Cathodic Tb(III) chelate electrochemiluminescence at oxide-covered magnesium and n-ZnO:Al/MgO composite electrodes

Some of the luminescent aromatic Tb(III) chelates can be excited at oxide-covered magnesium and n-ZnO:Al/MgO composite electrodes by cathodic pulse polarization in aqueous solution. This is based on the cathodic injection of hot electrons into the aqueous electrolyte solution and successive redox reactions in one-electron steps resulting in the excited states of the chelates. Due to the relatively long luminescence lifetime of multidentate Tb(III) chelates, these chelates can be very sensitively detected by time-resolved electrochemiluminescence (TR-ECL) measurements using the present working electrodes. Thus, metal or highly doped semiconductor electrodes coated by a thin MgO film lend themselves as nontransparent or in some cases, even optically transparent working electrodes for generation of free radicals and cathodic ECL in aqueous solution. The results suggest that also other even more efficient optically transparent composite tunnel emission electrodes than the present n-ZnO:Al/MgO electrodes could be constructed by coating n-ZnO:Al glass electrodes with other wide band gap insulating oxides.     

Crystallization of amorphous silicon thin films deposited by PECVD on nickel-metalized porous silicon

ABSTRACT: Porous silicon layers were elaborated by electrochemical etching of heavily doped p-type silicon substrates. Metallization of porous silicon was carried out by immersion of substrates in diluted aqueous solution of nickel. Amorphous silicon thin films were deposited by plasma-enhanced chemical vapor deposition on metalized porous layers. Deposited amorphous thin films were crystallized under vacuum at 750 [DEGREE SIGN]C. Obtained results from structural, optical, and electrical characterizations show that thermal annealing of amorphous silicon deposited on Ni-metalized porous silicon leads to an enhancement in the crystalline quality and physical properties of the silicon thin films. The improvement in the quality of the film is due to the crystallization of the amorphous film during annealing. This simple and easy method can be used to produce silicon thin films with high quality suitable for thin film solar cell applications.     

Influence of water vapour on high-temperature oxidation of Al2O3-MgO-doped hot-pressed silicon nitride

Silicon nitride is particularly sensitive to high-temperature oxidation. The intensity of oxidation is influenced by the chemical composition of the amorphous phases present at the grain boundaries and consequently by the sintering additives responsible for their formation. The presence of water vapour increases Si₃N₄ oxidation also in intermediate temperature conditions. In this study the influence of water vapour pressure at high temperature (1200°C) on the corrosion of hot-pressed silicon nitride (HPSN) doped with Al₂O₃-MgO was evaluated. The water vapour has a great influence on the devitrification of the amorphous oxide upper layer, due to the formation of crystalline oxides (primarily cristobalite and tridymite). This process increases the oxidation rate, consequently increasing the porosity of the exposed surface. The microstructural evolution of HPSN in the presence of water vapour at 1200°C was analysed by SEM and XRD.     

Integrated urea sensor module based on poly(3-methylthiophene)-modified p-type porous silicon substrate

Integrated three-electrode system module composed of a porous silicon (PS)-based sensing electrode, an Ag/AgCl thin film reference electrode (RE_tf), and a Pt thin film counter electrode (CE) was fabricated for monitoring urea level of artificially-prepared body fluid. After thermal evaporation of the 200 nm thick Ag on the Ti-underlayered planar p-type silicon (p-Si) substrate, the Ag Film was oxidized in a FeCl₃ solution to obtain the Ag/AgCl RE_tf. Multi-layered RE_tf was clearly shown from results of the auger electron spectroscopy (AES) depth profile. The nernstian slope of the RE_tf also showed good reproducibility. The PS layer was formed by electrochemical anodization with applying constant current to the p-Si substrate in an ethanolic HF solution and the macro PS (2 μm diameter and 10 μm depth) was obtained. The electrochemical active area (A_ea) of the PS-based Pt thin film electrode was determined from the cyclovoltammetric result of redox reactions of K₃Fe(CN)₆ on the electrode surface and compared with the A_ea of the planar silicon (PLS)-based Pt film substrate. After electropolymerization of the conductive poly(3-methylthiophene) (P3MT) on the PS-based Pt thin film, urease (isoelectric point ≈ 4.1) molecules were electrostatically doped into the P3MT film by applying positive bias. Amperometric calibration curves for both PS- and PLS-based sensing electrodes were compared in the range of 0.1–125 mM urea concentrations and the cross-sectional scanning electron microscopy (SEM) image of the PS-based sensing electrode was also shown.     

