Zinc Thin Films Research Articles

Electron-Beam-Induced Nucleation Centers and Selective Deposition of Thin Zinc Films

Selective deposition of pure metal films was achieved successfully by combining electron-beam irradiation and subsequent vapor deposition. A thin layer of hydrocarbon was used as a beam-sensitive material. It was found that organic materials such as different kinds of hydrocarbons possess much higher sensitivities to electron-beam irradiation than the inorganic material. Nucleation centers were produced by e-beam irradiation at an electron dose density as low as 5×10-3 C/cm2. This value is at least three orders of magnitude lower than the value reported for inorganic material to date and allows high-speed or large-area processing. It was observed that the behavior of the deposition is kinetics controlled. Due to this mechanism, the size of the deposition area was found to always be smaller than that of the irradiating beam and it varied with the electron dose. It is expected that this mechanism may possibly reduce the back-scattered-electron effect and achieve a spatial resolution better than the beam-spot diameter.

Growth of ZnO Thin Films and Whiskers

Copper-metallized silicon wafers were used as substrates for the deposition of zinc oxide thin films using a radio frequency sputter deposition technique. Copper metallization on silicon wafer was performed using two different methods, a plating technique and a sputter deposition technique. Copper-metallized silicon substrates were then deposited with zinc oxide thin films under various sputter deposition conditions. The characteristics of zinc oxide thin films were found to not only depend on the deposition conditions, but also be strongly influenced by the type and characteristics of the copper layers. In addition to polycrystalline thin-film zinc oxide, single-crystal zinc oxide whiskers were also found on silicon substrates with plated copper.

Addressing of Optoelectronic Memory of Thin Film Zinc Porphyrin with Crossed 5 μm Indium Tin Oxide Arrays

Addressing of Optoelectronic Memory of Thin Film Zinc Porphyrin with Crossed 5 μm Indium Tin Oxide Arrays

Properties of zinc thin film thermometers

Thin films of aluminum have for many years been used near T∼1.5 K to detect the tiny temperature fluctuations which accompany the propagation of waves of third sound in thin superfluid 4He films. For lower temperatures, zinc thermometers have been used to detect phonon propagation in bulk helium. We have fabricated zinc thermometers having zero-field sensitivities δR/δT∼20000 Ω/ K at T c ∼680 mK when operated at a bias current i b =10 μA . We describe here the fabrication techniques and the operating characteristics of thin film zinc thermometers which we have used to detect third sound for 100⩽T⩽680 mK .

Thin-film semiconductor sensors for hyperthermal oxygen atoms

In Earth orbit, atomic oxygen (AO) erodes and degrades many spacecraft materials. Several sensors have been employed to make in situ measurements of these oxygen atom fluxes, yet none has proved suitable for general application to microsatellites. We have investigated the potential of thin-film zinc oxide (ZnO) AO sensors. It is known that single crystal and thin-film semiconductor sensors may be used to measure fluxes of low-energy (thermal) oxygen atoms. This work extends the principle to the measurement of hyperthermal (high energy) oxygen atoms in a ground-based simulation facility. It is found that, upon exposure to AO, the conductance of the ZnO sensors decreases. Moreover, the rate of sensor conductance change is proportional to the flux of oxygen atoms. Two sensors, which were manufactured simultaneously, demonstrated very similar responses when exposed concurrently to hyperthermal AO. Further experiments showed that the sensors were not affected by fluxes of molecular oxygen, but were influenced by ultraviolet (UV) radiation. A ZnO film covered with silica — to prevent the action of AO — was used to examine the influence of UV, which was shown to cause a small, permanent change of the conductance of the semiconductor.

Visible Light Sensitization of Titanium Dioxide with Self-Organized Porphyrins: Organic P−I−N Solar Cells

Free base 5,10,15,20-tetrakis(4-n-octylphenyl) porphyrin (H{sub 2}TOPP) belongs to a class of self-organizing porphyrins. Since its LUMO lies above the conduction band of titanium dioxide (TiO{sub 2}) and its visible light absorption is very strong, sensitization of TiO{sub 2} with H{sub 2}TOPP thin films is possible. After spin-coating this porphyrin onto n-type TiO{sub 2}, the Fermi-level of H{sub 2}TOPP is measured, from which it is established that it behaves as intrinsic semiconductor, i.e., donor and acceptor densities, if present, compensate each other. Thin films of zinc 5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin (ZnTCPP) are also investigated and show profound p-type character. Moreover, the LUMO of ZnTCPP is located about 0.4 eV above that of H{sub 2}TOPP making an organic based heterostructure p-i-n solar cell possible. In this cell, H{sub 2}TOPP is sandwiched between n-type TiO{sub 2} and p-type ZnTCPP. The LUMO positions of these porphyrins is such that unidirectional energy transfer from ZnTCPP to H{sub 2}TOPP occurs. By carefully comparing the photocurrent action spectra with the absorption spectra, it could be established that a built-in field in the p-i-n structure is beneficial for solar-energy conversion.

