Silicon Ribbon Research Articles

On Finite Type Invariants of Welded String Links and Ribbon Tubes

Welded knotted objects are a combinatorial extension of knot theory, which can be used as a tool for studying ribbon surfaces in $4$-space. A finite type invariant theory for ribbon knotted surfaces was developed by Kanenobu, Habiro and Shima, and this paper proposes a study of these invariants, using welded objects. Specifically, we study welded string links up to $w_k$-equivalence, which is an equivalence relation introduced by Yasuhara and the second author in connection with finite type theory. In low degrees, we show that this relation characterizes the information contained by finite type invariants. We also study the algebraic structure of welded string links up to $w_k$-equivalence. All results have direct corollaries for ribbon knotted surfaces.

Optical Recrystallization of Nanocrystalline Silicon Ribbons

The Silicon on Dust Substrate (SDS) is a gas-to-wafer process that produces multicrystalline silicon ribbons directly from gaseous feedstock (silane), avoiding the standard industry steps of polysilicon deposition, crystal growth, and wafering. The SDS technique consists of three main steps: (i) micrometric-sized silicon powder production by grinding silicon chunks; (ii) chemical vapor deposition (CVD) of silicon over this silicon powder substrate; and (iii) zone-melting recrystallization (ZMR) of the nanocrystalline pre-ribbon obtained in the CVD step. Several samples were produced by this technique. During CVD, mechanically self-sustained nanocrystalline pre-ribbons were grown over silicon powder substrates, with growth rates in the order of 50 µm/min. The ZMR process performance is substantially impacted by the pre-ribbon physical characteristics. The best and largest recrystallizations were achieved on pre-ribbons grown over powder substrates with smaller particle sizes, which also have lower substrate powder incorporation ratios. Multicrystalline silicon ribbons with crystalline areas as large as 2 × 4 cm2 were successfully produced. These areas have visible columnar crystal growth with crystal lengths up to 1 cm. The SDS ribbons’ measured resistivity confirmed the high powder content of the resulting material. The ability to produce solar cells on SDS multicrystalline silicon ribbons was demonstrated.

Silicon Ribbon-Based Dual-Beam Optical Phased Array with Low Crosstalk and Large FoV

In this paper, a silicon ribbon (SR)-based microstructure is developed and added to a 32-channel optical phased array (OPA) to reduce the crosstalk between the antennas of grating waveguides. The spacing between the chirped grating antennas can be as close as 600 nm to effectively improve the field of view (FoV) of the OPA in the horizontal direction to 95 degrees. This SR-based approach substantially reduces the side lobe by 10 dB, effectively suppressing the noise and increasing the main lobe by 6 dB and considerably expanding the grating length with linear energy decay. The full width at the half maximum of the light spot reaches about 0.24 degrees. The antenna sites can simultaneously be scanned vertically by bi-directional inputs, effectively increasing the FoV to 30 degrees in the vertical direction.

A Multifaceted Challenge to Enhance Multicriteria Decision Support for Energy Policy

The necessity to enhance multicriteria decision in the industry is challenging to support the current energy policy. European Union regulations and guidelines provide the guideline for minimalizing environmental harms but are not enough in their actions for providing effective sustainability assessment. None of the available standalone assessment methods do capture the comprehensibility of multicriteria decision-making. The aim of this paper is to demonstrate a challenge to incorporate the multicriteria sustainability decision-making method to mainstream energy policy, which is lacking in European Union policies. The novelty of the research lies in constructing a multicriteria sustainability approach for assessing energy technologies performance for embodying into a mainstream energy policy. In this study, the multicriteria decision-making—an approach combining life cycle-based methods, analytical hierarchy process, as well as macroeconomic analysis, was used to demonstrate the applicability of the method based on three photovoltaic technologies. The results showed that sustainability assessment supported with multicriteria decision allows to better understand analyzed factors influencing the energy technology, contributing to selection of the best sustainability technology according to the realization of an energy policy. It was proved based on a real example of photovoltaics, where string ribbon technology represents the most sustainable along its life cycle, with a 0.503 sustainability score. The study highlighted the challenge to embody the integrated method assessing sustainability-oriented technologies into an energy policy. This challenge regarding example evidence places emphasis on the decision-making process to realize an energy policy and in consequence, to improve enterprise sustainability performance.

