Indium oxide, tin oxide and indium tin oxide nanostructure growth by vapor deposition

Indium oxide, tin oxide and indium tin oxide nanowires have been grown by vapor deposition on Si and quartz substrates. Under the growth conditions used, pure SiO_x nanowires, a mixture of SiO_x and indium oxide, tin oxide or indium tin oxide nanostructures, or pure indium oxide, tin oxide or indium tin oxide nanostructures could be obtained at different substrate temperatures. The growth mechanism of the obtained nanostructures at different substrate temperatures is discussed. Optical and electrical properties of the deposited pure indium oxide, tin oxide or indium tin oxide nanostructures have been measured, and low sheet resistances on quartz substrates have been obtained for indium oxide and indium tin oxide nanostructures.     

Indium tin oxide thin films by bias magnetron rf sputtering for heterojunction solar cells application

In this investigation ITO thin films were prepared by bias magnetron rf sputtering technique at substrate temperature of 180 °C and low substrate-target distance for future a-Si:H/c-Si heterojunction (HJ) solar cells application. Microstructure, surface morphology, electrical and optical properties of these films were characterized and analyzed. The effects of ion bombardments on growing ITO films are well discussed. XRD analysis revealed a change in preferential orientation of polycrystalline structure from (2 2 2) to (4 0 0) plane with the increase of negative bias voltage. Textured surface were observed on AFM graphs of samples prepared at high negative bias. Hall measurements showed that the carrier density and Hall mobility of these ITO films are sensitive to the bias voltage applied. We attributed these effects to the sensitivity of energy of Ar⁺ ions bombarding on growing films to the applied bias voltage in our experiments. At last the figure of merit was calculated to evaluate the quality of ITO thin films, the results of which show that sample prepared at bias voltage of −75 V is good to be used in HJ cells application.     

Functional nanowires of tin oxide

Quasi-one-dimensional nanostructures of tin oxide were produced in controlled conditions through condensation from the vapor phase. The preparation was assisted by noble metal catalysts and uniform single-crystalline nanowires were produced. The nucleation of nanowires was achieved at 470 °C, owing to the vapor–liquid–solid growth mechanism activated by the catalytic Pt clusters. The peculiar microstructural properties of these semiconducting metal oxide nanostructures will be summarized. The high aspect ratio and the high degree of crystallinity achieved for the nanowires foresee their functional exploitation. PACS 61.46.Hk; 81.07.Bc; 81.16.Hc; 68.37.Lp     

Indium oxide thin-film holographic recorders grown by excimer laser reactive sputtering

2 O₃) thin films on glass substrates is performed by pulsed laser ablation of a metallic indium target in an oxygen atmosphere. X-ray diffraction analysis verifies that a transition, from amorphous to polycrystalline film growth, occurs at a temperature of 150 °C. Films grown under optimized conditions exhibit optical transmission higher than 80% in the visible light. Ultraviolet radiation (λ= 325 nm) induced dynamic holographic recording in films deposited at specific temperature and oxygen pressure settings is also demonstrated. Received: 25 April 1997/Accepted: 27 May 1997     

Indium zinc oxide thin films deposited by sputtering at room temperature

The deposition of amorphous indium zinc oxide (IZO) thin films on glass substrates with n-type carrier concentrations between 10¹⁴ and 3 × 10²⁰ cm⁻³ by sputtering from single targets near room temperature was investigated as a function of power and process pressure. The resistivity of the films with In/Zn of ∼0.7 could be controlled between 5 × 10⁻³ and 10⁴ Ω cm by varying the power during deposition. The corresponding electron mobilities were 4-18 cm² V⁻¹ s⁻¹.The surface root-mean-square roughness was <1 nm under all conditions for film thicknesses of 200 nm. Thin film transistors with 1 μm gate length were fabricated on these IZO layers, showing enhancement mode operation with good pitch-off characteristics, threshold voltage 2.5 V and a maximum transconductance of 6 mS/mm. These films look promising for transparent thin film transistor applications.     

Indium tin oxide as an optical memory material

Indium Tin Oxide (ITO) films prepared by reactive rf sputtering show excellent properties for optical recording applications in a very narrow range of oxygen partial pressure (around 4×10^–5 Torr). This narrow range is at the edge of a plateau in the electrical conductivity of the films. A small increase in the oxygen partial pressure (P(O₂)5×10^–5 Torr) causes a large and abrupt change in the electrical conductivity as well as in the structural and optical properties of these films. In addition, irradiating films at the edge of the plateau (P(O₂)4×10^–5) with a low-power pulsed laser (25 mW) yields transparent films. These results suggest that the same mechanism may be responsible for the opaque to transparent transformations observed in these experiments.     