The significance of parallel electric field on the preferred orientation and surface morphology of ZnO thin films

Piezoelectric zinc oxide thin film, with its high electromechanical coefficient, has found applications in surface and bulk acoustic wave devices. A suitable polycrystalline zinc oxide thin-film transducer should possess the following two characteristics. First, structurally, the normals to the basal planes (0 0 2) must be predominantly oriented perpendicular to the plane of the substrate (c-axis oriented). Second, electrically, the resistivity of the film should be as high as possible. Having these requirements, polycrystalline zinc oxide can be satisfactorily used in place of ZnO single-crystal thin film in veryand ultra-high-frequency acoustic applications. Accordingly, if we could manipulate the c-axis orientation of the film, we would be able to tailor the device’s performance. We have investigated the effects of parallel electrical fields (detached electrodes) on the preferred c-axis orientation and surface morphology of polycrystalline zinc oxide thin films. Zinc thin films are oxidized at different temperatures with the application of parallel electrical fields. We have found that the application of parallel electrical fields slightly improves the c-axis orientation. The better c-axis–oriented structure is manifested by a less needle-shaped forest crystal morphology on the surface of the film.

Structural, electrical and optical properties of zinc oxide produced by oxidation of zinc thin films

We have investigated the effects of oxidation temperature on the physical properties of polycrystalline zinc oxide thin films. Zinc thin films are oxidized at different temperatures in air. We have found that increasing the oxidation temperature deteriorates the preferred c-axis orientation. Also, increasing the oxidation temperature enlarges the crystal size and increases the number of needle-shaped crystals on the surface of the ZnO samples. By increasing the oxidation temperature, more than zinc melting point, tensile stresses start to build up in the films. Also by increasing temperature, sheet resistance of the films decreases, while photoluminescence intensity ratio (green to orange) increases. Increasing the oxidation temperature reduces the transparency of the films, too. It is proposed that either an increase in the number of oxygen vacancies or a decrease in the volume of grain boundaries, is responsible for the observed behavior of the films at higher oxidation temperatures.

Third Sound and Quartz Crystal Microbalance Measurements of Helium on Rubidium

We present preliminary results from an experiment in progress which seeks to study third sound propagation on clean glass and rubidiated glass for several 4 He coverages. The third sound is driven thermally and detected with thin-film zinc bolometers over the temperature range 0.100≤T≤0.670 K. Measurements of the frequency of a quartz crystal microbalance which has rubidium deposited onto one side are made through the temperature range 0.100≤T≤1.5 K for each helium coverage studied. Results of measurements for pure 4 He films, primarily for third sound, are presented for coverages≤8.52 atomic layers.

Two-dimensionally oriented organic molecules as a substrate for vapor growth of zinc thin films

Zinc metal was vacuum deposited at room temperature onto cadmium stearate Langmuir-Blodgett (LB) films with surfaces of either hydrophilic head groups or hydrophobic tail groups. Different growth modes on different surfaces of the LB films were observed with an atomic force microscope (AFM). Fine Zn particles deposited onto the hydrophobic surface were uniform and similar in shape irrespective of the deposition rate. However, on the hydrophilic surface, triangular and/or quasi-hexagonal Zn crystals were observed when the deposition rate was very low. Chemical interaction between organic functional groups and deposited metal seems critical for the manner of growth. The possibility of control of the architecture over inorganic crystallization using two-dimensionally oriented organic surfaces is proposed.

Joint Texture Refinement

Correction for preferred orientation of crystallites using simple empirical functions has been extended for structure analysis of strongly textured materials by the method called joint texture refinement. The method is based on simultaneous fitting of calculated intensities to the whole set of intensities measured at several sample inclinations. Thin films of zinc and a powder sample of brucite have been used as testing materials with a modified version of the program POWLS.

