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Abstract Highly uniform and c-axis-aligned ZnO nanorod arrays were fabricated in predefined patterns by a low temperature homoepitaxial aqueous chemical method. The nucleation seed patterns were realized in polymer and in metal thin films, resulting in, all-ZnO and bottom-contacted structures, respectively. Both of them show excellent geometrical uniformity: the cross-sectional uniformity according to the scanning electron micrographs across the array is lower than 2%. The diameter of the hexagonal prism-shaped nanorods can be set in the range of 90–170 nm while their typical length achievable is 0.5–2.3 μm. The effect of the surface polarity was also examined, however, no significant difference was found between the arrays grown on Zn-terminated and on O-terminated face of the ZnO single crystal. The transmission electron microscopy observation revealed the single crystalline nature of the nanorods. The current–voltage characteristics taken on an individual nanorod contacted by a Au-coated atomic force microscope tip reflected Schottky-type behavior. The geometrical uniformity, the designable pattern, and the electrical properties make the presented nanorod arrays ideal candidates to be used in ZnO-based DC nanogenerator and in next-generation integrated piezoelectric nano-electromechanical systems (NEMS).

A combinatorial method is used to fabricate work function (WF) tuned Pt-W alloy films, which are used as metal electrodes for Hf[O.sub.2]/Si[O.sub.2]/Si capacitors. The results have shown that the control of bonding states at the metal/Hf[O.sub.2] interfaces on an atomic scale is necessary for the realization of a combination of metal and high-[kappa] dielectric films in metal-oxide-semiconductor devices.

The impact of nitridation on open volumes in thin HfSiO(sub x) films fabricated on Si substrates by atomic layer deposition is studied using monoenergetic positron beams. It is found that the size of open volumes increased with increasing nitrogen concentration in HfSiO(sub x) and the change in the size of open volumes is attributed to the trapping of nitrogen by open volumes, and an incorporation of nitrogen into the amorphous matrix of HfSiO(sub x) during postnitridation annealing (PNA).

The thin Hf(sub 0.6)Si(sub 0.4)O(sub x) and Hf(sub 0.3)Al(sub 0.7)O(sub x) films, which are fabricated by metal-organic chemical-vapor deposition and atomic-layer-deposition techniques, are characterized using monoenergetic positron beams. The results show that positron annihilation parameter is sensitive to change in the matrix structure of amorphous high-k materials and can be used to determine process parameters for the fabrication of high-k gate dielectrics.

The study presented reports on a systematic investigation of the structures, together with the electronic and magneto-optical properties, of thin films of anatase phase TiO(sub 2), doped with Co. Films of anatase Ti(sub 1-x)Co(sub x)O(sub 2) (x=0-0.10) were grown epitaxially on LaSrA1O(sub 4)(001) substrates, using pulsed laser deposition method.

Pt/Fe and Pt/Ag/Fe layered films were deposited by DC magnetron sputtering on MgO(001), SrTiO3(001), and Al2O3(0001) single crystalline substrates at room temperature. The films were post-annealed between 623K and 1173K for 30 s in flowing N2 atmosphere. The onset of the L10-FePt phase formation in films deposited on MgO(001) and SrTiO3(001) substrates was observed after annealing between 773 and 873 K, while chemical L10 ordering sets in for Pt/Fe bilayers on Al2O3(0001) at lower temperatures accompanied by strong (001)-texture. It is concluded that elastic stress, arising from the difference in thermal expansion coefficients between film and substrate, promotes ordering and texture formation. [ABSTRACT FROM AUTHOR]

GaN films with single-crystal and polycrystalline structure were deposited on (111) and (100) MgAl2O4 substrates by metalorganic chemical vapor deposition using a substrate modified by chemical etching and thermal passivation. The interface structure and chemical bonding state of the GaN/MgAl2O4 interface was investigated using angle-resolved x-ray photoelectron spectroscopy and resulting valence band spectra. Our results indicate that the Al2O3 buffered layer induced by thermal passivation of the (111) substrate remains unchanged during GaN deposition, which is primarily responsible for the epitaxial growth of GaN on (111) MgAl2O4 substrate. However, for the as-processed (100) substrate, interfacial reactions take place between the formed MgO-terminated surface and GaN films and GaN with a polycrystalline structure on (100) substrate forms. From the interface engineering viewpoint, the appropriate interface modification will allow control of the interface reaction to obtain high-quality GaN films for future optoelectronic devices. [ABSTRACT FROM AUTHOR]

