Intrinsic Oxide Research Articles

Comparative study on in situ surface cleaning effect of intrinsic oxide-covering GaAs surface using TMA precursor and Al2O3 buffer layer for HfGdO gate dielectrics

In this work, comparative study on the cleaning effect of the intrinsic oxide covering GaAs surface using TMA precursor and Al2O3 buffer layer were performed.

Dissolution and bandgap paradigms for predicting the toxicity of metal oxide nanoparticles in the marine environment: an in vivo study with oyster embryos

Dissolution and bandgap paradigms have been proposed for predicting the ability of metal oxide nanoparticles (NPs) to induce oxidative stress in different in vitro and in vivo models. Here, we addressed the effectiveness of these paradigms in vivo and under conditions typical of the marine environment, a final sink for many NPs released through aquatic systems. We used ZnO and MnO2 NPs as models for dissolution and bandgap paradigms, respectively, and CeO2 NPs to assess reactive oxygen radical (ROS) production via Fenton-like reactions in vivo. Oyster embryos were exposed to 0.5–500 μM of each test NP over 24 h and oxidative stress was determined as a primary toxicity pathway across successive levels of biological complexity, with arrested development as the main pathological outcome. NPs were actively ingested by oyster larvae and entered cells. Dissolution was a viable paradigm for predicting the toxicity of NPs in the marine environment, whereas the surface reactivity based paradigms (i.e. bandgap and ROS generation via Fenton-like reaction) were not supported under seawater conditions. Bio-imaging identified potential cellular storage-disposal sites of solid particles that could ameliorate the toxicological behavior of non-dissolving NPs, whilst abiotic screening of surface reactivity suggested that the adsorption-complexation of surface active sites by seawater ions could provide a valuable hypothesis to explain the quenching of the intrinsic oxidation potential of MnO2 NPs in seawater.

Highly conductive copper films based on submicron copper particles/copper complex inks for printed electronics: Microstructure, resistivity, oxidation resistance, and long-term stability

Submicron Cu particles mixed with Cu complex are used successfully to fabricate highly conductive Cu films for printed electronics. This study investigates the effects of Cu particle size on microstructure, conductivity and on the long-term stability of printed Cu films. In particular, the oxidation behaviors of printed Cu films at high temperatures are studied from the evolutions in microstructure and chemical composition. The submicron Cu particles are sintered efficiently due to the help of in-situ formed Cu nanoparticles from the decomposition of the Cu complex. Low resistivity of 5.8 μΩ cm is easily achieved. At temperatures of 140 °C and 180 °C, the printed Cu films prepared from 800 nm Cu particles are more stable than that from those 350 nm particles, which can be attributed to larger Cu particles possessing higher oxidation resistance. At 220 °C, the result becomes opposite because the loose structure with many large voids in the printed Cu films from large particles provides sufficient space for oxygen and accelerate the break of pathways between adjacent particles by the formation of Cu oxides layers. This indicates the long-term stability of printed Cu films is attributed to not only the intrinsic oxidation of Cu to Cu2O but also the degradation of microstructures. At all events, the printed Cu films from submicron Cu particles with Cu complex exhibit excellent oxidation resistance and are superior to those from Cu nanoparticles. This presents significant potential and favorable prospects for the fabrication of highly reliable and cost-effective printed electronics.

