Temporal evolution of laser-ablated Co ions probed by time-of-flight mass spectrometry

A pulsed-field time-of-flight mass spectrometric (TOFMS) technique was used to investigate the expansion dynamics of the ionic species ejected from the visible (λ=532 nm) laser ablation of cobalt target at low laser fluence less than 1 J/cm². The temporal evolution of Co⁺ ions was studied by varying the delay time of the ion repelling pulse with respect to the laser irradiation, which provides significant information on the ablated plume characterization. The obtained TOF mass spectra were well fitted by shifted Maxwell–Boltzmann distributions on a stream velocity, commonly used to describe the measured velocity distributions. The TOF distribution of Co⁺ ions showed a bimodal distribution with fast and slow velocities. These velocities show a decreasing tendency with delay time, which is attributed to the gas collisions between the plume ejecta and to the related gas dynamics. The present results suggest that the in situ measurements of the most probable velocity of ablated ions along the normal to the solid target can be accomplished by the simple technique of a laser ablation/TOFMS.     

激光剥蚀-电感耦合等离子体质谱测定植物样品中的元素

采用193 nm准分子激光剥蚀-电感耦合等离子体质谱(LA-ICP-MS)对标准植物粉末样品(GBW07602-GBW07603灌木枝叶、GBW07604杨树叶、GBW07605茶叶、GBW08514烟草)中13种元素(Li,B,Na,Mg,Al,K,Ca,Cr,Mn,Fe,Ni,Cu,Ba)进行定量测试.向植物粉末样...     

应用激光质谱法选择探测一氧化碳

此文解决了激光质谱法中从含同质量数的N2分子的混合气体中选择CO分子这一问题,由于用紫外266nm激光不能从含N2分子的混合气体中选择CO分子,因此采用了可见激光来探测,发现用可见激光430～435nm的激光能成功地将CO分子选择探测出来。此外还着重分析了在可见波段和266nm激光下产生CO+离子的机理：在可见光波段443.55nm所对应的共振峰是CO分子吸收3光子的激光能量与A1Π态的振动量子数为2的振动态共振产生的;434.3nm所对应的共振峰是CO分子吸收3光子的激光能量与A1Π态的振动量子数为3的振动态共振产生的;CO分子吸收两光子的266nm激光能量与A1Π态第7振动态的某一高转动态相共振,处于该振动态的CO分子再继续吸收一个光子的266nm激光的能量至其电离态电离产生CO+离子。     

Efficient fabrication of substrates for surface-assisted laser desorption/ionization mass spectrometry using laser ablation in liquids

Substrates for the surface-assisted laser desorption ionization (SALDI) technique were prepared using electrophoresis of gold nanoparticles produced by laser ablation in liquids. Throughout the preparation, no supplemental reagent was added for the stabilization and deposition of nanoparticles. Nanoparticles were deposited more uniformly using the electrophoresis technique than using dropping of the solution. Results demonstrated that the higher uniformity of the deposition of nanoparticles improved the reproducibility of SALDI measurements. Furthermore, the thickness of the deposited nanoparticles influences the SALDI efficiency.     

凝胶电泳与激光剥蚀-电感耦合等离子体质谱联用测定蛋白质中微量元素的应用进展

介绍了凝胶电泳(GE)和激光剥蚀-电感耦合等离子体质谱(LA-ICP-MS)联用测定蛋白质中微量元素的方法,对蛋白质分离、凝胶处理,包括染色及干燥,和检测过程中的定量校正等技术问题做了详述,并综述了LA-ICP-MS在硒蛋白、磷酸化蛋白及金属蛋白分析中的应用,指出了这种方法在蛋白质中微量元素检测中存在的问题和发展方向。     

Preparation of silicon oxycarbide films by laser ablation of SiO/3C-SiC multicomponent targets

Amorphous silicon oxycarbide (SiOC) films were prepared on Si (1 0 0) substrates by laser ablation at 773 K using mixed targets with different ratios of SiO to 3C-SiC. The structure and composition of the as-deposited films as a function of target content were investigated. With increasing the SiO content in the targets, the contents of Si-C and Si-O-C bonds decreased while that of Si-O bond increased. The mixing ratio of the targets had a dominant effect on the film composition and the stoichiometry of silicon oxycarbide films could be controlled by varying the mixing ratio of the targets.     

强激光烧蚀平面靶的实验研究

此文叙述了采用晶体谱仪和X射线条纹相机等探测器测量平面靶强激光烧蚀参数的方法 ,给出了铝平面靶和碳氢平面靶的质量烧蚀速率和烧蚀压。实验结果与收集到的国外数据进行了比较 ,二者在误差范围内一致。同时探索了金平面靶强激光烧蚀参数的实验研究方法。     

Characterization of laser ablation plasmas by laser beam deflection

Laser probe beam and multiple-pass deflection techniques were used for real time and in situ monitoring of laser ablation plasma plumes in the mTorr pressure regime. Intensity and transit time of shock wave fronts were studied as functions of focal lens position, laser energy and pressure. The velocity of the shock wave was determined to be up to 30 km s⁻¹ for a pressure of 40 mTorr and to drop below 4 km s⁻¹ at 1 Torr. For transparent targets rear-side shock wave velocity was on to be slower than the corresponding front one. This method promises a reliable diagnostic tool for pulsed laser deposition processing allowing an increase in the quality of coating technologies.     

