Investigation of SiO2 Etch Characteristics by C6F6/Ar/O2 Plasmas Generated Using Inductively Coupled Plasma and Capacitively Coupled Plasma

The etching properties of C₆F₆/Ar/O₂ in both an inductively coupled plasma (ICP) system and a capacitively coupled plasma (CCP) system were evaluated to investigate the effects of high C/F ratio of perfluorocarbon (PFC) gas on the etch characteristics of SiO₂. When the SiO₂ masked with ACL was etched with C₆F₆, for the CCP system, even though the etch selectivity was very high (20 ~ infinite), due to the heavy-ion bombardment possibly caused by the less dissociated high-mass ions from C₆F₆, tapered SiO₂ etch profiles were observed. In the case of the ICP system, due to the higher dissociation of C₆F₆ and O₂ compared to the CCP system, the etching of SiO₂ required a much lower ratio of O₂/C₆F₆ (~1.0) while showing a higher maximum SiO₂ etch rate (~400 nm/min) and a lower etch selectivity (~6.5) compared with the CCP system. For the ICP etching, even though the etch selectivity was much lower than that by the CCP etching, due to less heavy-mass-ion bombardment in addition to an adequate fluorocarbon layer formation on the substrate caused by heavily dissociated species, highly anisotropic SiO₂ etch profiles could be obtained at the optimized condition of the O₂/C₆F₆ ratio (~1.0).     

On Relationships between Gas-Phase Chemistry and Reactive Ion Etching Kinetics for Silicon-Based Thin Films (SiC,SiO2 and SixNy) in Multi-Component Fluorocarbon Gas Mixtures

This work summarizes the results of our previous studies related to investigations of reactive ion etching kinetics and mechanisms for widely used silicon-based materials (SiC, SiO₂, and Si_xN_y) as well as for the silicon itself in multi-component fluorocarbon gas mixtures. The main subjects were the three-component systems composed either by one fluorocarbon component (CF₄, C₄F₈, CHF₃) with Ar and O₂ or by two fluorocarbon components with one additive gas. The investigation scheme included plasma diagnostics by Langmuir probes and model-based analysis of plasma chemistry and heterogeneous reaction kinetics. The combination of these methods allowed one (a) to figure out key processes which determine the steady-state plasma parameters and densities of active species; (b) to understand relationships between processing conditions and basic heterogeneous process kinetics; (c) to analyze etching mechanisms in terms of process-condition-dependent effective reaction probability and etching yield; and (d) to suggest the set gas-phase-related parameters (fluxes and flux-to-flux ratios) to control the thickness of the fluorocarbon polymer film and the change in the etching/polymerization balance. It was shown that non-monotonic etching rates as functions of gas mixing ratios may result from monotonic but opposite changes in F atoms flux and effective reaction probability. The latter depends either on the fluorocarbon film thickness (in high-polymerizing and oxygen-less gas systems) or on heterogeneous processes with a participation of O atoms (in oxygen-containing plasmas). It was suggested that an increase in O₂ fraction in a feed gas may suppress the effective reaction probability through decreasing amounts of free adsorption sites and oxidation of surface atoms.     

Plasma Parameters and Etching Characteristics of SiOxNy Films in CF4 + O2 + X (X = C4F8 or CF2Br2) Gas Mixtures

In this work, we carried out the study of CF₄ + O₂ + X (X = C₄F₈ or CF₂Br₂) gas chemistries in respect to the SiO_xN_y reactive-ion etching process in a low power regime. The interest in the liquid CF₂Br₂ as an additive component is motivated by its generally unknown plasma etching performance. The combination of various diagnostic tools (double Langmuir probe, quadrupole mass-spectrometry, X-ray photoelectron spectroscopy) allowed us to compare the effects of CF₄/X mixing ratio, input power and gas pressure on gas-phase plasma characteristics as well as to analyze the SiO_xN_y etching kinetics in terms of process-condition-dependent effective reaction probability. It was found that the given gas systems are characterized by: (1) similar changes in plasma parameters (electron temperature, ion current density) and fluxes of active species with variations in processing conditions; (2) identical behaviors of SiO_xN_y etching rates, as determined by the neutral-flux-limited process regime; and (3) non-constant SiO_xN_y + F reaction probabilities due to changes in the polymer deposition/removal balance. The features of CF₄ + CF₂Br₂ + O₂ plasma are lower polymerization ability (due to the lower flux of CF_x radicals) and a bit more vertical etching profile (due to the lower neutral/charged ratio).     

