Reaction Of Thin Films Research Articles

Raman Spectroscopy of the Reaction of Thin Films of Solid-State Benzene with Vapor-Deposited Ag, Mg, and Al

Thin films of solid-state benzene at 30 K were reacted with small quantities of vapor-deposited Ag, Mg, and Al under ultrahigh vacuum, and products were monitored using surface Raman spectroscopy. Although Ag and Mg produce small amounts of metal–benzene adduct products, the resulting Raman spectra are dominated by surface enhancement of the normal benzene modes from metallic nanoparticles suggesting rapid Ag or Mg metallization of the film. In contrast, large quantities of Al adduct products are observed. Vibrational modes of the products in all three systems suggest adducts that are formed through a pathway initiated by an electron transfer reaction. The difference in reactivity between these metals is ascribed to differences in ionization potential of the metal atoms; ionization potential values for Ag and Mg are similar but larger than that for Al. These studies demonstrate the importance of atomic parameters, such as ionization potential, in solid-state metal–organic reaction chemistry.

Measuring Photochemical Kinetics in Submonolayer Films by Transient ATR Spectroscopy on a Multimode Planar Waveguide

Understanding the kinetics of reactions in molecular thin films can aid in the molecular engineering of organic photovoltaics and biosensors. We have coupled two analytical methods, transient absorbance spectroscopy (TAS) and attenuated total reflectance (ATR), in a relatively simple arrangement when compared with previous TAS/ATR instruments to interrogate molecular structure and photochemistry at interfaces. The multimode planar waveguide geometry provides a significant path length enhancement relative to a conventional transmission geometry, making it feasible to perform measurements on low-surface-coverage films. The performance of the instrument was assessed using a thin film composed of purple membrane (PM) fragments containing bacteriorhodopsin deposited onto PDAC, a positively charged polymer. The surface coverage of retinal chromophore in this film is ∼0.1 monolayer and its orientation distribution is anisotropic, with a mean tilt angle of 68° from surface normal. After photoinduced formation of the transient M state, the chromophore decays to the ground state in 4.4 ± 0.6 ms, equivalent to the decay of suspended PM fragments, which shows that deposition on PDAC does not alter M-state photokinetics. The surface coverage of the M state is calculated to be 2 pmol/cm(2), which is ∼1% of a close-packed monolayer. This work demonstrates that TAS/ATR can be used to probe structure and photochemical kinetics in molecular films at extremely low surface coverages.

Low-energy electron-induced reactions in thin films of glucose and N-acetyl-glucosamine

Reactions induced in thin films of α- d-glucose and N-acetylglucosamine by low-energy electron exposure at incident electron energies ( E 0) between 5 eV and 15 eV have been investigated by high-resolution electron energy loss spectroscopy (HREELS). The reactions of α- d-glucose upon electron exposure were also studied in the presence of molecular oxygen. Electron exposure leads to characteristic changes of the vibrational spectra indicating that OH groups are lost with the formation of CC double bonds taking place preferentially above the ionisation threshold of the investigated molecules. At lower E 0, OH groups are equally decomposed suggesting that dissociative electron attachment contributes to the reactions but formation of double bonds is not observed. The results show that different reaction channels are effective depending on E 0 and that the outcome of electron-driven chemistry in saccharides may be controlled by changing from the subionisation regime to E 0 above the ionisation threshold. Generally, low-energy electron exposure in the absence of O 2 produces a material with lower oxygen content, i.e. leads to a reduction of the saccharide. In the case of N-acetylglucosamine, removal of the amide group from the sugar is also important at subionisation energies. In contrast, as shown for α- d-glucose, low-energy electron exposure in the presence of O 2 leads to oxidation of the sugar even at cryogenic temperature.

Modeling of a reacting nanofilm on a composite substrate

This article provides a detailed computational analysis of the reaction of dense nanofilms and the heat transfer characteristics on a composite substrate. Although traditional energetic compounds based on organic materials have similar energy per unit weight, non-organic material in nanofilm configuration offers much higher energy density and higher flame speed. The reaction of a multilayer thin film of aluminum and copper oxide has been studied by varying the substrate material and thicknesses. The numerical analysis of the thermal transport of the reacting film deposited on the substrate combined a hybrid approach in which a traditional two-dimensional black box theory was used in conjunction with the sandwich model to estimate the appropriate heat flux on the substrate accounting for the heat loss to the surroundings. A procedure to estimate this heat flux using stoichiometric calculations is provided. This work highlights two important findings. One is that there is very little difference in the temperature profiles between a single substrate of silica and a composite substrate of silicon silica. Secondly, with increase in substrate thickness, the quenching effect is progressively diminished at a given speed. These findings show that the composite substrate is effective and that the average speed and quenching of flames depend on the thickness of the silica substrate, and can be controlled by a careful choice of the substrate configuration. (C) 2011 Elsevier Ltd. All rights reserved.

