Jun-Ying Zhang | University College London (original) (raw)
Papers by Jun-Ying Zhang
Journal of Hazardous Materials, 2006
Photodegradation of nitrobenzene (NB) using an excimer UV lamp at a wavelength of 172 nm is inves... more Photodegradation of nitrobenzene (NB) using an excimer UV lamp at a wavelength of 172 nm is investigated. Experimental results show that high concentration nitrobenzene can be efficiently degraded with irradiation by excimer UV lamp, and confirm that degradation of nitrobenzene is more efficient by UV/H 2 O 2 combination than UV only. In the case of using UV only, 60 min of treatment was found to be sufficient to degrade the major part of NB solution with a concentration of less than 4 mM. In the case of using the combination of UV/H 2 O 2 with a H 2 O 2 concentration of 7:1 molar ratio to NB, 4.07 mM NB solution drastically decreased to 0.41 mM after treatment for only 20 min. Degradation intermediate products are identified by analyzing the degradation products with GC/HRMS and possible degradation pathways of nitrobenzene are suggested.
Applied Surface Science, 1999
Thin films of Ta 2 O 5 have been deposited on quartz and silicon substrates by 532-nm (Nd:YAG) pu... more Thin films of Ta 2 O 5 have been deposited on quartz and silicon substrates by 532-nm (Nd:YAG) pulsed laser deposition (PLD) in various O 2 gas environments. The influence of the deposition parameters, such as oxygen pressure, substrate temperature and annealing under UV irradiation using a 172-nm excimer lamp, on the properties of the grown films, has been studied. The refractive index of the films increases with increasing pressure of O 2 . X-ray diffraction measurements show that the as-deposited films are amorphous at temperatures below 500°C and possess orthorhombic (β-Ta 2 O 5 ) crystal structure at temperatures above 600°C. The optical properties determined by UV spectrophotometry also strongly depend on the deposition parameters. At O 2 pressures above 0.15 mbar, the refractive index of the films was about 2.12 which is close to the bulk Ta 2 O 5 value of 2.2. Optical transmittance around 85% in the visible region of the spectrum was obtained at an oxygen pressure of 0.2 mbar.
Electronics Letters, 1996
Low temperature ͑250°C͒ photo-oxidation of silicon initiated by a Xe 2 * excimer lamp operating a... more Low temperature ͑250°C͒ photo-oxidation of silicon initiated by a Xe 2 * excimer lamp operating at a wavelength of 172 nm has been investigated. The induced reaction rate of 0.1 nm/min is 90 times greater than thermal oxidation at 612°C and more than three times greater than that previously obtained at 350°C using a low pressure mercury lamp. It was found to be strongly dependent upon oxygen pressure with the highest rates being achievable below 10 mbar. Ellipsometry, Fourier transform infrared spectroscopy, capacitance-voltage, and current-voltage measurements have been employed to characterize the oxide films and designate them as high quality. © 1997 American Institute of Physics. ͓S0003-6951͑97͒01346-6͔
Solid-state Electronics, 2001
The underlying principles and properties of vacuum ultraviolet (VUV) and ultraviolet (UV) radiati... more The underlying principles and properties of vacuum ultraviolet (VUV) and ultraviolet (UV) radiation (excimer lamps), generated by a dielectric barrier discharge in a rare-gas (Rg) or a mixture of Rg and halogen, are discussed. Compared with conventional sources, these excimer lamps oer narrow-band radiation at various wavelengths from 108±354 nm and over large areas with high eciencies and high power densities. The variety of available wavelengths oers an enormous potential for new industrial applications in materials processing. Previously, photo-oxidation of silicon, germanium and silicon±germanium and photo-deposition of single-and multi-layered ®lms of silicon oxide, silicon nitride, and silicon oxynitride have been demonstrated by using excimer lamps. This paper reviews the progress on excimer lamp-assisted growth of high dielectric constant (Ta 2 O 5 , TiO 2 and PZT) and low dielectric constant (polyimide and porous silica) thin ®lms by photo-CVD and sol±gel processing, summarizes the properties of photoinduced growth of Ta 2 O 5 ®lms and discusses the eect and mechanism of low temperature UV annealing with 172 nm radiation. Metal oxide semiconductor capacitors based on the photo-induced Ta 2 O 5 ®lms grown directly on Si at low temperatures exhibit excellent electrical properties. Leakage current densities as low as 5:2 Â 10 À7 A cm À2 and 2:41 Â 10 À7 A cm À2 at 1 MV cm À1 have been achieved for the as-grown Ta 2 O 5 ®lms deposited by photo-induced sol±gel processing and photo-CVD, respectively-several orders of magnitude lower than for any other as-grown ®lms prepared by any other technique. A subsequent low temperature (400°C) UV annealing step improves these to 10 À8 A cm À2 . These values are comparable to those only previously achieved for ®lms annealed at high temperatures between 600°C and 1000°C. These properties make the photo-induced growth of Ta 2 O 5 layers suitable alternative to SiO 2 for high density DRAM application. Ó
