Silicon Nano Research Articles

Estimation of Optical Properties of Multilayer Silicon Nano Films with Different Hydrogen Dilution

Silicon multilayer thin films with stack of amorphous silicon (a-Si:H) and nanocrystalline silicon (nc-Si:H) of varied hydrogen dilution were prepared by hot wire chemical vapor deposition (HWCVD). The optical properties of the thin films were measured by UV-visible spectroscopy. The smooth transmittance spectra measured in the range of 500-1100nm show films with uniform deposition. The optical constants such as refractive index, absorption coefficient, tauc band gap, extinction coefficient together with thickness were determined using envelope method. It is found that the optical band gap decreases from 1.78eV to 1.6eV as hydrogen dilution increases.

Valley blockade and multielectron spin-valley Kondo effect in silicon

We report on the valley blockade and the multielectron Kondo effect generated by an impurity atom in a silicon nano field effect device. According to the spin-valley nature of tunnelling processes, and consistently with those allowed by the valley blockade regime, the manifestation of Kondo effect obeys to the periodicity 4 of the electron filling sequence typical of silicon emerging at occupation N=1, 2, 3. The spin-valley Kondo effect emerges under different kinds of screening depending on the electron filling. By exploiting the valley blockade regime, valley index conservation in the Kondo SU(4) is deduced without the employment of an external magnetic field. Microwave irradiation suppresses the Kondo effect at occupancies up to three electrons.

Switchable resonant hyperpolarization transfer toSi29spins in natural silicon

Silicon nano- and microparticles containing polarized $^{29}\mathrm{Si}$ spins are promising inexpensive and biocompatible medical imaging agents, particularly for magnetic resonance imaging (MRI). Maximizing out-of-equilibrium polarization (i.e., hyperpolarization) of the $^{29}\mathrm{Si}$ nuclear spins as efficiently as possible is critical for such an application. Here we identify and exploit a frequency-matched resonant transfer process between easily hyperpolarized bulk $^{31}\mathrm{P}$ and otherwise insensitive $^{29}\mathrm{Si}$ nuclear spins in natural silicon, boosting the $^{29}\mathrm{Si}$ signal to over 200 times its thermal equilibrium signal. This technique could be used in tandem with microwave-based hyperpolarization schemes for even higher efficiencies. Lastly, this hyperpolarization buildup process does not necessarily introduce an additional source of decoherence; after hyperpolarization the resonant transfer process can be switched off to recover the ultralong lifetimes of $^{29}\mathrm{Si}$ spins for in vivo imaging.

High Capacity Silicon Electrodes with Nafion As Binders

Silicon is capable of delivering a high theoretical specific capacity of 3600 mAh/g which is much higher than that of the state-of-the-art graphite based negative electrodes for lithium ion batteries. However, the poor cycle life of silicon electrodes, caused by the large volumetric strain during cycling, limits the commercialization of silicon electrodes. As one of the essential components, the polymeric binder is critical to the performance and durability of lithium ion batteries as it keeps the integrity of electrodes. The binder must be stable as it interacts with the active material and the electrolyte during the life of the battery. In this work, we demonstrate that electrodes consisting of silicon nano particles mixed with commercially available and ion-exchanged Nafion can deliver a high capacity over 2000 mAh/g for 50 cycles. For comparison, the capacity of electrodes made of the same Si nanoparticles mixed with traditional polyvinylidene fluoride (PVDF) faded rapidly. The mechanisms responsible for Nafion’s superior performance as a binder, such as ionic conductivity and stability of the resulting solid-electrolyte interphase, will be reported.

The role of operations after the deposition on the performance of SiOx films in optoelectronics devices

In this study, we have investigated phase separation, silicon Nano crystal (Si-NC) formation and optoelectronics properties of Si oxide (SiOx, 0.7<x<1.3) films in high-vacuum annealing and ion bombardment conditions. The SiOx films were deposited by physical vapor deposition (PVD). The internal structure properties of these films were the main factor in applications of optoelectronic. Possible changes in the structure, composition and electro physical properties were investigated by FTIR and TEM spectroscopy. The measurements show that SiOx film is the dominant phase in the ultra-thin layer. Also, high-temperature annealing ion bombardment results in further increase of the phase separation of the whole layer.

