Direct Laser Processing Research Articles

Laser surface structuring of diamond-like carbon films for tribology

The paper overviews experimental findings of the direct laser processing and surface microstructuring (texturing) of various diamond-like carbon films (a-C:H, ta-C, DLN, metal-doped DLN), aimed at improvements of their tribological and nanotribological properties. The nanosecond UV and femtosecond IR/visible pulsed lasers were applied in microprocessing of the films, focusing on high precision surface structuring with fs-laser pulses. The studies were concentrated on the following tasks: (i) surface graphitization in laser microstructuring of the films under different irradiation conditions, (ii) lubricated friction performance of DLN films micropatterned with UV ns and visible fs pulsed lasers, and (iii) nanoscale friction of laser-structured DLN and metal-doped DLN films examined with contact-mode atomic force microscopy. The important findings of our studies are related to fabrication of highly-precise microgroove/microcrater patterns on DLN films and improvements of frictional properties of the laser-structured films at the macro, micro and nanoscale. The surface microstructures improved the film properties under oil-lubricated sliding in dependence on their geometrical parameters (size, depth, period) and ambient temperature. The nanoscale friction behavior of laser-structured films was shown to be controlled by the surface graphitization, nanoscale roughness, capillary forces and wear of AFM tips during friction force imaging.

Effects of TiS2 on Inhibiting Candida albicans Biofilm Formation and Its Compatibility with Human Gingival Fibroblasts in Titanium Implants.

Titanium is widely used in medical devices, such as dental and orthopedic implants, due to its excellent mechanical properties, low toxicity, and biocompatibility. However, the titanium surface has the risk of microbial biofilm formation, which results in infections from species such as Candida albicans (C. albicans). This kind of biofilm prevents antifungal therapy and complicates the treatment of infectious diseases associated with implanted devices. It is critical to developing a feasible surface to decrease microbial growth while not interfering with the growth of the host cells. This study reports the influence of titanium surface modification to titanium disulfide (TiS2) on inhibiting C. albicans biofilm formation while allowing the attachment of human gingival fibroblasts (HGFs) on their surface. The surface of titanium parts is directly converted to structured titanium and TiS2 using direct laser processing and crystal growth methods. C. albicans adhesion and colonization are then investigated on these surfaces by the colony counting assay and reactive oxygen species (ROS) assay, using 2',7'-dichlorofluorescin diacetate (DCFH-DA) and microscopy images. Also, the viability and adhesion of HGFs on these surfaces are investigated to show their adhesion and biocompatibility. Titanium samples with the TiS2 surface show both C. albicans biofilm inhibition and HGF attachment. This study provides insight into designing and manufacturing titanium biomedical implants.

Tunable laser induced periodic surface structures in Ge2Sb2Te5 thin films

Planar photonic structures, such as gratings and metasurfaces, are routinely used for beam steering, waveguide coupling, and light localization. However, conventional fabrication techniques that involve lithography are demanding in terms of time and cost. Much cheaper and simpler methods for surface patterning and formation of periodic surface structures are enabled by direct laser processing. Here, we demonstrate low-cost rapid fabrication of high-quality phase gratings based on the formation of laser induced periodic surface structures (LIPSS, or ripples) in Ge2Sb2Te5 (GST) thin films. Due to unique phase change properties of GST, the structures demonstrate strong modulation of refractive index with period controlled by the wavelength of laser irradiation. We study the formation of phase change LIPSS in a broad range of excitation wavelengths and observe transition between regimes with different orientations of generated ripples with respect to laser polarization.

Theoretical and experimental study on hybrid laser and shaped tube electrochemical machining (Laser-STEM) process

Laser and electrochemical machining (LECM) is extensively researched due to its high efficiency and good surface quality. Laser and shaped tube electrochemical machining (Laser-STEM) is a novel hybrid process, in which both the laser beam and electrolyte jet are guided to the machining zone through the inner hole of a specially designed tubular electrode. This process could be utilized to process small holes with a larger depth and a higher controlled precision, compared with the existing LECM processes. In Laser-STEM, the direct laser processing and the enhanced electrochemical machining (ECM) rate allow the high-efficiency material removal. ECM that is synchronously occurred in the side gap guarantees the high surface quality of the processed small holes. Through the total internal reflection of the laser beam in the inner hole of the tubular electrode, the laser energy is transmitted to the machining zone in high efficiency, and the laser energy has been confined in the inner hole exit area. Theoretical and experimental results showed that the electric current density in the machining zone for ECM could be increased by the assistance of a laser, which enhances the material removal rate of ECM. With the self-developed experimental setup, microcavities with a depth of 2 mm and small holes with a depth of 5 mm have been fabricated. A comparison of the effects of various machining parameters shows that the machining precision and material removal rate were improved by 60.7% and 122.7%, respectively. Both the machining precision and the material removal rate could be increased by using higher laser power. The mechanisms of machining precision improvement by adopting laser to STEM were explored, considering the generation of the passivating layer in the machining zone. Laser-STEM was also adopted to fabricating three-dimensional structures such as groove and channel.

Optical Fiber Sensors by Direct Laser Processing: A Review.

