ArF Pulsed Laser Research Articles

Surface structured silver-copper bimetallic nanoparticles by irradiation of excimer laser pulses to bilayer thin films

Optical chips based on plasmonic bimetal nanoparticles are of particular interest for various applications, including optical sensors, as well as plasmon-enhanced fluorescence and plasmon-enhanced Raman scattering due to their extraordinary optical properties. In the paper, the formation of the bimetallic nanoparticles on the BK7 substrate and tuning of the LSPR wavelengths by irradiation of excimer laser pulses (193 nm output wavelength and 15 ns temporal pulse linewidth) to silver-copper thin films deposited by the physical vapor deposition (PVD) method is studied. Applying four and five ArF laser pulses with the fluence of 140 mJ cm−2 leads to the formation of spherical Ag-Cu nanoparticles and clusters, respectively, with several LSPR peaks in the UV and visible ranges. Also, sharp and intense LSPR peaks in the 560 to 700 nm spectral range are observed in the absorption spectra of the produced samples with four laser pulses which indicates the ability of the method for tuning the LSPR wavelength. Furthermore, the highest enhancement in the Raman scattering of R6G solution is provided using this sample as a substrate for Raman spectroscopy. Therefore, the laser-produced spherical Ag-Cu NPs by these parameters of laser irradiation can be a good candidate for applications based on LSPR, and Raman or fluorescence enhancement.

Cu-Au core-shell nanostructures induced by ArF excimer laser irradiation

In this paper, Cu-Au nanospherical structures were formed on glass surfaces by nanosecond UV laser irradiation. ArF laser pulses (193 nm wavelength, 15 ns time duration) were used for the experiments. Cu-Au bimetallic thin-film sample surfaces are structured under ArF excimer laser irradiation during the ablation process. Laser irradiation experiments were carried out using different laser fluences, the number of pulses, and focusing optics. Morphology of the irradiated surfaces and images of the nanostructures were obtained by the scanning electron microscopy method. Also, the optical and plasmonic behaviors of the nanostructures were collected by UV-Vis spectroscopy. Elemental composition and its spatial distribution were obtained using energy-dispersive x-ray spectroscopy (EDS) and mapping. EDS mapping shows that bimetallic nanospheres have a core-shell structure. Our results show that different laser irradiation parameters change the nanostructures’ composition, size, distribution, morphology, and optical properties. Cu-Au nanospherical structures can be used for nano-biosensing, catalysis, and enhanced spectroscopy applications.

The effect of sub-second intervals of ArF laser irradiation on the formation of periodic micro-swelling structures on silicone rubber surfaces

Surface modification and microstructure formation of silicone rubber are gathering attention as popular methods of wettability control for microfluidic devices and biomedical applications. In this report, micro-swelling structures were fabricated on silicone rubber surfaces by ArF laser irradiation at various pulse repetition rates. The average height of the swelling structures shows a negative correlation with the pulse repetition rates of 2 Hz–20 Hz. The relationship between the microstructure height and the number of ArF laser shots was investigated at 2 Hz, 6 Hz, and 20 Hz pulse repetition rates, and it is presented that the growth of microstructures saturates with the smaller number of shots at the higher pulse repetition rate. These results imply the possibility of other competing mechanisms that disturb the swelling of silicone rubber by the ArF laser irradiation. The Attenuated Total reflection Fourier Transform Infrared spectroscopy measurement of the silicone rubber surface shows that the desorption of the –CH3 group proceeds more efficiently at the higher pulse repetition rate. It is concluded that the modification of silicone to the silica-like structure that increases in surface hardness disturbs the growth of the swelling structure, and the sub-second intervals of the ArF laser pulse suppress the modification of silicone to the silica-like structure. The understanding of the processes after photodissociation contributes not only to the effective formation of microstructures but also to the chemical modification of the silicone rubber surface.

Effect of pulsed UV laser irradiation on 4H-SiC MOS with thermal gate oxide

The impact of 193 nm ArF pulsed UV laser irradiation on thermally grown SiO2/4H-SiC structures was investigated. The effect of pulsed UV light on the near-interface oxide trap of SiO2/SiC structure is greater than that on the interface and the near-interface SiC substrate. The defects near the interface do not change monotonously with the increase in irradiation power, which indicates that UV irradiation has at least two effects on SiO2/SiC. When the irradiation power is too high, new defects will be introduced into the oxide layer. This article reveals a potential mechanism for high-energy photon irradiation to change device performance in semiconductor plasma technology.

