ZnO Film Thickness Research Articles

Strain-Induced ZnO Spinterfaces

A series of undoped ZnO films of different thicknesses was grown on different substrates over a range of different temperatures and oxygen partial pressures. Notably, ferromagnetism was detected in very thin ZnO films (∼20 nm), and its magnetic ordering was also found to be thermally stable up to 800 °C. To our surprise, magnetic ordering was destroyed as the ZnO overlayer grew thicker, just as its in-plane compressive strain was released and the ZnO/substrate interface damaged by misfit dislocations. The source of magnetism was found to be due to neither defects in the bulk of the ZnO overlayer nor the bulk of the substrate. Experimental results showed that strain at the ZnO/substrate interface led to a strain-induced magnetic effect. Using first-principles ab intio calculation, we confirmed that strain at the ZnO/substrate interface stabilizes zinc vacancy defects, which are magnetic. Ferromagnetic ordering is a result of the coupling of unpaired electron spins originating from the oxygen 2p orbitals su...

Detection of dimethyl methyl phosphonate – a simulant of sarin: The highly toxic chemical warfare – using platinum activated nanocrystalline ZnO thick films

Nanocrystalline ZnO powder was prepared using ultrasonic atomization technique. Thick films of this powder were prepared using simple screen printing technique. Pt-modified-ZnO (platinum activated) films were obtained by dipping pure ZnO films into an aqueous solution of chloroplatnic acid for different intervals of time, followed by firing at 500 °C for 30 min. The sensing performance of the unmodified (pure) and Pt-modified ZnO (Pt–ZnO) films was tested on exposure of CWAs (chemical warfare agents) simulants, such as, dimethyl methyl phosphonate (DMMP), 2-chloroethyl ethyl sulfide (CEES) and 2-chloroethyl phenyl sulfide (CEPS). Both pure ZnO and Pt–ZnO films showed higher response to DMMP than their responses to CEES and CEPS. The simulant response, selectivity, response time and recovery time of the sensors were measured and presented. The role played by surface platinum species in the better simulant sensing performance is discussed.

Growth of aligned ZnO nanorods on transparent electrodes by hybrid methods

The fabrication of ZnO (80 nm) thin film was achieved by hybrid atomic layer deposition (ALD) to prevent the reaction between the reactants and conductive layer of the substrates. ZnO nanorods (ZnO-NRs) growth over the substrates was performed by wet chemical procedure in which Zn(NO3)2 and hexamethylenetetramine were used as the precursors. HR-TEM, SAED, FE-SEM, X-ray diffraction (XRD), and UV–Vis spectroscopy were employed to characterize the ZnO-NRs samples on the substrates. XRD and HR-TEM analyses confirmed that the ZnO nanorod structure is hexagonal wurtzite type with growth in the [0001] direction. Length and thickness of the ZnO-NRs ranged between 45 and 90 nm and 480 and 600 nm, respectively. It was observed that the growth rate of NRs in [0001] direction is 10 times higher than in [1000] direction. The growth mechanism and resulted dimensions of nanorods are function of the synthesis parameters (in hybrid ALD process) such as reaction time, temperature, precursor molar ratio, and thickness of ZnO film.

Thickness and substrate orientation dependence of ferromagnetism in Mn doped ZnO thin films

AbstractThe effect of film thickness and substrate orientation on ferromagnetism in Mn doped ZnO thin films have been studied. The Mn doped ZnO films of different thickness (15, 35 and 105 nm) have been grown on both Si (100) and Si (111) substrates. The structural, electrical, optical, elemental and magnetic properties of the films have been investigated by X‐ray diffraction (XRD), Hall Effect measurements, photoluminescence (PL), energy dispersive spectroscopy (EDS) and vibrating sample magnetometer (VSM), respectively. It is found that all the properties are strongly influenced by the film thickness and substrate orientation. The XRD analysis confirmed that the formation of high quality monophasic hexagonal wurtzite structure for all the grown films. The room temperature VSM measurements showed that the films of lower thickness have better ferromagnetism than that of the thicker films grown on both the substrates. Among the lower thickness films, the film grown on Si (111) substrate has higher saturation magnetization (291×10‐5 emu cm‐3) due to high density of the defects. The observed ferromagnetism has been well justified by XRD, Hall measurements and PL. The presence of Mn atoms in the film has been confirmed by EDS. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

D 0 Ferromagnetism in undoped ZnO thin films: Effect of thickness, interface and oxygen annealing

We present a systematic study of the thickness dependency of the structural, electrical and magnetic properties of undoped ZnO thin films. The highest saturation moment (∼36.75 emu cm−3) was observed for the thinnest films. Both the undoped and 5% Co doped ZnO films of different thickness (0.066–1.1 μm) showed a diamagnetic behavior upon annealing in oxygen. Activation energy of quenching of ferromagnetism revealed oxygen vacancies as the key mediating defect in ferromagnetic ZnO thin films.

