Silicon Interface Research Articles

Hybrid mesoporous silica nanospheres modified by poly (NIPAM-co-AA) for drug delivery

The synthesis of drug delivery systems based on surface-modified mesoporous silica hollow structures remains a huge challenge. In this paper, we have obtained hollow mesoporous silica nanoparticles (MSNs) by surfactant directed sol-gel assisted hydrothermal treatment. The MSNs have the inorganic-organic hybrid frameworks with uniform diameter distribution (260 nm), and their specific surface area, mesoporous size and pore volume are 540 m2 g−1, 3.7 nm, 0.58 cm3 g−1, respectively. It was proved that the preparation of hollow ethane-bridged nanospheres with two silicon source was due to the high crosslinking of the silicone interface and hydrothermal treatment, providing a new approach for the study of drug-loaded and controlled release behavior. Based on the synthesis of MSNs, MSNs were modified by methacryloxy propyl trimethoxyl silane (MPS) on the surface of MSNs. Then N-isopropylacryamide (NIPAM) and acrylic acid (AA) were grafted onto the surface of modified MSNs. The hollow ethane-bridged PNA–MSNs (poly (NIPAM-co-acrylic acid)-MSNs) with two silicon source were prepared successfully. Due to their distinctive hollow structure, PNA–MSNs demonstrated high drug encapsulation efficiency (70.4% ± 2.9%). The experiment results proved that the modified hollow nanoparticles not only had good biocompatibility and stability, but also possessed pH-/thermal-dual responsiveness in drug release.

Spectral Noise Analysis of a CMOS Imager at Low Temperature for Logarithmic Mode

The most common and useful CMOS high-dynamic-range imager is the one employing the active pixel sensor (APS) operating in the logarithmic mode. Notwithstanding, temporal noise can compromise the quality of the image generated by the focal-plane array. Most of the image-sensor noise models and results found in the literature are limited to a temperature range higher than that of the freezeout temperature, where the semiconductor doping impurities are all activated. The focus of this paper is to compare the noise spectrum behavior of the logarithmic image sensor at room temperature with that of a temperature near and below the freezeout point. Experimental results carried out in a small bidimensional pixel array fabricated in a standard 4-metal 2-poly 0.35- $\mu \text{m}$ CMOS technology suggests that thermal noise remains quite steady as the temperature reduces due to the increase in the sense-node resistance of the pixel circuitry. On the other hand, “spikes” have been identified with significant intensity in the spectral noise in all pixels when studied individually. These spikes in the spectrum have the same value in frequency when the device is submitted to different light intensities and temperatures. However, they were only observed for temperatures below 150 K and for frequencies below the corner frequency. The nonrandomic presence of these spikes in the noise spectrum indicates the presence of traps related to the defects inside the gate oxide and at the oxide–silicon interface. At room temperature, these spikes are not observed due to the thermal energy being higher than the binding energy of these traps.

Tribocorrosion studies on diamond-like carbon film deposited by PECVD on 304 stainless steel in simulated body fluid

In this paper, a diamond-like carbon (DLC) film with a controlled content of hydrogen (20%) and carbon (80%) was deposited onto a 304 stainless steel (304SS). Tribocorrosion tests were performed following immersion in simulated body fluid (SBF) solution. The DLC film with hydrogen and carbon control decreased the SS304 corrosion susceptibility 59-fold, compared to the bare surface, improving on the corrosion protection provided by DLC reported in the literature. Debris or nanoparticles from corroded metals can cause cytotoxicity or genotoxicity towards many cells, so these possible effects were evaluated using A172 glial cells (ATCC #CRL-1620 glioblastoma). The DLC film was not genotoxic or cytotoxic towards the glial cells. Furthermore, no cytotoxicity or genotoxicity was observed in the A172 cells after exposure to the SS304 covered with DLC film, even after 24 h of incubation, when compared to untreated cells. The methodology adopted, using a silicon interface between the DLC and the 304SS, was effective in preventing delamination of the DLC film. This report provides full information concerning methods for the production and characterisation of this DLC film.

