Surface modifications of TiN coatings by a pulsed TEA CO<Subscript>2</Subscript> laser: Coating thickness effects

Interactions of a transversely excited atmospheric (TEA) CO₂ laser, pulse duration ∼2 μs (initial spike FWHM ∼120 ns), with polycrystalline titanium nitride (TiN) coatings deposited on high-quality steel (AISI 316 or M2) were studied. The experiments were carried out in a regime of high laser energy densities: 25, 48, and 50 J/cm². The energy absorbed from the laser beam was partially converted to thermal energy and the effects of the TiN coating thickness on the morphological changes were considered. The morphological features and processes that accompany the interaction can be summarized as follows: (i) exfoliation of the TiN coating in the central zone of the irradiated area (for coating thickness of 1 μm) or appearance of grainy structure (for coating thicknesses 3 and 10 μm); (ii) appearance of hydrodynamic changes in the surrounding peripheral zone; and (iii) appearance of plasma in front of the target during sample irradiation. The text was submitted by the authors in English.     

Pulsed TEA CO2 Laser Irradiation of Titanium in Nitrogen and Carbon Dioxide Gases

Surface changes created by interaction of transversely excited atmospheric carbon dioxide (TEA CO₂) laser with titanium target/implant in nitrogen and carbon dioxide gas were studied. TEA CO₂ laser operated at 10.6 μm, pulse length of 100 ns and fluence of ∼17 J/cm² which was sufficient for inducing surface modifications. Induced changes depend on the gas used. In both gases the grain structure was produced (central irradiated zone) but its forms were diverse, (N₂: irregular shape; CO₂: hill-like forms). Hydrodynamic features at peripheral zone, like resolidified droplets, were recorded only in CO₂ gas. Elemental analysis of the titanium target surface indicated that under a nitrogen atmosphere surface nitridation occurred. In addition, irradiation in both gases was followed by appearance of plasma in front of the target. The existence of plasma indicates relatively high temperatures created above the target surface offering a sterilizing effect.

     

Laser beam profiles in SF6: direct evidence for beam distortion

High-resolution spatial profile measurements of a CO₂ TEA laser beam propagating through SF₆/Ar mixtures indicate that IR multiple photon absorption measurements averaged over the entire laser beam spatial distribution can be in error by at least a factor of two, implying that accurate measurements require an optically thin sample. This is due to the intensity dependence of the absorption cross section.     

Low-temperature processing of sol-gel derived Pb(Zr,Ti)O<Subscript>3</Subscript> thick films using CO<Subscript>2</Subscript> laser annealing

Fabrication of ferroelectric Pb(Zr_0.52Ti_0.48)O₃ (PZT) thick films on a Pt/Ti/SiO₂/Si substrate using powder-mixing sol-gel spin coating and continuous wave CO₂ laser annealing technique to treat the specimens with at a relatively low temperature was investigated in the present work. PZT fine powders were prepared by drying and pyrolysis of sol-gel solutions and calcined at temperatures from 400 to 750°C. After fine powder-containing sol-gel solutions were spin-coated on a substrate and pyrolyzed, CO₂ laser annealing was carried out to heat treat the specimens. The results show that laser annealing provides an extremely efficient way to crystallize the materials, but an amorphous phase may also form in the case of overheating. Thicker films absorb laser energy more effectively and therefore melt at shorter periods, implying a significant volume effect. A film with thickness of 1 μm shows cracks and rough surface morphology and it was difficult to obtain acceptable electrical properties, indicating importance of controlling interfacial stress and choosing appropriate size of the mixing powders. On the other hand, a thick film of 5 μm annealed at 100 W/cm² for 15 s exhibits excellent properties (P _r = 36.1 μC/cm², E _c = 19.66 kV/cm). Films of 10 μm form a melting zone at the surface and a non-crystallized bottom layer easily at an energy density of 100 W/cm², showing poor electrical properties. Besides, porosity and electrical properties of thick films can be controlled using appropriate processing parameters, suggesting that CO₂ laser annealing of modified sol-gel films is suitable for fabricating films of low dielectric constants and high crystallinity.     

Isotope separation by a q-switched continuous discharge CO2 laser

For ¹³C isotope separation it is more economic to use a q-swiched CO₂ laser than a TEA laser. It is shown that 40 mJ pulses are needed for full use of photons. With a laser of 20 mJ, isotope selective dissociation of ¹³CHClF₂ and ³²SF₆ is demonstrated in this work.     