Growth of vertically aligned ZnO nanorods using textured ZnO films

A hydrothermal method to grow vertical-aligned ZnO nanorod arrays on ZnO films obtained by atomic layer deposition (ALD) is presented. The growth of ZnO nanorods is studied as function of the crystallographic orientation of the ZnO films deposited on silicon (100) substrates. Different thicknesses of ZnO films around 40 to 180 nm were obtained and characterized before carrying out the growth process by hydrothermal methods. A textured ZnO layer with preferential direction in the normal c-axes is formed on substrates by the decomposition of diethylzinc to provide nucleation sites for vertical nanorod growth. Crystallographic orientation of the ZnO nanorods and ZnO-ALD films was determined by X-ray diffraction analysis. Composition, morphologies, length, size, and diameter of the nanorods were studied using a scanning electron microscope and energy dispersed x-ray spectroscopy analyses. In this work, it is demonstrated that crystallinity of the ZnO-ALD films plays an important role in the vertical-aligned ZnO nanorod growth. The nanorod arrays synthesized in solution had a diameter, length, density, and orientation desirable for a potential application as photosensitive materials in the manufacture of semiconductor-polymer solar cells.PACS61.46.Hk, Nanocrystals; 61.46.Km, Structure of nanowires and nanorods; 81.07.Gf, Nanowires; 81.15.Gh, Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Structure, morphology and electrical characterizations of direct current sputtered ZnO thin films

ZnO thin films were deposited on glass substrates by direct current (DC) sputtering technique at room temperature (RT) to 400°C with a 99.999% pure ZnO target. Then the samples deposited at RT were annealed in air from the RT to 400°C. The effects of substrate temperature (Ts) and annealing treatment (Ta) on the crystallization behavior and the morphology have been studied by X-ray diffraction and atomic force microscopy. We also compared the structural properties of samples deposited at 400°C on glass to those deposited on Pt/silicon substrate. The resistivity, surface roughness and size of the grains have also been studied and correlated to the thickness of ZnO films deposited on Pt/Si substrates. The experimental results reveal that the substrate has a major influence on the structural and morphological properties. For the films deposited on glass, below 400°C, Ts and Ta have a similar influence on the structure of the films. Moreover, the ZnO samples deposited at RT and annealed in air have poor electrical properties.

Investigation into real-time pressure sensing properties of SnO2, TiO2, and TiO2/ZnO thick films with interdigitated electrodes

Abstract The pressure sensing properties of nanocomposite SnO 2 , TiO 2 , and TiO 2 /ZnO thick film capacitors with interdigitated electrodes are investigated. To form the dielectric layers, the metal oxides powders were respectively mixed with isopropanol, wet ball milled for 24 h, then the mixtures were dried at 120 °C and further the powders were placed under 2 tonnes of pressure to form pellets, which were fired at 1250 °C (rate of 5 °C/min) in a vacuum of 6 × 10 −3 mbar for 5 h, followed by cooling (rate of 3 °C/min). After firing, the resultant nanopowders were mixed with 7 wt.% of polyvinyl butyral (binder) and suitable amount of ethylenglycolmonobutylether (solvent) to form the pastes. These were screen-printed over the Ag electrodes on alumina substrates to form SnO 2 , TiO 2 , and TiO 2 /ZnO capacitor pressure sensors accordingly. The evaluation of pressure sensing properties of these sensors was performed using a HP 4192A Impedance Analyser, which recorded the changes in the values of the capacitances under different mechanical stresses. At the applied load of 5 kPa, the response times of 2.5 s, 5.6 s and 4 s were recorded for SnO 2 , TiO 2 , and TiO 2 /ZnO sensors, respectively. In addition to instant response times, these pressure sensors have the advantage of being reusable, as their electrical properties were restored to the original value after annealing for 2 h at 80 °C. Moreover, one year later after the initial testing, the sensors were still operational and produced similar time responses to pressure.

Effect of Thicknesses on the Structure, Conductivity, and Transparency of Al-doped ZnO Anodes in Organic Light-Emitting Diodes

Al-doped ZnO (AZO) films of various thicknesses were prepared by sputtering on glass substrates for use as transparent anodes of OLED devices. The effect of AZO film thickness on the structure, conductivity, and transparency of AZO films was investigated. The performance of OLEDs based on AZO anodes with various thicknesses is also discussed. The surface roughness of AZO is a crucial factor for the performance of OLEDs. The AZO thin film may be a potential alternative to an ITO anode due to its low price, and non-toxicity.