Thermal stability and oxidation resistance of V-alloyed TiAlN coatings

V-containing nitride coatings recently attract a wide range of research interests owing to their excellent tribological properties. To evaluate their comprehensive properties, a comparative study on the intrinsic thermal stability and oxidation resistance of TiAlN and TiAlVN coatings are conducted here. Ti0.56Al0.44N, Ti0.50Al0.44V0.06N, and Ti0.40Al0.50V0.10N coatings, deposited by cathodic arc evaporation, exhibit a single-phase face-centered cubic structure with a hardness of 28.9–29.8GPa. The V-containing coatings show a pronounced age-hardening upon annealing, which contributes to a hardness increase of 3.7 and 4.8GPa at 800°C for Ti0.50Al0.44V0.06N and Ti0.40Al0.50V0.10N, respectively, corresponding to 2.9GPa for Ti0.56Al0.44N. Also, alloying with V retards the formation of wurtzite AlN upon annealing, especially in Ti0.50Al0.44V0.06N, and thus contributes to a higher hardness above 30GPa even annealing at 1100°C, while the hardness of Ti0.56Al0.44N significantly reduces to 27.8 ± 0.6GPa. However, alloying with V into TiAlN leads to an earlier formation of rutile TiO2 and also Ti-rich oxide top-layer on the outside surface instead of dense Al2O3, and thus degrades the oxidation resistance. When exposed to air at 700°C for 10h, the Ti0.50Al0.44V0.06N and Ti0.40Al0.50V0.10N coatings suffer from a severe oxidation, whereas only a compact oxide scale with a thickness of ~ 80nm for Ti0.56Al0.44N is formed.

Hybrid Ag Nanowire–ITO as Transparent Conductive Electrode for Pure Sulfide Kesterite Cu2ZnSnS4 Solar Cells

We present the hybrid silver nanowire network–ultrathin ITO as the transparent conductive electrode for earth-abundant and environmentally friendly pure sulfide Cu2ZnSnS4 solar cells, replacing the scarce and expensive ITO. For this new hybrid transparent electrode, sputtered intrinsic zinc oxide is introduced as an antireflective coating replacing MgF2 in traditional Cu2ZnSnS4 solar cells. Random arrays of silver nanowire network with different densities hybridized with 20 nm ITO layer are employed in Cu2ZnSnS4 devices and their device performance is compared with the reference device with conventional ITO electrode. The devices with the hybrid electrodes with similar sheet resistance to ITO show generally improved current density due to their better optical transparency than ITO while maintaining similar fill factor. Cu2ZnSnS4 devices with low density Ag nanowire hybrid electrode give the highest efficiency of 6.4% on average mainly due to improved current density, among which the highest efficiency va...

Effect of Thermal Conductivity of Catalytic Materials on Soot Sensing Performance Based on a Combustion-type Sensor

Ag-supported HZSM-5 and SiO2 were used as a catalyst for a combustion-type soot senor. Although Ag/HZSM-5 catalyst showed a higher intrinsic soot oxidation activity than that of Ag/SiO2, the soot sensor with Ag/HZSM-5 catalyst exhibited a much lower sensing performance than that with Ag/SiO2. This is because the Ag/HZSM-5 catalyst showed a quite low thermal conductivity, inhibiting the soot oxidation heat from transferring to the Pt detector inside of the sensor element. Therefore, improvement of the soot sensing performance depends on not only the excellent intrinsic soot oxidation activity of the catalyst but also the superior thermal conductivity of catalytic materials.

Towards an optimum silicon heterojunction solar cell configuration for high temperature and high light intensity environment

We report on the performance of Silicon Heterojunction (SHJ) solar cell under high operating temperature and varying irradiance conditions typical to desert environment. In order to define the best solar cell configuration that resist high operating temperature conditions, two different intrinsic passivation layers were tested, namely, an intrinsic amorphous silicon a-SiOx:H with CO2/SiH4 ratio of 0.4 and a-SiOx:H with CO2/SiH4 ratio of 0.8, and the obtained performance were compared with those of a standard SHJ cell configuration having a-Si:H passivation layer. Our results showed how the short circuit current density Jsc, and fill factor FF temperature-dependency are impacted by the cell’s configuration. While the short circuit current density Jsc for cells with a-SiOx:H layers was found to improve as compared with that of standard a-Si:H layer, introducing the intrinsic amorphous silicon oxide (a-SiOx:H) layer with CO2/SiH4 ratio of 0.8 has resulted in a reduction of the FF at room temperature due to hindering the carrier transport by the band structure. Besides, this FF was found to improve as the temperature increases from 15 to 45 °C, thus, a positive FF temperature coefficient.

