Electrically conductive properties of tungsten-containing diamond-like carbon films

Tungsten-containing diamond-like carbon films with different metal concentrations were investigated. The films of several hundred nanometers in thickness were deposited on the silicon wafer using RF-PECVD (radio frequency plasma enhanced chemical vapor deposition) method. During deposition, metal component was co-sputtered using DC magnetron of tungsten target. The six samples with the concentration of 3.8, 6.1, 8.0, 16.3, 24.3 and 41.4 at.% of tungsten were made. The structural analyses were performed by TEM (transmission electron microscope) and Raman spectroscopy. These results indicated that tungsten clusters were well dispersed in amorphous carbon host matrix in the case of tungsten concentration from 3.8 to 24.2 at.%. However, no such a structure can be observed in the sample with 41.4 at.%. The AC electrical resistance was measured in the temperature range of 2–300 K using four-probe method in vacuum condition. The observed temperature dependence of electrical conductivity can be expressed by σ=σ₀exp−2(C₀/kT)^1/2 and tungsten concentration from 3.8 at.% to 24.2 at.%. In addition, the sample with 41.4 at.% showed the resistive superconducting transition at T_c of around  5.5 K.     

B/B 1D/2D solid-state high-resolution NMR studies on boron-doped diamond

In this work, three boron-doped diamond samples prepared from a high-pressure high-temperature synthesis method with the same starting materials but with different initial ratios for boron are studied. Magnetic susceptibility measurement shows that the increment of the initial amount of boron does not straightforwardly bring lower superconducting transition temperature. In accordance with our previous ¹¹B high-resolution magic-angle spinning (MAS) NMR results, we show that there are at least four boron signal components and the one at 28.5 ppm is ascribed to the substitutional boron in the diamond structure providing the carriers responsible for conductivity. From observed relative intensities of the four signal components, it is suggested that the excess boron, which does not contribute to the conductivity appears as a broad signal at around 65.5 ppm. We apply two-dimensional (2D) NMR to examine ¹H dipolar broadening and ¹¹B–¹¹B boron spin diffusion, and candidates purported so far for the excess boron, that is, a boron + hydrogen complex and –B–B– and/or –B–C–B– clusters are negated. From its chemical-shift value, it is suggested that the excess boron exists as trigonally coordinated boron. We further apply 2D nutation NMR to examine the size of its quadrupolar coupling and show that it is not very large. As for a structure that compromises the trigonal coordination invoked from the chemical-shift value and the small quadrupolar coupling, we postulate boron locally in a graphite-like structure but the symmetry of the electric field gradient around it is high. Furthermore, we show that ¹⁰B MAS NMR is useful to selectively observe the substitutional boron in the diamond structure appearing at 28.5 ppm, whose quadrupolar coupling is much smaller than that of the excess boron at 65.5 ppm.     

The application of polycrystalline diamond in a thin film packaging process for MEMS resonators

This paper reports the design, fabrication and testing of a polycrystalline diamond (poly-C) thin film packaging process for a MEMS cantilever type resonator using a 4-mask fabrication process, which integrates chemical vapor deposition (CVD) diamond thin film technology with an encapsulation packaging process. After poly-C cantilever beam resonators were fabricated using the first two masks, a sacrificial PECVD SiO₂ layer with a thickness in the range of 4–5 μm was deposited at 350 °C and patterned to create the package anchor. Then, a 4-μm-thick poly-C film was grown and patterned to create the thin film packaging structure containing fluidic access ports for the removal of the sacrificial layer. The fluidic access ports were finally sealed with an additional poly-C growth. To evaluate the efficacy of the poly-C encapsulation process, poly-C cantilever beam resonators were tested using a piezoelectric actuation and laser detection method before and after the poly-C packaging process. Resonance frequencies measured before and after are in the range of 240–320 kHz, which is consistent with predicted calculations. A modified fabrication process was designed to test the fluidic hermiticity of the thin film package.     

