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Nanoforest carbon nanotubes (CNTs) were synthesized by biased thermal chemical vapor deposition on cobalt-containing amorphous carbon composite films. The composite films were deposited on silicon by filtered cathodic vacuum arc using a Co-containing graphite target and then CNTs were grown at 580 °C using the composite film as a catalyst layer. The nanoforest multiwalled CNTs have thin diameters between 10 and 20 nm. Their tips point upwards while the rest is densely tangled. They exhibit good field emission properties with a low threshold field of 1.6 V/μm and a high current density of 2.1 mA/cm2 at 3 V/μm. [ABSTRACT FROM AUTHOR]

Iron containing diamond-like amorphous carbon (a-C:Fe) films were deposited by filtered cathodic vacuum arc technique. The influences of Fe content and substrate bias on the surface energy of the films were investigated. The surface energy of a-C:Fe films was determined by the contact angle measurement. Atomic force microscopy, Raman spectroscopy, and x-ray induced photoelectron spectroscopy were employed to analyze the origin of the variation of surface energy with various Fe content and substrate bias. It is found that the contact angle for water increases significantly after incorporating Fe into the films and the films become hydrophobic. The roughness of these films has no effect on the contact angle. The surface energy is reduced from 42.8 to 25 dyne/cm after incorporating Fe into the a-C film (10% Fe in the target), which is due to the reduction of both dispersive and polar component. The reduction in dispersive component is ascribed to the decrease of atomic density of the a-C:Fe films due to the increase in sp[sup 2] bonded carbon. When sp[sup 2] content increases to some extent, the atomic density remains constant and hence dispersive component does not change. The absorption of oxygen on the surface plays an important role in the reduction of the polar component for the a-C:Fe films. It is proposed that such network as (C[sub n]-O-Fe)-O-(Fe-O-C[sub n]) may be formed and responsible for the reduction of polar component. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The electroluminescent properties of three different device structures (A:ITO/SiO[sub 2]/Alq[sub 3]/SiO[sub 2]/Al, B:ITO/Alq[sub 3]/SiO[sub 2]/Al, and C:ITO/SiO[sub 2]/Alq[sub 3]/Al) based on the tris-(8-hydroxyquinoline) aluminum (Alq[sub 3]) were investigated. A blue electroluminescence at 457 nm was obtained from device (A) and (B), and the green emission at 518 nm was obtained from device (C). It is generally agreed that the green emission originates from the recombination of the singlet excitons. The blue emission, here, is attributed to the direct transitions between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital of Alq[sub 3]. This is due to the electric field-induced excitons dissociation and the space charge accumulation at the interface. The high internal electric field enhances the dissociation of neutral singlet excitations into LUMO states and inhibits the formation of the singlet excitons, therefore enhances the probability for direct interband transitions of the relaxed carriers. The intensity of the blue emission is dependent on the operating frequency. This indicates that space charge accumulation time and effective internal electric field are responsible for the blue emission intensity. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Titanium-containing tetrahedral amorphous carbon (ta-C:Ti) films with different titanium content were deposited by a filtered cathodic vacuum arc technique. The microstructure of these films was confirmed to be of ta-C+TiC[sub x](x<1) nanocomposite by Rutherford backscattering spectroscopy, x-ray diffraction, and micro-Raman spectroscopy experiments. With the increase of titanium content, the titanium carbide content increased and the sp[sup 3] fraction in the residual ta-C phase decreased gradually. In the electron field emission tests, it was found that proper conditioning processes are necessary for all these films in order to get a steady reproducible emission behavior. After conditioning, the emission threshold field of the films is about the same value, around 10 V/μm, except for the film with the lowest titanium content (∼1.2 at%) of which the threshold field is much higher, around 17-18 V/μm. The optimum titanium concentration in the film for field emission, showing the highest emission current and emission site density, is about 12 at%. After field emission testing, graphitization was involved and the titanium carbide phase, at least some of the sub-stoichiometric TiC[sub x] phase, in the ta-C:Ti films decomposed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Titanium oxide and zirconium oxide thin films were deposited at low temperatures (not exceeding 350°C) by off-plane filtered cathodic vacuum arc (FCVA). The film structures were studied by XRD and Raman spectra. For titanium oxide thin films, amorphous structure remains up to 230°C, and anatase film with the crystallite size of 16 nm is observed at 330°C as confirmed by XRD and Raman analysis. For zirconium oxide, the film structure develops from amorphous at room temperature to polycrystalline state at 150°C and above. Moreover, for the crystallized films, preferred orientation is along [-111] direction. At 150°C the films possess nano-sized crystallites (less than 15 nm). For these two kinds of metal oxide thin films, surface roughness both increases with the growth temperature. [ABSTRACT FROM AUTHOR]

