are relevant to applications in spectral filtering, structural color and beam steering with all-dielectric photonic devices.

Investigation of polymer-derived Si\u2013(B)\u2013C\u2013N ceramic/reduced graphene oxide composite systems as active catalysts towards the hydrogen evolution reaction

Hydrogen Evolution Reaction (HER) is an attractive technology for chemical conversion of energy. Replacement of platinum with inexpensive and stable electrocatalysts remains a major bottleneck hampering large-scale hydrogen production by using clean and renewable energy sources. Here, we report electrocatalytically active and ultra-stable Polymer-Derived Ceramics towards HER. We successfully prepared ultrathin silicon and carbon (Si–C) based ceramic systems supported on electrically conducting 2D reduced graphene oxide (rGO) nanosheets with promising HER activity by varying the nature and the composition of the ceramic with the inclusion of nitrogen, boron and oxygen. Our results suggest that oxygen-enriched Si-B-C-N/rGO composites (O-SiBCN/rGO) display the strongest catalytic activity leading to an onset potential and a Tafel slope of − 340 mV and ~ 120 mV dec−1 respectively. O-SiBCN/rGO electrodes display stability over 170 h with minimal increase of 14% of the overpotential compared to ~ 1700% for commercial platinum nanoparticles. Our study provides new insights on the performance of ceramics as affordable and robust HER catalysts calling for further exploration of the electrocatalytic activity of such unconventional materials.

Multi-Objective Optimization of Wire-Electric Discharge Machined Ultrathin Silicon Wafers Using Response Surface Methodology for Solar Cell Applications

Abstract Recent investigations on the fabrication of ultrathin silicon (Si) wafers using wire-electric discharge machining (wire-EDM) were observed to possess some inherent limitations. These include thermal damage (TD), kerf-loss (KL), and low slicing rate (SR), which constraints its industrial use. The extent of TD, KL, and SR largely depends on the process parameters such as open voltage (OV), servovoltage (SV), and pulse on-time (Ton). Therefore, optimizing the parameters that pertain to minimum TD and KL while maintaining a higher SR is the key to improvement in the fabrication of Si wafers using wire-EDM. Thus, this study is an effort to analyze and identify the optimal parameters that relate to the most effective Si slicing in wire-EDM. A central composite design (CCD)-based response surface methodology (RSM) was used for optimizing the process parameters. The capability to slice Si wafers in wire-EDM was observed to be influenced by the discharge energy, which significantly impacted the overall responses. The severities of TDs were observed to be mainly dominated by the variation in OV and Ton due to the diffusion of thermal energy into the workpiece, leading to melting and subsequent resolidification. For high productivity, the optimized parameters resulted in a SR of 0.72 mm/min, TD of 17.44 μm, and a kerf-loss of about 280 μm.

Evolution of {0kl} 〈1 0 0〉 texture and microstructure in preparation of ultra-thin grain-oriented silicon steel

In this paper, an ultra-thin grain-oriented silicon steel (UTGO steel) strip was prepared via rolling a commercial glassless grain-oriented silicon steel plate to 0.075 mm and then annealing it at 850 °C for less than 30 min in a protective atmosphere. The resultant UTGO steel strip has magnetic induction B800 higher than 1.80 T and iron loss P1.5/400 lower than 12.0 W/kg. These superior magnetic properties are due to predominant {0kl} 〈1 0 0〉 texture and appropriate microstructure. The study shows that preferential {0kl} 〈1 0 0〉 nucleation occurs either inside shear bands or at in-grain deformation-induced boundaries. The nucleation behavior varies at different nucleation sites. Nuclei inside shear bands are denser and show preferential transitional orientation along {0kl} 〈1 0 0〉, while new grains dispersed at in-grain split boundaries have shown orientations which are suggested to inherit corresponding initial grain orientation prior to rolling. Nucleation behavior is also highly dependent on the orientation of the roll-deformed matrix. Our study finds that shear banding nucleation of {0kl} 〈1 0 0〉 (including Goss and {0 2 1} 〈1 0 0〉) is reduced when the orientation of the deformed matrix deviates from {1 1 1} 〈1 1 2〉. With the extension of annealing time, the growth of {0kl} 〈1 0 0〉 nuclei in cluster is restricted because of orientation pinning effect, whereas the growth of grains with orientations other than {0kl} 〈1 0 0〉 is promoted. This phenomenon weakens the dominance of {0kl} 〈1 0 0〉 texture, causing deterioration in magnetic properties of the final silicon steel.

Mobility Modeling in Advanced MOSFETs with Ultra-Thin Silicon Body under Stress

We use a two-band k·p model to describe the subband structure in strained silicon thin films. The model provides the dependence of the conductivity effective mass on strain and film thickness. The conductivity mass decreases along tensile stress in [110] direction applied to a (001) film. This conductivity mass decrease ensures the mobility enhancement in MOSFETs even with extremely thin silicon films. The two-band k·p model also describes the dependence of the non-parabolicity parameter on film thickness and strain. The influence of the subband structure modification on the mobility in advanced MOSFETs with strained ultra-thin silicon body is investigated. It is shown that an increase of subband non-parabolicity in thin films with strain reduces the mobility enhancement due to the conductivity mass modification, especially at higher strain values.

Ultrathin Silicon Nanolayer Implanted NixSi/Ni Nanoparticles as Superlong‐Cycle Lithium‐Ion Anode Material

It has been claimed that the mechanical properties of electrodes in lithium‐ion batteries have a huge impact on their electrochemical performance. This is especially critical for Si‐based electrodes, which suffer from pulverization and formation of an unstable solid–electrolyte interphase during cycling. Herein, thin silicon‐coated nickel silicide nanoparticles grown on a nickel inner core support (designated as Si@NixSi/Ni) as anode material for a Li‐ion battery are reported. The ultrathin nano silicon layer contributes to achieve reasonably high energy density and allows fast Li‐ion diffusion due to its high specific capacity and shortened Li‐ion diffusion length. While the gradiently distributed NixSi layer enables the attainment of superior cycling stability and further enhances the specific capacity, the Ni inner core provides mechanical support to maintain the structural integrity of the nanoparticles during the extended lithiation/delithiation process. The Si@NixSi/Ni core–shell electrode exhibits a charge‐specific capacity of 706.1 mAh g−1 at a current density of 500 mA g−1. This structure also shows a high first‐cycle Coulombic efficiency of 81.5%. Interestingly, the Si@NixSi/Ni core–shell electrode demonstrates a cycle life of over 5000 cycles with capacity retention of 74% at a current density of 500 mA g−1.

Investigation of Side Wall Roughness Effect on Optical Losses in a Multimode Si3N4 Waveguide Formed on a Quartz Substrate

This article presents the results of the study of the influence of the most significant parameters of the side wall roughness of an ultra-thin silicon nitride lightguide layer of multimode integrated optical waveguides with widths of 3 and 8 microns. The choice of the waveguide width was made due to the need to provide multimode operation for telecommunication wavelengths, which is necessary to ensure high integration density. Scattering in waveguide structures was measured by optical frequency domain reflectometry (OFDR) of a backscattering reflectometer. The finite difference time domain method (FDTD) was used to study the effect of roughness parameters on optical losses in fabricated waveguides, the roughness parameters that most strongly affect optical scattering were determined, and methods of its significant reduction were specified. The prospects for implementing such structures on a quartz substrate are justified.