The consolidation of laser micro/nano processing technologies has led to a continuous increase in the complexity of optical fiber sensors. This new avenue offers novel possibilities for advanced sensing in a wide set of application sectors and, especially in the industrial and medical fields. In this review, the most important transducing structures carried out by laser processing in optical fiber are shown. The work covers different types of fiber Bragg gratings with an emphasis in the direct-write technique and their most interesting inscription configurations. Along with gratings, cladding waveguide structures in optical fibers have reached notable importance in the development of new optical fiber transducers. That is why a detailed study is made of the different laser inscription configurations that can be adopted, as well as their current applications. Microcavities manufactured in optical fibers can be used as both optical transducer and hybrid structure to reach advanced soft-matter optical sensing approaches based on optofluidic concepts. These in-fiber cavities manufactured by femtosecond laser irradiation followed by chemical etching are promising tools for biophotonic devices. Finally, the enhanced Rayleigh backscattering fibers by femtosecond laser dots inscription are also discussed, as a consequence of the new sensing possibilities they enable.

One-Step Fabrication and Functionalization of Nanostructured Silicon Surfaces for Advanced Sensing Applications

Direct laser processing of various materials with nano- and femtosecond (fs) laser pulses is known to be a facile and inexpensive technology for fabrication of various surface morphologies. Since ultrafast deposition of the laser energy to target material typically creates unique experimental conditions with extremely high pressure and temperature, we hypothesized that carrying out this process in anhydrous non-oxidizing environment containing functionalizing agent (fluorophore with vinyl functional group) will allow one-step fabrication and subsequent functionalization of the surface of high-n material. In this paper, we demonstrate successful implementation of this idea by fabricating high-spatial-frequency laser-induced periodic surface structures (LIPSS) via direct fs-pulse ablation of bulk crystalline Si wafer immersed in solution of N-vinylcarbazole in toluene. Laser processing with linearly polarized fs-laser pulses was found to produce LIPSS with a characteristic period around 100 nm functionalized with N-vinylcarbazole molecules via photo-activated hydrosililation reaction. The unique LIPSS with hierarchical roughness and remarkable light trapping performance functionalized with sensory fluorophore show high sensitivity due to implementation of surface enhanced fluorescence effect. By using N-vinylcarbazole as functionalizing agent we demonstrate one-step fabrication of high-performance sensor for detecting nitrobenzene in water with a detection limit of 40 nM.

Direct Laser Processing of Two-Scale Periodic Structures for Superhydrophobic Surfaces Using a Nanosecond Pulsed Laser

Hierarchical structures are promising geometries for superhydrophobic surfaces, however a processing method with a single laser light source that is capable of both one-pass and rapid processing has not been established. The purpose of this study was to propose a concept of direct laser processing of two-scale periodic structures exhibiting superhydrophobicity. We hypothesized that the molten material that occurs due to the expanding plasma and that is squeezed around the micro-holes could play an active role in the processing of two-scale periodic structures. Percussion drilling using a nanosecond pulsed laser (532 nm wavelength) was performed on a steel surface. Twenty four different test-pieces were prepared using pitch (16–120 μm), number of repetition shots (1–120), and fluence (2.49–20 J/cm2), as the parameters. As the results, micro-holes with bank-shaped outer rims were formed. The maximum apparent contact angle was 161.4° and the contact angle hysteresis was 4.2° for a pitch of 80 μm and 20 repetition shots. The calculated results for the apparent contact angles were consistent with the measured results. Finally, an equation for estimating the processing rate was proposed. We demonstrated that this direct processing method can achieve a maximum processing rate of 823 mm2/min.

Effect of Laser Wavelength on AZO Surface Texturing by Direct Laser Processing / Patterning for Thin-Film Silicon Solar Cells Applications

ABSTRACTSurface texturing of transparent conductive oxides is crucial to improve the fraction of incident light trapped in the absorber layer of thin film silicon based solar cells to improve the device performance. In this work, we fabricate and compare periodic, overlapping, and random surface textures and patterns on aluminium doped zinc oxide (AZO) using direct laser processing. The effects of the used laser wavelength, laser operating frequency, and pulse periodicity on the structural, morphological, and optical response of the AZO films were investigated. By optimizing the laser parameters and the associated process conditions, a drastic increase up to 60% in the transmittance haze over the entire solar was achieved.

Regularly arranged indium islands on glass/molybdenum substrates upon femtosecond laser and physical vapor deposition processing

A bottom-up approach is presented for the production of arrays of indium islands on a molybdenum layer on glass, which can serve as micro-sized precursors for indium compounds such as copper-indium-gallium-diselenide used in photovoltaics. Femtosecond laser ablation of glass and a subsequent deposition of a molybdenum film or direct laser processing of the molybdenum film both allow the preferential nucleation and growth of indium islands at the predefined locations in a following indium-based physical vapor deposition (PVD) process. A proper choice of laser and deposition parameters ensures the controlled growth of indium islands exclusively at the laser ablated spots. Based on a statistical analysis, these results are compared to the non-structured molybdenum surface, leading to randomly grown indium islands after PVD.

