Photoablation Process Research Articles

Targeted Phototherapy by Niobium Carbide for Mammalian Tumor Models Similar to Humans.

BackgroundIn the past few decades, nanomaterial‐mediated phototherapy has gained significant attention as an alternative antitumor strategy. However, its antitumor success is majorly limited to the treatment of subcutaneous tumors in nude mice. In fact, no studies have been previously conducted in this area/field on clinically‐relevant big animal models. Therefore, there is an urgent need to conduct further investigation in a typical big animal model, which is more closely related to the human body.ResultsIn this study, niobium carbide (NbC) was selected as a photoactive substance owing to the presence of outstanding near-infrared (NIR) absorption properties, which are responsible for the generation of NIR‐triggered hyperthermia and reactive oxygen species that contribute towards synergetic photothermal and photodynamic effect. Moreover, the present study utilized macrophages as bio‐carrier for the targeted delivery of NbC, wherein phagocytosis by macrophages retained the photothermal/photodynamic effect of NbC. Consequently, macrophage-loaded NbC ensured/allowed complete removal of solid tumors both in nude mice and big animal models involving rabbits. Meanwhile, two‐dimensional ultrasound, shave wave elastography (SWE), and contrast‐enhanced ultrasound (CEUS) were used to monitor physiological evolution in tumor in vivo post-treatment, which clearly revealed the occurrence of the photoablation process in tumor and provided a new strategy for the surveillance of tumor in big animal models.ConclusionAltogether, the use of a large animal model in this study presented higher clinical significance as compared to previous studies.

Micro-scale patterning of indium tin oxide film by spatially modulated pulsed Nd:YAG laser beam

Here we demonstrate that indium tin oxide (ITO) films deposited on glass can be directly patterned by a spatially -modulated pulsed Nd-YAG laser beam (wavelength=1064nm, pulse width=6ns) incident onto the film. This method utilizes a pulsed laser-induced thermo-elastic force exerting on the film which plays a role to detach it from the substrate. Sharp-edged clean patterns with feature size as small as 4μm could be obtained. The threshold pulse energy density for patterning was estimated to be ∼0.8J/cm2 for 150nm-thick ITO film, making it possible to pattern over one square centimeter by a single pulse with energy of 850mJ. Not only being free from photoresist and chemical etching steps, the presented method can also provide much higher throughput than the tradition photoablation process utilizing a tightly focused beam.

High Superhydrophobicity Achieved on Poly(ethylene terephthalate) by Innovative Laser-Assisted Magnetron Sputtering

The main development described in this paper consists of combining magnetron sputtering with a Nd:YAG laser to provide additional properties to the deposited thin films. The combination of both of these techniques has been revealed as an innovative methodology by the complementary effects able to respond to all the technical requirements of the desired ultrathin film properties. Plasma sputter-deposited fluoropolymers have been deposited on poly(ethylene terephthalate) (PET) substrates by this innovative Nd:YAG laser-assisted magnetron sputtering technique from a poly(tetrafluoroethylene) (PTFE) target. Laser irradiation of the substrate, occurring directly in the deposition chamber simultaneous to the first step of the deposition process, exhibits the advantage of inducing a micropatterning of the polymer surface by a photoablation process and then affords a high control of the roughness and microstructure. Deposition parameters of the fluoropolymer thin film have been optimized to obtain the maximum F/C atomic ratio to optimally functionalize the structure with fluoro groups; the F/C ratio was evaluated by X-ray photoelectron spectroscopy. Finally, the combination of the optimized sputtering parameters and the Nd:YAG laser treatment of the PET substrates led to superhydrophobic surfaces with a high water contact angle (θ = 160°). The films' morphology and topography were studied by scanning electron microscopy and atomic force microscopy, respectively.

Large-area, high-speed patterning of carbon nanotubes using material-assisted excimer laser photoablation

Large-area patterning of carbon nanotubes (CNTs) using a nonlithographic process is demonstrated. Projection imaging with deep ultraviolet radiation from 248 nm KrF excimer laser and material-assisted photoablation were used to pattern the CNTs. A matrix of CNTs dissolved in a DMF solution was deposited on a silicon wafer by spin coating, followed by coating of photodefinable polyimide on the CNTs. The CNTs and the polyimide layer were simultaneously patterned by the excimer laser projection photoablation process. Even though CNTs cannot be directly photoablated by low-fluence excimer laser radiation, simultaneous patterning of the illuminated CNT-polyimide combination region occurred due to the physical force of dissociated fragments of polyimide layer. We have demonstrated clean, large-area patterning of CNTs on 100 mm diameter Si wafers. Additionally, this patterning process is economical and provides higher throughput compared with conventional methods.

