Laser Ablation Of Silicon Target Research Articles

Functionalized silicon nanoparticles as fluorescent probe for detection of hypochlorite in water

In this work amine functionalized silicon nanoparticles colloid is utilized to prepare a fluorescent probe for detecting low concentration levels of hypochlorite in water. The sensor is prepared by adding organosilane in silicon nanoparticles colloidal solution which freshly synthesized by laser ablation of silicon target in distilled water. The amine-terminated surface of silicon nanoparticles is confirmed using Fourier transform infrared, UV–vis absorption spectroscopy and transmission electron microscopy methods. The photoluminescence measurements of the functionalized silicon nanoparticles colloid exhibit high photostability and good reproducibility making them ideal fluorescent probes for sensing applications. It shows high sensitivity, excellent selectivity and rapid response (˜6 min) toward hypochlorite. The room temperature fluorescent sensor detects hypochlorite of water in the linear concentration range from 1 to 5 μM with a 0.2 μM detection limit. The sensor properties including high sensitivity, fast response and facile synthesis of the amine-functionalized silicon nanoparticles are compared with other reports in literature for fluorescent detection of hypochlorite in water.

Synthesis of SiC nanoparticles by SHG 532 nm Nd:YAG laser ablation of silicon in ethanol

In this work, colloidal spherical nanoparticles NPs of silicon carbide SiC have been synthesized using second harmonic generation 532 nm Nd:YAG laser ablation of silicon target dipped in ethanol solution at various laser fluences (1.5–5) J/cm2. X-Ray diffraction XRD, scanning electron microscopy SEM, transmission electron microscope TEM, Fourier transformed infrared spectroscopy FT-IR, Raman spectroscopy, photoluminescence PL spectroscopy, and UV–Vis absorption were employed to examine the structural, chemical and optical properties of SiC NPs. XRD results showed that all synthesised SiC nanoparticles are crystalline in nature and have hexagonal structure with preferred orientation along (103) plane. Raman investigation showed three characteristic peaks 764,786 and 954 cm−1, which are indexing to transverse optic TO phonon mode and longitudinal optic LO phonon mode of 4H-SiC structure. The optical absorption data showed that the values of optical energy gap of SiC nanoparticles prepared at 1.5 J/cm2 was 3.6 eV and was 3.85 eV for SiC synthesised at 5 J/cm2. SEM investigations confirmed that the nanoparticles synthesised at 5 J/cm2 are agglomerated to form larger particles. TEM measurements showed that SiC particles prepared at 1.5 J/cm2 have spherical shape with average size of 25 nm, while the particles prepared at 5 J/cm2 have an average size of 55 nm.

Characterization of high photosensitivity nanostructured 4H-SiC/p-Si heterostructure prepared by laser ablation of silicon in ethanol

This paper presents the first study on characterization of high sensitivity 4H-SiC/Si heterojunction photodetector prepared by deposition of SiC nanoparticles NPs on silicon substrate by drop casting. Synthesis of the SiC NPs was performed by laser ablation of silicon target immersed in ethanol with 1.064µm Nd:YAG laser pulses at various laser fluences (318-9.55)J/cm2. The morphological, structural, electrical, and optical properties of SiC NPs were investigated as function of laser fluence. The absorption data showed that the value of optical energy gap of SiC nanoparticles depend on the laser fluence. TEM investigation showed that SiC NPs having spherical shape with sizes in the range (5–65)nm. The optical energy gap of SiC NPs prepared at different laser fluences has been determined from optical properties and found to be in the range (3.45–3.75eV). The electrical properties of SiC/Si heterojunction shows a good rectification ratio and the value of ideality factor varied from 1.72 to 3.51 depending on the laser fluence. Capacitance –voltage properties of heterojunctions showed a linear relationship between C−2 and reverse bias voltage and the value of built-in potential was found in the range (0.45–0.8)V. The effect of laser fluence on the photodetector figures of merit namely; photosensitivity, detectivity and rise time was discussed and analyzed.