Direct observation of excited-state dynamics by hot UV absorption spectroscopy after IR multiphoton excitation

Fluoroethylcycloheptatriene has been irradiated by pulses from a TEA CO₂ laser. During and after the pulses, the hot UV absorption of the excited molecules was monitored. At very low gas pressures, time-resolved observation of the rate of unimolecular isomerization of the excited molecules was possible. By adding collision partners, stepwise collisional deactivation of excited molecules was also observed. By analysis of the transient spectra, the intra- and inter-molecular dynamics of the excited molecules was found to be quantitatively consistent with data from single-photon excitation experiments. The dependence of the observed dynamics on the laser fluence is demonstrated.     

Introduction of a 20 kHz Nd:YVO4 laser into a hybrid quadrupole time-of-flight mass spectrometer for MALDI-MS imaging

A commercial hybrid quadrupole time–of–flight mass spectrometer has been modified for high-speed matrix-assisted laser desorption ionisation (MALDI) imaging using a short-pulse optical technology Nd:YVO₄ laser. The laser operating in frequency-tripled mode (λ = 355 nm) is capable of delivering 1.5-ns pulses of energy at up to 8 μJ at 5–10 kHz and 3 μJ at 20 kHz. Experiments to improve beam homogeneity and reduce laser speckle by mechanical vibration of the fibre-optic laser delivery system are reported along with data from trial and tissue imaging experiments using the modified instrument. The laser appeared to yield best results for MALDI-MS imaging experiments when operating at repetition rates 5–10 kHz. Combining this with raster imaging allowed images of rat brain sections to be recorded in 37 min. Similarly, images of the distribution of peptides in “on-tissue” digest experiments from tumour tissues were recorded in 1 h and 30 min rather than the 8-h acquisition time previously used. A brief investigation of targeted protein analysis/imaging by multiple reaction monitoring experiments “on-tissue” is reported. A total of 26 transitions were recorded over a 3-s cycle time and images of abundant proteins were successfully recorded.     

Time resolved HF vibrational fluorescence from the IR photodissociation of SF6/H2 mixtures

Time resolved measurements of HF spontaneous emission, following the irradiation of SF₆/H₂ mixtures with the focused output from a CO₂ TEA laser, are reported. Our results indicate that F atoms are produced directly by the photodissociation process, and that these atoms have a recoil energy which is ≤500 cm^?1, and varies only slightly with the radiation intensity. Further, our results show a linear dependence of fluorescence intensity with laser energy, indicating that processes other than direct photodissociation may play a significant role in the ultimate fate of species excited by IR collisionless multiple photon absorption.     

Systematic line selection for online coating thickness measurements of galvanised sheet steel using LIBS

LIBS can be used as an online method of characterizing galvanized coatings on sheet steel moving through a production line. The traversing sheet steel is irradiated with a series of single laser bursts, each at a different position on the sheet steel. An ablation depth in the same range as the coating thickness (about 10 μm) is achieved by using a Nd:YAG laser at 1064 nm in collinear double-pulse mode. The coating thickness is determined from the ratio of the intensities of an iron line and a zinc line measured at a burst energy high enough to penetrate the coating with a single burst. Experiments at different burst energies were carried out to optimize the thickness resolution, and a method of systematically selecting iron and zinc lines was deduced, which is based on multivariate data analysis (MVDA) of the intensity ratios calculated for a set of 6 zinc lines and 21 iron lines. A temperature correction was applied, because the parameters of the plasma change with burst energy, and the influence of this on the thickness resolution is discussed. The ambient atmosphere present (air, Ar, N₂) as well as self-absorption of spectral lines both have an influence on the thickness resolution. At optimum conditions, a thickness measurement accuracy of better than 150 nm was obtained for a set of electrolytic galvanized sheet steels with coating thicknesses in the range 4.1–11.2 μm.     

Mechanism of alkyl halide photolysis by a pulsed CO2 tea laser

A CO₂ TEA laser has been used to photolyze dilute samples of various alkyl halides in helium. The mechanism of the high intensity infrared photolysis of these molecules involves the decomposition of molecules into molecular or radical fragments. The reaction pathway is always dissociation into the lowest thermal dissociation channel(s) of the molecule photolyzed. Products from the initial process are also photo-dissociated by the laser pulse and their decomposition pathways are similarly governed. The molecules being photolyzed are not thermally equilibrated with the bath or with each other and the molecular-specific nature of the laser excitation is demonstrated.     

Formation,densification and properties of sol–gel TiO<Subscript>2</Subscript> films prepared from triethanolamine-chelated soluble precursor powders

Amorphous, soluble powders were synthesized with triethanolamine (TEA) as chelating agent as precursors for TiO₂ sol–gel solutions. Dip coating on glass substrates and subsequent annealing yielded thin films with excellent optical properties. Furthermore as-dried films were scraped of substrates, annealed at different temperatures and characterized in order to investigate the structural changes during processing. The observations were systematically compared with previous studies on precursor powders based on acetylacetone. Results indicate that triethanolamine provides both a sufficient hydrolytical stability of the Ti-precursor during coating and an adequate plasticity of the film material throughout thermal densification. These characteristics significantly improve the practical workability of the respective process. Additionally former assumptions regarding the relationship between film properties and intermediate structural features were verified and refined.     