Calculation of piezoelectric constants of poly(vinylidene fluoride)

Summary Piezoelectric constants of poly(vinylidene fluoride) form I crystal have been calculated to give a good agreement with observed values; d₃₃ = –2.5 × 10^–11 C/N (observed: –2 × 10^–11 C/N) and d₃₃ = –2.5 × 10^–13 C/N (observed: ca. 10^–13 C/N). The macroscopic piezoelectric constants have also been calculated using such a model that the piezoelectric crystal form I is embedded in the non-piezoelectric amorphous matrix to be d ₃₁ ^M 0.6 × 10^–11 C/N (at room temperature) and 4.6 × 10^–13 C/N (below glass transition temperature), and d ₃₃ ^M –1.4 × 10^–11 C/N and –0.5 × 10^–11 C/N, respectively, reproducing well the observed temperature dependence of these constants.     

Low temperature time of flight mobility measurements on synthetic single crystal diamond

We study the temperature dependence of low charge injection drift mobility in single crystal (SC) diamond using an alpha particle source. We present time of flight (ToF) mobility measurements to investigate the charge carrier scattering mechanisms in SC synthetic diamond in the temperature range 200 K–300 K. We have used a gold contacted pad detector, with a “sandwich” contact structure, fabricated using a SC chemical vapour deposition (CVD) diamond synthesised by Element Six Ltd. ToF analysis of alpha particle induced current pulses shows a strong increase in hole mobility at reduced temperatures, consistent with acoustic phonon scattering processes dominating the charge carrier transport. On the other hand, electron mobility values appear to remain relatively constant with lower temperatures suggesting different mechanisms than optical or acoustic phonon scattering limiting the charge transport.     

The role of pressure on thin amorphous carbon films deposited using microwave surface wave plasma CVD

We report the effects of gas composition pressure (GCP) on the optical, structural and electrical properties of thin amorphous carbon (a-C) films grown on p-type silicon and quartz substrates by microwave surface wave plasma chemical vapor deposition (MW SWP CVD). The films, deposited at various GCPs ranging from 50 to 110 Pa, were studied by UV/VIS/NIR spectroscopy, atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and current–voltage characteristics. The optical band gap of the a-C film was tailored to a relatively high range, 2.3–2.6 eV by manipulating GCPs from 50 to 110 Pa. Also, spin density strongly depended on the band gap of the a-C films. Raman spectra showed qualitative structured changes due to sp³/sp² carbon bonding network. The surfaces of the films are found to be very smooth and uniform (RMS roughness < 0.5 nm). The photovoltaic measurements under light illumination (AM 1.5, 100 mW/cm²) show that short-circuit current density, open-circuit voltage, fill factor and photo-conversion efficiency of the film deposited at 50 Pa were 6.4 μA/cm², 126 mV, 0.164 and 1.4 × 10^− 4% respectively.     

Pore structure development of in-situ pyrolyzed coals for pollution prevention in iron foundries

A protocol was devised for preparing pyrolyzed coals that could be made in-situ at foundries to capture volatile organic compound (VOC) emission. This pyrolysis created extensive micropore volume in lignite over a broad range of temperature and time; and could use waste heat from cupola exhaust gases by a heat-exchange tube. For foundry application, moderate porous carbon with relatively uniform pores over wide ranges of temperature and time would be more practical than highly porous activated carbon (AC) that requires narrowly-controlled operations. This pyrolysis protocol was developed in a thermogravimetric analyzer (TGA) and in a small tube furnace, while using lignite, bituminous coal, and anthracite. The lignite yielded the most pore volume; and this was relatively uniform (0.1–0.13 mL/g of pores) while temperatures were 600–900 °C, and times were 0–60 min. Smaller grain sizes yielded improved porosity; and this corresponded to more release of phenols and naphthalenes from smaller grains, as discerned by TGA–mass spectroscopy (MS). TGA–MS also revealed that improved pore development between 600–800 °C corresponded to the release of CO₂ and H₂O; and concurrently higher slurry pH linked to less oxygenated functionality. Adsorption of benzene was compared between the in-situ porous carbon and a commercial AC.     

Combustion in the Y2O3-BaO2-αCu system with gasifying additives

Burning has been examined on the system for various oxygen pressures. The value of determines whether the process accelerates or dies away. An explanation is proposed. Adding BaCO₃ as a gasifying additive enables one to avoid extensive melting and reduces the maximum temperature. The main reaction products have been identified. SHS with gasifying additive has made it possible to synthesize the tetra phase of the high-temperature superconductor Y₁₂₃, whose temperature of transition to the superconducting state T_c is dependent on the amount of additive used.Synthetic Materials Institute, Russian Academy of Sciences, Chernogolovka 142432. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 4, pp. 60–62, July–August, 1994.     

