Soon-Bo Lee

Growth of TiO2 thin films on Si(100) substrates using single molecular precursors by metal organic chemical vapor deposition

Abstract Growth of titanium dioxide (TiO2) thin films on Si(100) substrates was carried out using a single molecular precursor at deposition temperature in the range of 300–700°C by the metal organic chemical vapor deposition (MOCVD) method. Titanium(IV) isopropoxide, (Ti[OCH(CH3)2]4), was used as a precursor without any carrier gas. Crack-free, anatase type TiO2 polycrystalline thin films with a stoichiometric ratio of Ti and O were successfully deposited on Si(100) at temperature as low as 500°C. XRD and TED data showed the formation of the highly oriented anatase phase with the [211] direction for the TiO2 thin films grown on Si(100) at below 500°C, whereas with increasing the deposition temperature to 700°C, the main film growth direction was changed to be [200], suggesting a possibility of epitaxial thin film growth. Two distinct growth behaviors were observed from the Arrhenius plots. Below 500°C, the growth rate of TiO2 is apparently limited the substrate temperature. The activation energy for TiO2 film deposition calculated in this region is approximately 77.9 kJ/mol, while that for a film grown above 500°C shows a negative value, indicating a predominant diffusion controlled deposition process. Using Al/TiO2/p-Si metal-insulator semiconductor (MIS) diode structure, a dielectric constant was also obtained from a capacitance-voltage (C–V) curve to be 21.

Growth of magnesium oxide thin films using single molecular precursors by metal-organic chemical vapor deposition

Thin films of MgO have been deposited on Si(100) and c-plane sapphire substrates by the metal‐organic chemical vapor deposition (MOCVD) method using Mg(tmhd)2 and Mg(acac)2 as single molecular precursors and oxygen as carrier gas. We have synthesized the metal‐organic precursors used in this study. Strongly [111] oriented polycrystalline MgO films were obtained on both Si(100) and c-plane sapphire substrates using these precursors in the temperature range 500‐6008C. The MgO thin films grown on Si(100) at 6008C and on cplane sapphire at 5008C with Mg(tmhd)2 are highly oriented in the [111] direction, whereas the MgO film grown on Si(100) at 3508C and then annealed at 5208C has no preferred orientation. In the case of using Mg(acac)2 as precursor, however, the MgO film deposited on c-plane sapphire surface at a deposition temperature above 5008C was grown with more [110] and [100] dominant orientation relatively rather than [111]. Furthermore, we have also shown that the synthesized precursors Mg(tmhd)2 and Mg(acac)2 are suitable precursors for obtaining MgO thin films by MOCVD and the substrate or precursor type and the growth temperature will be important factors influencing either the crystal growth direction or the crystallinity of the films. q 1999 Elsevier Science S.A. All rights reserved.

P42 Ebp1 regulates the proteasomal degradation of the p85 regulatory subunit of PI3K by recruiting a chaperone-E3 ligase complex HSP70/CHIP

The short isoform of ErbB3-binding protein 1 (Ebp1), p42, is considered to be a potent tumor suppressor in a number of human cancers, although the mechanism by which it exerts this tumor-suppressive activity is unclear. Here, we report that p42 interacts with the cSH2 domain of the p85 subunit of phosphathidyl inositol 3-kinase (PI3K), leading to inhibition of its lipid kinase activity. Importantly, we found that p42 induces protein degradation of the p85 subunit and further identified HSP70/CHIP complex as a novel E3 ligase for p85 that is responsible for p85 ubiquitination and degradation. In this process, p42 couples p85 to the HSP70/CHIP-mediated ubiquitin–proteasomal system (UPS), thereby promoting a reduction of p85 levels both in vitro and in vivo. Thus, the tumor-suppressing effects of p42 in cancer cells are driven by negative regulation of the p85 subunit of PI3K.

Cesium-induced Reconstruction on Si(113)3×2 Surface Studied by Low Energy Electron Diffraction and X-ray Photoelectron Spectroscopy

We have investigated Cs-induced reconstruction on the Si(113)3×2 surface using low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). For Cs deposition at room temperature, the (3×1) LEED pattern was observed for a wide Cs coverage range. At high substrate temperatures, the (3×1), (1×5+2×) and (2×2) phases were observed with increasing Cs deposition time. The relative Cs saturation coverages of (3×1)-Cs at RT and (2×2)-Cs at 300°C were measured from Cs 3d/Si 2p core level XPS intensity ratios. The results are summarized in a phase diagram as a function of the Cs deposition time.