Aluminium nitride (AlN) films have been fabricated on Si(100) substrates by an ion-beam-assisted filtered cathodic vacuum arc technique at low temperature. The structural and mechanical properties of the AlN films have been investigated using x-ray photoelectron spectroscopy, by means of an x-ray diffractometer, visible Raman spectroscopy, atomic force microscopy and nanoindentation. The AlN films exhibit a predominant a-axis orientation with hardness as high as 14.5 GPa, which may be suitable for surface acoustic wave devices. [ABSTRACT FROM AUTHOR]

Ta-C and iron containing amorphous carbon (a-C:Fe) films were deposited by filtered cathodic vacuum arc technique. The influences of Fe contents on the wettability of the films were investigated in terms of surface energy. The surface energy of a-C:Fe films was determined by the contact angle measurement. Atomic force microscopy (AFM), Raman spectroscopy and X-ray induced photoelectron spectroscopy (XPS) were employed to analyze the origin of the variation of surface energy with various Fe content. It is found that the contact angle for water increases significantly after incorporating Fe into the films and the films become hydrophobic. The roughness of these films has a little effect on the contact angle. The surface energy is reduced after incorporating Fe into the a-C film which is due to the reduction of both dispersive and polar component. The reduction in dispersive component is ascribed to the decrease of atomic density of the a-C:Fe films due to the increase in sp² bonded carbon. The absorption of oxygen on the surface play an important role in the reduction of polar component for the a-C:Fe films. It is proposed that such network as (C[sub n]-O-Fe)-O-(Fe-O-C[sub n]) may be formed and responsible for the reduction of polar component. [ABSTRACT FROM AUTHOR]

Nanocomposite amorphous carbon (a-C:Me) films including a-C:Ni, a-C:Co, a-C:Ti, a-C:W, a-C:Fe, a-C:Al, and a-C:Si films were deposited using metal-carbon composite target by filtered cathodic vacuum arc (FCVA) technique. Atomic force microscopy (AFM), Raman, and X-ray photoelectron spectroscopy (XPS) were used to characterize the morphology and structure of the films. Nanoindenter and surface profilometer were used to determine the hardness, Young's modulus, and internal stress. Contact angle and field emission experiments were used to study the surface energy and field emission properties of the films respectively. The influence of the type of elements and its composition in the target on the structural, mechanical, surface energy, and field emission properties were studied. The incorporation of elements into the films results in the decrease of sp³ C fraction, internal stress in the deposited films, but the hardness and Young's modulus remains at high level. The effect of non-carbide forming elements in the films on the mechanical properties is more pronounced than that of carbide forming elements. The surface energy of the films increases with incorporating Ni atoms, but decreases after incorporating Fe and Al atoms into the films. After heat treatment, the incorporation of metal into ta-C films can greatly improve the field emission performance. [ABSTRACT FROM AUTHOR]

The adhesion, of a coating to the underlying substrate, in terms of critical load (using scratch test) is complex and is a function of many parameters such as coating thickness, interfacial stress, coefficient of friction, intermixing, hardness, structural parameters, etc. The present study examines the relationship of critical load to other properties such as film thickness, compressive stress, coefficient of friction, etc. of diamond-like carbon coatings prepared under floating condition (no substrate bias), on silicon substrates. The results show that the compressive stress increases with increasing thickness. However, the adhesive strength in terms of critical load increases with increasing the film thickness up to a certain value and then it decreases. The decrease in critical load with thickness of the films is due to the dominant effect of compressive stress. In order to obtain the parameters that affect the adhesion, a factor analysis has been carded out on the experimental data using SPSS — a statistical software package. Thickness, stress, and critical load emerged as one of the factors and hence it suggests that thickness and stress are two primary parameters that affect adhesion. None of the parameters of Raman study were emerged in the factor analysis along with critical load and thickness. This suggests that the variation of the sp³-bonded carbon with thickness is relatively small and that may not have any direct impact on the adhesion. In this case, stress shows a strong linear relationship with thickness. Moreover, it is not an operational parameter. Hence inclusion of stress in the model becomes unnecessary. Therefore, an empirical relation has been obtained for critical load as a function of thickness. [ABSTRACT FROM AUTHOR]

