Rutile TiO2 (1 0 1) and cassiterite SnO2 (1 0 1) epitaxial single and double nanolayers, the latter stacked in either sequence, are atomic layer deposited on r-cut alpha-Al2O3(0 1 (1) over bar 2) substrates. Thickness of the layers is varied. Epitaxial quality of the films is characterized by X-ray diffraction (XRD), reflection high-energy electron diffraction, and transmission electron microscopy. In gas response measurements, as-grown films and the films coated with electron-beam evaporated Pt nanoclusters are exposed, at 350 degrees C, to H-2, CO, and CH4 diluted in air. In response to test gas concentrations of 30 parts per million (ppm), the films with a thickness of order of 10 nm exhibit, depending on the makeup and gas, as high as two- to five-fold decrease in the resistance. It is shown that the platinum surface catalyst is effective in accelerating the response and recovery processes. The transition times of the order of a few tens of seconds are observed. The results demonstrate the feasibility of gas sensing with single-crystal-like nanolayer films. Comparison of sensor characteristics of such quasi-2D nanostructures and the literature data relevant to individual nanowires, nanorods, and nanobelts, i.e., typical representatives of the quasi-1D structures, shows that, as to H-2, CO, and CH4, both structures are worthy competitors.

In this work, we systematically studied the influence of the plasma treatment (PT) on the structural and electrical properties of Pt/rutile-TiO2/RuO2 metal-insulator-metal capacitors. The leakage current of the 12 nm thick TiO2 dielectrics prepared by atomic layer deposition was reduced below 10(-7) A cm(-2) while the capacitance equivalent thickness was kept below 0.5 nm using oxygen PT of the bottom RuO2 electrode. Reflection high energy electron diffraction, transmission electron microscopy, atomic force microscopy and x-ray photoelectron spectroscopy analyses allowed the conclusion that O-2 plasma smoothened the RuO2 surface and increased its oxygen content through plasma induced surface reconstruction. The nucleation of TiO2 on the plasma-treated surface was faster while the thickness of the capacitor dead layer at the TiO2/RuO2 interface was reduced.

Capacitor structures with undoped and Al-doped TiO2 dielectrics grown on RuO2 electrodes by TiCl4-based atomic layer deposition were investigated. In the undoped films, relative permittivity values up to 160 were obtained. The leakage current densities were as low as 3 x 10(-8) and 3 x 10(-7) A cm(-2) in the TiO2 films with capacitance equivalent thicknesses (CETs) of 0.49 and 0.39 nm, respectively, at a voltage of 0.8 V. Al doping of TiO2 led to a decrease of leakage current as well as permittivity. As a consequence, comparable leakage current densities were obtained for undoped and Al-doped films at similar CET values.

Ru thin films were grown on TiO2, Al2O3, HfO2, and ZrO2 films as well as on HF-etched silicon and SiO2-covered silicon by atomic layer deposition from 1-ethyl-1’-methyl-ruthenocene, (CH3C5H4)(C2H5C5H4)Ru, and oxygen. The growth of Ru was obtained and characterized at temperatures ranging from 250 to 325°C. On epitaxial rutile, highly oriented growth of Ru with hexagonal structure was achieved, while on other substrates the films possessed nonoriented hexagonal structure. Ruthenium oxide was not detected in the films. The lowest resistivity value obtained for 5.0–6.6nm thick films was 26μΩcm. The conductivity of the films depended somewhat on the deposition cycle time parameters and, expectedly, more strongly on the amount of deposition cycles. Increase in the deposition temperature of underlying metal oxide films increased the conductivity of Ru layers.

TiO2–Cr2O3 nanolaminates were atomic layer deposited on (0 1 2)-oriented sapphire and (1 0 0)-oriented silicon. The thickness of the alternating layers in the eight-layer laminates grown was close to 10nm. The laminates were characterized by cross-sectional high-resolution transmission electron microscopy, high-resolution scanning electron microscopy, atomic force microscopy, reflection high-energy electron diffraction, and micro-Raman spectroscopy. A highly oriented growth of the laminate on sapphire and its growth with a very little preferred orientation on silicon were revealed. The laminate grown on sapphire had, along with better crystallinity, more exactly defined and more planar interphase boundaries. The amount of indefiniteness of the boundaries increased with the layer distance from the substrate. The crystalline phase of titania was rutile in the laminate grown on sapphire and anatase in the laminate grown on silicon, while the crystalline phase of chromia had eskolaite structure. In the laminate grown on sapphire, titania contained numerous twins; compressively strained chromia had in this case more perfect structure.

