Function Of HF Concentration Research Articles

Dynamic Chemically Driven Dewetting, Spreading, and Self-Running of Sessile Droplets on Crystalline Silicon.

A chemically driven dewetting effect is demonstrated using sessile droplets of dilute hydrofluoric acid on chemically oxidized silicon wafers. The dewetting occurs as the thin oxide is slowly etched by the droplet and replaced by a hydrogen-terminated surface; the result of this is a gradual increase in the contact angle of the droplet with time. The time-varying work of adhesion is calculated from the time-varying contact angle; this corresponds to the changing chemical nature of the surface during dewetting and can be modeled by the well-known logistic (sigmoid) function often used for the modeling of restricted growth, in this case, the transition from an oxidized surface to a hydrogen-terminated silicon surface. The observation of the time-varying contact angle allows one to both measure the etch rate of the silicon oxide and estimate the hydrogenation rate as a function of HF concentration and wafer type. In addition to this, at a certain HF concentration, a self-running droplet effect is observed. In contrast, on hydrogen-terminated silicon wafers, a chemically induced spreading effect is observed using sessile droplets of nitric acid. The droplet spreading can also be modeled using a logistical function, where the restricted growth is the transition from hydrogen-terminated to a chemically induced oxidized silicon surface. The chemically driven dewetting and spreading observed here add to the methods available to study dynamic wetting (e.g., the moving three-phase contact line) of sessile droplets on surfaces. By slowing down chemical kinetics of the wetting, one is able to record the changing profile of the sessile droplet with time and gather information concerning the time-varying surface chemistry. The data also indicates a chemical interface hysteresis (CIH) that is compared to contact angle hysteresis (CAH). The approach can also be used to study the chemical etching and deposition behavior of thin films using liquids by monitoring the macroscopic droplet profile and relating this to the time-varying physical and chemical interface phenomena.

Liquid Crystal Aligning Capabilities in Solution-Processed HfZrO Layers Created via Ion-Beam Irradiation

Liquid crystal (LC) alignment on various HfZrO films as a function of Hf concentration was studied. In the HfZrO system, Hf can act as a supporter to produce a uniform alignment layer. From pre-tilt measurement, LC cells with 5% and 10% Hf were optimized to perform as a device. By X-ray photoelectron spectroscopy (XPS) analysis, the proper amount of Hf addition in the ZrO system resulted in less oxygen vacancies which caused the LCs to be orientated more uniformly. However, too much Hf led to degradation of the LC cells due to the formation of HfO2 in the HfZrO films.

Change of Surface and Electrical Characteristics of Silicon Wafer by Wet Etching(1) - Surface Morphology Changes as a Function of HF Concentration -

The electrical properties and surface morphology changes of a silicon wafer as a function of the HF concentration as the wafer is etched were studied. The HF concentrations were 28, 30, 32, 34, and 36 wt%. The surface morphology changes of the silicon wafer were measured by an SEM (<TEX>$80^{\circ}$</TEX> tilted at <TEX>${\times}200$</TEX>) and the resistivity was measured by assessing the surface resistance using a four-point probe method. The etching rate increased as the HF concentration increased. The maximum etching rate 27.31 <TEX>${\mu}m/min$</TEX> was achieved at an HF concentration of 36 wt%. A concave wave formed on the wafer after the wet etching process. The size of the wave was largest and the resistivity reached 7.54 <TEX>$ohm{\cdot}cm$</TEX> at an 30 wt% of HF concentration. At an HF concentration of 30 wt%, therefore, a silicon wafer should have good joining strength with a metal backing as well as good electrical properties.

Experimental determination of uranium (IV) speciation in HF solutions at 500°C and 1000 bar

Uraninite solubility in HF solutions (0.0001–0.5 m) was experimentally studied at 500°C, 1000 bar, and hydrogen fugacity corresponding to the Ni/NiO buffer. It was shown that the predominant U(IV) species in aqueous solution are U(OH)40, U(OH)3F0, and U(OH)2 F20. Using the results of uraninite solubility measurement, the Gibbs free energies of the uranium (IV) species were calculated at 500°C and 1000 bar (kJ/mol): −986.55 for UO2(aq), −1712.42 for U(OH)3F0, −1755.53 for U(OH)2F20, and the equilibrium constants of the uraninite solubility in water and HF solutions were estimated: UO2(κ) = UO2(aq), which is similar to UO2(cr) + 2H2O = U(OH)40, pK0 = 6.64; UO2(cr) + HF0 + H2O = U(OH)3F0, K1 = 0.0513; UO2(cr) + 2HF0 = U(OH)2F20K2 = 7.00 × 10−4. Approximate values K3 = 5.75 × 10−3 and K4 = 6.7 × 10−2 were obtained for equilibria UO2(cr) + 4HF0 =UF40 + 2H2O and UO2(cr) + 4HF = UF40 + 2H2O. Maximum observed in the uranium concentration curve as a function of HF concentration can be explained by the decrease (to < 1) of activity coefficient ratio of HF0 to U(OH)3F0 with increasing HF concentrations.

