Ultrathin Titanium Oxide Films Research Articles

Evolution of TiOx-SiOx nano-composite during annealing of ultrathin titanium oxide films on Si substrate

This paper discusses the formation of the TiOx-SiOx nano-composite phase during annealing of ultrathin titanium oxide films (~27 nm). The amorphous titanium oxide films are deposited on silicon substrates by sputtering. These films are important for high-k dielectrics and sensing applications. Annealing of these films at 750 °C in the O2 environment (for 15–60 min) resulted in the polycrystalline rutile phase. The films exhibit Raman peaks at 150 cm−1 (B1g), 435 cm−1 (Eg), and 615 cm−1 (A1g) confirming the rutile phase. The signature TO (1078 cm−1) and LO (1259 cm−1) infrared active vibrational modes of Si–O–Si bond confirms the presence of silicon-oxide. The X-ray photoelectron spectra of the TiOx films show multiple peaks corresponding to Ti metal (453.8 eV); Ti4+ state (458.3 eV (Ti 2p3/2) and 464 eV (Ti 2p1/2)); and Ti3+ state (456.4 eV (Ti 2p3/2) and 460.8 eV (Ti 2p1/2)). The O1s XPS spectra peaks at 530–533 eV can be attributed to Ti–O and Si–O bonds of the TiOx-SiOx nano-composite phase in the annealed films. The depth profiling XPS study shows that the top surface of the annealed film is mainly TiOx and the amount of SiOx increases with the depth.

Improving the wet chemical patterning of nichrome film by inserting an ultrathin titanium layer

We studied how to improve the quality of nichrome (NiCr) films patterned with wet chemical etching by inserting an ultrathin titanium film. The experimental results showed that inserting a 20-nm Ti layer between the photoresist (PR) and NiCr greatly improved the quality of the resultant pattern, which had minimal undercut and smooth edges. We attributed this improvement to the improved mask/NiCr interface, which we confirmed by scanning electron microscopy (SEM). In addition, we found that the undercutting of NiCr comprised two stages—an initial, relatively slow undercut stage and a second, faster stage—separated by the critical time point, the time at which the unmasked NiCr film etched away completely.

Fabrication of soft x-ray zone plates using carbon, titanium as sacrificial layer

In this paper, we report a novel process for the fabrication of Fresnel zone plate (FZP) in poly methyl methacrylate (PMMA) using ultra-thin titanium film on carbon as sacrificial layer by electron-beam lithography at 30 keV with proximity correction. The process involves fabrication of free standing structure with high mechanical stability. A study was undertaken to understand the interaction of an electron beam in the resist stack, leading to the optimization of the process for high aspect ratio structures in a single step of exposure and development. The negative tone of PMMA was also utilized to provide mechanical strength to the structure. FZPs of 800 μm diameter were designed and fabricated for a capillary discharge based argon x-ray laser operating at 46.9 nm, to have a focal length of 25 mm. Each FZP had 165 zones with an outer most zone width of 1.34 μm, and a numerical aperture of 17 mrad.

Investigation on ultrathin titanium oxide films synthesized by surface sol–gel method

Abstract Ultrathin titanium oxide films were synthesized on glass substrates by surface sol–gel method. The films were grown by sequential immersion in TiCl 4 solution and water. The film morphology, structure and property were characterized by atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV–visible spectroscopy. The results indicate that the films grow at a rate of about 2–3 nm per cycle and present an island-like growth mode. The film show an amorphous state and not a strict equilibrium TiO 2 structure. Furthermore, the film absorbance gradually increases with the depositing cycle.

Electrical properties of spin coated ultrathin titanium oxide films on GaAs

In recent years, ultrathin (<50 nm) metal oxide films have been being extensively studied as high-k dielectrics for future metal oxide semiconductor (MOS) technology. This paper discusses deposition of ultrathin TiO2 films (∼10 nm) on GaAs substrates (one sulfur-passivated, another unpassivated) by spin coating technique. The sulfur passivation is done to reduce the surface states of GaAs substrate. After annealing at 400 °C in a nitrogen environment, the TiO2 films are found to be polycrystalline in nature with rutile phase. The TiO2 films exhibit consistent grain size of 10–20 nm with thickness around 10–12 nm. Dielectric constants of the films are found to be 65.4 and 47.1 corresponding to S-passivated and unpassivated substrates, respectively. Corresponding threshold voltages of the MOS structures are measured to be −0.1 V to −0.3 V for the S-passivated and unpassivated samples, respectively. The S-passivated TiO2 film showed improved (lower) leakage current density (5.3 × 10−4 A cm−2 at 3 V) compared to the unpassivated film (1.8 × 10−3 A/cm2 at 3 V). Dielectric breakdown-field of the TiO2 films on S-passivated and unpassivated GaAs samples are found to be 8.4 MV cm−1 and 7.2 MV cm−1 respectively.