Electrochromism of Orientation-Controlled Naphthalocyanine Thin Films

Structure-dependent electrochromism was investigated with vapor-deposited thin films of zinc and vanadyl naphthalocyanines (ZnNc and VONc). The amorphous ZnNc film deposited on an indium tin oxide (ITO) coated glass electrode exhibited an irreversible electrochromic oxidation in 0.1 M KCl. This reaction gave rise to swelling of the film surface due to expansion of grains caused by incorporation of charge-compensating anions between the aggregated molecules. Epitaxially oriented films were prepared by deposition onto the (001) cleavage surface of NaCl and then transferred onto the ITO electrode. The epitaxial ZnNc film, in which the planar molecules are piled up in columns taking on the face-to-face, eclipsed stacking, exhibited both electrochromic reduction and oxidation. This electrochromic activity was attributed to a reversible incorporation of counterions through hollow channels between the molecular columns, which was accompanied with rearrangement in the molecular stacking. By contrast, no electroch...

The effect of perpendicular electric fields on the orientation of zinc oxide crystals during the oxidation of zinc thin films

The effect of direct current (d.c.) electric fields on the crystal orientation of zinc oxide thin films was investigated. Evaporated zinc thin films were oxidized in air under the application of perpendicular electric fields (detached electrodes) at different temperatures. The application of positive fields at 550 °C improved thec-axis orientations up to 1000 V cm−1. Further increase in field strength caused thec-axis orientations to decline to their original values (no applied field). The application of negative normal fields at 550 °C deteriorated thec-axis orientations up to 800 V cm−1. Thec-axis orientations improved to their original values by increasing the field strength to greater than 800 V cm−1. The crystal size remained unchanged, but the surface morphology was affected by the application of the electric fields at temperatures above the melting point of zinc. No significant change in optical properties was detected for samples that were subjected to electric fields. Whenever thec-axis orientation improved, crystals on the film surface became rounded and a more ordered microstructure was observed. On the other hand, the deterioration ofc-axis orientation was manifested by the increase in the number of whisker-shaped crystal needles on the surface of the ZnO thin films.

Interfacial Reactions between Thin Films of Zinc and (100)InP

Zinc is currently being used as a dopant element in ohmic contact metallizations to p-type III-V compound semiconductors. A low contact resistivity of Zn-containing contacts is attributed to a diffusion of Zn atoms, resulting in a highly doped interface layer. The results of our recent study on Zn-based metallizations to p-GaAs, however, strongly suggest that Zn plays a more fundamental role in the formation of an ohmic contact. When deposited directly onto GaAs, Zn penetrates the native oxide [1]. Added to Au metallization lowers the temperature of reaction between Au and GaAs. Furthermore, Zn stabilizes the size of metallization grains [2, 3]. In this work we focus on the reactivity of thin Zn films deposited on InP in order to determine to what extent the interaction of zinc with native oxides can be generalized to other compound semiconductors. We study stuctural and electrical properties of the contacts using XRD (X-ray diffraction), TEM (transmission electron microscopy), SIMS (secondary ion mass spectrometry), and specific contact resistance measurements. Conventional TEM and high resolution electron microscopy (HREM) investigations were made on cross-sectional specimens, with [110] InP normal to the surface, prepared by a standard technique with the final iodine ion milling. SIMS profiling was carried out using Cs+ as a primary beam with detection of CsM secondary cluster ions, enabling thus determination of the relative concentratiOn

Characterization of mixed zinc-oxidized zinc thin films deposited by a cold remote nitrogen plasma

A method for the deposition of a zinc-containing film on aluminium and polypropylene substrates by a cold remote nitrogen plasma (CRNP) was described. The reactivity of the CRNP was first used to clean the substrate which had to be metallized; when the substrate was a polymer, this step was also used to increase its wettability. The reactivity of the CRNP was then used to decompose diethylzinc vapour in order to deposit, at ambient temperature, a zinc-containing film with a blue-grey metallic appearance. XPS analyses were performed after transfer to ambient air during about 10 min. An Ar + etching procedure was then used to progressively investigate the inner layers. The evolution of the Zn Auger LMM transition and of the Ols, Cls and Nls photoelectron peaks were studied versus the Ar + etching duration. Under a contamination layer, the amounts of C and N relative to Zn in the coating film were very low while oxidized zinc species have been detected in the film. Oxidation of the Zn deposit may occur either during the process itself or during air exposure before XPS analyses considering the porosity of the film. The nature of the interface with the substrate appears different: with the aluminium substrate, the deposited film was a Zn-ZnO-Zn(OH) 2 mixture with a zinc rate equal to 55%. With the polypropylene substrate, Zn(OH) 2 appeared only on the outer layer. Inside it was a Zn-ZnO mixture.