Formation of periodic structures by laser ablation of metals in liquids

Experimental results are presented on ablation of metals (W, Cu, brass and bronze) in a liquid environment (e.g., ethanol or water) by irradiation with either a pulsed copper vapor laser (0.51 μm) or a pulsed Nd:YAG laser (1.06 μm). The target material is ejected into surrounding liquid in the form of nanoparticles. In a certain range of laser parameters (fluence and number of laser shots) the surface of the solid target is composed of micro-cones having a regular structure. The distance between neighboring micro-cones in the structure depends on the laser spot size. The structures allow the observation of up-conversion of the laser frequency due to generation of the second harmonics in the eye retina.     

Surface ablation of lithium tantalate by femtosecond laser

We report measurements of the laser induced breakdown threshold in lithium tantalate with different number of pulses delivered from a chirped pulse amplification Ti: sapphire system. The threshold fluences were determined from the relation between the diameter D² of the ablated area and the laser fluence F₀. The threshold of lithium tantalite under single-shot is found to be 1.84 J/cm², and the avalanche rate was determined to be 1.01 cm²/J by calculation. We found that avalanche dominates the ablation process, while photoionization serves as a free electron provider.     

Uranium passivation by C implantation: A photoemission and secondary ion mass spectrometry study

Implantation of 33 keV C⁺ ions into polycrystalline U²³⁸ with a dose of 4.3 × 10¹⁷ cm⁻² produces a physically and chemically modified surface layer that prevents further air oxidation and corrosion. X-ray photoelectron spectroscopy and secondary ion mass spectrometry were used to investigate the surface chemistry and electronic structure of this C⁺ ion implanted polycrystalline uranium and a non-implanted region of the sample, both regions exposed to air for more than a year. In addition, scanning electron microscopy was used to examine and compare the surface morphology of the two regions. The U 4f, O 1s and C 1s core-level and valence band spectra clearly indicate carbide formation in the modified surface layer. The time-of-flight secondary ion mass spectrometry depth profiling results reveal an oxy-carbide surface layer over an approximately 200 nm thick UC layer with little or no residual oxidation at the carbide layer/U metal transitional interface.     

Real time NDE of laser shock processing with time-of-flight of laser induced plasma shock wave in air by acoustic emission sensor

Acoustic emission sensor is used to research the time-of-flight of the shock wave induced by laser-plasma in air for real time nondestructive evaluation (NDE) of laser shock processing. The time-of-flight of the shock wave propagating from the source to the sensor declines nonlinearly and similarly at the different distances for different laser energies. The velocity of the shock wave at the distance of 30 mm increases faster than that of the distance of 35 mm. The relationship between the laser energy and the distance is almost linearly when the signal with distortion is measured by acoustic emission sensor. Finally, Taylor solution is used to analyze the experimental results, and the empirical formula between the energy of the shock wave and the laser energy is established, which will provide a theoretical basis for real time NDE of laser shock processing.     

Preparation of polyynes by laser ablation of graphite in aqueous media

Polyynes were prepared by liquid-phase laser ablation of a graphite target at 1064 nm and identified by analyzing UV absorption spectra in deionized water and various aqueous solutions. We observed that major UV absorption peaks coincide with the electronic transitions corresponding to linear hydrogen-capped polyynes (C_nH₂: n = 6, 8, 10). The peak intensities increased when polyynes were produced by irradiating the target immersed in acidic media, while those were relatively weak in basic media. This leads us to conclude that OH⁻ or H⁺ ions play a certain role in the formation of polyynes.     

Pulsed laser ablation of pepsin on an inorganic substrate

Pressed pepsin pellets used as targets were ablated with the pulses of the Nd-YAG laser. The activity of the pepsin thin layer, deposited on a glass substrate, was successfully detected by analyzing the proteolytic degradation areas on the polyacrylamide gel (PA-gel) copolymerized with albumin from the hen egg white (ovalbumin), used as an enzymatic substrate.     

Investigation of metal nanoparticles produced by laser ablation and their catalytic activity

Polydiphenylsilylenemethylene (PDPhSM) thin films, which are difficult to fabricate by conventional methods because of their insolubility and high melting point, have been synthesized by using laser-ablated metal nanoparticles for the thermal ring-opening polymerization of 1,1,3,3-tetraphenyl-1,3-disilacyclobutane (TPDC) in this paper. TPDC was first evaporated on silicon substrates and then exposed to metal (Pt, Cu and Ag) nanoparticles deposition by laser ablation prior to heat treatment. The catalytic activity of Pt, Cu and Ag nanoparticles has been studied. The results showed that the mean diameter of Pt nanoparticles was the smallest, Cu nanoparticles the moderate and Ag nanoparticles the biggest, while the polymerization efficiency for Pt nanoparticles was the highest, Cu nanoparticles the moderate and Ag nanoparticles the lowest. In addition, the penetration behaviours of Pt, Cu and Ag nanoparticles into the TPDC monomer films during laser ablation were different due to the particle size or the chemical interaction between metal nanoparticles and TPDC molecules.     

