Thin Silicon Oxide Layer Research Articles

A Unique System for Registering One‐Photon Signals in the Ultraviolet Range from An Isomeric 229mTh Nucleus Implanted on Thin SiO2/Si Films

Currently, an urgent task related to creating a nuclear frequency standard is the identification of a low‐lying nuclear state in the thorium‐229 isotope. Herein, a method for measuring the single‐photon energy during the decay of an isomeric thorium‐229 nucleus implanted in a wide‐gap dielectric SiO2 (Eg = 9 eV) is developed. The proposed method utilizes thin silicon oxide layers obtained by thermal oxidization of the pure silica wafers, which allows measurement of the energy of photons in the ultraviolet (UV) range using an electronic spectrometer. The modeling study of electronic state excitation is provided via UV radiation from Kr, Xe, and D resonance discharging lamps. The obtained spectra are analyzed, and a method for determining the UV photon's energy is proposed.

Nanowire reconfigurable FET as biosensor: Based on dielectric modulation approach

In this paper, we have developed analytical surface potential and threshold voltage model of nanowire reconfigurable Field Effect Transistor (FET) which acts as a biosensor to detect the biomolecules, based on dielectric modulation approach. Due to its reconfigurable behavior, it acts as both p-type and n-type depending on the polarity of the biasing and hence find wide spread applications in the field of Programmable Logic Arrays (PLAs). The same is employed here as a bio sensor device with split gates and a cavity for biomolecules immobilization on a thin layer of silicon dioxide as adhesive layer. When the biosensor interacts with the bio targets of the cavity, the electrostatic properties of the device including variation in potential profile and threshold voltage shift get affected and thus have been identified as detection metric in this present work. The characteristic trends of the biosensor are studied with varying height, dielectric constant and charge of the bio-species as polarity of the applied biases change. In addition to this, sensitivity of nanowire RFET is analyzed by assessing the threshold voltage variation which is further compared with equivalent MOSFET biosensor. All the analytical results obtained are corroborated with technology computer-aided-design (TCAD) simulation data to verify the precision of our model.

Extending the operational frequency range of high B – FeSiBP amorphous alloy to GHz by coating the powder surface with silicon oxide

Abstract We report on the fabrication, and magnetic properties of high saturation magnetic flux density (Bs) Fe76Si9B10P5 glassy alloy powder cores in which powder particles were electrically insulated by a thin layer of silicon oxide. Glassy Fe76Si9B10P5 alloy powders produced by the gas atomization technique were treated with silane coupling agent, which forms a thin silicone oxide layer on the powder surface. Toroidal shaped cores were prepared by spark plasma sintering (SPS) technique. Magnetization measurements revealed a slight decrease in the saturation magnetization from 164 emu/g (as prepared powders) to 161 emu/g after surface coating. We show that the powder surface coating is effective for decreasing the core loss at higher frequencies by suppressing the interparticle eddy currents. It is possible to have a high constant initial permeability (μi) of ~28 up to ~1.5 GHz by mixing with a small amount of resin. The constant permeability range can be extended to more than 3 GHz by completely insulating the powders electrically. Our results suggest that the metallic powder cores, which have the advantage of operating at higher Bs compared to ferrites can be used in the GHz frequency range by decreasing the powder particle size and electrically insulating the powders by coating their surface properly.

Ti3C2Tx (MXene)‐Silicon Heterojunction for Efficient Photovoltaic Cells

AbstractA novel type of solar cell has been developed based on charge separation at the heterojunction formed by a transparent conducting MXene electrode and an n‐type silicon (n‐Si) wafer. A thin layer of the native silicon dioxide plays an important role in suppressing the recombination of charge carriers. A two‐step chemical treatment can increase the device efficiency by about 40%. Promisingly, an average power conversion efficiency of over 10% under simulated full sunlight is achieved for this novel class of solar cell with the application of an antireflection layer. The efficiencies of these novel solar cells based on a MXene‐Si heterojunction achieved in this work point to great promise in emerging photovoltaic technology. In addition to their high efficiency, the excellent reproducibility of such devices establishes a solid base for possible future commercialization.

