Direct Femtosecond Laser Ablation Research Articles

Tungsten oxide nanoparticle and aggregate formation through direct femtosecond laser ablation in air

In this work, we report the generation of tungsten oxide (WO3) nanoparticles and aggregate structures through direct femtosecond laser ablation in air. The nanoparticle morphology is studied utilizing Raman spectroscopy and TEM analysis, showing the generation of nanorods in the monoclinic phase with an average width and length of 70 and 168 nm, respectively. A range of laser fluences (0.8 to 4.2 J/cm 2) were during the ablation process, demonstrating control over the spread and density of the aggregate structures. Moreover, through variation of the laser spot size we demonstrate controlled aggregate formation, creating structures ranging from a high-density web-like structure with high area coverage to longer wire-like structures with lengths above 100μm.

Deep Subwavelength Laser-Induced Periodic Surface Structures on Silicon as a Novel Multifunctional Biosensing Platform.

Strong light localization inside the nanoscale gaps provides remarkable opportunities for creation of various medical and biosensing platforms stimulating an active search for inexpensive and easily scalable fabrication at a sub-100 nm resolution. In this paper, self-organized laser-induced periodic surface structures (LIPSSs) with the shortest ever reported periodicity of 70 ± 10 nm were directly imprinted on the crystalline Si wafer upon its direct femtosecond-laser ablation in isopropanol. Appearance of such a nanoscale morphology was explained by the formation of a periodic topography on the surface of photoexcited Si driven by interference phenomena as well as subsequent down-scaling of the imprinted grating period via Rayleigh-Taylor hydrodynamic instability. The produced deep subwavelength LIPSSs demonstrate strong anisotropic anti-reflection performance, ensuring efficient delivery of the incident far-field radiation to the electromagnetic "hot spots" localized in the Si nanogaps. This allows realization of various optical biosensing platforms operating via strong interactions of quantum emitters with nanoscale light fields. The demonstrated 80-fold enhancement of spontaneous emission from the attached nanolayer of organic dye molecules and in situ optical tracing of catalytic molecular transformations substantiate bare and metal-capped deep subwavelength Si LIPSSs as a promising inexpensive multifunctional biosensing platform.

Morphological Study of Nanostructures Induced by Direct Femtosecond Laser Ablation on Diamond.

High spatial frequency laser induced periodic surface structure (HSFL) morphology induced by femtosecond laser with 230 fs pulse duration, 250 kHz repetition rate at 1030 nm wavelength on CVD diamond surface is investigated and discussed. The spatial modification was characterized and analyzed by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and 2D-Fast Fourier Transform (2D-FFT). We studied the effect of pulse number and laser power on the spatial development of nanostructures, and also deduced the impact of thermal accumulation effect on their morphology. A generalized plasmonic model has been used to follow the optical evolution of the irradiated surface and to determine the periodic value of the nanostructures. We suggest that non-thermal melting and plasmonic excitation are the main processes responsible for the formation of HSFL-type nanostructures.

Direct femtosecond laser ablation of large-area TaSe2, SnS2, and TiS2 thick films by a back ablation procedure.

Direct ablation of large-area graphene-like two-dimensional (2D) materials, i.e., tantalum diselenide (TaSe2), stannic disulfide (SnS2), and titanium disulfide (TiS2), by the back ablation method with a femtosecond laser with a repetition rate of 50 MHz and pulse width of 200 fs is studied for the first time to our knowledge. The ablation thresholds of the three kinds of materials are discussed. In addition, the optimization and ablation of narrow grooves on the films are demonstrated. Our work demonstrates the direct femtosecond laser ablation processing of the graphene-like 2D-material films and the potential of 2D-material-film-based devices.

Silicon microprotrusions with tailored chirality enabled by direct femtosecond laser ablation.

