共查询到20条相似文献,搜索用时 15 毫秒
1.
J.H.C. YangK. Teii 《Thin solid films》2012,520(21):6566-6570
The mechanism of wetting behavior of nanocrystalline diamond films is examined in terms of surface free energy, morphology, and bonding characteristics. The films are prepared by microwave plasma-enhanced chemical vapor deposition using Ar-rich/N2/CH4 and Ar-rich/H2/CH4 mixtures, followed by microwave hydrogen and oxygen plasma exposures separately. Contact angle measurement with water, ethylene glycol, and formamide reveals that both the as-deposited and hydrogen plasma treated films are hydrophobic, while the oxygen plasma treated film is extremely hydrophilic such that the contact angle is reduced down to almost zero degree. Fourier transform infrared spectroscopy reveals that the hydrogen atoms are dominantly bonded to diamond and amorphous sp3-bonded carbon, and they are removed by the oxygen plasma treatment. For the oxygen plasma treated film, the mean value of oxygen concentration for the top surface to bulk (~ 1 μm) measured by energy-dispersive X-ray spectroscopy is ~ 10 at.%, while that for the top several monolayers surface measured by X-ray photoelectron spectroscopy is much higher at ~ 37 at.%, indicating a higher degree of oxidation toward the surface. The carbon bonding state in the oxidized layer is disordered by incorporation of a large amount of oxygen in form of polar CO bonds, which is accountable for a greater polar component of the apparent surface free energy and stronger dipole-dipole interactions. 相似文献
2.
Nanocrystalline diamond/amorphous carbon (NCD/a-C) nanocomposite films have been deposited by microwave plasma chemical vapour deposition from CH4/N2 mixtures. In order to investigate their suitability as templates for the immobilization of biomolecules, e.g. for applications in biosensors, four differently prepared surfaces, namely as-grown, hydrogen plasma treated, oxygen plasma treated, and chemically treated with aqua regia, have been thoroughly characterized by methods such as XPS, TOF-SIMS, AFM, and contact angle measurements. In addition, in order to investigate the affinity of these surface to non-specific bonding of biomolecules, they have been exposed to bovine serum albumin (BSA). It turned out that already the as-grown surface is hydrogen terminated; the degree of the termination is even slightly improved by the hydrogen plasma treatment. Reaction with aqua regia, on the other hand, led to a partial destruction of the H-termination. The oxygen plasma treatment, finally, causes a termination by O and OH, rather than by carboxylic acid groups. In addition, an increase of sp2 bonded carbon is observed. All surfaces were found to be susceptible to attachment of BSA proteins, but the coverage of the hydrogen terminated was lower than that of the O-terminated film. The highest BSA concentrations were found for the aqua regia sample where the H-termination has been removed partially. Finally, our results show that even minor surface contaminations have a great influence on the BSA coverage. 相似文献
3.
The design, fabrication and test of piezoresistive sensors based on nanocrystalline diamond (NCD) films are reported. The CoventorWare FEM calculations of the mechanical stress and geometrical deformations of a 3-D structure are used for a proper localization of the piezoresistor on the carrying substrate. The boron-doped piezoresistive sensing element was realized using a directed patterned growth of NCD film on SiO2/Si by microwave plasma-enhanced chemical vapour deposition (CVD). The gauge factor of boron-doped NCD films was investigated in the range from room temperature up to 200 °C and from 0 to 5 N of the applied force. These NCD piezoresistive sensor elements are compared with a Silicon-on-Insulator (SOI) based piezoresistive sensor and their high-temperature applications are discussed. 相似文献
4.
Diamond thin films were grown by linear antenna microwave plasma CVD process over large areas (up to 20 × 10 cm2) from a hydrogen based gas mixture. The influence of the gas composition (H2, CH4, CO2) and total gas pressure (0.1 and 2 mbar) on the film growth is presented. For CH4/H2 gas mixtures, the surface crystal size does not show dependence on the methane concentration and total pressure and remains below 50 nm as observed by SEM. Adding CO2 (up to 10%) significantly improves the growth rate. However, still no significant change of morphology is observed on films grown at 2 mbar. The crucial improvement of the diamond film purity (as detected by Raman spectroscopy) and crystal size is found for deposition at 0.1 mbar. In this case, crystals are as large as 500 nm and the growth rate increases up to 38 nm/h. 相似文献
5.
