Search

In the manufacturing process of polyacrylonitrile (PAN) based carbon fiber (CF), stabilization, is crucial to both process efficiency and the mechanical properties of CFs. Highly effective stabilization was successfully demonstrated by plasma-assisted thermal treatment (PT) on electron-beam irradiated PAN fibers. The method was remarkably efficient to prepare carbonizable fibers within a total stabilization time of 13.3 min, which includes electron beam irradiation (3.3 min) and PT time (10 min). We believe that such a fast stabilization was achieved by coaction of diffusive and reactive oxygen species from atmospheric plasma source with oxygen-favored radicals introduced by pre-treatment of electron-beam irradiation.

Compared with wet processes, dry functionalization using plasma is fast, scalable, solvent-free, and thus presents a promising approach for grafting functional groups to powdery nanomaterials. Previous approaches, however, had difficulties in maintaining an intimate sample-plasma contact and achieving uniform functionalization. Here, we demonstrate a plasma reactor equipped with a porous filter electrode that increases both homogeneity and degree of functionalization by capturing and circulating powdery carbon nanotubes (CNTs) via vacuum and gas blowing. Spectroscopic measurements verify that treatment with O2/air plasma generates oxygen-containing groups on the surface of CNTs, with the degree of functionalization readily controlled by varying the circulation number. Gas sensors fabricated using the plasma-treated CNTs confirm alteration of molecular adsorption on the surface of CNTs. A sequential treatment with NH3 plasma following the oxidation pre-treatment results in the functionalization with nitrogen species of up to 3.2 wt%. Our approach requiring no organic solvents not only is cost-effective and environmentally friendly, but also serves as a versatile tool that applies to other powdery micro or nanoscale materials for controlled modification of their surfaces.

Various oxide films, such as SnO 2 , In 2 O 3 , Al 2 O 3 , SiO 2 , ZnO, and Sn-doped In 2 O 3 (ITO) have been deposited on glass and polymer substrates by advanced ion beam technologies including ion-assisted deposition (IAD), hybrid ion beam, ion beam sputter deposition (IBSD), and ion-assisted reaction (IAR). Physical and chemical properties of the oxide films and adhesion between films and substrates were improved significantly by these technologies. By using the IAD method, non-stoichiometry, crystallinity, and microstructure of the films were controlled by changing assisted oxygen ion energy and arrival ratio of assisted oxygen ion to evaporated atoms. IBSD method has been carried out for understanding the growth mode of the films on glass and polymer substrate. Relationships between microstructure and electrical properties in ITO films on polymer and glass substrates were intensively investigated by changing ion energy, reactive gas environment, substrate temperature, etc. Smooth-surface ITO films ( R rms ⩽ 1 nm and R p−v ⩽ 10 nm) for organic light-emitting diodes were developed with a combination of deposition conditions with controlling microstructure of a seed layer on glass. IAR surface treatment enormously enhanced the adhesion of oxide films to polymer substrate. In the case of Al 2 O 3 and SiO 2 films, the oxygen and moisture barrier properties were also improved by IAR surface treatment. The experimental results of the oxide films prepared by the ion beam technologies and its applications will be represented in detail.

Tin oxide films were deposited on amorphous SiO2/Si and Si (100) substrates by ion-assisted deposition (IAD) at various ion beam potentials (VI) at room temperature and a working pressure of 8 × 10−5 torr. The structural and chemical properties of the as-grown tin oxide films were investigated to determine the effects of the oxygen ion/atom arrival ratio (Ri). X-ray diffraction patterns indicated that the as-grown films with different average energy per atom (Eave) showed different growth directions. The as-grown films with oxygen/Sn ratio (NO/NSn) of 2.03 and 2.02 had preferred orientation of (101) and (002), respectively. In addition, the as-grown film with low Ri was amorphous. Comparison of the observed d spacings with those for standard SnO2 samples, indicated that the crystalline as-grown films had compressive and tensile stress depending on Eave. In transmission electron microscopy analysis, a buffer layer of amorphous tin oxide was observed at the interface between the substrate and the film, and the crystalline grains were grown on this buffer layer. The crystalline grains were arranged in large spherical clusters, and this shape directly affected surface roughness. Rutherford backscattering spectroscopy spectra showed that the tin oxide thin films were inhomogeneous. The density of films decreased and the porosity and oxygen trapped in the films increased with increasing Ri. The densest film had about 6% porosity.