Here, we report on formation of nanoprotrusions on the surface of a bulk crystalline silicon wafer under femtosecond-laser ablation with a donut-shaped laser beam. By breaking circular symmetry of the irradiating donut-shaped fs-pulse beam, a switch in geometry of the formed surface nanoprotrusions from regular to chiral was demonstrated. The chirality of the obtained Si nanostructures was promoted with an asymmetry degree of the laser beam. An uneven helical flow of laser-melted Si caused by asymmetry of the initial intensity and temperature pattern on the laser-irradiated Si surface explains this phenomenon. Chirality of the formed protrusions was confirmed by visualizing cross-sectional cuts produced by focused ion beam milling as well as Raman activity of these structures probed by circularly polarized light with opposite handedness. Our results open a pathway towards easy-to-implement inexpensive fabrication of chiral all-dielectric nanostructures for advanced nanophotonic applications and sensing of chiral molecules.

Femtosecond laser induced periodic surface structures for the enhancement of field emission properties of tungsten

Direct femtosecond laser ablation enables the maskless fabrication of nano- and micro-scale structures on variety of materials. A typical example is the formation of femtosecond Laser Induced Periodic Surface Structures (fs-LIPSSs), which can lead to strong modification in electrical, optical, wetting, and field emission properties of materials. Here, we study the field emission properties of fs-LIPSSs. We created fs-LIPSSs and fs-LIPSSs covered with nano- and micro-scale structures at different laser fluences on Tungsten (W) and showed that these structures offer significant enhancement in electron field emission properties. We provide a phenomenological model to explain the enhancement of electron emission parameters. The enhancement in the field emission properties of laser irradiated W is explained based on the convergence of electric field lines at the ridges of the fs-LIPSSs and fs-LIPSSs covered with nanoscale structures, which in turn, enhances the local field intensity and the electron emission parameters. The direct fabrication of 1D subwavelength structures is an important step towards the creation of low-cost cathodes for various potential applications.

Direct Laser Microperforation of Bioresponsive Surface-Patterned Films with Through-Hole Arrays for Vascular Tissue-Engineering Application.

Tissue architecture plays critical roles in the physiological functions of blood vessels. Surface-patterned films are promising to replicate cellular alignment as in the native vessels. However, for vascular tissue engineering (TE) applications, the current surface-patterned films lack structural support for the myoendothelial communications between tunica media and intima. Herein, we report the development of direct microperforation using a femtosecond laser on surface-patterned films for the native-like architecture reconstruction of blood vessels. Poly(ε-caprolactone) (PCL) thin films were surface-patterned with anisotropic microridges/grooves. Direct femtosecond laser ablation further resulted in microscale through-holes for the PCL films, without invasive thermal damage to the ridges/grooves on the nonprocessed surface. Laser fluence and pulse number were observed to significantly influence the microperforation on both hole quality and dimension. The PCL films after direct femtosecond laser microperforation exhibited improved flexible properties, without sacrificing the yield stress. Meanwhile, direct femtosecond laser microperforation resulted in PCL films with hydrophilic permeability to transport nutritional/signaling biomolecules and allowed for heterocellular protrusion ingrowth into the through-holes for physical myoendothelial contacts. Small-diameter vascular TE scaffolds based on the as-fabricated PCL films could enable a hybrid vascular wall construction with aligned stromal multilayers and a confluent endothelium similar to those of the native vascular tissue. These results showed that direct femtosecond laser microperforation could be a reliable approach for producing biomimetic films with through-holes. The developed vascular TE scaffolds with microridges/grooves and through-holes have the potential to offer structural support for vascular architecture reconstruction with the native-like stromal and endothelial components.

Femtosecond laser induced hierarchical ZnO superhydrophobic surfaces with switchable wettability.

A simple and one-step method to form a rough ZnO layer consisting of micro/nanoscale hierarchical structures via direct femtosecond laser ablation of the Zn surface is reported for the first time. The resultant surfaces show switchable wettability between superhydrophobicity and quasi-superhydrophilicity via alternate UV irradiation and dark storage.