Macropore density as a function of HF-concentration and bias

Usually, n-macropore density was determined by SCR (space charge region) width. In this paper, under both constant-voltage and galvanostatic conditions, a markedly positive correlation between pore density and HF concentration was evidenced despite a fixed SCR width on low-doped n-Si; the phenomena observed differ a bit from the results dependent on SCR effects. Based on breakdown mechanism and current-burst-model (CBM), an interpretation was given. Additionally, for a given electrolyte and illumination, the correlation between pore density and etching voltage was also found to be considerably positive: both penetrating and focusing power of field strength was supposed to be the underlying factors. The as-produced macropores could be probably significant due to their high density, fast etch-rate and good controllability.

Multi-target sputter deposition of Ni 50Ti 50 − xHf x shape memory thin films for high temperature microactuator application

High temperature shape memory NiTiHf thin films with varying hafnium contents up to 28.7 at.% were fabricated by DC magnetron sputtering using simultaneous sputter deposition from separate elemental targets. The required film composition was achieved by adjusting the power ratio to the targets. The as-deposited films were amorphous; a post deposition annealing was performed at 550 °C to crystallize the films. Two-micron thick films were characterized by energy dispersive spectroscopy in a scanning electron microscope, temperature controlled X-ray diffraction, differential scanning calorimetry, and atomic force microscopy. The results showed that above 10 at.% Hf additions the transformation temperatures increased considerably over NiTi. The crystallization temperature of the films varied as a function of Hf concentration and was as high as 519.2 °C, at Hf content of 28.7 at.%. The R-phase transformation was observed during cooling at compositions less than 16 at.% Hf. The transformation temperatures confirmed that the films are comparable with bulk NiTiHf alloy of similar composition.

Pore development in alumino-silicate fiber treated in hydrofluoric acid solutions

Melt-blown alumino-silicate ceramic fibers were treated in hydrofluoric acid solutions at room temperature to produce microporous refractory fibers. The pore development of the fibers was studied as a function of HF concentration and treatment time. Surface area and weight loss of fibers was measured simultaneously after exposure to the HF solutions. Changing the HF concentration of the solution from 0.25 to 1.5 mol dm −3 linearly increased the weight loss from 8 to 46%. At HF concentration ranged from 0.5 to 1.5 mol dm −3, BET area also linearly increased from 8 to 40 m 2 g −1 with increasing treatment time from 6 to 48 h. The dominant pore size of the HF treated fibers had a radius range of 1.7–1.9 nm. Fourier Transform infrared (FTIR) spectra of the obtained microporous fibers showed that absorption bands in the range of 2700–3100 cm −1 and 3200–3700 cm −1 increased with increasing BET area of fiber.

Mechanisms of the HF/H2O vapor phase etching of SiO2

In this paper we report on studies of the mechanisms responsible for HF/H2O etching and cleaning of Si surfaces. From these studies we have clearly established that the role of water is to provide a condensed solvent medium for the HF on the surface. Our results, as well as those in the literature, show that if the partial pressures of HF and H2O are too low (or sample temperature too high) condensation does not occur and little or no oxide etching is observed. Based on these ideas and vapor pressure data from the literature, we have developed a detailed model that provides for the calculation of the onset of condensation as a function of wafer temperature and reactant partial pressures. In addition, the model allows determination of the HF concentration in the condensed H2O film. Comparison of etch rates obtained for aqueous etching as a function of HF concentration and vapor phase etching as a function of calculated HF concentration show good agreement.

Mechanisms of the HF/H2O Vapor Phase Etching of SiO2

In this paper we report on studies of the mechanisms responsible for HF/H2O etching and cleaning of Si surfaces. From these studies we have clearly established that the role of water is to provide a condensed solvent medium for the HF on the surface. Our results, as well as those in the literature, show that if the partial pressures of HF and H2O are too low (or sample temperature too high), condensation does not occur and little or no etching is observed. Based on these ideas, and pressure data from the literature, we have developed a detailed model that provides for the calculation of the onset of condensation as a function of wafer temperature and reactant partial pressures. In addition, the model allows determination of the HF concentration in the condensed H2O film. Comparison of etch rates obtained for aqueous etching as a function of HF concentration, and vapor phase etching as a function of calculated HF concentration, show good agreement. The vapor phase etch rate data, as a function of wafer temperature, total HF + H2O pressure, and partial pressure ratios, will be presented in detail along with information on the model.