Effects of Wet Oxidation on the Properties of Sub-10-nm-Thick Silicon Nitride Films

Capacitors were prepared by wet oxidation of 8 nm (80 Å) thick silicon nitride films which had been deposited on polysilicon substrates. The capacitance and breakdown field of these capacitors were measured as a function of the wet oxidation conditions. The properties of the polysilicon films were also investigated by varying the preparation conditions to find a better substrate for the deposition of the ultrathin silicon nitride films. These polysilicon films were prepared using low-pressure chemical vapor deposition at 560° and 625°C on silicon wafers. The films were then annealed at 900°C for 30 min after As doping by implantation with a dose of more than 2 × 10¹⁵/cm². The films deposited at 560°C have a smooth surface and a low electrical resistivity and are thus suitable substrates for the ultrathin silicon nitride films as well as suitable contact electrodes. For the capacitors with an oxide nitride composite layer, the capacitance decreases sharply, but the breakdown field increases with an increase in the wet oxidation time at 900°C. This is due to an increase in the thickness of the oxide—nitride layer. For the capacitors with silicon oxynitride layers created by removing the top oxide of the silicon nitride wet-oxidized at 900°C for more than 35 min, however, the values of both the capacitance and the breakdown field are higher than those of capacitors with an unoxidized silicon nitride layer.     

Properties of SiO2 thin films prepared by anodic oxidation under UV illumination and rapid photothermal processing

Anodic oxidation under ultraviolet (UV) illumination and rapid photothermal processing technique used for high quality oxide preparation in terms of device surface passivation and gate or tunnel dielectrics are reported. A number of samples of SiO₂ thin films were prepared using this technique. It is shown that anodic oxidation under UV illumination followed by rapid photothermal processing (450 °C, 15 s) in the inert ambient yields the best optimization of the SiO₂ thin films properties. Avoiding high temperature process should result in a better performance of the semiconductor devices. Anodic oxidation under UV illumination at low temperature and post-oxidation photothermal processing can be a possible alternative to the furnace growth silicon oxide; not only because of the low temperature process, but also because this technology essential improves the oxides properties.     

Electrochemical degradation of phenol on the La and Ru doped Ti/SnO2-Sb electrodes

La and Ru doped Ti/SnO₂-Sb electrodes were prepared by thermal decomposition and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It confirmed that the surface of the La and Ru doped Ti/SnO₂-Sb electrodes presents a certain microspherical structure formed by aggregates of nanoparticles, which increases the specific area greatly and provides more active sites. The enhanced performance of the La and Ru doped electrodes arose from the increased adsorption capacity of hydroxyl radicals. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) showed an improvement of the electrochemical capacity for the La and Ru doped Ti/SnO₂-Sb electrodes. The electrochemical oxidation performance of the prepared electrode was further studied using phenol as a model pollutant. UV scans revealed that both phenol and its intermediate products are more rapidly decomposed, especially in the early stage of oxidation on the La and Ru doped electrodes. The removals of chemical oxygen demand (COD) were 86.4% and 82.1% on the Ti/SnO₂-Sb-La and Ti/SnO₂-Sb-Ru electrodes, respectively, which were higher than that on the SnO₂-Sb/Ti electrode (60.1%). The doped electrodes are demonstrated to have superior electrochemical oxidation ability for phenol.     

