Laser Generated MoS2 Nanomaterials and Its Applications: A Review

Laser ablation of a bulk graphite target in water using femtosecond laser pulses (pulse width ≤ 190 fs) was performed to investigate the synthesis of polyynes and carbon-based nanomaterials and compare them with the well-studied cases of longer pulse (picosecond or nanosecond) ablations. The laser ablation products were characterized using UV-vis absorption spectroscopy, Raman spectroscopy, X-ray diffraction, and transmission electron microscopy, whereas the induced plasma plumes were characterized using laser-induced breakdown spectroscopy. Carbon-based nanomaterials and short-chain polyynes (C6H2 and C8H2) are formed in the solutions as proven by their characteristic absorption band at ~262 nm and peaks in the region of 190–240 nm as well as at around 2100 cm−1 in the Raman spectra, respectively. Polyynes (C8H2) are present in the solutions that are produced under an ablation that is carried out in two intervals with a short pause between them, which is contrary to a continuous ablation that is performed for the same total time duration. The ablation products have a hexagonal graphite crystal structure. The carbon-based nanomaterials consist of large non-spherical and small spherical nanoparticles as well as sheet-like structures. The results of the study were compared with previous studies and discussed based on those studies.

The coagulation of impurities in superfluid helium, in contrast to that in all other liquids where spherical colloid particles are usually produced, led to producing thin and long nanowires with regular internal structure. This is due to the presence in HeII of quasi one-dimensional quantized vortices serving as condensation nuclei and providing a catalyzing effect on the process of any impurities coagulation. The metal was introduced into superfluid helium by laser ablation of targets made of gold, copper, nickel, permalloy, indium, lead, tin and bismuth immersed in liquid HeII. For all of these metals, the formation of thin (about 8 nm in diameter), long high-quality nanowires was observed after laser ablation. The structure of nanowires as well as of micron-sized metallic spheres, appeared as products at high laser pulse energy, providing evidence that they were formed via molten state. The spheres are metastable, and under damage of their surface, thousands of nanoballs emerge from their interior. The hollow shells left after this event are similar to those found as the products of laser ablation in normal fluids. The metal ablation into HeII bulk from thin film was found much less effective then that from thick foils.

Ultrafast pulsed laser ablation has been investigated as a technique to machine CdWO4 single crystal scintillator and segment it into small blocks with the aim of fabricating a 2D high energy X-ray imaging array. Cadmium tungstate (CdWO4) is a brittle transparent scintillator used for the detection of high energy X-rays and γ-rays. A 6W Yb:KGW Pharos-SP pulsed laser of wavelength 1028nm was used with a tuneable pulse duration of 10ps to 190fs, repetition rate of up to 600kHz and pulse energies of up to 1mJ was employed. The effect of varying the pulse duration, pulse energy, pulse overlap and scan pattern on the laser induced damage to the crystals was investigated. A pulse duration of ≥500fs was found to induce substantial cracking in the material. The laser induced damage was minimised using the following operating parameters: a pulse duration of 190fs, fluence of 15.3Jcm−2 and employing a serpentine scan pattern with a normalised pulse overlap of 0.8. The surface of the ablated surfaces was studied using scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy and X-ray photoelectron spectroscopy. Ablation products were found to contain cadmium tungstate together with different cadmium and tungsten oxides. These laser ablation products could be removed using an ammonium hydroxide treatment.

Irradiation of polyamide-6 (PA) with γ-rays reduces its resistance to subsequent IR laser radiation. The average rate of laser ablation of PA, preliminarily irradiated with γ-rays at a dose above ~300 kGy, is almost dose-invariant and is 30% higher than that of the initial unirradiated polymer. The pattern of the dose dependence of the laser ablation rate for the samples pre-irradiated with a dose of 3.24 MGy at a dose rate of 4.2 Gy/s is mixed in character, varying from the shape characteristic of the initial polymer at the initial stage to the shape typical of the maximum radiation dose in the stationary laser ablation mode. One of the products of PA laser ablation is a dispersed polymer, consisting of nano- to micrometer-sized particles, the size range of these particles shifting toward smaller values with an increase in the γ radiation dose, a trend that is explained by a decrease in melt viscosity.

Photopolymers designed for laser ablation – photochemical ablation mechanism

Structures of gold nanoparticles were formed by laser ablation of bulk gold immersed in water. An excimer laser with a wavelength of 351 nm and a pulse energy of 7 mJ was used. Ablation was performed in two configurations: without and with an external 0.2 T magnetic field parallel to the ablation plume. Both configurations result in structures that include chains of aggregated nanoparticles, but to different degrees. Ablation in a magnetic field results in a higher fraction of spherical nanoparticles and shorter nanowires, compared to the nanowire networks formed in the absence of the field. This can be explained by magnetic confinement of the plasma during plume expansion. A model explaining nanowire formation and dependence on fluence and magnetic field is proposed.

A critical review on the applications and potential risks of emerging MoS2 nanomaterials

Results of investigation of size distribution of aerosol products of submillimeter laser ablation of nanosized aluminium clusters, carbon-diamond and SiO2 nanopowders are discussed. Diffusion spectrometer of aerosols was used for detection of the particle formed. Free electron laser of Siberian center of photochemical research was used as the source of terahertz radiation. Intercomparison with the results, obtained with other popular methods (dynamic light scattering, atomic-force and scanning-electron microscopy) is presented.