Effect of Thickness on the Structural, Electrical and Optical Properties of ZnO Films Deposited by MBE

A set of ZnO films of different thickness have been deposited on sapphire substrates using molecular beam epitaxy (MBE) by varying the growth time and the effect of film thickness on the structural, electrical and optical properties have been investigated. The X-ray diffraction (XRD) results indicate that the full width at half maximum (FWHM) of the (002) diffraction peak is decreased as the film thickness increasing, and the stress along c-axis is stable. Scanning electron microscope (SEM) measurement shows that the grains become more uniform as the film grows thicker and the film surface present distinct hexagon shape as the film is grown up to a thickness of 500nm. The optical absorbance, Hall mobility and photoluminescence (PL) intensity are increased in accordance with the thickness of the film.

Effect of Sol-Gel Prepared ZnO Electron Selective Layer on the Performance of Inverted Organic Solar Cells

ZnO buffer layer was prepared as electron selective layers (ESL) for photo-induced electron transport and hole blocking in inverted organic solar cells (IOSCs) by sol-gel process. The effects of thickness and surface roughness of ZnO ESL on the performance of IOSCs were investigated. Power Conversion Efficiency (PCE) of the IOSC strongly varied as a function of ZnO film thickness and surface roughness, in particular, when the film thickness was <70 nm, increase in the surface roughness enhanced photovoltaic performances. It is demonstrated that optimization of the electrode thickness and roughness is essential for obtaining better performance of organic photovoltaic cells.

High-performance ZnO thin-film transistor fabricated by atomic layer deposition

We report the fabrication and characteristics of a ZnO thin-film transistor (TFT) using a 50 nm thick ZnO film as an active layer on an Al2O3 gate dielectric film deposited by atomic layer deposition. Lowering the deposition temperature allowed the control of the carrier concentration of the active channel layer (ZnO film) in the TFT device. The ZnO TFT fabricated at 110 °C exhibited high-performance TFT characteristics including a saturation field-effect mobility of 11.86 cm2 V−1 s−1, an on-to-off current ratio of 3.09 × 107 and a sub-threshold gate-voltage swing of 0.72 V decade−1.

Glass Substrate와 PET Film위에 Screen Printing된 ZnO Thick Film의 구조적 전기적 특성

As a II-IV compound semiconductor, ZnO has a wide band gap of 3.37 eV with transparent properties. Due to this transparent properties, ZnO materials can be also employed as the transparent conducting electrode materials. Recently, rapid progress has been made in the field of DSSC (dye sensitized solar cell)area. Therefore, strong demands have been required for the transparent electrodes with low temperature processing and cheap cost. In this paper, we will prepare ZnO thick films on the PET substrates for the electrode applications. We will investigate the structural and microstructure properties through the XRD, and SEM analysis, respectively. Also, we will study the electrical of specimens to apply the conducting electrode.

A novel ozone detection at room temperature through UV-LED-assisted ZnO thick film sensors

In this work a novel ozone detection at room temperature (RT) has been investigated. Two functional materials, ZnO and (W 0.9Sn 0.1)O 3 − x (WS10) oxides, have been synthesized to prepare thick film gas sensors, both used in conventional heated mode as well as at RT assisted by UV irradiation. As a source of light, a light emitting diode (LED) of 400 nm peak wavelength was used. Under typical operating conditions of the UV-LED, the radiation flux density ϕ over the sensor was of about 5 · 10 17 photons/cm 2. Powders and films have been characterized by means of TG-DTA, SEM, TEM and XRD. Finally, electrical measurements have been performed on sensing films with the aim to compare conductive properties, surface barrier heights and ozone sensing features with and without UV irradiation. Despite the fact that two types of conventional heated sensors offered quite similar results with respect to ozone sensing, it turned out that, at RT and with the assistance of UV light, ZnO behaved excellently fast detecting ozone at concentrations down to 10 ppb, while for WS10 under the same operating conditions an opposite result was observed, i.e. very low response and long response time.

Effect of aluminium doping on structural and gas sensing properties of zinc oxide thin films deposited by spray pyrolysis

A facile spray pyrolysis route is used to deposit aluminium doped ZnO (AZO) thin films on to the glass substrates. It is observed that on aluminium doping the particle size of ZnO reduces significantly; moreover, uniformity of particle also gets enhanced. Their XRD study reveals that intensity ratio of crystal planes depend on the aluminium doping concentration. The gas response studies of; ∼800 nm thick Al-doped ZnO films at different operating temperatures show that 5 at% Al-doped ZnO thin film exhibits highest response towards H 2S gas at 200 °C. The results suggest that the gas response strongly depends on the particle size and aluminium doping in the ZnO.