Scanning Tunneling Microscopy Investigation of Ultrathin Titanium Oxide Films Grown on Pt3Ti(111)

Ordered ultrathin titanium oxide films have been produced under ultrahigh vacuum (UHV) conditions by oxidation of a Pt3Ti(111) single crystal at elevated temperatures. Depending on substrate temperature, oxygen dosage, and partial pressure, four different titania phases have been observed. All phases have been investigated by low- energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Two commensurate phases with a rect-(6 × 3√3) and a hex-(7 × 7)R21.8° superstructure, respectively, are obtained at low oxygen pressures. Both structures form homogeneous films, which wet the complete surface and are stable against further annealing. At high oxygen partial pressures two incommensurate structures can be prepared. The first one contains several holes to release stress arising from the lattice mismatch between the oxide film and substrate. The second one shows a very rough surface morphology and is, like the other incommensurate phase, unstable against thermal treatment. The structures of the different phases are very similar to the structures found for the systems TiOx/Pt(111), VOx/ Rh(111), and VOx/Pd(111), which have been described extensively in the literature.

Ultra-thin titanium nanolayers for plasmon-assisted enhancement of bioluminescence of chloroplast in biological light emitting devices

Ultra-thin titanium films were deposited via ultra-high vacuum ion beam sputter deposition. Since the asymmetric electric field of the metal foil plane matches the B-band absorption of chlorophyll a, the ultra-thin titanium nanolayers were able to generate surface plasmon resonance, thus enhancing the photoluminescence of chlorophyll a. Because the density of the states of plasmon resonance increases, the enhancement of photoluminescence also rises. Due to the biocompatibility and inexpensiveness of titanium, it can be utilized to enhance the bioluminescence of chloroplast in biological light emitting devices, bio-laser, and biophotonics.

Structural and compositional characterization of ultrathin titanium oxide films grown on Pt3Ti(111)

We have investigated the growth of ultrathin titanium oxide (TiOx) films on a Pt3Ti(111) single crystal surface as a function of oxidation temperature (300–1000 K) and oxygen exposure (up to 4500 l) by means of Auger electron spectroscopy, low-energy electron diffraction, ultraviolet photoelectron spectroscopy and high-resolution electron energy loss spectroscopy (HREELS). Both the surface composition and the surface structure of the resulting TiOx films exhibit a strong dependence on the preparation conditions. Loss of the chemical order and Ti segregation are observed at the Pt3Ti(111) surface upon oxygen exposures of more than 135 l at 1000 K. Increasing oxygen exposure enhances Ti segregation and oxide growth. At a threshold of ≈220 l (at 1000 K) a transition in the oxide structure occurs, namely from a (6 × 3√3) rectangular structure (a = 16.6 Å, b = 14.4 Å) below 220 l to a (7 × 7)R21.8° hexagonal structure (a = b = 19.3 Å) above 220 l. Two additional incommensurate rectangular metastable structures are observed for the highest oxygen exposures (above 900 l) at intermediate oxidation temperatures (800–900 K). In all cases the changes in the valence band spectra and the work function with respect to the clean Pt3Ti(111) surface are independent of the chosen oxidation parameters. Based on their HREELS spectra we identify the (6 × 3√3) and (7 × 7)R21.8° structures grown at 1000 K with a stoichiometric TiO phase, while the other and less stable oxide phases grown at 800–900 K exhibit more complex phonon structures that could not simply be associated with any of the stoichiometric phases TiO, Ti2O3 or TiO2. Our results are rather similar to those found by Granozzi et al for the deposition of Ti onto a Pt(111) surface in an oxygen atmosphere, except a few interesting deviations as a consequence of the different preparation conditions.

Ultra-thin titanium oxide

We demonstrate the fabrication of ultra-thin titanium oxide films by plasma-induced surface oxidation. Ellipsometry measurements indicate an oxide thickness of about 2 nm. Electrical characterization was performed on microscale and nanoscale metal-insulator-metal tunneling diodes. Electrical fields up to 22 MV/cm were applied without destroying the titanium oxide films. The current-voltage-characteristic of the diodes are found to be asymmetric with respect to zero bias when employing electrodes with different work functions. The permittivity of the ultra-thin titanium oxide was determined to be less than 6, which is the smallest permittivity that has been reported for titanium oxide.

