Amorphous Hydrogenated Research Articles

Amorphous ferroelectric thin film capacitive device for hydrogen detection

Hydrogen is a promising alternative energy source for next generation automobile engines that meet the concern of energy shortage and global environmental pollution. Hydrogen detection is an important associated technology to be developed. The recently developed amorphous ferroelectric thin film capacitive gas sensors with a largely improved sensitivity to hydrogen show a great potential for this associated technology. This review presents an overall picture of amorphous ferroelectric thin film hydrogen gas sensors. It focuses on the correlation among processing, microstructural evolution and electrical properties of amorphous ferroelectric thin films. An attempt is made to detail the hydrogen sensitivity and transient response of various prototype capacitive devices with respect to the quality of the films and the hydrogen kinetic processes in the Pd/ferroelectric heterostructure. Recent advances on the hydrogen interface-blocking model for amorphous ferroelectric gas sensors are also described.

Effect of Post-treatment on Electrical Properties of Amorphous Hydrogenated Carbon Films Deposited by Gridless Ion Beam Deposition

Amorphous hydrogenated carbon (a-C:H) films were deposited from the gas mixtures of acetylene (C2H2) and argon (Ar) in a gridless ion beam deposition (GIBD) system fed with dc power. Vacuum annealing and hydrogen plasma treatment were performed on the a-C:H films and their effects on the physical and electrical properties of the films were investigated. Film structure and properties were investigated as a function of the C2H2 flow rate by Raman spectroscopy. Through the Raman spectra, we found that the Raman ID/IG intensity ratio increases as annealing temperature increases, which indicates a more graphite-like character in the annealed films. The dielectric constant of the annealed a-C:H films was reduced from 3.8 to 2.9 and the thickness also slightly decreased with increasing annealing temperature. However, the leakage current density and dielectric constant of the hydrogen-plasma-treated a-C:H films were clearly lower than the as-deposited a-C:H films.

Effects of Ammonia Plasma Treatment on the Electrical Properties of Plasma-Enhanced Chemical Vapor Deposition Amorphous Hydrogenated Silicon Carbide Films

Amorphous hydrogenated silicon carbide (a-SiC:H) films were deposited from a mixture of silane and methane gases using the plasma-enhanced chemical vapor deposition (PECVD) process. The properties of the film, following ammonia plasma treatment, are reported. A lower silane flow rate reduces the refractive index, but increases the carbon content and the optical band gap. Increasing the carbon concentration of the a-SiC:H films reduces the dielectric constant. The films were treated with ammonia plasma for various treatment periods. The original film has a smooth surface with a roughness of 0.231 nm, but increasing the ammonia plasma treatment period gradually roughens the surface. The chemical bonding nature of the a-SiC:H films with higher silicon content was investigated by X-ray photoelectron spectroscopy. Various nitrogen ionization species reacted with Si to promote the formation of silicon nitride. As a result, although the dielectric constant of the a-SiC:H films increased slightly, the leakage current density declined as the ammonia plasma treatment time increased.

Thermal stabilities and discharge capacities of melt-spun Mg–Ni-based amorphous alloys

Mg–Ni–M (M=Ca, La or Pd) ternary alloys were synthesized by the melt-spinning technique. All as-solidified alloys possessed an amorphous single phase by the additional effect of the third element, though it was difficult to obtain an amorphous Mg 67Ni 33 binary alloy by melt-spinning. We examined the thermal stability and electrochemical cyclic life property of the ternary amorphous alloys. The crystallization temperature of the amorphous alloys increases with increasing M content. All the alloys except Mg 67Ni 28Pd 5 examined in the present study maintain the amorphous structure even after hydrogen absorption at 373 K for Mg–Ni–Ca and Mg–Ni–Pd and at 423 K for Mg–Ni–La. The crystallization temperature increases by absorbing hydrogen, indicating that the alloys are thermally stabilized by hydrogen absorption. In the electrochemical cyclic life measurements up to five cycles, the Mg–Ni–Pd amorphous alloys exhibit high discharge capacities ranging from 100 to 400 mA h/g as well as small cyclic life degradation tendency, though the Mg–Ni–Ca and Mg–Ni–La amorphous alloys possess small discharge capacities of 10–100 mA h/g with significant cyclic life degradation. It is thus concluded that the good cyclic life property of the amorphous hydrogen storage alloys can be obtained by application of the melt-spinning technique to Mg-based alloys with appropriate alloy compositions.