Surface passivation of crystalline silicon solar cells: Present and future

In the first part of this paper, we review the developments which led to the present state-of-the-art in the surface passivation of today's industrially predominant dopant-diffused crystalline silicon (c-Si) solar cells, based on dielectric layers such as silicon oxide, silicon nitride, aluminum oxide and stacks thereof. In the second part of this review, we focus on the future developments in the field of c-Si solar cells based on carrier-selective passivation layers. Whereas the dielectric layers are insulating and are hence applied only for passivating the non-contacted areas of the silicon surface, the carrier-selective passivation layers are intended to provide an effective passivation of non-contacted as well as contacted areas of a c-Si solar cell, thereby increasing the efficiency potential of c-Si solar cells significantly. Due to the fact that the carrier-selective layers are implemented in a contact, besides the good passivation properties for minorities, these layers must also provide a good majority carrier transport, i.e. they have to provide a low contact resistance. Both properties, i.e. suppression of minority-carrier recombination as well as good majority-carrier transport, define the selectivity of the carrier-selective contact, which is an important figure of merit for the assessment and comparison of different types of carrier-selective contacts. One very promising type of carrier-selective passivation layer is based on heavily doped polycrystalline silicon layers deposited on a thin silicon oxide layer, the latter providing the excellent passivation while enabling efficient majority-carrier transport via pin-holes and/or tunneling. Moreover, we discuss metal oxides and conductive polymers, which have only recently been applied to c-Si photovoltaics, but seem to have a promising potential as low-cost selective contact materials. We finally compare combinations of the various options of carrier-selective layers concerning their combined selectivities and efficiency potentials.

Evaluating the impact of thermal annealing on c-Si/Al2O3 interface: Correlating electronic properties to infrared absorption

Al2O3 is the standard for the passivation of p-type PERC (Passivated Emitter Rear Contact) solar cells. It is well established that the thin interfacial silicon oxide layer in between Al2O3 and c-Si plays a key role in its surface passivation mechanism. In this work, we investigate the interface properties of c-Si/Al2O3 by non-destructive methods. We show that Brewster angle Fourier transform infrared spectroscopy has a remarkable sensitivity to the interfacial silicon oxide layer by exploiting the large cross-section of the longitudinal-optic mode. These measurements show that the interfacial SiOx layer increases in atomic density for higher annealing temperatures which coincide with an increase in negative fixed charge density (Qf) determined from contactless capacitance-voltage measurements. X-ray photoelectron spectroscopy results show a decrease of [OH] at higher annealing temperatures which could be correlated to denser SiOx increasing Qf. This work provides insight into the impact of thermal annealing on the Al2O3/c-Si interface.

Simple mechanics model and Hertzian ring crack initiation strength characteristics of silicon nitride ceramic ball subjected to thermal shock

This study investigated the ring crack initiation strength characteristics of silicon nitride ceramic balls subjected to thermal shock. Sphere indentation tests were conducted on ceramic balls following water quenching and furnace cooling operations performed in air and vacuum. The ring crack radius was significantly smaller because of the very thin silicon oxide (SiO2) layer formed owing to heat treatment in air at high temperatures. In addition, the ring crack initiation load and Weibull shape parameter of water-quenched ceramic balls decreased with increasing temperature difference and remained relatively unaffected by the high-temperature oxidation. This phenomenon was mainly due to microscopic damage, which occurs near the surface of ceramic balls, caused by transient thermal stress developed during water quenching. A simple mechanics model based on the constant energy release rate criterion has been proposed for comparing experimental results obtained in this study against theoretical predictions, and results of the said comparison adequately verify strength characteristics of the aforementioned ceramic balls subjected to thermal shock.

Scanning Electron Microscopy (SEM) Energy Dispersive X-ray Spectroscopy (EDS) Mapping and In-situ Observation of Carbonization of Culms of Bambusa Multiplex.

