Laser-assisted Methods Research Articles

Nanofabrication with Pulsed Lasers

An overview of pulsed laser-assisted methods for nanofabrication, which are currently developed in our Institute (LP3), is presented. The methods compass a variety of possibilities for material nanostructuring offered by laser–matter interactions and imply either the nanostructuring of the laser-illuminated surface itself, as in cases of direct laser ablation or laser plasma-assisted treatment of semiconductors to form light-absorbing and light-emitting nano-architectures, as well as periodic nanoarrays, or laser-assisted production of nanoclusters and their controlled growth in gaseous or liquid medium to form nanostructured films or colloidal nanoparticles. Nanomaterials synthesized by laser-assisted methods have a variety of unique properties, not reproducible by any other route, and are of importance for photovoltaics, optoelectronics, biological sensing, imaging and therapeutics.

C-Port Flex-A–assisted automated anastomosis for high-flow extracranial-intracranial bypass surgery in patients with symptomatic carotid artery occlusion: a feasibility study

Preliminary experience with the C-Port Flex-A Anastomosis System (Cardica, Inc.) to enable rapid automated anastomosis has been reported in coronary artery bypass surgery. The goal of the current study was to define the feasibility and safety of this method for high-flow extracranial-intracranial (EC-IC) bypass surgery in a clinical series. In a prospective study design, patients with symptomatic carotid artery (CA) occlusion were selected for C-Port-assisted high-flow EC-IC bypass surgery if they met the following criteria: 1) transient or moderate permanent symptoms of focal ischemia; 2) CA occlusion; 3) hemodynamic instability; and 4) had provided informed consent. Bypasses were done using a radial artery graft that was proximally anastomosed to the superficial temporal artery trunk, the cervical external, or common CA. All distal cerebral anastomoses were performed on M2 branches using the C-Port Flex-A system. Within 6 months, 10 patients were enrolled in the study. The distal automated anastomosis could be accomplished in all patients; the median temporary occlusion time was 16.6+/-3.4 minutes. Intraoperative digital subtraction angiography (DSA) confirmed good bypass function in 9 patients, and in 1 the anastomosis was classified as fair. There was 1 major perioperative complication that consisted of the creation of a pseudoaneurysm due to a hardware problem. In all but 1 case the bypass was shown to be patent on DSA after 7 days; furthermore, in 1 patient a late occlusion developed due to vasospasm after a sylvian hemorrhage. One-week follow-up DSA revealed transient asymptomatic extracranial spasm of the donor artery and the radial artery graft in 1 case. Two patients developed a limited zone of infarction on CT scanning during the follow-up course. In patients with symptomatic CA occlusion, C-Port Flex-A-assisted high-flow EC-IC bypass surgery is a technically feasible procedure. The system needs further modification to achieve a faster and safer anastomosis to enable a conclusive comparison with standard and laser-assisted methods for high-flow bypass surgery.

Laser-assisted combinatorial methods for rapid design of wear resistant iron alloys

Combinatorial design methods require the creation of large libraries of materials with varying composition. These libraries are screened for the desired properties, using rapid micro characterization techniques in order to find the most promising compositions for scale-up and final evaluation. These methods are particularly adequate for the systematic scrutiny of complex systems, aiming to find new materials with outstanding properties for particular applications, but they can also be used in the investigation of structure–properties relationships, alloying behaviour studies and phase diagram determination. Up till now, the application of combinatorial methods to the design of tribological materials has been constrained because, since material library preparation is usually carried out by thin film deposition techniques, the sample size is too small for microstructure-dependent properties to be reliably assessed, and no suitable screening tests are available. In the present paper a novel approach to the combinatorial design of abrasion resistant materials, where laser cladding with computer controlled variable powder feed rate is used to synthesize the material libraries and screening is based on microscratching tests is demonstrated. This method was applied to the optimization of the composition of alloys of the Fe–Cr–C system for abrasive wear resistance.

Ultrafast laser based “green” synthesis of non-toxic nanoparticles in aqueous solutions

Inorganic nanoparticles offer novel promising properties for biological sensing and imaging, as well as in therapeutics. However, these applications are often complicated by the possible toxicity of conventional nanomaterials, arising as a result of inadequate purification procedures of nanoparticles obtained via synthetic pathways using toxic or non-biocompatible substances. We review novel femtosecond laser-assisted methods, which enable the preparation of metal nanomaterials in clean, biologically friendly aqueous environment (“green” synthesis) and thus completely solve the toxicity problem. The proposed methods, including laser ablation and fragmentation, make possible the production of stable metal colloids of extremely small size (∼2 nm) with a low coefficient of variation (15–25%). Those nanoparticles exhibit unique surface chemistry and can be used for bio-imaging, cancer treatment and nanoparticle-enhanced Raman spectroscopy.