Applied Surface Science, 2000
The principle underlying the operation of excimer lamps relies on the radiative decomposition of ... more The principle underlying the operation of excimer lamps relies on the radiative decomposition of excimer states created by a dielectric barrier discharge in a rare gas or a mixture of rare gas±halogen. In excimer lamp technology, no electrodes are in direct contact with the discharge gases, thus avoiding any reaction between the discharge and the electrodes or contamination of the gas with evaporated electrode material, as well as electrode corrosion which can occur in conventional lamps leading to short operational lifetimes. Therefore, an investigation of the lifetime of these lamps is of vital importance before any industrial application can be seriously considered. In this paper, the detailed lifetime of 172, 222, and 308 nm excimer lamps as well as overall ef®ciency, stability, and any output¯uctuations, have been investigated. It was found that ef®ciency increased as input power decreased. It was noted however that colour centres were formed within the ®rst 60 h of operation for 172 nm excimer lamps which reduced their output intensity during their time. By contrast, 100% of the original UV intensity output by the 222 and 308 nm lamps was still maintained after up to 4000 h operating time. These results are compared with the lifetime of conventional mercury lamps. #
Applied Surface Science, 1996
&e-nucleation of surfaces with palladium from thin palladium acetate films on a range of substrat... more &e-nucleation of surfaces with palladium from thin palladium acetate films on a range of substrate materials by UV-induced decomposition is described. The optical transmission of the films after irradiation with incoherent UV radiation from several excimer lamp sources provided information about the deposition rate at different UV intensities and exposure times using three different wavelengths: A = 172 nm (Xe; 1, A = 222 nm (Krcl * ), and A = 308 nm (XeCl * 1. The gaseous products produced during UV exposure were measured using mass spectrometry (MS). The decomposed products such as H,O, CO,, +CCH3, +COCH, and +CH3 were observed. The decomposition mechanism of palladium acetate is discussed and a simple model calculation describing photolytic decomposition processes in the thin palladium acetate films is presented. Results will be compared to those obtained by laser and thermal decomposition of palladium acetate. The deposited palladium can act as an activator for subsequent patterned chemical metal deposition techniques in which micrometer thick copper, nickel, or gold layers with good electrical resistivity are applied.
Surface & Coatings Technology, 2000
We report the growth of single-and multilayer films of titanium dioxide (TiO 2 ) on Si substrates... more We report the growth of single-and multilayer films of titanium dioxide (TiO 2 ) on Si substrates at low temperature by a new photo-induced sol-gel process. Polymeric TiO 2 sols prepared by the hydrolysis and condensation of titanium isopropoxide were spin-coated on the silicon substrate and then irradiated by an excimer vacuum ultraviolet (VUV) lamp operating at a wavelength of 172 nm. Films with thicknesses between 10 and 200 nm were achieved readily by this technique. The effects of spin speed, irradiation time and substrate temperature on the films formed have been studied. The chemical bonding changes in the thin films were analysed by Fourier transform infrared spectroscopy (FTIR), while thickness and refractive indices were determined by ellipsometry. FTIR confirmed the removal of H 2 O and OH groups after VUV irradiation for 10 min at 300°C. The refractive index reached a value of 2.4, which compares favourably with the value of 2.58 recorded for the bulk material, while optical transmittance values in the visible region of the spectrum between 85 and 95% were obtained on quartz substrates.
