Nano Thin Films Research Articles

Comparative investigation on nanocrystal structure, optical, and electrical properties of ZnO and Sr-doped ZnO thin films using chemical bath deposition method

This paper reports on the comparative investigation of structural and optical properties of nano thin films of ZnO and Sr-doped ZnO (SZO) onto glass substrates synthesized by a two-step chemical bath deposition (CBD) technique. The mode of crystallization, structural properties, and morphologies have been investigated. The films are polycrystalline in nature with hexagonal phase having (002) preferential orientation. The typical crystallite size is also estimated and found to be around 30–80 nm. The shifts in optical band gap of the SZO films are estimated to be ∼3.25–3.27 eV with respect to the ZnO film and the refractive index is 2.35. The room temperature resistivity is of the order of ∼2,000 Ωcm. Thermoemf measurements show that films are of n-type. The sensitivity of the films was studied as a function of their temperature 275–575 K for a fixed ethanol concentration (400 ppm). The films have been tested for cross sensitivity for different gases and it has been confirmed that these are highly sensitive and selective for ethanol vapors around 200 °C in air atmosphere.

Quantum Size Effect of Inner Cladding Fibres with InP Nano Thin Films

Optical amplified characteristics of inner cladding fibres with InP thin films are tested. The results indicate that this kind of fibres exhibit better optical amplification, which is advantageous for short lengths of fibres. The amplification coefficients of per unit length are 1.40–5.12 dB/m at the wave band from 906 to 1044 nm, 1.40–15.35dB/m from 1080 to 1491 nm, and 1.86–7.44dB/m from 1524 to 1596 nm. Based on the hydrogen atomic model, we calculate the comparative size of the InP particle aB = 8.313nm. The result displays the quantum size effect. By calculating the change of the energy band of particles with different sizes, the experimental data are explained by quantum size effect.

Study the Conduction Mechanism and the Electrical Response of Strained Nano-thin 3C-SiC Films on Si used as Surface Sensors

AbstractVarious superior properties of SiC such as high thermal conductivity, chemical and thermal stability and mechanical robustness provide the basis for electronic and MEMS devices of novel design [1]. This work evaluates heterostructures that consist of a few nanometers-thick 3C-SiC films on silicon substrates. Nano-thin SiC films differ significantly in their electrical behavior compared to the bulk material [2], a finding that gives rise to a potential use of these films as surface sensors. To gain a better understanding of the effect of surface states on the electrical response of these thin, strained films, several metal-semiconductor-metal heterostructures have been examined under variable conditions. The nano-thin, strained films were grown using gas source molecular beam epitaxy. Reflection high-energy electron diffraction patterns obtained from several 3C-SiC films indicate that these films are strained nearly 3% relative to the SiC lattice constant. Al, Cr and Pt contacts to a nano-thin film 3C-SiC were deposited and characterized. I-V measurements of the strained nano-thin films demonstrate metal-semiconductor-metal characteristics. Band offsets due to biaxial tensile strain introduced within the 3C-SiC films were calculated and band diagrams incorporating strain effects were simulated. Electron affinity of 3C-SiC has been extracted from experimental I-V curves and is in good agreement with the value that has been calculated for a strained 3C-SiC film [3]. On the basis of experimental and simulation results, an empirical model for the current transport has been proposed. Fabricated devices have been characterized in a controlled environment under hydrogen flow and also in a reactive ambient, while heating the sample and oxidizing the surface, to investigate the effects of the environment on the surface states. Observed changes in I-V characteristics suggest that these nano-thin films can be used as surface sensors.

Implementation of linear trace moisture sensor by nano porous thin film moisture sensor and NLAmp

Abstract Almost all type of moisture sensors has a non-linear response. With out linearization it is difficult to apply such a non-linear sensor in electronics circuits, specially in analog electronics. Non linear sensor and transducers characteristic can be linearized using analog electronics or digital electronics. In this paper a method of linearization of such non-linear sensors characteristics using analog electronics is described. Theoretical explanation of the methods and its verification by experiment is stated in this paper. It may possible to linearize any non linear characteristic using this method. We use thin film nano porous trace humidity sensor as a non linear device for the circuit justification. The fabrication process of the sensor is also described in this paper.

Controlled Release of DSBP from Genipin-Crosslinked Gelatin Thin Films

Controlled release of a marker drug, 4,4′-bis(2-sulfostyryl) biphenyl (DSBP) from genipin crosslinked gelatin thin films, with application to drug delivery by transdermal patches is studied in this paper. A simple method for fabrication of nano-thin films, using basic lab equipment is introduced. This method consists of two steps: dipping of the substrate in a deposition solution, followed by centrifugation of the substrate. Also, swelling and drug release from thin films is modeled, using the Fick's second law of diffusion. The effect of genipin concentration on release of DSBP molecules from thin films is investigated, experimentally and numerically. The results show that controlled release of DSBP from the genipin-crosslinked gelatin thin films is achieved, using various concentrations of genipin in gelatin.