Nickel Oxalate Nanowires Grown on Electrochemically Deposited Ni Thin Film

Nickel oxalate nanowires were produced by the reaction of nickel thin films electrochemically deposited on ITO glass in ethanolic oxalic acid. Their densities and lengths were strongly influenced by the thickness and roughness of the deposited nickel layers. The nickel layers became thicker with increasing deposition time, producing longer nanowires. Increasing roughness of the nickel layer led to shorter and denser nanowires. The total surface area of the nickel oxalate nanowires can be manipulated by the thickness and surface roughness of the electrochemically deposited film.

Characterization of the Non-uniform Reaction in Chemically Amplified Calix[4]resorcinarene Molecular Resist Thin Films

The ccc stereoisomer-purified tert-butoxycarbonyloxy-protected calix[4]resorcinarene molecular resists blended with photoacid generator exhibit a non-uniform photoacid-catalyzed reaction in thin films. The surface displays a reduced reaction extent, compared with the bulk, with average surface-layer thickness 7.0 ± 1.8 nm determined by neutron reflectivity with deuterium-labelled tert-butoxycarbonyloxy groups. Ambient impurities (amines and organic bases) are known to quench surface reactions and contribute, but grazing-incidence X-ray diffraction shows an additional effect that the protected molecular resists are preferentially oriented at the surface, whereas the bulk of the film displays diffuse scattering representative of amorphous packing. The surface deprotection reaction and presence of photoacid were quantified by near-edge X-ray absorption fine-structure measurements.

Characterization of Remote Photocatalytic Activity of TiO2 with Ag Nanosheet

Remote photocatalytic reaction of a Pt-modified TiO2 thin film was investigated by using Ag nanosheet as a marker. The Ag nanosheet is a two-dimensional crystalline film composed of myristate-capped silver nanoparticles (d = 5 nm), which has a strong localized plasmon absorption band at λmax = 470 nm. The Ag nanosheet on a 50 nm gold film was set on a measurement cell at 10 μm distance from the Pt-modified TiO2 film. Then the refractive index change of Ag nanosheet was real-time monitored by a surface plasmon resonance (SPR) technique under UV light irradiation (wavelength: 365 nm) from the back side of the TiO2 film. The plasmon resonance angle shifted to lower angle in consequence of the degradation of Ag nanosheet due to the remote photocatalytic reaction. We found the reaction was continued even after stopping UV irradiation, i.e., a chain reaction in Ag nanosheet was suggested. The chain reaction was influenced by N2 gas purge as well as the ligand exchange of myristate capping molecules to alkyl thiolate.

Kinetic reactions in thin polyaniline films revisited through Raman–impedance dynamic coupling

Recently introduced as a new technique in electrochemistry, the Raman–impedance dynamic coupling allows one characterizing transfer functions so far not accessible to experiment such as instantaneous concentrations of adsorbed species in response to potential modulations. These were assessed from the measurement of the time-dependent Raman band intensities of different moieties of reduced and oxidized polyaniline. The local concentrations were assumed to be proportional to these instantaneous band intensities. This technique was used to analyze the kinetics of thin polyaniline films at high pH in the limit of electronic conductivity of the film (pH ≤ 3.7). A model was developed for the different available transfer functions such as Raman ( viz. concentrations)/potential, Raman/charge or classical EIS, from a mechanism based on two electron transfer between leucoemeraldine and emeraldine salt and base and a protonation reaction between the last two ones. Among the main results, the band ascribable to leucoemeraldine was found to be proportional to the total charge in the pH and potential ranges investigated which confirms the fact that it is the only reduced species involved in the redox process. A frequency-dependent relaxation was found for emeraldine base vs. charge, with an increase in intensity and a decrease of the characteristic frequency when both the pH and potential increased. Emeraldine salt (polaronic) showed practically no relaxation vs. charge at variance with the bipolaronic one but the response of the latter remained weak and noisy. An improvement in the accuracy of the coupled techniques would bring information that could not be resolved by any of the other alternative techniques alone.

HBr/Ar/CHF3혼합가스를 이용한 ZnO 박막의 유도결합 플라즈마 식각

In this work, the etching characteristics of ZnO thin films were investigated using an inductively coupled plasma(ICP) of HBr/Ar/<TEX>$CHF_3$</TEX> gas mixtures. The plasma characteristics were analyzed by a quadrupole mass spectrometer (QMS) and double langmuir probe (DLP). The surface reaction of the ZnO thin films was investigated using X-ray photoelectron spectroscopy (XPS). The etch rate of ZnO was measured as a function of the <TEX>$CHF_3$</TEX> mixing ratio in the range of 0-15% in an HBr:Ar=5:2 plasma at a fixed gas pressure (6mTorr), input power (700 W), bias power (200 W) and total gas flow rate(50sccm). The etch rate of the ZnO films decreased with increasing <TEX>$CHF_3$</TEX> fraction due to the etch-blocking polymer layer formation.