Influence of Deposition Techniques on the Thermal Boundary Resistance of Aluminum Thin-Films

The influence of film deposition techniques on the thermal boundary resistance of an aluminum (Al)/silicon (Si) interface was investigated in this study. Al films 100 nm in thickness were deposited on Si(100) wafers using an e-beam evaporator and a direct current (DC) magnetron sputtering system. Their microstructural characteristics were inspected using scanning electron microscopy with energy dispersive spectroscopy, atomic force microscopy, and X-ray diffraction. The thermal boundary resistance values of the samples were measured using the time-domain thermoreflectance technique and numerically analyzed based on the transient Fourier heat conduction equation. A non-equilibrium molecular dynamics (MD) study was carried out to understand the effect of the atomic disorder at the film/substrate interface. Results show that the film produced by DC sputtering has a rougher surface than that of the e-beam evaporated one and a higher thermal boundary resistance. This is in agreement with the qualitative trend observed from the MD simulation that showed increases in thermal boundary resistance with the depth of atom intermixing.

Effect of misorientation angle of grain boundary on the interaction with Σ3 boundary at crystal/melt interface of multicrystalline silicon

Interactions between Σ3 grain boundaries (GBs), small-angle GBs (SAGBs), and general GBs at a silicon crystal/melt interface are studied by in situ observation during directional solidification. The interactions exhibit a dependence on the misorientation angle. SAGBs can propagate through Σ3 GBs, but this behavior transitions into coalescence with Σ3s when the misorientation approaches the limit of a SAGB, i.e. 15°. On the other hand, general GBs show the ability to terminate Σ3 GBs continuously. The present findings suggest that the presence of intrinsic dislocations in GBs plays a role in GB interactions.

Recent Progress in Understanding the Properties of the Amorphous Silicon/Crystalline Silicon Interface

The authors review experimental and modeling approaches developed at GeePs to have a better knowledge and understanding of the interface between hydrogenated amorphous silicon (a‐Si:H) and crystalline silicon (c‐Si) in heterojunction solar cells. The authors emphasize the existence of a strong inversion layer at the c‐Si surface for both (n) a‐Si:H/(p) c‐Si and (p) a‐Si:H/(n) c‐Si heterojunctions. Conductive probe atomic force microscopy reveals the existence of a conductive channel at the c‐Si surface. The analysis of complementary lateral planar conductance and capacitance measurements allows for a better description of the band diagram in both types of heterojunctions especially through the determination of band offset values. Furthermore, the passivation properties of the (i) a‐Si:H buffer layer are studied by modeling the volume defects in a‐Si:H with the defect‐pool model. In particular, the DOS in the very thin (i) a‐Si:H layers is much larger than in bulk (i) a‐Si:H because the Fermi level position favors defect creation. Surface defects in c‐Si at the a‐Si:H/c‐Si interface are then quantified and the general trends of effective lifetime measurements with the (i) a‐Si:H layer thickness can be explained, notably the increase of the effective lifetime in c‐Si with increasing the (i) a‐Si:H buffer thickness.

Characterization of the Si : Se+ Spin-Photon Interface

Silicon is the most developed electronic and photonic technological platform and hosts some of the highest-performance spin and photonic qubits developed to date. A hybrid quantum technology harnessing an efficient spin-photon interface in silicon would unlock considerable potential by enabling ultra-long-lived photonic memories, distributed quantum networks, microwave to optical photon converters, and spin-based quantum processors, all linked using integrated silicon photonics. However, the indirect bandgap of silicon makes identification of efficient spin-photon interfaces nontrivial. Here we build upon the recent identification of chalcogen donors as a promising spin-photon interface in silicon. We determined that the spin-dependent optical degree of freedom has a transition dipole moment stronger than previously thought (here 1.96(8) Debye), and the T1 spin lifetime in low magnetic fields is longer than previously thought (> 4.6(1.5) hours). We furthermore determined the optical excited state lifetime (7.7(4) ns), and therefore the natural radiative efficiency (0.80(9) %), and by measuring the phonon sideband, determined the zero-phonon emission fraction (16(1) %). Taken together, these parameters indicate that an integrated quantum optoelectronic platform based upon chalcogen donor qubits in silicon is well within reach of current capabilities.

Active broadband terahertz wave impedance matching based on optically doped graphene–silicon heterojunction

Broadband terahertz (THz) impedance matching is important for both spectral resolution improvement and THz anti-radar technology. Herein, graphene–silicon hybrid structure has been proposed for active broadband THz wave impedance matching with optical tunability. The main transmission pulse measured in the time domain indicates a modulation depth as high as 92.7% totally from the graphene–silicon interface. The interface reflection from the graphene–silicon junction implies that an impedance matching condition can be actively achieved by optical doping. To reveal the mechanism, we propose a graphene–silicon heterojunction model, which gives a full consideration of both the THz conductivity of graphene and the loss in doped junction layer. The theory fits well with the experimental results. This work proves active THz wave manipulation by junction effect and paves the way for active anti-reflection coating for THz components.

