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1.
Hydrogenated diamond-like carbon films were implanted by 110 keV Fe + at doses ranging from 1 × 10 13 to 5 × 10 16 ions cm −2. The film resistivities and the infra-red transmittances of the specimens were determined as functions of the implanted doses. Raman spectra and the infra-red transmittances of the film layers were used to characterize the structural changes of the implanted films. It was found that, when the implantation dose was higher than about 5 × 10 14 or 1 × 10 15 ions cm −2, the film resistivity and the total infra-red transmittance of the specimens decreased significantly. However, when the dose was smaller than this value, the resistivity decreased firstly and then increased with dose and the measured values were higher than those of corresponding as-grown ones. The infra-red transmittance of the specimens was also improved to some extent under the lower dose range. By using structural characterization results, especially the infra-red transmittances of the film layers, we conclude that the electrical and optical property changes at doses higher than about 5 × 10 14 or 1 × 10 15 ions cm −2 were due to the following changes, i.e., the decrease in the population of both sp 2 C-H and sp 3 C-H bonds (compared with that of sp 3 C-H bonds, the decrease in speed of sp 2 C-H bonds is smaller), the decrease of bond-angle disorder and the increased population of sp 2 C-C bonds. However, at doses between 1 × 10 14 and 5 × 10 14 or 1 × 10 15 ions cm −2, the implantation induced increase of C-H bonds was responsible for the observed property changes. Compared with the previous reports, the novelty of the present work is: the IR transmittance curves of the single film layers give us direct evidence for the changes of different C-H bonds with increasing ion dose and thus proved the transformation mechanism proposed previously. 相似文献
2.
The Young's modulus for a crystal of poly(phosphonitrilic chloride) (poly-dichlorophosphazene) (NPCl 2) n has been calculated using force constants derived from spectroscopy. Assuming that the molecule is a uniform helix the value of the modulus is 1.38 × 10 9 dyne cm −2 [dyne cm −2 = 0.1 N m −2]; the result is 1.66 × 10 10 dyne cm −2 if a cis-planar structure is assumed for the molecule. Neither value is close to those obtained experimentally (1.8 × 10 6 to 6.5 × 10 6 dyne cm −2). This is because experimental values relate to the amorphous polymer whereas the calculated values are those for the crystal. There is good agreement between the values calculated for the (NPCl 2) n crystal and those for other polymer crystals. 相似文献
3.
Selective nucleation and deposition of diamonds were achieved on an SiO 2-patterned Si substrate. The substrate was pre-treated with an electric field in plasma to introduce diamond nuclei. This treatment did not affect the SiO 2 area. Consequently, diamonds grew only on the area where Si was exposed under the conventional conditions of diamond growth. The maximum nucleation density on the area of SiO 2was about 5 × 10 7 cm −2. The ratio of the selectivity was 2 × 10 2 or higher. This process will be useful and very promising for manufacturing diamond electronic devices. 相似文献
4.
A multi-step procedure to improve the zone-annealing method was attempted to prepare a high-modulus and high-strength nylon-6 fibre. By the adoption of this procedure, the dynamic storage modulus at room temperature was markedly increased and reached 15.7 × 10 10 dyne cm −2 which is 1.5 times that obtained by the previous zone-annealing method. Tensile properties, orientation, crystallinity and mechanical dispersion were also measured. Comparing the multi-step procedure with the previous one-step procedure, the excellent effects of the multi-step procedure on mechanical properties are discussed. Further, in order to prevent selective relaxation of amorphous molecular chains on removing the applied tension after zone-annealing, heat-setting at constant length was subsequently carried out on the as-zone-annealed fibre. The mechanical properties were further improved: for example, the dynamic storage modulus at room temperature of the resulting fibre was raised to 16.9 × 10 10 dyne cm −2, which was well beyond the highest modulus available in the literature, 14 × 10 10 dyne cm −2. 相似文献
5.
β-SiC surface layers were synthesized by implantation of C + into Si substrates at a comparatively low temperature of 400°C with a metal vapour vacuum arc ion source. X-ray diffraction patterns showed that these layers had a strong (111) preferred orientation. The amount of β-SiC formed increased significantly with the rise of the implantation dose, but the crystallinity of the layers formed relied little on the implantation dose. Both the broad X-ray diffraction peaks and the scanning electron microscopy photograph showed that the grain size of the sample with a dose of 7×10 17 cm −2 is relatively small. 相似文献
6.
