Sook-Il Kwun

Thermal boundary resistance at Ge2Sb2Te5/ZnS:SiO2 interface

The thermal conductivity of sputtered amorphous-Ge2Sb2Te5 (a-GST)/ZnS:SiO2 and crystalline-Ge2Sb2Te5 (c-GST)/ZnS:SiO2 multilayer films has been measured in the temperature range between 50 and 300 K using the 3ω method. The conductivity data in the direction of the cross plane of the films showed lower values than the series conductance of the constituent layers, which was calculated from the thermal conductivity of thick a-GST, c-GST, and ZnS:SiO2 films measured independently. From the reduction in the multilayer thermal conductivity, the thermal boundary resistance at the interface between GST and ZnS:SiO2 films was calculated. The boundary resistance in the c-GST multilayer was lower than that for the a-GST case in the whole measured temperature region.

The 3ω technique for measuring dynamic specific heat and thermal conductivity of a liquid or solid

We show how to measure dynamic specific heat and thermal conductivity of a solid or liquid sample using the 3ω technique, which is an ac‐modulation method where we use a heater simultaneously as the sensor. By varying the width of the heater relative to the thermal decay length, one can choose the proper regime to measure thermal conductivity or specific heat. The technique is applied to window glass and the results confirm the validity of the method. Experimental results for potassium dihydrogen phosphate crystal demonstrate the first‐order transition at the Curie point, and the dynamic specific heat of supercooled liquid potassium–calcium nitrate is shown.

Ferroelectric characterization of highly (0001)-oriented YMnO3 thin films grown by chemical solution deposition

Highly (0001)-oriented thin films of YMnO3 were grown directly on Si substrates by chemical solution deposition. The crystallinity of the films was investigated by using x-ray diffraction: θ–2θ scan, rocking curve, and pole figure. Analysis of the x-ray photoelectron spectroscopy data and Rutherford backscattering spectroscopy spectrum showed that the films had a single phase of stoichiometric YMnO3. The ferroelectric properties of YMnO3 were investigated by measuring the temperature dependence of the capacitance–voltage characteristics in the metal/ferroelectric/semiconductor structure. Screening of the ferroelectricity of YMnO3 thin film at room temperature was discussed in conjunction with the charge effects.

Structural and electro-optic properties of pulsed laser deposited Bi4Ti3O12 thin films on MgO

Ferroelectric Bi4Ti3O12 thin films have been grown on MgO (100) and MgO(110) substrates by the pulsed laser deposition. X‐ray diffraction studies show that the films on both substrates have preferential crystallographic orientation such that most of their c axes are close to the substrate normal direction. The film on MgO(110) shows quadratic and hysteretic electro‐optic characteristics with the effective coefficient of about 3.8×10−15 m2/V2.

Temperature dependence of capacitance/current–voltage characteristics of highly (0001)-oriented YMnO3 thin films on Si

Highly (0001)-oriented YMnO3 thin films on Si(100) substrates were obtained by using a stable precursor solution and rapid thermal annealing at a low temperature of 650 °C in a chemical solution deposition process. Temperature-dependent capacitance–voltage (C–V) and current–voltage (I–V) characteristics were discussed in a metal-ferroelectric-semiconductor structure. At 300 K, the voltage-dependent increase of the memory window (ΔV) in the C–V curve and the asymmetric I–V curve were attributed to the formation of positive interfacial charges by field- and thermal-excited electron transport. On the other hand, at 220 K, the voltage-independent ΔV was attributed to ferroelectric polarization switching.

Structural and electro‐optic properties of laser ablated Bi4Ti3O12 thin films on SrTiO3(100) and SrTiO3(110)

Bi4Ti3O12 thin films have been grown by laser ablation on SrTiO3(100) and SrTiO3(110) substrates. Substrate surface orientation is found to be an important growth parameter which determines crystal axis orientation, grain growth behavior, and electro‐optic properties of the Bi4Ti3O12 thin films. The films grown on SrTiO3(110) shows a ferroelectric phase transition near 720 °C and a large quadratic electro‐optic effect with the effective coefficient 1.1×10−16 m2/V 2.

