Fabricating gate insulator by low temperature solution-based process

Solution-processed gate insulator was fabricated using polymethylphenylsilane (PMPS) as a liquid precursor. The spin-coated PMPS films were transformed into SiO₂ films after exposing to ultraviolet (UV) with 365 nm of wavelength. Fourier transform infrared spectra showed the variations of photo oxidation according to UV exposing time. The peak intensity of Si-O-Si bond increases with the UV energy, while the intensities of the methyl and phenyl peaks decrease. The electrical characteristics of PMPS-based spin-on glass (PMPS-SOG) were analyzed by capacitance-voltage and leakage current measurements. The dielectric constant was 4.14 and leakage current density was 10^− 7 A/cm². The low temperature below 200 °C fabrication processing of PMPS-SOG could be achieved by UV exposing. PMPS-SOG, forming SiO₂, is applicable to gate insulator by low temperature solution-based process.     

Acoustic wave corrected current-voltage characteristics of GaAs-based structures with Schottky contacts

The effect of ultrasonic treatment (UST) on the current-voltage (I-U) characteristics of Au-TiB_x-n-n ⁺-GaAs diode structures has been studied. Upon acoustic loading with an intensity below 2 W/cm², the character of the UST-induced changes in the reverse branches of I-U curves depends on the predominating mechanism of current transfer. UST at a power density above 2.5 W/cm² increases the reverse current by one or two orders of magnitude. It is shown that UST favors a significant increase in the homogeneity of the characteristics of devices manufactured using integral heat sink technology.     

Hot top design and its influence on feeder channel segregates in 100-ton steel ingots

The influence of hot top design on feeder channel segregates (F-CS) and centerline shrinkage porosities (C-SP) were investigated both experimentally and numerically. Two 100-ton 30Cr2Ni4MoV steel ingots with different insulating hot tops were longitudinally sectioned. The experimental results showed few channel segregates but severe shrinkage porosities appeared in the ingot with poorly insulated hot top, while it was the opposite case after the improved hot topping practice. By employing the finite element numerical simulation, the critical condition for the formation of F-CS in 30Cr2Ni4MoV steel was verified to be R^2.1G ≤ 1.0 × 10^− 5 °C mm^1.1 s^− 2.1. Through coupling with the published C-SP criterion (GR^− 0.5 ≤ 2.5 °C mm^− 1.5 s^0.5), it was found out that the increase of hot-top height and preheating temperature would aggravate F-CS while alleviate C-SP contrarily. Hence, to comprehensively control those two defects, the optimum hot-top height and preheating temperature for 100-ton ingot were suggested to be 700 mm and 600 °C, respectively. Ultimately, the ratio of the solidification time for the whole ingot to the ingot body (t_f/t_b) was proposed as a novel criterion for hot top design. This practical criterion has been successfully utilized to optimize the hot top of a 5-ton steel ingot.     

Time and space resolved Langmuir probe measurements of a pulsed vacuum arc plasma

The time and space evolution of pulsed vacuum arc plasma parameters have been measured using a single cylindrical Langmuir probe in a free expansion cup. Electron density n_e, effective electron temperature T_eff and electron energy distribution function (EEDF) are derived from the I-V curves using Druyvesteyn method. Results show that during the discharge time, the electron density n_e is between 0.27 and 1.82 × 10¹⁸ m⁻³ and the effective electron temperature T_eff is between 6.14 and 14.72 eV, both of which decrease as a function of the discharge time. The electron energy distribution function (EEDF) is no-Maxwellian since the high-energy electrons depart from the Maxwellian distribution. Due to the plasma expansion, the electron density n_e decreases as increase of the expansion distance, but the effective electron temperature T_eff is weakly dependent on the distance in the free expansion cup.     

Towards physical and mechanical properties of the novel Al-Cr-Ni-Fe decagonal quasicrystal and crystalline approximants