The effect of heat treatment on superhydrophilicity of TiO2nano thin films

TiO2 thin films were synthesized by the sol-gel method and spin coating process. The calcination temperature was changed from 100 to 550 °C. XRD patterns show increasing the content of polycrystalline anatase phase with increasing the calcination temperature. The AFM results indicate granular morphology of the films, which particle size changes from 22 to 166 nm by increasing the calcination temperature. The RBS, EDX and Raman spectroscopy of the films show the ratio of Ti:O ~0.5, and diffusion of sodium ions from substrate into the layer, by increasing the calcination temperature. The UV-vis spectroscopy of the films indicates a red shift by increasing the calcination temperature. The contact angle meter experiment shows that superhydrophilicity of the films depends on the formation of anatase crystal structure and diffused sodium content from substrate to the layer. The best hydrophilicity property was observed at 450 °C calcination temperature, where the film is converted to a superhydrophilic surface after 10 min under 2 mW/cm2 UV irradiation. Water droplet on TiO2 thin film on Si(111), Si(100), and quartz substrates is spread to smaller angles rather than glass and polycrystalline Si substrates under UV irradiation.

Photoelectric organic nano-thin films prepared from diarylethene

Abstract A photoactive nano-film was prepared from a diarylethene derivative, 1,2-bis[6-(3,4-ethylenedioxythienyl)-2-methyl-1-benzothiophen-3-yl]perfluorocyclopentene (BTFTT) and 3,4-ethylenedioxythiophene (EDOT), by electrochemical anodic polymerization. The conductive polymer films prepared from a copolymer of BTFTT and EDOT, a homopolymer of PBTFTT and PEDOT, showed characteristic redox properties pertinent to their monomers and homopolymers as determined by cyclic voltammetry (CV). The growth of organic films was estimated by an alpha-step and UV–visible spectral change. The film growth (thickness) was linearly correlated to the cycle numbers in CV for the electropolymerization. The electrodeposited organic nano-film showed a reversible photocurrent switching effect in a liquid electrolyte solution containing redox couple (Q/H2Q) by the alternative UV irradiation (0.1 W/cm−2). Maximum photocurrent switching efficiency as well as fast response were obtained from the polymer film synthesized from a solution containing equivalent molar concentration of EDOT and BTFTT (1:1).

Water Formation on Clean and Vanadium Oxide Covered Pd(111) by Permeating Deuterium

In this work the formation of D2O on vanadium oxide (VOx) thin film nano structures on Pd(111) has been investigated. Quadrupole mass spectrometry has been used to determine the flux of the reaction products desorbing from the surface. In separate experiments low-energy electron diffraction and Auger electron spectroscopy were applied to monitor possible changes in the surface composition under reaction conditions. The experiments were carried out at sample temperatures of 523 and 700 K. The water reaction was fed with atomic deuterium via bulk permeation and simultaneous dosing of molecular oxygen. It turned out that the VOx coverage as well as the sample temperature have significant influence on the reaction. The D2O formation rate drops with increasing VOx coverage and increases with rising sample temperature. Additionally, we found evidence that the VOx structures change during water formation, especially at 700 K.

Thickness Effect and Mesoscopic Character of the Metal Oxide Gas Sensing Nano-Thin Films

The characters of metal oxide gas sensing nano-thin films are studied. The formula of the dynamical thickness effect characteristic time is given. The relation of the sensitivity Sn and the film thickness l, the character of existing the optimum thickness, the character of the change of conductance activity energy with the film thickness are given also. The idea of diffusion reaction of gas sensing mechanism and the idea of mesoscopic effect in the nano-thin films are proposed.

Investigation of Nano-thin β-SiC Layers for Chemical Sensors

ABSTRACTSilicon Carbide possesses a combination of properties that make it ideal for use in electronics. Its high values of electric breakdown field, melting point and saturated electron drift velocity have attracted the attention of the semiconductor community. Although the interest in β-SiC/Si devices has intensified in recent years [1-2], little focus has been given to the study of nano-thin film devices. Monocrystalline nano-thin β-SiC films have been reproducibly grown on Si (100) by Gas Source Molecular Beam Epitaxy (GSMBE). Auger Electron Spectroscopy and Reflection High Energy Electron Diffraction characterization have confirmed a growth consistent of β-SiC/Si. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) characterization has determined film thicknesses of 30nm. These nano-films have been used in the fabrication of Metal-Semiconductor-Metal (MSM) devices formed from aluminum Schottky contacts. Under electrical characterization, these MSM devices have exhibited unique properties in that the dominant conduction path does not occur at the β-SiC/Si interface [3] as previously reported, but within the entire β-SiC layer. It is proposed that the device is isolated from the Silicon substrate and due to the nano-thin β-SiC films used in this work the differentiation between surface and ‘bulk’ is not clear. Results obtained through chemical experimentation have indicated that conduction is largely dependent on the surface condition of the device. This suggests the possibility for nano-thin, surface-like, β-SiC films to be used in chemical agent sensors.

