SiO2 Thin Films Research Articles

Li4SiO4-Based Artificial Passivation Thin Film for Improving Interfacial Stability of Li Metal Anodes.

An amorphous SiO2 (a-SiO2) thin film was developed as an artificial passivation layer to stabilize Li metal anodes during electrochemical reactions. The thin film was prepared using an electron cyclotron resonance-chemical vapor deposition apparatus. The obtained passivation layer has a hierarchical structure, which is composed of lithium silicide, lithiated silicon oxide, and a-SiO2. The thickness of the a-SiO2 passivation layer could be varied by changing the processing time, whereas that of the lithium silicide and lithiated silicon oxide layers was almost constant. During cycling, the surface of the a-SiO2 passivation layer is converted into lithium silicate (Li4SiO4), and the portion of Li4SiO4 depends on the thickness of a-SiO2. A minimum overpotential of 21.7 mV was observed at the Li metal electrode at a current density of 3 mA cm-2 with flat voltage profiles, when an a-SiO2 passivation layer of 92.5 nm was used. The Li metal with this optimized thin passivation layer also showed the lowest charge-transfer resistance (3.948 Ω cm) and the highest Li ion diffusivity (7.06 × 10-14 cm2 s-1) after cycling in a Li-S battery. The existence of the Li4SiO4 artificial passivation layer prevents the corrosion of Li metal by suppressing Li dendritic growth and improving the ionic conductivity, which contribute to the low charge-transfer resistance and high Li ion diffusivity of the electrode.

Nanoscale High-k Dielectrics for Junctionless Nanowire Transistor for Drain Current Analysis

Hafnium oxide (HfO2) nanoparticles were prepared by a chemical precipitation method and its physical and electrical properties were investigated. HfO2 thin films were prepared via a dip-coating method using the synthesized HfO2 nanoparticles. The crystallinity and resistivity of both prepared thin films were analysed by x-ray diffraction and impedance analyser. The crystalline size was found to be 8 nm and 13 nm for HfO2 and SiO2 thin films, respectively. The electrical (bulk) resistance was calculated by fitting the complex impedance plane using z-view software, and was found to be 2.15 × 107 Ω for HfO2, whereas it was found to be 3.6 × 105 Ω for SiO2 thin films. Junctionless nanowire transistors were implemented using HfO2 dielectric and performance was compared to SiO2 gate dielectric. The results revealed that nano-sized HfO2 proves to be a better gate dielectric material than conventional gate dielectrics. Thus, the nano-sized HfO2 based junctionless transistor device is more suitable for future low power applications.

Mechanical and optical properties of SiO2 thin films deposited on glass

The optical and mechanical properties of amorphous SiO2 films deposited on soda-lime silicate float glass by reactive RF magnetron sputtering at room temperature were investigated in dependence of the process pressure. The densities of the films are strongly influenced by the process pressure and vary between 2.38 and 1.91 g cm−3 as the pressure changes from 0.27 to 1.33 Pa. The refractive indices of the films shift between 1.52 and 1.37, while the residual compressive stresses in the deposited films vary in the range from 440 to 1 MPa. Hardness and reduced elastic modulus values follow the same trend and decline with the increase of process pressure from 8.5 to 2.2 GPa and from 73.7 to 30.9 GPa, respectively. The abrasive wear resistance decreases with the density of the films.

Monitoring the Surface Chemistry of Functionalized Nanomaterials with a Microfluidic Electronic Tongue.