Atomic layer deposition of Cr2O3 thin films from CrO2Cl2 and CH3OH on amorphous SiO2 and crystalline Si(100) and α-Al2O3(11¯02) substrates was investigated, and properties of the films were ascertained. Self-limited growth with a rate of 0.05–0.1nm/cycle was obtained at substrate temperatures of 330–420°C. In this temperature range epitaxial eskolaite was formed on the α-Al2O3(11¯02) substrates. The predominant crystallographic orientation in the epitaxial films depended, however, on the growth temperature and film thickness. Sufficiently thick films grown on the SiO2 and Si(100) substrates contained also the eskolaite phase, but thinner films deposited at 330–375°C on these substrates were amorphous. The growth rate data of films with different phase composition allowed a conclusion that the crystalline phase grew markedly faster than the amorphous phase did. The amorphous, polycrystalline and epitaxial films had densities of 4.9, 5.1 and 5.1–5.3g/cm3, respectively.

Thin films in the Cr-Ti-O system were atomic layer deposited from CrO2Cl2, TiCl4, and CH3OH on Si(I 0 0), fused SiO2, and alpha-Al2O3(0 1 2) substrates at 420 degrees C. The proportion between Ti and Cr resulted from the ratio of the CrO2Cl2/CH3OH and TiCl4/CH3OH pulsing. The films were grown up to the thickness of about 70 rim. Annealing of the films was performed in O-2 at 1000 degrees C. A notable dependence of their microstructure, conductance, and conductometric response to CO, H-2, and CH4 in dry air on the substrates, Ti content, and annealing has been demonstrated. The films were polycrystalline on Si and SiO2, and epitaxial on alpha-Al2O3. At temperatures above 400 degrees C, the films had a conductance, advantageous from the point of view of semiconductor gas sensors. In response to a 30-ppm CO exposure at 450 degrees C, an annealed film on the alpha-Al2O3(0 1 2) substrate, distinguished by a relatively high Ti/Cr atomic ratio, showed a 16-% conductance decrease in 20 s, with a 120-s recovery.

Epitaxial chromium oxide (alpha-CrA) films grown by atomic layer deposition at 375 degrees C from CrO2Cl2 and CH3OH on (I T 0 2) oriented alpha-Al2O3 have been studied by reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD) and X-ray reflection (XRR). The thickness of the films ranged from 10 to 3 10 nm, and the average growth rate was 0.1 nm per deposition cycle. According to the XRD analysis, the orientation relationship in thinner films was (1102)[11O]Cr2O3 vertical bar vertical bar(1102)[110]Al2O3. Confirmed by the RHEED and XRD analyses, (T 10 2) became the preferred growth plane at the thicknesses above 40 nm. This change has been interpreted as the appearance of an asymmetric rhombohedral twin with the orientation relationship between the layers (1102)[110]top vertical bar vertical bar(1102)[110]bottom and (1102)[111]top I I (I T 0 2)[T 1 1]bottom. The match of the anion and cation sublattices of both layers was characterized in terms of the structural model of the twin interface. (c) 2006 Elsevier B.V. All rights reserved.

An electrical characterization of Al2O3 based metal-insulator-semiconductor structures has been carried out by using capacitance-voltage, deep level transient spectroscopy, and conductance-transient (G-t) techniques. Dielectric films were atomic layer deposited (ALD) at temperatures ranging from 300 to 800 °C directly on silicon substrates and on an Al2O3 buffer layer that was grown in the same process by using 15 ALD cycles at 300 °C. As for single growth temperatures, 300 °C leads to the lowest density of states distributed away from the interface to the insulator [disorder-induced gap states (DIGS)], but to the highest interfacial state density (Dit). However, by using 300∕500°C double growth temperatures it is possible to maintain low DIGS values and to improve the interface quality in terms of Dit. The very first ALD cycles define the dielectric properties very near to the dielectric-semiconductor interface, and growing an upper layer at higher ALD temperature produces some annealing of interfacial states, thus improving the interface quality. Also, samples in which the only layer or the upper one was grown at the highest temperature (800 °C) show the poorest results both in terms of Dit and DIGS, so using very high temperatures yield defective dielectric films.