Characterizing the Chemical Structure of Ti3C2Tx MXene by Angle-Resolved XPS Combined with Argon Ion Etching

Angle-resolved XPS combined with argon ion etching was used to characterize the surface functional groups and the chemical structure of Ti₃C₂T_x MXene. Survey scanning obtained on the sample surface showed that the sample mainly contains C, O, Ti and F elements, and a little Al element. Analyzing the angle-resolved narrow scanning of these elements indicated that a layer of C and O atoms was adsorbed on the top surface of the sample, and there were many O or F related Ti bonds except Ti–C bond. XPS results obtained after argon ion etching indicated staggered distribution between C–Ti–C bond and O–Ti–C, F–Ti bond. It is confirmed that Ti atoms and C atoms were at the center layer of Ti₃C₂T_x MXene, while O atoms and F atoms were located at both the upper and lower surface of Ti₃C₂ layer acting as surface functional groups. The surface functional groups on the Ti₃C₂ layer were determined to include O²⁻, OH⁻, F⁻ and O⁻–F⁻, among which F atoms could also desorb from Ti₃C₂T_x MXene easily. The schematic atomic structure of Ti₃C₂T_x MXene was derived from the analysis of XPS results, being consistent with theoretical chemical structure and other experimental reports. The results showed that angle-resolved XPS combing with argon ion etching is a good way to analysis 2D thin layer materials.     

Dry Etching Performance and Gas-Phase Parameters of C6F12O + Ar Plasma in Comparison with CF4 + Ar

This research work deals with the comparative study of C₆F₁₂O + Ar and CF₄ + Ar gas chemistries in respect to Si and SiO₂ reactive-ion etching processes in a low power regime. Despite uncertain applicability of C₆F₁₂O as the fluorine-containing etchant gas, it is interesting because of the liquid (at room temperature) nature and weaker environmental impact (lower global warming potential). The combination of several experimental techniques (double Langmuir probe, optical emission spectroscopy, X-ray photoelectron spectroscopy) allowed one (a) to compare performances of given gas systems in respect to the reactive-ion etching of Si and SiO₂; and (b) to associate the features of corresponding etching kinetics with those for gas-phase plasma parameters. It was found that both gas systems exhibit (a) similar changes in ion energy flux and F atom flux with variations on input RF power and gas pressure; (b) quite close polymerization abilities; and (c) identical behaviors of Si and SiO₂ etching rates, as determined by the neutral-flux-limited regime of ion-assisted chemical reaction. Principal features of C₆F₁₂O + Ar plasma are only lower absolute etching rates (mainly due to the lower density and flux of F atoms) as well as some limitations in SiO₂/Si etching selectivity.     

In Vitro Biodegradation of a-C:H:SiOx Films on Ti-6Al-4V Alloy

This paper focuses mainly on the in vitro study of a five-week biodegradation of a-C:H:SiO_x films of different thickness, obtained by plasma-assisted chemical vapor deposition onto Ti-6Al-4V alloy substrate using its pulsed bipolar biasing. In vitro immersion of a-C:H:SiO_x films in a solution of 0.9% NaCl was used. It is shown how the a-C:H:SiO_x film thickness (0.5–3 µm) affects the surface morphology, adhesive strength, and Na⁺ and Cl⁻ precipitation on the film surface from the NaCl solution. With increasing film thickness, the roughness indices are reducing a little. The adhesive strength of the a-C:H:SiO_x films to metal substrate corresponds to quality HF1 (0.5 µm in thickness) and HF2-HF3 (1.5–3 µm in thickness) of the Rockwell hardness test (VDI 3198) that defines strong interfacial adhesion and is usually applied in practice. The morphometric analysis of the film surface shows that on a-C:H:SiO_x-coated Ti-6Al-4V alloy surface, the area occupied by the grains of sodium chloride is lower than on the uncoated surface. The reduction in the ion precipitation from 0.9% NaCl onto the film surface depended on the elemental composition of the surface layer conditioned by the thickness growth of the a-C:H:SiO_x film. Based on the results of energy dispersive X-ray spectroscopy, the multiple regression equations are suggested to explain the effect of the elemental composition of the a-C:H:SiO_x film on the decreased Na⁺ and Cl⁻ precipitation. As a result, the a-C:H:SiO_x films successfully combine good adhesion strength and rare ion precipitation and thus are rather promising for medical applications on cardiovascular stents and/or friction parts of heart pumps.     