Vanadium oxide thin films deposited on indium tin oxide glass by radio—frequency magnetron sputtering

Highly oriented VO₂(B), VO₂(B) + V₆O₁₃ films were grown on indium tin oxide glass by radio-frequency magnetron sputtering. Single phase V₆O₁₃ films were obtained from VO₂(B) +V₆O₁₃ films by annealing at 480℃ in vacuum. The vanadium oxide films were characterized by x-ray diffraction and x-ray photoelectron spectra (XPS). It was found that the formation of vanadium oxide films was affected by substrate temperature and annealing time, because high substrate temperature and annealing were favourable to further oxidation. Therefore, the formation of high valance vanadium oxide films was realized. The V₆O₁₃ crystalline sizes become smaller with the increase of annealing time. XPS analysis revealed that the energy position for all the samples was almost constant, but the broadening of the V_2p3/2 line of the annealed sample was due to the smaller crystal size of V₆O₁₃.     

Optical and electrical properties of nanocrystal zinc oxide films prepared by dc magnetron sputtering at different sputtering pressures

The nanocrystal thin films of zinc oxide doped by Al (ZnO:Al) were deposited by dc reactive magnetron sputtering on the glass substrates, in the pressure range of 33-51 Pa. From the X-ray diffraction patterns, the nanocrystalline structure of ZnO:Al films and the grain size were determined. The optical transmission spectra depend from the sputtering pressure, but their average value was 90% in the range from 33 Pa to 47 Pa. Also, the sputtering pressure changes the optical band gap of ZnO:Al films, which is highest for films deposited at 37 Pa, 40 Pa and 47 Pa. The obtained films at room temperature have a sheet resistance of 190 Ω/cm² which increases with time, but the films annealed at temperature of 400 °C have constant resistance. The surface morphology of the films was studied by Scanning electron microscopy. XPS spectra showed that the peak of O1s of the as-deposited films is smaller than the peak of the annealed ZnO:Al films.     

Optical fiber refractometers based on indium tin oxide coatings fabricated by sputtering

This Letter presents the fabrication of optical fiber refractometers based on indium tin oxide (ITO) coatings deposited by sputtering with response in the visible region. ITO thin films have been sputtered by means of a rotating mechanism that enables the fabrication of smooth and homogeneous coatings onto the optical fiber core. The ITO coating acts as a resonance supporting layer. This permits us to couple light from the waveguide to the ITO-coating/external medium region at specific wavelength ranges. The device is sensitive to external medium refractive index, which allows its utilization as a refractometer. The sensitivity is dependent on the coating thickness, ranging from 523.21 to 1221 nm/refractive index unit in the explored sensors. The sensor development process is time effective compared to other techniques such as dip coating or layer-by-layer self-assembly, which is interesting in terms of mass production.     

Chemical characterization of as-deposited microcrystalline indium oxide films prepared by reactive dc magnetron sputtering

x ) films with a crystallite size of 20.6 nm and a thickness of 100–1600 nm were prepared by dc reactive magnetron sputtering onto Corning 7059 glass substrates in various mixtures of oxygen in argon at room temperature. In a previous article, we have shown that the conductivity of these films can change in a controllable and fully reversible manner by about six orders of magnitude between an insulating and a very conductive state by alternately exposing the films to ultraviolet light (hν≥3.5 eV) in vacuum and reoxidizing them in ozone. In the present article, we report on studies of the surface and depth composition of these films carried out by Auger electron spectroscopy (AES), combined with depth profiling analysis. Quantitative Auger and energy-dispersive X-ray analysis (EDX) were employed to determine the stoichiometry of the films. The effects of film thickness and oxygen content during the deposition on the stoichiometry were examined. Both AES and EDX analysis confirmed that the stoichiometry is invariant for these growth conditions. The depth profiling analysis showed that all films exhibit extremely good in-depth uniformity, regardless of their thickness. Received: 21 January 1998/Accepted: 23 January 1998     

Room temperature deposition of crystalline indium tin oxide films by cesium-assisted magnetron sputtering