Densification of silicon dioxide formed by plasma-enhanced atomic layer deposition on 4H-silicon carbide using argon post-deposition annealing

Post-deposition annealing (PDA) was used to improve gate oxide physical and electrical properties. Deposition was accomplished by plasma-enhanced atomic layer deposition (PEALD). We investigated the densification silicon dioxide (SiO₂) formed by PEALD on 4H-silicon carbide (SiC) using PDA without oxidation and nitridation. PDA was conducted at 400–1200?°C in argon (Ar) ambient. The thickness of the SiO₂ was reduced by up to 13.5% after Ar PDA at 1000?°C. As the temperature of the Ar PDA increased, the etching rate of SiO₂ decreased. At temperatures greater than 1000?°C, the SiO₂ etching rate was low compared with that of thermal SiO₂. After PDA, the SiO₂/4H-SiC interface was smoother than that of thermal SiO₂/4H-SiC. The current density versus oxide field and capacitance versus voltage of the SiO₂/4H-SiC metal oxide semiconductor (MOS) capacitors were measured. Sufficient densification of SiO₂ formed by PEALD on 4H-SiC was obtained using Ar PDA at 1200?°C.     

Fabrication of boron doped diamond microband electrodes for electrochemical detection in a microfluidic channel

The manufacturing and electrochemical characterisation of an array of 20 boron doped nanocrystalline diamond (BNCD) microband electrodes for use in a poly(dimethylsiloxane) (PDMS) based microfluidic system are described. The electrodes were fabricated by plasma etching of a silicon oxide- and BNCD thin film coated silicon wafer and the resulting surface structured silicon wafer was subsequently bonded to the PDMS so that the BNCD microband electrodes were located within the PDMS microchannel. The electrochemical performance of the BNCD electrodes was studied and the electrodes were found to exhibit significantly better stability than previously employed gold microband arrays.     

Inhibition of field crystallization of anodic niobium oxide by incorporation of silicon species

The present work demonstrates effective inhibition of field crystallization of amorphous anodic niobium oxide by incorporation of silicon species from substrate. The field crystallization, detrimental for capacitor application of niobium, occurs during anodizing of magnetron sputtered niobium at 100 V in 0.1 mol dm⁻³ ammonium pentaborate electrolyte at 333 K, while amorphous structure of the anodic oxide is totally retained during anodizing of magnetron sputtered Nb–12 at%Si. Even after prior thermal treatment in air, which accelerates field crystallization of anodic oxide on niobium, no crystallization occurs on the Nb–12 at%Si. Through examination of the crystallization behaviours of anodic films formed on a thin Nb–12 at%Si layer superimposed on a niobium layer as well as on a thin niobium layer superimposed on an Nb–12 at%Si layer, it has been confirmed that air-formed oxide or thermal oxide becomes a nucleation site for crystallization. Modification of the air-formed or thermal oxide by incorporation of silicon species inhibits the nucleation of crystalline oxide. The modification, however, does not influence the growth of crystalline oxide. The growth is suppressed by continuous incorporation of silicon species into anodic film from the substrate during anodizing.     

Millimeter-tall single-walled carbon nanotube forests grown from ethanol

Millimeter-tall vertically-aligned carbon nanotubes (VA-CNTs) were grown from ethanol under ambient pressure by Co-catalyzed chemical vapor deposition (CVD), with systematic optimization of the CVD temperature and catalytic conditions using combinatorial catalyst libraries. We investigated the use of both aluminum oxide and silicon oxide as underlayers for the Co catalyst and found that VA-CNTs grew to millimeter heights in 15-30 min when the pyrolysis of ethanol was carried out at high temperatures (?850 °C) and long residence times (?10 s). Thick Co catalytic layers (?1.3 nm) produced (sub)millimeter-tall multi-walled VA-CNTs on both the aluminum oxide and silicon oxide underlayers. However, thin Co catalytic layers (0.62-1.0 nm) produced (sub)millimeter-tall VA-CNTs, which consisted mainly of single-walled CNTs, only on the aluminum oxide underlayers. Stripe patterns were found in the VA-CNTs near the substrate on both aluminum oxide and silicon oxide, indicating some instability prior to growth termination. The possible roles of aluminum oxide in growing millimeter-tall single-walled VA-CNTs were discussed.     