High optical quality cellulose thin films grown from raw natural cotton by pulsed laser deposition

Raw natural cotton harvested in the fields of Thessaly, Central Greece, was used to grow high optical quality, highly durable cellulose thin films by pulsed laser deposition, using 193 nm ArF laser pulses. Standard pulsed laser deposition conditions at room temperature were applied and raw, unprocessed, natural cotton targets were used. The semi-crystalline cellulose of natural cotton converts to very durable solid films that are fully transparent in the visible wavelength range and exhibit amorphous structure. Thin film quality and surface morphology are parametrically investigated and show a strong dependence on laser fluence. Films deposited at the lowest fluence levels ~ 5 mJ/cm2 on target, close to the observed ablation threshold, exhibit roughness of ~ 1.7 nm rms. The high optical quality of the grown biocompatible cellulose materials proves the unique capacities of laser deposition and processing methods and promise novel biophotonics and other interdisciplinary applications for the health and safety of the citizen.

A novel membrane-type apatite scaffold engineered by pulsed laser ablation.

Cell sheet technology is a scaffold-free method for tissue reconstruction. A sheet-shaped scaffold would be suitable for the regeneration of periodontal membrane. We designed a stem cell sheet combining human mesenchymal stromal cells (hMSCs) and a 10-µm thick biological apatite (BAp) membrane fabricated with an ArF pulsed laser ablation for periodontal regeneration. X-ray diffraction showed that crystalline hydroxyapatite (HAp) was present in BAp and HAp membranes after post-annealing. Energy dispersive analysis of the BAp membrane revealed peaks of Na and Mg in addition to Ca and P. Approximately 3×10(4) hMSCs were cultured on BAp and HAP membranes for 7 and 14 days. From in vitro assays, hMSCs grew faster and had higher osteoblast differentiation when cultured on the BAp membrane than did the cell culture on the HAp membrane. Stem cell sheets combined with a BAp membrane may have potential applications in guided bone regeneration and osteoconductive scaffolds.

Nano-crystalline Ag–PbTe thermoelectric thin films by a multi-target PLD system

It has been evaluated the ability of ArF pulsed laser ablation to grow nano-crystalline thin films of high temperature PbTe thermoelectric material, and to obtain a uniform and controlled Ag blending, through the entire thickness of the film, using a multi-target system in vacuum. The substrate used was a mirror polished technical alumina slab. The increasing atomic percentage of Ag effect on physical–chemical and electronic properties was evaluated in the range 300–575K. The stoichiometry and the distribution of the Ag component, over the whole thickness of the samples deposited, have been studied by XPS (X-ray photoelectron spectroscopy) and corresponding depth profiles. The crystallographic structure of the film was analyzed by grazing incidence X-ray diffraction (GI-XRD) system. Scherrer analysis for crystallite size shows the presence of nano-structures, of the order of 30–35nm. Electrical resistivity of the samples, studied by the four point probe method, as a function of increasing Ag content, shows a typical semi-conductor behavior. From conductivity values, carrier concentration and Seebeck parameter determination, the power factor of deposited films was calculated. Both XPS, Hall mobility and Seebeck analysis seem to indicate a limit value to the Ag solubility of the order of 5%, for thin films of ∼200nm thickness, deposited at 350°C. These data resulted to be comparable to theoretical evaluation for thin films but order of magnitude lower than the corresponding bulk materials.

Na I spectra in the 1.4–14 micron range: transitions and oscillator strengths involving f-, g-, and h-states

Context. Compared with the visible and ultraviolet ranges, fewer atomic and ionic lines are available in the infrared spectral region. Atlases of stellar spectra often provide only a short list of identified lines, and modern laboratory-based spectral features for wavelengths longer than 1 micron are not available for most elements. For the efficient use of the growing capabilities of infrared (IR) astronomy, detailed spectroscopical information on atomic line features in the IR region is needed. Aims. Parts of the infrared stellar (e.g., solar) spectra in the 1200–1800 cm-1 (5.6–8 μ m) range have never been observed from the ground because of heavy contamination of the spectrum by telluric absorption lines. Such an infrared spectrum represents a great challenge for laboratory observations of new, unknown infrared atomic transitions involving the atomic levels with high orbital momentum and their comparison with the available spectra. Methods. The vapors of excited Na i atoms are produced during the ablation of the salt (sodium iodide, Na i) targets by a high-repetition rate (1.0 kHz) pulsed nanosecond ArF laser ExciStar S-Industrial V2.0 1000, pulse length 12 ns, λ = 193 nm, output energy of 15 mJ, fluence about 2–20 J/cm2 inside a vacuum chamber (average pressure 10-2 Torr). The time-resolved emission spectrum of the neutral atomic potassium (Na i) was recorded in the 700–7000 cm-1 region using the Fourier transform infrared spectroscopy technique with a resolution of 0.02 cm-1 . The f -values calculated in the quantum-defect theory approximation are presented for the transitions involving the reported Na i levels. Results. This study reports precision laboratory measurements for 26 Na i lines in the range of 700–7000 cm-1 (14–1.4 μ m), including 20 lines not measured previously in the laboratory. This results in newly observed 7h, 6h, and 6g levels, and improved energy determination for ten previously known levels. The doublet structure of the 4f level has been observed for the first time. For transitions between the observed levels, we report calculated f -values that agree reasonably well with experiment.Conclusions. The recorded Na i line features agree with the data from the available solar spectrum atlases. The energy values of Na i 4s, 4p, 5p, 6p, 4f, 5f, and 5g levels extracted from our spectra have lower uncertainties as compared to the values reported several decades ago, but the latter values slightly differ from ours.

