Laser ablation synthesis of indium oxide nanoparticles in water

Colloidal solutions of Indium oxide nanoparticles have been produced by means of laser ablation in liquids (LALs) technique by simply irradiating with a second harmonic (532 nm) Nd:YAG laser beam a metallic indium target immersed in distilled water and varying the laser fluence up to 10 J cm⁻² and the ablation time up to 120 min. At all the investigated fluences the vaporization process of the indium target is the dominant one. It produces a majority (>80%) of small size (<6 nm) nanoparticles, with a very limited content of larger ones (size between 10 and 20 nm). The amount of particles increases regularly with the ablation time, supporting the scalability of the production technique. The deposited nanoparticles stoichiometry has been verified by both X-ray photoelectron spectroscopy (XPS) and Energy Dispersive X-ray (EDX) analysis. Optical bandgap values of 3.70 eV were determined by UV-vis absorption measurements. All these results confirm the complete oxidation of the ablated material.     

Measurements of nanoparticle size distribution produced by laser ablation of tungsten and boron-carbide in N2 ambient

Nanoparticles (NPs) were produced by ablating tungsten and boron-carbide (B₄C) target materials in atmospheric pressure nitrogen ambient using ArF excimer laser pulses. The size distributions of the NPs formed during the ablation were monitored—within a 7-133 nm size window—by a condensation particle counter connected to a differential mobility analyzer. The laser repetition rate was varied between 1-50 Hz, and the fluence was systematically changed in the range of 0.5-15 J/cm², for both materials, allowing a comparative study in an extended laser parameter regime. The multishot ablation threshold (Φ_th) of B₄C was determined to be ∼1.9 J/cm² for the laser used (ArF excimer, λ = 193 nm). Similarly to earlier studies, it was shown that the size distributions consist of mainly small nanoparticles (<∼20 nm) attributed to a non-thermal ablation mechanism below Φ_th. An additional broad peak appears (between 20 and 40 nm) above Φ_th as a consequence of the thermally induced macroscopic ablation. Chemical composition of deposited polydisperse nanoparticles was studied by X-ray photoelectron spectroscopy showing nitrogen incorporation into the boron-carbide.     

Characterization of Ag and Au nanoparticles created by nanosecond pulsed laser ablation in double distilled water

Pulsed laser ablation of Ag and Au targets, immersed in double-distilled water is used to synthesize metallic nanoparticles (NPs). The targets are irradiated for 20 min by laser pulses at different wavelengths—the fundamental and the second harmonic (SHG) (λ = 1064 and 532 nm, respectively) of a Nd:YAG laser system. The ablation process is performed at a repetition rate of 10 Hz and with pulse duration of 15 ns. Two boundary values of the laser fluence for each wavelength under the experimental conditions chosen were used—it varied from several J/cm² to tens of J/cm². Only as-prepared samples were measured not later than two hours after fabrication. The NPs shape and size distribution were evaluated from transmission electron microscopy (TEM) images. The suspensions obtained were investigated by optical transmission spectroscopy in the near UV and in the visible region in order to get information about these parameters. Spherical shape of the NPs at the low laser fluence and appearance of aggregation and building of nanowires at the SHG and high laser fluence was seen. Dependence of the mean particle size at the SHG on the laser fluence was established. Comments on the results obtained have been also presented.     

Analyses of surface coloration on TiO2 film irradiated with excimer laser

TiO₂ film of around 850 nm in thickness was deposited on a soda-lime glass by PVD sputtering and irradiated using one pulse of krypton-fluorine (KrF) excimer laser (wavelength of 248 nm and pulse duration of 25 ns) with varying fluence. The color of the irradiated area became darker with increasing laser fluence. Irradiated surfaces were characterized using optical microscopy, scanning electron microscopy, Raman spectroscopy and atomic force microscopy. Surface undergoes thermal annealing at low laser fluence of 400 and 590 mJ/cm². Microcracks at medium laser fluence of 1000 mJ/cm² are attributed to surface melting and solidification. Hydrodynamic ablation is proposed to explain the formation of micropores and networks at higher laser fluence of 1100 and 1200 mJ/cm². The darkening effect is explained in terms of trapping of light in the surface defects formed rather than anatase to rutile phase transformation as reported by others. Controlled darkening of TiO₂ film might be used for adjustable filters.     