Multileveled tunable silicon grating array bonded on large scale integration substrate by polymers

A multileveled tunable silicon grating array is designed and fabricated on a large-scale-integration (LSI) substrate. The grating consists of 250 single crystalline silicon ribbons of 260 nm in thickness, 400 μm in length, and 10 μm in period. The LSI substrate generates voltages to vary the heights of respective grating ribbons addressed by digital signal input. Each grating ribbon is attracted by an electrostatic force generated by 6-bit applied voltage in the range from 0 to 5 V. In the fabrication, the LSI substrate and a silicon-on-insulator wafer are bonded by the two kinds of polymers. A photosensitive polyimide polymer is used for patterning the bonding pads and also for bonding the wafers at the pressure of 0.25 MPa and the temperature of 350°C. Another epoxy polymer fills the space underneath the grating ribbons for subsequent process, which is finally removed by sacrificial etching to make the grating ribbons freestanding. The tunability of the grating is examined experimentally under the basic operation conditions.

The realization of the intermediate layer (IML) in a tandem solar cell using silicon-based photonic ribbon structure

The silicon-based 1D photonic structure is proposed in this research to realize an intermediate layer, which could be used in tandem solar cell, where 1 D photonic structure deals with a silicon ribbon with having 10 number of circular periodic air hole on it. Further, the principle of realization of the present intermediate layer is based on the generation of photonic band gap with respect to the visible light, which is evaluated with the help of the plane wave expansion method. Finally, photonic band gap analysis confirms that the proposed one-dimensional photonic ribbon structure can be a suitable layer to introduce in a tandem solar cell to envisage better efficiency.

In-field monitoring of eight photovoltaic plants: degradation rate along seven years of continuous operation

<p class="Abstract">The results of more than seven years (October 2010-December 2017) of continuous monitoring are presented in this paper. Eight outdoor photovoltaic (PV) plants were monitored. The monitored plants use different technologies: mono-crystalline silicon (m-Si), poli-crystalline silicon (p-Si), string ribbon silicon, copper indium gallium selenide (CIGS), thin film, and cadmium telluride (CdTe) thin film. The thin-film and m-Si modules are used both in fixed installations and on x-y tracking systems. The results are expressed in terms of the degradation rate of the efficiency of each PV plant, which is estimated using the measurements provided by a multi-channel data acquisition system that senses both electrical and environmental quantities. A comparison with the electrical characterization of each plant obtained by means of the transient charge of a capacitive load is also made. In addition, three of the monitored plants are characterized at module level, and the estimated degradation rates are compared to the values obtained with the monitoring system. The main outcome of this work can be summarized as the higher degradation rate of thin-film based PV modules with respect to silicon-based PV modules.</p>

Monolithic Wafer Scale Integration of Silicon Nanoribbon Sensors with CMOS for Lab-on-Chip Application.

Silicon ribbons (SiRi) have been well-established as highly sensitive transducers for biosensing applications thanks to their high surface to volume ratio. However, selective and multiplexed detection of biomarkers remains a challenge. Further, very few attempts have been made to integrate SiRi with complementary-metal-oxide-semiconductor (CMOS) circuits to form a complete lab-on-chip (LOC). Integration of SiRi with CMOS will facilitate real time detection of the output signal and provide a compact small sized LOC. Here, we propose a novel pixel based SiRi device monolithically integrated with CMOS field-effect-transistors (FET) for real-time selective multiplexed detection. The SiRi pixels are fabricated on a silicon-on-insulator wafer using a top-down method. Each pixel houses a control FET, fluid-gate (FG) and SiRi sensor. The pixel is controlled by simultaneously applying frontgate (VG) and backgate voltage (VBG). The liquid potential can be monitored using the FG. We report the transfer characteristics (ID-VG) of N- and P-type SiRi pixels. Further, the ID-VG characteristics of the SiRis are studied at different VBG. The application of VBG to turn ON the SiRi modulates the subthreshold slope (SS) and threshold voltage (VTH) of the control FET. Particularly, N-type pixels cannot be turned OFF due to the control NFET operating in the strong inversion regime. This is due to large VBG (≥25 V) application to turn ON the SiRi sensor. Conversely, the P-type SiRi sensors do not require large VBG to switch ON. Thus, P-type pixels exhibit excellent ION/IOFF ≥ 106, SS of 70–80 mV/dec and VTH of 0.5 V. These promising results will empower the large-scale cost-efficient production of SiRi based LOC sensors.