We prepared ZnO/n-Si heterojunctions by depositing ZnO films on n-Si substrates with different resistivities by radio-frequency magnetron sputtering. The microstructure of ZnO film was analyzed by X-ray diffraction and scanning electron microscopy. The current-voltage characteristics and ethanol gas sensing properties of the junctions were investigated at room temperature. It is found that optimization of n-Si substrate resistivity is critical to enhance the ethanol gas sensitivity of ZnO/n-Si heterojunction. The ZnO/n-Si heterojunction with n-Si substrate of 2-3 Ω cm exhibits the best ethanol gas sensing property. The junction shows the sensitivity of 29.41% to 0.24 g/L ethanol gas under + 0.52 V forward bias voltage. 相似文献
6.
采用热丝化学气相沉积法,改变工作气压和偏流,在硅基片上沉积了高掺硼金刚石膜。利用扫描电镜(SEM)、拉曼光谱和X射线衍射仪对沉积的金刚石膜表面形貌和结构进行表征。结果显示:当气体压强从3kPa降低到1.5kPa时,金刚石膜有较平的表面形貌和和较好的晶形,薄膜的晶体性质得到良好的改善。但是继续降气体压强,从1.5kPa到0.5kPa时,却呈现出相反的趋势。固定气体压强(1.5kPa),改变偏流,结果表明:适当的偏流(3A)可以改善掺硼金刚石的质量,偏流较高会导致薄膜中非金刚石相增多。 相似文献
7.
The structure, functionality and sensing response of metal oxide films is discussed with emphasis on ZnO and InOx prepared by Aerosol Spray Pyrolysis in ambient atmosphere and DC Magnetron Sputtering techniques under vacuum. Optical, structural and electrical characterization techniques applied for the in-depth analysis of the film properties are described. Sensing response towards ozone is presented utilizing a conventional conductivity technique as well as surface acoustic wave (SAW) structures and devices. It is shown that sensing responses of extremely low ozone concentrations in the range of a few parts per billion (ppb), at room temperature (RT), may be obtained by appropriate control of the film nanostructure. It is also shown that InOx employed as sensitive layer on top of surface acoustic wave structures can lead to strong frequency shifts for low concentrations of NO2, H2 and O3 gases. 相似文献
8.
Boron nitride films on diamond buffer layers of varying grain size, surface roughness and crystallinity are deposited by the reaction of B2H6 and NH3 in a mixture of H2 and Ar via microwave plasma-assisted chemical vapor deposition. Various forms of boron nitride, including amorphous α-BN, hexagonal h-BN, turbostratic t-BN, rhombohedral r-BN, explosion E-BN, wurzitic w-BN and cubic c-BN, are detected in the BN films grown on different diamond buffer layers at varying distances from the interface of diamond and BN layers. The c-BN content in the BN films is inversely proportional to the surface roughness of the diamond buffer layers. Cubic boron nitride can directly grow on smooth nanocrystalline diamond films, while precursor layers consisting of various sp2-bonded BN phases are formed prior to the growth of c-BN film on rough microcrystalline diamond films. 相似文献
9.
Qian-Jing Ruan 《Materials Letters》2008,62(27):4303-4305
La-Bi-Fe-O nanorods were prepared for the first time via a facile hydrothermal method without any surfactant. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the structure and morphology of the material. The semiconductive La-Bi-Fe-O nanorods are mainly composed of orthorhombic Bi2Fe4O9 and a small amount of orthorhombic La1.08Bi0.92O3.03. The gas sensing properties of the sensor based on La-Bi-Fe-O nanorods were studied and the nanorods exhibited a p-type behavior. Both the sensitivity and selectivity of the sensor towards formaldehyde were very high, and the sensor could be used to detect formaldehyde as low concentration as 5 ppm. More importantly, the operation temperature of the La-Bi-Fe-O sensor was low. This would be very significant in applications, such as detecting and preventing indoor formaldehyde pollution. 相似文献
10.
The present investigation deals with the fabrication of liquid petroleum gas (LPG) sensor materials based on semiconducting oxide SnO2. The gas sensor materials have been prepared by conventional solid-state route. The effect of Pb incorporation, operating temperature, morphology, and sensitivity is discussed using the results of X-ray diffraction (XRD), along with sensing performance. Out of various sensor compositions, Pb doped SnO2 sintered at 1000 °C for 2 h has shown high sensitivity towards LPG at an operating temperature of 150 °C. Different characterization techniques have been employed, such as surface area analyzer, X-ray diffraction (XRD), to study the formation of SnO2, surface area and crystallite size, respectively. The results suggested the possibility of utilizing the sensor element for the detection of LPG. 相似文献
11.