Green culms of bamboo and charcoal of Bambusa multiplex were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) mapping. A dynamic observation of the initial stage of carbonization was also performed in-situ by heating a radial longitudinal section of the bamboo culm at a rate of 20°C/min up to 500°C. EDS mapping of the green bamboo culms detected Si signals in the harder cells such as the epidermis (Ep), cortex (Cor) and vascular bundle sheath (Bs) and between these cells as silicon oxide particles. Appreciable morphological change of the cells occurred in a temperature range of about 300-400°C due to the decomposition of cellulose that is the main component of the bamboo cells. The charcoal of the bamboo culm has a skin layer which originates from the Ep and Cor and the main central cylinder with many openings that originate from the expanded xylem and phloem holes. During carbonization, the Si atoms in the Ep and Cor were segregated as thin silicon oxide layers onto both the sides of the skin layer and the Si included in the Bs fibers and parenchyma cells accumulated near the walls of the openings.

Experimental studies of thorium ion implantation from pulse laser plasma into thin silicon oxide layers

We report the results of experimental studies related to implantation of thorium ions into thin silicon dioxide by pulsed plasma flux expansion. Thorium ions were generated by laser ablation from a metal target, and the ionic component of the laser plasma was accelerated in an electric field created by the potential difference (5, 10 and 15 kV) between the ablated target and a SiO2/Si (0 0 1) sample. The laser ablation system installed inside the vacuum chamber of the electron spectrometer was equipped with a YAG:Nd3 + laser having a pulse energy of 100 mJ and time duration of 15 ns in the Q-switched regime. The depth profile of thorium atoms implanted into the 10 nm thick subsurface areas together with their chemical state as well as the band gap of the modified silicon oxide at different conditions of implantation processes were studied by means of x-ray photoelectron spectroscopy and reflected electron energy loss spectroscopy methods. Analysis of the chemical composition showed that the modified silicon oxide film contains complex thorium silicates. Depending on the local concentration of thorium atoms, the experimentally established band gaps were located in the range 6.0–9.0 eV. Theoretical studies of the optical properties of the SiO2 and ThO2 crystalline systems were performed by ab initio calculations within hybrid functional. The optical properties of the SiO2/ThO2 composite were interpreted on the basis of the Bruggeman effective medium approximation. A quantitative assessment of the yield of isomeric nuclei in ‘hot’ laser plasma at the early stages of expansion was performed. The estimates made with experimental results demonstrated that the laser implantation of thorium ions into the SiO2 matrix can be useful for further research of low-lying isomeric transitions in a 229Th isotope with energy of 7.8 0.5 eV.

Bio-catalytic mesoporous Janus nano-motors powered by catalase enzyme

Enzyme triggered bio-catalytic reactions convert chemical energy into mechanical force to power micro/nano-machines. Though there have been reports about enzymes powered micro/nano-motors, enzymatic Janus nano-motor smaller than 100 nm has not been reported yet. Here, we prepared an enzyme powered Janus nano-motor by half-capping a thin layer of silicon dioxide (4 nm SiO2) onto a mesoporous silica nanoparticle (MSNP) of 90 nm, enabling asymmetry to the nano-architecture. The nano-motors are chemically powered by the decomposition of H2O2 triggered by the enzyme catalase located at one face of the nanoparticles. The self-propulsion is characterized by dynamic light scattering (DLS) and optical microscopy. The apparent diffusion coefficient was enhanced by 150% compared to their Brownian motion at low H2O2 concentration (i.e. below 3 wt%). Mesoporous nano-motors might serve as active drug delivery nano-systems in future biomedical applications such as intracellular drug delivery.

Focused ion beam-assisted fabrication of soft high-aspect ratio silicon nanowire atomic force microscopy probes