TiO2 films were grown by atomic layer deposition on Mo electrodes in order to elucidate the dominating conductance mechanism and its dependence on the growth chemistry. TiCl4 and Ti(OC2H5)4 served as titanium precursors, and H2O or H2O2 as oxygen precursors. The films grown at lower temperatures were amorphous. With increasing growth temperatures the crystallization first started in the TiCl4–H2O process. The films grown in this process were clearly leakier compared to the films grown from Ti(OC2H5)4 and H2O and from Ti(OC2H5)4 and H2O2. In the Ti(OC2H5)4-based processes, the application of H2O2 instead of H2O resulted in the films with considerably lowered conductivity, although structural differences in these films were insignificant. Space–charge-limited currents were prevailing in all our amorphous Mo–TiO2–Al packages. Measurements at different temperatures suggested quite high trap densities likely due to the presence of impurities and structural disorder, while the strong differences in conductivity seemed to be due to different densities of gap states.

The X-ray photoabsorption spectra of ZrO2 films with different phase compositions were measured. The analysis of the results obtained shows that due to the site-sensitivity the X-ray photoabsorption spectroscopy is an attractive method for characterization of the ZrO2 structure. This allows application of the X-ray spectroscopy in investigation of the crystal structure in the various stages of the thin film growth including the initial stage of the ZrO2 growth.

Transmission spectra of TiO2 films grown by atomic layer deposition on fused silica have been analysed by using Lorentz dispersion and a model consisting of two sublayers inside a film. It has been shown that the deposition process parameters significantly influenced the refractive index gradient in the film growth direction. The films grown at a lower flow of the carrier gas showed a 35 nm thick sublayer with low refractive index at the silica substrate and a layer with a higher refractive index at the film surface. The films deposited at higher carrier gas flow had a higher refractive index at the substrate and a lower refractive index at the film surface. The results also demonstrate that by using a parameter modelling one can obtain some information about the internal structure of a film even if there are no clearly defined interference fringes in a transmission spectrum.

HfO2 films were atomic layer deposited from HfCl4 and H2O on Si(100) in the temperature range of 300–600 °C. At low temperatures, films grow faster and are structurally more disordered, compared to films grown at high temperatures. At high temperatures, the films are better crystallized, but grow slower and contain grain boundaries extending from substrate to gate electrode. Film growth rate and capacitance of HfO2 dielectric layers was improved by depositing stacked structures with polycrystalline films of higher purity at 600 °C on thin HfO2 sublayer grown on Si at 300 °C.

In the present work, pulsed laser deposition (PLD) technique was applied to Cr2O3–TiO2 mixed oxide (5–20at.% TiO2) gas sensing materials with the aim to find the feasibility and optimal conditions for the growth of nanostructured thin films. The films were deposited by KrF laser (λ=248nm) on Si(100) substrates in low-pressure oxygen environment, and characterised by X-ray diffraction, X-ray reflection, reflection high-energy electron diffraction and atomic force microscopy. The substrate temperature (450–700°C), oxygen pressure (10−3 to 5×10−2mbar), and laser energy density (1.5–4.5J/cm2) were varied for optimising the growth conditions. Structural and morphological analysis showed that the films started to crystallize at oxygen pressures above 10−2mbar. At the highest oxygen pressure the first traces of crystallization appeared at raising the temperature over 400°C (20at.% of Ti) or 450°C (at 5at.% Ti). Smallest particle sizes (10–20nm) were obtained at 500–550°C, whereas the best degree of crystallinity of nanostructured films was observed at higher temperature but at lower laser energy densities. When the films were grown or annealed at temperatures over 600°C the crystallinity further improved but the particle size grew over 100nm.

Oxide–semiconductor interface quality of high-pressure reactive sputtered (HPRS) TiO2 films annealed in O2 at temperatures ranging from 600 to 900 °C, and atomic layer deposited (ALD) TiO2 films grown at 225 or 275 °C from TiCl4 or Ti(OC2H5)4, and annealed at 750 °C in O2, has been studied on silicon substrates. Our attention has been focused on the interfacial state and disordered-induced gap state densities. From our results, HPRS films annealed at 900 °C in oxygen atmosphere exhibit the best characteristics, with Dit density being the lowest value measured in this work (5–6 × 1011 cm−2 eV−1), and undetectable conductance transients within our experimental limits. This result can be due to two contributions: the increase of the SiO2 film thickness and the crystallinity, since in the films annealed at 900 °C rutile is the dominant crystalline phase, as revealed by transmission electron microscopy and infrared spectroscopy. In the case of annealing in the range of 600–800 °C, anatase and rutile phases coexist. Disorder-induced gap state (DIGS) density is greater for 700 °C annealed HPRS films than for 750 °C annealed ALD TiO2 films, whereas 800 °C annealing offers DIGS density values similar to ALD cases. For ALD films, the studies clearly reveal the dependence of trap densities on the chemical route used.