XPS studies of short pulse laser interaction with copper

The effect of laser ablation on copper foil irradiated by a short 30 ns laser pulse was investigated by X-ray photoelectron spectroscopy. The laser fluence was varied from 8 to 16.5 J/cm² and the velocity of the laser beam from 10 to 100 mm/s. This range of laser fluence is characterized by a different intensity of laser ablation. The experiments were done in two kinds of ambient atmosphere: air and argon jet gas.The chemical state and composition of the irradiated copper surface were determined using the modified Auger parameter (α′) and O/Cu intensity ratio. The ablation atmosphere was found to influence the size and chemical state of the copper particles deposited from the vapor plume. During irradiation in air atmosphere the copper nanoparticles react with oxygen and water vapor from the air and are deposited in the form of a CuO and Cu(OH)₂ thin film. In argon atmosphere the processed copper surface is oxidized after exposure to air.     

Laser fluence, repetition rate and pulse duration effects on paint ablation

The efficiency (mm³/(J pulse)) of laser ablation of paint was investigated with nanosecond pulsed Nd:YAG lasers (λ = 532 nm) as a function of the following laser beam parameters: pulse repetition rate (1-10,000 Hz), laser fluence (0.1-5 J/cm²) and pulse duration (5 ns and 100 ns). In our study, the best ablation efficiency (η ≅ 0.3 mm³/J) was obtained with the highest repetition rate (10 kHz) at the fluence F = 1.5 J/cm². This ablation efficiency can be associated with heat accumulation at high repetition rate, which leads to the ablation threshold decrease. Despite the low thermal diffusivity and the low optical absorption of the paint (thermal confinement regime), the ablation threshold fluence was found to depend on the pulse duration. At high laser fluence, the ablation efficiency was lower for 5 ns pulse duration than for the one of 100 ns. This difference in efficiency is probably due to a high absorption of the laser beam by the ejected matter or the plasma at high laser intensity. Accumulation of particles at high repetition rate laser ablation and surface shielding was studied by high speed imaging.     

Picosecond pulsed laser ablation and micromachining of 4H-SiC wafers

Ultra-short pulsed laser ablation and micromachining of n-type, 4H-SiC wafer was performed using a 1552 nm wavelength, 2 ps pulse, 5 μJ pulse energy erbium-doped fiber laser with an objective of rapid etching of diaphragms for pressure sensors. Ablation rate, studied as a function of energy fluence, reached a maximum of 20 nm per pulse at 10 mJ/cm², which is much higher than that achievable by the femtosecond laser for the equivalent energy fluence. Ablation threshold was determined as 2 mJ/cm². Scanning electron microscope images supported the Coulomb explosion (CE) mechanism by revealing very fine particulates, smooth surfaces and absence of thermal effects including melt layer formation. It is hypothesized that defect-activated absorption and multiphoton absorption mechanisms gave rise to a charge density in the surface layers required for CE and enabled material expulsion in the form of nanoparticles. Trenches and holes micromachined by the picosecond laser exhibited clean and smooth edges and non-thermal ablation mode for pulse repetition rates less than 250 kHz. However carbonaceous material and recast layer were noted in the machined region when the pulse repetition rate was increased 500 kHz that could be attributed to the interaction between air plasma and micro/nanoparticles. A comparison with femtosecond pulsed lasers shows the promise that picosecond lasers are more efficient and cost effective tools for creating sensor diaphragms and via holes in 4H-SiC.     

Morphology and composition on Al surface irradiated by femtosecond laser pulses

We study the surface chemicals and structures of aluminum plates irradiated by scanning femtosecond laser pulses in air for a wide range of laser fluence from 0.38 to 33.6 J/cm². X-ray photoelectron spectroscopy and X-ray diffraction analyses indicate clearly that crystalline anorthic Al(OH)₃ is formed under femtosecond laser pulse irradiation. Besides aluminum hydroxide, crystalline Al₂O₃ is also found in the samples irradiated at high laser fluence. Field emission scanning electron microscopy demonstrates that the surfaces of the samples irradiated with low laser fluence are colloidal-like and that nanoparticles with a few nanometers in size are embedded in glue-like substances. For high laser fluence irradiated samples, the surfaces are highly porous and covered by nanoparticles with uniform size of less than 20 nm.     