High-Energy Heavy Ion Irradiation of Al2O3, MgO and CaF2

High-energy heavy ion irradiation can produce permanent damage in the target material if the density of deposited energy surpasses a material-dependent threshold value. It is known that this threshold can be lowered in the vicinity of the surface or in the presence of defects. In the present study, we established threshold values for Al₂O₃, MgO and CaF₂ under the above-mentioned conditions, and found those values to be much lower than expected. By means of atomic force microscopy and Rutherford backscattering spectrometry in channelling mode, we present evidence that ion beams with values of 3 MeV O and 5 MeV Si, despite the low density of deposited energy along the ion trajectory, can modify the structure of investigated materials. The obtained results should be relevant for radiation hardness studies because, during high-energy ion irradiation, unexpected damage build-up can occur under similar conditions.     

The pH Value Control of Morphology and Luminescence Properties of Gd2O2S: Tb3+ Phosphors

Developing rare-earth doped oxysulfide phosphors with diverse morphologies has significant value in many research fields such as in displays, medical diagnosis, and information storage. All of the time, phosphors with spherical morphology have been developed in most of the related literatures. Herein, by simply adjusting the pH values of the reaction solution, Gd₂O₂S:Tb³⁺ phosphors with various morphologies (sphere-like, sheet-like, cuboid-like, flat square-like, rod-like) were synthesized. The XRD patterns showed that phosphors with all morphologies are pure hexagonal phase of Gd₂O₂S. The atomic resolution structural analysis by transmission electron microscopy revealed the crystal growth model of the phosphors with different morphology. With the morphological change, the band gap energy of Gd₂O₂S:Tb³⁺ crystal changed from 3.76 eV to 4.28 eV, followed by different luminescence performance. The samples with sphere-like and cuboid-like microstructures exhibit stronger cathodoluminescence intensity than commercial product by comparison. Moreover, luminescence of Gd₂O₂S:Tb³⁺ phosphors have different emission performance excited by UV light radiation and an electron beam, which when excited by UV light is biased towards yellow, and while excited by an electron beam is biased towards cyan. This finding provides a simple but effective method to achieve rare-earth doped oxysulfide phosphors with diversified and tunable luminescence properties through morphology control.     

One-Step Etching Characteristics of ITO/Ag/ITO Multilayered Electrode in High-Density and High-Electron-Temperature Plasma

This paper presents the dry etching characteristics of indium tin oxide (ITO)/Ag/ITO multilayered thin film, used as a pixel electrode in a high-resolution active-matrix organic light-emitting diode (AMOLED) device. Dry etching was performed using a combination of H₂ and HCl gases in a reactive ion etching system with a remote electron cyclotron resonance (ECR) plasma source, in order to achieve high electron temperature. The effect of the gas ratio (H₂/HCl) was closely observed, in order to achieve an optimal etch profile and an effective etch process, while other parameters—such as the radio frequency (RF) power, ECR power, chamber pressure, and temperature—were fixed. The optimized process, with an appropriate gas ratio, constitutes a one-step serial dry etch solution for ITO and Ag multilayered thin films.     

Investigating the Impact of Cu2+ Doping on the Morphological,Structural, Optical,and Electrical Properties of CoFe2O4 Nanoparticles for Use in Electrical Devices