Atomic Layer Deposition of Conductive Coatings on Cotton, Paper, and Synthetic Fibers: Conductivity Analysis and Functional Chemical Sensing Using “All‐Fiber” Capacitors

AbstractConductive coatings on complex fibrous systems are attracting interest for new electronic and other functional systems. Obtaining a quantitative conductivity value for complex surface coatings is often difficult. This work describes a procedure to quantify the effective electrical conductivity of conductive coatings on non‐conductive fibrous networks. By applying a normal force orthogonal to the current and field direction, fiber/fiber contact is improved and consistent conductance values can be measured. Nylon fibers coated with an electroless silver plating shows effective conductivity up to 1950 S cm−1, and quartz fibers coated with tungsten by atomic layer deposition (ALD) show values up to ∼1150 S cm−1. Cotton fibers and paper coated with a range of ZnO film thicknesses by ALD show effective conductivity of up to 24 S cm−1 under applied normal force, and conductivity scaled as expected with film coating thickness. Furthermore, we use the conductive coatings to produce an “all‐fiber” metal–insulator–metal capacitor that functions as a liquid chemical sensor. The ability to reliably analyze the effective conductivity of coatings on complex fiber systems will be important to design and improve performance of similar devices and other electronic textiles structures.

ZnO Tip-Coated Carbon Nanotubes Core–Shell Structures for Photoluminescence and Electron Emission Properties

A multifunctional ZnO tip-coated carbon nanotubes (CNT) core–shell structure was synthesized for the application of a CNT-based device with photoluminescence and field emission properties. The synthesis first includes the growth of vertically aligned carbon nanotubes core by plasma-enhanced chemical vapor deposition and then the deposition of ZnO shell by radio-frequency magnetron sputtering. Transmission electron microscope showed that the ZnO shell formed a polycrystalline coating with bead-shaped nanoparticles on nanotube tips. As the sputtering time increases, the bead-shaped coating becomes a thick layer ZnO film fully encapsulating the CNT tips. Improved threshold field of 3.20 V/µm was measured, compared to carbon nanotubes without ZnO coating at 4.90 V/µm. A monochromatic photoluminescence peak in the ultraviolet region (∼ 370 nm) was obtained and a gradual blueshift was observed with increasing ZnO coating thickness. The coexistence of electron field emission and photoluminescence has the potential for application in dual-functional devices. We further show that full-length encapsulation is not necessary. In this application, a thin tip-coating is sufficient to observe the unique properties.

Influence of growth temperature on the optical and structural properties of ultrathin ZnO films

This study investigates the effect of growth temperature on the optical and structural properties of ultrathin ZnO films on the polished Si substrate. Thickness of the ultrathin ZnO films deposited by atomic layer deposition (ALD) method was about 10 nm. Photoluminescence (PL), X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM) techniques were used to measure the properties of ultrathin ZnO films. Experimental results showed that the ultrathin ZnO film deposited at 200 °C had excellent ultraviolet emission intensity, and the average roughness of the film surface was about 0.26 nm.

Microwave-assisted synthesis, characterization and ammonia sensing properties of polymer-capped star-shaped zinc oxide nanostructures

Zinc oxide nanostructures were prepared by microwave-irradiation technique in the presence of polyvinyl pyrrolidone as a shape modifier. The synthesized nanostructures were analyzed using scanning and transmission electron microscopy, selected-area electron diffraction, X-ray diffraction, and Fourier transform infrared spectroscopy (FT-IR). Characterization techniques revealed the formation of crystalline ZnO with a star-like shaped morphology, having the crystal structure of wurtzite. The microwave irradiated samples were further investigated to exploit their electrical and sensing properties. The good sensitivity and relatively short response and recovery times of chemoresistive sensors based on star-like ZnO thick films in the monitoring of low concentration of ammonia gas in air were related to the peculiar nanostructure of the sensing layer.

Investigation into Texture, Preferential Orientation, and Optical Properties of Zinc Oxide Nanopolycrystalline Thin Films Deposited by the Sol–Gel Technique on Different Substrates

ZnO nanopolycrystalline thin films were deposited by the sol–gel technique on glass and silicon, and compared systematically via atomic force microscopy, scanning electron microscopy, x-ray diffraction, UV–Vis spectrophotometry, and fluorescence spectrophotometry. The thickness of the ZnO films was measured by ellipsometric microscopy. A higher preheating temperature was needed to obtain films with a strong preferential orientation. The optimal annealing temperatures for c-axis films on glass and silicon substrates were 525°C and 750°C, respectively. The relative intensity of the blue–green emission peak tends to increase with the annealing temperature. When the film is annealed in N2, the transmittance of the film reduces while the intensity of the blue–green emission increases.