Synthesis of nanosized particles during laser ablation of gold in water

In this paper we report the formation of gold nanoparticles during laser ablation of gold target in water in the absence of any additives. The experiments were carried out by using the radiation of the pulsed Nd:YAG laser, operating at the second (532 nm, 10 ns, 10 Hz), or the fourth harmonic (266 nm) wavelengths. The properties of the nanoparticles were found to be susceptible to the additional 532 and 266 nm laser irradiation. It has been established that both the mean size of the nanoparticles and their stability could be varied by proper selection of the parameters of laser ablation and postirradiation such as laser fluence and wavelength combinations.     

Effect of spot size on cone formation in a XeCl laser ablation of polyethersulfone films

Radiation from the UV excimer lasers, with the fluence above the ablation threshold, can etch the polymer surfaces by photoablation. In some cases different microstructures may appear on the surface during the laser ablation. In this paper the effect of the laser spot size on the cone formation on polyethersulfone films has been investigated. The experiments have been performed with a XeCl laser at the wavelength of 308 nm and at the fluences of 70 and 100 mJ/cm² at air. For the investigation of the effect of the laser spot size on cone formation, the samples were irradiated at two different laser spot sizes of w₁ and w₂ = 0.1 w₁. The morphology of the processed surface was studied by scanning electron microscopy (SEM). It has shown that the shape, size and density of cones change with the change of the laser spot size. Also, the number of pulses and the pulse repetition rate which are needed for threshold of cone formation are affected by the laser beam spot size on the surface.     

Spectroscopic characterization approach to study surfactants effect on ZnO2 nanoparticles synthesis by laser ablation process

Zinc peroxide nanoparticles having grain size less than 5 nm were synthesized using pulsed laser ablation in aqueous solution in the presence of different surfactants and solid zinc target in 3% H₂O₂. The effect of surfactants on the optical and structure of ZnO₂ was studied by applying different spectroscopic techniques. Structural properties and grain size of the synthesized nanoparticles were studied using XRD method. The presence of the cubic phase of zinc peroxide in all samples was confirmed with XRD, and the grain sizes were 4.7, 3.7, 3.3 and 2.8 nm in pure H₂O₂, and H₂O₂ mixed with SDS, CTAB and OGM respectively. For optical characterization, FTIR transmittance spectra of ZnO₂ nanoparticles prepared with and without surfactants show a characteristic ZnO₂ absorption at 435-445 cm⁻¹. FTIR spectrum revealed that the adsorbed surfactants on zinc peroxide disappeared in case of CTAB and OGM while it appears in case of SDS. This could be due to high critical micelles SDS concentration comparing with others which is attributed to the adsorption anionic nature of this surfactant. Both FTIR and UV-vis spectra show a red shift in the presence of SDS and blue shift in the presence of CTAB and OGM. The blue shift in the absorption edge indicates the quantum confinement property of nanoparticles. The zinc peroxide nanoparticles prepared in additives-free media was also characterized by Raman spectra which show the characteristic peaks at 830-840 and 420-440 cm⁻¹.     

Investigation on upconversion photoluminescence of Bi3TiNbO9:Er:Yb thin films

Bi₃TiNbO₉:Er³⁺:Yb³⁺ (BTNEY) thin films were fabricated on fused silica by pulsed laser deposition. It was demonstrated that different laser fluence and substrate temperature during growth of BTNEY upconversion photoluminescence (UC-PL) samples control the film’s grain size and hence influences the UC-PL properties. The average grain size of BTNEY thin films deposited on fused silica substrates with laser fluence 4, 5, 6, and 7 J/cm² are 30.8, 35.9, 40.6, and 43.4 nm, respectively. The 525 nm emission intensities increase with the deposition laser fluence and the emission intensities of BTNEY thin film deposited under 700 and 600 °C are almost 24 and 4 times, respectively, as strong as those of samples under 500 °C. The grain size of BTNEY thin film increases with the increasing temperature. UC-PL of BTNEY films is enhanced by increasing grain size of the films.     