Gasochromic performance of WO3-nanorod thin films fabricated with an ArF excimer laser

Thin films with tungsten trioxide (WO3) nanorods were fabricated by using an ArF pulsed laser deposition system. Because the ArF excimer laser operates at a very short wavelength of 193 nm, short enough to expect strong absorption of the photons in the semiconductor oxide targets, and because the clusters incoming to the substrates have high momentum, we could build thin films with good surface morphology. Highly homogeneous arrays of nanorods with sizes mostly in the range of 30–40 nm were observed. The absorbance response towards hydrogen (H2) gas was investigated for a WO3 film coated with 25-A-thick palladium (Pd). The Pd/WO3-nanorod thin films exhibited excellent gasochromic response when measured in the visible-NIR range (400–1000 nm). As low as 0.06% H2 concentration was clearly sensed. A significant reversible absorbance change and fast recovery (<2 min) were observed when the films were exposed to H2 at different concentrations.

Effect of deposition temperature on chemical composition and electronic properties of amorphous carbon nitride ( a-CNx) thin films grown by plasma assisted pulsed laser deposition

The effect of deposition temperature and nitrogen inclusion in amorphous carbon ( a-C) films, deposited by plasma enhanced pulsed laser deposition, on chemical composition and electronic transport has been studied. a-CNx films were deposited on Si (100) by pulsed ArF laser ablation of a graphite target, under N 2 atmosphere. A radiofrequency (13.56 MHz RF) apparatus was used to generate plasma of excited nitrogen species, and its effect on nitrogen uptake and CNx film formation has been studied. Chemical and micro-structural changes associated to increased deposition temperature and nitrogen incorporation were examined by x-ray photoelectron spectroscopy; electrical properties were analyzed by the four-point-probe methods. Temperature-dependent conductivity measurements are tentatively interpreted and discussed in reference to chemical composition.

Time-resolved FTIR emission spectroscopy of Cu in the 1800–3800 cm−1 region: transitions involving f and g states and oscillator strengths

Time-resolved Fourier-transform spectroscopy was applied to the study of the emission spectra of Cu vapours in a vacuum (10−2 Torr) produced in ablation of a Cu metal target by a high-repetition rate (1.0 kHz) pulsed nanosecond ArF laser (λ = 193 nm, output energy of 15 mJ). The time-resolved infrared emission spectrum of Cu was recorded in the 1800–3800 cm−1 spectral region with a resolution of 0.017 cm−1. The time profiles of the measured lines have maxima at 18–20 µs after a laser shot and display non-exponential decay with a decay time of 5–15 µs. This study reports 17 lines (uncertainty 0.0003–0.018 cm−1) of Cu I not previously observed. This results in seven newly-found levels and revised energy values for 11 known levels (uncertainty 0.01–0.03 cm−1). We also calculate transition probabilities and oscillator strengths for several transitions involving the reported Cu levels.

Multi-element analysis of ceramic and polymeric samples by ArF laser excited atomic fluorescence of ablated plumes

Laser-excited-atomic-fluorescence at the single excitation wavelength of the ArF laser was demonstrated for numerous analytes. These analytes were present in the material plumes produced by pulsed laser ablation of ceramic and polymeric targets. Under minimally destructive conditions, the fluorescence spectra were orders of magnitude brighter than the corresponding laser-induced breakdown spectra. Simultaneous emissions from Al, Ca, Co, Cr, Cu, Fe, In, Mg, Mn, Na, Pb, Sn, and Si were observed. The technique was applied to four analytical problems: the analysis of dried paint for trace lead when μg g−1 detection limits were achieved; the analysis of valuable potteries when two look-alike specimens were differentiated based on practically non-destructive single-shot analysis; the elemental analysis of ink when lines written with different pens could be discriminated without discernable sample destruction even under the microscope; and the analysis of electrode-plastic interfaces when the detection sensitivity was comparable to SIMS. The fluorescence intensity varied with the fluence and the timing of the ArF laser pulse in ways suggestive of particulates in the plume.