Modeling of dual-metal Schottky contacts based silicon micro and nano wire solar cells

We study solar cell properties of single silicon wires connected at their ends to two dissimilar metals of different work functions. Effects of wire dimensions, the work functions of the metals, and minority carrier lifetimes on short circuit current as well as open circuit voltage are studied. The most efficient photovoltaic behavior is found to occur when one metal makes a Schottky contact with the wire, and the other makes an Ohmic contact. As wire length increases, both short circuit current and open circuit voltage increase before saturation occurs. Depending on the work function difference between the metals and the wire dimensions, the saturation length increases by approximately an order of magnitude with a two order magnitude increase in minority carrier length. However current per surface area exposed to light is found to decrease rapidly with increase in length. The use of a multi-contact interdigitated design for long wires is investigated to increase the photovoltaic response of the devices.

Harvesting High Loading Electrode with Nanosized Particles for Rechargeable Lithium Batteries

Contributed by significantly improved solid/liquid interface and kinetics of Li+ diffusion, nanostructured electrode materials offer wide and promising applications in Li-ion and rechargeable lithium batteries, especially for the high power demand.[1] For example, by embedding electronic insulating sulfur into the nanostructured carbon frameworks, the obtained sulfur/carbon composites deliver high capacity and greatly improved cycling stability as cathode.[2, 3] Similarly, silicon exhibits outstanding properties as promising anode for Li-ion batteries after reduced to nanosize or combined with carbon by forming Si/C composites.[4] Despite these superiorities of nanosized novel structures, materials in nano-scale still face the challenge with respect to the practical applications in batteries. Besides side reactions initiating on the high surface electrode, it is difficult to achieve high loading electrode with nanosized active materials through slurry coating technique due to the generation of sever cracking or pinholes during the drying process. One of the reasons behind this phenomenon is the large volume shrink of nanosized materials accompanying the solvent removing from slurry. These downsides have plagued the practical application of nano-sized materials in energy storage systems. Attempts have been made to address these issues by increasing the particle size through spray drying, introducing conductive polymer or other self-assemble approaches, which are either complicated with special equipment or not cost-effective for large scale applications. We herein propose a facile and up-scale available approach to coat nano particles into electrodes with practically usable thickness and active mass loadings. Successful demonstration of this approach was shown in sulfur and silicon nano particles. High loading but crack-free coating for sulfur (loading: 2-8 mg sulfur/cm2) and Si (loading: 2-4 mg Si/ cm2) electrodes have been displayed. In addition, we did detailed screen for the binder selection and slurry composition modification. Base on the obtained high loading electrodes, systematical study was performed on the relationships of electrode loading, pressure, energy density and rate capability. All these obtained results will be presented at the meeting.

Correction: Corrigendum: Quantum Limit of Quality Factor in Silicon Micro and Nano Mechanical Resonators

Micromechanical resonators are promising replacements for quartz crystals for timing and frequency references owing to potential for compactness, integrability with CMOS fabrication processes, low cost, and low power consumption. To be used in high performance reference application, resonators should obtain a high quality factor. The limit of the quality factor achieved by a resonator is set by the material properties, geometry and operating condition. Some recent resonators properly designed for exploiting bulk-acoustic resonance have been demonstrated to operate close to the quantum mechanical limit for the quality factor and frequency product (Q-f). Here, we describe the physics that gives rise to the quantum limit to the Q-f product, explain design strategies for minimizing other dissipation sources, and present new results from several different resonators that approach the limit.

Magnesium Vapor Reduction of Structured Silica for Lithium Ion Battery Applications

ABSTRACTThree types of silica materials with different morphology, specifically SiO2 hollow microspheres, mesoporous silica, and silica aerogel were tested as potential precursors for synthesis of silicon nano- and meso-structures that resemble the original morphology of the precursors. In the optimized magnesium thermal reduction process, magnesium vapor was delivered to silica surface through a stainless steel mesh placed on top of a zirconia boat filled with silica precursor. This approach allowed for better control of silicon nanostructure formation by minimizing reaction by-products that can affect performance of lithium ion battery anode. Material morphological properties of the reduced silica precursors are discussed in terms of X-ray diffraction, BET, BJH pore size distribution, Raman spectroscopy, and TGA.

Quantum Limit of Quality Factor in Silicon Micro and Nano Mechanical Resonators

Micromechanical resonators are promising replacements for quartz crystals for timing and frequency references owing to potential for compactness, integrability with CMOS fabrication processes, low cost, and low power consumption. To be used in high performance reference application, resonators should obtain a high quality factor. The limit of the quality factor achieved by a resonator is set by the material properties, geometry and operating condition. Some recent resonators properly designed for exploiting bulk-acoustic resonance have been demonstrated to operate close to the quantum mechanical limit for the quality factor and frequency product (Q-f). Here, we describe the physics that gives rise to the quantum limit to the Q-f product, explain design strategies for minimizing other dissipation sources, and present new results from several different resonators that approach the limit.