In this study, high-aspect ratio silicon nanowire (SiNW) – modified atomic force microscopy (AFM) probes are fabricated using focused ion beam (FIB) microfabrication technology and vapor-solid-solid synthesis. Commercially available soft silicon nitride probes are used for localized nanowire growth yielding soft high-aspect ratio AFM probes. The SiNW-modified cantilevers are used here for imaging in PeakForce Tappingۛ (PFT) mode, which offers high force control along with valuable information about tip-sample adhesion. A platinum catalyst, deposited accurately at a truncated AFM tip by ion beam-induced deposition (IBID), was used for localized nanowire synthesis. It could be shown that the deposition of a thin silicon dioxide layer prior to the catalyst deposition resulted in controlled SiNW growth on silicon as well as silicon nitride probes. In addition, a FIB-based method for post-growth alignment of the fabricated SiNW tips is presented, which allows tilt-compensation specifically tailored to the specifications of the used AFM instrumentation. To demonstrate the capability of such soft, high-aspect ratio AFM probes, optical gratings fabricated in GaAs and silver halide fibers were imaged in PFT mode. Additionally, the mechanical stability of these high-aspect AFM probes was evaluated on a sapphire substrate.

Silicon-Rich Silicon Carbide Hole-Selective Rear Contacts for Crystalline-Silicon-Based Solar Cells.

The use of passivating contacts compatible with typical homojunction thermal processes is one of the most promising approaches to realizing high-efficiency silicon solar cells. In this work, we investigate an alternative rear-passivating contact targeting facile implementation to industrial p-type solar cells. The contact structure consists of a chemically grown thin silicon oxide layer, which is capped with a boron-doped silicon-rich silicon carbide [SiCx(p)] layer and then annealed at 800-900 °C. Transmission electron microscopy reveals that the thin chemical oxide layer disappears upon thermal annealing up to 900 °C, leading to degraded surface passivation. We interpret this in terms of a chemical reaction between carbon atoms in the SiCx(p) layer and the adjacent chemical oxide layer. To prevent this reaction, an intrinsic silicon interlayer was introduced between the chemical oxide and the SiCx(p) layer. We show that this intrinsic silicon interlayer is beneficial for surface passivation. Optimized passivation is obtained with a 10-nm-thick intrinsic silicon interlayer, yielding an emitter saturation current density of 17 fA cm-2 on p-type wafers, which translates into an implied open-circuit voltage of 708 mV. The potential of the developed contact at the rear side is further investigated by realizing a proof-of-concept hybrid solar cell, featuring a heterojunction front-side contact made of intrinsic amorphous silicon and phosphorus-doped amorphous silicon. Even though the presented cells are limited by front-side reflection and front-side parasitic absorption, the obtained cell with a Voc of 694.7 mV, a FF of 79.1%, and an efficiency of 20.44% demonstrates the potential of the p+/p-wafer full-side-passivated rear-side scheme shown here.

Beam reconfigurable antenna for the THz band based on a graphene high impedance surface

In this paper a reconfigurable beam antenna is proposed for THz applications, based on a switchable Graphene High Impedance Surface (G-HIS) that acts as a reflector for a primary radiator. The Graphene-HIS structure composed of two layers of graphene cells arranged in a 5×5 array, the two planes of the array are separated by a thin silicon oxide layer; patches in the same row are connected together, to be biased by a common DC voltage to the entire row; this gives the ability to control the graphene conductivity σ. The results show that the shape of the radiation pattern can be changed by changing the voltage applied to each row of G-HIS array. The antenna was fabricated and characterized using a THz-TDS laser system. Measurements are in good agreement with simulations as far as the graphene surface impedance and the resonance frequency are concerned. The scanning reflection on the antenna surface due to the change on the applied voltage is presented to show the effect of biased graphene layer on the dipole properties.

Retention in Porous Layer Pillar Array Planar Separation Platforms.

This work presents the retention capabilities and surface area enhancement of highly ordered, high-aspect-ratio, open-platform, two-dimensional (2D) pillar arrays when coated with a thin layer of porous silicon oxide (PSO). Photolithographically prepared pillar arrays were coated with 50-250 nm of PSO via plasma-enhanced chemical vapor deposition and then functionalized with either octadecyltrichlorosilane or n-butyldimethylchlorosilane. Theoretical calculations indicate that a 50 nm layer of PSO increases the surface area of a pillar nearly 120-fold. Retention capabilities were tested by observing capillary-action-driven development under various conditions, as well as by running one-dimensional separations on varying thicknesses of PSO. Increasing the thickness of PSO on an array clearly resulted in greater retention of the analyte(s) in question in both experiments. In culmination, a two-dimensional separation of fluorescently derivatized amines was performed to further demonstrate the capabilities of these fabricated platforms.