Excimer Laser Projection Photoablation Patterning of Metal Thin Films for Fabrication of Microelectronic Devices and Displays

A nonlithographic process is demonstrated for patterning Al, Cr, Cu, Ni, Ti, and W thin films, which are widely used in microelectronic and display fabrication. A projection photoablation process using 248-nm-deep ultraviolet radiation from a KrF excimer laser was used to pattern a polyimide film coated on a SiN layer deposited on glass. The photoablation-patterned polyimide film was used as a sacrificial layer in a lift-off patterning process for the metal films, which resulted in clean metal patterns with fine line-edge definition being fabricated after lift-off. This process provides a simpler and more economical patterning technique compared to conventional lithography methods, eliminating the developing and etching steps.

Patterning of single walled carbon nanotubes using a low-fluence excimer laser photoablation process

Carbon nanotube films were patterned by an excimer laser projection photoablation process at low incident energy conditions. The carbon nanotubes were deposited on a quartz substrate and then a conventional photoresist was coated on it as a photoablation assistor. The photoresist and the carbon nanotubes were simultaneously patterned by the projection photoablation process, and then the photoresist was removed. It was possible to make clean patterns of carbon nanotubes even though the incident fluence on the carbon nanotubes was significantly lower than the threshold energy otherwise needed for their direct ablation.

Patterning of indium tin oxide by projection photoablation and lift-off process for fabrication of flat-panel displays

Indium tin oxide (ITO), an important material used as a transparent conductive oxide in thin-film transistor liquid-crystal display fabrication, was patterned by a nonlithographic process. First, a Si3N4 substrate coated with photoresist was patterned by a projection photoablation process using 248nm wavelength KrF excimer laser radiation. ITO was then deposited by sputtering and patterned by lift-off. The resulting ITO pattern was clean even though it was patterned without the conventional steps of photoresist development and ITO etching. This process technology provides a faster and more economical patterning capability compared to conventional photolithography and etch processes used in the display industry.

Pulsed laser induced synthesis of scheelite-type colloidal nanoparticles in liquid and the size distribution by nanoparticle tracking analysis

Pulsed laser ablation (PLA) of ceramic target in liquid phase was successfully employed to prepare calcium tungstate (CaWO 4) and calcium molybdate (CaMoO 4) colloidal nanoparticles. The crystalline phase, particle morphology and optical property of the colloidal nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy. The produced stable colloidal suspensions consisted of the well-dispersed nanoparticles showing a spherical shape. The mechanism for the laser ablation and nanoparticle forming was discussed under consideration of photo-ablation process. Nanoparticle tracking analysis using optical microscope combined with image analysis was proposed to determine the size distribution function of the prepared colloidal nanoparticles. The mean size of the CaWO 4 and CaMoO 4 colloidal nanoparticles were 16 and 29 nm, with a standard deviations of 2.1 and 5.2 nm, respectively.

Interaction of pulsed metal vapor plasma with insulator wall

An experimental method is proposed to investigate the radiation emitted from the boundary layer, which is formed near the insulator wall. This experimental method consists of a fast-pulsed exploding aluminum wire set initially on the low-density polyethylene (LDPE) flat wall. Various phases of brightness and darkness between the narrow bright aluminum vapor plasma and the surface of the LDPE have been observed. It was observed that a formed dark layer moves away from the LDPE surface according to the released input energy. The shape of the formed layer was affected by both the interaction with the insulator wall and the electrodes. The radial reflected visible light by the insulator wall consists of two different expansion velocities showing a cooling of the vapor plasma source and an enhancement in the radiation emitted from the formed layer. Two phases have been observed in the temporal behavior of the intensity of the aluminum and the carbon atoms lines showing an enhancement during the collisionless interaction regime. The photoablation process of the LDPE wall occurred during the plateau observed in the intensity shape of the carbon atom line which match with both the observed peak value in the emitted UV radiation and the framing picture taken at 200 ns.