In the present article, mechanically alloyed AlCrNiFe alloy powders, including quasicrystalline and crystalline phases, were compacted through a cold isostatic pressing at 400 MPa pressure, 25 °C temperature, and 1 h soaking time. The main objective of this work is to examine the surface porosity and relative density, microhardness, compressive strength, wettability, electrical resistivity, and optical and luminescence properties of the AlCrNiFe compacts. The effect of the crystalline/quasicrystalline structures on the mentioned properties was studied. It should be noted that the physical and mechanical characteristics of the AlCrNiFe alloys were first investigated. It was diagnosed that the Vickers microhardness of the decagonal quasicrystalline compacts possesses the maximum value of 12 GPa. The AlCrNiFe compacts containing the decagonal phase acquire the maximum compressive strength and low ductility of 363 MPa and 2.53%, respectively. The highest contact angle value (θ_avg = 103.3° ± 2.3°) beside the lowest wettability and surface free energy values (W_A = 56.1 ± 2.8 mJ m^?2, SFE = 21.1 ± 1.3 mJ m^?2) belongs to the decagonal quasicrystal as compared to the PTFE. It was recognized that the presence of the decagonal quasicrystal resulted in the high electrical resistivity value of 930 μΩcm at room temperature with a negative temperature coefficient of resistivity (ρ_?253/ρ₂₇ = 1.13). Decagonal quasicrystal comprises the highest optical absorption and bandgap, which made it suitable for solar-selective absorbers.     

The synthesis and photoluminescence of nanocrystalline Zr0.80Zn0.20O1.80+δ powders via glycine nitrate process

Nanocrystalline Zr_1−xZn_xO_2−x+δ (x = 0, 0.20, 1.00) powders were synthesized by glycine nitrate process route and the Zr_0.80Zn_0.20O_1.80+δ powders were calcined in the temperature range between 500 and 800 °C. An intense UV emission band centered at 382 nm with excitation at 292 nm has been observed in Zr_0.80Zn_0.20O_1.80+δ powders calcined at 600 °C, and X-ray diffraction analysis indicates that the powders exhibit a single phase with cubic ZrO₂ structure with the average grain size is about 7 nm. According to the results of photoluminescence and annealing experiments in different atmospheres, it can be proposed that the intense UV emission band is related to the defect states involving oxygen vacancies. Compared with pure ZrO₂, the incorporation of Zn²⁺ ions enhances UV emission intensity. Our experimental results also show that photoluminescence intensity depends on the concentration of defects and the peak position is related to the crystal phase structure. The novel strong UV emission properties of this material may be very interesting for further application.     

UV photooxidation induced structural and photoluminescence behaviors in vapor-etching based porous silicon

In this paper, we investigate the effect of UV irradiation on Vapor-Etching (VE) based Porous Silicon (PS) structure and luminescence under controlled atmosphere (N₂, air, O₂). The oxidation evolution is monitored by Fourier transform infrared (FTIR) spectroscopy. FTIR measurements show that the SiH_x bond, initially present in the freshly prepared PS layers, decreased progressively with UV irradiation time until they completely disappear. We found that this treatment accelerates the oxidation process. SiO_x structures appear and gradually become dominant as regard to the SiH_x species, while UV irradiation is in progress. Generally, the photoluminescence (PL) intensity of the PS layer decreases instantaneously at the starting by the UV excitation and stabilizes after a period depending on the ambient gas and the specific surface area of the porous structure. Further UV exposure leads to a linear decrease of the PL intensity due to change of surface passivation from SiH_x to O_ySiH_x. After less than 100 min of UV irradiation, the PL intensity exhibits an exponential decay. UV exposure in air and O₂ leads approximately to the same PL behavior, although faster PL intensity decrease was observed under O₂-rich ambient. This was explained as being due to intense hydrogen desorption in presence of oxygen. Correlations of PL results with FTIR measurements show that surface passivation determine the electronic states of silicon nano-crystallites and influence the photoluminescence efficiency.     

Enhanced photoluminescence of Gd0.94(P1−xVx)O4:Eu0.06 red-emitting (0 ≤ x ≤ 1.0) phosphors

High-quality Gd_0.94(P_1−xV_x)O₄:Eu_0.06 (0 ≤ x ≤ 1.0) powders having small size, spherical morphology, smooth surface, and nonaggregation are synthesized by the ultrasonic spray pyrolysis. The complex host composition, Gd_0.94(P_1−xV_x)O₄:Eu_0.06 (x ≥ 0.5), shows a single phase with the tetragonal xenotime structure. The introduction of V⁵⁺ ions in the P⁵⁺ lattice yields the deviation from the centrosymmetry of Eu³⁺ ions. By increasing the V⁵⁺ content, the emission intensity corresponding to the ⁵D₀ → ⁷F₁ transition decreases. On the other hand, the emission intensity corresponding to the ⁵D₀ → ⁷F₂ transition increases up to x = 0.5, and then decreases upon further increasing the V⁵⁺ content. The emission intensity, peaking at 620 nm, of complex composition Gd_0.94(P_0.5V_0.5)O₄:Eu_0.06 is approximately five and two times stronger than that of the Gd_0.94PO₄:Eu_0.06 and Gd_0.94VO₄:Eu_0.06, respectively. It is believed that the introduction of the complex composition Gd_0.94(P_1−xV_x)O₄:Eu_0.06 is highly effective for improving the emission properties.     

