KrF Excimer Laser Irradiation Research Articles

CVD Encapsulation of Laser-Graphitized Electrodes in Diamond Electro-Optical Devices

Conductive graphitized grooves on the dielectric surface of diamond have been created by KrF excimer laser radiation. The advantages of such a circuit board in high-field applications is rather limited because the crystal surface has a relatively low electrical breakdown threshold. To increase the electrical strength, a method of encapsulating surface conductive graphitized structures by chemical vapor deposition of an epitaxial diamond layer has been proposed and realized. The quality of the growth diamond is proved by Raman spectroscopy. A comparative study of the electrical resistivity of graphitized wires and the breakdown fields between them before and after diamond growth was carried out. The proposed technique is crucial for diamond-based high-field electro-optical devices, such as THz photoconductive emitters.

Ultrafast ultraviolet laser-induced voltage of air

In this work, the time-scale laser-induced voltage (LIV) of air was investigated under KrF excimer laser irradiation. The LIV response was fitted by a sum of three exponential functions, where the fitted parameters were influenced by the bias voltage Vb and the laser energy Ein. Higher Vb produced significant LIV. An exponential relationship was observed between the Ein and LIV signal amplitude (Vp). After decreasing the adjustable resistor, the LIV trace was almost triangular and symmetrical due to the impedance effect with the response time which was completely limited by the laser pulse duration. As a potential application, the LIV of air presented a viable method for single-pulse laser detection.

Laser doping mechanism of 4H-SiC by KrF excimer laser irradiation using SiNx thin films

In this study, nitrogen is doped into 4H-SiC by irradiating 4H-SiC with a SiNx thin film and a KrF excimer laser. The doping depth profile, crystal structure, electrical properties, and surface roughness results are analyzed to evaluate the excimer-laser doping mechanism. High-concentration doping is possible at a fluence of 2.5 J cm−2 and 10 shots, while maintaining the 4H-SiC crystal structure via solid-phase diffusion. However, changes in the 4H-SiC crystalline state are observed upon liquid-phase diffusion at a fluence of ≥2.8 J cm−2. At a fluence of 2.5 J cm−2 and 100 shots, nitrogen can be deeply diffused via solid-phase diffusion; however, an amorphous layer is formed on the surface and there is an increase in contact resistance.

Enhanced Long-Term Reliability of Seal DeltaSpot Welded Dissimilar Joint between 6061 Aluminum Alloy and Galvannealed Steel via Excimer Laser Irradiation.

Structural-adhesive-assisted DeltaSpot welding was used to improve the weldability and mechanical properties of dissimilar joints between 6061 aluminum alloy and galvannealed HSLA steel. Evaluation of the spot-weld-bonded surfaces from lap shear tests after long-term exposure to chloride and a humid atmosphere (5% NaCl, 35 °C) indicated that the long-term mechanical reliability of the dissimilar weld in a corrosive environment depends strongly on the adhesive–Al6061 alloy bond strength. Corrosive electrolyte infiltrated the epoxy-based adhesive/Al alloy interface, disrupting the chemical interactions and decreasing the adhesion via anodic undercutting of the Al alloy. Due to localized electrochemical galvanic reactions, the surrounding nugget matrix suffered accelerated anodic dissolution, resulting in an Al6061-T6 alloy plate with degraded adhesive strength and mechanical properties. KrF excimer laser irradiation of the Al alloy before adhesive bonding removed the weakly bonded native oxidic overlayers and altered the substrate topography. This afforded a low electrolyte permeability and prevented adhesive delamination, thereby enhancing the long-term stability of the chemical interactions between the adhesive and Al alloy substrate. The results demonstrate the application of excimer laser irradiation as a simple and environmentally friendly processing technology for robust adhesion and reliable bonding between 6061 aluminum alloy and galvannealed steel.

Solid-phase epitaxial crystallization of β-Ga2O3 thin film by KrF excimer laser irradiation from backside of NiO (111)-buffered α-Al2O3 (0001) substrate at room temperature

We have investigated the solid-phase epitaxial crystallization of β-Ga2O3 thin films on NiO (111) (3 nm thick)-buffered α-Al2O3 (0001) substrates prepared by pulsed KrF excimer laser irradiation onto amorphous Ga2O3 thin films from the backside of the substrate at room temperature. The results of x-ray diffraction, reflection high-energy electron diffraction, and transmission electron microscopy indicated that the solid-phase crystallization of the amorphous Ga2O3 thin film to epitaxial β-Ga2O3 film started from the film/substrate interface toward the film surface with an average growth rate of about 0.1 nm thickness per one pulse irradiation. The optical bandgap of the epitaxial β-Ga2O3 thin films (∼80 nm thick) was estimated to be 4.9 eV from the UV/Vis transmittance measurement.