Applied Surface Science, 2002
We report the deposition of thin TiO 2 films on crystalline Si and quartz by photo-induced chemic... more We report the deposition of thin TiO 2 films on crystalline Si and quartz by photo-induced chemical vapour deposition (CVD) using UV excimer lamps employing a dielectric barrier discharge in krypton chloride (KrCl * ) to provide intense narrow band radiation at . The precursor used was titanium isopropoxide (TTIP). Films from around 20-510 nm in thickness with refractive indices from 2.20 to 2.54 were grown at temperatures between 50 and 350 °C. The higher refractive index values compare favourably with the value of 2.58 recorded for the bulk material. The measured deposition rate was around 50 nm/min at 350 °C. Fourier transform infrared spectroscopy (FTIR) revealed the presence of TiO 2 through the observation of a Ti-O absorption peak and the absence of OH in films deposited at 250-350 °C indicated relatively good quality films. The phase of films deposited at 200-350 °C was anatase as determined by X-ray diffraction.
Journal of Adhesion Science and Technology, 1994
Photochemical dry etching and surface modification of various polymers, e.g. polymethylmethacryla... more Photochemical dry etching and surface modification of various polymers, e.g. polymethylmethacrylate (PMMA), polyimide (PI), polyethyleneterephthalate (PET) and polytetrafluoroethylene (PTFE) were investigated with coherent and incoherent excimer UV sources. Ablation rates of PMMA were measured as a function of laser fluence and laser pulse at the wavelength λ = 248 nm (KrF*). Decomposition and etch rates of PMMA and PI were determined as a function of UV intensity and exposure time at three different wavelengths λ = 172 nm (Xe*2), λ = 222 nm (KrCl*) and λ = 308 nm (XeCl*). The transmittance of the polymeric films was determined with a UV-spectrophotometer after different exposure times. The morphology of the exposed polymers was investigated with scanning electron microscopy (SEM). The gaseous products occurring during UV exposure were measured using mass spectrometry (MS). Chemical surface changes of the photoetched PMMA were determined by X-ray photoelectron spectroscopy (XPS). The mechanism of the photo-oxidation process of PMMA is discussed. The etching of PMMA can be explained as a result of extensive photo-oxidation. The results are compared with those obtained from mercury lamp and excimer laser experiments. Good adhesion of electrolessly deposited metal layers was achieved by irradiation of the polymeric surfaces from incoherent UV source before depositing the metal layer.
Applied Surface Science, 2002
In this paper, UV curing of optical ®bre coatings using excimer lamp radiation has been demonstra... more In this paper, UV curing of optical ®bre coatings using excimer lamp radiation has been demonstrated for the ®rst time. These layers were prepared on silicon and quartz substrates by conventional spin coating and subsequently exposed to 172, 222 nm or 308 nm light from different excimer lamp sources. Ellipsometry, Fourier transform infrared (FTIR) spectroscopy and ultraviolet spectrophotometry have been used to characterise any modi®cations to the coatings and to generally monitor the evolution of the curing process. The absorption coef®cient and photon penetration depth, as well as the intensity pro®les in the coating, of each of the different wavelengths have been measured and calculated. The FTIR spectra revealed that the coatings were cured in less than 1 s under the 308 nm excimer lamp while the 222 nm excimer lamp was found to be extremely inef®cient for the curing of the optical ®bre coatings. After curing with the 172 nm excimer lamp, the surface of the coatings became cracked, irregular and milky in appearance. Such features are not observed when irradiating with 222 and 308 nm. The different UV curing effects of these three wavelengths will be discussed. #
Journal of Non-crystalline Solids, 2002
We report the deposition of thin titanium dioxide films on Si(1 0 0) and silica glass at low temp... more We report the deposition of thin titanium dioxide films on Si(1 0 0) and silica glass at low temperatures between 200 and 350°C by a technique of ultraviolet-assisted injection liquid source chemical vapor deposition (UVILS-CVD) with 222 nm radiation. The composition and optical properties of the films deposited have been studied using a variety of standard characterisation methods. A strong absorption peak around 438 cm À1 , corresponding to Ti-O stretching vibration, was observed by Fourier transform infrared spectroscopy for different deposition temperatures. Nanostructured films on Si wafers were observed by atomic force microscopy while X-ray diffraction results showed that crystalline TiO 2 layers could be formed at deposition temperatures as low as 210°C. The deposition kinetics and influence of the substrate temperature on the film are discussed. The activation energy for this photo-CVD process at temperatures between 200 and 350°C was found to be 0.435 eV. This is much lower than the value (E a ¼ 5:64 eV) obtained by conventional thermal CVD. The thicknesses of the films grown, from several nanometers to micrometers can be accurately controlled by changing the number of drops introduced by the injection liquid source. Under optimum deposition conditions, refractive index values as high as 2.5 and optical transmittance of between 85% and 90% in the visible region of the spectrum can be obtained. Ó