In this paper, electrical characteristics by various oxygen content in ZnO films were studied. To control the oxygen content of ZnO films, post-thermal annealing was performed in N 2 and air ambient, led to improve crystallinity and optical properties of ZnO films. The oxygen concentration was measured by Auger electron spectroscopy. The ZnO films having the deficiency of oxygen showed the electron concentrations between 10 21 and mid 6 × 10 17 cm −3 and resistivity at 10 −3–10 −1 Ω cm. On the other hand, when the oxygen concentration of the ZnO films was up to the stoichiometry with Zn, the ZnO films showed low electron concentration at −10 17 cm −3 and resistivity at 10 Ω cm. 相似文献
7.
Secondary electron emission from boron doped diamond polycrystalline membranes (hole concentration 5×10 18 cm −3), prepared by microwave plasma assisted CVD, was investigated in both the reflection and transmission configurations. The model of secondary electrons behavior taking into account the distribution and diffusion mechanism of secondary electrons is proposed to explain the yield dependencies on primary electron energy in both configurations. The model predicts the SEE yield K=19 at the primary electron energy E0 close to 1 keV for reflection configuration and K=3–7 at E0=15–30 keV for transmission configuration for polycrystalline films used in the study. Experimental measurements of the SEE yield vs. primary electron energy (18 at E0=950 eV for the reflection scheme and 3.5–4 at E0=25 keV for the transmission one) are found to accord well with the theoretical results. Estimations, which were made using the model, show that SEE yield in transmission configuration can be increased up to 60 for the primary electron energy of about 10 keV. Since such high yields in transmission scheme may be obtained in monocrystalline membrane, another approach using porous polycrystalline diamond membranes is considered. Porous diamond membranes having SEE yield in transmission scheme of more than 10 at the primary electron energy E0=1 keV were fabricated. 相似文献
8.
The effects of boron (B) doping on the field emission (FE) of diamond films grown by a microwave plasma chemical vapor deposition technique were studied. Raman scattering spectroscopic analysis revealed that B-doping significantly suppressed formation of non-diamond components in the diamond film. The B-doped p-type diamond films had low resistivity, ranging from 0.07 to 20 Ω cm, and various volume fractions of non-diamond components in the diamond films. The turn-on electric field, FT, was independent of the resistivity, the film thickness, and the volume fraction of the non-diamond components. The lowest FT value of 8 V μm −1 and the highest emission current of 3×10 −2 A cm −2 were obtained in the B-doped diamond films. The high efficiency of the electron emission in the B-doped diamond films was believed to be due to the increase in volume fraction of the conductive regions in the film and the high density of emission sites on the film surface. 相似文献
9.
The electrochemical reduction of oxygen in 0.88 M KOH at 25°C was studied using two silver plated copper electrodes that contained uniform, parallel, tapered pores. Photolithography, etching, and plating techniques were used to fabricate these electrodes. Exchange current densities of 2 × 10 −5 A cm −2 and 2 × 10 −6 A cm −2 were measured using an initial slope method. Diffusion limiting currents increased with differential pressure across the gas-electrolyte interface which suggests smaller contact angles at higher pressures. A wedge meniscus model that treats activation, ohmic, and concentration overpotential was applied to fit the polarization curves. 相似文献
10.
A new class of polymer electrolytes, based on the interpenetrating polymer network approach, was obtained starting from functionalised macromers, of poly-ether nature, in the presence of a lithium salt (LiBF 4, LiClO 4, LiCF 3SO 3) and propylene carbonate (PC) or tetraethyleneglycol dimethylether (TGME), as plasticizers. The macromers were synthesised by living polymerisation employing a HI/I2 system as the initiator. The macromer has a polymerisable end group, which can undergo radical polymerisation, attached to a monodisperse poly-vinylether, containing suitable ethylene oxide groups for ion coordination. Monomers and macromers were characterised by FTi.r., u.v.–vis, 1H- and 13C-n.m.r. Self-consistent and easily handled membranes were obtained as thin films by a dry procedure using u.v. radiation to polymerise and crosslink the network precursors, directly on suitable substrates, in the presence of the plasticizer and the lithium salt. The electrolytic membranes were studied by complex impedance and their thermal properties determined by differential scanning calorimetry analysis. Ionic conductivities (σ) were measured for PC and TGME-based membranes at various plasticizer and salt contents as a function of T (60 to −20°C). LiClO4/PC/PE electrolytes, with 3.8% (w/w) salt and 63% PC, have the highest σ (1.15×10−3 and 3.54×10−4 S cm−1 at 20°C and −20°C, respectively). One order of magnitude lower conductivities are achieved with TGME; samples with 6% (w/w) LiClO4 and 45% (w/w) TGME exhibit σ values of 2.7×10−4 and 2.45×10−5 S cm−1 at 20°C and −20°C. 相似文献
11.