Generation of web-like structures and nanoparticles by femtosecond laser ablation of silicon target in ambient air

Silicon nanoparticles were produced by femtosecond laser ablation in ambient air. Obtained samples were studied using dark-field optical microscopy, scanning electron microscopy and Raman-scattering spectroscopy. Two groups of structures can be found: (1) branched amorphous structures with a minimum element size of about 10 nm and incorporations of nanocrystals (0.6–6.6 nm from Raman scattering analysis); (2) larger crystal particles with smooth surface and a typical size of 50–200 nm that provide directional visible light scattering (at dark-field optical microscopy observations). An influence of environment on resulting phase composition of silicon nanoparticles was investigated by numerical evaluation of nanoparticle’s cooling rate. The calculation shows that cooling in ambient air ensures cooling rate sufficient for crystallization.

Direct surface modification of ligand-free silicon quantum dots prepared by femtosecond laser ablation in deionized water

Amine-terminated, ultra-small silicon nanoparticles (Si-NPs) were prepared in one step avoiding the conventional chemical or thermal treatment of Si surface, by introducing organosilane in Si-NPs colloidal solution freshly prepared by ultra-fast laser ablation of silicon target in deionized water. Surface chemistry studies of Si-NPs conducted by Raman and Fourier infrared spectroscopy demonstrated the hydroxyl-terminated surface of Si-NPs. The reactivity of hydroxyl-terminated surface with aminopropyltriethoxysilane in aqueous solution was investigated. Electron microscopy, dynamic light scattering, infrared spectroscopy and stability studies confirmed the successful functionalization of Si-NPs leading to 5nm Si dots covered by aminopropyltriethoxysilane thick layer. Detailed infrared spectroscopy analysis of the Si–O–Si region as a function of immersion time revealed the formation of interfacial Si–O bonds between the organosilane and hydroxyl groups of the nanoparticles. The biocompatible Si nanostructure containing amine functional group prepared using a one-step green protocol opens the route for biomedical applications and successful translation into clinical setting, as bio-labels, contrast agents and vector delivery.

Dynamics of the pulsed picosecond laser ablation of silicon targets

This paper discusses the dynamics of nanoparticle formation during the pulsed picosecond laser ablation of samples of crystalline and porous silicon by means of elastic light scattering. Experimental measurements are presented of how the signal produced by scattering at the ablation products depends on the distance between the probe radiation and the target surface. The differences of these dependences for crystalline and porous silicon wafers are discussed. It was found that the scattering kinetics of the probe radiation on the ablation products has two characteristic peaks at times of about several microseconds and several tens of microseconds, respectively.

飞秒激光在大气及真空中烧蚀硅靶的实验研究

Femtosecond (fs) pulse laser ablation of silicon targets in air and in vacuum is investigated using a time-resolved shadowgraphic method. The observed dynamic process of the fs laser ablation of silicon in air is significantly different from that in vacuum. Similar to the ablation of metallic targets, while the shock wave front and a series of nearly concentric and semicircular stripes, as well as the contact front, are clearly identifiable in the process of ablation under 1?105 Pa, these phenomena are no longer observed when the ablation takes place in vacuum. Although the ambient air around the target strongly affects the evolution of the ablation plume, the three rounds of material ejection clearly observed in the shadowgraphs of fs laser ablation in standard air can also be distinguished in the process of ablation in vacuum. It is proven that the three rounds of material ejection are caused by different ablation mechanisms.

Study the Effect of CO2 Laser Annealing on Silicon Nanostructures

The recent discovery of strong room-temperature photoluminescence from silicon nanocrystals fabricated by different methods is an extremely important scientific breakthrough with enormous technological implications because of possibility of integration of silicon based electronic and optoelectronic devices. This paper the effect of Laser annealing technique used to produce nanoparticales by CW laser was proposed. The laser spot was focused within 0.6 mm beam radius to synthesize silicon rich oxide SiOx nanostructures in silicon nanostructures thin films by laser ablation of silicon target on glass. The CO2­ laser beam λ (10.6µm) with power Plaser ranging from 1 to 10 Watt. Two lasers were employed; the first, Q-switched Nd:YAG laser to prepare an amorphous silicon film on glass substrate and the second, CW CO2 laser beam to produce local heating and synthesize a silicon oxide nanostructures. A sufficient absorbing CO2 laser beam was used to induce local heating at optimizing surface temperature. The optical and surface morphological properties of SiOx films annealed by CO2 laser are primarily investigated the effect of parameters such as power density and elimination time.