Effect of metallic precursors on the thin film thickness and reaction resistances in the selenization process

In the selenization process, the sputtered metallic precursors transformed into CIGS thin films, which were investigated by novel in-situ resistance measurement. Simultaneously, the crystal phases and thicknesses of the selenized thin films at various selenization temperatures are obtained by XRD and XRF, respectively. According to the analysis of phase evolutions and reaction characteristics, it can be confirmed metallic In existed in the precursors will transform into the In–Se compound directly and then results in CIS formation as well as the thickness increase below 370 °C. Otherwise, if alloy phases Cu–In and Cu–Ga co-exist in the precursors, not CIS but CIGS will form above 470°, which will lead to both thickness and resistance increase in the corresponding temperature range. Consequently, it can be concluded the thickness increase are decided by the formation of CIS or CIGS, whereas the strong reaction peak in the temperature-resistance curves are caused only by stoichiometric CIGS.

Phase formation and thermal stability of ultrathin nickel-silicides on Si(100)

The solid-state reaction and agglomeration of thin nickel-silicide films was investigated from sputter deposited nickel films (1–10 nm) on silicon-on-insulator (100) substrates. For typical anneals at a ramp rate of 3 °C/s, 5–10 nm Ni films react with silicon and form NiSi, which agglomerates at 550–650 °C, whereas films with a thickness of 3.7 nm of less were found to form an epitaxylike nickel-silicide layer. The resulting films show an increased thermal stability with a low electrical resistivity up to 800 °C.

Formation of cobalt hydroxide single-crystal platelets from pulsed laser deposited cobalt thin film

Uniform size hexagonal shaped cobalt hydroxide single crystals of about 100–200 nm thick were produced on glass substrates. They were formed by the reaction of a cobalt thin film with the sodium hydroxide solution. The film was prepared by the pulsed laser deposition (PLD) process of which the second harmonic of a pulsed Nd:YAG laser (wavelength = 532 nm) was employed to ablate the rotating cobalt target in vacuum. As revealed by SEM the smoothed surface of the as-prepared cobalt film changed into individual hexagonal platelets after the chemical reaction. The platelets were grown with the hexagonal planes mostly parallel to the substrate surface. From the XRD and FTIR results, as well as the SAED provided by TEM, these platelets are evidently the single crystals of β-cobalt hydroxide. It is believed that the formation of these single crystals is benefited from the nanosized grains of PLD cobalt, which promote the chemical reaction.

Coke yield and heat transfer in reaction of liquid–solid agglomerates of Athabasca vacuum residue

AbstractThe ultimate coke yield was determined for agglomerates of Athabasca vacuum residue and coke particles by heating on Curie‐point alloy strips in an induction furnace at 503 and 530°C until all toluene‐soluble material was converted. Coke yield results from agglomerates were compared to the coke yield results from reacting thin films of vacuum residue. The average coke yield from the agglomerates was 23%, while the coke yield from thin films of 20 µm thickness was 11%, which supports the role of mass transfer in coke formation reactions. The ultimate coke yield was insensitive to vacuum residue concentration, agglomerate size, and reaction temperature. The temperature profile within agglomerates was measured by implanting a thermocouple, and a simple heat transfer model was used to describe the temperature variation with time. The effective thermal diffusivity of the agglomerates was 0.20 × 10−6 m2/s. Control experiments on reaction in thin liquid films confirmed that heating rates in the range of 14.8–148 K/s had no effect on the ultimate yield of coke yield.

Kinetics of a transient silicide during the reaction of Ni thin film with (100)Si

In situ measurements of the kinetics of the transient θ-Ni2Si phase formation have been obtained by x-ray diffraction and differential scanning calorimetry. A possible mechanism for the transient phase is proposed. It allows to simulate the growth and the consumption of the θ-Ni2Si during the growth of the δ-Ni2Si silicide.

Experimental flame speed in multi-layered nano-energetic materials

This paper deals with the reaction of dense Metastable Intermolecular Composite (MIC) materials, which have a higher density than conventional energetic materials. The reaction of a multilayer thin film of aluminum and copper oxide has been studied by varying the substrate material and thicknesses. The in-plane speed of propagation of the reaction was experimentally determined using a time of- flight technique. The experiment shows that the reaction is completely quenched for a silicon substrate having an intervening silica layer of less than 200 nm. The speed of reaction seems to be constant at 40 m/s for silica layers with a thickness greater than 1 μm. Different substrate materials such as glass and photoresist were also used.