This study investigated the production of Cu²⁺-doped CoFe₂O₄ nanoparticles (CFO NPs) using a facile sol−gel technique. The impact of Cu²⁺ doping on the lattice parameters, morphology, optical properties, and electrical properties of CFO NPs was investigated for applications in electrical devices. The XRD analysis revealed the formation of spinel-phased crystalline structures of the specimens with no impurity phases. The average grain size, lattice constant, cell volume, and porosity were measured in the range of 4.55–7.07 nm, 8.1770–8.1097 Å, 546.7414–533.3525 ų, and 8.77–6.93%, respectively. The SEM analysis revealed a change in morphology of the specimens with a rise in Cu²⁺ content. The particles started gaining a defined shape and size with a rise in Cu²⁺ doping. The Cu_0.12Co_0.88Fe₂O₄ NPs revealed clear grain boundaries with the least agglomeration. The energy band gap declined from 3.98 eV to 3.21 eV with a shift in Cu²⁺ concentration from 0.4 to 0.12. The electrical studies showed that doping a trace amount of Cu²⁺ improved the electrical properties of the CFO NPs without producing any structural distortions. The conductivity of the Cu²⁺-doped CFO NPs increased from 6.66 × 10⁻¹⁰ to 5.26 × 10⁻⁶ ℧ cm⁻¹ with a rise in Cu²⁺ concentration. The improved structural and electrical characteristics of the prepared Cu²⁺-doped CFO NPs made them a suitable candidate for electrical devices, diodes, and sensor technology applications.     

H(2)O(2)-induced left ventricular dysfunction in isolated working rat hearts is independent of calcium accumulation

Reactive oxygen species (ROS) and intracellular Ca²⁺ overload play key roles in myocardial ischemia-reperfusion (IR) injury but the relationships among ROS, Ca²⁺ overload and LV mechanical dysfunction remain unclear. We tested the hypothesis that H₂O₂ impairs LV function by causing Ca²⁺ overload by increasing late sodium current (I_Na), similar to Sea Anemone Toxin II (ATX-II). Diastolic and systolic Ca²⁺ concentrations (d[Ca²⁺]_i and s[Ca²⁺]_i) were measured by indo-1 fluorescence simultaneously with LV work in isolated working rat hearts. H₂O₂ (100 μM, 30 min) increased d[Ca²⁺]_i and s[Ca²⁺]_i. LV work increased transiently then declined to 32% of baseline before recovering to 70%. ATX-II (12 nM, 30 min) caused greater increases in d[Ca²⁺]_i and s[Ca²⁺]_i. LV work increased transiently before declining gradually to 17%. Ouabain (80 μM) exerted similar effects to ATX-II. Late I_Na inhibitors, lidocaine (10 μM) or R56865 (2 μM), reduced effects of ATX-II on [Ca²⁺]_i and LV function, but did not alter effects of H₂O₂. The antioxidant, N-(2-mercaptopropionyl)glycine (MPG, 1 mM) prevented H₂O₂-induced LV dysfunction, but did not alter [Ca²⁺]_i. Paradoxically, further increases in [Ca²⁺]_i by ATX-II or ouabain, given 10 min after H₂O₂, improved function. The failure of late I_Na inhibitors to prevent H₂O₂-induced LV dysfunction, and the ability of MPG to prevent H₂O₂-induced LV dysfunction independent of changes in [Ca²⁺]_i indicate that impaired contractility is not due to Ca²⁺ overload. The ability of further increases in [Ca²⁺]_i to reverse H₂O₂-induced LV dysfunction suggests that Ca²⁺ desensitization is the predominant mechanism of ROS-induced contractile dysfunction.     

Synthesis and Characterization of Li2MgGeO4:Ho3+

In this work, the synthesis and characterization of Li₂MgGeO₄:Ho³⁺ ceramics were reported. The X-ray diffraction measurements revealed that the studied ceramics belong to the monoclinic Li₂MgGeO₄. Luminescence properties were analyzed in the visible spectral range. Green and red emission bands correspondent to the ⁵F₄,⁵S₂→⁵I₈ and ⁵F₅→⁵I₈ transitions of Ho³⁺ were observed, and their intensities were significantly dependent on activator concentration. Luminescence spectra were also measured under direct excitation of holmium ions or ceramic matrix. Holmium ions were inserted in crystal lattice Li₂MgGeO₄, giving broad blue emission and characteristic 4f-4f luminescent transitions of rare earths under the selective excitation of the ceramic matrix. The presence of the energy transfer process between the host lattice and Ho³⁺ ions was suggested.     