Reversible Na-Ion Uptake in Si Nanoparticles

Na ion batteries attract significant research interest since they provide potentially high energy density while using low cost and abundant sodium as the active ion. Si has been extensively investigated for its operation as anode in lithium based batteries since it has a high theoretical lithiation capacity up to Li4.4Si. However, the sodium analogue with successful reversible electrochemical sodiation of Si has not been reported yet. Si sodiation is anticipated to be different with respect to phase behaviour, insertion voltages and kinetic barriers when compared to Li ion, for instance because of the difference in ionic radius of Na+ (0.97 Å) and Li+(0.68 Å). From thermal synthesis of Na-Si materials it is known that NaSi is the most Na rich phase for Na-Si binary compounds, which would enable a sizeable capacity of 954 mAh/g. Anticipating that nanoscaling is of advantage for the kinetics of ion insertion and extraction, we studied Si particles with much reduced size (~ 20 nm) containing a large fraction of amorphous Si. The nano particles were obtained from Expanding Thermal Plasma Chemical Vapour Deposition (ETPCVD) of silane. The materials consist of aggregated individual nano particles with a very thin silicon oxide layer that forms after contact with air. The work presented here reports, to our knowledge for the first time, reversible electrochemical Na ion uptake in these Si based materials for a significant capacity. The desodiation capacity is stable around 260 mAh/g, while the initial sodiation shows a large irreversible Na loss attributed to SEI formation. The experiments show that during Na insertion a two phase equilibrium may be present between NaSi and Si: x Na + Si -> x NaSi + (1-x) Si, where the NaSi becomes amorphous. For desodiation a sloping voltage profile is observed indicative of a solid solution behaviour. Therefore we propose that desodiation occurs as NaSi -> Na1-xSi + x Na, where the Na1-xSi phase remains amorphous. After 100 cycles all Si has been transformed to amorphous phases, and no crystalline nano Si particles remain. In conclusion, nanoparticles containing both amorphous and crystalline Si, produced by ETPCVD, demonstrate an excellent reversible capacity of 279 mAh/g for Si at 10 mA/g and a capacity retention of 248 mA/g after 100 cycles at 20 mA/g. Significant reversible capacities can be achieved at high dis-/charge rates as well. Nanoscaling benefits the Na insertion and extraction kinetics in Si although reversible Na uptake and release for the full theoretical capacity has not been reached. Initial amorphous and crystalline Si are performing an equally active role in the electrochemical sodiation. Coexistence of Si and NaSi may occur during Na insertion into amorphous Si and on the surface of the Si crystallites; while a solid solution desodiation reaction is evidenced when Na is being extracted. Y. Xu, E. Swaans, S. Basak, H. W. Zandbergen, D. M. Borsa, F. M. Mulder, Adv. Energy Mater. 2015, doi 10.1002/aenm.201501436 early view Figure 1

Photoluminescent polysaccharide-coated germanium(IV) oxide nanoparticles

In current biomedically oriented research, the development of a biomimetic nanoparticle platform is of interest to provide a molecular toolbox (i.e., allowing easy modular exchange of its parts depending on actual needs while being nontoxic and allowing real-time recognition and tracking using various methods, such as fluorescence). We report the development of germanium(IV) oxide-polysaccharide composite particles possessing these properties. The nanoparticles are based on a crystalline germanium oxide core with a size range of 20–30 and 300–900 nm. Two new simple coating techniques were compared for the preparation of the photoluminescent polysaccharide-coated germanium(IV) oxide nanoparticles. The germanium(IV)-based core allows for in situ polysaccharide attachment via direct chelation. In addition, the nanoparticles were coated with thin layer of silicon oxide. After coating, 3-(triethoxysilyl)propyl isocyanate was grafted onto the surface, and the polysaccharides were immobilized on the particle surface via a covalent urethane linkage, which allows for an even more stable polysaccharide coating than that obtained via chelation. This approach provides access to a new material platform for biological track and image applications.