The carbon substrate in RST Si ribbon technology for solar cells

The carbon substrate used in the RST (silicon Ribbon growth on a Sacrificial carbon Template) process, a silicon ribbon growth technology aimed at the fabrication of silicon solar cells, is a composite made of a compressed expanded natural graphite (CENG) ribbon coated by a protective rough lamellar high-temperature (RLHT) pyrocarbon. It is shown that the reactivity of RLHT pyrocarbon with molten silicon is stimulated by the presence of topological defects of the CENG ribbon. This reactivity generates a contamination of the silicon melt by carbon and its metallic impurities and, in turn, adversely affects the performances of solar cells made from RST silicon films. Reactivity with molten silicon can be drastically reduced by the control of the deposition conditions of pyrocarbon and of the roughness of the CENG ribbon. A new model is proposed to explain the mechanism of the intrinsic reactivity of RLHT pyrocarbon with molten silicon. Based on this model the reactivity problem can virtually be eliminated by the deposition of a SiC coating about 0.3 μm on the RLHT pyrocarbon. Improvements of the carbon ribbon, described in this study, especially its pyrocarbon coating, should lead to flexible silicon solar cells 70–80 μm thick with conversion efficiency above 18%.

LCA study of photovoltaic systems based on different technologies

ABSTRACTThis work deals with the application of a Life Cycle Assessment approach for evaluating the environmental and energy impacts ascribed to the production of photovoltaic (PV) cells of first and second generations. PV technologies based on silicon and CuInSe2 (CIS) thin films were taken into account herein. PV systems prepared with amorphous silicon (a-Si) showed a low environmental impact and short energy payback time when compared to those ones obtained using crystalline silicon (c-Si). PV technologies associated with mono-crystal (mono-Si) and polycrystalline silicon (multi-Si) showed large emissions of CO2, nitrogen oxides, non-methane volatile organic compounds, particulates, and SO2 into air per square meter of PV panel processed. In addition, these technologies displayed a significant fossil fuel demand, biological oxygen demand, and global warming potential, which make them eco-unfriendly. Ribbon silicon (ribbon-Si) and CIS thin films showed intermediate impact scores, but further improvements in their production chain are needed before these devices are commercially used. The technologies examined herein were categorized in first- and second-generation technologies in order to compare their environmental impact and conversion efficiency. Much attention was also paid to the development of third-generation PV cells with improved conversion efficiencies and lower environmental impacts.

Simulating the horizontal growth process of silicon ribbon

In this paper, we present a solidification growth model that primarily describes the principal components of horizontal ribbon growth process, but also discusses the interaction between fluid flow and heat transfer, crystallization dynamics, and the effects of oxygen impurity distribution in melts, particularly with respect to the morphology of the interface. The effects of the jet cooling rate, pulling speed, and transfer coefficient on solute transport were studied. The results showed that a higher jet velocity produces a sharper temperature gradient at the interface and a stronger Marangoni effect, facilitates solute transport in the silicon melt, and promotes higher oxygen concentration in crystal. The stronger Marangoni convection causes more rapid oxygen transfer in the silicon melt and a higher oxygen concentration. Solidification front increases the downward flow velocity of the eddy current as the pulling speed is increased; this leads to a decrease in solute concentration at the interface. An increase in the downward flow of the vortex confluence facilitates the reduction of solute concentration in the crystal. An increase in the upward flow of the vortex confluence will increase the concentration in the crystal. The oxygen concentration is concentrated at the top and bottom of the silicon ribbon.