We investigated the Schottky barrier height (SBH) behavior of binary alloy Schottky contacts on n-type zinc oxide (n-ZnO) single crystals. Pt–Ru alloy electrodes were deposited on the Zn-polar and O-polar faces of ZnO substrates by combinatorial ion-beam deposition under identical conditions. The crystal structures of the Pt–Ru alloy film changed from the Pt phase (cubic structure) to the Ru phase (hexagonal structure) in the Pt–Ru alloy phase diagram with decreasing Pt content. The SBH, determined from current–voltage measurements, decreased with decreasing Pt content, indicating that the SBH behavior also followed the Pt–Ru alloy phase diagram. The alloy electrodes on the Zn-polar face showed better Schottky properties than those on the O-polar face. Hard x-ray photoelectron spectroscopy revealed a difference in the interface oxidization of the Pt–Ru alloy: the interface of the O-polar face and Pt–Ru mixed phase with poor crystallinity had a more oxidized layer than that of the Zn-polar face. As a result of this oxidization, the O-polar face, Pt–Ru mixed, and Ru phases showed poor Schottky properties. [ABSTRACT FROM AUTHOR]

We have applied a combinatorial technique to fabricate work function (WF) tuned Pt-W alloy films and used the films as metal electrodes for HfO2/SiO2/Si capacitors. As the ratio, RPt, of Pt to W changes from 0 to 1, the WF value varies continuously from 4.7 to 5.5 eV. This tunability enables us to systematically investigate the effect of WF variation on electrical properties. After a forming gas annealing process, the values of flatband voltage (Vfb) from capacitance-voltage properties are almost constant, regardless of the WF variation, because of oxygen vacancy formation that results in Fermi level pinning. On additional oxidizing gas annealing (OGA), the effect of WF value on Vfb becomes dominant. However, the difference in Vfb between W and Pt is 0.34 V, which is much smaller than the observed WF difference of 0.8 eV. We attribute this phenomenon to the lowering of the effective WF due to an electric dipole, induced by oxygen vacancy formation at the metal/HfO2 interface. Moreover, a decrease in Vfb in W-rich regions was observed following the OGA, suggesting the formation of a W-O bond at the interface. These results clearly indicate that the control of bonding states at the metal/HfO2 interfaces on an atomic scale is essential for the realization of a combination of metal and high-k dielectric films in future complementary metal-oxide-semiconductor devices. [ABSTRACT FROM AUTHOR]

The impact of TiN deposition on thin HfO2 films formed on Si substrates was studied using x-ray photoelectron spectroscopy and a monoenergetic positron beam. For the predeposition sample, the positrons implanted into Si were found to diffuse toward the HfO2/Si interface under the influence of the electric field, suggesting the presence of negative charges in HfO2. After TiN was deposited by chemical vapor deposition, no large change in the defect species was observed. After TiN was deposited by physical vapor deposition, however, positive charges were introduced at the TiN/HfO2 interface, which were associated with the incorporation of nitride into HfO2 and/or the plasma damage at the surface of HfO2, and the resultant formation of positively charged oxygen vacancies. [ABSTRACT FROM AUTHOR]

The impact of nitridation on open volumes in thin HfSiOx films fabricated on Si substrates by atomic layer deposition was studied using monoenergetic positron beams. For HfSiOx, positrons were found to annihilate from the trapped state due to open volumes which exist intrinsically in an amorphous structure. After plasma nitridation, the size of open volumes decreased at a nitrogen concentration of about 20 at. %. An expansion of open volumes, however, was observed after postnitridation annealing (PNA) (1050 °C, 5 s). We found that the size of open volumes increased with increasing nitrogen concentration in HfSiOx. The change in the size of open volumes was attributed to the trapping of nitrogen by open volumes, and an incorporation of nitrogen into the amorphous matrix of HfSiOx during PNA. We also examined the role of nitrogen in HfSiOx using x-ray photoelectron spectroscopy and first principles calculations. [ABSTRACT FROM AUTHOR]

We describe the screening of large combinatorial oxide libraries for their electric transport characteristics. Complete ternary composition spreads of NiO–Mn2O3–CuO oxide alloys were deposited onto conducting Nb-doped SrTiO3 substrates using the combinatorial pulsed laser deposition technique. Resistance-temperature relations for each composition in the spread were determined using a custom-designed scanning probe. Ternary and binary electrically conducting alloys are located around Ni0.45Cu0.75Mn1.65O4 (the lowest resistance point) and CuMn2O4 compositions, respectively. The temperature sensitivities of the compositions Ni0.3Cu0.3Mn2.4O4,Cu0.84Mn2.16O4, and Cu1.35Mn1.65O4 were 5.0%/°C, 3.5%/°C, and 3.0%/°C, respectively. From this screening we propose compounds for thin-film negative temperature coefficient thermistors with standardized characteristics. [ABSTRACT FROM AUTHOR]