Deposition of potassium-oxygen on silicon surfaces by pulsed laser ablation of potassium superoxide: Study of work function changes

Potassium-oxygen species were deposited on pure, Si nanoparticles coated and H-terminated Si nanoparticles coated p-Si(1 0 0) surfaces by pulsed laser ablation of potassium superoxide (KO₂) target. The deposition properties, composition and the work function changes of the deposited species were investigated in situ using an X-ray photoelectron spectroscopy (XPS) and a Kelvin probe measurement. The deposited species were assigned to K₂O₂ and KO₂, and they can be selectively deposited by controlling the laser fluence: i.e., at 200 mJ/cm² and at those more than 300 mJ/cm², respectively. Experimental results showed that the work function decreased drastically with depositing of KO_x (x = 1 or 2), and the minimum work function values observed were 1.0 eV and 0.7 eV for pure p-Si(1 0 0) and Si nanoparticles coated substrates, respectively. The study demonstrates the formation of the surface species with minimum work function can be identified by XPS.     

Femtosecond laser micromilling of Si wafers

Femtosecond laser micromilling of silicon is investigated using a regeneratively amplified 775 nm Ti:Sapphire laser with a pulse duration of 150 fs operating at 1 kHz repetition rate. The morphological observation and topological analysis of craters fabricated by single-shot laser irradiation indicated that the material removal is thermal in nature and there are two distinct ablation regimes of low fluence and higher fluence with logarithmical relations between the ablation depth and the laser fluence. Crater patterns were categorized into four characteristic groups and their formation mechanisms were investigated. Femtosecond laser micromilling of pockets in silicon was performed. The effect of process parameters such as pulse energy, translation speed, and the number of passes on the material removal rate and the formation of cone-shaped microstructures were investigated. The results indicate that the microstructuring mechanism has a strong dependence on the polarization, the number of passes and laser fluence. The optimal laser fluence range for Si micromilling was found to be 2-8 J/cm² and the milling efficiency attains its maximum between 10 and 20 J/cm².     

Pulsed plasma ion source to create Si nanocrystals in SiO2 substrates

A pulsed KrF excimer laser of irradiance of about 10⁸ W/cm² was utilized to synthesize Si nanocrystals on SiO₂/Si substrates. The results were compared with that ones obtained by applying low bias voltage to Si(1 0 0) target in order to control the kinetic energy of plasma ions. Glancing incidence X-ray diffraction spectra indicate the presence of silicon crystalline phases, i.e. (1 1 1) and (2 2 0), on SiO₂/Si substrates. The average Si nanocrystal size was estimated to be about 45 nm by using the Debye-Scherrer formula. Scanning electron microscopy and atomic force microscopy images showed the presence of nanoparticles of different size and shape. Their distribution exhibits a maximum concentration at 49 nm and a fraction of 14% at 15 nm.     

Effect of laser fluence on the size of copper oxide nanoparticles produced by the ablation of Cu target in double distilled water

Copper oxide nanoparticles produced in double distilled water at room temperature by laser ablation of the Cu target have been investigated using TEM, SEM, AFM, X-ray diffraction, photo-spectrometry and PIXE. Q-switched Nd:YAG laser operating at 1064 nm with a pulse duration of 5–6 ns was used to conduct the experiments in the fluence range of 5.73–9.87 J/cm². In each experiment, 12,000 laser pulses were used to ablate the target placed in double distilled water. Different diagnostic techniques reveal that the nanoparticles have a size between 2–55 nm and their mean size as well as the width of particle distribution increases with the laser fluence. Since no surface active material (surfactant) was added to water, the nanoparticles aggregated and settled down at the bottom of the container within a week. In addition to stable Cu₂O, the XRD spectrum also shows the presence of suboxide Cu₆₄O in the colloidal solution of nanoparticles produced in the present study.     