High Dielectric Constant and Dielectric Relaxations in La2/3Cu3Ti4O12 Ceramics

La_2/3Cu₃Ti₄O₁₂ ceramics were prepared by the same method of solid-state reaction as CaCu₃Ti₄O₁₂ ceramics. The structure and dielectric responses for La_2/3Cu₃Ti₄O₁₂ and CaCu₃Ti₄O₁₂ ceramics were systematically investigated by X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, and impedance analyzer. Compared with CaCu₃Ti₄O₁₂ ceramics, La_2/3Cu₃Ti₄O₁₂ ceramics with higher density and refined grain exhibit a high dielectric constant (ε′ ~ 10⁴) and two dielectric relaxations in a wide temperature range. The dielectric relaxation below 200 K with an activation energy of 0.087 eV in La_2/3Cu₃Ti₄O₁₂ ceramics is due to the polyvalent state of Ti³⁺/Ti⁴⁺ and Cu⁺/Cu²⁺, while the dielectric relaxation above 450 K with higher activation energy (0.596 eV) is due to grain boundary effects. These thermal activated dielectric relaxations with lower activation energy in La_2/3Cu₃Ti₄O₁₂ ceramics both move to lower temperatures, which can be associated with the enhanced polyvalent structure in La_2/3Cu₃Ti₄O₁₂ ceramics. Such high dielectric constant ceramics are also expected to be applied in capacitors and memory devices.     

Combustion Synthesis and Photoluminescence Properties of Red-Emitting CaAlSiN3:Eu2+ Phosphor for White-LEDs

A combustion synthesis method has been developed for synthesis of Eu²⁺ doped CaAlSiN₃ phosphor and its photoluminescence properties were investigated. Ca, Al, Si, and Eu₂O₃ powders were used as the Ca, Al, Si and Eu sources. The addition of NaN₃, NH₄Cl and Si₃N₄ powders was found to increase significantly the product yield. These powders were mixed and pressed into a compact, which was then wrapped up with an igniting agent (i.e., Mg+Fe₃O₄). The compact was ignited by electrical heating under a N₂ pressure of ≤1.0 MPa. Effects of these experimental parameters on the product yield were investigated and a reaction mechanism was proposed. The synthesized CaAlSiN₃:Eu²⁺ phosphor absorbs light in the region of 200–600 nm and shows a broad band emission in the region of 500–800 nm due to the 4f⁶5d¹ → 4f⁷ transition of Eu²⁺. The sample doped with Eu²⁺ at the optimized molar ratio of 0.04 is efficiently excited by the blue light (460 nm) and generates emission peaking at ~650 nm with peak emission intensity ~106% of a commercially available phosphor, YAG:Ce³⁺(P46-Y3).The internal quantum efficiency of the synthesized phosphor was measured to be 71%, compared to 69% of the YAG:Ce³⁺ (P46-Y3).     

Dynamics of O2 consumption in rat pancreatic islets

Summary The O₂ consumption of rat pancreatic islets was determined by monitoring pO₂ in the perifusate from groups of 200–300 islets. Basal respiration was maintained for up to 2 h. The insulin secretagogues, glucose and 4-methyl-2-oxopentanoate, provoked an immediate (<5 s) increase in islet respiration which attained a new steady-state within 10–40 min. The respiratory changes were immediately reversible upon removal of the substrate and were parallelled by changes in insulin release and substrate oxidation. The concentration dependence of glucose-induced respiratory changes was sigmoidal with a threshold at 3 mmol/l. The concentration dependence with 4-methyl-2-oxopentanoate was characterised by a hyperbolic relationship. The weak insulin secretagogues 3-methyl-2-oxobutyrate and d,1-3-methyl-2-oxopentanoate, although stimulating islet respiration were not more effective than 4-methyl-2-oxopentanoate at non-insulinotropic concentrations. Rotenone, antimycin and oligomycin inhibited both basal O₂ consumption and the ability of glucose and 4-methyl-2-oxopentanoate to increase islet respiration. 2,4-Dinitrophenol increased islet O₂ consumption. The omission of Ca²⁺ and Mg²⁺ from the perifusing media, or the addition of the ionophore A23187, had little effect on respiration. The omission of K⁺ inhibited glucose-induced changes but had a lesser effect in the absence of substrate or in the presence of 4-methyl-2-oxopentanoate. The omission of HCO₃ ^- reduced both basal and secretagogue-induced changes in islet respiration. It is concluded that mitochondrial O₂ consumption linked to oxidative phosphorylation is a major component in the respiratory response, and that some energy consuming process in the islets depends on the availability of HCO₃ ^-. Mitochondrial reactions may generate a signal initiating the secretory process.     