Excimer laser annealing method for achieving low electrical resistivity and high work function in transparent conductive amorphous In2O3:Zn films on a polyethylene terephthalate substrate

We have developed an excimer laser annealing method to achieve low electrical resistivity (ρ) and a high work function in amorphous In2O3:Zn (IZO) films on polyethylene terephthalate (PET) substrates. The effect of excimer laser irradiation of the films on crack formation, electrical properties (ρ, carrier concentration, and Hall mobility), and work function were investigated. KrF excimer laser irradiation produced cracks in the surface of the IZO films on PET as a result of thermal expansion of the PET substrate. By inserting an amorphous SiO2 layer as a heat barrier between the IZO layer and PET substrate, crack formation was prevented. Moreover, it was found that the work function of IZO film could be controlled by the laser fluence and repetition rate. Irradiation of a 150-nm-thick amorphous IZO film on a SiO2-coated PET substrate achieved a low ρ of 3.55 × 10−4 Ω cm and a high work function of 5.4 eV due to the reduction of oxygen and carbon while maintaining a flat surface.

Enhanced properties of hierarchically-nanostructured undoped acceptor-rich ZnO single-crystal microtube irradiated by UV laser

Here a variety of hierarchic nanostructures on the undoped acceptor-rich ZnO (A-ZnO) single-crystal microtube are fabricated by KrF excimer laser irradiation. The effects of process parameters, i.e. laser fluence and number of pulse (NOP), on nanostructure morphology of the A-ZnO microtube are investigated, by which the controllable hierarchic nanostructures are achieved. The mechanism of the nanostructure formation is attributed to self-assembled growth by decomposition and re-nucleation owing to rapid heating and cooling down during laser irradiation near Zn-vacancy-related point defects. The Raman and photoluminescence spectra confirm that the nanostructures possess massive surface defects, e.g. oxygen vacancies (VO) and zinc interstitials (Zni). The electrical resistivity of the nanostructured A-ZnO microtube is down to ∼10−3 Ω cm, about one order of magnitude lower than that of the as-grown A-ZnO microtube. The great ratio of surface area to volume of the nanostructures realizes the improved UV detection and photodegradation performance. The optimal photoresponsivity can be up to 27.08 A/W using the process parameters of 200 mJ/cm2 and 100 pulses. The catalytic degradation rate of the A-ZnO microtube irradiated by 150 mJ/cm2 and 200 pulses with 6-nm Au nanoparticles decoration for methylene blue solution is ∼3.4 times higher than the commercial nanoparticles. The present work paves a new way to design and fabricate a variety of hierarchic nanostructures on undoped A-ZnO microtube for enhanced electrical and photocatalytic performance.

Improved Structural and Electrical Properties of ZnO-Based Thin Film Transistors by Using Pulsed KrF Excimer Laser Irradiation

We report on the characteristics of ZnO-based thin film transistors (TFT) fabricated by radio frequency magnetron sputtering. The surface of the ZnO channel layers were treated by pulsed KrF excimer laser irradiation (ELI) to improve the structural and electrical properties. The ZnO TFT device is of bottom gate type, which consists of SiO2 as a gate insulator and indium tin oxide as a gate deposited onto Corning glass substrates. The root-mean-square surface roughness and structural property of ZnO channel layer was significantly improved by the ELI treatment. The laser-treated ZnO TFT exhibited a saturation mobility of 19.27 cm2/V s, an on/off ratio greater than 105, the off current of less than 10−7 A, and a threshold voltage of 1.1 V. These results revealed the significant improvement of device characteristics and demonstrated that the pulsed KrF ELI treatment is an effective way to improve the ZnO TFT device performance.

Formation of Ohmic contacts on laser irradiated n-type 6H-SiC without thermal annealing

In this work, KrF excimer laser irradiation of n-type SiC is used to form Ohmic contacts at the interfaces between the irradiated SiC and various types of metals with different work functions without subsequent thermal annealing. Ohmic contacts are formed between laser-treated 6H-SiC and Ti at a laser fluence of 0.7 J/cm2. Moreover, in the fluence range of 0.7–1.3 J/cm2, Ohmic characteristics are also observed between irradiated 6H-SiC and Au, which is a representative inert metal. The laser-induced heavy doping effect reduces the thickness of the Schottky barrier between the metal and SiC, and the formation of graphene sheets on the irradiated SiC surface reduces the barrier height, resulting in the direct formation of Ohmic contacts. Our findings thus demonstrate the potential of this laser treatment method to achieve Ohmic contacts between n-type SiC and a broad range of metal electrodes without requiring high-temperature annealing.