Indium tin oxide (ITO) films were deposited on a Si (1 0 0) substrate at room temperature by cesium-assisted magnetron sputtering. Including plasma characteristics, the structural, electrical, and optical properties of deposited films were investigated as a function of cesium partial vapor pressure controlled by cesium reservoir temperature. We calculated the cesium coverage on the target surface showing maximum formation efficiency of negative ions by means of the theoretical model. Cesium addition promotes the formation efficiency of negative ions, which plays important role in enhancing the crystallinity of ITO films. In particular, the plasma density was linearly increased with cesium concentrations. The resultant decrease in specific resistivity and increase in transmittance (82% in the visible region) at optimum cesium concentration (4.24 × 10⁻⁴ Ω cm at 80 °C of reservoir temperature) may be due to enhanced crystallinity of ITO films. Excess cesium incorporation into ITO films resulted in amorphization of its microstructure leading to degradation of ITO crystallinity. We discuss the cesium effects based on the growth mechanism of ITO films and the plasma density.     

A study of the optical properties of titanium oxide films prepared by dc reactive magnetron sputtering

TiO₂ thin films were deposited on the glass substrates by dc reactive magnetron sputtering technique at different sputtering pressures (2 × 10⁻³ to 2 × 10⁻² mbar). The films prepared at low pressures have an anatase phase, and the films prepared at high pressures have an amorphous phase. The optical properties were studied by measuring the transmittance and the ellipsometric spectra. The optical constants of the films in the visible range were obtained by fitting the transmittance combined with the ellipsometry measurements using the classical model with one oscillator. The refractive index of the films decreases from 2.5 until 2.1 as the sputtering pressure increases from 2 × 10⁻³ to 2 × 10⁻² mbar. The films prepared at the pressure higher than 6 × 10⁻³ mbar show a volume inhomogeneity. This volume inhomogeneity has been calculated by fitting the transmittance and the ellipsometric spectra. The volume inhomogeneity of the film prepared at the highest sputtering pressure is about 10%. Although the films prepared at high pressures show a large volume inhomogeneity, they have low extinction coefficients. It is suggested that the anatase phase results in more light scattering than amorphous phase does, and then a high extinction coefficient.     

Indium tin oxide surface treatments for improvement of organic light-emitting diode performance

We have systematically investigated the influence of UV ozone and acid (HCl) treatments (separate and combined) of the surface of indium tin oxide (ITO) on the ITO parameters and the performance of organic light-emitting diodes (OLEDs) fabricated on the treated substrates. The ITO substrates were characterized by Hall measurements, Seebeck coefficient measurements and surface-probe microscopy. After ITO characterization, two types of devices (ITO/NPB/rubrene/Alq₃/LiF/Al and ITO/TPD/rubrene/Alq₃/LiF/Al) were fabricated on the differently treated substrates. It was found that in both cases the optimal treatment was HCl followed by UV ozone, which resulted in the lowest turn-on voltage and the highest luminous efficiency. The maximum luminous efficiency in the ITO/NPB/rubrene/Alq₃/LiF/Al OLED with HCl followed by UV ozone treatment was 2.15 lm/W compared to 1.46 lm/W with UV ozone treatment only. PACS 81.65Cf; 85.60.Jb     

Synthesis, characterization and photoluminescence of tin oxide nanoribbons and nanowires

In this work we report the successful formation of tin oxide nanowires and tin oxide nanoribbons with high yield and by using simple cheap method. We also report the formation of curved nanoribbon, wedge-like tin oxide nanowires and star-like nanowires. The growth mechanism of these structures has been studied. Scanning electron microscope was used in the analysis and the EDX analysis showed that our samples is purely Sn and O with ratio 1:2. X-ray analysis was also used in the characterization of the tin oxide nanowire and showed the high crystallinity of our nanowires. The mechanism of the growth of our1D nanostructures is closely related to the vapor–liquid–solid (VLS) process. The photoluminescence PL measurements for the tin oxide nanowires indicated that there are three stable emission peaks centered at wavelengths 630, 565 and 395 nm. The nature of the transition may be attributed to nanocrystals inside the nanobelts or to Sn or O vacancies occurring during the growth which can induce trapped states in the band gap.     

Plasma-based sputtering of indium tin oxide for the application of photovoltaic cells

Transparent and conducting indium tin oxide (ITO) thin films were deposited on soda lime glass substrates by RF plasma magnetron sputtering at room temperature. The effect of thickness (100, 200 and 300?nm) on the physical (structural, optical, electrical) properties of ITO thin films was investigated systematically. It is observed that with an increase in thickness, the X-ray diffraction data indicate polycrystalline films with grain orientations predominantly along (222) and (400) directions; the average grain size increases from 10 to 30?nm; the optical band gap increases from 3.68 to 3.73?eV and the transmission decrease from 80% to 70% . Four-point probes show a low resistivity (2.4×10^?5?Ω?cm) values for film with a thickness 300?nm. Present work shows that the ITO is a promising transparent conductive oxide material for the solar cell application.     