1O2-mediated retrograde signaling during late embryogenesis predetermines plastid differentiation in seedlings by recruiting abscisic acid

Plastid development in seedlings of Arabidopsis thaliana is affected by the transfer of ¹O₂-mediated retrograde signals from the plastid to the nucleus and changes in nuclear gene expression during late embryogenesis. The potential impact of these mechanisms on plastid differentiation is maintained throughout seed dormancy and becomes effective only after seed germination. Inactivation of the 2 nuclear-encoded plastid proteins EXECUTER1 and EXECUTER2 blocks ¹O₂-mediated retrograde signaling before the onset of dormancy and impairs normal plastid formation in germinating seeds. This long-term effect of ¹O₂ retrograde signaling depends on the recruitment of abscisic acid (ABA) during seedling development. Unexpectedly, ABA acts as a positive regulator of plastid formation in etiolated and light-grown seedlings.     

A Review: Inductively Coupled Plasma Reactive Ion Etching of Silicon Carbide

The inductively coupled plasma reactive ion etching (ICP-RIE) is a selective dry etching method used in fabrication technology of various semiconductor devices. The etching is used to form non-planar microstructures—trenches or mesa structures, and tilted sidewalls with a controlled angle. The ICP-RIE method combining a high finishing accuracy and reproducibility is excellent for etching hard materials, such as SiC, GaN or diamond. The paper presents a review of silicon carbide etching—principles of the ICP-RIE method, the results of SiC etching and undesired phenomena of the ICP-RIE process are presented. The article includes SEM photos and experimental results obtained from different ICP-RIE processes. The influence of O₂ addition to the SF₆ plasma as well as the change of both RIE and ICP power on the etching rate of the Cr mask used in processes and on the selectivity of SiC/Cr etching are reported for the first time. SiC is an attractive semiconductor with many excellent properties, that can bring huge potential benefits thorough advances in submicron semiconductor processing technology. Recently, there has been an interest in SiC due to its potential wide application in power electronics, in particular in automotive, renewable energy and rail transport.     

Thermal Annealing Effects of V2O5 Thin Film as an Ionic Storage Layer for Electrochromic Application

A vanadium pentoxide (V₂O₅) thin film with thermal annealing as an ionic storage layer for electrochromic devices is presented in our study. The V₂O₅ thin film was deposited on an ITO glass substrate by an RF magnetron sputtering. The electrochromic properties of the film were evaluated after various thermal annealing temperatures. The structural analysis of the film was observed by X-ray diffraction (XRD), field emission electron microscopy (FE-SEM), and atomic force microscopy (AFM). The structure of the V₂O₅ thin film transformed from an amorphous to polycrystalline structure with directions of (110) and (020) after 400 °C thermal annealing. The electrochromic properties of the film improved compared with the unannealed V₂O₅ thin film. We obtained a charge capacity of 97.9 mC/cm² with a transparent difference ΔT value of 31% and coloration efficiency of 6.3 cm²/C after 400 °C thermal annealing. The improvement was due to the polycrystalline orthorhombic structure formation of V₂O₅ film by the rearrangement of atoms from thermal energy. Its laminate structure facilitates Li⁺ ion intercalation and increases charge capacity and transparent difference.     

Structural Features of Y2O2SO4 via DFT Calculations of Electronic and Vibrational Properties

The traditional way for determination of molecular groups structure in crystals is the X-Ray diffraction analysis and it is based on an estimation of the interatomic distances. Here, we report the analysis of structural units in Y₂O₂SO₄ using density functional theory calculations of electronic properties, lattice dynamics and experimental vibrational spectroscopy. The Y₂O₂SO₄ powder was successfully synthesized by decomposition of Y₂(SO₄)₃ at high temperature. According to the electronic band structure calculations, yttrium oxysulfate is a dielectric material. The difference between the oxygen–sulfur and oxygen–yttrium bond nature in Y₂O₂OS₄ was shown based on partial density of states calculations. Vibrational modes of sulfur ions and [Y₂O₂²⁺] chains were obtained theoretically and corresponding spectral lines observed in experimental Infrared and Raman spectra.