Photoluminescence properties of amorphous silicon-based oxygen and hydrogen alloys

We prepared hydrogen and oxygen alloys of a-Si by the method of rf sputtering and found similarities in their photoluminescence (PL) features. Depression of PL intensity at high temperature is reduced by alloying and results in a larger PL intensity at room temperature. Nonradiative recombination processes in the alloys are discussed in terms of the temperature dependence of the PL intensity. It is concluded that band gap fluctuations induced by alloying reduce transitions to nonradiative defect centers in these systems.

Hydrogen-Sensitive Amorphous Ferroelectric Thin Film Capacitive Devices

Amorphous ferroelectric thin film capacitive gas sensors with a largely improved sensitivity to hydrogen have been developed recently, showing a great promising potential for the next generation hydrogen detection technology. This review presents an overall picture of amorphous ferroelectric thin film hydrogen gas sensors, starting from the hydrogen-damage phenomena of ferroelectric thin films during the forming gas annealing (FGA) process. It stresses on the correlation among processing, microstructural evolution and electric properties of amorphous ferroelectric thin films for fabrication concerns. An attempt is made to detail the hydrogen sensitivity and transient response of various prototype capacitive devices with respect to the instinct of the films and the hydrogen kinetic processes in the Pd/ferroelectric heterostructure. Recent advances on the hydrogen-damage mechanism of ferroelectric thin films and the hydrogen interface-blocking model for amorphous ferroelectric gas sensors are also described.

Hydrogen bonding with adsorbent during storage governs drug dissolution from solid-dispersion granules.

To investigate changes in drug dissolution on storage of ternary solid-dispersion granules containing poorly water-soluble drugs. Hot-melt granulation was used to prepare ternary solid-dispersion granules in which the drug was dispersed in a carrier and coated onto an adsorbent. Seven drugs including four carboxylic acid-containing drugs (BAY 12-9566, naproxen, ketoprofen, and indomethacin). a hydroxyl-containing drug (testosterone), an amide-containing drug (phenacetin), and a drug with no proton-donating group (progesterone) were studied. Gelucire 50/13 and polyethylene glycol (PEG) 8000 were used as dispersion carriers whereas Neusilin US2 (magnesium aluminosilicate) was used as the surface adsorbent. Two competing mechanisms have been proposed to explain the complex changes observed in drug dissolution upon storage of solid dispersion granules. Conversion of the crystalline drug to the amorphous hydrogen bonded (to Neusilin) state seems to increase dissolution, whereas, the phenomenon of Ostwald ripening can be used to explain the decrease in drug dissolution upon storage. The solubility of the drug in Gelucire is a crucial factor in determining the predominant mechanism by governing the flux toward the surface of Neusilin. The mobility for this phenomenon was provided by the existence of the eutectic mixture in the molten liquid state during storage. A competitive balance between hydrogen bonding of the drugs with Neusilin and Ostwald ripening determines drug dissolution from solid-dispersion granules upon storage.