Chemical surface characterization of electrochemically and thermally oxidized boron-doped diamond film electrodes

In situ Cyclic Voltammetric analysis and ex situ X-ray Photoelectron Spectroscopy investigations have been carried out on highly boron-doped diamond film electrodes subjected to different oxidative treatments. Both the electrochemical and thermal oxidation modify, at different extent, the qualitative and quantitative chemical surface composition of the as prepared samples by partially converting the non diamond carbon species, for instance graphitic-like and hydrogenated carbon forms, to oxygenated ones. These modifications are relatively stable: less oxidized (e.g., alcoholic) groups can be converted into more oxidized ones (e.g., carboxyls, ethers, esthers) under extreme polarization conditions, resulting in a loss of electrochemical activity for the surface species. Surface silicon enrichment has been observed after a thermal treatment at 400 °C, as a result of the silicon diffusion, along the columnar structure of the diamond layers, from the substrate.     

Repair of thin thermally grown silicon dioxide by anodic oxidation

Anodic oxidation in 0.1 M HCl followed by a post-rapid thermal annealing process has been used to repair defects existing in thin thermally grown oxide layers (3 and 6 nm) on a p-type silicon substrate. The improved quality of the insulator layer is particularly useful for applications that require large gate areas in Metal-Insulator-Semiconductor (MIS) or Electrolyte-Insulator-Semiconductor (EIS) devices such as Light-Addressable Potentiometric Sensors (LAPS) and Scanning Photo-induced Impedance Microscopy (SPIM). Different methods have been used to characterize the oxide. High-frequency capacitance-voltage curves and ac impedance spectra showed that there was no significant change of the oxide thickness after repair, and the number of the interface states of the oxide was increased for both types of samples. Ramped voltage stress (RVS) measurements of Metal-Oxide-Semiconductor (MOS) structures with gate electrodes 2 mm in diameter showed leakage currents of 0.75 nA cm⁻² for the repaired and annealed 3 nm thick oxide and 1.31 nA cm⁻² for the repaired and annealed 6 nm thick oxide at accumulation voltage. XPS measurements confirmed that there was no change of the oxide thickness and no contamination with other ionic species after repair. AFM results showed a good agreement with the other characterization methods.     

三(二乙胺基)氯化硅烷的合成

随着半导体集成电路技术的发展,器件表面钝化保护膜的重要性日益显著。氮化硅薄膜是半导体集成电路中最具应用前景的表面钝化材料之一,发展低温的热化学气相沉积(CVD)工艺来沉积氮化硅表面钝化膜是集成电路发展的趋势,而开发新的硅源、氮源前驱体是实现低温淀积氮化硅薄膜的有效途径。设计了一种新的低温CVD氮化硅薄膜的有机硅源前驱体——三(二乙胺基)氯化硅烷,以四氯化硅和乙二胺为原料,在氮气气氛下,研究了原料预处理、二乙胺用量、反应温度和反应时间等工艺因素对合成收率的影响。最佳工艺条件下,收率达77.4%,并利用核磁共振、元素分析及红外光谱表征了产物的组成及结构。     

The Passivation Characteristics of Poly-Si/SiOx Stack for High-Efficiency Silicon Solar Cells

Silicon - The Poly-Si/SiOx stack passivation structure incorporate doped polycrystalline silicon (Poly-Si) and tunneling silicon oxide (SiOx) thin films allows for majority-carrier transport as...     

Oxidation characteristics of nanodot and nanobump on TiN thin films by atomic force microscopy

The electrochemical oxidation characteristics of TiN thin films by atomic force microscopy (AFM) was investigated. The TiN films were produced on silicon substrate by atomic layer chemical vapor deposition (ALCVD). The anodization parameters, such as the anodized voltages, the oxidation times, and how they affected the creation and growth of the oxide nanostructures were explored. The results showed that the height of the TiN oxide dots grew as a result of either the anodization time or the anodized voltage being increased. The oxide growth rate was dependent on the anodized voltage and the resulting electric field strength. Furthermore, the oxide growth rate decreased immediately when the electric field strength reached (2-3) × 10⁷ V/cm rapidly decrease to a growth rate of 0.     