High-Thermoresistant Temporary Bonding Technology for Multichip-to-Wafer 3-D Integration With Via-Last TSVs

In this paper, a high-thermoresistant temporary bonding/debonding system using spin-on glass (SOG) and hydrogenated amorphous silicon layers is proposed for the multichip-to-wafer (MCtW) 3-D integration based on a via-last/backside-via through-silicon via (TSV) approach. The shear strengths of chips bonded to wafers through the SOG layers are evaluated. In addition, the debonding performance of the chips from the wafers is investigated by using the KrF excimer laser irradiation. Finally, a via-last/backside-via MCtW 3-D integration process using the temporary bonding/debonding system is demonstrated to show the high feasibility with the successful interconnect formation of a Cu-TSVs daisy chain (10 $\mu \text{m}$ in diameter and 50 $\mu \text{m}$ in depth) with a SiO2 liner dielectric deposited by O3-tetraethylorthosilicate chemical vapor deposition at 350 °C.

Optimization of silver nanowire formation on laser processed PEN: Surface properties and antibacterial effects

Combination of polymers with their excellent workability and long-term stability with inorganic nanomaterials exhibiting unique physic-chemical properties opens the way for preparation of nanocomposites with wide range of potential applications in electronic, environmental, medical and biomedical industry. Despite of testing of various metal nanostructures in biomedicine, the best results, particularly antibacterial effects, have been achieved with the silver-based ones. Silver nanowire arrays on the surface of polyethylene naphthalate (PEN), first modified by KrF excimer laser irradiation and then silver coated, were prepared. The laser fluence and angle of incidence of laser beam, were changed to achieve required sample surface morphology, which was controlled by AFM, SEM and FIB-SEM techniques. The surface properties of the samples in different phases of their preparation were characterized by XPS and UV–Vis. The influence of the surface morphology of the samples on their antibacterial effect was investigated by drop plate method using Gram-negative bacteria E. coli and Gram-positive S. epidermidis. The release of Ag ions into working medium was controlled by ICP-MS. The surface morphology of polymeric substrate was found to have a great influence on the resulting antibacterial effect of such silver/polymer composites.

Investigation on stable superhydrophobic polycarbonate based compound induced by KrF excimer laser irradiation

This study demonstrates a reliable method for the manufacturing of Polycarbonate based compound (PCBC) superhydrophobic surface by KrF excimer laser irradiation. The water contact angle (CA) of PCBC samples surface was increased from 75° to 170°, and the CAH of most samples was between 2° and 6°. The CA of samples remained at about 158° for 2 months. The abrasion resistance test showed that the CA reached about 115° for 1% mass losses. Optical contact angle meter, XRD, LCM, SEM, EDS, FTIR and XPS were used to analyze surface properties of PC samples. It was indicated that the increase in surface roughness caused by PC surface precipitation of small organometallic complexes particles was the main factor to the preparation of superhydrophobic surface. It showed that the hydrophilicity of PCBC surface could be converted into superhydrophobicity quickly and effectively by laser irradiation.

Waveguide Bragg Gratings in Ormocer®s for Temperature Sensing.

Embedded channel waveguide Bragg gratings are fabricated in the Ormocer® hybrid polymers OrmoComp®, OrmoCore, and OrmoClad by employing a single writing step technique based on phase mask technology and KrF excimer laser irradiation. All waveguide Bragg gratings exhibit well-defined reflection peaks within the telecom wavelengths range with peak heights of up to 35 dB and −3 dB-bandwidths of down to 95 pm. Furthermore, the dependency of the fabricated embedded channel waveguide Bragg gratings on changes of the temperature and relative humidity are investigated. Here, we found that the Bragg grating in OrmoComp® is significantly influenced by humidity variations, while the Bragg gratings in OrmoCore and OrmoClad exhibit linear and considerably high temperature sensitivities of up to −250 pm/C and a linear dependency on the relative humidity in the range of −9 pm/%.

Photo-Reduced Graphene as Electrode Active Materials for Supercapacitor Applications

Graphene is a form of carbon that has high electrical conductivity, a planar structure and substantially high surface area, thereby having the potential for more storage of electrostatic charge for high energy supercapacitors (SC). In this paper, the recent developments on the fabrication of graphene by means of photo-reduction of graphene oxide will be overviewed. The main advantage of the photo-process is that it does not rely on the use of chemicals or high temperature. For example, KrF excimer laser irradiation process for the fabrication of N-doped graphene from graphene oxide will be illustrated and the performance of laser reduced N-doped graphene when it is used as electrode active materials in supercapacitors will also be evaluated.