Thin Hf0.6Si0.4Ox and Hf0.3Al0.7Ox films fabricated by metal-organic chemical-vapor deposition and atomic-layer-deposition techniques were characterized using monoenergetic positron beams. Measurements of the Doppler broadening spectra of annihilation radiation and the lifetime spectra of positions indicated that positrons annihilated from the trapped state by open volumes that exist intrinsically in amorphous structures of the films. For HfSiOx, the mean size of the open volumes and their size distribution decreased with increasing postdeposition annealing (PDA) temperature. For HfAlOx, although the overall behavior of the open volumes in response to annealing was similar to that for HfSiOx, PDA caused a separation of the mean size of the open volumes. When this separation occurred, the value of the line-shape parameter S increased, suggesting an oxygen deficiency in the amorphous matrix. This fragmentation of the amorphous matrix can be suppressed by decreasing the annealing time. [ABSTRACT FROM AUTHOR]

There has been considerable debate regarding the origin of ferromagnetism in the ferromagnetic semiconductor anatase phase TiO2 doped with Co, ranging from carrier induced ferromagnetism in a framework of diluted magnetic semiconductor to merely the precipitation of ferromagnetic and metallic Co precipitates in the TiO2 matrix. This paper reports on a systematic investigation of the structures, together with the electronic and magneto-optical properties, of thin films of anatase phase TiO2, doped with Co. Films of anatase Ti1-xCoxO2 (x=0–0.10) were grown epitaxially on LaSrAlO4 (001) substrates, using pulsed laser deposition method. In order to control n-type carrier concentration, the oxygen pressure during the growth was systematically varied, yielding films with insulative, semiconductive (carrier concentration n∼1×1017 cm-3), and metallic (n∼2×1019 cm-3) properties. Reflection high energy electron diffraction patterns, atomic force microscopy, and transmission electron microscopy show no evidence of Co segregation in these films. Magneto-optical response was examined by measuring magneto-optical circular dichroism (MCD) spectra at room temperature. A large MCD peak appears at a photon energy close to the band gap of TiO2. The magnetic field dependence of MCD signal indicates ferromagnetic behavior, which is similar to that of the magnetization. The MCD intensity increases systematically with the increase of n or x. Since MCD response originates from charge carriers at the band edge, one can conclude that interaction between the charge carriers and Co impurities is essential to realize ferromagnetism. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Co-doped ZnO(Zn[sub 1-x]Co[sub x]O) and Co, Al codoped ZnO(Zn[sub 1-x]Co[sub x]O:Al) films were grown on c-plane sapphire (0001) substrates by pulsed laser deposition using a KrF excimer laser. In order to enhance homogeneous substitution of Co[sup 2+] for Zn[sup 2+] in the ZnO film, an alternating deposition (AD) method was employed for doping. ZnO films doped with the same elements were grown without employing the AD method under the same fabrication conditions to compare with the corresponding AD films. Despite Co incorporation, the Zn[sub 1-x]Co[sub x]O film by AD methods showed better crystallinity than pure ZnO film. Also, the crystallinity of Zn[sub 1-x]Co[sub x]O:Al films by AD methods was better than those of Zn[sub 1-x]Co[sub x]O and ZnO:Al films by conventional doping methods. Root mean square roughnesses of the films by AD methods were less than 1.6 nm. Absorption peaks caused by d–d transitions were observed at 1.88, 2.01, and 2.19 eV in Zn[sub 1-x]Co[sub x]O films. The electric conductivity of Zn[sub 1-x]Co[sub x]O:Al film by AD methods was comparable to that of ZnO:Al film by conventional methods in spite of Co doping and lower Al concentration. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effect of hydrogen on near-atmospheric nitrogen plasma and low temperature growth of GaN thin film is examined by using optical emission spectroscopy (OES). OES has shown that hydrogen has increased the generation of the nitrogen first positive system and first negative systems by providing an additional kinetic pathway.

A study on the impact of TiN deposition on thin HfO2 films formed on Si substrates is conducted using x-ray photoelectron spectroscopy and a monoenergetic positron beam. For the predeposition sample, the positrons implanted into Si are found to diffuse toward the HfO2/Si interface under the influence of the electric field, suggesting the presence of negative charges in HfO2.

Carrier induced ferromagnetism in Nb and transition metal codoped anatase [Ti.sub.1-x-y][Nb.sub.x][M.sub.y][O.sub.2] (M=Co, Fe) epitaxial films grown by pulsed laser deposition method was investigated. The results of the investigation reveal that the charge carriers are spin polarized and mediate ferromagnetic interaction between local spins on transition metal ions.

The screening of large combinatorial oxide libraries for their electric transport characteristics was described. Complete ternary composition spreads of NiO-Mn(sub 2)O(sub 3)-CuO oxide alloys were deposited onto conducting Nb-doped SrTiO(sub 3) substrates using the combinatorial pulsed laser deposition technique and resistance-temperature relations for each composition in the spread were determined using a custom-designed scanning probe.