Determination of activation energy of intermixing in textured metal-metal multilayer films via two-dimensional X-ray diffraction

Activation energies for the intermixing reaction of textured metal-metal multilayer thin films have been determined using X-ray diffraction analysis. Kinetic data were collected utilizing an area detector so as to reduce intensity bias from changes in out-of-plane texture during the intermixing reaction. Activation energies for Al/Pt, Ni/Ti, and Co/Al metal-metal multilayer thin films have been determined as 95.4(2) kJ/mol, 201(13) kJ/mol, and 247(19) kJ/mol, respectively.

Interface stability in advanced high-κ-metal-gate stacks

Thin film reactions and interface formation in advanced high-κ-metal-gate stacks containing rare-earth oxides have been studied. In particular, interfacial reactions of Dy2O3 and HfSiO4 with TiN- or TaCN-based metals were studied. It is shown that Dy diffusion is considerably stronger than Hf diffusion. It is further demonstrated that for TaCN-based materials, the material density and the microstructure are of much larger influence than the chemical composition.

Copper oxide thin film and nanowire as a barrier in ZnO dye-sensitized solar cells

The ZnO dye-sensitized solar cells (DSSCs) with different photoelectrodes were studied on the effect of CuO layer as a barrier layer toward power conversion characteristics. The structures of DSSCs based on ZnO as a photoelectrode, Eosin-Y as a dye sensitizer, iodine/iodide solution as an electrolyte and Pt/FTO as a counterelectrode. CuO powder, nanowire prepared by oxidation reaction of copper powder and CuO thin film prepared by evaporation copper thin film, were used as a layer on the top of ZnO layer to form blocking layer. The photocurrent, photovoltage and power conversion efficiency characteristics for DSSCs were measured under illumination of simulated sunlight obtained from a solar simulator with the radiant power of 100 mW/cm 2. It was found that ZnO DSSCs with CuO thin film exhibited highest current density of 5.10 mA/cm 2 and highest power conversion efficiency of 0.92% than those of CuO powder and nanowire. The enhancement of the power conversion efficiency can be explained in terms of the retardation of the interfacial recombination dynamics of CuO blocking layer.

Reaction of neptunium with molecular and atomic oxygen: Formation and stability of surface oxides

The surface reactions of thin films of Np metal with molecular and atomic oxygen were investigated by X-ray and Ultra-Violet Photoelectron Spectroscopy (XPS and UPS, respectively). Goal of this work was to study the entire range of oxides, starting with the very early reaction stages, in presence of metal, up to the highest possible oxides, reached at saturation under highly reactive, oxidative conditions. Emphasis was given to the surface layers, whose properties often differ from the bulk, and which are directly involved in corrosion processes of solids. Molecular O 2 reacts readily with the metallic neptunium surface to form the sesquioxide and dioxide. The sesquioxide is observed as thin ‘bulk’ species of up to nine monolayers thickness. A higher oxide, identified as Np 2O 5, is formed when the NpO 2 surface is exposed to atomic oxygen. It is stable under UHV conditions up to a temperature of about 200 °C. The high oxide, Np 2O 5, is still capable of chemisorbing further oxygen. This is shown in UPS spectra by the additional O-2p line at 5–6 eV BE, superimposing onto the valence band (VB). The formation of both a lower (Np 2O 3) and higher oxide (Np 2O 5) besides the dioxide is discussed in the framework of ongoing 5f localization throughout the actinide series.

Room temperature synthesis of nanostructured mixed-ordered-vacancy compounds (OVCs) and chalcopyrite CuInSe2 (CIS) thin films in alkaline chemical bath

Room temperature synthesis of ordered-vacancy-compounds (OVCs) and copper indium diselenide (CuInSe2, CIS) by cation and anion exchange reactions of solid CdS thin films with CIS ionic solution in an alkaline chemical bath is reported. The growth parameters such as pH, deposition time and concentration of the solutions were optimized to achieve uniform thin films. Nanostructured CdS thin films (150 nm thick) prepared by chemical bath deposition are used for the deposition of OVC and CIS thin films. The ion exchange reaction between the CdS thin film and the CIS ionic solutions transforms the yellow colour CdS film into faint black, indicating the formation of OVC and CIS film. The resultant films were annealed in air at 200 °C for 1 h and further subjected to characterization using the x-ray diffraction, transmission electron microscopy, energy dispersive x-ray analysis, x-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, optical absorption and electrical measurement techniques. The OVC and CuIn3Se5 nanodomains are observed in chalcopyrite CIS thin films and these films have nanostructured morphology onto amorphous/nanocrystalline phase of CdS. The OVC–CIS films are p-type with a band gap energy of 1.453 eV.