Development of a TOF measurement system of charge carrier dynamics in diamond thin films using a UV pulsed laser

A fast TOF measurement system with 150 ps time resolution for transport behavior of free charge carriers in an intrinsic diamond film by using a UV pulsed laser was developed. The 213 nm UV laser light narrowed to approximately 80 μm widths could locally create hole–electron pairs in selected locations on a diamond film between two parallel electrodes on the surface. This system measured accurate charge transport characteristics in a diamond film, because created charge carriers moved in a part of the diamond film where they did not get any influence from the laser irradiation. Diamond samples used for verification of the TOF system were intrinsic CVD diamond films with thickness between 4 and 10 μm grown on HP/HT diamond substrates. Transit time of holes for one diamond film was 4.7 ns with a traverse distance of 250 μm. The local irradiation of laser made it possible to measure transport characteristics of electrons and holes separately. In addition, it substantially reduced the influence of photoelectron, because the laser beam did not irradiate electrodes. Through several examinations, excellent reliability of the TOF system was confirmed.     

Oxygen diffusion into polystyrene–bentonite films

A simple fluorescence technique is proposed for the measurement of the diffusion coefficient of oxygen into polystyrene–clay composite films. The composite films were prepared from the mixture of surfactant-free pyrene (P)-labeled polystyrene latexes (PS) and modified bentonite (MNaLB) at various compositions at room temperature. These films were annealed at 200 °C above the glass transition (T_g) temperature of polystyrene for 10 min. Oxygen diffusion into the films was monitored with steady state fluorescence (SSF) measurements. Measurements were performed at room temperature for different film compositions (0, 5, 10, 20, 30, 50 and 60 mass% modified bentonite) films to evaluate the effect of MNaLB content on oxygen diffusion. The diffusion coefficient, D of oxygen was determined by the fluorescence quenching method by assuming Fickian transport and increased from 7.4 × 10^− 10 to 26.9 × 10^− 10 cm² s^− 1 with increasing MNaLB content. This increase in D value was explained by formation of microvoids in the film. These voids are large enough to contribute to the penetration of oxygen molecules through the films. The montmorillonite content did not affect the quenching rate constant, k_q and mutual diffusion coefficient, D_m values.     

Molecular motion of isolated polybutadiene chains tethered on the fresh surface of polytetrafluoroethylene

The polybutadiene (PBD) chains tethered on the fresh surface of a polytetrafluoroethylene (PTFE) were produced by a block copolymerization of PTFE with 1,3-butadiene in vacuum at 77 K. The extremely low segmental density of the tethered chains was estimated by a spin labelling technique. The tethered chains can be regarded as ‘isolated polymer chains’. The PBD tethered chain has an unpaired electron at the chain end. We studied the molecular mobility of the PBD tethered chains by electron spin resonance (e.s.r.) spectroscopy, using the PBD chain end radical as a probe. The site exchange motion between two conformations at the chain end was observed in the temperature range 77–173 K and the rate of the exchange motion was determined by spectral simulations. The tethered chains are mobile even below 218 K which is a glass transition temperature of 1,4-PBD in the bulk. The high mobility of the PBD chains tethered on the PTFE surface is attributed to: the PBD chains have a very large space around the chains because of an extremely low segmental density on the PTFE surface. © 1997 Elsevier Science Ltd.     

Characterization of sepiolite as a support of silver catalyst in soot combustion

Turkish sepiolite–zirconium oxide mixtures were applied as a support for the silver catalyst in a soot combustion. Sepiolite–Zr–K–Ag–O catalyst was characterized by XRD, N₂ adsorption, SEM, TPR-H₂ and EGA-MS. The combustion of soot was studied with a thermobalance (TG-DTA). The modification resulted in a partial degradation of the sepiolite structure, however, the morphology was preserved. The adsorption of N₂ of the modified sepiolite is a characteristic for mesoporous materials with a wide distribution of pores. The specific surface area S_BET equals 83 m²/g and the pores volume is 0.23 cm³/g. The basic character of the surface centers of sepiolite is indicated by CO₂ desorption (TPD-MS) at 170 °C and at about 620 °C due to a surface carbonates decomposition. The thermodesorption of oxygen at 650–850 °C indicates the decomposition of AgO_x phases at the surface. The presence of AgO_x phases is also confirmed by TPR-H₂ spectrum (low temperature reduction peak at 130 and 180 °C). The high-temperature reduction at about 570 °C is probably related to Ag–O–M phases on the support.The soot combustion takes place at T₅₀ = 575 °C. Without silver (sepiolite–Zr–K–O) T₅₀ = 560 °C but sepiolite modified with silver (sepiolite–Zr–K–Ag–O) undergoes the same process at T₅₀ = 490 °C.     