Selective growth of TiO2 thin films on Si(100) surfaces by combination of metalorganic chemical vapor deposition and microcontact printing methods

We successfully patterned TiO2 thin films by metalorganic chemical vapor deposition (MOCVD) on Si(100) substrates where the surface was first modified by an organic thin film. The organic thin film [octadecyltrichlorosilane (OTS)] of self-assembled monolayers (SAMs) was deposited by microcontact printing. Selective deposition of a 130 nm thick TiO2 film was done on a 300–500 °C surface prepared by MOCVD without any carrier or bubbler gas. Auger electron spectroscopy and x-ray diffraction analyses showed that the deposited TiO2 material was stoichiometric, polycrystalline, and consisted of anatase phase. Alpha-step profile and optical-microscopic images also showed that the boundaries between the OTS SAMs and selectively deposited TiO2 thin film areas are definite and sharp. Capacitance–voltage measurement of a TiO2 thin film yielded a dielectric constant of 29, suggesting possible application to electronic materials.

Structures and properties of BON and multilayered TiN/BON thin films prepared by PAMOCVD method

Hard multilayered TiNyBON thin films have been deposited on steel and copper substrates in the deposition temperature range of RT;300 8C by low frequency RF derived plasma assisted MOCVD. Trimethylborate and tetrakisdimethylaminotitanium precursors were used to grow multilayered TiNyBON thin films. We used Ar gas for a plasma source and N gas as a reactive 2 and additional nitrogen source. In this study, we have mainly investigated the relationship between hardness and structures of the coating layers by the effects of deposition parameters such as deposition time and substrate temperature. We found that the microhardness strongly depended on film thickness and structures of the bilayer films. In addition, the sequence of deposition procedure for the TiNyBON bilayers highly affected the hardness. The maximum hardness obtained from TiNyBON bilayer was 30 GPa. 2002 Elsevier Science B.V. All rights reserved.

Molecular orbital study of the interactions of CO molecules adsorbed on a W(111) surface

We present a molecular orbital calculation for interaction of CO on W(111) surface. The atomic superposition and electron delocalization molecular orbital (ASED-MO) method is employed to calculate geometries, binding energies and reduced overlap populations in order to understand α-state and β-states behavior of the CO on W(111). A three-layer-thick (19, 12, 12) cluster with 43 tungsten atoms is used for modeling the W(111) surface. Geometry optimizations are performed for four end-on and five lying-down configurations. From the binding energies, it may be seen that the CO molecule in the lying-down configuration binding to the first layer was the most stable. The next configurations in order of decreasing stability are two others of lying-down binding with the first and the second layers and the end-on onefold configurations. From the electronic structures decomposed into the components of states (or bands), it is revealed that the main interactions in the lying-down configuration are di-σ bonds originating from the 5σ orbital of CO and the sp-band of W. We propose the pseudo-di-σ bonds bridged structure model to explain the stability of the lying-down configuration. Through this model, the binding energy and the dissociation of CO molecule on W(111) are discussed with available experimental works.

Influence of deposition parameter on the structural and electrical properties of ZrO/sub 2/ thin films

Summary form only given, as follows. Thin films of ZrO/sub 2/ were deposited on Si(100) substrates using RF magnetron sputtering technique. To study an influence of the sputtering parameters such as RF power magnitude O/sub 2/ flux and annealing temperature, etc on the film structure and electrical properties, a systematic study using I-V and C-V was mainly carried out in this study.

Phases of Ag-adsorbed si surfaces studied by low energy electron diffraction and Auger electron spectroscopy

The Ag-adsorbed Si(110)2×16 surfaces were investigated using low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES). When Ag was deposited on a Si(110)2×16 surface at room temperature (RT) and annealed at several elevated temperatures, diffuse 1×1, 1×2+streak, 1×2, and (-1, 6)×(-7, 0) structures were observed by LEED. The relative Ag coverage of the reconstructed structures were estimated from Ag(MNN)/Si(LVV) AES intensity ratios and previous results. The structural model of the Ag/Si(110)1×2 surface was proposed from the LEED and AES results.