Ki-Seok An

Impedance spectroscopy characterization of resistance switching NiO thin films prepared through atomic layer deposition

To understand electrical/dielectric phenomena and the origins of bistable resistive switching, impedance spectroscopy was applied to NiO thin films prepared through atomic layer deposition. The dc current-voltage characteristics of the NiO thin films were also determined. Frequency-dependent characterizations indicated that the switching and memory phenomena in NiO thin films did not originate from the non-Ohmic effect at the electrode/NiO interfaces but from the bulk-related responses, i.e., from an electrocomposite where highly conducting components are distributed in the insulating NiO matrix. Low dielectric constants and bias-independent capacitance appeared to corroborate the bulk-based responses in resistive switching in NiO thin films.

Atomic layer deposition of nickel oxide films using Ni(dmamp)2 and water

A precursor originally synthesized for the chemical vapor deposition of metallic nickel, Ni(dmamp)2 (dmamp=1-dimethylamino-2-methyl-2-propanolate, -OCMe2CH2NMe2), has been adopted as a nickel source for the atomic layer deposition of nickel oxide (NiO) using water (H2O) as the oxygen source. The precursor is a solid at room temperature, but readily sublimes at 90 °C. The self-limiting atomic layer deposition (ALD) process by alternate surface reactions of Ni(dmamp)2 and H2O was confirmed from thickness measurements of the NiO films grown with varying Ni(dmamp)2 supply times and numbers of the Ni(dmamp)2-H2O ALD cycles. The ALD temperature window for this precursor was found to be between 90 and 150 °C. Under optimal reaction conditions, the growth rate of the NiO films was ∼0.8A∕cycle. The NiO films deposited on Si(001) at 120 °C were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. The x-ray diffraction patterns showed no dis...

Atomic layer deposition of Al2O3 thin films using dimethylaluminum isopropoxide and water

Dimethylaluminum isopropoxide (DMAI), (CH3)2AlOCH(CH3)2, a precursor originally developed for the metalorganic chemical vapor deposition of alumina, was adopted as a new precursor for growing aluminum oxide thin films on HF-treated Si(001) substrates by atomic layer deposition (ALD). This precursor is stable for a prolonged period of storage time under inert atmosphere (such as in nitrogen or argon) and does not react vigorously in air, and therefore is easy to handle and safe, without causing hazards. The self-limiting ALD process by alternate surface reactions of DMAI and H2O was confirmed by thicknesses of the grown aluminum oxide films measured as functions of the DMAI pulse time and the number of DMAI-H2O cycles. A maximum growth rate of ∼1.06 A/cycle was achieved in the substrate temperature range ∼120–150 °C. Growth of stoichiometric Al2O3 thin films without appreciable carbon incorporation was verified by Rutherford backscattering spectrometry. Atomic force microscopy images showed atomically flat...

Mg-induced Si(111)3 × 1 structure studied by photoelectron spectroscopy

Abstract By means of angle resolved photoelectron spectroscopy using synchrotron radiation, we have measured the valence band and surface sensitive Si 2p core-level spectra for the Si(111)3 × 1Mg surface. The dispersion of the valence band shows the fact that this surface has a semiconducting property and two surface states in the projected bulk band gap at the K point. From the fitting results of the Si 2p core-level spectra, we find that the two surface shifted core-level components, S′1 and S′2 stem from the Si atom with single dangling bond and the Si atom bonding to the Mg atom, respectively. From experimental observations we suggest that the Si(111)3 × 1Mg structure is formed by ordering of Mg atoms on the ideal Si(111)1 × 1 surface, not by reconstruction of Si atoms of the substrate.

Initial interface formation study of the Mg/Si(111) system

The initial interface and silicide formation induced by Mg adsorption on the Si(111)7×7 surface have been studied using low‐energy electron diffraction, x‐ray photoelectron spectroscopy, and synchrotron radiation photoelectron spectroscopy. At room temperature, it is found that Mg atoms are preferably adsorbed on top sites of Si adatoms and rest atoms on the Si(111)7×7 surface and with increasing of Mg deposition, a Mg2Si epitaxial layer is formed and the surface structure transforms from the diffuse (1×1) phase into the (2/3√3×2/3√3)R30°. After growing up to a critical thickness, the Mg film grew in a disordered phase on the epitaxial layer. The Fermi level of the Mg2Si film is positioned at 0.51±0.05 eV above the valence band maximum. On the other hand, at 300 °C the Mg2Si epitaxial layer was formed in the (1×1) phase on the Si(111)7×7 and grew up to a critical thickness in the initial stage. For the successive evaporation, the Mg film grew in a disordered phase on the Mg2Si(111)1×1 surface.

ZnO nanowhiskers on ZnO nanoparticle-deposited Si(111) by MOCVD

Vertically aligned ZnO nanowhiskers have been grown on Si substrates spin-coated with ZnO nanoparticles by metal organic chemical vapor deposition (MOCVD) using Me2Zn·tmeda and a mixture of O2 and Ar gases. The ZnO nanowhiskers grown are single crystals with a growth rate of 3 μm h−1.

Surface structure and segregation of ordered Pt3Co(110) induced by oxygen

Abstract We have investigated the surface structure and segregation induced by oxygen adsorption on the ordered Pt3Co(110) alloy using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). For the clean Pt3Co(110) surface, two different LEED patterns of 1×1 and 2×1 were observed depending on the annealing temperature, which had different Pt (237eV)/Co (LMM) AES intensity ratios. With increasing oxygen exposure at the substrate temperature of 300–500°C, the 2×1 LEED pattern of the clean Pt3Co(110) surface changed to c(2×4), 1×2, and 1×2+2×1+extra spots patterns, successively, and the Pt/Co AES intensity ratios showed a drastic decrease. Co 2p and O 1s core level spectra by XPS and normal emission valence band spectra by UPS indicated that a Co monoxide overlayer is formed due to a reaction with oxygen at a high-temperature substrate. From these results, it was found that the observed several surface structures are due to the reaction between the segregated Co and adsorbed O atoms to form the stoichiometric CoO-typed overlayer.

Crystallization of amorphous silicon thin films using self-limiting ALD of nickel oxide

The crystallization of amorphous Si (a-Si) thin films was performed using atomic layer deposition (ALD) of nickel oxide. Nickel oxide layers were deposited using nickel aminoalkoxide as a precursor in Ni and water as a precursor in oxygen. The presence of nickel oxide caused significant crystallization to occur in a-Si at 575 °C under a reducing atmosphere. Even one single ALD layer of nickel oxide was high enough to crystallize the a-Si thin films. Self-limiting layer controllability in ALD is useful in providing a catalytic layer for formation of polycrystalline Si thin films for application to large-scale flat panel displays.

Field emission properties of ZnO nanorods coated with NiO film

The field emission (FE) properties of ZnO and NiO-coated ZnO (NiO∕ZnO) nanorods are investigated under vacuum of 7×10−7Torr and oxygen rich vacuum of 1×10−5Torr. The ZnO nanorods were synthesized on a Si(100) substrate by metal-organic chemical vapor deposition, and the NiO film with the thickness of ∼15nm was coated by using atomic layer deposition. The turn-on voltages of the NiO∕ZnO nanorod and the ZnO nanorod were ∼5.2 and ∼3.0V∕μm at 1μA∕cm2, respectively. The electron FE stability of the NiO∕ZnO nanorods to the ZnO nanorod was significantly improved in oxygen rich vacuum even.

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.