All-black front surfaces for building-integrated photovoltaics

Widespread implementation of building integrating photovoltaics requires aesthetically pleasant panels. Black surfaces are often visually appealing and, if based on a black photoabsorber, may lead to increased panel efficiency. Here, we demonstrate a combination of black silicon and black ribbons (or bus-bars), both fabricated with methods that are compatible with production lines of screen-printed, front contacted solar panels. Maskless, non-cryogenic reactive ion etch of silicon and subsequent coating with aluminum oxide for passivation purposes results in average reflectance of less than 1% in the UV–vis part of the solar spectrum, and in minority carrier lifetimes similar to those obtained on polished reference samples thanks to minimized surface damage, as confirmed by transmission electron microscopy. Inorganic blackening of bus-bars by a combination of electroplating and chemical etching results in reflectance values lower than 3.5% in the UV–vis, with no modifications to standard stringing equipment required.

Silicon on Dust Substrate: The Effect of Powder Size on Ribbon Production

The silicon on dust substrate process is a two‐step technique to produce multicrystalline silicon (mc‐Si) ribbons directly from gaseous feedstock. Silicon pre‐ribbons of very small grain size (ranging from nano to microcrystalline), with a porous structure and dimensions up to 25 × 100 mm2, are obtained using an inline optical chemical vapor deposition (CVD) system operating at atmospheric pressure and at low temperatures (<600 °C). Using silane as the gaseous precursor, nano or microcrystalline silicon layers can be grown, on top of silicon powder substrates, moving at constant speed, and crossing three hot deposition regions several times. The growth rates (GR) vary from 13.4 to 73.2 μm min−1, depending on the grain size of silicon powder. The last step is a floating zone (FZ) recrystallization technique, where the silicon pre‐ribbons obtained in the CVD step, become solid mc‐Si ribbons. The success of recrystallization depends on the grain size of silicon powder used as substrate on the CVD step, with lower grain sizes powders delivering better results. For the lower size powder substrates, multi‐crystalline areas of 5–20 mm2 were obtained, with an average crystal size in the (0.1; 1) mm range.

Spontaneous Periodic Delamination of Thin Films To Form Crack-Free Metal and Silicon Ribbons with High Stretchability.

Design of electronic materials with high stretchability is of great importance for realizing soft and conformal electronics. One strategy of realizing stretchable metals and semiconductors is to exploit the buckling of materials bonded to elastomers. However, the level of stretchability is often limited by the cracking and fragmentation of the materials that occurs when constrained buckling occurs while bonded to the substrate. Here, we exploit a failure mechanism, spontaneous buckling-driven periodic delamination, to achieve high stretchability in metal and silicon films that are deposited on prestrained elastomer substrates. We find that both globally periodic buckle-delaminated pattern and ordered cracking patterns over large areas are observed in the spontaneously buckle-delaminated thin films. The geometry of periodic delaminated buckles and cracking periodicity can be predicted by theoretical models. By patterning the films into ribbons with widths smaller than the predicted cracking periodicity, we demonstrate the design of crack-free and spontaneous delaminated ribbons on highly prestrained elastomer substrates, which provides a high stretchability of about 120% and 400% in Si and Au ribbons, respectively. We find that the high stretchability is mainly attributed to the largely relaxed strain in the ribbons via spontaneous buckling-driven delamination, as made evident by the small maximum tensile strain in both ribbons, which is measured to be over 100 times smaller than that of the substrate prestrain.

CVD silicon film growth on powder substrates using an inline optical system

This paper presents the results achieved with an inline optical chemical vapor deposition (CVD) system operating at atmospheric pressure and at low temperatures (<600° C). Using silane as the gaseous precursor, microcrystalline silicon layers were grown on compressed silicon micrometric powder substrates, moving at constant speed, and crossing three hot deposition regions several times. Microcrystalline silicon (µc-Si) ribbon samples measuring up to 25×70 mm were obtained with growth rates (GR) varying from 13 to 53 µm/min. Grain size of silicon powder has a great influence in GR. It was observed that using lower grain size powders as substrates, higher GR were obtained. Also, it was observed that for the larger grain size powders used, after deposition the silicon films grown were stuck to the quartz substrate holder and could not be removed pristine.

Polymer-based interconnection cables to integrate with flexible penetrating microelectrode arrays.

