Hideomi Koinuma

Growth of ZnO Thin Film by Laser MBE: Lasing of Exciton at Room Temperature

High quality ZnO thin film was grown by Laser MBE. A pure ceramic ZnO target was ablated by the KrF laser pulses (248 nm, 10 Hz, 1 J/cm2) in an ultra high vacuum to deposit ZnO film on sapphire (0001) substrate. The lateral grain size was about 50 nm for the sample with thickness of 55 nm. At room temperature, the peak of the exciton absorption and the photoluminescence have the same energy. Under high density excitation (355 nm, 35 ps, 10 Hz), an exciton–exciton collision process was observed as P2 and P lines where 2S exciton and ionized exciton remain. From the edge of the sample, a very rapid increase of the P line was observed with the increase of the excitation power. A fine structure that comes from the cavity mode was also observed. These facts suggest that the lasing of the exciton was observed at room temperature.

Open air plasma chemical vapor deposition of highly dielectric amorphous TiO2 films

By using the cold plasma torch we developed, TiO2 films were deposited on substrates exposed to air by feeding Ti(OEt)4 into the plasma. XPS and x‐ray analyses revealed that all films were stoichiometric and amorphous TiO2, but Raman spectra indicated the existence of short‐range crystallinity in films deposited above 350u2009°C. The short range structure changed from anatase to rutile by admixing of hydrogen to the plasma. The rutile containing TiO2 film had a higher breakdown electric field as well as a higher dielectric constant than the anatase containing film.

Laser MBE of ceramic thin films for future electronics

The advantages of pulsed laser deposition for oxide film growth and of molecular beam epitaxy for two-dimensional film growth were combined to develop a method for atomically controlled layer-by-layer epitaxy of complex oxides and other ceramic thin films. This laser MBE method has been proved to be particularly useful for the purpose. Two-dimensional molecular layer epitaxy has been verified by the clear observation of RHEED intensity oscillations for the growth of various ceramics including perovskites, infinite-layer cuprates, rock salt oxides, corundum, and fluorites on oxide substrates. Epitaxial growth of BaTiO3, BaO and sapphire films was achieved even at such a low temperature as 20°C. Some phenomena indicating novel quantum effects were observed in high quality ZnO film and SrTiO3/SrVO3 superlattice, both fabricated by laser MBE. In view of the versatility and structure-sensitive properties of oxides, lattice engineering by laser MBE is expected to be a promising technology for opening a new field of oxide electronics.

Two-dimensional laser molecular beam epitaxy and carrier modulation of infinite-layer BaCuO2 films

Abstract BaCuO 2 thin films were fabricated on SrTiO 3 substrates by laser MBE to elucidate the conditions for two-dimensional heteroepitaxial growth of the infinite-layer structure. The fine streak pattern and intensity oscillations observed by in situ reflection high-energy electron diffraction (RHEED) verified that tetragonal BaCuO 2 (001) was grown in a two-dimensional unit cell-by-cell mode. Effective carrier injection into the BaCuO 2 films was investigated in two different modes, i.e. homogeneous and molecular-layer dopings. In the former mode, 1 mol% of Ba was substituted to form a (Na 0.01 , Ba 0.99 )CuO 2 film. In the latter, BaCuO 2 and (Na 0.01 , Ba 0.99 )CuO 2 molecular layers were alternately deposited to form carrier modulated multilayered films. Both homogeneous BaCuO 2 and (Na 0.01 , films were semiconductive, whereas the carrier modulated multilayered films turned out to be metallic without showing any indication of superconductivity at 4 K and above.

Laser MBE for atomically defined ceramic film growth

Laser MBE is a process especially useful for epitaxial layer-by-layer growth of ceramic thin films directly from sintered ceramic targets. By employing high vacuum MBE conditions, the process has a restriction in the controllability of chemical composition, e.g., nonstoichiometry in oxides and nitrides, as compared with conventional pulsed laser deposition, but instead gains the possibility of in situ monitoring of surface reaction on an atomic scale by RHEED. Ever since their first success in observing RHEED intensity oscillation for CeO{sub 2} film growth on Si(111), the authors have verified the molecular layer epitaxy by laser MBE for perovskite oxides (SrTiO{sub 3}, BaTiO{sub 3}, SrVO{sub 3}, etc.) and infinite-layer cuprates MCuO{sub 2} (M = Sr, Ba, Ca) on SrTiO{sub 3} substrates as well as for oxide and nitride films on Si substrates. Key factors to design the laser MBE system, operation parameters, and recent experimental results are presented and discussed.