Recovery of gold from hydrometallurgical leaching solution of electronic waste via spontaneous reduction by polyaniline

The present study is primarily designed to develop an environmentally-benign approach for the recovery of precious metals, especially gold, from the ever increasingly-discarded electronic wastes (e-waste). By coupling the metal reduction process with an increase in the intrinsic oxidation state of the aniline polymers, and the subsequent re-protonation and reduction of the intrinsically oxidized polymer to the protonated emeraldine (EM) salt, polyaniline (PANi) films and polyaniline coated cotton fibers are able to recover metallic gold from acid/halide leaching solutions of electronic wastes spontaneously and sustainably. The current technique, which does not require the use of extensive extracting reagents or external energy input, can recover as much as 90% of gold from the leaching acidic solutions. The regeneration of polyaniline after gold recovery, as confirmed by the X-ray photoelectron spectroscopy measurements, promises the continuous operation using the current approach. The as-recovered elemental gold can be further concentrated and purified by incineration in air.

Superior silicon surface passivation in HIT solar cells by optimizing a-SiOx:H thin films: A compact intrinsic passivation layer

Abstract The microstructure of the intrinsic amorphous silicon oxide (i-a-SiO x :H) thin films is the key for crystalline silicon surface passivation in high-performance HIT solar cells. Understanding and subsequently optimizing the i-a-SiO x :H microstructure is essential in improving defect passivation and carrier transportation in a-SiO x :H films. In this work, we investigate the relationship between the bulk microstructure of i-a-SiO x :H thin films at different oxygen content and the passivation quality of the silicon surface. The results revealed that, as the oxygen content increases, the dominating growth mechanism of i-a-SiO x :H films changes. Consequently, the component contents of i-a-SiO x :H thin films were varied and the microstructure showed a first improved and then deteriorated trend with increasing oxygen content. A compact, less-defective and ordered microstructure of the a-SiO x :H film can only be obtained when there comes a tradeoff between Si O and Si H(Si 3 ) bonding formation. Correspondingly, the improved defect passivation and the enhanced carrier transportation in a-SiO x :H films lead to the increase of V oc , FF and QE of HIT solar cells, all of which are key solar cell performance parameters.

Aluminum Nanocrystals: A Sustainable Substrate for Quantitative SERS-Based DNA Detection.

Since its discovery in the 1970s, surface-enhanced Raman scattering (SERS) has been primarily associated with substrates composed of nanostructured noble metals. Here we investigate chemically synthesized nanocrystal aggregates of aluminum, an inexpensive, highly abundant, and sustainable metal, as SERS substrates. Al nanocrystal aggregates are capable of substantial near-infrared SERS enhancements, similar to Au nanoparticles. The intrinsic nanoscale surface oxide of Al nanocrystals supports molecule-substrate interactions that differ dramatically from noble metal substrates. The preferential affinity of the single-stranded DNA (ssDNA) phosphate backbone for the Al oxide surface preserves both the spectral features and nucleic acid cross sections relative to conventional Raman spectroscopy, enabling quantitative ssDNA detection and analysis.

Electrochemical label-free and sensitive nanobiosensing of DNA hybridization by graphene oxide modified pencil graphite electrode

Based on the strong interaction between single-stranded DNA (ss-DNA) and graphene material, we have constructed a novel label-free electrochemical biosensor for rapid and facile detection of short sequences ss-DNA molecules related to hepatitis C virus 1a using graphene oxide modified pencil graphite electrode. The sensing mechanism is based on the superior adsorption of single-stranded DNA to GO over double stranded DNA (ds-DNA). The intrinsic guanine oxidation signal measured by differential pulse voltammetry (DPV) has been used for duplex DNA formation detection. The probe ss-DNA adsorbs onto the surface of GO via the π– π* stacking interactions leading to a strong background guanine oxidation signal. In the presence of complementary target, formation of helix which has weak binding ability to GO induced ds-DNA to release from the electrode surface and significant variation in differential pulse voltammetric response of guanine bases. The results indicated that the oxidation peak current was proportional to the concentration of complementary strand in the range of 0.1 nM–0.5 μM with a detection limit of 4.3 × 10−11 M. The simple fabricated electrochemical biosensor has high sensitivity, good selectivity, and could be applied as a new platform for a range of target molecules in future.