Angular distribution of liquid droplets during the laser ablation of silicon target

AbstractPulsed laser deposition of thin films involves an extremely complex process, and therefore, the study of the different aspects of the basic mechanism of laser ablation is still under investigation and development.In this work, the initial stages of laser ablation process have been studied by considering the roughness of the deposited surfaces, their continuous morphological changes and the angular distribution of liquid droplets produced by laser irradiation.Various experiments on silicon wafers, using a KrF excimer laser (248 nm) impinging at 45° with respect to the target were performed. Scanning electron microscopy technique was used to investigate the morphological changes of the silicon surface and the angular emission distribution of the liquid droplets. Copyright © 2010 John Wiley & Sons, Ltd.

Synthesis of Si–C nanostructures by laser ablation of silicon target in n-heptane vapor

Controllable synthesis of Si–C nanostructures was realized in a laser ablation system by adopting solid silicon target and n-heptane vapor as starting materials. Ultrafine SiC nanocrystals and graphite-coated SiC nanocrystals were synthesized with the laser frequency of 1 Hz and 20 Hz, respectively. According to the real-time observation on the plasma evolvement, we proposed a formation mechanism of Si–C nanostructure related to vapor-phase reaction. Our method can be extended to other material systems for diverse novel nanostructures.

Surface hydrogenation of silicon nanocrystallites during pulsed laser ablation of silicon target in hydrogen background gas

The surface hydrogenated silicon nanocrystallites can be prepared by pulsed laser ablation of a silicon target in hydrogen background gas. Formation processes of the surface Si–H bonds were found by correlation between the surface structure of the deposited nanocrystal film and the time- and space-resolved spectra of plume emission during the deposition. A precursor of the hydrogenation is SiH species created in blast-wave stage by collision between ejected Si species and background hydrogen gas. Results of plume diagnostics indicate that the spatial or temporal separation between Si and SiH species is not an origin of the formation of the surface hydrogenated Si nanocrystallite. It is concluded that the correlation between the thermal stability of the Si–H bond and the temperature variation of the formed nanoparticle during the deposition is important for the formation of the chemical bonding on the surface.

Characterization of laser ablation of solid targets with near-infrared laser pulses of 100fs and 1ps duration

Abstract The process of laser ablation of silicon targets with ≈1 ps/1055 nm and ≈100 fs/780 nm laser pulses has been investigated by exploiting optical emission spectroscopy and fast photography of the ablated species in the gas phase, and atomic force microscopy of less than one layer deposits of the ablated material. We have observed, for both durations, the presence of a fast atomic component followed by a much slower plume of nanoparticles of the target material. For both laser pulses, experimental ablation thresholds have been compared with the prediction of a simple theoretical model, resulting in pretty good agreement. The properties of size distribution of the silicon nanoparticles have been analyzed as a function of the laser pulse intensity, and also compared with the results for metallic targets. Our experimental results show that the generation of nanoparticles, with pretty narrow size distributions, is a characteristic feature of the interaction of ultrashort laser pulses with solids (namely, metals and semiconductors), for both ≈1 ps and ≈100 fs laser pulse durations.

Generation of silicon nanoparticles via femtosecond laser ablation in vacuum

We demonstrate that femtosecond laser ablation of silicon targets in vacuum is a viable route to the generation and deposition of nanoparticles with radii of ≈5–10 nm. The nanoparticles dynamics during expansion has been analyzed through their structureless continuum optical emission, while atoms and ions, also present in the plume, have been identified by their characteristic emission lines. Atomic force microscopy analysis of the material deposited at room temperature has allowed the characterization of the nanoparticles size distribution. Taking into account the emissivity of small particles we show that the continuum emission is a blackbody-like radiation from the nanoparticles. Our results suggest that nanoclusters are generated as a result of relaxation processes of the extreme material state reached by the irradiated target surface, in agreement with recently published theoretical studies.

ESR studies of nanocrystalline silicon films obtained by pulsed laser ablation of silicon targets

Nanocrystalline silicon films formed using laser ablation of silicon targets were studied using electron spin resonance. The measurements were performed in the X band with modulation of the magnetic field at a frequency of ∼100 kHz at temperatures of 300 and 77 K. Two types of spectra were observed. The first type of spectra is related to the high concentration of dangling silicon bonds in Si nanocrystals and SiOx sheaths of nanocrystals and are inherent in nanocrystalline silicon (nc-Si) films that do not exhibit photoluminescence in the visible region of the spectrum. The second type of spectra is related to the presence of E′ centers, nonbridging oxygen hole centers (NBOHC), and peroxide radicals and is characteristic of films with photoluminescence in the visible region of the spectrum, which indicates that high-barrier SiO2 layers exist in these films. An increase in the photoluminescence intensity and a decrease in the signal of electron spin resonance were observed in porous nc-Si films exposed to atmospheric air for a long time.