The unique electron field emission properties of carbon nanotube films are promising for fiat panel display application as the cold cathode. In this work, the multiwall carbon nanotube (10-10² nm in diameter, and 10³-10[sup 4] nm in length) film arrays (the pixel size: 50 µm × 50 µm) were deposited on the patterned Ni-Si substrate from hydrocarbon precursor (C[sub 2]H[sub 2]/H[sub 2]) by chemical vapor deposition at low temperature (550°C). The patterned films were characterized by scanning electron microscopy and Raman spectroscopy. The carbon nanotube film arrays exhibit good electron emission properties, e.g. low threshold emission field (below 2 V/µm), high emission current density (above 1 mA/cm² at 10 V/µm), and high emission luminance spot density on the phosphor coated-ITO(indium tin oxide)glass anode. These properties are good enough for high-resolution flat panel display application using carbon nanotube film arrays as the cathode. [ABSTRACT FROM AUTHOR]

A new Filtered Cathodic Vacuum Arc coating system with a magnetic macroparticle filter design consisting of an off-plane double-bend (OPDB) filter is described. The transport of the vacuum arc plasma through this OPDB filter is investigated using Langmuir and deposition probes. Films of amorphous hard carbon have been deposited using a 90° single bend and the OPDB filter and the macroparticle contents of the films are compared. The experimental results were found to be in good agreement with the simulations results based on an improved drift approximation model. The results demonstrate that OPDB filter has a relatively better transmission efficiency than the 90° single bend filter, lower macroparticle counts and is suitable for preparation of diamond-like carbon coatings with high quality. Some important applications of the ta-C coating produced by using the new FCVA system have been identified and where applicable industrial testing results are presented. [ABSTRACT FROM AUTHOR]

Hydrogen-free amorphous carbon films were deposited at different deposition bias voltage on a single silicon wafer by a process known as Filtered Cathodic Vacuum Arc (FCVA). The influences of different deposition bias voltages on the microstructure and the properties of thin tetrahedral amorphous carbon (ta-C) films, such as surface roughness, film mass density and thickness, have been studied by means of the x-ray reflectivity technique (XRR) for the first time. The microstructure of these films deposited on silicon wafers was simulated by a four-layer model consisting of a ta-C layer, a mixed ta-C:Si layer, Si-O layer and the silicon substrate. The mixed ta-C:Si layer consisting of the mixture of ta-C and silicon simulates the carbon ion impinging / diffusion into the surface of the silicon substrate. The mass density and the roughness of the film are found to be dependent on the impinging ion bombardment energy. The mass density increases with increase in ion bombardment energy up to 100 eV. Beyond 100 eV, the mass density decreases with further increase in ion bombardment energy. The surface roughness decreases with increasing ion bombardment energy to a minimum value at 100 eV, after which it increases with further increase in ion bombardment energy. The thickness of the films obtained by XRR technique correlates well with the thickness measurement obtained by spectral reflectometry. The existence of the Si-O layer was verified by Auger depth profiling. [ABSTRACT FROM AUTHOR]

Carbon-doped ZnO (ZnO:C) thin films exhibiting Curie temperature above room temperature were fabricated using ion beam technique. The magnetic moment of the ZnO:C films was found to be around 1.35 μB per carbon atom. The ZnO:C films showed p-type conduction with a hole concentration of ∼5×1017 cm-3. In addition, the anomalous Hall effect and negative magnetoresistance can be detected in the ZnO:C films. The magnetotransport properties of the ZnO:C suggested that the films possessed charge carrier spin polarization. [ABSTRACT FROM AUTHOR]

We have demonstrated visible and ultraviolet random laser actions simultaneously from highly disordered ZnO polycrystalline thin films under optical excitation. It is found that the realization of ZnO grain boundaries by thermal annealing can provide sufficient optical gain (i.e., related to deep-defect-level radiative recombination) and coherent feedback to achieve random laser action at visible wavelength. Furthermore, the coexistence of visible and ultraviolet random lasings inside the highly disordered ZnO films is due to the size difference of the random cavities at different wavelengths. [ABSTRACT FROM AUTHOR]