Applied Surface Science, 2000
The growth of tantalum and tantalum oxide ®lms grown on Si (1 0 0) and quartz by 532 nm (Nd:YAG) ... more The growth of tantalum and tantalum oxide ®lms grown on Si (1 0 0) and quartz by 532 nm (Nd:YAG) pulsed laser deposition (PLD) in various O 2 gas environments has been investigated. Ellipsometry has been used to determine the refractive index and thickness of the ®lms whilst Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and UV spectrophotometry were used to identify tantalum and tantalum oxide formation and optical transmittance as well as optical constants. The FTIR, XPS and UV spectra reveal a strong dependence of the ®lm properties on the O 2 gas pressure used. The results showed that oxygen pressure could be used to control the composition of the ®lms. XPS analysis showed that the composition of the layers changed from Ta 2 O 5 to metal tantalum as the oxygen pressure was varied from 0.2 to 0.005 mbar. Under optimum deposition conditions, the refractive index of the oxide layers was found to be around 2X10 AE 0X05 which is close to the value of the bulk Ta 2 O 5 of 2.2 while an optical transmittance in the visible region of the spectrum up to 90% was obtained. These properties compare very favourably with those of ®lms produced by other techniques. #
Applied Surface Science, 2000
In this paper, we report the results of ultraviolet UV annealing of tantalum oxide and tantalum f... more In this paper, we report the results of ultraviolet UV annealing of tantalum oxide and tantalum films deposited on Si Ž .
Applied Surface Science, 2003
We report an investigation of rapid oxidation of silicon using a 126nm excimer lamp at low pressu... more We report an investigation of rapid oxidation of silicon using a 126nm excimer lamp at low pressures. Oxidation rates as high as 8nm/min were achieved. Unlike thermal and high pressure oxidation processes, no saturated growth rate was observed for the oxidation times used. Furthermore, thickness up to 24nm have been obtained, which are not possible with conventional thermal oxidation processes
Applied Surface Science, 2002
Over the years, photo-oxidation of silicon has been found to proceed fastest when the progressive... more Over the years, photo-oxidation of silicon has been found to proceed fastest when the progressively lower wavelength radiation has been used. Here, we use the shortest UV lamp radiation yet applied to Si oxidation, by employing 126 nm radiation from an Ar excimer lamp source. Oxidation rates as high as 5 nm/min were readily achievable at room temperature, which are more than two orders of magnitude higher than those for UV-induced oxidation of silicon using a low pressure mercury lamp at a temperature of 350 8C, and immeasurably higher than for thermal oxidation at room temperature. This enhancement is believed to arise from two effects: ozone produced by 126 nm light and more ef®cient photochemical reaction at lower wavelengths. Furthermore, thicknesses up to 9 nm have been obtained, which are not possible in reasonable times with conventional dry thermal oxidation processes at temperatures less than even 500 8C. The ®lms are found by XPS and FTIR to be stoichiometric in nature. Current±voltage measurements from metal oxide±semiconductor (MOS) devices fabricated using a 9 nm SiO 2 layer showed that leakage current densities as low as 10 À6 A/cm 2 at an electric ®eld of 1 MV/cm can be obtained in the as-grown ®lms. Further properties of these ®lms will be reported. #
Journal of Hazardous Materials, 2006
Photodegradation of nitrobenzene (NB) using an excimer UV lamp at a wavelength of 172 nm is inves... more Photodegradation of nitrobenzene (NB) using an excimer UV lamp at a wavelength of 172 nm is investigated. Experimental results show that high concentration nitrobenzene can be efficiently degraded with irradiation by excimer UV lamp, and confirm that degradation of nitrobenzene is more efficient by UV/H 2 O 2 combination than UV only. In the case of using UV only, 60 min of treatment was found to be sufficient to degrade the major part of NB solution with a concentration of less than 4 mM. In the case of using the combination of UV/H 2 O 2 with a H 2 O 2 concentration of 7:1 molar ratio to NB, 4.07 mM NB solution drastically decreased to 0.41 mM after treatment for only 20 min. Degradation intermediate products are identified by analyzing the degradation products with GC/HRMS and possible degradation pathways of nitrobenzene are suggested.
