Investigation of the defect density in ultra-thin Al2O3 films grown using atomic layer deposition

The film perfection in terms of pinhole defect densities of ultra-thin Al₂O₃ grown by atomic layer deposition (ALD) has been quantitatively characterized. A significant defect density reduction from ~ 1.2 × 10⁵/cm² to ~ 90/cm² was demonstrated for 2 nm-thick Al₂O₃ by using an ALD tungsten (W) buffer layer on the nickel (Ni) substrate. The reason for the defect reduction was attributed to efficient nucleation of ALD Al₂O₃ on ALD W. The effect of the buffer layer becomes less essential as the Al₂O₃ thickness increases, where the substrate surface physical conditions such as particle contamination become the main cause for defects.     

Experimental Study of the Isochoric Heat Capacity of Diethyl Ether (DEE) in the Critical and Supercritical Regions

Two- and one-phase liquid and vapor isochoric heat capacities (C _{V ρ} T relationship) of diethyl ether (DEE) in the critical and supercritical regions have been measured with a high-temperature and high-pressure nearly constant-volume adiabatic calorimeter. The measurements were carried out in the temperature range from 347 K to 575 K for 12 liquid and 5 vapor densities from 212.6 kg·m⁻³ to 534.6 kg·m⁻³. The expanded uncertainties (coverage factor k =  2, two-standard deviation estimate) for values of the heat capacity were 2% to 3% in the near-critical region, 1.0% to 1.5% for the liquid isochores, and 3% to 4% for the vapor isochores. The uncertainties of density (ρ) and temperature (T) measurements were 0.02% and 15 mK, respectively. The values of the internal energy, U(T, V), and second temperature derivative of pressure, (∂² P/∂T ²) _ρ , were derived using the measured C _V data near the critical point. The critical anomaly of the measured C _V and derived values of U(T, V) and (∂² P/∂T ²) _ρ in the critical and supercritical regions were interpreted in terms of the scaling theory of critical phenomena. The asymptotic critical amplitudes (A₀⁺ and A₀^- ){({A_0^+} {\rm and} {A_0^- )}} of the scaling power laws along the critical isochore for one- and two-phase C _V were calculated from the measured values of C _V . Experimentally derived values of the critical amplitude ratio for C_V (A₀⁺ /A₀^- = 0.521){C_{V} \left({A_0^+ /A_0^- = 0.521}\right)} are in good agreement with the values predicted by scaling theory. The measured C _V data for DEE were analyzed to study the behavior of loci of isothermal and isochoric C _V maxima and minima in the critical and supercritical regions.     

Thermodynamic Properties of Aqueous Solutions of Alkanes under Supercritical Conditions

P–V–T–X relationships for the water–methane, water–n-pentane, water–n-hexane, water–n-heptane, and water–n-octane systems are derived by piezometry at a constant volume in the vicinity of the critical point of water (647.096 K) and up to 673.15 K at pressures up to 40 MPa and alkane mole fractions of 0–1.0. Conditions are determined under which real mixtures behave as an ideal gas or have a constant compressibility factor. It is demonstrated that the concentration dependence of the partial molar volumes of alkanes in the range of small concentrations is asymptotic if the isothermal isobar of the solvent is critical. The molecular parameters of the equation of state that is based on perturbed-hard-chain theory are determined and used in the calculation of thermodynamic parameters for this class of solutions.     

Effect of temperature and pressure on the thermal conductivity of sandstone

Effective thermal conductivity (ETC) of dry sandstone was measured over a temperature range from 275 to 523 K and at pressures up to 400 MPa with a guarded parallel-plate apparatus. The estimated uncertainty of the ETC measurements is 2%. The porosity of the sample was 13%. A rapid increase of ETC was found for dry sandstone at low pressures between 0.1 and 100 MPa along various isotherms. At high-pressure range (P>100 MPa) a weak linear dependence of the ETC with pressure was observed. The pressure effect is negligibly small after first 80–100 MPa where bridging of microcracks or improvement of grain contacts takes place. We interpreted the measured ETC data using a various theoretical and semi-empirical models in order to check their accuracy and predictive capability. The effect of structure (size, shape, and distribution of the pores), porosity, and mineralogical composition on temperature and pressure dependences of the ETC of sandstone was discussed. To estimate the effect of temperature and pressure on the ETC of sandstone the pressure, β_P, and temperature, β_T, coefficients of ETC were calculated from the measured values of ETC. The measured values of the ETC were also used to calculate the values of the isothermal compressibility, χ_T, and thermal expansion coefficient, α. The equation of state of sandstone was developed using the measured ETC data.     

