Ju Hyung Suh

Deposition and mechanical evaluation of superhard Ti–Al–Si–N nanocomposite films by a hybrid coating system

New superhard TiAlSiN films, characterized by a nanocomposite comprising nano-sized (Ti,Al,Si)N crystallites embedded in amorphous Si3N4 matrix, could be successfully synthesized on WCCo substrates by a hybrid coating system of arc ion plating (AIP) and sputtering method. The hardness and Youngs modulus value of the TiAlSiN film increased with incorporation of Si, and had the maximum value of ∼55 GPa and ∼650 GPa at the Si content of 9 at.%, respectively. The average friction coefficient of the TiAlSiN films largely decreased with an increase of the Si content. This behavior would be attributed to the tribo-chemical reaction between Si and ambient humidity, which enabled to form SiO2 or Si(OH)2 tribo-layer playing a role as self-lubricant. The harder TiAlSiN film was found to be more wear-resistant against steel. A systematic work on the microstructure and mechanical properties of TiAlSiN films is reported in this paper.

Topography Evolution of Si (001) Substrate Fabricated by Ar + Ion Beam Sputter Etching

Self-formed nanopatterns on Si (001) substrates fabricated by ion beam sputter etching were investigated by atomic force microscopy (AFM). The ion beam sputtering was performed with an Ar + ion beam produced from a Kaufman type ion gun. In order to fabricate the periodic nanoscale patterns on Si surface, the effects of sputter parameters such as ion energy, flux, incident angle and etching time on surface morphology was investigated. As a result, nanometer scale ripples and 3-dimensioal nanodots were formed uniformly after ion beam sputtering. The surface morphology of Si was significantly dependent on incident angle and ion beam flux.

Terrace Formation of SrTiO3 (111) Substrates for Epitaxial Thin Film Growth with Various Etching Conditions

The optimized terrace formation of SrTiO3 (111) substrates was investigated in various etching conditions. HCl-HNO3 solution was unstable for etching the SrTiO3 (111) substrates with different surface states. It was found that etching in buffered HF (BOE) solution for 2min provides a stable etching condition for SrTiO3 (111) substrates with various surface states and etching process is an important factor for the formation of step-terrace structures. The surface degradation of SrTiO3 (111) in normal atmosphere was also observed and it is considered that the humidity is a important factor for the surface degradation.

Microstructures and Growth Characteristics of Self-Assembled InAs/GaAs Quantum Dots Investigated by Transmission Electron Microscopy

The microstructure and strain characteristics of self-assembled InAs/GaAs quantum dots (QDs) were studied by using transmission electron microscopy. Compressive strain was induced to uncapped QDs from GaAs substrate and the misfit strain largely increased after the deposition of GaAs cap layer. Tensile strain outside QD was extended along the vertical growth direction; up to 15 nm above the wetting layer. Vertically nonaligned and aligned stacked QDs were grown by adjusting the thickness of GaAs spacer layers. The QDs with a lens-shaped morphology were formed in the early stage of growth, and their apex was flattened by the out-diffusion of In atoms upon GaAs capping. However, aligned QDs maintained their lens-shaped structure with round apex after capping. It is believed that their apex did not flatten because the chemical potential gradient of In was relatively low due to the adjacent InAs QD layers.

Interfacial structure and crystallinity of YSZ thin films grown by ion beam sputtering for MFIS-FRAM

Yttria stabilized zirconia (YSZ) thin films, having cube-on-cube epitaxial relationship with Si, have been often fabricated by using ion beam sputtering for various buffer layer applications. Since the charging of Ar+ ion on targets is detrimental to the sputtering, an appropriate neutralizer eliminating the charging of YSZ target should be used in the sputtering. In order to identify optimum neutralizer for the YSZ film growth, various neutralizers, such as tungsten (W) and zirconium (Zr) have been tried for the ion beam sputtering of YSZ film at 800degC. For the evaluation of the crystallinity and texture of YSZ films, X-ray diffraction (XRD) analysis and high resolution electron microscopy (HREM) were performed. The YSZ films grown with W neutralizer exhibited a texture with (111) preferred orientation. In addition, W particles of a 2~3 nm in diameter were often observed at the interface between the YSZ and Si substrate. Evaporated W during the deposition process was suggested to prevent the formation of (002) textured grain. The YSZ films with Zr neutralizer, however, revealed (002) preferred orientation without any precipitations present at the interface. Oxygen pressure with Zr neutralizer could increase effectively the (002) texture. Present results suggest that a Zr neutralizer is the best neutralizer for the growth of (002) textured YSZ thin film.

Misfitstrain and growth characteristics of InAs/GaAs quantum dots Grown by molecular beam epitaxy

Self-assembled InAs/GaAs quantum dots (QDs) were grown by molecular-beam epitaxy and their structure and strain characteristics were studied by using transmission electron microscopy (TEM). TEM investigations were performed by conventional bright field TEM, high-resolution electron microscopy (HREM), annular dark field (ADF) and high angle annular dark field(HAADF)-STEM techniques. In addition, strain analysis was performed on an atomic-length scale by measuring the space of lattices in HREM. Compressive strain was induced to uncapped QDs from GaAs substrate and the strain increased more than 3.5 % after GaAs cap layer growth. On the other hand, tensile strain by capped QDs was induced to GaAs up to 10 nm over the QDs, i.e. 15 nm over the wetting layer. It was also confirmed that the tensile strain extension resulted in aligned QD growth with 15 nm thick spacers

Electrical Properties of Bi 3.25 La 0.75 Ti 3 O 12 Thin Films with Various Grain Orientations Deposited by r.f. Magnetron Sputtering

Effects of grain orientation on the electrical polarization and leakage current characteristics of Bi 3.25 La 0.75 Ti 3 O 12 (BLT) thin films have been investigated with respect to c-axis off-alignment. The BLT thin films from epitaxially aligned along c-axis to (117) and (014) off-aligned orientations have been successfully grown by using both different electrode materials (Pt and SrRuO3) and heat-treatments. In order to evaluate the crystallinity and the film texture of various off-aligned BLT thin films, X-ray diffraction (XRD) and transmission electron microscopy (TEM) were carried out. The BLT thin films deposited on SrRuO 3 /SrTiO 3 (100) substrate was grown epitaxial c-axis alignment. That is, the c-axis of the film was completely parallel to the substrate normal, resulting in a cube on cube epitaxial relationship with the underlying SrRuO 3 film. The corresponding P-E curve showed nearly paraelectric property. The polycrystalline (117) and (014) oriented BLT thin films revealed that remnant polarization increased remarkably due to the anisotropy of spontaneous polarization of BLT. The surface roughness of BLT thin films was increased to result in degraded leakage current characteristic. According to the present results, it can be concluded that the grain orientation of BLT thin films is a crucial factor controlling the polarization properties and leakage current characteristics.