Laser micro-patterning of biodegradable polymer blends for tissue engineering

We propose a multistep all laser, maskless, and solvent free synthesis of micro-patterned substrates of biodegradable polymer blends, with applicability for guided cell adhesion and localized hyaluronic acid (HA) immobilization. The polymer blends comprised polyurethane (PU), poly(lactic-co-glycolic acid) (PLGA), and polylactide-polyethylene glycol-polylactide (PPP) in 1:1:1 blending ratios. Polymer patterning was performed by laser processing in two steps. First, the polymers were patterned with periodic micro-channels by direct femtosecond laser ablation, which provided flexibility in design and spatial accuracy for the patterns. As a second step, the micro-patterned polymers were coated with thin layers of polymer blends using matrix assisted pulsed laser evaporation (MAPLE). The resulted sandwich substrates were composed of a bottom, micro-patterned layer and thin, top layer which conserved the patterns from the underlying layer and preserved the polymers chemical composition. Depending on the bottom/top layers, the substrates were denominated PU/PU:PLGA:PPP and PU:PLGA:PPP/PU:PLGA:PPP, respectively. The laser generated micro-patterns were used for selective attachment of oral keratinocyte stem cells and for HA immobilization. The highest cellular density was found on the PU:PLGA:PPP/PU:PLGA:PPP substrate, where the spongy-like micro-channels provided multiple anchoring points for the cells. For both substrates, the micro-channels enabled localized immobilization of HA. The effectiveness of HA immobilization was tested against cell adhesion and protein adsorption.

Direct femtosecond laser ablation of copper with an optical vortex beam

Laser surface structuring of copper is induced by laser ablation with a femtosecond optical vortex beam generated via spin-to-orbital conversion of the angular momentum of light by using a q-plate. The variation of the produced surface structures is studied as a function of the number of pulses, N, and laser fluence, F. After the first laser pulse (N = 1), the irradiated surface presents an annular region characterized by a corrugated morphology made by a rather complex network of nanometer-scale ridges, wrinkles, pores, and cavities. Increasing the number of pulses (2 < N < 100), the surface texture progressively evolves towards larger structures, while the central, non-ablated area is gradually decorated by nanoparticles produced during laser ablation. At large number of pulses (200 < N < 1000), a micro-tip with a nanostructured surface forms in the center of the irradiated area, which eventually disappears at still larger number of pulses (N > 1000) and a deep crater is formed. The nanostructure variation with the laser fluence, F, also evidences an interesting dependence, with a coarsening of the structure morphology as F increases. Our experimental findings demonstrate that direct femtosecond laser ablation with optical vortex beams produces interesting patterns not achievable by the more standard beams with a Gaussian intensity profile. They also suggest that appropriate tuning of the experimental conditions (F, N) can allow generating micro- and/or nano-structured surface for any specific application.

Microstructuring of Polypyrrole by Maskless Direct Femtosecond Laser Ablation

Ultrafast laser micromachining was optimized for microstructuring polypyrrole as a facile new approach towards tailoring electrochemical and mechanical responses desirable for microactuator, sensors, neural probing, and nerve conduit applications. Laser perforation of high-density and high aspect ratio through-holes generated greater than 5-fold increase in surface area. The flexible machining technique offers micron-size resolution and fast prototyping capability for optimizing properties and opening new directions for polypyrrole-based devices.

Near-field imaging of femtosecond laser ablated sub-λ/4 holes in lithium niobate

We report on the direct femtosecond laser ablation of sub-λ/4 (80–250 nm) holes in LiNbO3 crystals and on its local near-field imaging. We show that the near-field transmission of holes can feature an attenuation of ∼75% at hole central position, and a ∼20% transmission enhancement at its sides. This high-contrast ring-shaped near-field distribution is found to be in agreement with simulations, suggesting the surface relief as the main contrast mechanism.

Large area uniform nanostructures fabricated by direct femtosecond laser ablation

An approach for fabricating large area uniform nanostructures by direct femtosecond (fs) laser ablation is presented. By the simple scanning technique with appropriate irradiation conditions, arbitrary size of uniform, complanate nano-grating, nano-particle, and nano-square structures can be produced on wide bandgap materials as well as graphite. The feature sizes of the formed nanostructures, which can be tuned in a wide range by varying the irradiation wavelength, is about 200 nm with 800 nm fs laser irradiation. The physical properties of the nano-structured surfaces are changed greatly, especially the optical property, which is demonstrated by the extraordinary enhancement of light transmission of the treated area. This technique is efficient, universal, and environmentally friendly, which exhibits great potential for applications in photoelectron devices.