Ultrathin Titanium Dioxide Nanolayers by Atomic Layer Deposition for Surface Passivation of Crystalline Silicon

We demonstrate a low surface recombination velocity of 14 cm/s with only 1.5 nm thin titanium dioxide (TiO2 ) layers on undiffused 10 Ωcm p-type crystalline silicon. The TiO2 nanolayers were deposited by thermal atomic layer deposition at 150 °C and 200 °C substrate temperatures using tetrakis-dimethyl-amido titanium as the Ti precursor and water as the oxidant. The influence of a post-deposition anneal in forming gas at different temperatures was investigated. We have observed that a subsequent anneal in forming gas at 350 °C enhances the surface passivation quality of the TiO2 layers tremendously. Increasing the thickness of the TiO2 layers leads to a reduction of the surface passivation quality. Introducing a thin interfacial layer of silicon oxide (1.6 nm) grown by rapid thermal oxidation underneath the TiO2 layer improves the surface passivation of thicker TiO2 layers (5.5 and 15 nm). These results show that ultrathin TiO2 layers with a thickness of only 1.5 nm can be used to effectively passivate the c-Si surface.

Spin-Relaxation Dynamics ofE′Centers at High Density inSiO2Thin Films for Single-Spin Tunneling Force Microscopy

Methods for the creation of thin amorphous silicon dioxide (aSiO2) layers on crystalline silicon substrates with very high densities of silicon dangling bonds (so called E' centers) have been explored and volume densities of [E']> 5x10^18 cm-3 throughout a 60nm thick film have been demonstrated by exposure of a thermal oxide layer to a low pressure Argon radio frequency plasma. While the generated high E' center densities can be annealed completely at 300C, they are comparatively stable at room temperature with a half life of about one month. Spin relaxation time measurements of these states between T = 5K and T = 70K show that the phase relaxation time T2 does not strongly depend on temperature and compared to SiO2 films of lower E' density, is significantly shortened. The longitudinal relaxation time T1 ~195(5)us at room temperature is in agreement with low-density SiO2. In contrast, T1 ~625(51)us at T = 5K is much shorter than in films of lower E' density. These results are discussed in the context of E' centers being used as probe spins for spin-selection rules based single spin-readout.

Manipulation of stored charge density and polarity in anodic aluminium oxide for silicon solar cell passivation

This paper introduces a method to manipulate stored charge density and polarity in anodic aluminium oxide (AAO) for silicon solar cell passivation. The method involves the use of a pulse current source to anodise aluminium layers instead of the typically used constant current/voltage source, with the test structures experiencing positive and negative cycles periodically. By tuning the positive cycle percentage, it is demonstrated that the effective stored charge can be manipulated in a range from -5.2×1011 to 2.5×1012 q/cm2 when the AAO is formed over a thin silicon dioxide layer. Photoconductance decay measurements on symmetrical n-type test structures with ∼ 150Ω/□ boron-diffused surfaces were used to estimate the recombination current density associated with the diffused surface (Jop+), which was then correlated to the stored charge. As the effective stored charge changed from positive towards negative values, the Jop+ was reduced from 210 fA/cm2 to 100 fA/cm2. The stored charge in various test structures was monitored constantly to study the stability. It was found that the positive stored charge deteriorated with time while the negative charge was relatively stable.

Ultra-thin Tunnel Oxides Formed by Field-induced Anodisation for Carrier-selective Contacts

Tunnel oxides for carrier-selective contacts must be sufficiently thin that carriers can tunnel through the oxide whilst minimising recombination at the silicon interface if high open circuit voltages are to be achieved. We report the formation of ultra-thin silicon oxide layers by a field-induced anodisation process in which the anodisation current is directed through the wafer in such a way that very uniform oxides can be grown. Spectroscopic analyses of these thin silicon oxide layers demonstrate the ability to adjust their atomic density and valence band offset by varying the anodisation conditions, suggesting that anodisation may provide a viable method to form tuneable silicon oxide layers for carrier selectivity.