Undoped SnOx thin films were deposited by a reactive ion assisted deposition technique at various ion beam potential (VI) onto amorphous SiO2/Si substrates at room temperature. Crystalline structures of the films were investigated in terms of grain size, composition ratio, porosity and peak area percent of adsorbed oxygen. Sensitivities for propane (C3H8), methane (CH4) and hydrogen (H2) gas in SnOx gas sensor devices were characterized at the substrate temperatures of 100–500°C. The gas sensitivities depend on the grain size rather than the porosity. It is also proportioned to the amounts of adsorbed oxygen at room temperature by XPS analysis.

Undoped oxygen-deficient SnO x films were deposited on Si (100) and BK7 glass substrates by the reactive ion-assisted deposition technique. The average impinging energy ( E a ) of the oxygen ion on depositing a Sn atom, a relative arrival ratio of ion to atom ( Γ ), was varied from Γ = 0.025 ( E a = 25 eV atom −1 ) to Γ = 0.1 ( E a = 100 eV atom −1 ) by controlling the discharge voltage at a fixed ion-beam potential of 500 V. Crystalline structures of as-deposited SnO x films appeared to be amorphous for all E a values. In order to precisely examine the dependence of oxidation from SnO to SnO 2 on initial oxygen content and annealing temperature, as-deposited SnO x films containing initially different oxygen contents were annealed at 400 ∼ 500 °C in a low vacuum (∼5 × 10 −3 Torr) for 1 h to remove the external oxygen diffusion effect during the annealing process. The heat-treated SnO x films at 400 °C showed polycrystalline SnO structure until E a = 50 eV atom −1 and were still amorphous over E a = 75 eV atom −1 . But after annealing over 500 °C those films over E a = 75 eV atom −1 exhibited diffraction peaks at (110), (101), and (211), characteristic of polycrystalline SnO 2 . Scanning electron microscopy (SEM) micrographs for the as-deposited SnO x films show grains as small as a few tens of angstroms in size, but those after 500 °C annealing reveals that the number of granular grain became larger in cross-sectional SEM and the grain grew to 300 A at E a = 100 eV atom −1 . For as-deposited films, the root-mean-square of surface roughness ( σ ) slightly increased from 9 to 25 A as E a was increased, but conversely it reduced from 36 A to 13 A after annealing. From quantitative Auger electron spectroscopy, it was observed that characteristic transitional Auger peaks of Sn MNN shift to lower kinetic energy by as much as 3.8 ∼ 4.2 ± 0.02 eV in the case of the SnO films and 4.8 ∼ 5.2 ± 0.02 eV for SnO 2 films, respectively, with respect to that of Sn metal (Sn 0 ). Based on the valence band spectra taken by using He I angle-resolved ultraviolet photoelectron spectroscopy (angle-resolved UPS), two different phases of polycrystalline SnO and SnO 2 films were clearly distinguished. The binding energy difference between the first peaks derived from SnO and SnO 2 films in angle-resolved UPS spectra below the Fermi level was 1.6 eV. This value is very close to the value obtained from clean SnO and SnO 2 samples by previous valence-band XPS spectra. As-deposited and annealed films showed optical transmittance as high as more than 80% grown at higher than E a = 50 eV atom −1 in the visible wavelength and refractive index close to the bulk SnO 2 value for the film deposited at E a = 100 eV atom −1 after annealing.

SnOx-based gas-sensor devices have been fabricated by a reactive ion-assisted deposition technique. SnOx films of 400 A thickness are deposited on sputtered amorphous SiO2 substrates and then Pt films (600 A) are sputtered on top of them as upper electrodes. From XRD and TEM studies, as-deposited SnOx films are seen to be amorphous and become polycrystalline after annealing at 500°C in air. In quantitative XPS analyses, the O/Sn atomic ratio in the annealed films shows the nearly stoichiometric value of two and the binding energy of Sn 3d5/2 is 486.43 eV, very close to 486.75 eV of the standard tin oxide powder. When sensitivity is defined as a relative decrement in resistance, these sensor devices show nearly 100% sensitivities to 1000–5000 ppm H2 in air at 200°C and above. By attaching an ultra-thin metal activator, the response time can be reduced to less than one tenth of its previous value.

Summary form only given. We fabricated nano-sized silicon and nickel powders using a radio frequency (RF) induction thermal plasma process with 10~30 micro-size powders as precursor materials. The several key variables with the nano-particle size such as RF power, working pressure, and flow rate of carrier, central, sheath, and quenching gas were investigated and characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). As a result, we found the average particle size of silicon and nickel powders distribute in the range of 40~100 nm and 20~50 nm, respectively. The color of nano silicon powders was changed from dark gray to yellow brown with particle size variation from micro-scale to nano-scale, while the color of nickel powder was not changed. We also used computational fluid dynamics (CFD) for more information on the temperature and fluid behavior in torch. The position of a powder injection tube, the plasma discharge characteristics with various input-current and length of a ceramic tube, and the characteristics of plasma temperature with the process gas flow rate were simulated.