Time-resolved Fourier-transform infrared emission spectroscopy of Ag in the (1300–3600)-cm−1region: Transitions involvingfandgstates and oscillator strengths

We report on a study of the emission spectra of Ag vapor in a vacuum (${10}^{\ensuremath{-}2}$ Torr) formed in ablation of an Ag metal target by a high-repetition rate (1.0 kHz) pulsed nanosecond ArF laser ($\ensuremath{\lambda}=193$ nm, output energy of 15 mJ). The time-resolved infrared emission spectrum of Ag was recorded in the 1300- to 3600-cm${}^{\ensuremath{-}1}$ spectral region using the Fourier transform infrared spectroscopy technique with a resolution of $0.02$ cm${}^{\ensuremath{-}1}$. The time profiles of the measured lines have maxima at 5\char21{}6 $\ensuremath{\mu}$s after a laser shot and display nonexponential decay with a decay time of 3\char21{}7 $\ensuremath{\mu}$s. The lines reported here are given with an uncertainty of 0.0005\char21{}0.016 cm${}^{\ensuremath{-}1}$. The line classification is performed using relative line strengths expressed in terms of transition dipole matrix elements calculated with the help of the Fues model potential; these calculations show agreement with the large experimental and calculated data sets available in the literature. In addition to these data we also calculate transition probabilities and line and oscillator strengths for a number of transitions in the 1300- to 5000-cm${}^{\ensuremath{-}1}$ range between $(4{d}^{10}){\mathit{nl}}_{j}$ states of Ag.

Influence of Na-related defects on ArF laser absorption in CaF2

ArF laser pulse transmission through commercial high purity CaF2 is determined by measuring the energy of each pulse before and behind the sample up to an incident fluence H of 10 mJ/cm2. The steady state transmission of ArF laser pulses decreases with increasing fluence. The related absorption coefficients αst(H) are proportional to H and rationalized by effective 1- and 2-photon absorption coefficients 2.4×10−4 cm−1≤αeff≤16.8×10−4 cm−1 and 1.7×10−9 cm W−1≤βeff≤9.3×10−9 cm W−1, respectively. The αeff and βeff values increase with the Na content of the CaF2 samples as identified by the fluorescence of Na-related MNa centers at 740 nm. This relation is simulated by a rate equation model describing the ArF laser induced MNa generation in the dark periods between the laser pulses and their annealing during laser irradiation. MNa generation starts with intrinsic 2-photon absorption in CaF2, yielding self-trapped excitons (STE). These pairs of F and H centers move upon thermal activation and the F centers combine with FNa to form MNa centers. MNa annealing occurs by its photo dissociation into a pair of F and FNa centers.

Time-resolved Fourier-transform infrared emission spectroscopy of Au in the1800–4000−cm−1region: Rydberg transitions

Time-resolved Fourier-transform infrared spectroscopy was applied for observations of the emission arising after irradiation of a Au target with a pulsed nanosecond ArF ($\ensuremath{\lambda}=193$ nm) laser. A high-repetition-rate laser ($1.0$ kHz) with an output energy of $15$ mJ was focused on a rotating metal target inside a vacuum chamber (average pressure ${10}^{\ensuremath{-}2}$ Torr). The infrared emission spectra were observed in the $1800--4000{\mathrm{cm}}^{\ensuremath{-}1}$ spectral region with a time profile showing maximum emission intensity in $9--11$ $\ensuremath{\mu}$s after a laser shot. Seven prominent lines are reported; most of them are identified as being due to transitions between low Rydberg $\mathit{nl}$ states of Au with $n=5--10$ and $l=0--3$. An alternative identification ($6{f}_{5/2}\ensuremath{\rightarrow}7{d}_{3/2}$) is given for the $2518.489{\mathit{cm}}^{\ensuremath{-}1}$ line previously classified as $8{d}_{5/2}\ensuremath{\rightarrow}5{f}_{5/2}$. On the basis of the measured lines, three $f$ levels of the Au atom are reported and revised values are given for six other levels.