VUV-light-induced deposited silica films

A novel technique to deposit dielectric films at room temperature is described. The deposition of the silica takes place inside a cylindrical glass chamber where a silent discharge is generated between two electrodes connected to a high voltage, high frequency AC source. The chamber contains two parallel glass tubes where the electrodes are located and is filled with argon or xenon at a pressure of 100 mbar. Under these conditions, it has been shown that high intensity VUV light is generated peaking at 126 nm for argon and at 172 nm for xenon. This VUV radiation seems to produce photoablation of the glass tubes that surround the electrodes. Upon operation of the lamp, polyimide, polypropylene and silicon wafer substrates lying at the bottom of the vessel became coated with silica. The films, identified using X-ray photoelectron spectroscopy (XPS), revealed that the silica is oxygen-deficient with a composition of SiO x where x is between 1.7 and 1.8. The deposition rate on silicon wafers was measured by ellipsometry. When Xe gas is used the deposition rate is much lower than when Ar is used. This result is consistent with a photoablation process since the energy of the photons generated in Ar peaks at 10 eV while those generated in Xe peaks at 7 eV. These energy values should be compared with the O–Si bond strength energy that is 8.3 eV. The morphology and structure of the films were examined by scanning and transmission electron microscopies. Deposition of carbonaceous films occurred when the glass tubes containing the electrodes were coated with carbon.

Modeling of infrared soft-tissue photoablation process

Modeling of infrared soft-tissue photoablation process

Process Technology for Micromachines. Precise Hole Array Drilling of Ceramics by Excimer Laser Photo-ablation Process.

A precise drilling technology with cross section control for use on thin ceramic materials has been developed using Excimer laser photo-ablation process. An homogenous illumination optical system and projection system of high resolution optical elements are applied to a newly designed mass production system. Homogeneity of laser energy under±5% on the mask surface has been obtained by the illumination system, making a final hole array with a distribution of exit hole diameter of 3.5±0.7μm in one processing field of 1.2×1.2mm square area. If a crack occurs in the process because of high repetition rate or high energy from the laser, productivity declines. Designing a specimen holder and He-gas assist enabled cracks to be avolded even at high repetition rate of 200Hz.This paper describes hole array drilling technique with cross section control of ceramics by multi musk method, production system and an application.

Time-of-flight analysis of the plume dynamics of laser-ablated 6H-silicon carbide

The mass and velocity distributions of neutral species, ejected from a laser-ablated 6H-SiC target, are measured by time-of-flight mass spectroscopy. The laser-generated plume is shown to consist of atomic silicon and carbon and small neutral clusters. Measured values of the mean kinetic energies of neutral Si and SiC2 species are 1.1 and 1.5 eV, respectively, when a 6H-SiC target is irradiated with 248 nm radiation at a power density of 1×108 W/cm2. The kinetic energy distribution of Si+ ions is also measured for comparison with the neutral species, and shows a peak in the distribution at 38 eV. These data illustrate that an electronic, and not a thermal, mechanism for particle emission is active during the ablation of a 6H-SiC target. The relationship between the dynamics of the photoablation process and the properties of pulsed-laser-deposited films is also briefly discussed.

Photoablation: Schottky barriers on patterned Si surfaces

Easy to make, patterned, Schottky barriers are investigated. In particular, the following aspects have been considered: the patterning technique, the electrical barrier height, and potential usage as solar cells. Patterning of the Si surfaces was achieved by photoablation process using an UV excimer laser in a presence of various solutions. Using a 5 mW red HeNe laser launched at various angles on the Si surface we have found that patterned solar cells ablated with 2:3:100 of HF:HNO3:H2O were as much as 23% more efficient than nonpatterned cells.

Printed microelectrode array and amperometric sensor for environmental monitoring

A disposable electrochemical sensor for the determination of heavy metal traces has been designed for environmental field analysis. The sensor is supported on a polycarbonate film and consist of an amperometric transducer in combination with an adjacent silver-ink reference electrode. The transducer itself is composed of a network of carbon disc microelectrodes. This array of microelectrodes covers a sensing area of 5 × 5 mm and is made up of some 1000–3000 electrodes. Individual disc microelectrodes measuring 15 μm diameter, have a recessed geometry with hole depth of less than 10 μm and centre-to-centre separation between 100 and 300 μm. A novel three-stage fabrication process based on conventional thick-film printing techniques, vacuum polymerisation of a dielectric and a uv excimer laser photoablation process was used to pattern the disc array structure. This microfabrication method has been evaluated on a laboratory scale and batch production. Amperometric performance and structural characteristics of the electrochemical sensor have been examined by chronoamperometry and electron microscopy. Variations in the sensor current response were studied in order to reduce the diffusion shielding characteristics of individual discs. An optimal microelectrode spacing was assigned to the sensor of 160 μm giving more than one thousand discs per device. The printed sensor is currently under development for single-use field measurements of heavy metals using potentiometric stripping analysis.