Surface and bulklike phonon modes of Si(1 0 0) nanometer thin film

The surface and bulklike phonon modes of Si(1 0 0) c(4 × 2) nanometer-thin film were investigated using density functional calculations with a 4 × 4 supercell consisting of 10 layers. The surface phonon modes were dispersed over a wide range with two collective peaks around 120 and 190 cm −1, including interference from both surface phonons. The distribution of the bulklike phonon modes revealed similar peaks to the bulk phonons, and the two collective peaks were newly confirmed on the lower frequency side. These characteristic peaks provide large spectral variation in the phonons of nano-thin films.

Computer Simulation of a Hardness Indent Test into Nickel Nano Thin Films

Current experiments suggest that mechanical properties of thin films are different at thicknesses less than 100 nm.In this study, embedded atom method computer simulations are used to examine the differences in strengthening mechanisms at the nano scale.The simulation shows the mechanisms responsible for the differences in hardness with varying sample thicknesses from 12.8, 8, 6, and 4 nm.The simulation results show that as film thickness decreases the hardness of the film increases.Simulations were performed in single crystal films as well as model tricristals in order to study the effects of the grain boundaries.Tricrystalline films emitted dislocations at a lower pressure than single crystals.

Selective Deposition of Hafnium Oxide Nanothin Films on OTS Patterned Si(100) Substrates by Metal–Organic Chemical Vapor Deposition

Soft lithography is a method for the manufacture of micro/nano size patterns and structures by using organic materials without the use of high energy. In particular, microcontact printing (muCP) is a very convenient and nonphotolithographic technique that can generate patterned features of self-assembled monolayers (SAMs). In this study, we carried out the selective deposition of HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nano-thin films on Si(100) substrates by combination of muCP using octadecyltrichlorosilane (OTS) and metal-organic chemical vapor deposition (MOCVD). Single molecular precursor of Hf(O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sup> Bu) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> was used for the growth of HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nano-films, and the deposition was carried out between 150degC and 400degC at a pressure of 3times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> torr. The as-grown films were characterized by x-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive x-ray (EDX), x-ray photoelectron spectroscopy (XPS), and capacitance-voltage (C-V) and current-voltage (I-V) measurement. It is expected that the combination of muCP of SAM and MOCVD is a better method for fabricating the HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin films between micro and nano sizes

Local Acceleration Effects of Adatom at the Vicinity on the Surface: Case of Co Nano Thin-Films on Al Surface

The local acceleration effects, which are peculiar phenomena during atomic scale deposition process, were investigated byMolecular Dynamics (MD) simulation. The values of local acceleration were distributed widely for various surface orientations. Deposited atoms were accelerated along the potential energy surface, and accelerated values were evidently dependent on the local configuration of the surface. In contrast, the local acceleration became negligibly small for clusters consisting of many atoms.

Adsorption of dansylated amino acids on molecularly imprinted surfaces: A surface plasmon resonance study

Surface plasmon resonance spectroscopy (SPR) was used to measure the adsorption kinetics and isotherms of dansylated amino acids onto surface-confined molecularly imprinted polymer films (MIP-Fs) and the corresponding non-imprinted polymer control films (NIP-Fs). The surface-confined polymer films were grafted from flat gold surfaces using atom transfer radical polymerization (ATRP). This approach allowed uniform nanothin films to be grown, thereby ensuring that the amino acids see a uniform surface during adsorption. N,N'-Didansyl-l-cystine (DDC) and didansyl-l-lysine (DDK) were used as the template molecules to form the MIP-Fs. Adsorption kinetics data were analyzed using single- and dual-site Langmuir adsorption models. It was found that, within the experimental measurement range, adsorption isotherm data were well described by any of four isotherm models: Langmuir, dual-site Langmuir, Freundlich, or Langmuir-Freundlich (LF). The relatively high heterogeneity index values regressed using the Freundlich and LF isotherms suggest the formation of fairly homogeneous MIP-Fs; although Scatchard analysis reveals binding site heterogeneity does exist. Selectivity studies showed that the MIP-Fs display cross-reactivity between DDC and DDK; nevertheless, MIP-Fs prepared against one template showed selectivity for that template. Solution pH and polymer layer thickness were studied as independent parameters to determine their impacts on amino acid adsorption, as monitored by SPR.