ArF Laser-induced Deposition of Carbon Encapsulated CoFe Nanoparticles

The decomposition of the gaseous acetylene - Fe(CO)5 - Co(CO)3(NO) mixtures induced by a single ArF laser pulse is a very efficient and novel method for formation of amorphous cobalt/iron alloy nanoparticles completely encapsulated in amorphous carbon shell. The properties of the CoFe(core)-carbon(shell) nanocomposites were examined by spectroscopy, microscopy and diffraction techniques. Magnetic measurements revealed the superparamagnetic behaviour of the as-prepared samples with diameter ≈ 5 nm at temperatures above 200K. The properties of the CoFe alloy nanoparticles annealed at 600, 900 and 1150oC were studied. Heating leads to structural changes in both the alloy core and the carbon shell. The cobalt/iron core crystallizes as syn-wairauite and carbon affords graphite outer part.

Bismuth activated alumosilicate optical fibers fabricated by surface-plasma chemical vapor deposition technology

Plasma chemical technology is experimentally applied to the fabrication of a Bi-activated alumosilicate-core pure-silica-cladding fiber preform. To the best of our knowledge, this is the first time this technology has been applied in this way. We measure gain efficiency at pumping by a 1058 nm wavelength Yb fiber laser in a piece of a newly obtained fiber 20 m in length within 100-1200 nm wavelengths band. The gain efficiency reaches as high as 0.2 dB/mW. Bi-activated alumosilicate-core pure-silica-cladding fiber that is not more than 12 m in length serves a basis for a 1 W output power fiber laser emitting at the wavelength of 1160 nm with 8% slope efficiency. We also measure the photoluminescence spectrum and kinetics of Bi centers responsible for laser emission under the excitation of 193 nm wavelength ArF laser pulses.

Ultraviolet light-induced water-droplet formation from wet ambient air

We report the formation of water droplets by irradiating wet ambient air with deep UV light. The light sources were either a continuous low-pressure mercury lamp or pulsed ArF laser, which both emit light shorter than 200 nm. Water droplets were produced in reaction vessels under different temperature, relative humidity, and moisture-supply conditions. The particles grew as large as about 0.2 mm. The suggested mechanism is discussed with the photo-dissociations of oxygen and successively formed ozone, and further dark reactions giving hydrogen peroxide as a seeding nucleus. Observed concentrations of intermediates were well explained by simulating the proposed chemical reactions. A possible application to artificial rain is briefly described.

Generation and annealing of defects in virgin fused silica (type III) upon ArF laser irradiation: Transmission measurements and kinetic model

The transmission of ArF laser pulses in virgin fused silica (type III) samples changes during N = 10 6 pulses at an incoming fluence H in = 5 mJ cm −2 pulse −1. The related absorption is determined by the pulse energy absorption coefficient α( N, H in) using a modified Beer’s law, yielding initial values α ini around 0.005 cm −1, a maximum α max ⩽ 0.02 cm −1 at N = 10 3–10 4 and stationary values 0.0045 cm −1 ⩽ α end ⩽ 0.0094 cm −1 after N ≈ 6 × 10 5 pulses. The development α( N, H in = const.) is simulated by a rate equation model assuming a pulse number dependent E′ center density E′( N). E′( N) is determined by a dynamic equilibrium between E′ center generation and annealing. Generation occurs photolytically from the precursors ODC II and unstable SiH structures upon single photon absorption and from strained SiO bonds via two-photon excitation. Annealing in the dark periods between the laser pulses is dominated by the reaction of E′ with H 2 present in the SiO 2 network. The development α( N, H in = const.) is observed for the very first sample irradiation only (virgin state). The values α end are not accessible by simple spectrophotometer measurements.

Cytocompatibility of calcium phosphate coatings deposited by an ArF pulsed laser

In the current studies, we deposited ultra-thin hydroxyapatite films on a pure titanium substrate by pulsed laser deposition, and we examined the effects of these surfaces on rat bone marrow (RBM) cells. This method allowed deposition of 500-, 2,000-, and 5,000-A-thick hydroxyapatite films. X-ray diffraction showed that the amorphous films recrystallized to a hydroxyapatite crystal structure after annealing. The proliferation of RBM cells was unaffected by the hydroxyapatite films, but osteocalsin and alkaline phosphatase mRNA and protein levels were elevated in cells grown on 2,000- and 5,000-A-thick films. These results indicate that ultra-thin hydroxyapatite films generated by pulsed laser deposition are better at promoting osteogenesis than pure titanium surfaces.