The Fabrication of Silicon Nanopin with CsCl Nanoislands and Dry Etching for Field Emission

Silicon nano pin arrays with heights of 1.3-3.66um and diameter of 315-899nm, are fabricated by CsCl self-assemble for CsCl nano islands for mask and ICP etching for silicon pins. CsCl film is firstly deposited on the wafer by thermal evaporation and putted in the humid controlled environment to be developed to the CsCl islands with diameter of 341-915 nm as self-assembled technology. Then the ICP etching with SF6, CCl4, He gas is introduced to make the silicon nano pin by the mask of CsCl nano islands, and the silicon nano pins with the different height of 1.3-3.66 um are finished for field emission. The gated FEA templates are fabricated by photolithography process and the lift-off technology with Ti-Si film as the gate electrodes. The final template for field emission has the silicon nano pins with diameters of 31.7 nm on top, Ti-Ag film with thickness of 105nm and gate holes of 30um in diameter, and SU8 resist insulator structure with thickness of 4um and holes of 10um in diameter. The optimization of the fabrication process and the performance for the configuration will be made.

Electrical transport in ensembles of semiconductor quantum dots

The novelty of nano physics is associated with the basic changes that take place in systems that consist of particles when their size is reduced to the nano scale. While the corresponding changes in the individual particles are relatively well understood the understanding of the effect of these changes on the properties of ensembles of such particles is still at a rudimentary level. This is in particular so for the electrical transport in such systems. In this paper we will try to evaluate the effect of the changes in the density and properties of the individual particles on the corresponding global electrical transport in the ensembles. This evaluation is based on our experimental results and their analyses as obtained on ensembles of silicon nano crystallites that are embedded in an insulating matrix.

Электролитическое получение нановолокон кремния из расплава KCl-KF-K2SiF6-SiO2 для композиционных анодов литий-ионных аккумуляторов

Silicon nano- and microwires have been obtained by KCl-KF-K2SiF6-SiO2 melt electrolysis in air; this material is suitable as anode component for lithium ion batteries. Optimal conditions of electrolysis were determined. Morphology, phase and chemical composition of silicon deposits were established. Electrochemical behavior of silicon nanowires as anode component was evaluated using solid polymer electrolyte cells.

Electrical Contacts to Vertically Oriented Silicon Nano and Microdevices for Applications in Flexible Systems

ABSTRACTFlexible devices utilizing crystalline semiconductor nano or microstructures materials are attractive for many applications. However, these materials are fabricated or grown in unusable forms for flexible systems due to their rigid crystalline mother substrates. We demonstrate a transfer printing technique for transferring vertical arrays of one-dimensional (1D) materials from mother substrates to flexible substrates with subsequent device fabrication steps to create flexible devices from these arrays. The transfer printing technique is based on vertical embossing of arrays of 1D materials into thermoplastic (Poly (methyl methacrylate) (PMMA)) transfer layers, while the device fabrication steps rely on encapsulation with insulating polymers and contact deposition. We investigated the use of flexible insulating layers like polydimethylsiloxane (PDMS) and polyurethane (PU) which are shown to be effective for encapsulation and contact isolation. Representative flexible resistive devices were created from these transferred arrays and insulating layers which showed a reversible tactile characteristic. Electronic characterization and flexibility testing was carried out to show the potential of these methods for enabling large-scale integrations of nano and microstructures into vertical and flexible packages.

J211016 FIB加工シリコンナノワイヤの機械特性に及ぼす超高真空アニールの影響([J211-01]"壊れない"マイクロシステムのためのナノ力学・ナノ計測(1))

J211016 FIB加工シリコンナノワイヤの機械特性に及ぼす超高真空アニールの影響([J211-01]"壊れない"マイクロシステムのためのナノ力学・ナノ計測(1))

A Study of Nano Materials and Their Reactions in Liquid Using in situ Wet Cell TEM Technology