Fast steel-cleanness characterization by means of laser-assisted plasma spectrometric methods

Laser-assisted plasma spectrometry is a palette of analytical techniques (L-OES, LA-ICP-MS) capable of fast spatially-resolved elemental analysis in the micrometer range. For fast estimation of the occurrence in steel samples of non-metallic inclusions, which degrade the material's technical properties, simultaneous OES detection and sequential ICP-MS detection were compared. Histograms were obtained for the intensity distribution of the acquired signals (laser pulse statistics). The skewness coefficient of the histograms for Al (indicator of non-metallic inclusions) was found to be clearly dependent on the fraction of non-metallic inclusions in the case of scanning L-OES. For LA-ICP-MS less clear dependence was observed, which was influenced by the acquisition characteristics. In fact, less measurement throughput limited for LA-ICP-MS the counting statistics to an extent that overrides the benefit of higher detection power as compared to L-OES.

Microgenomics: Identification of new expression profiles via small and single-cell sample analyses.

Since the sequencing of the human genome has been finished, microgenomics has been booming, employing highly sophisticated, high-throughput platforms. But these mainly chip-based methods can only generate biologically relevant data if the samples investigated consist of homogeneous cell populations, in which no unwanted cells of different specificity and/or developmental stage obscure the results. Different sampling methods have been routinely applied to overcome the problem presented by heterogeneous samples, e.g., global surveys, cell cultures, and microdissection. Various methods of laser-assisted microdissection, employing either positive or negative selection of tissue areas or even single cells, are available. These laser-assisted microdissection methods allow for fast and precise procurement of extremely small samples. Through subsequent application of recently developed methods of linear mRNA amplification in a pool of isolated total RNA, it has now become possible to perform complex high-throughput RNA expression profiling by microdissecting and processing even single-cell samples. Studies using the tools and methods of microgenomics have shed light on how those new approaches will eventually aid in the development of a new generation of diagnostics, e.g., leading to new patient-specific drugs tailored to the requirements assessed by assaying only a few biopsy cells.

Measurement of Tritium on Surfaces

The quantitative significance of surface-contamination levels determined by different methods was assessed by carrying out measurements using the wipe-assay method and a commercial surface-contamination monitor (Whitlock Vacuum Scintillation Counter (VSC)). The results were compared to the total tritium desorbed from the sample. Simple correlations between these measurements were not found. Laser-assisted desorption methods are currently being investigated to measure total tritium on surfaces. Preliminary results obtained with a Nd:YAG laser (532 nm) are reported. Only water vapor and CO2 were found in the gas released under laser irradiation by mass spectroscopy. Approximately 65–95% of the surface tritium could be desorbed from all metal samples investigated.

Laser-assisted methods for deposition, diagnostics and modification of optical thin films

A cw CO 2 laser with a power of 200 W has been used to evaporate thin multilayer films of HfO 2SiO 2 and ZrO 2SiO 2. Higher values of laser damage resistance were found in comparison to similar layers deposited by electron beam evaporation. We also used the laser beam as a diagnostic tool to characterize optical thin films by absorption and laser damage resistance. We investigated the increase in resistance to laser damage of optical layers by laser irradiation of the substrates under vacuum immediately before the coating process. Moreover, we investigated the optical properties of oxide films after uv-laser irradiation delivered from a KrF excimer laser.

Thin-film ferrite materials for microwave and millimeter wave integrated circuits (invited) (abstract)

Conventional microwave and millimeter wave systems use ferrites in a variety of components. In general, each application imposes specific requirements on the magnetic properties of the ferrite. In addition, some devices require the ferrite to be in single-crystal form. In order to produce ferrite components that are compatible with microwave and millimeter wave integrated circuits, additional constraints are imposed on the ferrite, especially if fully monolithic integration is required. In general, the ferrites must be prepared in thin film form on substrates that are chosen primarily to meet requirements other than compatibility with the ferrite film. Moreover, as is well known, the magnetic properties of ferrites are quite sensitive to the conditions that exist during their preparation. Thus, ferrites prepared by thin film deposition techniques may have properties different from bulk ferrites. This talk will review progress on methods for preparing polycrystalline ferrite films by techniques such as sputter deposition and laser-assisted deposition and methods for preparing single-crystal ferrite films in forms that may be compatible with epitaxial deposition of compound semiconductors.