Laser Fabrication Method Research Articles

Femtosecond laser fabrication of nanopillar arrays for Surface-Enhanced Raman scattering substrates

This work presents a femtosecond laser fabrication method for precision-engineered nanopillar arrays, applicable for surface-enhanced Raman scattering (SERS) substrates. The proposed method consists of two steps: (1) fabrication of nanopillar arrays using femtosecond laser-induced two-photon polymerization (TPP) technology; and (2) deposition of Ag nanoparticles on the fabricated nanopillar arrays. Nanopillar arrays of the proposed SERS substrates are optimized with geometrical parameters of diameter, height, spacing, and arrangement. A limit of detection (LOD) down to 10-7 mol/L for Rhodamine 6G solution is achieved and the enhancement factor is estimated to be up to 2 × 103. The experimental results indicate that the proposed SERS substrates have potential applications in biomedical detection, food safety monitoring, and quality control.

All-Automated Fabrication of Freestanding and Scalable Photo-Thermoelectric Devices with High Performance.

Flexible photo-thermoelectric (PTE) devices have great application prospects in the fields of solar energy conversion, ultrabroadband light detection, etc. A suitable manufacturing process to avoid the substrate effects as well as to create a narrow transition area between p-n modules for high-performance freestanding flexible PTE devices is highly desired. Herein, an automated laser fabrication (ALF) method is reported to construct the PTE devices with rylene-diimide-doped n-type single-walled carbon nanotube (SWCNT) films. Thewet-compressing approach is developed to improve the thermoelectric power factors and figure of merit (ZT) of the SWCNT hybrid films. Then, the films are cut and patterned automatically to make PTE devices with various structures by the proposed ALF method. The freestanding PTE device with a narrow transition area of ≈2-3 µm between the p and n modules exhibits a high-power density of 0.32 µW cm-2 under the light of 200 mW cm-2, which is among the highest level for freestanding-film-based PTE devices. The results pave the way for the automatic production process of PTE devices for green power generation and ultrabroadband light detection.

Direct Freeform Laser Fabrication of 3D Conformable Electronics

Abstract3D conformable electronic devices on freeform surfaces show superior performance to the conventional, planar ones. They represent a trend of future electronics and have witnessed exponential growth in various applications. However, their potential is largely limited by a lack of sophisticated fabrication techniques. To tackle this challenge, a new direct freeform laser (DFL) fabrication method enabled by a 5‐axis laser processing platform for directly fabricating 3D conformable electronics on targeted arbitrary surfaces is reported. Accordingly, representative laser‐induced graphene (LIG), metals, and metal oxides are successfully fabricated as high‐performance sensing and electrode materials from different material precursors on various types of substrates for applications in temperature/light/gas sensing, energy storage, and printed circuit board for circuit. Last but not the least, to demonstrate an application in smart homes, LIG‐based conformable strain sensors are fabricated and distributed in designated locations of an artificial tree. The distributed sensors have the capability of monitoring the wind speed and direction with the assistance of well‐trained machine‐learning models. This novel process will pave a new and general route to fabricating 3D conformable electronic devices, thus creating new opportunities in robotics, biomedical sensing, structural health, environmental monitoring, and Internet of Things applications.

Dual‐Modal Fluorescence‐SERS Detection of Blood Glucose Engineered by Hierarchical Laser‐Induced Micro/Nano Structures for Diabetes Screening

AbstractSurface‐enhanced Raman spectroscopy (SERS) is a highly sensitive and selective vibrational spectroscopy, which has promising application in diabetes detection. However, the current detection methods usually suffer from poor reproducibility, time‐consumption, and complicated fabrication procedures, which limit their practical applications for large‐scale diabetes screening. Herein, a one‐step laser fabrication method to realize the integration of SERS and surface‐enhanced fluorescence (SEF) is introduced for rapid detection of glucose by generating controllable hierarchical laser‐induced periodic surface structures (LIPSS) on Si substrate. The proposed dual‐modal detection is to use SEF for first rapid qualitative analysis, and to apply SERS for later quantitative analysis of the glucose concentration. The SERS and SEF enhancement is up to 2.11 × 106 and 24.83, respectively, while the detection limit of SERS and SEF is × 10−9 and 1 × 10−6 mol L−1, respectively. Moreover, clinical verification of this dual‐modal detection of glucose in human blood samples is investigated, and the results are in good agreement with the clinical report. The present SERS‐SEF dual‐modal detection provides a facile and promising method for large‐scale diabetes screening.