Thermoelectric transport at F4TCNQ–silicon interface

Hybrid organic-inorganic materials are among the latest class of materials proposed for thermoelectric applications. The organic-inorganic interface is critical in determining the effective transport properties of the hybrid material. We study the thermoelectric properties of the tetrafluoro-tetracyanoquinodimethane (F4TCNQ)–silicon interface. Transfer of electrons from silicon to F4TCNQ results in holes trapped within the screening length of the interface that can move parallel to the interface. We measure the response of these trapped charges to applied temperature differential and compare the thermoelectric transport properties of the silicon with and without F4TCNQ. The results confirm the presence of interface charges and demonstrate an enhanced interface thermoelectric power factor. These outcomes of this study could be used in designing 3D hybrid structures with closely packed interfaces to replicate a bulk thermoelectric material.

Delivery of External Volume Expansion through Microdeformational Interfaces Safely Induces Angiogenesis in a Murine Model of Intact Diabetic Skin with Endothelial Cell Dysfunction.

External volume expansion promotes angiogenesis in tissues by inducing a subcritical hypoxia, mechanically stimulating endothelia, and creating mild inflammation. Application of external volume expansion to less-vascularized tissues with endothelial cell dysfunction poses a risk for ineffectiveness or ischemic damage. The authors investigated the effects of external volume expansion on a murine model of type 2 diabetes mellitus and tested whether the adoption of microdeformational interfaces optimizes its angiogenic properties while limiting complications to tissues. Adult diabetic mice received stimulation with external volume expansion on their dorsal skin using a standard cup-shaped silicone interface, a polyurethane foam-shaped interface, or a silicone microarray chamber interface; controls received no treatment. Skin damage was assessed visually on the last day of stimulation and 5 days later. At 5-day follow-up, skin specimens (n = 5 per group) were procured and analyzed by histology to assess angiogenesis, adipose tissue and skin remodeling, and inflammation. All treatments significantly increased the density of blood vessels in skin compared to controls; the polyurethane foam-shaped interface showed the most robust effect (+80 percent). No relevant complications were observed using a polyurethane foam-shaped interface or silicone microarray chamber interface, but a cup-shaped silicone interface led to substantial skin damage and caused intense inflammation, fibrosis of the subcutaneous tissue, and dermal remodeling. The adoption of external volume expansion with microdeformational interfaces allows the effective and safe preconditioning of tissues with endothelial cell dysfunction and could improve outcomes in diabetic patients at high risk for surgical complications.

Dimethylacrylamide, a novel electrolyte additive, can improve the electrochemical performances of silicon anodes in lithium-ion batteries.

To enhance the electrochemical properties of silicon anodes in lithium-ion batteries, dimethylacrylamide (DMAA) was selected as a novel electrolyte additive. The addition of 2.5 wt% DMAA to 1.0 M LiPF6/EC : DMC : DEC : FEC (3 : 3 : 3 : 1 weight ratio) electrolyte significantly enhanced the electrochemical properties of the silicon anode including the first coulombic efficiency, rate performance and cycle performance. The solid electrolyte interphase (SEI) layers developed on the silicon anode in different electrolytes were investigated by a combination of electrochemical and spectroscopic studies. The improved electrochemical performances of the Si anode were ascribed to the effective passivation of DMAA on the silicon anode. The addition of DMAA helped develop a uniform SEI layer, which prevented side reactions at the interface of silicon and electrolyte.

Top-Bottom Gate Coupling Effect on Low Frequency Noise in a Schottky Junction Gated Silicon Nanowire Field-Effect Transistor

In this letter, strong low frequency noise (LFN) reduction is observed when the buried oxide (BOX)/silicon interface of a Schottky junction gated silicon nanowire field-effect transistor (SJGFET) is depleted by a substrate bias. Such LFN reduction is mainly attributed to the dramatic reduction in Coulomb scattering when carriers are pushed away from the interface. The BOX/silicon interface depletion can also be achieved by sidewall Schottky junction gates in a narrow channel SJGFET, leading to an optimal LFN performance without the need of any substrate bias.