Local anodic oxidation kinetics of chemical vapor deposition graphene supported on a thin oxide buffered silicon template

Study of local anodic oxidation (LAO) of single layer graphene (SLG) supported on thin oxide buffered silicon template is reported. Centimeter scaled SLG sheet grown through chemical vapor deposition on Cu foil is transferred onto patterned silicon template covered with thin oxide steps. LAO are performed on the supported SLG through contact mode atomic force microscopy in ambient condition. LAO bumps with heights exceed physical carbon–oxygen stacking are formed on thin oxide buffered samples. Micro-Raman spectroscopy reveals the coexistence of surface graphene oxide formation and local strain near the LAO patterns. The writing speed dependence of LAO bump shows a multi-exponent behavior, indicating inhomogeneous chemical profiles involved in the LAO process. The observation points to a sequential kinetics of surface SLG oxidation prior to subsurface silicon oxide protrusion formation. Our work shows the necessity to consider oxidation of substrate through the subsurface buffer layer during nano-scaled field effect device fabrication with LAO method. The strain generation from the subsurface protrusion suggests possible tuning knob for local distortion of SLG structure.     

Poly(2‐allyl)phenylene‐oxide electropolymer film growth on steel

The variation of film structure and properties with growth conditions was examined for poly(2‐allyl)phenylene‐oxide films grown electrochemically on a mild steel substrate from a basic hydro‐alcoholic monomer solution, to establish the best conditions for the production of thin, continuous, adherent films. The use of sodium hydroxide as the base led to the production of discontinuous, irregular films (upon drying). Substitution of allylamine as the base produced continuous, regular films, initially gel‐like, but becoming hard and glassy upon drying or thermal treatment. Film thickness increased substantially as the pH was raised from 9.0 to 11.0, with substrate corrosion decreasing over the same range. Platinum was used as a comparable noncorroding substrate. Film thickness also increased with monomer concentration, but current flow minimized at a monomer concentration of 0.25M. Double bond functionality was retained through the polymerization process, but lost upon heat curing of the polymer films. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1563–1571, 2001     

Preparation and characterization of boron doped diamond electrodes on diamond anvil for in situ electrical measurements under high pressure

A layer of boron doped diamond (BDD) film was deposited selectively on a diamond anvil and employed as electrodes for measuring the electrical resistivity of matter under high pressure. Both heavily doped and lightly doped electrodes were characterized by Raman spectroscopy and scanning electron microscopy. Though the BDD film electrodes contain sp² carbon, it is still suitable for in situ high pressure electrical measurements. The dependability of diamond film electrodes was tested at high pressure up to 36 GPa, by measuring the electric resistance of C60 fullerene powder, and no damage of the electrodes was observed.     

Influence of the boron doping level on the electrochemical oxidation of the azo dyes at Si/BDD thin film electrodes

In this study the efficiency of electrochemical oxidation of aromatic pollutants, such as reactive dyes, at boron-doped diamond on silicon (Si/BDD) electrodes was investigated. The level of [B]/[C] ratio which is effective for the degradation and mineralization of selected aromatic pollutants, and the impact of [B]/[C] ratio on the crystalline structure, layer conductivity and relative sp³/sp² coefficient of a BDD electrode were also studied. The thin film microcrystalline electrodes have been deposited on highly doped silicon substrates via MW PE CVD. Si/BDD electrodes were synthesized for different [B]/[C] ratios of the gas phase. Mechanical and chemical stability of the electrodes was achieved for the microcrystalline layer with relatively high sp³/sp² band ratio. Layer morphology and crystallite size distribution were analyzed by SEM. The resistivity of BDD electrodes was studied using four-point probe measurements. The relative sp³/sp² band ratios were determined by deconvolution of Raman and X-ray photoelectron spectra. The efficiency of degradation and mineralization of the reactive azo dye rubin F-2B was estimated based on the absorbance measurements at 545 nm. The influence of commonly used electrolytes NaCl and Na₂SO₄ on the dye removal efficiency was also investigated. The results suggest that, in general, the oxidation occurs indirectly at the anode through generation of hydroxyl radicals •OH, which react with the dye in a very fast and non-selective manner. In NaCl electrolyte the dye was also decomposed by more selective, active chlorine species (Cl₂, HOCl). However the efficiency of this process in BDD depended on the electrode's doping level. Higher amounts of dopant on the surface of BDD resulted in the higher efficiency of dye removal in both electrolytes.