Magnetization and crystal structure of RF-sputtered nanocrystalline CuFe2O4 thin films

Cu-ferrite films were deposited on glass substrates by RF-magnetron sputtering in pure Ar and mixture of (Ar + O₂) environment. The XRD studies of the as-deposited films indicate nanocrystalline cubic spinel structure. The observed increase in the intensity of (400) line at the expense of (220) line with increase in O₂ content is ascribed to the change in distribution of Cu and Fe-ions among tetrahedral A-site and octahedral B-sites. The highest saturation magnetization (M_S) of 264 emu/cm³ (in-plane) and 188 emu/cm³ (out of-plane) was obtained for the as-deposited films in pure Ar. The high deposition rate in reducing atmosphere leads to the formation of Cu⁺ ions which prefer occupation of the A-site in the spinel structure displacing Fe³⁺ cations to occupy the B-sites giving rise to the change in cation distribution among A and B-sites and consequently leading to high value of M_S. The decrease in M_S value with increase in oxygen content is ascribed to the decrease in film growth rate and Cu⁺ concentration which allow the cations to take up their preferable sites. The observed change in the film properties with environment is due to the presence of multivalent copper and iron ions with differing site preferences.     

Electrical, optical and morphological properties of nanoparticle indium-tin-oxide layers

Porous layers were prepared from DEGUSSA's ITO (In₂O₃:Sn) nanoparticle dispersion by doctor blading followed by annealing in air. We investigated the influence of various annealing parameters on electrical, optical and morphological thin film properties.Conductance rises with increasing annealing temperature and time by more than three orders of magnitude up to 44 Ω^− 1cm^− 1. Besides this we found an abrupt decrease in free charge carrier concentration above a critical annealing temperature of 250 °C, which leads to a step in conductance curve. In spite of particle growing during annealing no decrease in porosity was observed and in opposite to compact material, nanoparticle layers do not exhibit an appreciable shrinkage below recrystallisation temperature. These both indicate a densification hindering particle pinning effect, which is believed to be currently the main obstruction to achieve higher electrical conductivities.     

Influence of tetramethylammonium hydroxide treatment on the electrical characteristics of Ni/Au/GaN Schottky barrier diode

The effect of tetramethylammonium hydroxide (TMAH) treatment on the electrical properties of Ni/Au/GaN Schottky diodes have been investigated by current–voltage (I–V) and capacitance–voltage (C–V) techniques. The barrier heights and ideality factors measured from I–V characteristics are found to be 0.70 eV and 1.32 for without TMAH treatment, and 0.78 eV and 1.14 for with TMAH treatment, respectively. Cheung method is used to measure the series resistance and barrier height of the Schottky diodes, and the barrier height consistency is checked using the Norde method. The magnitude of interface state density for the diodes without and with TMAH treatment are varied from 7.45 × 10¹³ eV⁻¹ cm⁻² to 6.09 × 10¹² eV⁻¹ cm⁻² and 4.03 × 10¹³ eV⁻¹ cm⁻² to 1.79 × 10¹² eV⁻¹ cm⁻² in the below the conduction band from E_C-0.19 eV to E_C-0.63 eV and E_C-0.22 eV to E_C-0.73 eV. Based on the results, the TMAH treatment effectively removes of surface oxide (Ga_xO_y) layer, formed due to the incorporation of the residual oxygen with Ga atom at the GaN surface during the plasma etching. The decrease in interface state density at the Ni/Au/GaN interface could be the reason for the improvement in the electrical properties.     

Optical Study of 4He Condensation into a Silica Aerogel

We use optical methods to study condensation of ⁴He into a 95% porosity silica aerogel at temperatures below the bulk critical point. Simugtaneous pressure and optical measurements are performed along isotherms, as the cell is very slowly filled or emptied. We find that the pressure presents a quasiplateau below the bulk saturation pressure P _sat over a finite range of densities inside the aerogel. In this range, strong light scattering is observed, which shows that the helium density fluctuates on a microscopic scale. Quantitative analysis shows that the helium density is correlated over distances somewhat larger than the gel correlation length. We discuss our resugts in terms of two possible scenarios, capillary condensation and liquid-gas transition.     