Layer-by-layer homoepitaxial growth process of MgO(001) as investigated by molecular dynamics, density functional theory, and computer graphics

We applied molecular dynamics, density functional theory, and computer graphics techniques to the investigation of the homoepitaxial growth process of the MgO(001) surface. MgO molecules are deposited over the MgO(001) plane one by one at regular time intervals with definite velocities. Any deposited MgO molecule migrated on the surface, and later a two-dimensional and epitaxial growth of MgO thin layer was observed at 300 K which is in agreement with the experimental result. However, some defects were constructed in the grown film at low temperature of 300 K, which is in remarkable contrast to that at 1000 K. In the latter case, a single flat and smooth MgO layer without defects was formed, which also agreed with the experimental result. Self-diffusion coefficients and activation energy for the surface diffusion of the deposited MgO molecule on the MgO(001) plane were discussed to clarify the temperature-dependency of the epitaxial growth process.

Growth and Characterization of Ferroelectric Pb(Zr, Ti)O3 Films on Interface-Controlled CeO2(111)/Si(111) Structures

Pb(Zr0.52Ti0.48)O3(PZT)/CeO2 films were grown on Si(111) substrates by the pulsed laser deposition method. Room-temperature (20° C) deposition of the CeO2 film on a hydrogen-terminated Si surface resulted in a sharp hetero-interface with no amorphous transition layer. PZT films were grown on the CeO2 layer in {101} orientation with in-plane three directions at substrate temperatures higher than 450° C. An Al/PZT(80 nm)/CeO2(24 nm)/Si structure showed a threshold voltage shift as large as 1.6 V (when bias voltage was 3 V) in a capacitance–voltage ( C–V ) curve due to the surface charges induced by ferroelectric polarization of the PZT film.

Pulsed laser deposition of epitaxial ferroelectric Pb(Zr, Ti)O3 films on Si(100) substrate

Pb(Zr0.52Ti0.48)O3 (PZT)/ SrTiO3/TiN trilayered films were grown heteroepitaxially on Si(100) substrate by pulsed laser deposition. The TiN layer was employed as a bottom electrode for the PZT capacitor and the thin SrTiO3 layer was used as a seed layer for epitaxial growth of PZT. Good crystallinity and sharp interfaces of the structure were verified by X-ray diffraction analysis and secondary ion mass spectrometry, respectively. Polarization-electric field ( P-E) curve showed a remanent polarization of 12 µ C/ cm2 and a coercive field of 130 kV/cm for a PZT film of 400 nm thickness. Leakage current at E=400 kV/cm was less than 10-7 A/cm2.

Molecular layer-by-layer growth of SrTiO3 and BaTiO3 films by laser molecular beam epitaxy

Abstract Layer-by-layer growth of SrTiO 3 and BaTiO 3 films was achieved by laser molecular beam epitaxy (laser MBE) using SrTiO 3 (100) substrate with alomieally Hat terraces and 0.4 nm steps. Fine streak pattern and intensity oscillation were persistently observed by reflection high-energy electron diffraction (RHHED) during the film growth under optimized conditions. When the growth was halted at any levels of RHEED intensity, there was no substantial change in the intensity, which means the growth in a two-dimensional (2-D) layer-by-layer mode without step flow. From the atomic force microscopy (AFM) analysis, it was found that the RHEED oscillation period agreed with the growth time of a molecular layer [MO TiO 2 (M = Sr or Ba)] and the oscillation resulted from the periodic change of surface roughness by 2-D epitaxial growth on the terrace.

Pulsed Laser Processing of Carbon and Silicon Clusters and Thin Films

Abstract Several new processes have been developed for the preparation of fullerenes and thin films by using a pulsed excimer laser. The irradiation of a pulsed KrF excimer laser beam onto a C60 powder target produced single phase C60 thin films when the laser energy fluence was in the range between 40 and 50mJ/cm2. By atomic force microscopy, the laser-deposited C60 thin film was verified to have a surface far smoother that the surfaces of films produced by the conventional evaporation method. The stainless steel rods coated with this film exhibited an excellent tribological property. Cluster formation from SiC and other carbides MCn(M=Ti,W,B) was investigated by laser desorption time-of-flight mass spectrometry. No clear indication was observed for the production of such clusters as (SiC)60 and (MxC60-x) from the sintered targets directly as well as from the films laser deposited from the targets. However, C60 and C70 were found to exists in the laser-deposited films, indicating a new applicability of p...