Improved amorphous/crystalline silicon interface passivation for silicon heterojunction solar cells by hot-wire atomic hydrogen during doped a-Si:H deposition

Intrinsic/doped stacked hydrogenated amorphous silicon (a-Si:H) are widely used passivation layers for amorphous/crystalline silicon (a-Si/c-Si) heterojunction solar cells. This work reports that hot wire chemical vapor deposition of doped a-Si:H can significantly modify the property of the underlying intrinsic a-Si:H (a-Si:H(i)) as well as a-Si/c-Si interface passivation, which stems from the in-diffusion of highly reactive atomic hydrogen. Fourier transform infrared spectroscopy, spectroscopic ellipsometry and Raman analyses indicate that the underlying a-Si:H(i) films become more compact and less defected as a result of network reconstruction during doped a-Si:H capping. After this reconstruction, underdense a-Si:H(i) films obtained superior passivation quality than widely used dense layers, despite the inferior quality in the initial state. Effective minority carrier lifetime of c-Si passivated by underdense a-Si:H(i) was 19.9 ms, much higher than 15.2 ms in the case of using dense a-Si:H(i). The porous structure of underdense a-Si:H(i) facilitates hydrogen diffusion towards a-Si/c-Si interface and hence a rapid reduction of interface defect densities occurs, accounting for the better passivation quality. SHJ solar cells (160 μm, 156 × 156 mm2) with industry-compatible process were fabricated, yielding the efficiency up to 23.0% with high Voc values of 741 mV.

Experimental investigations of heat transfer mechanisms of a pulsating heat pipe

Experimental work was carried out to clarify the heat transfer mechanism of a pulsating heat pipe (PHP). A micro pulsating heat pipe (MPHP) with five turns was fabricated by engraving an interconnected micro-channel on a 1.1 mm thick transparent glass wafer. The engraved glass wafer and a 500 μm thick silicon wafer were anodically bonded to form a closed-loop MPHP. Ethanol was charged into the MPHP as the working fluid. The MPHP was vertically oriented with a bottom-heating mode. Using infrared (IR) thermometry, the distributions of temperature and heat flux were measured at the fluid-wall interface for the first time over the entire MPHP with high spatial and temporal resolution. High-speed flow visualization, which was synchronized to heat transfer measurements, was utilized to identify the local flow patterns corresponding to the local temperature and heat flux. The heat transfer at the fluid–silicon interface in the channels could be divided into the two parts: sensible heat transfer and latent heat transfer, and quantitative analysis of the data clarified the contributions of sensible/latent heat transfer to overall heat transfer. The overall contribution of latent heat transfer was estimated to be between 66% and 74%. Latent heat transfer not only induces the oscillating flow but also contributes significantly to overall heat transfer, whereas sensible heat transfer is a byproduct of the oscillating flow.

Efficiency improvement of PERC solar cell using an aluminum oxide passivation layer prepared via spatial atomic layer deposition and post-annealing

In this study, Al2O3 thin films are deposited on p-type silicon using spatial atomic layer deposition with trimethylaluminum and H2O. The films are annealed in atmosphere (ATM), forming gas (FG) and nitrogen (N2) at temperatures of 300–750 °C. Effects of annealing gas ambient and temperature on structural, electrical, and passivation properties of Al2O3/Si are systematically investigated. The experimental results show that the ATM annealing leads to an interfacial silicon oxide more than two times thicker than that of the samples annealed in FG and N2. The ratio of tetrahedral AlO4 to octahedral AlO6 can be correlated to the negative fixed oxide charge density (Qf) near the interface of Al2O3/Si. The 600 °C ATM-annealed sample has the highest Qf of 3.23 × 1012 cm−1 and thus gives the best field effect passivation. The sample annealed in FG at 450 °C has the lowest interface trap density (Dit) of 3.98 × 1011 eV−1 cm−2, indicating that the hydrogen is more effective than oxygen for chemical passivation. Overall, the FG-annealed sample has the highest lifetime of 933.8 μs, showing that chemical passivation is the primary consideration. The ATM annealing requires higher temperatures (~600 °C) to reach the optimal passivation, whereas the FG and N2 annealing temperature is limited to 450 °C to avoid dehydrogenation. Finally, for passivated emitter and rear contact cell fabrication, the cell with FG annealing has the best conversion efficiency of 21.43%, which is 0.17 and 0.54 percentage point higher than that of the cells with ATM and N2 annealing, respectively.