高放熱性プリント基板のCuダイレクトレーザ加工における高速度カメラによるモニタリングに基づく止まり穴品質の制御方法

Recently, printed circuit boards (PCBs) have become multi-layered and complex. It is to provide both multiple functions and to be compact with the development of electronic device such as smartphones. Processing by CO2 laser is frequently used as an effective method of generating blind via holes (BVHs) to connect the circuit layers of multi-layer board. However, there are some kinds of laser drilling methods in this manufacturing field. Among them, Cu direct laser processing is attracted attention, which is a drilling method of both the surface Cu circuit layer and insulation substrate layer at the same time. In the present report, we propose a laser irradiating controlling method based on monitoring the variation of processing luminance when generating the BVH. Especially, we perform the BVH drilling of high heat radiation PCBs, which becomes to be use for high performance electronic devices, and investigate the influence of laser irradiation condition on the drilled hole quality. As a result, the proposed method is found out to be effective to achieve the high BVH quality in the PCB manufacturing fields.

Tuning cell adhesion by direct nanostructuring silicon into cell repulsive/adhesive patterns

Developing platforms that allow tuning cell functionality through incorporating physical, chemical, or mechanical cues onto the material surfaces is one of the key challenges in research in the field of biomaterials. In this respect, various approaches have been proposed and numerous structures have been developed on a variety of materials. Most of these approaches, however, demand a multistep process or post-chemical treatment. Therefore, a simple approach would be desirable to develop bio-functionalized platforms for effectively modulating cell adhesion and consequently programming cell functionality without requiring any chemical or biological surface treatment. This study introduces a versatile yet simple laser approach to structure silicon (Si) chips into cytophobic/cytophilic patterns in order to modulate cell adhesion and proliferation. These patterns are fabricated on platforms through direct laser processing of Si substrates, which renders a desired computer-generated configuration into patterns. We investigate the morphology, chemistry, and wettability of the platform surfaces. Subsequently, we study the functionality of the fabricated platforms on modulating cervical cancer cells (HeLa) behaviour. The results from in vitro studies suggest that the nanostructures efficiently repel HeLa cells and drive them to migrate onto untreated sites. The study of the morphology of the cells reveals that cells evade the cytophobic area by bending and changing direction. Additionally, cell patterning, cell directionality, cell channelling, and cell trapping are achieved by developing different platforms with specific patterns. The flexibility and controllability of this approach to effectively structure Si substrates to cell-repulsive and cell-adhesive patterns offer perceptible outlook for developing bio-functionalized platforms for a variety of biomedical devices. Moreover, this approach could pave the way for developing anti-cancer platforms that selectively repel cancer cells while favoring the adhesion of normal cells.

Direct laser processing of bulk lead zirconate titanate ceramics

Laser Engineered Net Shaping (LENS™) has been used to fabricate dense, net shape melt-cast structures of lead zirconate titanate (PZT), in a single step, directly on a metallic substrate by complete melting and resolidification of PZT powders. From our results, it appears that reasonable dielectric properties can be obtained in LENS™ processed PZT structures without post-fabrication heat treatments. Our results also demonstrate potential application of LENS™ towards direct fabrication of PZT based embedded sensors and transducers on structural components.

Direct laser processing of a tantalum coating on titanium for bone replacement structures

Recently tantalum is gaining more attention as a new metallic biomaterial as it has been shown to be bioactive and biologically bonds to bone. However, the relatively high cost of manufacture and an inability to produce a modular all Ta implant has limited its widespread acceptance. In this study we have successfully deposited a Ta coating on Ti using laser engineered net shaping (LENS™) to enhance the osseointegration properties. In vitro biocompatibility study, using human osteoblast cell line hFOB, showed excellent cellular adherence and growth with abundant extracellular matrix formation on the Ta coating surface compared with the Ti surface. A six times higher living cell density was observed on the Ta coating than on the Ti control surface by MMT assay. A high surface energy and wettability of the Ta surface were observed to contribute to its significantly better cell–material interactions. Also, these dense Ta coatings do not suffer from low fatigue resistance due to the absence of porosity and a sharp interface between the coating and the substrate, which is a major concern for porous coatings used for enhanced/early biological fixation.

60.3: Advanced Application of Direct Laser Process on SnO2 Thin Films for FPDs

AbstractA Nd:YAG laser process on pure and doped SnO2 thin films was investigated as a key technology for a next generation flat panel displays manufacture replacing photolithography etching process on Indium‐Tin‐Oxide that is currently in use. It is found that the laser process is capable of making fine micro patterns on SnO2 thin films that have high carrier concentration by as low laser energy as 6J/cm2.

Direct laser fabrication of superalloy cermet abrasive turbine blade tips

This paper presents the development of a new technique for the production of abrasive turbine blade tips by direct laser processing. This superalloy cermet component is an integral part of the low-pressure turbine sealing system in a demonstrator engine. Direct laser fabrication of this component from a bed of loose powder results in significant cost savings and improved performance over the currently employed production technique. The technology has been demonstrated by fabricating a prototype lot of 100 blade tips, which will be subjected to an engine test. This is the first instance of a direct fabrication method applied to the production of functional engine hardware.