We demonstrate a nanoscale palladium (Pd) based inverse surface plasmon resonance (ISPR) setup for sensing highly inflammable hydrogen (H2) gas. The ISPR setup was employed in Kretschmann configuration to assess the sensitivity of the Pd-films when subjected to H2 gas exposure. With an adequate broadening of the SPR peak maxima, the SPR angle was found to shift from a value of 46.57° to 50.97°, when the concentration of H2 was varied between 0% and 0.9%. The shifting can be attributed to the transient development of isolated PdHx (x < 1) clusters within Pd lattices, resulting in an appreciable change of refractive index locally. The dynamical behaviour of switching on/off states exhibited by a ∼20 nm Pd-film and exposed to 0.1% H2 gas was monitored over several cycles repetitively. The ISPR based H2 sensor, as demonstrated in ambient environment, would find scope to detect low level H2 in industrial and other hazardous areas. 相似文献
12.
P. Lobotka P. KunzoE. Kovacova I. VavraZ. Krizanova V. SmatkoJ. Stejskal E.N. KonyushenkoM. Omastova Z. SpitalskyM. Micusik I. Krupa 《Thin solid films》2011,519(12):4123-4127
We have studied the gas sensing properties of five polyaniline-based materials—thick and thin PANI films, nanocomposite PANI/MWNT and PANI/SWNT films, and PANI nanogranules embedded in a polyvinylpyrrolidone matrix. The films (except for the latter) were deposited within the induction period of the polymerization process on gold interdigitated micro electrodes. Their sensitivity to NH3, H2, ethanol, methanol, and acetone was measured. The thin PANI film (~ 100 nm thick) prepared by a lift-off process had the sensitivity to ammonia below 0.5 ppm, which was higher than that of nanocomposite films. Two materials—thick PANI film and nanocomposite PANI/MWNT film—exhibited a shallow minimum in the temperature dependence of resistance (at 313 K and 319 K), which is a feature exploitable in practical applications, since the gas sensors should be insensitive to small temperature fluctuations at these temperatures. 相似文献
13.
Nanocrystalline diamond (NCD) films were prepared by microwave plasma-enhanced chemical vapour deposition (CVD) on Si substrates of different roughness (1 and 500 nm). Diamond nano-crystals are up to 50 nm in size and RMS surface roughness is less than 20 nm. The NCD films were cleaned chemically and terminated by hydrogen using plasma treatment (800 °C, 10 min) to generate a hydrophobic surface. Photolithography mask and oxygen plasma (300 W r.f. power, 3 min) were used to generate O-terminated (hydrophilic) patterns (30-200 μm wide) separated by a H-terminated (hydrophobic) surface. Osteoblast-like human cells were seeded on the patterned flat and rough NCD films in McCoy's 5A medium supplemented with 15% fetal bovine serum (FBS). After two days incubation the cells preferentially adhered on the O-terminated stripes. This phenomenon is not suppressed by the surface roughness and is general for other cell types (fibroblast and cervical carcinoma cells), too. The data are discussed with view to further application of NCD thin films in biotechnology and bio-electronics applications. 相似文献
14.
Various metal oxide-silica nanocomposite films have been recently proposed as gas-sensitive materials. This paper presents results on cobalt oxide-SiO2 mesoporous nanocomposite thin films templated by a cationic surfactant. The films were deposited on glass substrate by dip-coating process, using [Co(CH3COO)2]·4H2O and tetraethoxysilane (TEOS) as starting materials. The effect of withdrawal speed, number of layers and thermal treatment on the crystalline structure, morphology, Co-doping states, optical, electrical and gas sensing properties of the thin films has been investigated using X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, optical transmittance and room temperature photoreduction-oxidation data. 相似文献
15.
Nanocrystalline diamond (NCD) film was deposited on a silicon substrate utilizing microwave plasma-enhanced chemical vapor deposition in a mixed flow of methane, hydrogen and argon. The deposited film had a cauliflower-like morphology, and was composed of NCD, carbon clusters and mixed sp2- and sp3-bonded carbon. Electron field emission (EFE) in vacuum and electrical discharges in Ar, N2 and O2 using the NCD film as the cathode were characterized. The turn-on field for EFE and the geometric enhancement factor for the NCD film were 8.5 V/μm and 668, respectively. The breakdown voltages for Ar, N2 and O2 increased with pressures from 1.33 × 104 Pa to 1.01 × 105 Pa, following the right side of the normal Paschen curve. 相似文献
16.