Advances in nanomaterials have led to tremendous progress in different areas with the development of high performance and multifunctional platforms. However, a relevant gap remains in providing the mass-production of these nanomaterials with reproducible surfaces. Accordingly, the monitoring of such materials across their entire life cycle becomes mandatory to both industry and academy. In this paper, we use a microfluidic electronic tongue (e-tongue) as a user-friendly and cost-effective method to classify nanomaterials according to their surface chemistry. The chip relies on a new single response e-tongue with association of capacitors in parallel, which consisted of stainless steel microwires coated with SiO2, NiO2, Al2O3, and Fe2O3 thin films. Utilizing impedance spectroscopy and a multidimensional projection technique, the chip was sufficiently sensitive to distinguish silica nanoparticles and multiwalled carbon nanotubes dispersed in water in spite of the very small surface modifications induced by distinct functionalization and oxidation extents, respectively. Flow analyses were made acquiring the analytical readouts in a label-free mode. The device also allowed for multiplex monitoring in an unprecedented way to speed up the tests. Our goal is not to replace the traditional techniques of surface analysis, but rather propose the use of libraries from e-tongue data as benchmark for routine screening of modified nanomaterials in industry and academy.

Synchrotron analysis of structure transformations in V and V/Ag thin films

Crystal structure transformations in V(25 nm)/SiO2(001) and V(25 nm)/Ag(25 nm)/SiO2(001) thin films during annealing in vacuum of 10−3 Pa in the temperature range from 400 °C to 600 °C have been investigated by synchrotron X-ray powder diffraction. Crystal lattice parameters of VOx phase were evaluated for all transformations stages as well as its tetragonality degree. Additional techniques such as in-situ electron diffraction, secondary ion mass-spectrometry and transmission electron microscopy have been applied as well. Introduction of the Ag layer affects the V film structure and its oxidation property during annealing. The body-centered monoclinic (bcm) lattice forms in V films after annealing. On the other hand, presence of the Ag layer leads to formation of the body-centered tetragonal (bct) structure during annealing at the same temperature. Ag suppresses oxygen incorporation into the film during annealing due to its diffusion into V grain boundaries and following diffusion induced grain boundary migration, leading to decrease of vanadium grains size. Mentioned above structural changes have not been detected for samples annealed in a vacuum of 10−7 Pa in the same temperature range.

Adhesion characterization of SiO2 thin films evaporated onto a polymeric substrate

To ensure good adhesion between a 200 nm thick silicon dioxide layer and a 4.5 μm thick hardcoat polymeric coating, a better understanding of mechanisms of adhesion at this interface is needed. To reach this purpose, focus is placed on two axes: characterizing mechanical properties of materials composing the system and in parallel, finding an applicable and effective method to quantify adhesion. Small dimension of SiO2 thin film makes it challenging to accurately characterize it. Hence the use of both nano-indentation and AFM to attempt assessment of SiO2 thin film elastic modulus Ef; taking into account limitations and uncertainty associated with each technique. Elastic modulus of SiO2 thin film determined by nano-indentation is roughly 50 GPa on a wafer substrate and 15 GPa on a lens substrate. As for AFM, modulus measured is approximatively 56 GPa on a wafer substrate and 22 GPa on a lens substrate. This highlights significant influence of substrate for both techniques. Impact on mechanical properties between SiO2 thin films under different intrinsic stresses was also investigated. Results suggest that higher density of SiO2 thin film leads to higher elastic modulus. To quantify adhesion, micro-tensile and micro-compression tests were performed. Micro-tensile experiments give ultimate shear strengths of hardcoat-substrate interface ranging from 9 to 14 MPa. Values of energy release rates of SiO2 / Hardcoat, range from 0.1 J/m² to 0.5 J/m², depending on moduli values found on wafer or lens substrate.

Surfactant Effect on the Synthesis of Mesoporous TiO<sub>2</sub>-SiO<sub>2</sub> Coatings Using Sol-Gel Technology

The aim of the research was to develop the area of mesoporous thin films of a binary TiO2–SiO2 system. Sol was synthesized from tetraethylorthosilicate as the silica source and titanium isopropoxide solution as the TiO2 source, while triblock copolymer surfactant (Pluronic F 127 (10% solution in water, (P))) was used as the mesostructure-directing agent. In this paper we present sol-gel obtained TiO2–SiO2 with a mesoporous structure. The effects of added titanium on the mesostructure and on the porosity are presented and discussed. Four different molar percentage ratios of Ti: Si were used for the synthesis of mixed TiO2–SiO2 mesoporous thin films on glass substrate. The mesoporous structure of thin films was characterized by X-ray diffraction (XRD) patterns, atomic force microscopy (AFM), scanning electron microscopy (SEM) and the water contact angle. These mesoporous TiO2–SiO2 thin films could have many potential applications in many areas such as separation membranes, catalysis, optics, and self-cleaning surfaces.