Influence of current density on crystalline structure and magnetic properties of electrodeposited Co-rich CoNiW alloys

The influence of current density, at the interval 5–100 mA cm⁻², on the structural and magnetic properties of electrodeposited (Co_100−xNi_x)_100−yW_y alloys (x = 23–33.5 at. % Ni, y = 1.7–7.3 at. % W) was studied from a glycine-containing bath. W-content decreases with the increase of the current density magnitude. X-ray data have shown stabilization of hexagonal close packed, face centered cubic or a mixture of these structures by modulating the applied cathodic current density, for values lower than 50 mA cm⁻². Two structural phase transitions were observed: one from hexagonal close packed to face centered cubic structural transition occurring for a current density of 20 mA cm⁻², and another one, from cubic crystalline phase to amorphous state, which happens for values higher than 50 mA cm⁻². These structural phase transitions seem to be associated with the W-content as well as average crystalline grain sizes that reduce with increasing the current density value. The grain size effect may explain the face centered cubic stabilization in Co-rich CoNiW alloys, which was initially assumed to be basically due to H-adsorption/incorporation. Magnetic properties of Co-rich CoNiW alloys are strongly modified by the current density value; as a result of the changes on the W-content and their structural properties.     

Analysis of precursors for crystal growth of YBaCuO thin films in magnetron sputtering deposition

We correlated the crystallinity of YBaCuO films prepared by magnetron sputtering deposition using Ar/O₂ mixture gas with the atomic and molecular composition in the gas phase. YBaCuO films were deposited on MgO substrates at 670 °C. Two-dimensional distributions of Y, Ba, Cu, YO, BaO, and CuO densities and one-dimensional distribution of O density were measured by laser-induced fluorescence spectroscopy. The Y and Ba densities decreased significantly with the increase of the O₂ partial pressure, and they were below the detection limit at an O₂ flow ratio of 10% and a total gas pressure of 53 Pa. The decrease in the Y and Ba densities was compensated by an increase in the YO and BaO densities. The decrease in the Cu density with the increase of the O₂ partial pressure was less significant, while the CuO density was below the detection limit at all the discharge conditions. The O density was evaluated to be 10¹²-10¹³ cm^− 3, which was much higher than the Cu density. On the other hand, YBaCuO films with high crystallinity were obtained at total gas pressures of 53-80 Pa and O₂ flow ratios of 50-70%. Therefore, it is concluded that the precursors for the deposition of YBaCuO films with high crystallinity are Cu, YO, BaO, and O.     

Microstructure and dielectric properties of glass/Al2O3 composites with various low softening point borosilicate glasses

The effects of various low softening point borosilicate glasses on both the sintering behavior and dielectric properties of glass/Al₂O₃ composites were investigated by FTIR, DSC, XRD, SEM and EDS. Results show that the addition of alkali oxides and PbO can decrease the glass softening temperature. While, the addition of Al₂O₃ and more SiO₂ content in the glass can increase the continuity of glass network and further increase the glass softening temperature of samples. Glass with lower softening temperature has more time to flow to finish the densification of samples, and that can contribute to get better sintered composites. By contrast, CaO–PbO–B₂O₃–SiO₂–Na₂O–K₂O glass/Al₂O₃ composites sintered at 875?°C for 15?min exhibit better properties of a bulk density of 3.06?g/cm³, a porosity of 0.17?%, a λ value of 2.47?W/m?K, a ε _r value of 8.05 and a tan δ value of 8.8?×?10^?4 at 10?MHz.     

New polyurethane-anatase titania porous hybrid composite for the degradation of azo-compounds wastes

New TiO₂-based organic–inorganic porous hybrid materials were developed for color degradation and tested in azo-compounds aqueous solution. Porous composite materials, with pore size between 100 and 200 μm and pore volume fraction between 62% and 76%, were synthesized using micro-particles of TiO₂ in anatase phase agglutinated with solvent-free, mono-component polyurethane; the pores were generated by the CO₂ produced during the chemical reaction. The high porosity of the samples improves the contact with the colored solution increasing the photocatalytic effect. The degradation process was well fitted using a first order chemical reaction and the constant rate k determined. The best samples showed k values of 0.091 h⁻¹ and 0.076 h⁻¹ using visible light with a power of 100 mW/cm² and k values of 1.465 h⁻¹ and 1.652 h⁻¹ using UV light with a power of 80 mW/cm²; these values are comparable or better to other reported in literature obtained under similar conditions. Additionally, the use of polyurethane increases the abrasion resistance improving the lifetime of the photocatalytic material. The materials were characterized using X-rays diffraction, SEM and UV–Vis spectroscopy.     