Nanomaterials with controllable morphology and composition are synthesized by a simple one-step vapor condensation process using a mini-arc plasma source. Through systematic investigation of mini-arc reactor parameters, the roles of carrier gas, electrode material, and precursor on producing diverse nanomaterial products are revealed. Desired nanomaterial products, including tungsten oxide nanoparticles (NPs), tungsten oxide nanorods (NRs), tungsten oxide and tin oxide NP mixtures and pure tin dioxide NPs can thus be obtained by tailoring reaction conditions. The amount of oxygen in the reactor is critical to determining the final nanomaterial product. Without any precursor material present, a lower level of oxygen in the reactor favors the production of W18O49 NRs with tungsten as cathode, while a high level of oxygen produces more round WO3 NPs. With the presence of a precursor material, amorphous particles are favored with a high ratio of argon:oxygen. Oxygen is also found to affect tin oxide crystallization from its amorphous phase in the thermal annealing. Results from this study can be used for guiding gas phase nanomaterial synthesis in the future.

The synthesis of gold and titanium (OT4-0) nanoparticles by laser ablation in D2O and H2O using the radiation of an Nd: YAG laser with a wavelength λ = 1064 nm is considered. The influence of a liquid absorption capacity in which laser radiation interacts with a target on laser ablation products is studied. In the case of ablation in heavy water, the optical density of nanoparticles colloids was increased in comparison with the optical density of colloids obtained with the same parameters, but in the H2O medium. Also, when D2O was used, the absorption bands of the particles were shifted to the long-wavelength region of the spectrum by ~ 15 nm. SEM - analysis of synthesized nanoparticles by laser ablation in H2O and D2O media revealed the formation of dense aggregates. SEM - surface analysis of targets after treatment in both heavy and H2O water showed the formation of structures with a transverse dimension of the order 2 μm. Also, according to the energy dispersive analysis, when irradiating in H2O and D2O, an oxide layer of the same thickness was formed on the targets surface. The same morphology of laser-modified surfaces also leads to the equality of their conductive properties. The measurements of the current-voltage characteristics recorded the S-shaped behavior of the curves, which can be explained by the manifestation of the memristor properties of the modified titanium target surface coated with an oxide layer.

Direct chemical analysis of UV laser ablation products of organic polymers by using selective ion monitoring mode in gas chromatography/mass spectrometry

Production of single-walled carbon nanotubes (SWNT) has taken place for a number of years and by a variety of methods such as laser ablation, chemical vapor deposition, and arc-jet ablation. Yet, little is actually understood about the exact chemical kinetics and processes that occur in SWNT formation. In recent time, NASA Johnson Space Center has devoted a considerable effort to the experimental evaluation of the laser ablation production process for SWNT originally developed at Rice University. To fully understand the nature of the laser ablation process it is necessary to understand the development of the carbon plume dynamics within the laser ablation oven. The present work is a continuation of previous studies into the efforts to model plume dynamics using computational fluid dynamics (CFD). The ultimate goal of the work is to improve understanding of the laser ablation process, and through that improved understanding, refine the laser ablation production of SWNT.

The design of a two-color pyrometer is described, allowing not only measurement of the temperature of a single flying luminous particle with sizes from submicron to millimeters but also the 3D reconstruction of its flight trajectory, the determination of its real velocity, size, frequencies of oscillations of its radiation intensities, and the type of the particle. A distinctive feature of the pyrometer is that two photographs of the flying particle (each in its own spectral band) used for the measurement of particle temperature are made from two mutually perpendicular directions. This device was used to investigate individual condensed particles emitted from the crater by the pulsed laser ablation of alumina. It was found that among the particles the micron and submicron drops are observed as well as the hollow bubbles with diameters up to several millimeters; the drops formed from the boiling and supercooled melt of Al2O3 can be ejected practically at the same time during the laser pulse. The digital processing of the particle streaks has shown that the luminosity of most of the observed particles is isotropic, although the particles radiating nonisotropically are also observed. The radiation of both types of particles may be oscillating. Surprisingly, frequencies of oscillations of the radiation intensity of the flying particle may differ for two channels of the pyrometer registration. The obtained results can be useful to characterize the phase state, properties of alumina particles, and specific features of relaxation of overheated alumina melt. They are interesting both for basic and applied science.

Nanoparticles anchored strategy to develop 2D MoS2 and MoSe2 based room temperature chemiresistive gas sensors

Chemical kinetic models for the nucleation and growth of clusters and single-walled carbon nanotube (SWNT) growth are developed for numerical simulations of the production of SWNTs. Two models that involve evaporation and condensation of carbon and metal catalysts, a full model involving all carbon clusters up to C80, and a reduced model are discussed. The full model is based on a fullerene model, but nickel and carbon/nickel cluster reactions are added to form SWNTs from soot and fullerenes. The full model has a large number of species--so large that to incorporate them into a flow field computation for simulating laser ablation and arc processes requires that they be simplified. The model is reduced by defining large clusters that represent many various sized clusters. Comparisons are given between these models for cases that may be applicable to arc and laser ablation production. Solutions to the system of chemical rate equations of these models for a ramped temperature profile show that production of various species, including SWNTs, agree to within about 50% for a fast ramp, and within 10% for a slower temperature decay time.