Relationship between growth condition and quality of homoepitaxially grown B-doped diamond (001) film has been studied using physical measurements of defect density as a function of doping concentration. In particular, electrical properties of the homoepitaxial diamond film were characterized using measurements of conductivity, carrier concentration and mobility. The highest mobility is found to be about 1000 cm 2V −1s −1 at 293 K, indicating that the quality of the CVD diamond film is further improved through optimizing the growth condition. The density of the compensation donor was determined from the temperature-dependent hole concentration. The lowest donor density is found to be 8.4 × 10 15 cm −3 in the present work. This is an order of magnitude greater than the lowest value measured in natural IIb diamond. Furthermore, it is also found that the donor density increases with increasing doping concentration during the growth. On the other hand, the mobility decreases rapidly with increasing doping concentration. From these results, we speculate that the compensation donor is an origin of an additional scattering center in diamond, and excessive B-doping makes the quality of the CVD diamond worse. 相似文献
12.
Whiskers of MoO 3 have been grown by a thermal transport process. A set of samples was then implanted with nitrogen ions at a dose of 5 × 10 16 ion/cm 2. The implanted whiskers changed from transparent to semi-transparent. Raman spectroscopy of the whiskers was observed and compared with those of unimplanted whiskers. The results revealed that the Raman intensity of the implanted whiskers was decreased about 10 times with respect to that of unimplanted whiskers. Only the case of the wave propagation parallel to the a-axis, a lower suppression ratio of the B 3g modes was observed. No extra mode due to the nitrogen implantation was observed. This indicates that implantation could only induce defects and oxygen vacancies but not the structural transformation. From electrical conductivity and Hall measurement, it was found that the whiskers exhibited an n-type semiconductor and its conductivity drastically increased due to the defects and oxygen vacancies. 相似文献
13.
Nanocrystalline diamond films with different size were characterized by ultraviolet (UV) (244 nm) Raman spectroscopy. It was found that a diamond peak at 1333 cm −1 was enhanced, while the D and G peak of graphite as well as photoluminescence was suppressed, compared with that measured by visible (514.5 nm) Raman. With decreasing the particle size from 120 to 28 nm, the diamond peak shifts from 1332.8 to 1329.6 cm −1, the line width of the peak becomes broader, the intensity ratio of diamond and G peak decreases. The down shift and broadening of the diamond peak depending on the particle size by UV Raman measurements are consistent with the phonon confinement model. 相似文献
14.
Polycrystalline (PbS) 1.14(TaS 2) 2, a misfit layer sulfide, was used as cathodic material for lithium secondary battery. One molar LiClO 4 in propylene carbonate (PC) was used as electrolyte. The cell could be galvanostatic discharged down to x = 4.6 [Li x(PbS) 1.14(TaS 2) 2] when the current density was 65 μA cm −2 and the cell was cycled more than 100 times between 3.5 and 1.5 V at a current density of 260 μA cm −2. Lattice expansion increased linearly with lithium content and was less than that reported for the Li/TaS 2 system. Chemical diffusion coefficients were determined by a modified version of the galvanostatic intermittent titration technique and they were fairly constant in the composition range 0.2 < x < 1, and an average value of 8.1 × 10 −11 cm 2 s −1 was calculated. Sodium intercalation was also accomplished, but the uptake of this ion resulting in a significant lattice expansion compared with that observed for lithium ions. Moreover, a similar dependence of the sodium chemical diffusion coefficient on the composition was observed with an average value of 1.4 × 10 −10 cm 2 s −1, somewhat higher than that of lithium ion. We believe that differences in lattice expansion may be responsible for the differences found in the chemical diffusivity values. 相似文献
15.
The adsorption of radioactive aerosols is of prime importance when assessing the hazard of inhalation of radioactive materials, especially in the uranium mining industry. In previous studies of the attachment rate, contradicting results on the dependence on particle size have been found. The attachment rate for the attachment of the decay products of Rn-222 to monodispersed polystyrene aerosols (of a diameter from 1.2 to 5.3 μm) in the concentration range 1–67 particles cm −3 was measured directly. This is compared with the attachment rate of radon-220 decay products which was measured in a previous experiment. As before, the attachment between the radioactive atoms and the aerosols was found to be directly proportional to the particle concentration N, as well as to the square of the particle radius R. The attachment coefficient of 4.1 × 105 R2 cm3 min−1 and the sticking probability of 0.13 for Rn-222 decay products were found to be larger than that for the decay products of Rn-220 (2.4 × 105 R2 cm3 min−1 and 0.08, respectively). The mechanism for the attachment, however, is the same. 相似文献
16.