Patterned assembly of silicon nanoparticles via femtosecond laser bubble printing for high-performance photodetector applications

With the ever-growing development for nanomaterials, the integration of nanomaterials into electronic devices and sensors requires flexible and efficient selective patterning deposition of the nanomaterials. However, existing patterning techniques of these nanomaterials is limited in practical applications due to the use of templates and tedious preparation process. Here, a facile femtosecond laser bubble printing (FsLBP) technique without mask and tedious preparation process that integrates patterning, assembly, and deposition of nanomaterials is presented. Benefiting from the advantages of this processing technology, arbitrarily patterned assembled silicon (Si) nanoparticles were successfully prepared. In addition, the effect of viscosity and surface tension of the solution in the process of FsLDW on the deposited Si nanoparticles is explored. Owing to the rough and porous structure of the assembled microwires, the microwires have a high-efficiency light trapping ability with an average reflectivity of 2% for visible light and the photodetector based on porous Si microwires exhibits a responsivity of 231 A/W under the irradiation of 365 nm ultraviolet (UV) light. Finally, a device for real-time monitoring of ultraviolet light intensity was obtained, which demonstrate the potential application of the ultrafast laser fabrication method in patterned assembly of nanomaterials.

Ablation-Free Laser Printing of Structural Colors in Reflection at 25,000 DPI

Using direct femtosecond laser patterning of metal-insulator-metal (MIM) sandwich designed to support Fabry-Perot mode in the visible spectral range we demonstrate new practically relevant strategy for high-resolution color printing. Irradiation of the MIM sandwich by tightly focused laser pulses allows to produce unique 3D surface nanostructures – hollow nanobumps and nanojets - locally modulating surface reflectivity. Laser processing parameters control the 3D shape of such nanostructures allowing to gradually tune the reflected color from reddish brown to pure green. Up-scalable ablation-free laser fabrication method paves the way towards various applications ranging from large-scale structural color printing to optical sensors and security labeling at a lateral resolution of 25,000 dots per inch.

Wide Two-Degree-of-Freedom Static Laser Scanner with Miniaturized Transmission Mechanism and Piezoelectric Actuation.

In recent years, laser scanners have attracted significant attention for applications such as laser radars. However, the establishment of a two-degree-of-freedom scanner that can quasi-statically drive a large mirror with a large deflection angle has proven to be challenging. In this paper, we propose a laser scanner design and fabrication method by combining two unimorph piezoelectric actuators composed of piezoelectric single-crystal Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 and a miniature translation-rotation conversion mechanism with flexible polyimide hinges. The size of the entire scanner was 32 mm × 12 mm × 10 mm. We successfully demonstrated that the scanner could achieve a large quasi-static mechanical deflection angle amplitude of 20.5° in two axes with a 6-mm-square mirror.

One-Step Fabrication Method of GaN Films for Internal Quantum Efficiency Enhancement and Their Ultrafast Mechanism Investigation.

The third-generation semiconductors are the cornerstone of the power semiconductor leap forward and have attracted much attention because of their excellent properties and wide applications. Meanwhile, femtosecond laser processing as a convenient method further improves the performance of the related devices and expands the application prospect. In this work, an approximate 3 times improvement of the internal quantum efficiency (IQE) and a 5.5 times enhancement of the photoluminescence (PL) intensity were achieved in the GaN film prepared using a one-step femtosecond laser fabrication method. Three types of final micro/nanostructures were found with different femtosecond laser fluences, which could be attributed to the decomposition, melting, bubble nucleation, and phase explosion of GaN. The mechanisms of the microbump structure formation and enhancement of IQE were studied experimentally by the time-resolved reflection pump-probe technique, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Simulations for the laser-GaN interaction have also been performed to ascertain the micro/nanostructure formation principle. These results promote the potential applications of femtosecond lasers on GaN and other wide band gap semiconductors, such as UV-light-emitting diodes (LEDs), photodetectors, and random lasers for use in sensing and full-field imaging.