Hydrogen-Induced Chemical Erosion of Amorphous Hydrogenated Carbon Thin Films: Structure and Reactivity

In the present study, we investigated the effects of annealing of amorphous hydrogenated carbon (a-C:H) films, particularly with respect to structural changes of the carbon network and their impact on the hydrogen-atom-induced erosion. The a-C:H films were deposited at 300 K on a Pt(111) single crystal using the ion-beam deposition (IBD) method. Electron energy loss spectroscopy (EELS) and high-resolution electron energy loss spectroscopy (HREELS) were employed to monitor structural changes of the carbon network as a function of the annealing temperature. A transition from an sp3-rich carbon network toward an sp2 dominated, “graphitic” structure was observed around 900 K. The hydrogen-induced erosion of as-deposited and annealed a-C:H films was investigated by in situ mass spectrometry. The postdeposition annealing did not change the overall erosion rates of a-C:H films; however, the product distribution indicates the growth of existing graphitic structures as a consequence of annealing at temperatures ab...

Defect kinetics in new model of metastability in a-Si:H

We recently developed a new atomistic model of metastability of amorphous hydrogen silicon (a-Si:H), involving changes in silicon and H bonding, and driven by the breaking of weak silicon bonds. The kinetics of degradation in this model are simulated with coupled rate equations which show saturation behavior similar to experiment. Dangling bond (DB) defects follow the well-known G 2/3 t 1/3 kinetics of defect creation. Saturated defect densities of neutral DBs are accompanied by a much smaller density of floating bonds (FBs).

The effect of benzenesulfonamide plasticizers on the glass transition temperature of an amorphous aliphatic polyamide

AbstractThe plasticizing effect of benzenesulfonamides (BSAs) on an amorphous aliphatic polyamide (AAPA) has been studied using dynamic mechanical analysis of copper‐supported spin‐coated mixtures. It follows that N‐(n‐butyl)BSA (BBSA), an amorphous liquid hydrogen bonding BSA, is fully miscible with AAPA because their mixtures are characterized by a single glass transition (Tg) throughout the compositional range. The Tg–composition dependence, however, is not linear because experimental results suggest a 20 K fall in Tg occurring around 0.65 BBSA units per amide unit, which coincides with the system shifting from a polymer‐like to a liquid‐like glass‐forming material. When considering a crystallizable hydrogen‐bonding plasticizer such as ethylBSA (EBSA), AAPA/EBSA mixtures become fully crystalline at a 1.3 EBSA unit per amide group. Nevertheless, melting point depression together with the single Tg observed throughout the compositional range on quenched (and therefore amorphous) samples confirms the miscibility of AAPA chains with the plasticizer. N,N‐DialkylBSAs, which lack the sulfonamide proton and therefore the possibility of hydrogen bonding with amide groups, quickly phase separate from AAPA, the glass transition of the latter staying mainly unaffected apart from a small (9 K) decrease at 10–15 mol% plasticizer.© 2001 Society of Chemical Industry

Improvement of electrode performances of Mg 2Ni by mechanical alloying

Nanocrystalline and amorphous Mg 2Ni-based hydrogen storage alloys for Ni–MH batteries had been synthesized by mechanical alloying. The surface modification and Zr addition had also been carried out for improvement of its electrode performance. In comparison with the arc-melted polycrystalline one, the nanocystalline Mg 2Ni phase showed a higher discharge capacity. By increasing milling time from 120 to 160 h, the grain size of Mg 2Ni phase was more refined and the discharge capacity was raised from 180 to 370 mAh g −1. The discharge capacity of the 160-h milled Mg–Ni–Zr amorphous alloys also reached 530 mAh g −1. XPS (X-ray photoelectron spectroscopy) analysis showed that Mg2p spectra were shifted to lower binding energy implying the enhancement of the hydrogen diffusion and charge transfer reaction, and resulted in increasing the discharge capacity in amorphous alloys. To prevent the rapid degradation, the alloy powders were also coated with Ni and graphite by additional ball milling. The Ni and graphite protected the Mg from oxidation, and the coated powders showed a better cyclic stability. After 50 cycles, the degradation of bare electrode was 94% of maximum capacity, but that of coated electrode with Ni and graphite was 45 and 76% of maximum capacity, respectively.