Growth of highly textured aluminum films on LiTaO 3 with optimized titanium intermediate layers

Ultra thin titanium films in the range of a few nanometers have been deposited on monocrystalline lithiumtantalate (LiTaO 3) followed by deposition of 400 nm pure aluminum (Al). Texture measurements by means of electron backscatter diffraction show that the thickness of the intermediate titanium (Ti) layer significantly influences texture and grain structure of the overlying Al film. Increasing the thickness of the Ti layer from 0 nm to 20 nm leads to a change of aluminums texture from unoriented polycrystalline over highly oriented in single direction to highly oriented in twin structure.

Radiation effects in nanoelectronic elements

Radiation defects induced in planar nanosized structures by steady and pulsed ionizing radiation have been analyzed. Characteristics of test samples with a planar nanosized structure fabricated by deposition of an ultrathin titanium film onto a semi-insulating GaAs substrate and of field-effect transistor structures based on bundles of carbon nanotubes have been studied. Physical mechanisms responsible for the radiation-induced changes in characteristics of the nanoelectronic elements under consideration have been established.

Sum Frequency Generation Spectroscopic Investigation of TiOx/Pt(111): Surface Active Sites and Reaction Paths Probed by Formate

The catalytic behavior of ultrathin titanium oxide films deposited on platinum (111) surfaces is investigated through sum frequency generation (SFG) spectroscopy of the adsorption and decomposition of formate. TiOx films of 7 Å or less in thickness are prepared on Pt(111) substrates by evaporation of titanium under oxygen, and samples are examined as-prepared or after annealing at 873 or 973 K. Formate is adsorbed to the samples by exposure to 1000 langmuir of formic acid at 250 K. The frequency of the stretching vibration (ν(C−D)) of the deuterated formate C−D bond is found to be sensitive to the interaction between the adsorption sites and formate. SFG observations under different polarization combinations reveal that most formate is adsorbed to the surface with a bridge configuration, and that only a small amount of monodentate formate is present on the surface of TiOx/Pt(111) annealed at 973 K. Investigation of the effect of annealing temperature, time, and atmosphere on formate ν(C−D) frequency and intensity, in combination with low-energy electron diffraction (LEED) observations, reveals three kinds of surface active sites: defect sites, disordered titanium ion sites, and ordered 5-fold coordinated Ti4+ sites. These adsorption sites are responsible for ν(C−D) responses at frequencies of 2134−2184, 2195, and 2210−2226 cm−1, respectively. The defect sites are suggested to be located at the boundary between the disordered phase and the ordered phase of titanium oxide. Upon heating, formate adsorbed to defect sites undergoes decomposition at temperatures below 250 K, while formate adsorbed to ordered 5-fold coordinated Ti4+ sites decomposes via reaction paths: dissociation via monodentate formate as an intermediate, and diffusion onto defect sites before dissociation. The temperature of direct decomposition of bridge formate adsorbed to Ti4+ sites appears to be related to the formate ν(C−D) frequency, with lower frequencies corresponding to higher decomposition temperatures.

Ultra-thin Titanium Oxide Films on Mo(112), Measured by XPS

Two preparation methods were employed to grow a well-ordered ultra-thin titanium oxide film on Mo(112). The first method consisted of growing the films by direct deposition of Ti by chemical vapor deposition, followed by oxidation. Better film quality was obtained by the second method which involved deposition of Ti onto monolayer SiO2/Mo(112), as described in our prior work. By using x-ray photoelectron spectroscopy, Ti was determined to be in +3 oxidation state.

Formation of Ti and TiN ultra-thin films on Si by ion beam sputter deposition

Ultra-thin titanium and titanium nitride films on silicon substrate were obtained by ion beam sputtering of titanium target in vacuum and nitrogen atmosphere, using argon ions with energy of 5 keV and 15 μA target current. Elemental composition and chemical state of obtained films were investigated by X-ray photoelectron spectroscopy with using Mg-Kα X-ray radiation (photon energy 1253.6 eV). It was shown that it is possible to form both ultra-thin titanium films (sputtering in vacuum) and ultra-thin titanium nitride films (sputtering in nitrogen atmosphere) in the same temperature conditions. Photoelectron spectra of samples surface, obtained in different steps of films synthesis, detailed spectra of photoelectron emission from Si 2p, Ti 2p, N 1s core levels and also X-ray photoelectron spectra of Auger electrons emission are presented.