Femtosecond Laser Precision Engineering: From Micron, Submicron, to Nanoscale

As a noncontact strategy with flexible tools and high efficiency, laser precision engineering is a significant advanced processing way for high-quality micro-/nanostructure fabrication, especially to achieve novel functional photoelectric structures and devices. For the microscale creation, several femtosecond laser fabrication methods, including multiphoton absorption, laser-induced plasma-assisted ablation, and incubation effect have been developed. Meanwhile, the femtosecond laser can be combined with microlens arrays and interference lithography techniques to achieve the structures in submicron scales. Down to nanoscale feature sizes, advanced processing strategies, such as near-field scanning optical microscope, atomic force microscope, and microsphere, are applied in femtosecond laser processing and the minimum nanostructure creation has been pushed down to ~25 nm due to near-field effect. The most fascinating femtosecond laser precision engineering is the possibility of large-area, high-throughput, and far-field nanofabrication. In combination with special strategies, including dual femtosecond laser beam irradiation, ~15 nm nanostructuring can be achieved directly on silicon surfaces in far field and in ambient air. The challenges and perspectives in the femtosecond laser precision engineering are also discussed.

Electrochemical and chronoamperometry assessment of nano‑gold sensor surfaces produced via novel laser fabrication methods

New developments in laser ablation have shown great potential as nanofabrication methodologies, offering many significant advantages over more traditional methods. Herein, we have developed a method for applying two of these techniques, confined atmospheric pulsed-laser (CAP) deposition and laser ablation synthesis in solution (LASiS), to the fabrication of a nanostructured sensor platform. Following deposition, additional steps were then used to crosslink the deposited nanostructures and fabricate counter and reference electrodes. Chronoamperometry and cyclic voltammetry (CV) were used to assess the effects of these crosslinking steps on the properties of the sensor surfaces. These experiments resulted in the development of a simple, inexpensive and readily scalable process for the fabrication of 3-electrode sensor systems. As an example of a readily measurable surface interaction, electrochemical impedance spectroscopy (EIS) was applied to demonstrate the use of these systems in the detection of 6-mercaptohexanol. This interaction was examined in real-time by measuring the change in the EIS of the sensor system over time following its exposure to the thiol. This experiment clearly showed a measurable EIS response, demonstrating the effectiveness of these newly fabricated sensors for the detection of a simple surface interaction and suggesting the future potential of these laser based methods as the basis for an inexpensive, facile, rapid and scalable sensor fabrication process. • Development of a novel, inexpensive, scalable, laser based method for the fabrication of nanostructured biosensors. • Comparison of several sensor designs from various stages of the development process. • Demonstration of basic sensor activity using chronoamperometry and electrochemical impedance spectroscopy. • Examination of the effects of a key fabrication step on the properties of the sensor surface.

Cost-effective microfabrication of sub-micron-depth channels by femto-laser anti-stiction texturing

Micro Electro Mechanical Systems (MEMS) and microfluidic devices have found numerous applications in the industrial sector. However, they require a fast, cost-effective and reliable manufacturing process in order to compete with conventional methods. Particularly, at the sub-micron scale, the manufacturing of devices are limited by the dimensional complexity. A proper bonding and stiction prevention of these sub-micron channels are two of the main challenges faced during the fabrication process of low aspect ratio channels. Especially, in the case of using flexible materials such as polydimethylsiloxane (PDMS). This study presents a direct laser microfabrication method of sub-micron channels using an infrared (IR) ultrashort pulse (femtosecond), capable of manufacturing extremely low aspect ratio channels. These microchannels are manufactured and tested varying their depth from 0.5 μm to 2 μm and width of 15, 20, 25, and 30 μm. The roughness of each pattern was measured by an interferometric microscope. Additionally, the static contact angle of each depth was studied to evaluate the influence of femtosecond laser fabrication method on the wettability of the glass substrate. PDMS, which is a biocompatible polymer, was used to provide a watertight property to the sub-micron channels and also to assist the assembly of external microfluidic hose connections. A 750 nm depth watertight channel was built using this methodology and successfully used as a blood plasma separator (BPS). The device was able to achieve 100% pure plasma without stiction of the PDMS layer to the sub-micron channel within an adequate time. This method provides a novel manufacturing approach useful for various applications such as point-of-care devices.

Ultra-low-cost fabrication of polymer-based microfluidic devices with diode laser ablation.

In this work, a diode laser ablation approach was used for the fabrication of PMMA-based microfluidic devices. Compared with the conventional CO2 or femtosecond laser fabrication method, the proposed laser ablation method based on diode laser significantly lowered the cost in the fabrication of polymer-based microfluidic devices with comparable resolution and surface quality. PMMA substrate was used for the laser ablation process, due to the transparency of PMMA in the diode laser's working wavelength, a layer of Kraft tape was applied on the surface of PMMA for the absorption of laser energy, and microchannels were then achieved on the surface of PMMA with the proposed low-cost diode laser system. The comparison between the proposed method and the CO2 laser ablation method was also conducted in this study. The profile of the fabricated microchannels was carefully characterized, several microfluidic devices were also fabricated for the demonstration of the proposed fabrication method using a diode laser.