Substrate Bias Effect on Amorphous Hydrogenated Carbon Films Deposited by Filtered Cathodic Arc Deposition

In the present study, we briefly describe the 45° angle magnetic filtered arc deposition (FAD) process and investigate the effect of substrate bias on the hardness of amorphous carbon (a-C) films. An attempt is made to correlate the microstructure, chemical composition and chemical bonding states with the hardness of the corresponding films. After deposition, the film properties were analyzed by Raman spectroscopy and nanoindentation system (NIS). It was found that amorphous carbon films possess highest hardness when deposited at substrate biases ranging from -50 V to -100 V. The hardness values do not show good correlation with Raman I(D)/I(G) ratio. Hydrogen additions to the system help prevent the nucleation of the graphite phase, and stabilize the sp3 bonding of amorphous hydrogenated carbon films. Hydrogen affected on the small graphitic crystalline growth. Films have higher hardness when they have higher fraction of sp3 content.

ChemInform Abstract: UHV Study of Hydrogen Atom Induced Etching of Amorphous Hydrogenated Silicon Thin Films.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

UHV Study of Hydrogen Atom Induced Etching of Amorphous Hydrogenated Silicon Thin Films

Amorphous hydrogenated silicon (a-Si:H) films were deposited at 300 K by the ion-beam-deposition (IBD) method on a Pt(111) single crystal and characterized by means of Auger electron spectroscopy (AES), electronic and vibrational electron energy loss spectroscopy (EELS, HREELS), and thermal desorption spectroscopy (TDS). The a-Si:H films appear to grow in a two-dimensional mode, and exhibit a polymer-like structure with a hydrogen content of approximately 45 at. %, bonded in monohydride (SiH) and dihydride (SiH2) groups. The films are stable up to 500 K; above this temperature the evolution of hydrogen and the formation of platinum silicides were observed. Exposure to atomic hydrogen leads to the formation of silane, disilane, and higher silicon hydrides. Between 100 and 300 K a constant etching rate of Si/H = ∼0.01 was observed. At higher temperatures the etching rate decreased due to the beginning instability of higher hydrides and the competing process of silicide formation.

Formation of Hard Amorphous Hydrogenated Carbon Films with Low Hydrogen Concentration and Their Erosion in Air

Hard amorphous hydrogenated carbon (a-C:H) films are prepared by radio-frequency plasma deposition from a mixture of CH4 and Ar. When these films are heated up to 1220 K under vacuum, they release Ar, a large amount of H2 and a small amount of hydrocarbon, but the thickness of the films does not decrease. In addition, their micro-Vickers hardness decreases, but they remain hard. If these hydrogen-free semihard a-C:H films are heated at 670 K in air for 1 h, they become soft and uptake oxygen and hydrogen. On the other hand, if the original hard a-C:H films are heated under similar conditions, they remain hard without releasing argon or uptaking oxygen. It is concluded that the reduction of hydrogen does not lead to the formation of new cross linking C–C bonds, and the pore size of the films increases after heating allowing the penetration of oxygen and water vapor into the films.

Structure–Property Relationships of Amorphous Hydrogenated Silicon–Carbon Films Produced by Atomic Hydrogen–Induced CVD from a Single-Source Precursor

Amorphous hydrogenated silicon–carbon (a-Si:C:H) films were produced by atomic hydrogen–induced (AH) CVD using hexamethyldisilane (HMDS) as a single-source precursor. Radio frequency (rf) hydrogen plasma was the source of atomic hydrogen. The effect of substrate temperature (Ts) on the chemical structure, composition, surface morphology, mechanical properties (dynamic hardness, total stress), and optical properties (refractive index, optical bandgap) of a-Si:C:H film has been examined. Fourier transform infrared (FTIR) spectroscopy and Auger electron spectroscopy (AES) data revealed a drastic drop in hydrogen content in the film, and a rise of the atomic concentration ratio Si/C with increasing Ts, thus accounting for the elimination of organic moieties from the film and the formation of a Si–carbidic structure. In the light of scanning electron microscopy (SEM) and atomic force microscopy (AFM) examinations, the films were found to be morphologically homogeneous materials with a maximum size of surface roughness not exceeding 2 nm at Ts = 300 °C. Both hardness and stress (tensile in nature) are strongly affected by the film composition, their values increasing with rising atomic ratio Si/C. The investigated optical properties of a-Si:C:H film, i.e., refractive index (n) and optical bandgap (E0), can be controlled by the atomic ratio Si/C for a wide range of values: n = 1.58–2.02 and E0 = 2.3–3.2 eV.