Adsorption of Pb(II) from aqueous solution to MX-80 bentonite: Effect of pH, ionic strength, foreign ions and temperature

The adsorption of Pb(II) from aqueous solution to MX-80 bentonite was studied using batch technique under ambient conditions. Removal percent (%) and distribution coefficient (K_d) were determined as a function of shaking time, pH, ionic strength and temperature. The results showed that the adsorption behavior of Pb(II) on bentonite was strongly dependent on pH and ionic strength. The presence of complementary cations depressed the adsorption of Pb(II) on bentonite in the order of Li⁺ ≈ Na⁺ > K⁺ at pH 2–5. The adsorption isotherms were simulated by the Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) models very well. The thermodynamic parameters (ΔH⁰, ΔS⁰, and ΔG⁰) for the adsorption of Pb(II) were determined at three different temperatures of 291 K, 308 K and 328 K. The adsorption reaction was exothermic and the process of adsorption was favored at low temperature. The results suggest that bentonite is suitable as a sorbent material for the recovery and adsorption of Pb(II) from aqueous solution.     

SrMoO4 powders processed in microwave-hydrothermal: Synthesis, characterization and optical properties

In this work, we report on the synthesis of SrMoO₄powders by co-precipitation method and processed in a microwave-hydrothermal at 413 K for 5 h. These powders were analyzed by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL). XRD analyses revealed that the SrMoO₄ powders are free of secondary phases and crystallize in a tetragonal structure. FT-Raman investigations showed the presence of Raman-active vibration modes correspondent for this molybdate. UV–vis technique was employed to determine the optical band gap of this material. SrMoO₄ powders exhibit an intense PL emission at room temperature with maximum peak at 540 nm (green region) when excited by 488 nm wavelength of an argon ion laser.     

Structural Fe(III) reduction in smectites

Manipulation of the oxidation state of structural Fe in clay minerals is a potential method for altering important physical–chemical properties of the clay and several studies have focussed on this phenomenon. This paper summarizes current knowledge on reduction of structural Fe(III) in iron-rich dioctahedral smectites and partial stabilization of Fe(II) in reduced SWa-1 ferruginous smectite via fixation of Li⁺ cations upon heating. Fe(III) in Fe-rich dioctahedral smectites was completely reduced in citrate–bicarbonate buffer using sodium dithionite. Progress in the reduction or reoxidation process was followed by monitoring the Fe(II)–O–Fe(III) intervalence electron transfer transition using visible spectroscopy at 730 nm. Reduction proceeds from basal surfaces rather than from particle edges. One study found that trioctahedral domains and vacancies may occur within the structure of reduced minerals, but another study indicated less radical structural changes. Fully reoxidized minerals contain less OH groups. About 20% of total Fe can be stabilized as Fe(II) in reduced SWa-1 via Li⁺-saturation and heating the Li-form of a highly reduced mineral in N₂ atmosphere at 260 °C for 24 h. Part of the Li⁺ is trapped in previously vacant octahedral sites, forming trioctahedral AlFe(II)LiOH or Fe(III)Fe(II)LiOH groupings.     

Spectroscopic and porosimetry studies to estimate the firing temperature of some archaeological pottery shreds from India

The present study aims to estimate the firing temperature of archaeological pottery shreds collected from the three archaeological sites namely Maligaimedu, Thiruverkadu and Palur in Tamilnadu state, India. The spectroscopic method Fourier Transform Infrared Spectroscopy (FT-IR) has been employed to find the lower limit of firing temperature of the archaeological pottery shreds by refiring the samples to four different temperatures from 200 °C to 800 °C. From the observation of the hydroxyl band and appearance/disappearance of octahedral sheet structure the firing temperature of the shreds has been estimated. The samples from Maligaimedu site named as MM1, MM3 and MM5, Thiruverkadu and Palur samples were fired to a temperature above 800 °C and the samples of Maligaimedu MM2, MM4 and MM6 were fired below 800 °C. Additionally, porosimetry measurements such as water absorption and mercury intrusion (MIP) were also carried out. The samples MM1, MM3, TK2–TK6, PL3 and PL5 were fired to a temperature less than 900 °C and the other samples to less than 1000 °C.     