Applied Surface Science, 1999
Thin films of Ta 2 O 5 have been deposited on quartz and silicon substrates by 532-nm (Nd:YAG) pu... more Thin films of Ta 2 O 5 have been deposited on quartz and silicon substrates by 532-nm (Nd:YAG) pulsed laser deposition (PLD) in various O 2 gas environments. The influence of the deposition parameters, such as oxygen pressure, substrate temperature and annealing under UV irradiation using a 172-nm excimer lamp, on the properties of the grown films, has been studied. The refractive index of the films increases with increasing pressure of O 2 . X-ray diffraction measurements show that the as-deposited films are amorphous at temperatures below 500°C and possess orthorhombic (β-Ta 2 O 5 ) crystal structure at temperatures above 600°C. The optical properties determined by UV spectrophotometry also strongly depend on the deposition parameters. At O 2 pressures above 0.15 mbar, the refractive index of the films was about 2.12 which is close to the bulk Ta 2 O 5 value of 2.2. Optical transmittance around 85% in the visible region of the spectrum was obtained at an oxygen pressure of 0.2 mbar.
Electronics Letters, 1996
Low temperature ͑250°C͒ photo-oxidation of silicon initiated by a Xe 2 * excimer lamp operating a... more Low temperature ͑250°C͒ photo-oxidation of silicon initiated by a Xe 2 * excimer lamp operating at a wavelength of 172 nm has been investigated. The induced reaction rate of 0.1 nm/min is 90 times greater than thermal oxidation at 612°C and more than three times greater than that previously obtained at 350°C using a low pressure mercury lamp. It was found to be strongly dependent upon oxygen pressure with the highest rates being achievable below 10 mbar. Ellipsometry, Fourier transform infrared spectroscopy, capacitance-voltage, and current-voltage measurements have been employed to characterize the oxide films and designate them as high quality. © 1997 American Institute of Physics. ͓S0003-6951͑97͒01346-6͔
Solid-state Electronics, 2001
The underlying principles and properties of vacuum ultraviolet (VUV) and ultraviolet (UV) radiati... more The underlying principles and properties of vacuum ultraviolet (VUV) and ultraviolet (UV) radiation (excimer lamps), generated by a dielectric barrier discharge in a rare-gas (Rg) or a mixture of Rg and halogen, are discussed. Compared with conventional sources, these excimer lamps oer narrow-band radiation at various wavelengths from 108±354 nm and over large areas with high eciencies and high power densities. The variety of available wavelengths oers an enormous potential for new industrial applications in materials processing. Previously, photo-oxidation of silicon, germanium and silicon±germanium and photo-deposition of single-and multi-layered ®lms of silicon oxide, silicon nitride, and silicon oxynitride have been demonstrated by using excimer lamps. This paper reviews the progress on excimer lamp-assisted growth of high dielectric constant (Ta 2 O 5 , TiO 2 and PZT) and low dielectric constant (polyimide and porous silica) thin ®lms by photo-CVD and sol±gel processing, summarizes the properties of photoinduced growth of Ta 2 O 5 ®lms and discusses the eect and mechanism of low temperature UV annealing with 172 nm radiation. Metal oxide semiconductor capacitors based on the photo-induced Ta 2 O 5 ®lms grown directly on Si at low temperatures exhibit excellent electrical properties. Leakage current densities as low as 5:2 Â 10 À7 A cm À2 and 2:41 Â 10 À7 A cm À2 at 1 MV cm À1 have been achieved for the as-grown Ta 2 O 5 ®lms deposited by photo-induced sol±gel processing and photo-CVD, respectively-several orders of magnitude lower than for any other as-grown ®lms prepared by any other technique. A subsequent low temperature (400°C) UV annealing step improves these to 10 À8 A cm À2 . These values are comparable to those only previously achieved for ®lms annealed at high temperatures between 600°C and 1000°C. These properties make the photo-induced growth of Ta 2 O 5 layers suitable alternative to SiO 2 for high density DRAM application. Ó
