Mingdong Hou

Electrochemical fabrication of single-crystalline and polycrystalline Au nanowires : the influence of deposition parameters

We report the electrochemical growth of gold nanowires with controlled dimensions and crystallinity. By systematically varying the deposition conditions, both polycrystalline and single-crystalline wires with diameters between 20 and 100 nm are successfully synthesized in etched ion-track membranes. The nanowires are characterized using scanning electron microscopy, high resolution transmission electron microscopy, scanning tunnelling microscopy and x-ray diffraction. The influence of the deposition parameters, especially those of the electrolyte, on the nanowire structure is investigated. Gold sulfite electrolytes lead to polycrystalline structure at the temperatures and voltages employed. In contrast, gold cyanide solution favours the growth of single crystals at temperatures between 50 and 65 °C under both direct current and reverse pulse current deposition conditions. The single-crystalline wires possess a [110] preferred orientation.

Swift heavy ion induced amorphisation and chemical modification in polycarbonate

Polycarbonate (Makrofol kg) film stacks were irradiated by 15.14 MeV/amu Xe-136 and 11.4 MeV/amu U-238 in the electronic stopping power range (7.6-17.1 keV/nm) and the fluence range from 9 x 10(9) to 1 x 10(12) ions/cm(2). The chemical degradation of the function group was investigated by Fourier-transform infrared (FTIR) spectroscopy and the crystallinity was analyzed by X-ray diffraction (XRD) measurement. FTIR results reveal that the material suffers serious degradation after irradiation. The alkyne group was found after irradiation and their formation cross-sections were evaluated. XRD measurements show the decrease of the main XRD peak intensity, confirming that the material to be amorphised under irradiation. The ion induced amorphisation cross-section was extracted from the fitting of the experimental data for different electronic energy loss irradiations. The degradation cross-section, the formation cross-section and the amorphisation cross-section versus electronic energy loss were discussed

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.

Controlled crystallinity and crystallographic orientation of Cu nanowires fabricated in ion-track templates.

The hallmark of materials science is the ability to tailor the structures of a given material to provide a desired response. In this work, the structures involving crystallinity and crystallographic orientation of Cu nanowires electrochemically fabricated in ion-track templates have been investigated as a function of fabrication condition. Both single crystalline and polycrystalline nanowires were obtained by adjusting applied voltages and temperatures of electrochemical deposition. The anti-Hall-Petch effect was experimentally evidenced in the polycrystalline nanowires. The dominant crystallographic orientations of wires along [111], [100], or [110] directions were obtained by selecting electrochemical deposition conditions, i.e., H(2)SO(4) concentration in electrolyte, applied voltage, and electrodeposition temperature.

STM and Raman Spectroscopic Study of Graphite Irradiated by Heavy Ions

Highly oriented pyrolytic graphite was irradiated with swift heavy ions (Ne, Cr, Fe, Ni, Zn, Xe and U) of fluences between 10 11 and 10 14 ions/cm 2 in energy range MeV–GeV. The combination of scanning tunneling microscopy (STM) and Raman spectroscopy studies shows that large numbers of tracks protrude from the surface. The disordered crystal lattice is leading to a Raman-active D mode. Quantitative analysis of the peak intensity indicates that the size of the crystallite domain is larger than the mean distance between in-plane tracks observed by STM. � 2003 Elsevier B.V. All rights reserved.

The effects of high electronic energy loss on the chemical modification of polyimide

Abstract In order to observe the role of electronic energy loss (d E /d X ) e on chemical modification of polyimide (PI), the multi-layer stacks (corresponding to different d E /d X ) were irradiated by different swift heavy ions (1.37 GeV Ar 40 , 1.98 GeV Kr 84 , 1.755 GeV Xe 136 and 2.636 GeV U 238 ) under vacuum and room temperature. The chemical changes of modified PI films were studied by Fourier transform infrared (FTIR) and ultraviolet/visible (UV/Vis) absorption spectroscopy. The degradation of PI was investigated in the fluence range from 1×10 10 to 5.5×10 12 ions/cm 2 and different electronic energy loss from 0.77 to 11.5 keV/nm. The FTIR results show the absorbance of the typical function group decrease exponentially as a function of fluence. The alkyne end group was found after irradiation and its formation radii were 5.6 and 5.9 nm corresponding to 8.8 and 11.5 keV/nm Xe irradiation respectively. UV/Vis analysis indicates the radiation induced absorbance change follows a linear relation as function of fluence corresponding to various ion and the production efficiency of the chromophores depends strongly on the electronic energy loss (d E /d X ) e with a power relation.

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.

Microstructural changes in a low-activation Fe–Cr–Mn alloy irradiated with 92 MeV Ar ions at 450°C

In this work, a solution-annealed specimen of a low-activation Fe-Cr-Mn alloy was irradiated with 92 MeV Ar ions at 450 degreesC to a dose of 1.7 x 10(21) m(-2) which was expected to produce a peak displacement damage of 90 dpa. After irradiation, damage microstructure was investigated from the cross-sectional specimens using a transmission electron microscope. High number density cavities were observed in the peak dose region. Size of cavities was the largest at the peak displacement damage. Formation of alpha -phase was found at a grain boundary in the peak dose region. Well-dispersed carbide particles was found in the matrix. The carbide/matrix interfaces supplied favorable site for growth of large cavities, whereas only small cavities were found inside the particles

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