Xiaoxi Chen

Chemical modifications in polyethylene terephthalate films induced by 35 MeV/u Ar ions

Abstract Semicrystalline polyethylene terephthalate (PET) foil stacks were irradiated under vacuum and at room temperature with 35 MeV/u Ar ions to fluences ranging from 1×10 10 to 5×10 12 ions/cm2. Ion induced modifications in crystalline and chemical structures were studied by means of differential scanning calorimetry (DSC), Fourier-transform infrared absorption spectroscopy (FTIR), and X-ray diffractometer (XRD). The DSC and XRD data show a significant loss of crystallinity at the absorbed doses higher than 4.0 MGy. FTIR measurements indicate that the loss of crystallinity of the irradiated PET is related to the scission processes of the main chains at the trans configuration of the ethylene glycol residue. Meanwhile, at the absorbed dose above about 4.0 MGy, bond breaking processes at the para position of benzene are also observed. The benzene ring structures are found to be more stable under irradiation.

Study of effects in polyethylene terephthalate films induced by high energy Ar ion irradiation

Abstract Semicrystalline polyethylene terephthalate (PET) foil stacks were irradiated with 1.373 GeV Ar ions to different fluences ranging from 1.0×1010 to 5.0×1012 ions/cm2. The induced effects were investigated by means of the Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible absorption spectroscopy (UV/VIS) and electron spin resonance spectroscopy (ESR). FTIR measurements show that bond breaking processes are mainly observed at the ethylene glycol residue of trans configuration and at the para position of benzene rings above a critical dose of about 4.0 MGy. Damage cross-section has been extracted for the band at 973 cm−1 from the dependence of the absorbance on fluence and it shows a linear dependence on the mean electronic energy loss. UV/VIS measurements show a strong increase in absorbance in the ultraviolet and visible regions. It is found that for the same absorbed dose, more increase in absorbance is induced at higher electronic energy loss. ESR measurements indicate the creation of free radicals. The radical concentration is found to increase rapidly with the increasing absorbed dose above 4.0 MGy.

Molecular conformation changes of PET films under high-energy Ar ion bombardment

Abstract Investigation of the surface modification in molecular structure of semicrystalline polyethylene terephthalate (PET) films induced by Ar ion bombardment is presented. The PET samples are analysed by using Fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD), and X-ray photoelectron spectroscopy (XPS). A significant loss of crystallinity is observed, which is related to the configuration transformation of ethylene glycol residue from the trans into the gauche. Chain scissions are observed at the para position of di-substituted benzene rings, –CO bonds and C–O bonds. The C–O bonds are destroyed more selectively than –CO bonds. The benzene ring structures show only small change under irradiation and do not participate in degradation process. Extra CC bonds and alkyne end groups are created above a critical dose of 4.0 MGy. The results are briefly discussed.

Photoluminescence from high-energy heavy ion irradiated C-doped SiO2 thin films

SiO2 thin films were implanted at room temperature (RT) with 120 keV carbon ions to a dose of 1.0 x 10(17) ions/cm(2) and then irradiated at RT with high-energy Kr-84 or Ar-40 ions to a fluence of 1.0 x 10(12) ions/cm(2). Using 320 nm monochromatic ultra-violet light for excitation, photoluminescence (PL) properties of these samples were examined and intense blue PL bands were observed. It was found that the blue PL peak intensity changes with electronic energy loss of the irradiation ion in the sample. With increasing the electronic energy loss level, the PL peak intensity decreases and the peak position shifts towards to the short-wavelength direction. Furthermore, the existence of C-dopants enhances the luminescence property of the irradiated samples

Chemical modifications of ion irradiated polystyrene probed by optical absorption measurements