Role of dual SiOx: H based buffer at the p/i interface on the performance of single junction microcrystalline solar cells

In p-i-n structure a-Si solar cell a buffer layer with proper characteristics plays important role in improving the p/i interface of the cell, reducing mismatch of band gaps and number of recombination centres. However for p-i-n structure microcrystalline ( µc-Si: H) cell which has much less light induced degradation than a-Si:H cell, not much work has been done on development of proper buffer layer and its application to µc-Si:H cell. In this paper we have reported the development of two intrinsic oxide based microcrystalline layer having different characteristics for use as buffer layers at the p/i interface of µc-Si:H cell. Previously SiOx:H buffer layer has been used at the p/i interface which showed positive effects. To explore the possibility of improving the performance of p-i-n structure µc-Si:H cell further we have thought it interesting to use two buffer layers with different characteristics at the p/i interface. The two buffer layers have been characterized in detail and applied at the p/i interface of the µc-Si:H cell with positive effects on all the PV parameters mainly improves the open circuit voltage (Voc) and enhances short circuit current (Isc). The maximum initial efficiency obtained is 8.97% with dual buffer which is 6.7% higher than that obtained by using conventional single buffer layer at the p/i interface. Stabilized efficiency of the cell with dual buffer is found to be ~9.5% higher than that with single buffer after 600h of light soakings.

Effects of epitaxial growth on the optimum condition of intrinsic amorphous silicon oxide buffer layers for silicon heterojunction solar cells

Intrinsic amorphous silicon oxide (a-Si1−xOx:H) buffer layers were deposited on both sides of crystalline silicon (c-Si) wafers using plasma-enhanced chemical vapor deposition (PECVD) technique. The input gas flow ratio of carbon dioxide (CO2) to silane (SiH4) was varied in a wide range to study the passivation and structural properties of the a-Si1−xOx:H buffer layers. In this work, when the a-Si1−xOx:H layer was quite thick (>15nm), an extremely high effective lifetime of ~10ms was achieved on the n-type float-zone c-Si (~3Ω-cm, ~280μm) at moderate CO2/SiH4 flow ratios, resulting in an exceptionally low surface recombination velocity (<1.4cm/s). However, when CO2/SiH4 flow ratio was either rather low (<0.13) or extremely high (>0.47), the surface passivation quality would deteriorate significantly. In addition, a certain amount of epitaxial phase (epi-Si) was observed in some excellent buffer layers made at the moderate CO2/SiH4 ratios. Moreover, it was found that the epi-Si content could be gradually suppressed by slightly increasing the CO2/SiH4 ratio without affecting passivation quality. When the a-Si1−xOx:H buffer layer thickness was kept at only a few nanometers as required by silicon heterojunction (SHJ) solar cells, the PECVD optimum condition (CO2/SiH4 ratio) for buffer layers was revealed by applying the a-Si1−xOx:H buffer layers directly in a practical SHJ solar cell. We found that when the a-Si1−xOx:H buffer layer containing a certain amount (~22%) of epi-Si was employed at the back-surface-field side of the solar cell, a high open-circuit voltage (VOC) and a high fill factor (FF) were obtained at the same time. By contrast, at the emitter side of the solar cell, only the buffer layer without any epi-Si can be used to provide high-quality surface passivation for an excellent SHJ solar cell.

