Changlin Li

Evidence for metal interaction in gold metallized polycarbonate films: An x-ray photoelectron spectroscopy investigation

The interfacial interactions between in situ thermally evaporated Au and polycarbonate (PC) film, a technologically important polymeric material, is studied by x-ray photoelectron spectroscopy (XPS). Angle resolved XPS is performed to investigate the Au reactivity if any, in forming the metal-polymer interface. The spectral evidence from the above suggests that the metal interacts predominantly with the carbonyl carbon of the monomeric unit with only minor interactions with the phenyl carbons without any complex formation. In contrast to previous findings of Au to be inert at the M-polymer interfaces, this work emphasizes the salient charge transfer type interactions of Au (as electron injector) at the C=O as the primary interaction site, distributing a net charge density to C=O with the formation of a Au-CO π-back bond. The conclusions are supported by the observed new C 1s feature at 282.6 eV and the O 1s and Au 4f7/2 XPS spectral changes. The growth mode of Au on PC was proceeded by the metal monolayer...

SURFACE MODIFICATION OF POLYETHYLENE TEREPHTHALATE IMPLANTED BY ARGON IONS

Modification of polyethylene terephthalate (PET) was carried out by 120 Modification of polyethylene terephthalate (PET) was carried out by 120

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.

Correlation between the structure modification and conductivity of 3 MeV Si ion-irradiated polyimide

Abstract The surface modification of the polyimide (PI/Kapton) films was carried out by 3 MeV Si + implantation to fluences ranging from 1×10 12 to 1.25×10 15 ions/cm 2 . Fourier transform infrared (FTIR), Raman and ultraviolet/visible (UV/Vis) spectroscopes were employed to investigate the chemical degradation of function groups in the irradiated layer. FTIR results show that the absorbance of typical function group decreases exponentially as a function of fluence. The damage cross-section of typical bonds of PI was evaluated from the FTIR spectra. Raman analysis shows the absorbed dose for destruction of all function groups is above 218 MGy. The red shifting of the absorption edge from UV to visible reveals the band gap closing which results from increase of the cluster size. The production efficiency of the chromophores was discussed according to UV/Vis analysis. Irradiation dramatically enhances the electrical conductivity and the sheet resistivity in our experiment descends nearly 10 orders of magnitude compared with its intrinsic value.

Friction and wear behaviour of carbon ion-implanted PS against steel

Abstract A 25 μm thick polystyrene (PS) film was implanted with 120 keV ions of carbon to doses of 1×1014, 1×1015, 3×1015, 5×1015 and 1×1016 ions cm−2, respectively. The structure of the implanted PS was characterized by X-ray photoelectron spectroscopy (XPS), whereas the friction and wear behaviour of both implanted and unimplanted PS were investigated using an one-way reciprocating friction tester against a steel ball. Friction results indicate that ion implantation at a dose of 1×1014 ions cm−2 increases friction coefficient, whereas the ion implantation at a dose of 1×1015 ions cm−2 or higher decreases friction coefficient, and all the tests show that ion implantation lowers wear rate. XPS analyses reveal that ion implantation at dose of 1×1014 ions cm−2 results in partial break of benzene ring, and at a dose of 1×1016 ions cm−2 results in complete break of benzene ring.

Effect of InAs quantum dots on the Fermi level pinning of undoped-n+ type GaAs surface studied by contactless electroreflectance

Self-assembled InAs quantum dots (QDs) have been fabricated by depositing 1.6, 1.8, 2.0 and 2.5 monolayer (ML) InAs on surfaces of the undoped-n(+) (UN+) type GaAs structure. Room temperature contactless electroreflectance (CER) was employed to study the built-in electric field and the surface Fermi level pinning of these QD-covered UN+ GaAs samples. The CER results show that 1.6 ML InAs QDs on GaAs do not modify the Fermi level, whereas for samples with more than 1.6 ML InAs coverage, the surface Fermi level is moved to the valence band maximum of GaAs by about 70 meV (which is independent of the InAs deposition thickness) compared to bare GaAs. It is concluded that the modification of InAs coverage on the Fermi level on the GaAs surface is due to the QDs, rather than to the wetting layer

Defects in SiO2 glass irradiated with high energy Ar ions

Abstract SiO2 glass specimens are irradiated at room temperature with 560 MeV and 1.15 GeV Ar ions. Defect production is investigated by positron lifetime spectra, EPR and UV absorption measurements. Free volumes of about 0.065 nm3 in size are found to be present in the virgin specimen from the corresponding Ortho-Positronium lifetimes. With increasing dose the intensity of the component corresponding to positronium decreases sharply. This is attributed to the preferred annihilation of positrons with the radiation-ionized-electrons wandering in free volumes of the material. Optical absorption bands are induced at about 5.8, 5 and 4.5 eV by the irradiations and the absorption coefficients increase gradually with increasing dose. The EPR spectra of the irradiated specimens show the occurrence of the E′ center, the number density of which reveals two distinct regimes according to its dependence on dose. In the low dose range the number density of E′ center follows a 0.23 power law dose dependence whereas at high dose it increases linearly with dose. Furthermore the EPR spectra show fine structure which changes with dose.

Interface configuration in gold/polycarbonate bilayer structure: an in situ study through Ar+ ion depth profiling

Abstract The formation, configuration and the interactions at the gold/polycarbonate (Au/PC) interface formed by thermally evaporated Au on PC film, a technologically important polymer, is studied by X-ray photoelectron spectroscopy (XPS) at an Au thickness of 35.4 A. XPS depth profiling with 3 keV Ar + ion sputtering at 1 μA revealed the interface between the as-deposited 35.4 A Au film and the PC substrate to be sharp covering a few monolayers. A substantial Au atomic concentration of ∼3% in the bulk PC indicated that Ar + ion assisted diffusion of the metal into the bulk. Existence of weak Au→C charge transfer interactions with Au as the electron injector distributing a net charge density at the CO as the primary interaction site was deduced from the appearance of the 282.6 eV C 1s feature, thus resulting in the formation of Au–CO π back bond. The sputtering experiments revealed the growth-mode of Au on PC to proceed by metal monolayer deposition followed by cluster growth on the already weakly bonded Au onto the CO carbon of the polymeric backbone.

Interface configuration and metal adhesion in Au-polycarbonate bilayer structure: Influence of 27Al+ ion mixing

Structural modification at the Au-polycarbonate (PC) interface upon 100 keV 27Al+ ion implantation at a dose and beam current density 5×1016 ions cm−2 and 30–50 nA cm−2, respectively, was studied through x-ray photoelectron spectroscopy (XPS) with a Au thickness of 28.2 nm. XPS depth profiling with 3 keV Ar+ ion sputtering at 1 μA revealed the interface to be sharp covering a few monolayers. A substantial Au atomic concentration of ∼5% in the bulk PC indicated the Ar+ ion assisted diffusion of the metal into the bulk. Existence of weak Au→C charge transfer interactions with Au as the electron injector distributing a net charge density at the C=O bond as the primary interaction site was deduced from the appearance of the 282.4 eV C1s feature [H. A. Mizes, K. G. Loh, R. J. D. Miller, S. K. Ahuja, and E. F. Grabowski, Appl. Phys. Lett. 59, 2901 (1991)]. Al+ ion implantation induced interfacial mixing of the substrate C with the Au film in the bilayer target was observed with the evolution of a broad interfac...