Laser induced dielectric breakdown studies of the reaction UF6 + H2

Laser induced dielectric breakdown (LIDB) has been documented in UF₆ at pressures ranging from 8–100 torr. A high power, line selectable TEA CO₂ laser has been used as the source to induce the dielectric breakdown (DB). Reactions of the fragmented UF₆ with H₂ have been studied at various pressure ratios. In all cases a rapid and large pressure drop and heavy deposits of suspended particulates were observed and attributed to the LIDB driven reaction 2UF₆ + H₂ → 2UF₆ + H₂ → 2UF₅ + 2HF.     

Effect of CO2 laser treatment on cotton surface

In this study, CO₂ laser was used for treating cotton fabric to create surface effects which were found to vary with laser process parameters, i.e. resolution and pixel time. The resolutions used were 40, 50 and 60 dpi while the pixel time used were 100, 110 and 120 μs. Both physical and chemical properties at the surface of fabrics treated with different combinations of resolution and pixel time were analysed by the Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy with Attenuated Total Reflection mode (FTIR-ATR), and X-ray Photoelectron Spectroscopy (XPS). SEM investigation revealed the appearance of various numbers of pores, cracks and fragments present on the fibre surface after laser treatment. FTIR-ATR spectra showed that the laser-treated cotton fabric suffered changes in chemical structure with the hydroxyl (–OH) stretching group being oxidised to carbonyl/carboxyl groups. The XPS analysis revealed a change in surface elemental composition after laser treatment. Furthermore, the wicking property of the laser-treated cotton fabrics was evaluated.     

Synthesis and properties of niobia films derived from niobium pentaethoxide

The hydrolysis of niobium pentaethoxide precursor in the presence of triethylamine (TEA) is discussed. Three precursors with TEA/Nb(OEt)₅ mole ratios of 0.25, 0.4 and 0.8 were prepared. Niobia colloids with different appearance were obtained after autoclaving the above precursors at 250°C during 12 h. The surface roughness and microstructure of niobia films prepared with the colloids by spread coating method are strongly dependent on the TEA/Nb(OEt)₅ mole ratio. At a value of 0.4 TEA/Nb(OEt)₅ mole ratio, a niobia film with large surface roughness can be achieved. It is opaque and mechanically stable and has differently ordered needle microstructure. The crystalline structure and photoelectrochemical property of niobia film with the largest surface roughness were examined. The effect of CO₂ gas bubbling, reflux and addition of 2-methoxyethanol on the hydrolysis of Nb(OEt)₅ and the nature of the Nb₂O₅ films is also discussed.     

Generation of shaped pulses for IR — laser chemistry

10 μm laser pulses with different temporal shape and a duration between 2 and 80 ns were produced in a TEA-CO₂ laser by the technique of a saturable absorber in an intracavity cell. At low absorber gas pressures (≤ 400 Pa) single longitudinal mode operation of the laser was obtained at a great number of CO₂ laser lines with 9 different selective absorbers. Stable mode locked operation has been achieved over the entire range of the CO₂ laser leading to pulses of 2 ns duration. Single peaks of the mode locked pulse train were sliced out by a fast CdTe electro-optical switch and amplified in a second CO₂ laser up to an energy of 2 J corresponding to an intensity of 1 GW. The spectral properties of the useful absorbers are presented systematically. As an application we show some quantitative results on the nonlinear intensity dependence of the IR-laser chemical reaction CF3B→^nhvCF₃ + Br in the transition range from case C to case B.     

A new approach to determine soil microbial biomass by calorimetry

A method to determine soil microbial biomass (SMB) by isothermal calorimetry is reported. Soil samples ranging in pH from 6.2 to 9.4 and different textures were used to develop the method. Soil at 60% of its field capacity humidity was amended with a previously determined amount of glucose as to give the maximal response of CO₂ evolution. Then, an aliquot was weighed in the calorimeter ampoule and specific thermal power (p)–time (t) curves were obtained at 25 °C. After 1–2 h, a vial containing a 0.5 M NaOH solution was introduced to determine the specific thermal power due to CO₂ evolution, pCO₂ during 1–2 h. Then, the vial was removed and the experiment continued for 1–2 h. Specific thermal power due to CO₂ evolution was converted to rate (CO₂-C/mm³ g⁻¹ h⁻¹) by using the heat of reaction of CO₂ with NaOH and the molar volume. This value was further converted into SMB/μg g⁻¹ by using a conversion factor of 32.4. A guide to perform the calculations is given. Values of log SMB were linearly related with values of log p giving a similar relation to a previously reported where SMB was determined by conventional methods.     