Simultaneous ultra-long data retention and low power based on Ge10Sb90/SiO2 multilayer thin films

In this article, Ge10Sb90/SiO2 multilayer thin films were prepared to improve thermal stability and data retention for phase change memory. Compared with Ge10Sb90 monolayer thin film, Ge10Sb90 (1 nm)/SiO2 (9 nm) multilayer thin film had higher crystallization temperature and resistance contrast between amorphous and crystalline states. Annealed Ge10Sb90 (1 nm)/SiO2 (9 nm) had uniform grain with the size of 15.71 nm. After annealing, the root-mean-square surface roughness for Ge10Sb90 (1 nm)/SiO2 (9 nm) thin film increased slightly from 0.45 to 0.53 nm. The amorphization time for Ge10Sb90 (1 nm)/SiO2 (9 nm) thin film (2.29 ns) is shorter than Ge2Sb2Te5 (3.56 ns). The threshold voltage of a cell based on Ge10Sb90 (1 nm)/SiO2 (9 nm) (3.57 V) was smaller than GST (4.18 V). The results indicated that Ge10Sb90/SiO2 was a promising phase change thin film with high thermal ability and low power consumption for phase change memory application.

Real-Time Stress Measurement in SiO2 Thin Films during Electrochemical Lithiation/Delithiation Cycling

Oxide coatings have been shown to improve the cyclic performance of high-energy density electrode materials such as Si. However, no study exists on the mechanical characterization of these oxide coatings. Here, thin film SiO2 electrodes are cycled under galvanostatic conditions (at C/9 rate) in a half-cell configuration with lithium metal foil as counter/reference electrode, with 1 M LiPF6 in ethylene carbonate, diethyl carbonate, dimethyl carbonate solution (1:1:1, wt%) as electrolyte. Stress evolution in the SiO2 thin film electrodes during electrochemical lithiation/delithiation is measured in situ by monitoring the substrate curvature using a multi-beam optical sensing method. Upon lithiation SiO2 undergoes extensive inelastic deformation, with a peak compressive stress of 3.1 GPa, and upon delithiation the stress became tensile with a peak stress of 0.7 GPa. A simple plane strain finite element model of Si nanotube coated with SiO2 shell was developed to understand the mechanical response of the core-shell type microstructures under electrochemical cycling; measured stress response was used in the model to represent SiO2 constitutive behavior while Si was treated as an elastic-plastic material with concentration dependent mechanical properties obtained from the literature. The results reported here provide insights and quantitative understanding as to why the highly brittle SiO2 coatings are able to sustain significant volume expansion (300%) of Si core without fracture and enhance cyclic performance of Si reported in the literature. Also, the basic mechanical properties presented here are necessary first step for future design and development of durable Si/SiO2 core shell structures or SiO2-based electrodes.

Fabrication of omnidirectional anti-reflection and super hydrophilicity SiO2 nanorods by oblique angle deposition

Growth of silicon dioxide (SiO2) nanorods were fabricated via electron beam evaporation with oblique angle deposition technique approach at different film thickness. The morphologies, optical and wettability properties were characterized by field-emission scanning electron microscopy, spectrophotometry with angle dependence technique and contact angle measurement, respectively. Compared with that on the SiO2 thin films, the transmission on the SiO2 nanorods is significantly improved. The transmission is decreased with the height of the SiO2 nanorods. In addition, the result indicated that the SiO2 nanorods provide enhancement wettability which can function as the super-hydrophilicity surface. The experiment analysis of the thickness dependence omnidirectional anti-reflection and super-hydrophilic characteristics will benefit the design of self-cleaning glass application.