Additions and Corrections - Structural Characterization of Solid Self-Ordered Thin Films of Zinc(II) and Palladium(II)Octakis(β-deoxyethyl)porphyrin

Additions and Corrections - Structural Characterization of Solid Self-Ordered Thin Films of Zinc(II) and Palladium(II)Octakis(β-deoxyethyl)porphyrin

Gold and zinc thin films deposited by the ionized cluster beam technique

Thin film deposition from beams of atom clusters, some of which are ionized and accelerated to the growing surface, was first proposed in 1972. This idea created interest because it was fundamentally different from other deposition methods and was expected to have unique capabilities. Development of a suitable cluster source has been difficult, and large clusters of zinc (about 2000 atoms per cluster) have only recently been produced. Two source parameters were change to accomplish this. The crucible pressure was increased from 2 Torr to over 1000 Torr, and a converging-diverging nozzle 18 mm long and 0.4 mm in diameter at the throat was used in place of the older nozzle with dimensions of 1 mm × 1 mm. To separate the pressure and nozzle effects, gold thin films are being deposited with the new converging-diverging nozzle. The vapor pressure of gold is much lower than that of zinc at a given temperature. Cluster size measurements show no significant numbers of gold clusters. The effect of the crucible pressure on the formation of the large cluster is much more significant than that of the nozzle geometry. The effects of varying ion energy bombardment on film microstructure are also evaluated using atomic force microscopy.

Triple-beam resonant silicon force sensor based on piezoelectric thin films

Abstract A resonant force sensor with semidigital frequency output based on a triple-beam resonator structure in silicon is presented. The piezoelectric excitation of the resonator operating in an antisymmetric vibration mode is realized by thin-film zinc oxide layers. An advantage of this triple-beam design is a high mechanical quality factor combined with high force sensitivity due to the antisymmetric vibration mode and the load-dependent stress concentration in the triple beam. Extensive finite-element modelling has been carried out to determine the static and dynamic behaviour and to obtain optimum sensor performance. Several resonator designs have been fabricated to study mechanical decoupling from the clamping region. Experimental characterization of the triple-beam sensor and of the zinc oxide thin-film properties has been performed.

Mechanisms of electronic conduction through thin film ZnS:Mn

Abstract Gold deposited by d.c. sputtering is found to form an ohmic contact to thin-film manganese-doped zinc sulphide (ZnS: Mn). This has facilitated the investigation of electron transport mechanisms in the bulk of thin-film ZnS: Mn, deposited by r.f. sputtering on to silicon substrates. Analysis of current density versus voltage characteristics as a function of temperature reveals the existence of ohmic and trap-limited space-charge currents. From analysis of these characteristics, the Fermi level in the ZnS: Mn is calculated to be 0.30 ± 0·01 e V below the conduction band edge, and a discrete trap is identified at 0.25 ± 0·01 eV with a density of approximately 2 × 1017 cm−3. Evidence suggests that the origin of this trap may be linked to sulphur vacancies.

Interaction between Thin Films of Zinc and (100) GaAs

Zinc is currently being used as a dopant element in ohmic contact metallization systems to p-type GaAs. The results of our recent studies on interfacial reactions occurring during formation of Au(Zn)/p-GaAs ohmic contact indicate that Zn plays a more universal role facilitating the dispersion of the native oxide on GaAs [1]. On the other hand, in plating and soldering technologies zinc is widely used as a component enabling one the of metallic surfaces before further processing [2, 3]. To our knowledge, the precise mechanism of these cleaning action of zinc has not been yet established. The aim of the present work is to elucidate the metallurgical behavior of Zn in contact with GaAs. The microstuctural analysis of the Zn/GaAs interface, under as-deposited state and annealed conditions, was carried out by transmission electron microscopy (TEM) methods. Emphasis was placed on the determination of the stucture and composition of reaction products. High resolution electron microscopy (ΗREM) images were recorded with the JEOL JEM 2000EΧ (200 keV). The substrates used in this study were (100) oriented p-type GaAs wafers doped with Zn to a concentration of 8 x 10 17 cm-3 . Prior to metal deposition the samples were degreased in trichloroethylene (TCE), acetone and isopropyl alcohol, and then etched in solution of ΝΗ4OH:H2O2:H2O (20:7:973), followed by a rinse in deionized H2 O and immersion into ΝH4 OH:H2O (1:10) for 10 s. Zinc fflms, 150 nm thick, were deposited by vacuum thermal evaporation using 99.999% Zn source, in