Formation of Hydrogen-passivated Silicon Nanochains by Pulsed Laser Ablation without Thermal Annealing

ABSTRACTHydrogen-passivated silicon nanochains were synthesized by pulsed laser ablation of silicon target in hydrogen gas atmosphere at room temperature. When the hydrogen gas pressure was higher than 670Pa, nanochains, which have crystalline silicon core, were formed. Transmission electron microscopy showed the silicon nanochains consist of connections of silicon nanocrystals with mean diameter of 4.6 nm. It is of great interest that the silicon nanochain has crystalline structure without any intentional annealing process. Optical properties of the hydrogen-passivated silicon nanochains were presented.

Plume dynamics during film and nanoparticles deposition by pulsed laser ablation

The gas dynamics of pulsed laser ablation of silicon target in the helium gas ambient is investigated via direct simulation Monte Carlo method with a real physical scale of target-substrate configuration. A shock driven process is clearly observed. It is shown that the interaction of the shock front with the target surface and the vapor front induce significant backward flux of ablated particles and oscillating behavior of vapor front. A confined layer mixed with high density Si and He atoms is formed around the contact front. Its behavior is important to the nanoparticle formation and deposition.

Effects of hydrogen on Si nanoparticles formed by pulsed laser ablation

We examined reactive pulsed laser ablation of silicon target in hydrogen atmosphere to form hydrogenated silicon nanoparticles. A correlation between hydrogen pressure and sample properties or structure was investigated by varying hydrogen pressure from 5 to 532 Pa. We could form hydrogenated silicon nanoparticles above 30 Pa. The size of nanoparticles could be changed by controlling hydrogen pressure. The bonding configuration of silicon and hydrogen changes between 20 and 30 Pa, which is demarcation of the sample structure from film-like to nanoparticles. These results imply reactive laser ablation has a possibility to produce a well-designed sample both size and bonding configuration.

Hydrogenation dynamics of Si nanoparticles with green photoluminescence

We have investigated the formation dynamics of silicon nanoparticles after laser ablation of silicon targets in H 2 gas and O 2 gas diluted with Ar gas by 2D imaging of time-resolved photoluminescence (PL). PL intensity from silicon nanoparticles is found to be enhanced in H 2 gas with partial pressures up to 400 Pa. In O 2 gas, the PL intensity drastically decreases with increasing partial pressures. A broad band green PL indicates that hydrogenated Si nanoparticles are formed in the H 2 gas.

Preparation and evaluation of nitrogen-terminated silicon nanoparticles: laser annealing effect

Nitrogen-terminated silicon nanoparticles were synthesized on AFI AlPO4-5 zeolite by pulsed laser ablation of silicon target in the presence of 1.33×10−5Pa of ammonia and were annealed by multiple laser shots at 532nm. The samples were characterized by X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and UV–vis absorption measurements. The results indicate that they are composed of nonstoichiometric silicon nitride nanoparticles as well as silicon species with dangling bonds. NHx (x=1,2) polyhydride species are dissociated by pulsed laser annealing, which shows the improvement of the silicon and silicon nitride crystallinities. It is suggested that the nanoparticles will agglomerate as clusters after laser annealing. According to the Tauc plot obtained from UV–vis absorption data, a blue shift of band gap energy from bulk silicon was observed.

Formation process of Si nanoparticles in rare gas observed by a decomposition method

We have investigated the formation process of silicon nanoparticles after laser ablation of silicon targets in argon gas. The nanoparticles exhibit bright photoluminescence in the visible wavelength range and can be applied to opto-electronic devices. In order to observe silicon nanoparticles, we have developed a decomposition method. The nanoparticles were probed by detecting light emission resulting from decomposition using a second laser. This method enables us to observe nanoparticles that cannot be observed directly by the methods applied so far. We have observed that the nanoparticles grow in time periods of 1.0–1.8 ms following ablation in Ar gas at 5 Torr when Si targets are ablated at 5 J/cm2 with a pulse width of 7 ns. The nanoparticles begin to grow above ablation spots slightly apart from the targets just after thermalization of the plume. We also found that the growth is delayed at higher fluxes of ablation laser light.