Ion irradiation with various oxygen flow rates has been carried out to improve the wettability of polymethylmethacrylate (PMMA) to water and to enhance the adhesion between Al and the polymer. Ar+ ion and oxygen ion were irradiated on the polymer, and amounts of ions were changed from 5 × 1014 Ar+/cm2 to 5 × 1016 Ar+/cm2 by a broad ion beam source. Oxygen gas from 0 ml/min to 7 ml/min was flowed near the polymer surface during the ion irradiation, and the energy of ions was changed from 500 eV to 1500 eV. The wetting angle was reduced from 68° to 49° with the Ar+ ion irradiation only at 1 keV energy, to 43° with the oxygen ion irradiation, and dropped to 8° with Ar+ ion irradiation with flowing 4 ml/min oxygen gas near the polymer surface. Changes of wetting angle with oxygen gas and Ar+ ion irradiation were explained by a two-step chemical reaction among polymer matrix, energetic ions, and oxygen gas. The effects of Ar+ ion and oxygen ion irradiation were explained by considering formation of hydrophilic groups due to a reaction between irradiated polymer chain by energetic ion irradiation and blown oxygen gas, and enhanced adhesion between Al and PMMA was explained by the formation of electron acceptor groups in polymer and electron donors in metal, and by the chemical reaction in the interface between irradiated polymer surface and deposited metal.

Improving wettability of the polycarbonate (PC) surface to triple distilled water has been carried out by Ar+ ion irradiation with blowing oxygen gas. The amount of Ar+ was changed from 1014 to 5 × 1016 ions/cm2 at 1 keV energy by a Kaufman-type ion source. Contact angle of the water to PC has been reduced from 78°to 50°with Ar+ irradiation, and to 12°with Ar+ irradiation in various vacuum pressures adjusted by oxygen gas flow rate (0-4 sccm). Strong O-H stretching vibration peaks at about 3370 cm−1 on FT-IR spectra of the polymer appeared after the surface treatments, and the wetting angle of the treated PC was returned to its value (78°) when the PC was exposed in air environment. The minimum contact angles were maintained with the same value when the irradiated polymers were kept in dilute HCl solution. The improved wettability and surface chemical reaction by Ar+ ion irradiation with oxygen was explained by the formation of a hydrophilic functional group. Enhanced adhesion between aluminum and PC was confirmed by the scotch tape test, and was discussed with relation between the hydrophilic group on the polymer surface and the deposited metal.

Undoped tin oxide films were grown on Si substrates by a reactive ion-assisted deposition technique in which oxygen ions were irradiated on depositing Sn particles. In order to investigate the oxidation from SnO to SnO2, the effects of initial oxygen contents and heat treatment on the final crystalline structure of tin oxide films were thoroughly examined. Oxygen to Sn metal ratio (No/Nsn) of as-deposited films were controlled from 1.1 to 1.9 by varying the relative arrival ratio (F) of oxygen ion to Sn particle from 0.025 to 0.1. Heat treatment was carried out in two different ways; one was post vacuum-annealing at 400 ∼ 600°C and the other was in-situ annealing 400 ∼ 500°C. Crystalline structure of as-deposited tin oxide films at room temperature was amorphous. After post-annealing at 400°C, only SnO phase was found below No/Nsn= 1.6 in x-ray diffraction and crystalline structure of the films comprising higher oxygen contents still appeared to be amorphous. Even though the films still showed SnO phase until Γ50 after 500°C post-annealing, however, mixed structures of SnO, SnO2, and intermediate Sn2O3/Sn3O4 were observed for the films Γ75 and Γ100 with higher oxygen contents. At 600°C annealing, perfect SnO2 phase was attained for the films having No/Nsn=1.9. On the other hand, pure polycrystalline SnO2 films could be obtained by in-situ annealing at low temperature. The values of No/Nsn and the chemical shifts with the variation of oxidation were carefully determined by the comparison of Sn MNN and O KLL Auger transitions. Surface microstructure of deposited films was also analyzed using a scanning electron microscopy (SEM) and an atomic force microscope (AFM).