High Quality Oxide Films Deposited at Room Temperature by Ion Beam Sputtering

ABSTRACTWe have deposited dense and pinhole-free thin films of SiO2, Al2O3 and ITO at room temperature via ion beam sputtering. The SiO2 films were found to be of similar quality as thermal oxide with a resistivity greater than 1015 Ω·cm and breakdown field in excess of 7 MV/cm. The Al2O3 films were part of a Pt- Al2O3-Pt vertical tunnel junction and were kept extremely thin, from 2 nm to 4 nm. The current-voltage characteristics of these junctions indicated a breakdown field in excess of 20 MV/cm, roughly twice that achieved by ALD films. This breakdown voltage was found to be independent of junction area, strongly suggesting the absence of pinholes in the film. The ITO films were 50 nm to 100 nm thick. As deposited, they are fully transparent with an electrical resistivity of 5x10-4 Ω·cm.

The effect of adsorbates on the electrical stability of graphene studied by transient photocurrent spectroscopy

Adsorbate induced variations in the electrical conductivity of graphene layers with two different types of charge carriers are investigated by using the Transient Photocurrent Spectroscopy (TPS) measurement technique. In-vacuum TPS measurements taken for a duration of 5 ks revealed that the adsorption/desorption of atmospheric adsorbates leads to more than a 110% increment and a 45% decrement in the conductivity of epitaxial graphene (n-type) and chemical vapor deposition graphene (p-type) layers on semi-insulating silicon carbide (SiC) substrates, respectively. The graphene layers on SiC are encapsulated and passivated with a thin SiO2 film grown by the Pulsed Electron Deposition method. The measurements conducted for short periods and a few cycles showed that the encapsulation process completely suppresses the time dependent conductivity instability of graphene independent of its charge carrier type. The obtained results are used to construct an experimental model for identifying adsorbate related conductivity variations in graphene and also in other 2D materials with an inherently high surface-to-volume ratio.

Preparation and Characterization of SiO2 Thin Films as an Antireflective Layer

Preparation and Characterization of SiO2 Thin Films as an Antireflective Layer

GaSb基PECVD法制备SiO2薄膜的应力研究

GaSb基PECVD法制备SiO₂薄膜的应力研究

Preparation of metal doped SiO<sub>2</sub> films by magnetron sputtering deposition using metal oxide mixture powder target

Metal doped SiO2 thin films, which show strong luminescence by UV excitation, were prepared by a sputtering deposition method using metal oxide and SiO2 powder mixed targets. Electron density and temperature of the plasma using powder target was almost same independent for the mixture of powder target. However, peak intensity ratio of the plasma depends on the intensity of the powder target mixture. XPS measurements suggest that metal doped SiO2 thin films can be prepared using metal oxide and SiO2 mixture powder target, and their concentration ratio also depend on the powder target mixture.

Effect of oxygen flow rate on microstructure properties of SiO2 thin films prepared by ion beam sputtering

Optical constants and micro-structure characteristics of SiO2 films deposited by ion beam sputtering were studied. The samples were prepared on substrates of silicon and silica with different oxygen flow rates ranged from 0sccm to 40sccm with a step of 10sccm. Refractive index of the samples were obtained by spectra inversion technique. It's suggested that the value of refractive index presents first decrease and then increase as the oxygen flow rate larger, and the turning point is about 30sccm both at 0.633μm and 10.6μm. And the SiO2 thin films were confirmed all amorphous structure by the XRD measurement. The proportion of hydroxyl in SiO2 thin film were determined by XPS, which is beneficial to analyze the film defects. Also the Si-O-Si angle and vibration frequency in TO mode and LO mode were researched by FTIR spectra.

Effect of strain on thermal conductivity of amorphous silicon dioxide thin films: A molecular dynamics study

The effect of strain on thermal conductivity of amorphous SiO2 thin films is simulated by using molecular dynamics simulation (MD). The calculated results indicate that the thermal conductivity decreases monotonically as the strain varies from compression to tension and the thermal conductivity changes with thicknesses and temperatures under applied strain. Phonon density of states of strained thin films is used to explain the phenomena. The results can be potentially used to design the MEMS devices, which work at the enhanced temperature and use the amorphous SiO2 film and other similar thin films.