Carbon nanocrystals produced by pulsed laser ablation of carbon

Plasma laser ablation experiments were performed irradiating glassy-carbon targets placed in vacuum through a pulsed Nd:YAG laser operating at the second harmonic (532 nm), 9 ns pulse width and 10⁹ W/cm² density power.

Thin films of ablated carbon were deposited on silicon oxide substrates placed at different distances and angles with respect to the target.

The analysis of the deposited material was carried out by using surface profiler, scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and Raman spectroscopy.

Results show the evidence of carbon nanocrystals and nanostructures with dimension of the order of 100 nm deposited on the substrates together with a large amount of amorphous phase. The spectroscopic investigations and the SEM images indicate the formation of nanodiamond seeds as a nucleation process induced on the substrate surface. Nanostructures were investigated as a function of the laser intensity and angle distribution. Experimental results were compared with the literature data coming from nanodiamonds growth with different techniques.

Experiments performed at Instituto Nazionale di Fisica Nucleare-Laboratori Nazionali del Sud (INFN-LNS) of Catania (Italy) and data analysis conducted at Dipartimento di Fisica and DFMTA of the Università of Messina (Italy), CNR-ITIS of Messina and ST-Microelectronics of Catania will be presented and discussed.     

Laser ablation mechanism and plume dynamics of polyarylsulfone films studied by laser ionization time-of-flight mass spectrometry

The KrF laser ablation of polyarylsulfone (PAS) was investigated for fluences between 90 and 200 mJ/cm². Neutral fragments were probed using laser post ionization (193 nm) time-of-flight (TOF) mass spectrometry. Decomposition of PAS was found to occur mainly through scission of C-S and C-O bonds as well as via decomposition of the phenylene rings in the chain. The dependencies of both the flight velocities and the Knudsen layer temperature of the fragments on fluence suggest that PAS ablation is a photothermal process. In contrast, the high average translational energies (up to a few tens of eV) indicate the existence of a non-thermal component in the process. In terms of the plume dynamics, the fitting of the arrival profiles of the fragments with a shifted Maxwell-Boltzmann distribution over the full fluence range indicates the existence of a collision during the adiabatic expansion process.     

Cluster formation in UV laser ablation plumes of ZnSe and ZnO studied by time-of-flight mass spectrometry

The composition of nitrogen laser (wavelength 337 nm, pulse width 3 ns) induced ablation plumes from ZnSe and ZnO targets was studied at different laser fluences using a time-of-flight mass spectrometer. In the case of ZnSe, abundant ion signals corresponding to Se and ZnSe clusters, some of which were Se-rich, were detected with fluence-dependent distributions. At a laser fluence of 1250 J m^-2, clusters with elevated intensity were observed at sizes of 6, 13, 19, 23 and 33 ZnSe molecules (magic numbers), which match quite well with the earlier observation by others of magic numbers of chemically similar ZnS produced by a conventional vaporization and quenching scheme. In the case of ZnO, we detected the presence of atomic Zn and molecular species of ZnO, as well as a series of (ZnO)_n-type clusters with fluence-dependent distributions. Unlike the case of ZnSe, no magic numbers were observed for ZnO. PACS 61.46.+w; 82.80.Rt; 42.62.-b; 81.16.Mk     

Micromachining of a thin film by laser ablation using femtosecond laser with masks

A gold thin film was machined by laser ablation using a femtosecond laser with mask patterns in the shape of lines and numbers. The patterns were successfully transferred with proper focusing and laser fluence. The optimal femtosecond laser fluence to keep the line width was about 5.2 mJ/cm² on the mask, and 99 mJ/cm² on the film. The processing resolution was 13 μm, and the narrowest line width was about 4 μm.     

Detection of explosive-related compounds by laser photoionization time-of-flight mass spectrometry

We report studies using laser photoionization and time-of-flight mass spectrometry to detect several explosive-related compounds (ERCs). The ultimate goal of this work is the detection of buried land mines through their chemical signatures. Resonantly enhanced multiphoton ionization using jet expansion cooling, with a nanosecond pulse laser, results in complete photofragmentation of the parent ERC and appearance only of the NO⁺ ion, which forms all of the detected signal. This will also occur for compounds naturally occurring in the environment, such as NO₂ or peroxyacetylnitrate, rendering too many false alarms for this approach to be viable. Therefore, two other techniques were evaluated. Single-photon ionization with nanosecond pulses in the vacuum ultraviolet is shown to produce only the parent ion, and is probably the most suitable choice. For 2,4-dinitrobenzene we find a limit of detection of about 40 ppb, for a signal to noise ratio of 3. This may be sufficient for land-mine detection, but improvement is likely with future work. Nonresonant multiphoton ionization in the ultraviolet with a femtosecond laser produces fragmentation but retains some parent ERC ion signal. The limit of detection is similar to that of single-photon ionization but it is harder to implement with lasers now commercially available. Future directions are outlined. PACS 07.07.Df; 33.80.Rv; 82.80.Ms; 82.80.Rt