Electrochemical behavior of the water-soluble C 60-γ-CD (1:2) inclusion complex has been studied on the hanging mercury drop electrode. A one-electron reversible adsorptive electro-reduction and three irreversible adsorptive electro-reductions were detected by cyclic voltammetry. The amount of C 60-γ-CD adsorbed at saturation is 2.50 × 10 −11 mol cm −2, the diffusion coefficient is 4.36 × 10 −6cm 2s −1 and the standard rate constant of the surface reaction ks are 0.745 s −1, 0.612 s −1 and 0.513s −1, respectively. 相似文献
17.
Model networks of ,ω-dihydroxy-poly(dimethylsiloxane) (PDMS) were prepared by tetrafunctional crosslinking agent tetraethyl orthosilicate (TEOS) and the catalyst stannous 2-ethylhexanoate. Hydroxylterminated chains of PDMS having molecular weights 15 × 10 3 and 75 × 10 3 g mol −1 were used in the crosslinking reaction. Bimodal networks were obtained from a 50% (w/w) mixture of PDMS chains with Mn = 15 × 10 3 and 75 × 10 3 g mol −1. A sequential interpenetrating network of these PDMS chains was also prepared. Physical properties of the elastomers were determined by stress-strain tests, swelling and extraction experiments, and differential scanning calorimetry measurements. 相似文献
18.
Solar light photodegradation, catalysed by a pyrylium salt, of seven benzoic acids present in olive oil mill, has been studied. Significant percentages of photodegradation (20–40%) have been achieved after 6 h of solar exposure for six of the acids, even though they were expected to be difficult to oxidise, due to the presence of an electron-withdrawing carboxylic acid group directly attached to the aromatic ring. Quenching constants for the electron-transfer process between the substrate and the excited catalyst were calculated by means of fluorescence measurements for syringic acid (66×10 9 M −1 s −1), gallic acid (51×10 9 M −1 s −1), veratric acid (51×10 9 M −1 s −1), vanillic acid (48×10 9 M −1 s −1), protocatechuic acid (37×10 9 M −1 s −1) and p-hydroxybenzoic acid (15×10 9 M −1 s −1); no quenching was found for benzoic acid. These photophysical measurements are in good correlation with the yields obtained in the pyrylium salt photocatalysed degradation of those phenolic acids. 相似文献
19.
Ion implantation is a versatile tool for the formation of compound semiconductor nanocrystal precipitates in a host medium with the ultimate goal to form quantum dots for use in device technology. Low dose (1 × 10 16 cm −2) implantations of tellurium and zinc ions have been performed in a 250 nm thick SiO 2 layer thermally grown on 1 1 1 silicon. Their respective energies (180 and 115 keV) have been chosen to produce 5–10 at.% profiles overlapping at a mean depth of about 100 nm. Subsequent thermal treatments at 700 and 800 °C lead to the formation of nanometric precipitates of the compound semiconductor ZnTe. Their size, crystalline structure and depth distribution have been studied as a function of annealing temperature using transmission electron microscopy (TEM) and Rutherford backscattering spectrometry. For the lowest temperature the TEM images shows a cloudy band of ZnTe, but for the highest temperature, the ZnTe nanocrystals are self organized into two layers parallel to the surface. Their mean diameter ranges between 4 and 30 nm, as a function of annealing temperature. 相似文献
20.
The use of ATR–FTIR to probe the adsorption of oxalic and salicylic acids, and of mixtures of both, onto TiO 2 (Degussa P-25) demonstrates the potential of the technique to characterise the evolution of the catalyst with time, including surface poisoning. Under equilibrium dark conditions, three surface species are formed by oxalate, and two by salicylate. Their stabilities, described by conditional Langmuir-type equilibria involving the dissociative, electroneutral adsorption of the acids H 2L, are at pH 3.7, 2.4×10 6, 3.0×10 4 and 3.0×10 3 mol −1 dm 3 for oxalic acid, and 2.9×10 5 and 9.1×10 3 mol −1 dm 3 for salicylic acid. The nature of the species is discussed in terms of their spectral features. The displacement of each acid from the surface by addition of the other one was followed also by ATR–FTIR. The results demonstrate that oxalate displaces totally chemisorbed salicylate, whereas salicylate displaces oxalate only partially. These results are explained by assuming competitive chemisorption onto two different surface sites, plus oxalate adsorption onto a site that exhibits negligible affinity for salicylate. Irreversible adsorption by partially oxidised products in the course of photocatalytic processes can therefore be assessed by ATR–FTIR. 相似文献
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