In recent years, extensive researches have been carried out on transparent and conducting thin oxide films such as indium tin oxide (ITO), SnO{sub 2}, and ZnO. Among these, tin oxide films have been actively investigated because of wide applications as high sensitivity gas sensors for reducing gas, high conversion efficiencies in SnO{sub 2}/Si solar cells, and liquid crystal displays, etc. Here, tin oxide films with highly preferred orientation along axis were grown on Si(100) substrate by using reactive ion assisted deposition method. The impinging average ion energy per depositing Sn atom was changed from 10 to 100 eV/atom. Oxygen content in the deposited tin oxide films increased as average impinging ion energy were raised. The maximum XRD peak intensity appeared when the average energy of about 50 eV/atom was applied. From quantitative Auger electron spectroscopy, characteristic transitional Auger peaks of Sn MNN were shifted to lower kinetic energies as much as 4 {approximately} 6 {+-} 1.0 eV as the Sn{sup 4+} component became dominant in the deposited tin oxide films. On the basis of a tin 3d core level spectra analysis by XPS, it was determined that a sizable chemical shift of 1.0 {+-} 0.02 eV occurred between stannousmore » tin (Sn{sup 2+}:SnO) and stannic tin (Sn{sup 4+}:SnO{sub 2}). The optical transmittance was also measured in the wavelength range from 200 to 800 nm for tin oxide films deposited on BK7 glass substrate.« less

Tin oxide thin films were grown on Si(100) substrates by a hybrid ion beam consisting of a partially ionized beam and a cold hollow cathode ion source. Tin metal particles were ionized and accelerated by a partially ionized ion beam source while oxygen gas was introduced or ionized oxygen was introduced upon the Si substrate. When oxygen gas was blown near the substrate during Sn metal evaporation, the composition of deposited tin oxide films revealed mainly Sn metal and SnO, whereas tin dioxide films with highly preferred orientation of SnO222(200) film was approximately 1.98. Moreover, the binding energy of Sn 3d5/2 was determined to be at 486.74 eV by XPS measurement, and the result coincided well with that of standard SnO2 powder. Compared with two different deposition processes, ionized oxygen assistance during tin metal evaporation would be considered to effectively improve oxygen content for the formation of tin dioxide thin films.

A surface of thin square PTFE samples (1×1×0.2 cm3) was irradiated with Ar+ ion at 1 keV with varying ion dose from 5 x 1014 to 1 x 1017 ions/cm2 with and without oxygen environment. The chemical structure of the surface was examined by XPS. The high resolution XPS spectra showed decreased intensity of the Fls peak and formation of the Ol s peak when irradiated with O2 environment. The Ols peak reached the maximum height at the ion dose of 1 x l015 ions/cm2. The increase of the Ols peak may be attributed to the reaction of oxygen atoms and the free radicals created by Ar+ bombardment. Adhesion tests were conducted on 2000 Å thick Al or Cu film which was evaporated on the irradiated and unirradiated PTFE samples with and without O2 environment. Full detachment of the metal films was observed when PTFE samples were not modified. With regard to the Al film, partial detachment of the film occurred when PTFE was irradiated without O2 environment, regardless of ion dose. No detachment of the film occurred when PTFE was irradiated with O2 environment with the ion dose exceeding 1 x 1016 ions/cm2. As to the Cu film, partial detachment was observed with or without O2 environment when the ion dose was 5 x 1014 ions/cm2. No detachment occurred with or without O2 environment when the ion dose was 1 x 1015 ions/cm2 or greater. The adhesion of an adhesive (Crystal Bond) to the irradiated PTFE samples was found to increase significantly with increasing ion dose up to 1 x 1016 ions/cm2 in tensile tests. It appears that three separate mechanisms are at work in improving adhesion of Cu/PTFE and Al/PTFE system. The first is the surface roughness of PTFE caused by Ar+ bombardment, the second is the chemical changes on the PTFE surface, and the third is a change of the interface between the metal and PTFE. The wettability of the PTFE surface was also determined by dropping water droplets on the modified surfaces. The contact angle between water droplets and the irradiated surface of PTFE samples decreased with ion dose up to 1 x 1015ions/cm2, increased at higher dose, and finally increased to the extent that no wetting was possible at 1 x 1017 ions/cm2. The PTFE samples irradiated with Ar+ without O2 gas environment had lower contact angle than those with O2, even though the samples with O2 developed hydrophilic groups on the irradiated surface. This result on wettability is not consistent with our earlier results on PMMA and PC and is due to the unusually high level of surface roughness of PTFE caused by Ar+ bombardment.