Patterned perforation of polyester films by excimer laser ablation

The effects of 248 nm KrF excimer laser irradiation on combinations of different thickness polyethylene terephtalate (PET) films and different stainless steel mask mesh opening sizes were considered as a possible method to achieve different size perforation patterns on different thickness PET films. The findings of this work will provide an effective and controllable perforation technology. Therefore, ablation behavior of PET films was investigated for different laser energy fluence and number of laser pulses. The morphology of irradiated samples was observed by optical microscopy, and atomic forced microscopy was employed to study the topography and microstructures after laser ablation. An attempt has been made to correlate these findings with the orientation, strength, and mechanical properties of the polymer. The experimental results reveal that the percentage of perforation and the average perforated area increase with increasing number of pulses for all film thicknesses. The affected area, defined as...

Effect of optical fiber hydrogen loading on the inscription efficiency of chirped Bragg gratings by means of KrF excimer laser radiation

Effect of optical fiber hydrogen loading on the inscription efficiency of chirped Bragg gratings by means of KrF excimer laser radiation

Surface, structural and mechanical properties of zirconium ablated by KrF excimer laser radiation

We study the effect of the ambient – dry (air) and wet (propanol) – environment on the surface, structural and mechanical properties of zirconium samples after irradiation with a KrF excimer laser (wavelength of , pulse duration of and repetition rate of ). The samples are exposed to an increasing number of laser pulses varying from 500 to 2000 in both media. Various features of the treated targets such as surface morphology, chemical composition, crystalline structure and hardness are analysed by complementary characterisation techniques, such as scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy and Vickers hardness tester, respectively. Surface morphology and hardness are explained on the basis of modifications in crystalinity, residual pressures and chemical properties of the sample surface after its irradiation.

Incubation phenomena during UV‐pulse excimer laser processing of silicone elastomers

ABSTRACTObservations of the interaction of poly(dimethylsiloxane) (PDMS) sheet (210 μm thick) with KrF excimer laser irradiation (λ = 248 nm), with low energy of 50 mJ/pulse are presented. The negative ablation or swelling of the material caused by low frequency pulse irradiation is characterized by optical microscopy, μ‐Raman spectrometry and X‐ray micro‐tomography. The appearance of defected areas in the form of cones inside the sheet and changes of material chemistry are discussed. These phenomena are considered as a precursor of the ablation occurring after passing a threshold of absorbed laser irradiation energy. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44541.

Effect of KrF excimer laser irradiation on the surface changes and photoelectric properties of ZnO single crystal

In this paper, the effect of KrF pulsed excimer laser irradiation on the structural, surface morphology, photoluminescence and electrical properties of ZnO single crystal was investigated. Compared to the as-grown sample, at an irradiation energy density of 257 mJ/cm2, the ZnO single crystal exhibits a series of phenomenon: XRD and Raman results show that the crystallization of ZnO quality change slightly, resistivity is decreased by two orders of magnitude, carrier concentration is increased by one order of magnitude. After laser irradiation, the surface shows some strip lines and no cracks. Formula calculation and simulation results show that the stripes are not caused by surface melting. We speculate that these stripes are caused by the precipitation of ZnO material inside to the surface. Due to the reduction of oxygen vacancies, UV emission has been enhanced and visible emission has been declined after irradiation. After the laser irradiation, the visible light of ZnO surface can be regulated. The experimental results show that KrF laser irradiation could effectively improve the optical and electrical properties of ZnO single crystal, which is important for the application of high performance of emitting optoelectronic devices.

Rapid-melt-mediated recrystallization of ZnO thin films grown at low temperature by using KrF excimer laser irradiation

ZnO thin films with thickness of 150 nm were grown on ITO/glass (ITO-coated glass) substrates by using the radio-frequency (RF) sputtering technique at 400 °C in an Ar atmosphere. An excimer laser irradiation (ELI) treatment was performed on the surface of ZnO thin films at different excimer laser energy densities of 150, 200, and 250 mJ/cm2 in a N2 atmosphere. The ELI treatment promoted the lateral recystallization of the surface area of the ZnO, resulting in a significant improvement of the crystallinity of the ZnO thin films without substrate damage. As-grown ZnO and ELI-treated ZnO thin films were characterized by using scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD). The analyses showed that the ZnO thin film treated with ELI at an excimer laser energy density of 150 mJ/cm2 exhibited the best structural properties.