Applied Surface Science, 2000
The principle underlying the operation of excimer lamps relies on the radiative decomposition of ... more The principle underlying the operation of excimer lamps relies on the radiative decomposition of excimer states created by a dielectric barrier discharge in a rare gas or a mixture of rare gas±halogen. In excimer lamp technology, no electrodes are in direct contact with the discharge gases, thus avoiding any reaction between the discharge and the electrodes or contamination of the gas with evaporated electrode material, as well as electrode corrosion which can occur in conventional lamps leading to short operational lifetimes. Therefore, an investigation of the lifetime of these lamps is of vital importance before any industrial application can be seriously considered. In this paper, the detailed lifetime of 172, 222, and 308 nm excimer lamps as well as overall ef®ciency, stability, and any output¯uctuations, have been investigated. It was found that ef®ciency increased as input power decreased. It was noted however that colour centres were formed within the ®rst 60 h of operation for 172 nm excimer lamps which reduced their output intensity during their time. By contrast, 100% of the original UV intensity output by the 222 and 308 nm lamps was still maintained after up to 4000 h operating time. These results are compared with the lifetime of conventional mercury lamps. #
Applied Surface Science, 1996
&e-nucleation of surfaces with palladium from thin palladium acetate films on a range of substrat... more &e-nucleation of surfaces with palladium from thin palladium acetate films on a range of substrate materials by UV-induced decomposition is described. The optical transmission of the films after irradiation with incoherent UV radiation from several excimer lamp sources provided information about the deposition rate at different UV intensities and exposure times using three different wavelengths: A = 172 nm (Xe; 1, A = 222 nm (Krcl * ), and A = 308 nm (XeCl * 1. The gaseous products produced during UV exposure were measured using mass spectrometry (MS). The decomposed products such as H,O, CO,, +CCH3, +COCH, and +CH3 were observed. The decomposition mechanism of palladium acetate is discussed and a simple model calculation describing photolytic decomposition processes in the thin palladium acetate films is presented. Results will be compared to those obtained by laser and thermal decomposition of palladium acetate. The deposited palladium can act as an activator for subsequent patterned chemical metal deposition techniques in which micrometer thick copper, nickel, or gold layers with good electrical resistivity are applied.
Surface & Coatings Technology, 2000
We report the growth of single-and multilayer films of titanium dioxide (TiO 2 ) on Si substrates... more We report the growth of single-and multilayer films of titanium dioxide (TiO 2 ) on Si substrates at low temperature by a new photo-induced sol-gel process. Polymeric TiO 2 sols prepared by the hydrolysis and condensation of titanium isopropoxide were spin-coated on the silicon substrate and then irradiated by an excimer vacuum ultraviolet (VUV) lamp operating at a wavelength of 172 nm. Films with thicknesses between 10 and 200 nm were achieved readily by this technique. The effects of spin speed, irradiation time and substrate temperature on the films formed have been studied. The chemical bonding changes in the thin films were analysed by Fourier transform infrared spectroscopy (FTIR), while thickness and refractive indices were determined by ellipsometry. FTIR confirmed the removal of H 2 O and OH groups after VUV irradiation for 10 min at 300°C. The refractive index reached a value of 2.4, which compares favourably with the value of 2.58 recorded for the bulk material, while optical transmittance values in the visible region of the spectrum between 85 and 95% were obtained on quartz substrates.