Ion irradiation has been carried out to improve wettability of PMMA to water. The polymer was irradiated by argon and oxygen ions, and amount of ions was changed from 1014 ArVcm2 to 5xl016Ar+/cm2. Ions energies were varied from 0.5 keV to 1.5 keV, and oxygen gas was flowed from 0 seem to 6 scan near the polymer surface during ion irradiation. Wetting angle was reduced from 68 degree to 49 degree with increasing Ar+ ion irradiation, to 43 degree with Ch+ ion irradiation, and dropped to 8 degree with Ar+ ion irradiation with flowing 4 seem oxygen gas near the polymer surface. Recovery of wettability in dry air condition, and maintenance of it in dilute HC1 solution were explained in a view of formation of hydrophilic groups due to a reaction between irradiated polymer chain by energetic ion irradiation and flowing oxygen near the surface. Reactions among polymer matrix, energetic ions and oxygen gas to form hydrophilic group by energetic ions were discussed in terms of a two-step reaction, in which the first step is the creation of an unstable polymer chain by the ion irradiation and the second step is a reaction between the radicals and the oxygen gas.

A model of the electrical conductance of a resistive or semiconductive substrate, as a function of the average thickness d of a deposited film in initial growth on the substrate is proposed. The total conductance has two terms: one proportional to d2/3 for three-dimension (3D) growth, and one proportional to d for 2D growth or for increasing number of islands. The model was applied to the conductance of a Sn film deposited on a SiOx substrate showing that the initial growth is dominated by 3D growth. The proposed model may be useful for in situ study of the growth of ultra thin films prior to the onset of tunneling conductance.

A model for the electrical conductance of a semiconductive substrate with an average thickness is proposed for a region of initial growth before the appearance of a tunneling effect. Based on this model, we propose 6 different growth modes according to the film thickness, measuring in situ electrical conductivity. As the film thickness increased, the island size was constant and then increased, while the number of islands first increased and then decreased. The proposed model may be useful for in situ study of the growth of ultrathin films prior to the onset of tunneling conductance.

The initial growth behaviors of Au thin films on tin oxide substrates were investigated by in situ conductance measurement. The crystallinity of tin oxide films fabricated by ion-beam-assisted deposition was changed from amorphous to preferred oriented structure with ion beam energy. As the surface energy of tin oxide substrates increases with the irradiation of ion beams, an onset thickness of Au films is decreased. That means high surface energy of the substrate enhances surface mobility of Au adatoms so that it changes the growth mode of Au films from 3D to 2D growth. So the distance between islands where electron tunneling can occur is decreased with the surface energy of the substrate. Therefore, we conclude that different surface properties of tin oxide substrates play an important role in the early growth aspects of Au thin films.

Tin oxide ( SnO x ) thin films were deposited by ion-assisted deposition (IAD) at various ion beam voltages (V I) onto amorphous SiO2/Si substrate at room temperature. Tin oxide thin films with nonstoichiometric/stoichiometric composition were fabricated. The as-deposited SnO x films were mostly amorphous, but they exhibited various degrees of crystallinity and fine grain size after annealing at 500° C for 1 h in air. The annealed film deposited using an ion beam energy (E I) of 300 eV showed a preferred orientation along the SnO2 (110) plane. The preferred orientation changed to SnO2 (002) for film 1000 (the annealed film deposited with E I=1000 eV) through an amorphous intermediate structure of film 500 (the annealed film deposited with E I=500 eV). X-ray photoelectron spectroscopy study showed that the main Sn3d peaks in all samples were similar to the binding energy of Sn4+ and the atomic ratios for all the films were higher than 1.51. For the film grown under an average energy of 123 eV/atom, the refractive index was 2.0 and the estimated porosity was 5.2% smaller than that of the other films.

In order to accurately determine the oxidation state of tin and to investigate the chemical shifts between tin and its oxides, quantitative Auger electron spectroscopy and X-ray photoelectron spectroscopy studies were performed using Sn metal, stoichiometric SnO2 powder, and polycrystalline SnO x thin films. Films with different oxygen contents were grown using a reactive ion-assisted deposition technique. As the atomic ratio of tin to oxygen in the deposited films increased to the stoichiometric value of 2, the tin M 4 N 4,5 N 4,5 Auger transition and the corresponding Sn 3d 5/2 core-level photoelectron line gradually shifted to lower kinetic energy and higher binding energy by as much as 6±1 eV and 2.39±0.02 eV, respectively, relative to those of the tin metal. An explanation for the observed systematic difference between the chemical shifts of Auger and photoelectron lines is given. It is based on the difference in electronic polarization energy between the final two-hole state produced by the Auger electron emission and the final single-hole state produced by the photoelectron emission.