Abstract Polystyrene (PS) films are irradiated at room temperature with 3 MeV silicon ions and 1.4 GeV argon ions to fluences ranging from 1×10 10 to 3×10 14 cm −2 . Fourier transform infrared (FTIR) specula reflection spectra and ultraviolet/visible (UV/Vis) transmission spectra are measured to investigate the radiation-induced chemical modifications. It is found that the intrinsic absorption bands show reduction in intensity with increasing fluence and electronic energy loss, indicating the degradation of the polymeric structure. For Si ion implanted specimens, significant chemical modifications occur above about 3×10 13 cm −2 , corresponding to an average energy deposition of about 45 MGy. For Ar ion irradiated specimens, the critical electronic energy loss is around 0.77 keV/nm at the fluence of 5.5×10 12 cm −2 , corresponding to an energy deposition of about 6.4 MGy. The increase in absorbance in the UV/Vis range and a shift of the absorption edge toward the visible is attributed to carbonization of the material. The results are discussed on the basis of ion fluence and energy loss.

Chemical modification of polycarbonate induced by 1.4 GeV Ar ions

Abstract Polycarbonate foil stacks were irradiated with 1.4 GeV Ar ions at room temperature. The induced modifications in chemical structure were studied by Fourier transform infrared (FTIR) and ultraviolet/visible absorption (UV/VIS) spectroscopies. FTIR measurements reveal that material degradation through bond breaking are the main effects. Significant reduction in absorbance of the typical infrared bands is observed at energy densities higher than 8×10 22 eV / cm 3 . Alkyne end groups are produced by the irradiations and the electronic energy loss threshold for production of the alkyne end group is found to be below 0.61 keV/nm. UV/VIS measurements indicate a shifting of the absorption edge from ultraviolet towards visible and a strong increase of absorbance in the ultraviolet and visible regions. The irradiation induced changes in absorbance at wavelengths of 380, 450 and 500 nm follow roughly linear relationship with fluence and scale rather good with the square of electronic energy loss. The results are briefly discussed.

Blue-violet PL band formation in C : SiO2 films after swift heavy ion irradiation

Abstract One hundred and twenty keV C-ion doped SiO2 films were irradiated at RT with swift Ar, Kr, Xe or U ions and their photoluminescence (PL) properties were examined. From the obtained results, we found that an intense blue–violet PL band centred at ∼435±10 nm was formed in all ion irradiated samples and a weak ultraviolet PL band centred at ∼380 nm was formed only in the samples after Kr, Xe or U ion irradiations. The PL peak intensity of the blue–violet band (i) increases with the increase of the swift heavy ion irradiation fluence, (ii) decreases with the increase of electronic energy loss Se when Se 4.85 keV/nm. Furthermore, the peak central position of the blue–violet PL is shifted slightly to violet with increasing Se and some substructures appeared in the PL spectra of the samples irradiated with Xe or U ions. The appearance of these substructures is due to the high electronic energy loss. For the violet PL band, the intensity increases with Se. Possible origins and formation mechanism of light-emitters corresponding to the observed PL bands are discussed.

Swift heavy ion irradiation induced luminescence from C-doped SiO2 films

Abstract In the present work, a novel technique, “low energy ion implantation+high-energy heavy ion irradiation”, was used to synthesis light-emitting material. Experimentally, thermal-grown SiO 2 films were firstly implanted with 120 keV C + ions at room temperature (RT) to total doses in the range of (5.0×10 16 –1.0×10 18 ) ions/cm 2 . These C-doped SiO 2 films were then irradiated at RT with 335 and 855 MeV 40 Ar or 1.98 GeV 84 Kr ions to a fluence of 1.0×10 12 ions/cm 2 , or with 1.75 GeV 136 Xe ions to 1×10 11 , 5×10 11 or 1×10 12 ions/cm 2 , respectively. By measuring photoluminescence (PL) spectra of these samples excited by 320 nm light, the PL bands were investigated as functions of implantation ion dose, irradiation ion fluence and electronic energy loss S e . It was found that this technique is a useful tool to produce high quality light-emission structures, and that high-energy heavy ion irradiated C-doped SiO 2 films should be an efficient blue–violet emitting material. Furthermore, S e plays a dominant role in the formation of the PL bands, and proper C-dopant and suitable irradiation fluence will enhance the PL efficiency. Possible origins of the blue-violet PL bands formed in the ion irradiated C-doped SiO 2 films were discussed.