Predicting the Conversion Efficiencies of Any Coal Type in CFBCs

This study uses simulations with detailed chemistry to characterize the conversion of the various fuel components—noncondensable gas mixtures, soot, char fines, and coarse char—and to identify the factors that determine unburned carbon emissions (a.k.a. LOI) from CFBCs. It covers virtually the entire operating domain for commercial CFBCs with 20 test cases in 11 full-scale CFBCs for a range of coal quality from brown coals through anthracite. Soot burnout was complete for all cases except one. LOI was entirely determined by incomplete burnout of coarse char particles, except that an anthracite produced fines that burned slower than coarse char. Simulations for a Chinese CFBC accurately depicted how hotter furnace temperatures and load variations affect LOI. The intrinsic char oxidation reactivity determines whether or not char fines and coarse char can effectively compete with noncondensable fuel mixtures for the available O2 at lower elevations, and thereby influence NO production. More reactive chars co...

An intrinsic amorphous silicon oxide and amorphous silicon stack passivation layer for crystalline silicon heterojunction solar cells

Intrinsic amorphous silicon oxide (i-a-SiO:H) films were used as passivation layers in crystalline silicon heterojunction (c-Si-HJ) solar cells. The effective lifetime (τeff) and photovoltaic (PV) parameters were improved by controlling the CO2/SiH4 ratio in the i-a-SiO:H rear passivation layer. The enhancement of the open circuit voltage (Voc) and solar cell efficiency (η) caused by the i-a-SiO:H/i-a-Si:H stack passivation layer was investigated. The c-Si-HJ solar cells using an i-a-SiO:H/i-a-Si:H stack passivation layer showed a high Voc and η compared to using a conventional i-a-SiO:H passivation layer. The highest efficiency obtained for a c-Si-HJ solar cell using an i-a-SiO:H/i-a-Si:H stack passivation layer was 19.4% (Voc=715mV, Jsc=34.9mA/cm2, FF=0.78).

Hot Hole Enhanced Synergistic Catalytic Oxidation on Pt‐Cu Alloy Clusters

Hot holes in Pt-Cu alloy clusters can act as catalyst to accelerate the intrinsic aerobic oxidation reactions. It is described that under visible light irradiation the synergistic alcohol catalytic oxidation on Pt-Cu alloy clusters (≈1.1 nm)/TiO2 nanobelts could be significant promoted by interband-excitation-generated long-lifetime hot holes in the clusters.

Microwave-Assisted Synthesis of NaCoPO4 Red-Phase and Initial Characterization as High Voltage Cathode for Sodium-Ion Batteries.

Transition metal-containing polyanion compounds are attractive for use as cathode materials in sodium-ion batteries (SIB) because they possess elevated higher intrinsic electrochemical potentials versus oxide analogs given the same Mn+/(n+1)+ redox couple, which leads to higher energy densities. NaMPO4 (M = transition metal) compounds have a driving force to form into the electrochemically inactive maricite phase when using conventional methods. Herein we report on the synthesis of a NaCoPO4 (NCP) polymorph ("Red"-phase) by a microwave-assisted solvothermal process at 200 °C using tetraethylene glycol as the solvent. Ex situ XRD, XANES, and electrochemical data are used to determine the reversibility of the Co2+/3+ redox center.

Wide gap microcrystalline silicon carbide emitter for amorphous silicon oxide passivated heterojunction solar cells

Wide gap n-type microcrystalline silicon carbide [µc-SiC:H(n)] is highly suitable as window layer material for silicon heterojunction (SHJ) solar cells due to its high optical transparency combined with high electrical conductivity. However, the hot wire chemical vapor deposition (HWCVD) of highly crystalline µc-SiC:H(n) requires a high hydrogen radical density in the gas phase that gives rise to strong deterioration of the intrinsic amorphous silicon oxide [a-SiOx:H(i)] surface passivation. Introducing an n-type microcrystalline silicon oxide [µc-SiOx:H(n)] protection layer between the µc-SiC:H(n) and the a-SiOx:H(i) prevents the deterioration of the passivation by providing an etch resistance and by blocking the diffusion of hydrogen radicals. We fabricated solar cells with µc-SiC:H(n)/µc-SiOx:H(n)/a-SiOx:H(i) stack for the front side and varied the µc-SiOx:H(n) material properties by changing the microstructure of the µc-SiOx:H(n) to evaluate the potential of such stack implemented in SHJ solar cells and to identify the limiting parameters of the protection layer in the device. With this approach we achieved a maximum open circuit voltage of 677 mV and a maximum energy conversion efficiency of 18.9% for a planar solar cell.