Characteristics of growth of complex ferroelectric oxide films by plasma-ion sputtering

An experimental investigation was made of the process of growth of a complex oxide film, such as BaTiO₃ or (Ba, Sr)TiO₃, by plasma-ion sputtering. It was found that ion bombardment of a ceramic target knocked out neutral excited atoms. These atoms lost energy away from the target by collisions and at a certain critical distance h_cr they were capable of oxidation to produce BaO, TiO, TiO₂, and SrO. Therefore, depending on the distance between the cathode and the substrate, the construction material arrived in the form of atoms or molecules of simple oxides. These two (atomic and molecular) deposition mechanisms corresponded to two mechanisms of synthesis and crystallization differing in respect of the dependences of the growth rate, unit cell parameters, and other structural properties on the deposition temperature. The role of re-evaporation and of oxidation-reduction processes was analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 7–11, February, 1981.     

Structural and electrical properties of fluorine-doped zinc tin oxide thin films prepared by radio-frequency magnetron sputtering

Transparent and conductive thin films of fluorine doped zinc tin oxide (FZTO) were deposited on glass substrates by radio-frequency (RF) magnetron sputtering using a 30 wt% ZnO with 70 wt% SnO₂ ceramic targets. The F-doping was carried out by introducing a mixed gas of pure Ar, CF₄, and O₂ forming gas into the sputtering chamber while sputtering ZTO target. The effect of annealing temperature on the structural, electrical and optical performances of FZTO thin films has been studied. FZTO thin film annealed at 600 °C shows the decrease in resistivity 5.47 × 10⁻³ Ω cm, carrier concentration ∼10¹⁹ cm⁻³, mobility ∼20 cm² V⁻¹ s⁻¹ and an increase in optical band gap from 3.41 to 3.60 eV with increasing the annealing temperatures which is well explained by Burstein–Moss effect. The optical transmittance of FZTO films was higher than 80% in all specimens. Work function (ϕ) of the FZTO films increase from 3.80 eV to 4.10 eV through annealing and are largely dependent on the amounts of incorporated F. FZTO is a possible potential transparent conducting oxide (TCO) alternative for application in optoelectronics.     

Indium oxide nanostructures

In this report we review the growth of indium oxide (In₂O₃) nanostructures, including octahedral nanocrystals (NCs), nanobelts (NBs), nanosheets (NSs), and nanowires (NWs), by hot-wall chemical vapor deposition (HW-CVD). This system is highly controllable, allowing the user to easily access different growth regimes – each corresponding to the growth of a different nanostructure – by changing growth variables of the HW-CVD system. Hot-wall CVD produces crystalline nanostructures; here we present a survey of microstructural characterizations of the four types of In₂O₃ nanostructures using transmission- and scanning-electron microscopy. Interestingly, the In₂O₃ nanostructures have different preferred growth directions: NCs have (111) faces, NBs are predominantly (200), and NWs are predominantly (110). We end the review by discussing the current shortcomings of HW-CVD growth of In₂O₃ nanostructures. PACS 61.46.-w; 61.82.Rx; 73.31.Hb; 81.02.-b     

Deposition and characterization of TiZrV-Pd thin films by dc magnetron sputtering

TiZrV film is mainly applied in the ultra-high vacuum pipes of storage rings.Thin film coatings of palladium,which are added onto the TiZrV film to increase the service life of nonevaporable getters and enhance H_2pumping speed,were deposited on the inner face of stainless steel pipes by dc magnetron sputtering using argon gas as the sputtering gas.The TiZrV-Pd film properties were investigated by atomic force microscope(AFM),scanning electron microscope(SEM),X-ray photoelectron spectroscopy(XPS) and X-Ray Diffraction(XRD).The grain size of TiZrV and Pd films were about 0.42-1.3 nm and 8.5-18.25 nm respectively.It was found that the roughness of TiZrV films is small,about 2-4 nm,but for Pd film it is large,about 17-19 nm.The PP At.%of Pd in TiZrV/Pd films varied from 86.84 to 87.56 according to the XPS test results.