Applied Surface Science, 2002
We report the deposition of thin TiO 2 films on crystalline Si and quartz by photo-induced chemic... more We report the deposition of thin TiO 2 films on crystalline Si and quartz by photo-induced chemical vapour deposition (CVD) using UV excimer lamps employing a dielectric barrier discharge in krypton chloride (KrCl * ) to provide intense narrow band radiation at . The precursor used was titanium isopropoxide (TTIP). Films from around 20-510 nm in thickness with refractive indices from 2.20 to 2.54 were grown at temperatures between 50 and 350 °C. The higher refractive index values compare favourably with the value of 2.58 recorded for the bulk material. The measured deposition rate was around 50 nm/min at 350 °C. Fourier transform infrared spectroscopy (FTIR) revealed the presence of TiO 2 through the observation of a Ti-O absorption peak and the absence of OH in films deposited at 250-350 °C indicated relatively good quality films. The phase of films deposited at 200-350 °C was anatase as determined by X-ray diffraction.
Journal of Adhesion Science and Technology, 1994
Photochemical dry etching and surface modification of various polymers, e.g. polymethylmethacryla... more Photochemical dry etching and surface modification of various polymers, e.g. polymethylmethacrylate (PMMA), polyimide (PI), polyethyleneterephthalate (PET) and polytetrafluoroethylene (PTFE) were investigated with coherent and incoherent excimer UV sources. Ablation rates of PMMA were measured as a function of laser fluence and laser pulse at the wavelength λ = 248 nm (KrF*). Decomposition and etch rates of PMMA and PI were determined as a function of UV intensity and exposure time at three different wavelengths λ = 172 nm (Xe*2), λ = 222 nm (KrCl*) and λ = 308 nm (XeCl*). The transmittance of the polymeric films was determined with a UV-spectrophotometer after different exposure times. The morphology of the exposed polymers was investigated with scanning electron microscopy (SEM). The gaseous products occurring during UV exposure were measured using mass spectrometry (MS). Chemical surface changes of the photoetched PMMA were determined by X-ray photoelectron spectroscopy (XPS). The mechanism of the photo-oxidation process of PMMA is discussed. The etching of PMMA can be explained as a result of extensive photo-oxidation. The results are compared with those obtained from mercury lamp and excimer laser experiments. Good adhesion of electrolessly deposited metal layers was achieved by irradiation of the polymeric surfaces from incoherent UV source before depositing the metal layer.
Applied Surface Science, 2002
In this paper, UV curing of optical ®bre coatings using excimer lamp radiation has been demonstra... more In this paper, UV curing of optical ®bre coatings using excimer lamp radiation has been demonstrated for the ®rst time. These layers were prepared on silicon and quartz substrates by conventional spin coating and subsequently exposed to 172, 222 nm or 308 nm light from different excimer lamp sources. Ellipsometry, Fourier transform infrared (FTIR) spectroscopy and ultraviolet spectrophotometry have been used to characterise any modi®cations to the coatings and to generally monitor the evolution of the curing process. The absorption coef®cient and photon penetration depth, as well as the intensity pro®les in the coating, of each of the different wavelengths have been measured and calculated. The FTIR spectra revealed that the coatings were cured in less than 1 s under the 308 nm excimer lamp while the 222 nm excimer lamp was found to be extremely inef®cient for the curing of the optical ®bre coatings. After curing with the 172 nm excimer lamp, the surface of the coatings became cracked, irregular and milky in appearance. Such features are not observed when irradiating with 222 and 308 nm. The different UV curing effects of these three wavelengths will be discussed. #
Journal of Non-crystalline Solids, 2002