Evaluation of parylene derivatives for use as biomaterials for human astrocyte cell patterning.

Cell patterning is becoming increasingly popular in neuroscience because it allows for the control in the location and connectivity of cells. A recently developed cell patterning technology uses patterns of an organic polymer, parylene-C, on a background of SiO2. When cells are cultured on the parylene-C/SiO2 substrate they conform to the underlying parylene-C geometry. Parylene-C is, however, just one member of a family of parylene polymers that have varying chemical and physical properties. In this work, we investigate whether two commercially available mainstream parylene derivatives, parylene-D, parylene-N and a more recent parylene derivative, parylene-HT to determine if they enable higher fidelity hNT astrocyte cell patterning compared to parylene-C. We demonstrate that all parylene derivatives are compatible with the existing laser fabrication method. We then demonstrate that parylene-HT, parylene-D and parylene-N are suitable for use as an hNT astrocyte cell attractive substrate and result in an equal quality of patterning compared to parylene-C. This work supports the use of alternative parylene derivatives for applications where their different physical and chemical properties are more suitable.

Implementation of an optimized microfluidic mixer in alumina employing femtosecond laser ablation

Manipulation of liquids at the lowest levels of volume and dimension is at the forefront of materials science, chemistry and medicine, offering important time and resource saving applications. However, manipulation by mixing is troublesome at the microliter and lower scales. One approach to overcome this problem is to use passive mixers, which exploit structural obstacles within microfluidic channels or the geometry of channels themselves to enforce and enhance fluid mixing. Some applications require the manipulation and mixing of aggressive substances, which makes conventional microfluidic materials, along with their fabrication methods, inappropriate. In this work, implementation of an optimized full scale three port microfluidic mixer is presented in a slide of a material that is very hard to process but possesses extreme chemical and physical resistance—alumina. The viability of the selected femtosecond laser fabrication method as an alternative to conventional lithography methods, which are unable to process this material, is demonstrated. For the validation and optimization of the microfluidic mixer, a finite element method (FEM) based numerical modeling of the influence of the mixer geometry on its mixing performance is completed. Experimental investigation of the laminar flow geometry demonstrated very good agreement with the numerical simulation results. Such a laser ablation microfabricated passive mixer structure is intended for use in a capillary force assisted nanoparticle assembly setup (CAPA).

레이저를 이용한 구리나노와이어 패터닝 공정 개발

This paper introduces a facile method to enhance the functionality of a patterned metallic transparent conductor through selective laser ablation of the metal nanowire percolation network. By scanning focused nanosecond pulsed laser a on copper nanowire percolation network, the copper nanowires are selectively ablated and patterned without resorting to any conventional chemical etching or photolithography steps. Several arbitrary patterns of copper nanowire transparent conductors are readily created on the percolation network by changing various laser parameters, such as repetition rate and power. Finally, in a few seconds, the copper nanowire electrode is continuously ablated to a 1 × 1 mm square area. This research thereby proves the advantage of the laser fabrication method.

Fabrication of rectangular cross-sectional microchannels on PMMA with a CO2 laser and underwater fabricated copper mask

CO2 lasers are commonly used for fabricating polymer based microfluidic devices. Despite several key advantages like low cost, time effectiveness, easy to operate and no requirement of clean room facility, CO2 lasers suffer from few disadvantages like thermal bulging, improper dimensional control, difficulty to produce microchannels of other than Gaussian cross sectional shapes and inclined surface walls. Many microfluidic devices require square or rectangular cross-sections which are difficult to produce using normal CO2 laser procedures. In this work, a thin copper sheet of 40μm was used as a mask above the PMMA (Polymethyl-methacrylate) substrate while fabricating the microchannels utilizing the raster scanning feature of the CO2 lasers. Microchannels with different width dimensions were fabricated utilizing a CO2 laser in with mask and without-mask conditions. A comparison of both the fabricating process has been made. It was found that microchannels with U shape cross section and rectangular cross-section can efficiently be produced using the with mask technique. In addition to this, this technique can provide perfect dimensional control and better surface quality of the microchannel walls. Such a microchannel fabrication process do not require any post-processing. The fabrication of mask using a nanosecond fiber laser has been discussed in details. An underwater laser fabrication method was adopted to overcome heat related defects in mask preparation. Overall, the technique was found to be easy to adopt and significant improvements were observed in microchannel fabrication.