Zachary Mark Seeley Amit Bandyopadhyay Susmita Bose 《Materials Science and Engineering: B》2009,164(1):38-43
In the present research, carbon monoxide (CO) gas sensing response was studied for TiO2 thick films calcined and sintered between 700 and 900 °C. Crystalline phase, crystallite size, surface area, particle size, and amorphous content were measured for the calcined powder. Crystallinity of the powder was found to affect sensing response significantly towards CO. Anatase phase of TiO2 thick film was stable up to 900 °C however, as calcination temperature increased from 700 to 900 °C, surface area and amorphous phase content decreased. Films calcined and sintered at 700 °C showed a lower response towards CO than those calcined at 800 °C. Upon increasing the calcination temperature further, particle growth and reduced surface area hindered the sensing response. A calcination temperature of 800 °C was necessary to achieve sufficient order in the crystal structure leading to more efficient adsorption and desorption of oxygen ions on the surface of TiO2. 相似文献
17.
We report on the synthesis and the gas-sensing properties (CO and NO2 detection) of mesoporous zinc oxide. A two-step structure replication method for the synthesis is employed. In the first step mesoporous SBA-15 silica is prepared by the utilization of self-organization of amphiphilic organic agents. This mesoporous silica is used as the structure matrix for synthesizing mesoporous carbon CMK-3, which, in turn, is employed for yet another replication step, using zinc nitrate as the precursor. The resulting material is characterized by X-ray diffraction and nitrogen physisorption and its gas-sensing properties are compared with a non-porous ZnO sample. 相似文献
18.
Rishi Sharma Nicolas WoehrlMilan Vru?ini? Monika TimpnerVolker Buck P.K. Barhai 《Thin solid films》2011,519(22):7632-7637
Nanocrystalline diamond (NCD) films are synthesized using microwave plasma enhanced chemical vapour deposition technique at 2 × 104 Pa and 600 °C with microwave power of 600-1600 W. Deposition is carried out on n-type (100) silicon wafer with Ar/H2/CH4 gas mixtures. The film properties are analyzed using micro Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy and atomic force microscopy. Raman spectra show two predominant peaks centered around 1335 cm−1 and 1560 cm− 1 and two humps around 1160 cm− 1 and 1450 cm− 1, respectively. FTIR spectra show C:H stretching modes around 3000 cm− 1. XRD patterns show a peak at 44° (2θ). In situ diagnostic of plasma is carried out using Optical Emission Spectroscopy. It has been observed that C2 dimer plays an important role in the nucleation of diamond crystals during NCD film deposition and the emission intensity of C2 can be adjusted by varying the microwave power. It has also been observed that the structural properties like growth rate, surface morphology and grain size of the growing film are dependent on the C2 intensity during deposition. 相似文献
19.
Molybdenum oxide thin films were thermally evaporated on a glass substrate and monitored by an annealing process in a variable oxygen atmosphere. The effects of post annealing condition on the microstructural, morphological, optical and electrical properties were investigated using X-ray diffraction, Raman spectroscopy, atomic force microscope, spectroscopic ellipsometry and impedance spectroscopy. As-deposited amorphous films crystallized into tetragonal metastable phase of Mo5O14 on annealing at 500 °C in vacuum and air. This structure transformed to stable orthorhombic of MoO3 with annealing in oxygen environment. The optical parameters such as the refractive index, extinction coefficient, optical band gap energy and the Urbach energy were calculated from Cauchy formalism. Ellipsometric measurements reveal that the samples present optical gap located between 3.24 and 3.90 eV when the atmosphere becomes rich on oxygen. The variation of the conductivity in terms of the temperature shows an electrical behavior with oxygen environment. Finally, it has been found that MoO3 thin films had high sensitivity to ethanol, which made them as a good candidate for the ethanol sensor. 相似文献
20.
A method of controlling the feeding concentration of methane was applied in a hot-filament chemical vapor deposition (HFCVD)
in order to improve the nucleation of diamond on the beryllium oxide substrates. The nucleation density and the morphologies
of diamond were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) while the thermal conductivities
of substrates and the composites were detected by laser-diathermometer. The results show that the diamond thin film is in
larger grain size with lower roughness when CH4 and H2 enter the chamber, respectively, rather than as a mixture, and the composites’ conductivity soared by 21%–31% compared with
BeO substrates. At the conditions of separated gas entry, several projects with changes of the CH4 flux during depositing were designed to discuss the influence of CH4 concentration on diamond nucleation. The uniform and compact diamond thin films were acquired when the ratio of CH4:H2 at nucleation stage was in the range of 4%–8%. 相似文献