Crossover SAFT Equation of State and Thermodynamic Properties of Propan-1-ol

In this work we have developed a new equation of state (EOS) for propan-1-ol on the basis of the crossover modification (CR) of the statistical-associating-fluid-theory (SAFT) EOS recently developed and applied to n-alkanes. The CR SAFT EOS reproduces the nonanalytical scaling laws in the asymptotic critical region and reduces to the analytical-classical SAFT EOS far away from the critical point. Unlike the previous crossover EOS, the new CR SAFT EOS is based on the parametric sine model for the universal crossover function and is able to represent analytically connected van der Waals loops in the metastable fluid region. The CR SAFT EOS contains 10 system-dependent parameters and allows an accurate representation of the thermodynamic properties of propan-1-ol over a wide range thermodynamic states including the asymptotic singular behavior in the nearest vicinity of the critical point. The EOS was tested against experimental isochoric and isobaric specific heats, speed of sound, PVT, and VLE data in and beyond the critical region. In the one-phase region, the CR SAFT equation represents the experimental values of pressure with an average absolute deviation (AAD) of less than 1% in the critical and supercritical regions and the liquid densities with an AAD of about 1%. A corresponding states principle is used for the extension of the new CR SAFT EOS for propan-1-ol to higher n-alkanols.     

Thermal Conductivity Measurements of Aqueous SrCl2 and Sr(NO3)2 Solutions in the Temperature Range Between 293 and 473 K at Pressures up to 100 MPa

Accurate high-pressure thermal conductivity measurements have been performed on H₂O+SrCl₂ and H₂O+Sr(NO₃)₂ mixtures at pressures up to 100 MPa over a temperature range between 293 and 473 K using a parallel-plate apparatus. The concentrations studied were 0.025, 0.05, 0.10, 0.15, and 0.20 mass fraction of the salts. The estimated accuracy of the method is about ±1.6%. The pressure, temperature, and concentration dependences of the thermal conductivity have been studied. Measurements were made on six isobars, namely, 0.1, 20, 40, 60, 80, and 100 MPa. The thermal conductivity shows a linear dependence on pressure and concentration for all isotherms. Along each isobar, a given concentration shows the thermal-conductivity maximum at a temperature of about 413 K. The measured values of thermal conductivity at atmospheric pressure are compared with the results of other investigators. Literature data at atmospheric pressure reported by Ridel and by Zaitzev and Aseev agree with our thermal conductivity values within the estimated uncertainty.     

Method for calculating the stability boundary (spinodal) of a homogeneous state of a material

A method is developed for calculating the stability limit of a homogeneous state of a material based on isochoric heat-capacity measurements.     

EXTREMA OF ISOCHORIC HEAT CAPACITY OF WATER AND CARBON DIOXIDE

The experimental and predicted loci extrema behavior of the isochoric heat capacity C V was examined for water and carbon dioxide along the subcritical and supercritical isotherms and along the liquid and vapor isochores. The studies were based on a nonanalytical Helmholtz energy-volume-temperature equation ( AVT , fundamental equation of state), the IAPWS-95 formulation for water, and scaling-type crossover equations of state (CREOS). The measured isochoric heat capacity data for these fluids near the critical point were analyzed to study the behavior of loci of C V maxima and to compare these with predictions by the equations of state. A CREOS was applied to study the behavior of the isochoric heat capacity maxima in the immediate vicinity of the critical point. Good agreement with the CREOS prediction and experimental isothermal C V maxima loci was observed near the critical point. The basic characteristic points on the C V extrema loci curves in the P - T and ρ- T planes were determined on the basis of detailed analysis of the experimental and prediction of C V extrema loci behavior. Qualitative explanations are given for the nature of isochoric and isothermal C V maxima-minima curves. The role of C V extrema loci behavior in developing high-accuracy equations of state in the supercritical region and in the study of supercritical phase-transition phenomena are discussed.