Using a simple process of the deposition of ZnO thin films on SiOx/Si substrates and subsequent thermal annealing, we fabricated ZnO quantum dots embedded in silicon oxide matrix. The ZnO quantum dots were characterized using transmission electron microscopy, and time-integrated and time-resolved photoluminescences. We measured an exciton radiative lifetime of 65 ps at 4.3 K, which is much shorter than the exciton radiative lifetime of 322 ps in bulk ZnO. The short exciton radiative lifetime can be explained in terms of exciton superradiance. [ABSTRACT FROM AUTHOR]

Random lasing was observed from ZnO polycrystalline thin film deposited by filtered cathodic vacuum arc technique. It is found that the random lasing action results from exciton-exciton scattering process when the excitation intensity is low. However, with increasing excitation intensity, the well-resolved discrete lasing modes evolve into broad stimulated emission band due to electron-hole plasma formation when the photogenerated exciton density exceeds the Mott density. The short spontaneous emission decay time measured at low temperature suggests that the radiative recombination rate is enhanced by the nanosized ZnO grains in the polycrystalline film through exciton-light coupling. [ABSTRACT FROM AUTHOR]

An ion-beam technique has been employed to fabricate nanoscale needlelike structures in ZnO thin films on silicon and plastic substrates at room temperature. The ZnO nanoneedles showed a single-crystalline wurtzite structure, the stem of which was around 100 nm in diameter. The sharp tips of the nanoneedles exhibited an apex angle of 20° as measured by transmission electron microscopy. Room-temperature ultraviolet random lasing action was observed in the ZnO nanoneedle arrays under 355 nm optical excitation. [ABSTRACT FROM AUTHOR]

The lasing characteristics of highly disordered ZnO thin films deposited on SiO2/Si substrates with and without a MgO buffer layer have been investigated. We observed that the emission spectra of the ZnO epilayers with and without a MgO buffer are associated with the radiative recombination of free-exciton (∼380 nm) and electron-hole plasma (∼395 nm), respectively. The difference in the lasing wavelength is due to the induced compressive (tensile) strain along the c axis of the ZnO epilayers as a result of the presence (absence) of the MgO buffer layer. It is demonstrated that the strain-induced variation of Mott density inside the ZnO epilayers is responsible for the observed lasing characteristics. [ABSTRACT FROM AUTHOR]

A polymer, poly(phenylcarbyne) (PPC), was converted to carbon film by ultraviolet pulsed-laser (KrF, λ=248 nm) irradiation in nitrogen atmosphere at room temperature. The irradiated PPC consisted of fine graphitic carbon particles of several tens of nm in size, and exhibited good field emission properties. Low turn-on emission field of 2 V/μm (at 1 nA/cm[sup 2]), high emission current density of 20 mA/cm[sup 2] (at 12 V/μm), and high emission luminescent spots density of 10[sup 4]/cm[sup 2] were observed for the polymer film irradiated by a pulsed-laser fluence of 40 mJ/cm[sup 2]. We demonstrate multiple-lines and 2x5 array field emission patterns using the laser irradiation of PPC. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Thin films of pentacene were deposited by thermal evaporation and by pulsed laser deposition (PLD). Surface characterization using atomic force microscopy shows that PLD leads to a reduction in surface roughness, which can be reduced further using heated substrates. Observation of enhanced field-effect carrier mobilities in the PLD films, together with increased electrical conductivity and reduced activation energy for electrical conduction, is consistent with increased molecular ordering in the pentacene films and suggests a direct correlation between molecular ordering in the bulk and surface roughness. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Cobalt-containing amorphous carbon composite films have been prepared by the filtered cathodic arc technique using a cobalt-containing graphite target at room temperature. After heat treatment at 550 °C in a mixture of acetylene and nitrogen gases, the field emission properties were significantly improved. A threshold electric field of 1.7 V/μm and an emission site density of 10[sup 5]/cm[sup 2] were obtained without conditioning. The composite films, which can be deposited with a high rate at room temperature and require a relatively low temperature heat-treatment process to enhance electron emission, are promising for practical applications in field emission display. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]