Vacuum-UV excitation and visible luminescence of nano-scale and micro-scale NaLnF4:Pr3+ (Ln = Y,Lu)

The UV–Vis luminescence of NaLnF₄:Pr³⁺ (Ln = Y, Lu) materials can be efficiently excited by vacuum UV radiation (VUV) such as the 172 nm emission of mercury-free Xe-discharge lamps. In this work, the optical properties of the cubic α-phase and the hexagonal β-phase of NaLnF₄:Pr³⁺ (Ln = Y, Lu) powders are compared regarding particle sizes in the nano- and micrometer regime. Upon VUV excitation, the emission spectra of both crystal phases are found to be dominated by intraconfigurational [Xe]4f²–[Xe]4f² transitions, which is explained by the chemical properties of the ternary fluorides. Furthermore it is observed that the emission and excitation spectra of nano- and micro-scale powders are very similar, but that the luminescence intensity is affected by the average particle size.     

Synthesis of three dimensional photoluminescent [In10S20 − xSex] supertetrahedral clusters: (x < 0.3)

Two strong solid state luminescence peaks, centered at 457 nm and 538 nm, were observed from the newly synthesized ternary [In₁₀S_20 − xSe_x]¹⁰⁻ T3 clusters, under excitation by UV radiation (λ = 360 nm). The 457 nm peak is due to the porosity property of T3 clusters. Nevertheless, the 538 nm peak has not been reported for the T3 clusters before. In this letter, we demonstrate that the 538 nm peak is attributed to the trace Se atoms confined in the [In₁₀S_20 − xSe_x]¹⁰⁻ clusters. The luminescent output from the ternary [In₁₀S_20 − xSe_x]¹⁰⁻ T3 clusters is independent of temperature from 298 K until 77 K.     

The electronic structure and luminescence properties of Ce3+ doped Sr10[(PO4)5.5(BO4)0.5]BO2 under UV/VUV and X-ray excitation

The apatite related compound Sr₁₀[(PO₄)_5.5(BO₄)_0.5]BO₂ (SrBPO) doped with Ce³⁺ was synthesized via solid state reaction method. Undoped SrBPO shows blue-green emission under ultraviolet (UV) and X-ray excitation due to the defects in the host. When excited by vacuum ultraviolet–ultraviolet (VUV–UV) light or X-ray, Ce³⁺ doped SrBPO shows a broad emission band peaking at 450 nm originating from 5d–4f transition of Ce³⁺ and defects in the host. The phosphor exhibits strong excitation bands in UV range and a weak broad excitation band in VUV region. The site occupation of Ce³⁺ was proposed based on fluorescence decay curves. Electronic structure shows the compound is an indirect semiconductor with a band gap of 3.04 eV. The extremely small density of states of [PO₄]³⁻ or [BO₄]⁵⁻ group near Fermi level or in the conduction band is a possible origin of the weak excitation band in the VUV range. A possible mechanism was proposed to explain the luminescence properties observed.     

Electrical properties and deep traps spectra of a-plane GaN films grown on r-plane sapphire

Electrical properties, deep traps spectra and luminescence spectra were studied for two undoped a-plane GaN (a-GaN) films grown on r-plane sapphire using metalorganic chemical vapor deposition and differing by structural perfection. For sample A, the a-GaN film was directly deposited on AlN buffer. A two-step growth scheme was implemented for sample B, including an initial islanding growth stage and a subsequent enhanced lateral growth. Preliminary detailed X-ray analysis showed that the stacking faults density was 8 × 10⁵ cm^?1 for sample A and 1.7 × 10⁵ cm^?1 for sample B. Electrical properties of a-GaN films were largely determined by deep traps with a level near E_c ?0.6 eV, with other prominent traps having the activation energy of 0.25 eV. The Fermi level was pinned by the E_c ?0.6 eV deep traps for sample A, but shifted to the vicinity of the shallower 0.25 eV traps for sample B, most likely due to the reduced density of the 0.6 eV traps. This decrease of deep traps density is accompanied by a very pronounced improvement in the overall luminescence intensity. A correlation of the observed improvement in deep traps spectra and luminescence efficiency with the improved crystalline quality of the films is discussed.