AbstractSeveral nano material and reaction systems were in situ monitored with an electrochemical TEM wet cell set up. In a 1 g/L sliver particle aqueous solution, the particles were observed to be ca. 10 nm sized, in both discrete particle and nano cluster forms. The silver particles were attached to the 50 nm‐thick Si3N4 windows of the wet cell and could not move freely in the liquid. With a SiCl4 liquid loaded in the wet cell, silicon nano materials were controllably grown on the wet cell windows by means of a liquid phase electron beam induced deposition (EBID) method. The deposited nano dots were nicely round‐shaped, and demonstrated a power law growth dependency on beam exposure time in a log‐log plot. In a NiCl2 solution/Ni system, both electrochemical deposition and dissolution of the nickel nano films were observed while applying electric biases on to the nickel electrodes in the wet cell. Instead of extensional growth on existing crystals, interestingly, it is more commonly observed that new nickel nano particles grow out in front of the existing film first and then merged into the film. The wet cell set up is demonstrated to be a versatile tool for nano liquid system research.

Synthesis and characterization of nano silicon and titanium nitride powders using atmospheric microwave plasma technique

We have demonstrated a simple, scalable and inexpensive method based on microwave plasma for synthesizing 5 to 10 g/h of nanomaterials. Luminescent nano silicon particles were synthesized by homogenous nucleation of silicon vapour produced by the radial injection of silicon tetrachloride vapour and nano titanium nitride was synthesized by using liquid titanium tetrachloride as the precursor. The synthesized nano silicon and titanium nitride powders were characterized by XRD, XPS, TEM, SEM and BET. The characterization techniques indicated that the synthesized powders were indeed crystalline nanomaterials. A simple, scalable and inexpensive method based on microwave plasma was developed for synthesizing 5 to 10 g/h of silicon and titanium nitride nanopowders. Silicon was synthesized by homogenous nucleation of silicon vapour while titanium nitride was synthesized by using liquid titanium tetrachloride as the precursor.

Nanowire solar cells using hydrogenated amorphous silicon: A modeling study

AbstractAn interesting example of device combining amorphous material and nano‐ or microstructure is the wire solar cell. Solar cells based on silicon nano‐ or microwires have attracted much attention as a promising path for low cost photovoltaic technology. The key point of this structure is the decoupling of the light absorption from the carriers collection. In this work, we use numerical modeling to study two types of radial junction structures: (i) a p–n heterojunction for which p‐or n‐type crystalline silicon (c‐Si) wires are covered by a conformal n‐ or p‐ doped amorphous silicon (a‐Si:H) thin layer and (ii) thin film a‐Si:H p–i–n radial structures realized by conformal covering on thinner c‐Si wires. In the first structure, the a‐Si:H layer is only intended to form the heterojunction and light absorption takes place in the c‐Si wires, whereas in the second one, the absorber material is the a‐Si:H i‐layer and its thickness can be optimized to facilitate the carrier separation and collection. The potential of those both types of Si wires based solar cells will be compared according to the structure design and material properties. Furthermore, the sensitivity of the a‐Si:H p–i–n radial cells to the light‐soaking effect, i.e., the increase of deep defect density resulting from the breaking of weak silicon bonds, will be studied and compared to what is commonly observed on classical a‐Si:H planar p–i–n cells.

Ebeam fabrication of silicon nanodome photovoltaic devices without metal catalyst contamination

In this paper, the fabrication of silicon nanodome solar cells on crystalline wafers is reported. Crystalline silicon was patterned by ebeam lithography to define the silicon nano pillars with diameter of 100nm, 1μm and 5μm. Unlike conventional bottom up growth of silicon nanowire from gold (Au), our method is free from contaminant. Consequently, it is a valuable method to fully evaluate the effect of nanostructures on solar cell performances. The fabricated devices were characterized through scanning electron microscopy, absorption measurements, illuminated solar cell I–V characteristics and monochromatic incident photon-to-electron conversion efficiency.

The Impact of Structural Parameters on the Electrical Characteristics of Silicon Nano Wire Transistor Based on Non Equilibrium Green's Function

In this paper we have used a fully ballistic quantum mechanical transport approach to analyse electrical characteristics of rectangular silicon nanowire field effect transistor in 7 nm gate length. We have investigated the impact of structural parameters of Gate all around Silicon nano wire transistor (GAA-SNWT) on its electrical characteristics in subthreshold regime. In particular we have shown the effect of increasing the Source/Drain and channel length (L(S), L(D) and L(Ch)) on short channel effects as well as change in body thickness and independent back gate voltage. We also investigate the effect of increasing the gate underlap on the electrical characteristics and on the switching speed of device. We show that if the Lun is increased the gate capacitance and DIBL will reduce while the I(ON)/I(OFF) ratio is increased.