Experimental and Theoretical Investigation of the Effect of Lubricant Structure on the Bonding Kinetics of Perfluoroalkylpolyethers on CHx Amorphous Hydrogenated Carbon

Perfluoropolyethers (PFPEs) are widely used as topical lubricants on rigid magnetic media to provide a low wear interface. The tribological reliability of the disk storage device is strongly depend...

An electrochemical investigation of mechanical alloying of MgNi-based hydrogen storage alloys

The electrochemical properties of amorphous MgNi-based hydrogen storage alloys synthesized by mechanical alloying (MA) were evaluated. The results show that these amorphous Mg 50Ni 50 alloys exhibit a higher discharge capacity and relatively good rate capacity at a suitable grinding time while their cycle life is very poor. In order to improve the cycle life, the surface of the amorphous Mg 50Ni 50 alloy was coated with Ti, Al and Zr in Spex 8000 mill/mixer and the coating effects were further investigated. Based on experimental results, two kinds of MgNi-based amorphous alloys are designed by substituting part of Mg in MgNi-based alloys by suitable elements. These alloys are then composed of four components. Thus, the cycle life of electrodes consisting of these quaternary amorphous alloys is greatly improved.

Amorphous carbon coatings and their tribological behaviour at high temperatures and in high vacuum

Abstract The aim of this research work is a comparative study of three different types of amorphous, diamond-like carbon (DLC) coating, performing under high temperature and high vacuum conditions. A series of hard carbon coatings have been produced by PVD magnetron sputtering and plasma decomposition (low-pressure PACVD) using standard in-house equipment. Sputtered amorphous hydrogen free carbon (a-C), r.f. plasma deposited hydrogen containing amorphous carbon (a-C:H) and titanium doped hydrogen containing amorphous carbon (Ti–C:H) have been prepared on steel disks. Different tests have been carried out for the characterisation of the mechanical properties and the tribological behaviour at high temperatures (up to 450°C) and/or in high vacuum (up to 3×10 −3 Pa). A recently self-built vacuum pin-on-disk test rig was used for the investigations. The examined tribological coatings show good microhardness and excellent friction properties, when sliding against steel at ambient air. Unfortunately, in high vacuum and at high temperatures the friction coefficients are high and the coatings fail rapidly. After a running-in at ambient air, however, the coatings depict initially ultralow friction in vacuum and during heating. The coefficients of friction fall to values of about 0.02 to 0.04. The results of the tribological model tests will be discussed.

High field effect mobility deuterated amorphous silicon thin-film transistors based on the substitution of hydrogen with deuterium

The characteristics of amorphous silicon hydrogen and deuterium thin-film transistors (a-Si:H/a-Si:D TFT) were studied. The deuterated and hydrogenated amorphous silicon channels were prepared by first annealing the as-deposited a-Si:H layer at 550/spl deg/C in N/sub 2/ environment to expel all the hydrogen atoms out of the films, then the D/sub 2/ or H/sub 2/ plasma were applied to treat the amorphous silicon layers. The field effect mobility of the conventional hydrogen TFT is usually smaller than 1 cm/sup 2//V-s. It was found that substitution of hydrogen with deuterium improved the field effect mobility of the TFT. The maximum field effect mobility of a-Si:D TFT obtained from the saturation region was 1.77 cm/sup 2//V-s.