Leakage current conduction, hole injection, and time-dependent dielectric breakdown of n-4H-SiC MOS capacitors during positive bias temperature stress

The conduction mechanism(s) of gate leakage current JG through thermally grown silicon dioxide (SiO2) films on the silicon (Si) face of n-type 4H-silicon carbide (4H-SiC) has been studied in detail under positive gate bias. It was observed that at an oxide field above 5 MV/cm, the leakage current measured up to 303 °C can be explained by Fowler-Nordheim (FN) tunneling of electrons from the accumulated n-4H-SiC and Poole-Frenkel (PF) emission of trapped electrons from the localized neutral traps located at ≈2.5 eV below the SiO2 conduction band. However, the PF emission current IPF dominates the FN electron tunneling current IFN at oxide electric fields Eox between 5 and 10 MV/cm and in the temperature ranging from 31 to 303 °C. In addition, we have presented a comprehensive analysis of injection of holes and their subsequent trapping into as-grown oxide traps eventually leading to time-dependent dielectric breakdown during electron injection under positive bias temperature stress (PBTS) in n-4H-SiC metal-oxide-silicon carbide structures. Holes were generated in the heavily doped n-type polycrystalline silicon (n+-polySi) gate (anode) as well as in the oxide bulk via band-to-band ionization by the hot-electrons depending on their energy and SiO2 film thickness at Eox between 6 and 10 MV/cm (prior to the intrinsic oxide breakdown field). Transport of hot electrons emitted via both FN and PF mechanisms was taken into account. On the premise of the hole-induced oxide breakdown model, the time- and charge-to-breakdown (tBD and QBD) of 8.5 to 47 nm-thick SiO2 films on n-4H-SiC were estimated at a wide range of temperatures. tBD follows the Arrhenius law with activation energies varying inversely with initial applied constant field Eox supporting the reciprocal field (1/E) model of breakdown irrespective of SiO2 film thicknesses. We obtained an excellent margin (6.66 to 6.33 MV/cm at 31 °C and 5.11 to 4.55 MV/cm at 303 °C) of normal operating field for a 10-year projected lifetime of 8.5 to 47 nm-thick SiO2 films on n-4H-SiC under positive bias on the n+-polySi gate. Furthermore, the projected maximum operating oxide field was little higher in metal gate devices compared to n+-polySi gate devices having an identically thick thermal SiO2 films under PBTS.

DNA-wrapped multi-walled carbon nanotube modified electrochemical biosensor for the detection of Escherichia coli from real samples

This paper introduces DNA-wrapped multi-walled carbon nanotube (MWCNT)-modified genosensor for the detection of Escherichia coli (E. coli) from polymerase chain reaction (PCR)-amplified real samples while Staphylococcus aureus (S. aureus) was used to investigate the selectivity of the biosensor. The capture probe specifically recognizing E. coli DNA and it was firstly interacted with MWCNTs for wrapping of single-stranded DNA (ssDNA) onto the nanomaterial. DNA-wrapped MWCNTs were then immobilised on the surface of disposable pencil graphite electrode (PGE) for the detection of DNA hybridization. Electrochemical behaviors of the modified PGEs were investigated using Raman spectroscopy and differential pulse voltammetry (DPV). The sequence selective DNA hybridization was determined and evaluated by changes in the intrinsic guanine oxidation signal at about 1.0V by DPV. Numerous factors affecting the hybridization were optimized such as target concentration, hybridization time, etc. The designed DNA sensor can well detect E. coli DNA in 20min detection time with 0.5pmole of detection limit in 30µL of sample volume.