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Erscheinungsjahr
- 2001 (8) (entfernen)
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Schlagworte
- Band structure (1)
- Diamond growth & characterization (1)
- Electron Spectroscopy (1)
- FTIR Ellipsometry (1)
- Femtosecond pulse laser (1)
- Laser processing (1)
- Nanoindentation (1)
- Nanostructures (1)
- Nitrides (1)
- Polymer ablation (1)
Multi-shot investigations of Ti:sapphire laser (wavelength (lambda) approximately equals 800 nm) induced damage were performed in three different laboratories (BAM, Berlin; LZH, Hannover; UNM, Albuquerque). The ablation behavior of a high reflecting mirror consisting of alternating (lambda) /4- layers of Ta2O5 and SiO2 was studied. Fused silica served as substrate. The influence of the pulse duration ((tau) equals 13 - 130 fs), the pulse number (30 - (infinity) ) and the repetition rate (10 Hz - 100 MHz) on the damage threshold will be discussed.
Ablation of indium phosphide wafers in air was performed with low repetition rate ultrashort laser pulses (130 fs, 10 Hz) of 800 nm wavelength. The relationships between the dimensions of the craters and the ablation parameters were analyzed. The ablation threshold fluence depends on the number of pulses applied to the same spot. The single-pulse ablation threshold value was estimated to be fth(1)=0.16 J/cm2. The dependence of the threshold fluence on the number of laser pulses indicates an incubation effect. Morphological and chemical changes of the ablated regions were characterized by means of scanning electron microscopy and Auger electron spectroscopy.
Zusammenfassung
The surface chemical modification of polyurethane (PU) films was performed by an UV laser-induced chemical reaction in a polysaccharide solution. This process may be applicable as hydrophilic packaging of implantable medical devices and in vivo sensors. When a PU film in contact with an aqueous alginic acid (AAC) solution was irradiated with a XeCl laser, the PU film turned hydrophilic. Contact angles of water on the film were reduced from 110° to 60°. Since light absorption of the AAC solution at 308 nm was negligibly small, reactive sites were generated solely on the PU surface. There, AAC could be immobilized by chemical bonds thus allowing for a nanometer-scaled grafting of this biomolecule. The mechanism was investigated by surface analyses with Fourier-transform infrared spectroscopy (FT-IR), dye staining, ultraviolet-visible (UV-VIS) spectroscopy, and scanning electron microscopy (SEM) techniques. A one-photon photochemical process could beidentified.
A study on the bonding structure and mechanical properties of magnetron sputtered CNx thin films
(2001)
Carbon nitride (CNx) films have been deposited by reactive (RF) magnetron sputtering, in order to investigate the effect of the energetic ion bombardment during deposition (IBD), in terms of applied Vb, on their bonding structure. Fourier Transform IR Ellipsometry (FTIRE) and X-ray photoelectron spectroscopy (XPS) were used for the investigation of the films bonding structure, while their mechanical properties were evaluated by nanoindentation measurements. At films grown with low negative Vb, (low energy IBD) the N atoms are distributed homogeneously in substitutional sites in graphitic rings through both sp2 and sp3 bonds and in linear chains, through sp2 bonds. In contrast, the high negative Vb (high energy IBD) has been suggested to promote the non-homogeneous N distribution at localized regions in the films where the formation of sp3 C---N bonds is favored. This behavior was also evidenced by the C1s and N1s XPS peak components, assigned to the sp3 and sp2 carbonnitrogen bonds. Also, high energy IBD films revealed increased values of hardness and elasticity, while hardness values up to 45 GPa were measured at localized regions.
A complementary study of composition and bonding of sputtered a-C films, deposited on Si(001) substrates with various bias voltages (Vb) applied to the substrate during deposition is presented. The sp3 and sp2 fractions in the films were calculated by deconvolution of the X-ray photoelectron spectroscopy (XPS) C1s peak and studied by the differential auger electron spectroscopy (AES) CKLL peak signal. The results of this analysis are compared with the estimation of sp3 fraction calculated by spectroscopic ellipsometry (SE) and validated using density measurements by X-ray reflectivity. It was observed a considerable increase of sp3 content in films deposited with negative Vb. The respective sp3 and sp2 fractions and Ar concentration with respect to the Vb and the depth profile analysis give valuable information on the deposition mechanism of the sputtered a-C films. XPS valence band spectra provided the electron density of states in the a-C films valence band. The characteristic broad p band of diamond was prominent in most of the films. The valence band structure of the films was correlated with their optical response measured by SE.