A novel way of modifying nano grain size by solution concentration in the growth of ZnAl2O4 thin films

A novel route to the growth of thin films of ZnAl2O4 in nano-scale order was developed and nano-thin films of ZnAl2O4 are grown. The variation of grain size with solution concentration is reported. The thin film was deposited by modified liquid-phase deposition (LPD) technique using a novel acid based chemical reaction for the first time to ternary system. This modified LPD is based on a novel reaction that favours the formation of nanostructures during the treatment of a precursor (here ZnO) and a metal foil (Al) in diluted HF acid. The acid serves both as a solvent and catalyst. Usually, in wet process synthesis of binary systems, the metal foil will act as F− ion scavenger. In this method, formation of a ternary compound as well as growth of thin film nanostructures of that compound was achieved by the same chemical reaction at room temperature. The role of acid concentration in the nanostructure formation is discussed. The relationship between HF concentration and grain size were also graphically enumerated. Structural, compositional and surface morphological properties of thin films were studied using Philips, Xpert-MPD: X-ray diffractometer and Philips, ESEM-TMP + EDAX, Nanoscope-III: AFM. The technique is a novel, simple and low cost route for the growth of nano-thin films of ternary oxide material.

Synthesis of polypyrrole and carbon nano-fiber composite for the electrode of electrochemical capacitors

Nano-thin polypyrrole (PPy) films were deposited on vapor grown carbon fibers (VGCF) by using an in situ chemical polymerization of the monomer in the presence of FeCl3 oxidant. An ultrasonic cavitational stream was used during polymerization of pyrrole, to enable the deposition of uniformly nano-thin PPy films on the surface of VGCF. The PPy/VGCF composite was characterized by FTIR spectroscopy. Surface morphology of the polymer films was characterized by using scanning electron microscopy and scanning transmission electron microscopy. The capacitance of the composite electrodes was investigated with cyclic voltammetry. As results of this study, thinner layer of PPy in the composite electrode (<10 nm) was effective to obtain fully reversible and very fast Faradaic reaction. Hence, most mass of the PPy could contribute to the pseudo-capacitive charge storage. This nano-thin PPy layer exhibited higher specific capacitance of ∼588 F g−1 at 30 mV s−1 and ∼545 F g−1 at 200 mV s−1 along with an excellent power capability.

Characterization of Diffusion-Controlled Mass Transport through Nanoporous and Nanothin Films Plasma Polymerized on a Sputtered Platinum Electrode

We demonstrate the diffusion mode of various redox chemical species through a plasma-polymerized nanothin coating with nanometer-sized pores on a sputtered platinum (Pt) electrode. In this work, hexamethyldisiloxane plasma-polymerized films (PPFs) were added onto the sputtered platinum film, both of which were sequentially deposited in the same vacuum chamber. Results of atomic force microscopy, X-ray photoelectron spectroscopy, and electrochemical studies showed that the PPF provided the platinum electrode with a coating with a complete surface coverage. Sub-nanometer-sized pores (less than 1 nm) responsible for a highly crosslinked polymer network in the PPF coatings offered diffusivity-controlled permeation of redox molecules (i.e., size-exclusivity) rather than solubility-controlled permeation (i.e., chemoselectivity). Consequently, variation of the plasma power could give control over the size of the nanometer-sized cavities.

Evaluation of the thermal stability of reactively sputtered (Ti, Zr)N x nano-thin films as diffusion barriers between Cu and Silicon

Refractory binary metal nitride films, (Ti, Zr)N x , were prepared by direct current reactive magnetron sputtering from a Ti-5 at.% Zr alloy target in N 2 / Ar gas mixtures and then used as diffusion barriers between Cu and Si substrates. In order to investigate the thermal stability of Cu (60 nm) / (Ti, Zr)N x (6 nm) / Si contact systems, sheet resistance measurement, X-ray diffraction, scanning electron microscopy, cross-section transmission electron microscopy, and X-ray photoelectron spectroscopy depth profile were performed. Experimental results indicate that the barrier performance are significantly affected by the chemical composition of (Ti, Zr)N x films, N / (Ti, Zr) atomic ratio. Besides, our results also suggest that the refractory binary metal nitride film, (Ti, Zr)N x , can be used as a superior diffusion barrier for Cu metallization as compared to the well-known TaN film.

Synthesis and application of nanoparticles by a high gravity method

Synthesis and application of nanoparticles by a high gravity method