Electrochemical behavior of nitrogenated nanocrystalline diamond electrodes

Nitrogenated nanocrystalline diamond films with controlled conductivity are deposited from microwave plasma in CH₄-Ar-H₂-N₂ gas mixtures. They are characterized using atomic force microscopy, Raman spectroscopy, and electrophysical measurements. Their electrochemical properties are studied by cyclic voltammetry and electrochemical impedance spectroscopy. Kinetic parameters of reactions in [Fe(CN)₆]^3-/4- redox system are determined. The character of electrode behavior is controlled by the degree on nitrogenation. With the increasing of the nitrogen content in the reaction gas mixture (from 0 to 25%), the potential window somewhat narrows, the background current increases, the reversibility of reactions in the [Fe(CN)₆]^3-/4- redox system increases. By and large, the transition occurs from the electrochemical behavior of a “poor conductor” to that of a metal-like electrode.     

Optical characterisation of organosilane-modified nanocrystalline diamond films

We report on an optical characterisation of nanocrystalline diamond films photochemically functionalised with the organosilane-coupling agent, N ¹-(3-(trimethoxysilyl)propyl)hexane-1,6-diamine (alternative names: N-(6-aminohexyl)aminopropyl-trimethoxysilane, (3-(6-aminohexylamino)propyl) trimetoxysilane, AHAPS). The presence and homogeneity of the organosilane layers were detected by fluorescence microscopy and infrared reflectance-absorbance spectroscopy. The results indicated that a homogeneous surface coverage with organosilane layers was achieved on diamond surfaces which were modified either by hydrogen or by oxygen plasma treatment. The functionalised nanocrystalline diamonds present a promising solution in future biosensor applications.     

Electrochemical behavior of silver thin films interfaced with yttria-stabilized zirconia

Thin silver films (100–800 nm) were deposited by physical vapor deposition (PVD) on yttria-stabilized zirconia solid electrolyte. The electric percolation as a function of the film thickness was studied during deposition and annealing using a two-electrode in-situ resistance measurement technique. Electrical percolation was achieved in as-deposited films greater than 5.4?±?0.4 nm; however, thermal treatment (550 °C in air) resulted in film dewetting for Ag films as thick as 500 nm and formation of electronically isolated Ag nanoparticles, as was confirmed by SEM and XPS. In thermally treated samples, stable electronic conductivity associated with a continuous percolated network was only observed in samples greater than 600 nm in thickness. The effect of polarization on the electrochemical reactions at the three-phase (electrode-gas-electrolyte) and two-phase (electrode-electrolyte) boundaries of the electrode was investigated by solid electrolyte cyclic voltammetry (SECV) at 350 °C and P _O2?=?6 kPa. With the application of positive potential, silver oxide (Ag₂O) was found to form along the three-phase boundary and then extends within the bulk of the electrode with increasing anodic potentials. By changing the hold time at positive potential, passivating oxide layers are formed which results in a shift in favor of the oxygen evolution reaction at the working electrode. This oxide forms according to a logarithmic rate expression with thick oxides being associated with decrease in current efficiency for subsequent oxide formation.     

Interfacial electrical properties of DNA-modified diamond thin films: intrinsic response and hybridization-induced field effects

We have investigated the frequency-dependent interfacial electrical properties of nanocrystalline diamond films that were covalently linked to DNA oligonucleotides and how these properties are changed upon exposure to complementary and noncomplementary DNA oligonucleotides. Frequency-dependent electrical measurements at the open-circuit potential show significant changes in impedance at frequencies of >10(4) Hz when DNA-modified diamond films are exposed to complementary DNA, with only minimal changes when exposed to noncomplementary DNA molecules. Measurements as a function of potential show that at 10(5) Hz, the impedance is dominated by the space-charge region of the diamond film. DNA molecules hybridizing at the interface induce a field effect in the diamond space-charge layer, altering the impedance of the diamond film. By identifying a range of impedances where the impedance is dominated by the diamond space-charge layer, we show that it possible to directly observe DNA hybridization, in real time and without additional labels, via simple measurement of the interfacial impedance.     

Study of the structure of thin nanocrystalline films

Structure and phase composition of thin nanocrystalline films of semiconductors and insulators CdS, Cd_xZn_1?xS, SiC_xN_y, and BC_xN_y were studied using registration of weak diffraction intensities with synchrotron radiation. Three methods were developed and applied to obtain diffraction patterns, namely, θ—2-scan (Bragg—Brentano geometry); 2θ-scan (grazing incidence scheme); a scheme with an image plate as detector. The characteristic features of the diffraction patterns, obtained from the aforementioned samples, are discussed. The X-ray diffraction data are compared with the results obtained by HREM, SAED, electron spectroscopy, ellipsometry, IR and Raman spectroscopy. It is stated that: 1) the films are composed of nanocrystals, their size depending on the conditions of film deposition; 2) single crystalline substrate favors formation of oriented crystals, i.e., of the domains comprising uniformly oriented nanocrystals.     