Electrochemical etching of silicon carbide

Both n- and p-type SiC of different doping levels were electrochemically etched by HF. The etch rate (up to 1.5 μm/min) and the surface morphology of p-type 6H-SiC were sensitive to the applied voltage and the HF concentration. The electrochemical valence of 6.3 ± 0.5 elementary charge per SiC molecule was determined. At p-n junctions (p-type layer on a n-type 6H-SiC substrate) a selective etching of the p-type epilayer could be achieved. For a planar 6H-4H polytype junction (n-type, both polytypes with equal doping concentrations) the 4H region was selectively etched under UV illumination. Thus polytype junctions could be marked by electrochemical etching. With HCl instead of HF no etching of SiC occurs, but a SiO₂ layer (thickness up to 8 μm) is formed by anodic oxidation. Received: 29 October 1998 / Accepted: 27 January 1999     

Effect of internal diffusion on preferential CO oxidation in a hydrogen-rich mixture on a copper-cerium oxide catalyst in a microchannel reactor

The effect of internal diffusion on preferential CO oxidation in a hydrogen-rich mixture on a copper-cerium catalyst in a microchannel reactor was estimated. It was found that the internal effectiveness factor η_CO > 0.8 was reached at a catalytic coating thickness of ∼30 μm.     

Quantification of sodium contaminant on steel surfaces using pulse CO2 laser-induced breakdown spectroscopy

Corrosion is one of the main reasons for in-core accidents in liquid sodium-cooled fast reactors, especially accidents due to fuel cladding pipe damage. It is urgently required to investigate what kind of compound is produced as a corrosion product after the interaction between stainless steel and sodium in fast breeder reactors (FBR). In this work, the identification and quantification of sodium contaminant on steel surfaces has been conducted using laser-induced breakdown spectroscopy utilizing the specific characteristics of a pulse transversely excited atmospheric CO₂ laser. Experimentally, a pulse TEA CO₂ laser (Shibuya, 10.64 μm, 200 ns) was directed and bombarded onto the sodium contaminant deposited on the surface of stainless steel. An excellent emission spectrum of sodium from the contaminant was obtained without any disturbance from analytical lines from the steel itself. A quantification of sodium contaminant on the steel surface has been successfully made by a linear calibration curve obtained from steel containing various concentrations of sodium. The limit of detection of sodium on the metal surface was estimated to be 0.5 mg/kg. Also, a comparative sodium analysis study was qualitatively made by using LIBS utilizing a pulse Nd:YAG laser. The results demonstrate that the present technique of TEA CO₂ LIBS is far superior to the case of Nd:YAG LIBS, as proven by an excellent emission spectrum of sodium with optimum intensity, and low noise and background emission.     

A comparative evaluation on the anodic behavior of Cu and Ag electrodes in non-aqueous fluoride and fluoroborate media

The voltammetric responses of copper and silver had been extensively studied and compared in a variety of non-aqueous solvents such as acetonitrile (AN), propylene carbonate (PC) and sulfolane containing two different supporting electrolytes namely triethylaminetrishydrogen fluoride (TEA.3HF) and tetrabutylammonium tetrafluoroborate (TBABF₄). The dissolution rate and surface transformation on the electrode surfaces as a result of anodic polarization was investigated using atomic absorption spectroscopy (AAS) and scanning electron microscopy (SEM), respectively. In solvent-free TEA.3HF medium, the copper electrode shows high charge recovery ratio (Q _c/Q _a), and the difference between the initial anodic and cathodic potentials, obtained at a current density of 2 mA cm⁻², is around 0.11 V, suggesting that in this medium, Cu can certainly serve as reference electrode. On the other hand, on Ag electrode, substantial dissolution was observed leading to very high anodic (Q _a) and cathodic (Q _c) charges, and the surface morphology after the cyclic polarization results in roughened surface with large pores. The effects of incorporating AN and water as additives in TEA.3HF on the solubility and stability of these metal fluoride films are also reported. The dissolution pattern and film formation behavior of these two metals in the different solvents containing fluoride and fluoroborate ionic species have several qualitative similarities, as noted from cyclic voltammetry responses and SEM morphology. Anodic dissolution and precipitation process for both Cu and Ag depends significantly on the nature of supporting electrolytes as well as solvents. In AN containing 0.1 M TEA.3HF, the dissolution of Cu and Ag electrodes was very high. Fluoride salts of Cu show lesser solubility than Ag in those solvents, while fluoroborate salts exhibit the reverse trend. The AAS data suggest that for a particular salt, which may be either fluoride or fluoroborate of Cu and Ag, the relative solubility decreases in the order AN > PC > sulfolane.