There have been various types of interconnection methods for neural interfacing electrodes, such as silicon ribbon cables, wire bonding and polymer-based cables. In this study, interconnection cables were developed for integration with a Flexible Penetrating Microelectrode Array (FPMA) that was previously developed for neural signal recording or stimulation. Polyimide and parylene C were selected as base materials for the interconnection cables as both materials can preserve the flexibility of the FPMA better than other interconnection methods such as silicon ribbon cable or wire bonding. We conducted durability tests to determine if the interconnection cables were suitable for in-vivo implantation, by long-term soaking of the cables in phosphate buffered saline solution. We measured the changes in impedance over time, and equivalent circuit models were used to analyze the electrochemical phenomena on the surface of the cables. Lastly, we implanted the cable-integrated electrodes device onto rabbit's sciatic nerve and recorded neural signals to prove the feasibility of the developed FPMA integration system.

Upper limits on the mechanical loss of silicate bonds in a silicon tuning fork oscillator

Silicon optics suspended by silicon ribbons or silicon fibers and kept at low temperature are being considered, because of promising optical and mechanical properties, for the test masses of third generation interferometric gravitational-wave detectors. To interconnect the suspension elements the technique of hydroxide catalysis (or silicate) bonding can be used. In order to estimate the bond loss a tuning fork was fabricated from silicon ribbons, which were then silicate bonded. The temperature dependence of mechanical loss of this tuning fork was measured in the temperature range of 95–295 K. The ratio of the energy stored in the bond layer to the total energy of the tuning fork was calculated by numerical simulation. This provided an upper limit of the bond loss as a function of the temperature. It is (5±2)×10−3 at 123 K, a proposed operating temperature of cryogenically operating ground based interferometric gravitational-wave detectors.

An Introduction to Dynamic Load Test on Photovoltaic Modules

The front cover of solar photovoltaic modules is mostly made of 3.2mm, 2mm or thinner glass. When under wind or other dynamic loading stress, the performance of the PV modules might be affected. This article analyzed data of dynamic load test on several different types of PV modules, and got the conclusion that the dynamic load stress could harm the string ribbon or interior circuits of the PV modules, and would therefore lead to capacity reduction and less insulation.

Temperature dependent evolution of wrinkled single-crystal silicon ribbons on shape memory polymers.

Shape memory polymers (SMPs) can remember two or more distinct shapes, and thus can have a lot of potential applications. This paper presents combined experimental and theoretical studies on the wrinkling of single-crystal Si ribbons on SMPs and the temperature dependent evolution. Using the shape memory effect of heat responsive SMPs, this study provides a method to build wavy forms of single-crystal silicon thin films on top of SMP substrates. Silicon ribbons obtained from a Si-on-insulator (SOI) wafer are released and transferred onto the surface of programmed SMPs. Then such bilayer systems are recovered at different temperatures, yielding well-defined, wavy profiles of Si ribbons. The wavy profiles are shown to evolve with time, and the evolution behavior strongly depends on the recovery temperature. At relatively low recovery temperatures, both wrinkle wavelength and amplitude increase with time as evolution progresses. Finite element analysis (FEA) accounting for the thermomechanical behavior of SMPs is conducted to study the wrinkling of Si ribbons on SMPs, which shows good agreement with experiment. Merging of wrinkles is observed in FEA, which could explain the increase of wrinkle wavelength observed in the experiment. This study can have important implications for smart stretchable electronics, wrinkling mechanics, stimuli-responsive surface engineering, and advanced manufacturing.

Tailoring the Electronic and Magnetic Properties of Two-Dimensional Silicon Carbide Sheets and Ribbons by Fluorination

Fluorination has been instrumental for tuning the properties of several two-dimensional (2D) materials, including graphene, h-BN, and MoS2. However, its potential application has not yet been explored in 2D silicon carbide (SiC), a promising material for nanoelectronic devices. We investigate the structural, electronic, and magnetic properties of fully and partially fluorinated 2D SiC sheets and nanoribbons by means of density functional theory combined with cluster expansion calculations. We find that fully fluorinated 2D SiC exhibits chair configurations and a nonmagnetic semiconducting behavior. Fluorination is shown to be an efficient approach for tuning the band gap. Four ground states of partially fluorinated SiC, SiCF2x with x = 0.0625, 0.25, 0.5, 0.75, are obtained by cluster expansion calculations. All of them exhibit nanoroad patterns, with the x = 0.5 structure identified as the most stable one. The x = 0.0625 structure is a nonmagnetic metal, while the other three are all ferromagnetic half-me...