Nickel containing diamond like carbon thin films

Diamond like carbon (DLC) coatings are well established for multiple applications. The electrical conductivity of DLC or amorphous carbon can be influenced by several orders of magnitude via doping with different metals. Depending on the deposition process hydrogen may be incorporated as well, thereby decreasing the conductivity. Recent investigations of DLC disclose nice piezoresistive properties.Our work was focused on Ni:a-C:H thin films on different substrates by reactive sputtering from a nickel target. Several carbon precursors were added to the sputtering gas to create an amorphous carbon hydrogen network with embedded crystal clusters. In order to optimize the piezoresistive properties we varied various process parameters. The piezoresistive response was monitored by measuring the resistance change during bending. Our Ni:a-C:H films develop gauge factors of approx. 12 in a wide range of process parameters.For sensor applications the temperature coefficient of resistance (TCR) is important as well. It depends on the metal concentration in the thin film and can be adjusted by the concentration of the incorporated nickel. It can be set to approximately zero in a wide temperature range of 80–400 K. The combination of a high gauge factor and a very small TCR is achieved and described in this paper.XRD measurements reveal nickel or nickel carbide clusters with diameters of approx. 8–30 nm depending on the metal concentration. The clusters crystallize in the hexagonal hcp structure which could be transformed into the cubic fcc structure of nickel by thermal annealing in a vacuum.     

Positron/positronium annihilation in nanocrystalline silicon thin films

Positron and positronium annihilation investigations were applied to nanocrystalline silicon (nc-Si) thin films, for the first time. The nc-Si thin films with average grain diameters of 3–5 nm show intense blue luminescence at room temperature. The nanometer-sized Si crystallites formed in amorphous Si (a-Si) matrix give rise to this luminescence. Very highS-parameters up to 0.62 were observed in the as-grown a-Si thin film suggesting positronium formation in the a-Si layer. The average lifetime of the positrons in the a-Si was determined to be about 520 ps. TheS-parameters dropped significantly to 0.53 by crystallization of the thin film at 800 °C for 10 seconds, which was almost the same to the value observed in bulk Si (100) substrate. Further crystallization from 60 seconds to 1 hour showed smaller change in theS-parameters than that from the a-Si to 10 seconds. The large change in theS-parameters due to the annealing might be caused by the formation of Si nanocrystallites in a-Si matrix suggesting that positron is a sensitive probe for structural investigations of the nc-Si materials.     

Electrochemical insertion of lithium in thin tin films

The behavior of model electrodes made of lithiated thin films of tin during their cycling is studied. The electrodes show high values of useful specific capacity for the extension of several tens of operation cycles. Dependences of the diffusion coefficient for lithium into tin on the initial electrode potential, temperature, and direction of the electrode process are determined by a chronopotentiometric method. The dependences have a complex character, which is connected with the phase composition of the lithium-tin alloy.     

Electrochemical supercapacitor application of pervoskite thin films

We have explored electrochemically deposited pervoskite nanocrystalline porous bismuth iron oxide (BiFeO₃) thin film electrode from alkaline bath for electrochemical supercapacitors. The pervoskite BiFeO₃ nanocrystalline thin film electrode showed comparable specific capacitance of 81 F g⁻¹ and electrochemical supercapacitive performance and stability in an aqueous NaOH electrolyte to that of commonly used ruthenium based pervoskites.     

Electrochemical behavior of polyaniline films in acetonitrile

The electro-oxidation and electroreduction behavior of polyaniline films in acetonitrile in the absence and presence of added acid or base were investigated using cyclic voltammetry. A general mechanism is proposed that enables the interpretation of the electroactivity loss and the catalytic and autocatalytic properties of the film. The electroactivity loss was found to be a reversible phenomenon which is accelerated in alkaline solutions through deprotonation. Electroactivity was recovered when the electroinactive films were reduced in an acidic solution. The films that lose their electroactivity on electro-oxidation were found to be conducting, and various cation radicals in the structure are believed to be responsible for this nonprotonic conductivity. The proton content of the polyaniline film was found to be crucial in determining its electrochemical and physical properties. Autocatalysis was detected when protons were produced electrolytically in situ during electropolymerization.     

Photoinduced hydrophilicity of heteroepitaxially grown ZnO thin films

Single crystalline ZnO thin films were heteroepitaxially grown on sapphire substrates by rf-magnetron sputtering. The ZnO films on sapphire A and C face were oriented along the (0001) direction, whereas the ZnO film on sapphire R face was oriented along the (11-20) direction. The rate of photoinduced hydrophilic conversion strongly depended on the surface crystal structure. The ZnO film oriented along the (11-20) direction exhibited a higher hydrophilicizing rate than those oriented along the (0001) direction. The high hydrophilicizing rate of the ZnO oriented along the (11-20) direction is due to its surface atomic arrangement. The outermost layer of the ZnO surface of the (11-20) face contains oxygen ions, which are considered to be energetically reactive sites and responsible for the hydrophilic conversion.     