We report the deposition of thin titanium dioxide films on Si(1 0 0) and silica glass at low temp... more We report the deposition of thin titanium dioxide films on Si(1 0 0) and silica glass at low temperatures between 200 and 350°C by a technique of ultraviolet-assisted injection liquid source chemical vapor deposition (UVILS-CVD) with 222 nm radiation. The composition and optical properties of the films deposited have been studied using a variety of standard characterisation methods. A strong absorption peak around 438 cm À1 , corresponding to Ti-O stretching vibration, was observed by Fourier transform infrared spectroscopy for different deposition temperatures. Nanostructured films on Si wafers were observed by atomic force microscopy while X-ray diffraction results showed that crystalline TiO 2 layers could be formed at deposition temperatures as low as 210°C. The deposition kinetics and influence of the substrate temperature on the film are discussed. The activation energy for this photo-CVD process at temperatures between 200 and 350°C was found to be 0.435 eV. This is much lower than the value (E a ¼ 5:64 eV) obtained by conventional thermal CVD. The thicknesses of the films grown, from several nanometers to micrometers can be accurately controlled by changing the number of drops introduced by the injection liquid source. Under optimum deposition conditions, refractive index values as high as 2.5 and optical transmittance of between 85% and 90% in the visible region of the spectrum can be obtained. Ó
Applied Surface Science, 2000
The growth of tantalum and tantalum oxide ®lms grown on Si (1 0 0) and quartz by 532 nm (Nd:YAG) ... more The growth of tantalum and tantalum oxide ®lms grown on Si (1 0 0) and quartz by 532 nm (Nd:YAG) pulsed laser deposition (PLD) in various O 2 gas environments has been investigated. Ellipsometry has been used to determine the refractive index and thickness of the ®lms whilst Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and UV spectrophotometry were used to identify tantalum and tantalum oxide formation and optical transmittance as well as optical constants. The FTIR, XPS and UV spectra reveal a strong dependence of the ®lm properties on the O 2 gas pressure used. The results showed that oxygen pressure could be used to control the composition of the ®lms. XPS analysis showed that the composition of the layers changed from Ta 2 O 5 to metal tantalum as the oxygen pressure was varied from 0.2 to 0.005 mbar. Under optimum deposition conditions, the refractive index of the oxide layers was found to be around 2X10 AE 0X05 which is close to the value of the bulk Ta 2 O 5 of 2.2 while an optical transmittance in the visible region of the spectrum up to 90% was obtained. These properties compare very favourably with those of ®lms produced by other techniques. #
Applied Surface Science, 2000
In this paper, we report the results of ultraviolet UV annealing of tantalum oxide and tantalum f... more In this paper, we report the results of ultraviolet UV annealing of tantalum oxide and tantalum films deposited on Si Ž .
Applied Surface Science, 2003
We report an investigation of rapid oxidation of silicon using a 126nm excimer lamp at low pressu... more We report an investigation of rapid oxidation of silicon using a 126nm excimer lamp at low pressures. Oxidation rates as high as 8nm/min were achieved. Unlike thermal and high pressure oxidation processes, no saturated growth rate was observed for the oxidation times used. Furthermore, thickness up to 24nm have been obtained, which are not possible with conventional thermal oxidation processes
Applied Surface Science, 2002
Over the years, photo-oxidation of silicon has been found to proceed fastest when the progressive... more Over the years, photo-oxidation of silicon has been found to proceed fastest when the progressively lower wavelength radiation has been used. Here, we use the shortest UV lamp radiation yet applied to Si oxidation, by employing 126 nm radiation from an Ar excimer lamp source. Oxidation rates as high as 5 nm/min were readily achievable at room temperature, which are more than two orders of magnitude higher than those for UV-induced oxidation of silicon using a low pressure mercury lamp at a temperature of 350 8C, and immeasurably higher than for thermal oxidation at room temperature. This enhancement is believed to arise from two effects: ozone produced by 126 nm light and more ef®cient photochemical reaction at lower wavelengths. Furthermore, thicknesses up to 9 nm have been obtained, which are not possible in reasonable times with conventional dry thermal oxidation processes at temperatures less than even 500 8C. The ®lms are found by XPS and FTIR to be stoichiometric in nature. Current±voltage measurements from metal oxide±semiconductor (MOS) devices fabricated using a 9 nm SiO 2 layer showed that leakage current densities as low as 10 À6 A/cm 2 at an electric ®eld of 1 MV/cm can be obtained in the as-grown ®lms. Further properties of these ®lms will be reported. #