Amplified emission and modified spectral features in an opal hetero-structure mediated by passive defect mode localization

A photonic crystal hetero-structure consisting of a passive planar defect of SiO2 thin film sandwiched between two identical opals grown by inward growing self-assembly method using Rhodamine-B dye-doped polystyrene microspheres is studied for the characteristics of dye emission. The optical properties and the defect mode characteristics of the hetero-structure are studied from the reflection and transmission measurements. Laser-induced fluorescence from the hetero-structure showed amplified and spectrally narrowed emission compared to the photonic crystal emphasizing the role of the defect mode and distributed feedback. The enhanced emission is also complemented by the reduction in fluorescence decay time in the case of the hetero-structure in comparison to the 3D photonic crystals.

A large-area, wide-incident-angle, and polarization-independent plasmonic color filter for glucose sensing

We develop an effective method for glucose sensing by using a plasmonic color filter (PCF) integrated with a microfluidic chip. The morphology of PCF is composed of hybrid nanopillars fabricated with SiO2 and Au thin-films on silicon substrate. It exhibits angle-independence, polarization-independence and wafer-level fabrication, which are the most important factors for color filters for industrial applications. The shift of resonant wavelength is 56 nm with a stable bandwidth (∼30 nm) by varying concentration of glucose solution. The sensitivity is 157.61 nm/RIU and the corresponding figure-of-merit is 5.25. Such strategy can be exploited to further increase the detection and potentially enter the ultra-strong coupling regime in chemical solution sensors.

Optical constants of SiO2 from 196 to 1688 nm (0.735–6.33 eV) from 20, 40, and 60 nm films of reactively sputtered SiO2 on Eagle XG® glass by spectroscopic ellipsometry

Three thicknesses of reactively sputtered SiO2, nominally 20, 40, and 60 nm, deposited on Corning Eagle XG® (EXG), an important display glass, were analyzed by spectroscopic ellipsometry. Reflection ellipsometry data from the samples were analyzed from 196 to 1688 nm at angles of 55°–60°, inclusive, in 1° increments. These angles were chosen because they bracket the Brewster angles of both EXG glass and SiO2. The backsides of the samples were roughened by sand blasting to suppress backside reflections from the substrates. A total of nine datasets were collected from nine different samples (three for each nominal thickness of SiO2), each at six different angles of incidence (54 spectra). The optical constants for each thickness of SiO2 was determined, as well as a set of constants for all the films (the material in general) via a multisample analysis (MSA). The optical constants of the SiO2 films were modeled using two poles with transparency assumed over the entire spectral range (a Sellmeier model). A Bruggeman effective medium approximation (BEMA) roughness layer was included in the model, which assumed 50/50 volume fractions that corresponded to the modeled SiO2 optical constants and void. The fit did not substantially improve when an interface layer between the Eagle XG® and the sputtered film was included, so it was omitted. Three sets of previously reported optical constants for the substrate over two wavelength ranges were considered in the modeling. The thin SiO2 films analyzed herein have very similar optical properties to those of their EXG substrate—this is a challenging analytical problem involving a transparent film on a transparent substrate. Accordingly, analysis of multiple samples, an MSA that included multiple film thicknesses analyzed at multiple angles, and an exploration of multiple modeling approaches helped ensure that the optical constants reported herein are accurate and the modeling robust. In particular, these measures helped avoid correlation between the optical constants, the layer thicknesses, and the thicknesses of the BEMA layers. Atomic force microscopy roughness measurements were made on the SiO2 films and compared to the roughness values obtained by spectroscopic ellipsometry. In summary, the authors provide here the optical constants and some accompanying physical characterization of sputtered 20–60 nm SiO2 films from 196 to 1688 nm.