Novel phthalocyanines containing substituted salicyclic hydrazone-1,3-thiazole moieties: Microwave-assisted synthesis, spectroscopic characterization, X-ray structure and thermal characterization

Novel, metal-free and metallo(Cu, Co, Ni, Zn, Pb and Mn)phthalocyanine compounds were synthesized by exposure to microwave irradiation and the products purified. The newly prepared compounds were characterized using elemental analyses, IR, ¹H/¹³C NMR, ¹H–¹H COSY measurements, MS, UV–vis spectroscopy and DTA/TG analysis. The electronic spectra exhibited an intense π → π* transition with characteristic Q and B bands of the phthalocyanine core, as expected. All decomposition products obtained from DTA/TG analysis were identified; it was found that the thermal stability of each phthalocyanine compound followed the order: MnPc < Metal-free < ZnPc < PbPc < CuPc < CoPc < NiPc.     

Mineralogical transformations of calcareous rich clays with firing: A comparative study between calcite and dolomite rich clays from Algarve, Portugal

Mineralogical transformations during firing of two extremely calcareous clays, one calcite and other dolomite rich, and relatively poor in silica were studied. Original clays were mineralogical and chemically characterized with X-ray diffraction (XRD) and X-ray fluorescence (XRF). Firing of both clays was carried out in the temperature range 300–1100 °C under oxidizing conditions and the mineralogical transformations were investigated with XRD, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy associated with energy dispersive X-ray spectroscopy (SEM-EDS).Important compositional differences in the neoformed phases were observed between calcite and dolomite rich clays. In the Ca-rich clay the assemblage gehlenite + wollastonite + larnite was observed. In the Mg(Ca)-rich clay the reaction products included akermanite, diopside, monticellite, forsterite, periclase and spinel.XRD and SEM-EDS showed the presence, in both clays, of a potassium–calcium sulfate in samples fired between 900 and 1100 °C.     

Low-temperature thermionic emission from nitrogen-doped nanocrystalline diamond films on n-type Si grown by MPCVD

Temperature-dependent emission current–voltage measurements were carried out for nitrogen (N)-doped nanocrystalline diamond (NCD) films grown on n-type Si substrates by microwave plasma-assisted chemical vapor deposition (MP-CVD). Low threshold temperature (~ 260 °C) and low threshold electric field (~ 5 × 10^− 5 V/µm) were observed. Both the temperature dependence and the electric field dependence have shown that the obtained emission current was based on electron thermionic emission from N-doped NCD films. We have also studied the relation between nitrogen concentration and the saturation emission current. The saturation current obtained was as high as 1.4 mA at 5.6 × 10^− 3 V/µm at 670 °C when the nitrogen concentration was 2.4 × 10²⁰ cm^− 3. Low value of effective work function (1.99 eV) and relatively high value of Richardson constant (~ 70) were estimated by well fitting to Richardson–Dushman equation. The results of smaller φ and larger A′ suggest that N-doped NCD has great possibility of being a highly efficient thermionic emitter material.     

Preparation of Co–Al layered double hydroxides by the hydrothermal urea method for controlled particle size

In order to control particle size and the distribution, Co–Al layered double hydroxides were prepared from aqueous glycerol solutions of cobalt chloride and aluminum chloride by urea hydrolysis under hydrothermal conditions. Effects of the synthetic conditions including heating temperature and time, and glycerol/water ratio on the particle size and its distributions of Co–Al layered double hydroxide were discussed. Particle diameter was controlled from 1.0 (glycerol/water ratio = 10 g/40 mL) to 38.3 μm (glycerol/water ratio = 0 g/40 mL, heating at 50 °C for 150 days). Narrow particle diameter distribution as low as 20% coefficient of variation was achieved under optimized synthetic conditions (glycerol/water ratio = 10 g/40 mL, heating temperature < 80 °C).