Universal liquid-phase laser fabrication of various nano-metals encapsulated by ultrathin carbon shells for deep-UV plasmonics.

The exploration of localized surface plasmon resonance (LSPR) beyond the usual visible waveband, for example within the ultraviolet (UV) or deep-ultraviolet (D-UV) regions, is of great significance due to its unique applications in secret communications and optics. However, it is still challenging to universally synthesize the corresponding metal nanostructures due to their high activity. Herein, we report a universal, eco-friendly, facile and rapid synthesis of various nano-metals encapsulated by ultrathin carbon shells, significantly with a remarkable deep-UV LSPR characteristic, via a liquid-phase laser fabrication method. Firstly, a new generation of the laser ablation in liquid (LAL) method has been developed with an emphasis on the elaborate selection of solvents to generate ultrathin carbon shells, and hence to stabilize the formed metal nanocrystals. As a result, a series of metal@carbon nanoparticles (NPs), including Cr@C, Ti@C, Fe@C, V@C, Al@C, Sn@C, Mn@C and Pd@C, can be fabricated by this modified LAL method. Interestingly, these NPs exhibit LSPR peaks in the range of 200-330 nm, which are very rare for localized surface plasmon resonance. Consequently, the UV plasmonic effects of these metal@carbon NPs were demonstrated both by the observed enhancement in UV photoluminescence (PL) from the carbon nanoshells and by the improvement of the photo-responsivity of UV GaN photodetectors. This work could provide a universal method for carbon shelled metal NPs and expand plasmonics into the D-UV waveband.

Femtosecond-laser-structured nitrocellulose membranes for multi-parameter Point-of-Care tests

Cheap and disposable Point-of-Care diagnostic devices are of great interest to combat the rising cost of healthcare in industrial nations but also for a widespread use in the developing world. Paper based microfluidic devices as well as well-established lateral flow tests (LFTs) are both well suited for this role. However, they share various disadvantages including restricted reproducibility for quantitative readouts and are in most cases limited to a single parameter per test. In order to address these drawbacks we present a novel laser fabrication method for multi-parametric lateral flow tests based on nitrocellulose membranes. Using a femtosecond laser the membrane can be structured into barriers and channels which separate and guide the test liquid. By varying the laser parameters the presented method allows the rapid area-selective ablation of the entire membrane-thickness to the polyester backing thus creating a barrier for the fluid transport as well as a much finer, but slower, removal of the membrane material which leaves the membranes pore structure and fluid transport characteristics intact. With barrier and channel widths of 100μm and 300–600μm this process enables the integration of complex multi-parametric detection fluidic networks in the footprint of commercially available LFTs.

Fiber optic stress-independent helical torsion sensor.

Femtosecond laser-fabricated waveguides have been formed into helical paths throughout the cladding of single-mode optical fibers to demonstrate a strain-independent fiber torsion sensor. A comparison between a Bragg grating sensor and a Mach-Zehnder based on helical waveguides (HWs) showed a much weaker twist sensitivity of 1.5 pm/(rad/m) for the grating in contrast with a value of 261 pm/(rad/m) for the interferometer. The HW geometry provided an unambiguous determination of the rotational direction of the twist while facilitating a convenient and efficient means for optical coupling into the single-mode core of the fiber. The flexible three-dimensional writing by the femtosecond laser fabrication method enabled the direct inscription of compact and robust optical cladding devices without the need for combining or splicing multiple-fiber segments.

Laser fabrication of gold nanoparticle clustered tips for use in apertureless near-field scanning optical microscopy.

A laser fabrication method was developed to make gold nanoparticle clustered (GNC) tips for apertureless near-field scanning optical microscopes (ANSOMs) and tip-enhanced Raman spectroscopy (TERS). The near-field Rayleigh and Raman scattering of samples are highly enhanced when a gold nanoparticle cluster is synthesized on the end of the tip. This is due to the lightning rod effect in the sharp tips. The localized electromagnetic field enhancement and the spatial resolution (~30 nm) of the fabricated GNC tip were verified by TERS and ANSOM measurements of carbon nanotubes.