Patterning of indium-tin oxide on glass with picosecond lasers

The results of patterning of the indium-tin oxide (ITO) film on the glass substrate with high repetition rate picosecond lasers at various wavelengths are presented. Laser radiation initiated the ablation of the material, forming grooves in ITO. Profile of the grooves was analyzed with a phase contrast optical microscope, a stylus type profiler, scanning electron microscope (SEM) and atomic force microscope (AFM). Clean removal of the ITO film was achieved with the 266 nm radiation when laser fluence was above the threshold at 0.20 J/cm², while for the 355 nm radiation, the threshold was higher, above 0.46 J/cm². The glass substrate was damaged in the area where the fluence was higher than 1.55 J/cm². The 532 nm radiation allowed getting well defined grooves, but a lot of residues in the form of dust were generated on the surface. UV radiation with the 266 nm wavelength provided the widest working window for ITO ablation without damage of the substrate. Use of UV laser radiation with fluences close to the ablation threshold made it possible to minimize surface contamination and the recast ridge formation during the process.     

ZnO nanoparticles produced by novel reactive physical deposition process

This paper reports the deposition of ZnO nanoparticles with controlled sizes and different particle densities and their structural, composition and optical properties. They were deposited by means of a DC magnetron based vacuum nanoparticle source onto different substrates (GaAs, Si and Ti/SiO₂/Si). We believe that this is the first time that such nanoparticles have been produced using this unique technique. Zinc was used as sputtering target to produce zinc nanoparticles which were oxidized in-line using molecular oxygen. The structural properties and chemistry of the ZnO were studied by transmission electron microscopy. An average particle size of 6(±2) nm was produced with uniform size distribution. The particle density was controlled using a quartz crystal monitor. Surface densities of 2.3 × 10¹¹/cm², 1.1 × 10¹³/cm² and 3.9 × 10¹³/cm² were measured for three different deposition runs. The ZnO particles were found to be single crystalline having hexagonal structure. Photoluminescence measurements of all samples were performed at room temperature using a cw He-Cd laser at 325 nm excitation. The UV emission around 375 nm at room temperature is due to excitonic recombination and the broad emission centered at 520 nm may be attributed to intrinsic point defects such as oxygen interstitials.     

Laser surface treatment of screen-printed carbon nanotube emitters for enhanced field emission

This paper investigates the surface treatment of screen-printed carbon nanotube (CNT) emitters using a 248 nm (KrF) excimer laser. The field emission characteristics of the CNT emitters are measured following irradiation using laser fluences ranging from 80 to 400 mJ/cm². The results show that the turn-on electric field, the current density, and the distribution of the emission sites are highly dependent on the value of the laser fluence and are optimized at a fluence of 150 mJ/cm². Two distinct laser fluence regimes are identified. In the low fluence regime, i.e. 80-150 mJ/cm², the surface treatment process is dominated by a photo ablation mechanism, which results in the gradual removal of the binding material from the cathode surface and leads to an improvement in the emission characteristics of the CNT cathodes with an increasing fluence. However, in the high fluence regime, i.e. 150-400 mJ/cm², the thermal ablation mechanism dominates; resulting in a removal of the CNTs from the cathode surface and a subsequent degradation in the emission characteristics.     

Formation of TiN-Ir particle films using pulsed-laser deposition and their electrolytic properties in producing hypochlorous acid

Using sintered TiN and TiN-Ir (Ir contents: 5.9-14.2 at.%) targets, pulsed-laser deposition (PLD) was carried out to produce thin films composed of nanoparticles and particulates in the presence of nitrogen gas. The size (2-100 nm) of the produced crystalline TiN nanoparticles increased as nitrogen pressure was increased in the range from 1.33 to 1.33 × 10² Pa. At a pressure of 1.33 × 10³ Pa, amorphous TiN nanoparticles combined in the form of chains. Large Ir particulates with diameters of up to 2 μm were particularly prominent in TiN-Ir films. Size distributions of the Ir particulates were dependent on ablation laser wavelength; that is, the diameter decreased at laser wavelength shortened. The TiN-Ir films with different Ir contents and morphologies on Ti substrates were evaluated as electrolysis electrodes for water disinfection. The highest current efficiency was 0.45%, which is comparable to that of conventional Ti-Pt electrodes, for a chloride-ion concentration of 9 mg dm⁻³.