Pulsed r.f.‐glow‐discharge time‐of‐flight mass spectrometry for fast surface and interface analysis of conductive and non‐conductive materials

AbstractGlow discharge (GD) is a highly specialised source that especially meets the requirements for accuracy, simplicity and speed for content depth profiling and bulk analysis in both optical emission (OES) and mass spectrometry (MS). The pulsed radio frequency GD source has the potential for both elemental and molecular analysis of conductive and non‐conductive materials. To exploit the information delivered by pulsed radio frequency (r.f.)‐GD sources, fast sampling is required, and is available only through time‐of‐flight mass spectrometry (ToF‐MS). Compared to optical glow discharge (GD‐OES) instrumentation, a GD‐ToF‐MS system shows much simpler spectra, lower background signals and lower detection limits. The presented new r.f.‐GD‐ToF‐MS system is a successful combination of a commercial high‐end glow discharge instrument and an extremely fast and high‐resolution time‐of‐flight mass spectrometer. This new instrument was applied to analyse conductive and non‐conductive materials like anodic thin films. We could resolve 2‐nm Cr makers in aluminium oxide layers and measure trace elements in ultra thin titanium oxide films. Furthermore, we show the potential of the pulsed mode to separate analyte species from elements originating from residual gas. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Synthesis of well-ordered ultra-thin titanium oxide films on Mo(1 1 2)

Well-ordered Mo(1 1 2)–(8 × 2)-TiO x films were grown on the Mo(1 1 2) surface. Two preparation methods, direct growth on the Mo(1 1 2) surface and indirect growth by deposition of Ti onto monolayer SiO 2/Mo(1 1 2), were used. The latter method was found to be more reproducible with respect to film quality as determined by low-energy electron diffraction and scanning tunneling microscopy. The well-ordered (8 × 2)-TiO x film, for which a structure is proposed, was determined to be 1 ML and the Ti to be in an oxidation state of +3 using Auger spectroscopy, high-resolution electron energy loss spectroscopy and X-ray photoelectron spectroscopy.

Structure and growth of ultrathin titanium oxide films on Ru(0 0 0 1)

Structure, chemical composition and thermal stability of TiO x films with a thickness of up to 3 ML grown on a Ru(0 0 0 1) substrate were investigated by scanning tunneling microscopy, X-ray photoelectron spectroscopy and Auger electron spectroscopy. The films were prepared by evaporation of Ti in 10 −7 mbar O 2 onto Ru(0 0 0 1) at 640 K, followed by annealing in 10 −7 mbar O 2 or in UHV at temperatures between 700 K and 1000 K. Depending on the deposition and post-annealing conditions, we find several different structures of the Ti oxide, with the layers post-annealed in an O 2 environment being generally better defined than those post-annealed in vacuum. The layers consist of triangular units which coalesce upon annealing. O 2 annealing of monolayer films leads to an oxygen deficient TiO 2 layer. Annealing to 900–1000 K changes the structure and composition of the film, a coincidence structure with a Moiré pattern is observed upon O 2 annealing.

Preliminary Exploration of Nanoscale Titanium Dots using STM

Quasinanoscale dots on ultrathin titanium film are discussed preliminarily with SPM as fabrication and analysis tool. The possible mechanisms are suggested and discussed.

Nanopatterning by biological templating and laser direct writing in thin laser deposited films

We report on three alternative approaches to laser-supported sub-micro- and nanopatterning of ultrathin films. The inherent non-linearities of direct writing techniques can be used to fabricate structures far below the optical resolution limit. Due to the non-linear dependence of light absorption and reaction rate on film thickness and temperature (a) the lateral self-limitation of the oxidation reaction in ultrathin titanium films on a transparent heat insulating substrate in air can occur. The polarization of sharp conducting tips results in (b) near-field enhancement of the optical field in nanometer regions that allows diminishing of the effective size of the radiation source. The third approach (c) is based on the nanometer-period pattern transfer from a biomolecular template to a Pt/C overlayer deposited by cross-beam pulsed laser deposition.

The search for an ultra-thin tritium source for the neutrino mass measurement

The mass of the electron anti-neutrino can be determined from a precise measurement of the shape of the tritium spectrum near its end point. Several methods of producing appropriate tritium sources have been investigated including the tritiating of ultra-thin titanium films on quartz substrates.