Controlled growth of a-/b- and c-axis oriented epitaxial SrBi2Ta2O9 ferroelectric thin films

Thin films of a-/b- and c-axis oriented SrBi2Ta2O9 (SBT) were epitaxially grown on (110) MgO and (100) MgO substrates, respectively, by a rf magnetron sputtering deposition method. The orthorhombic SBT phase was confirmed by electron probe microanalysis and infrared reflectance spectra. The oriented growth was proved by transmission electron microscopy together with x-ray diffraction. The orientation relationship of the a-/b-axis oriented film with the substrates was determined to be SBT[001]//MgO[001] and SBT[010]//MgO[110](SBT[100]//MgO[110]) from electron diffraction patterns.Thin films of a-/b- and c-axis oriented SrBi2Ta2O9 (SBT) were epitaxially grown on (110) MgO and (100) MgO substrates, respectively, by a rf magnetron sputtering deposition method. The orthorhombic SBT phase was confirmed by electron probe microanalysis and infrared reflectance spectra. The oriented growth was proved by transmission electron microscopy together with x-ray diffraction. The orientation relationship of the a-/b-axis oriented film with the substrates was determined to be SBT[001]//MgO[001] and SBT[010]//MgO[110](SBT[100]//MgO[110]) from electron diffraction patterns.

Size effects on the quantum paraelectric SrTiO3 nanocrystals

Abstract Nano-size effects on the dielectric properties in the quantum paraelectric SrTiO 3 were studied. Nanocrystalline SrTiO 3 powders were prepared by the sol-gel method, and the particle sizes were controlled by varying firing temperatures. The sizes were determined to be from 12 to 44 nm using Scherrers formula. The classical paraelectric to quantum paraelectric phase transition temperatures were suggested to be increased for the smaller particle size samples. These results could be explained with the aid of transverse Ising model.

Solid phase regrowth of low temperature Be‐implanted GaAs

Infrared reflection and transmission measurements were used to study the thermally induced regrowth of (100) oriented, Be‐implanted GaAs samples. The samples used in this study were implanted at low temperature (−100 °C) with 250‐keV Be ions to a fluence of 6×1015 cm−2. The samples were postannealed at temperatures ranging from 100 to 550 °C. Isochronal and isothermal annealing at a series of temperatures between 180 and 240 °C were performed. Infrared reflection spectra were analyzed by using a three or four layer dielectric model. Analysis of the annealing data suggests that an amorphous layer first anneals to a second metastable amorphous state and then becomes a damaged crystalline layer after annealing at 220 °C for 12 h. The observed regrowth is not by a simple epitaxial process. After annealing at 400 °C for 1 h, the damage in the layer is reduced sufficiently for the refractive index to recover almost to the preimplantation value. On annealing at 450 °C free carriers are observed. From the measure...

Optical properties of SbSi: Co and SbSeI: Co single crystals

Abstract Single crystals of SbSI: Co and SbSeI: Co were prepared by the Bridgman technique. The optical absorption spectra of these single crystals were investigated in the wavelength range 500–2500 nm. We determined the optical energy gaps of these compounds, and identified the electric states of cobalt impurity in these single crystals. We observed the impurity absorption peaks at energies of 14000-4000 cm−1 range due to cobalt impurity. It can be explained that the impurity absorption peaks are attributed to the electronic transitions between the energy levels of cobalt ions, which are sited in tetrahedral (Td) symmetry of crystal lattice as Co3+ and Co2+ ions. The crystal field parameters Dq are given by 697 cm−1 for Co3+ and 454 cm−1 for Co2+ ions in SbSI: Co single crystals, and also 847 cm−1 for Co3+ and 452 cm−1 Co2+ ions in SbSeI: Co single crystals.