Nanocrystals grown in amorphous Cr and CrNi thin films

The structure of vacuum annealed amorphous sputtered Cr and CrNi (55:45) thin films has been studied by transmission electron microscopy (TEM) and electron diffraction (TED). The thin films with thicknesses ranging from 150 to 600 Å were annealed while still on their alkali halide substrates under high vacuum at temperatures ranging from 200 to 370°C. The TEM and TED data permitted to establish the annealing conditions (temperature, duration), which lead to the nucleation and growth of nanosized crystals in the Cr and CrNi icosahedral glasses.     

Defect and transport properties of nanocrystalline ceramics and thin films

This paper presents an overview of recent research on the defect and transport properties of nanocrystalline ionic and mixed conducting ceramics and thin films. In the first part, some basic concepts and properties of boundaries are reviewed, including diffusion, segregation, and space charge regions. Experimental data on nanoceramics and thin films made from pure and doped CeO₂, TiO₂, ZrO₂, and CaF₂ are presented and discussed in the second part; opportunities for future work on this topic are outlined. Electronic Publication     

Synthetic diamond electrodes: Photoelectrochemical behavior of vacuum-annealed undoped polycrystalline diamond films

The photocurrent and photopotential for undoped polycrystalline diamond film electrodes prepared by chemical vapor deposition and annealed in vacuum at 1500–1640°C are measured. The metal-like samples (annealed at 1630°C) have a negligible photosensitivity. Judging from the positive sign of the photopotential and the cathodic direction of the photocurrent, the material under study formally behaves as a p-type semiconductor. The photoeffects are presumably caused by structure defects, in particular, the dislocations in diamond crystallites formed close to intercrystalline boundaries during the high-temperature annealing.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 343–349.Original Russian Text Copyright © 2005 by Pleskov, Krotova, Ralchenko, Khomich, Khmelnitskii.     

Electrochemical deposition and characterization of SnS thin films

Thin films of SnS were cathodically deposited onto stainless steel substrates from bath containing 0.025 M SnSO₄, 0.25 M KSCN and 0.25 M Na₂SO₄. The mechanism of electrochemical co-deposition of tin and sulphur was investigated by cyclic voltammetry. Analysis of the chronoamperometric current–time transients suggested that, in the potential range −560 to −590 mV vs saturated calomel electrode, the electrodeposition of SnS involved progressive nucleation model. However, at a potential −600 mV, the electrodeposition involved instantaneous nucleation model. The deposits have been characterized by scanning electron microscopy, X-ray diffraction and optical measurements. SnS films were found to be polycrystalline with an optical energy gap of 1.38 eV.     

Uniformity analysis in nanocrystalline silver thin films using fuzzy inference system

An automatic and efficient technique to analyze the uniformity of nanoscale images using wavelets, feature similarity index measure (FSIM) and fuzzy inference system is reported. It has been successfully tested on scanning electron micrographs of nanocrystalline silver thin films. Thin films are prepared using on‐axis and off‐axis pulse laser deposition (PLD) technique. It is found that the film prepared using on‐axis PLD is more uniformly distributed and has smoother texture compared with that of the off‐axis technique. In order to analyze the images quantitatively, they are transformed to the wavelet domain to extract the localized frequency variations and a uniformity measure is derived using a fuzzy inference system for quantitatively analyzing the uniformity of each image. The surface plot of the FSIM values of the image is found to be an efficient tool for nanoscientists to evaluate the smoothness of the thin film surfaces. This study is expected to help the nanoscientists to understand these nanostructures in detail. Copyright © 2014 John Wiley & Sons, Ltd.     

HREELS investigation of the surfaces of nanocrystalline diamond films oxidized by different processes

This article reports on the use of high-resolution electron energy loss spectroscopy (HREELS) for the investigation of as-grown (hydrogen-terminated) and oxidized nanocrystalline diamond films (NCD) using chemical, physical, and electrochemical approaches. The results indicate that the nature and number of oxygen-related chemical groups generated on the NCD surface depend strongly on the oxidation process. A high concentration of C-O functions has been obtained on the NCD surface oxidized by rf (radio frequency) oxygen plasma, whereas the highest C═O/C-O ratio has been achieved by electrochemical oxidation. The NCD surface oxidized by rf plasma was totally free of C═O groups. Traces of surface hydroxyl groups (C-OH) have been detected upon annealing in air or through UV/ozone oxidation.     

Interfacial passivation mechanism of sulfide towards quantum dot-sensitized nanocrystalline thin films

Journal of Solid State Electrochemistry - We report on the interfacial passivation mechanism in CdSe quantum dot-sensitized ZnO nanocrystalline thin film, where different sulfide semiconductors...