Effect of hot-dip siliconizing time on phase composition and microstructure of Mo–MoSi2 high temperature structural materials

Mo–MoSi2 high temperature structural materials were obtained by hot-dip siliconizing method. The results show that the silicon melt and molybdenum substrate have good wettability, molten silicon reacts with molybdenum substrate to form a molybdenum silicide phase with a columnar structure, and a strong MoSi2 crystallographic preferred orientation (CPO) on the (110) crystal face is characterized. While, the Mo–MoSi2 high temperature structural materials consist mainly of silicon rich layer, MoSi2 layer, interface layer and molybdenum substrate. The coating surfaces contain a high silicon concentration (55–65 wt%) than the MoSi2 layer (30–35 wt%). Moreover, the thicknesses and the average grain sizes of siliconized coatings increase sharply with increasing siliconizing time. The coatings thicknesses are 20, 25, 30, and 50 µm, respectively. And the average grain sizes are 6.9, 9.3, 11.7, and 11.8 µm, respectively.

Determination of Metallization-Induced Recombination Losses of Screen-Printed Silicon Solar Cell Contacts and Their Dependence on the Doping Profile

This paper presents an easy-to-implement, but rigorous method to determine the dark saturation current densities $J_{01m}$ and $J_{02m}$ under the metallized region of a silicon solar cell contact. The method is based on an autofitting procedure by the Griddler artificial intelligence finite-element simulation program to measured photoluminescence images of samples with especially designed test structures. It is found that a deeper p-n junction strongly reduces the recombination losses at the metal–silicon interface. By carefully tailoring the boron diffusion profile, the $J_{01m}$ is reduced from 839.2 to 274.2 fA/cm2.

Dielectric Properties and Ion Transport in Layered MoS2 Grown by Vapor-Phase Sulfurization for Potential Applications in Nanoelectronics.

Electronic and dielectric properties of vapor-phase grown MoS2 have been investigated in metal/MoS2/silicon capacitor structures by capacitance–voltage and conductance-voltage techniques. Analytical methods confirm the MoS2 layered structure, the presence of interfacial silicon oxide (SiOx) and the composition of the films. Electrical characteristics in combination with theoretical considerations quantify the concentration of electron states at the interface between Si and a 2.5–3 nm thick silicon oxide interlayer between Si and MoS2. Measurements under electric field stress indicate the existence of mobile ions in MoS2 that interact with interface states. On the basis of time-of-flight secondary ion mass spectrometry, we propose OH– ions as probable candidates responsible for the observations. The dielectric constant of the vapor-phase grown MoS2 extracted from CV measurements at 100 kHz is 2.6 to 2.9. The present study advances the understanding of defects and interface states in MoS2. It also indicates opportunities for ion-based plasticity in 2D material devices for neuromorphic computing applications.

Fabrication of gadolinium particle-based absorption gratings for neutron grating interferometry.

The imaging performance of a neutron-based Talbot-Lau interferometer depends to a great extent on the absorption characteristics of the source and analyzer gratings. Due to its high neutron attenuation, gadolinium (Gd) is the preferred material for grating fabrication, but suffers from difficulties with deposition time, stability, uniformity, and selectivity into high aspect ratio structures. Here we present a simple alternative method of Gd deposition into grating structures based on metallic particle suspension casting and subsequent doctor-blading. Surface analysis by confocal and electron scanning microscopy shows that a nearly clear, particle free silicon interface of the grating structure over a large area could be reached. Additionally, characterization by neutron radiography confirms a high effective Gd height and homogeneity over the whole grating area. In particular, grating trenches well below 10 μm width could be successfully filled with Gd and deliver excellent absorbing performance down to the sub-2 Å wavelength range. The findings confirm that we obtained an effective binary absorption profile for the fabricated gratings which is of great benefit for grating-based neutron imaging.

From atomic-scale interfaces - to new nanomaterials

The problem of the synthesis of new type nanomaterials in the form of nanocoatings with subnanometric heterogeneity has been formulated. It has been presented an analysis of influences of physical vapor deposition in ultrahigh vacuum on the process of intermixing a film with a substrate, including the results, which has been obtained under the formation of transition metal – silicon interface. The generalization of the obtained experimental results allowed to develop an approach to the development of new nanocoatings with low-dimensional heterogeneity. The principles of constructing such low-dimensional nanocoatings, their properties and their possible applications are considered.