Dynamic optical properties of collagen-based tissue during ArF excimer laser ablation

Various attenuation mechanisms affecting the absorption of ArF excimer laser light in collagenous tissues have been studied. Temporal distortion of the laser pulse reflected from the cornea has been observed over a range of incident pulse fluences including the ablation threshold. Reflected pulse shortening begins near the ablation threshold and advances with increasing fluence. The measurement of laser light scattered 30 degrees off specular axis from collagen gel targets indicates that the reflected-pulse distortion is partially a result of scattering. Collagen film transmission studies show an increase in 193-nm light transmission in ablation conditions. These nonlinear attenuation mechanisms may impact significantly on the photoablation process.

Photodegradation of polyimides. 5. An explanation of the rapid photolytic decomposition of a selected polyimide via anhydride formation

Abstract : The photolytic decomposition in air of a polymide film based on a dianhydride and a diarylamine with hexafluoroisopropylidene 6F bridging groups is extremely rapid leading to efficient chain cleavage and subsequent photooxidative decomposition. Relatively short photolysis times with an unfiltered medium pressure mercury lamp are required to give a clean photoablation process of the 6F-6F polyimide films in the air. IR difference spectroscopy shows the appearance of anhydride groups on photolysis in air indicating a photooxidation process via decomposition of the arylimide linkage. A photophysical and photochemical analysis of several model N-arylphthalimides indicates that both solvent polarity and electron withdrawing/donating substituents can greatly after all the efficiency of the photolysis process.

Biophysics of the photoablation process

Besides the coagulation, where the body digests the necrotic tissue and direct evaporation of tissue, the photoablation effect turns out to be very important in tissue removal.

157 nm F2 Lasers.

Current research activities on the electric discharge pumped molecular fluorine lasers at 157 nm, and the present understanding for the laser kinetics are reviewed. Fast and intense discharge excitation, which is more than one order of magnitude higher than excitation rates used for conventional rare-gas halide excimer lasers, improved both output laser energy (100-200 mJ) and efficiency (up to 0.4 %). Successful introduction of cryogenic gas purification that traps various impurity molecules introduced by gases supplied or by secondary reactions during the discharge extended the F2 laser gas lifetime to > 5×105 shots. Further development of high repetition rate high-power exciters, excellent optics with higher damage thresholds, and large aperture and well-controlled low divergence laser beams will open up various useful applications in photochemistry or photo ablation processes.

Use of temporally coincident ultraviolet laser pulses of two different wavelengths to ablate organic polymers

The etching of polymethyl methacrylate (PMMA), by pulsed ultraviolet laser radiation [20-ns full width at half maximum (FWHM), 193 nm] can be increased more than threefold by overlapping both spatially and temporally laser pulses of 308 nm (20 ns FWHM) along with the 193 nm pulses. At a constant fluence of 193 nm, increasing the fluence of the 308 nm pulses progressively increases the etch depth/pair of pulses even though the fluence of the 308 nm radiation is kept below the value at which it would etch the polymer by itself at 1 Hz repetition rate. When a time delay of +300 to −400 ns is introduced between the two pulses, the 193 nm pulse being set as time zero, the enhancement due to pairing the pulses is found to be a maximum at nearly total overlap. A similar enhancement in the etching of PMMA by pulsed 248-nm laser radiation can be achieved by mixing 308 nm pulses with the 248 nm, and in the etching of polyethylene terephthalate, by mixing 351-nm laser pulses with 308-nm laser pulses. Chemical analysis of the solid polymeric product from the laser ablation of PMMA by 248 and 308 nm alone, and by a mixture of 248 and 308 nm laser radiation shows that the mixed laser radiation etches in a way that is chemically similar to pulsed 248-nm laser light and the effect can probably be attributed to an enhancement of the photoablation process.