Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials,...

Laser Synthesis and Processing of Colloids: Fundamentals and Applications

The properties of pristine, free-standing graphene monolayers prepared by mechanical exfoliation of graphite are investigated. The graphene monolayers, suspended over open trenches, are examined by means of spatially resolved Raman spectroscopy of the G-, D-, and 2D-phonon modes. The G-mode phonons exhibit reduced energies (1580 cm-1) and increased widths (14 cm-1) compared to the response of graphene monolayers supported on the SiO2 covered substrate. From analysis of the G-mode Raman spectra, we deduce that the free-standing graphene monolayers are essentially undoped, with an upper bound of 2x10^11 cm-2 for the residual carrier concentration. On the supported regions, significantly higher and spatially inhomogeneous doping is observed. The free-standing graphene monolayers show little local disorder, based on the very weak Raman D-mode response. The two-phonon 2D mode of the free-standing graphene monolayers is downshifted in frequency compared to that of the supported region of the samples and exhibits a narrowed, positively skewed line shape.

Probing the Intrinsic Properties of Exfoliated Graphene: Raman Spectroscopy of Free-Standing Monolayers

Status and demand of research to bring laser generation of nanoparticles in liquids to maturity

In the present study, carbon nanostructures were synthesized by laser ablation of graphite in de-ionized water. Q-switched Nd:YAG laser of 1064nm wavelength, 9ns pulse width, and different laser fl...

Carbon nanoparticles prepared by laser ablation in liquid environment

The demand is growing for new nanoscience-based technologies with unique properties that are different from traditional wet-chemical techniques. In recent years, laser ablation in liquid (LAL) has attracted increasing attention for nanomaterial synthesis, which has rapidly advanced both fundamental research and applications. Compared to other techniques, LAL is easy to set up and simple to perform. A large diversity of bulk and powder targets can be employed for LAL, which combined with an enormous variety of liquids, greatly diversify the nanomaterials that can be synthesized by LAL in terms of size, composition, shape, and structure. Although many reviews related to LAL have been published, a comprehensively thorough introduction that deals with the diversity of the targets and liquids used for LAL is still missing. To fill this gap, this review gives a comprehensive summary of the nanomaterials synthesized by LAL using different types of target and liquid, with an emphasis on the effects of liquids on the final nanoproducts. In order to provide a better understanding of the liquids’ effects, this review also discusses liquid additives such as salts, polymers, support materials, and their mixtures. Since many reactions occur during LAL, the scope of reactive laser ablation in liquid (RLAL) is redefined, and the representative reactions for each type of liquid used for LAL are summarized and highlighted. Consequently, this review will be a useful guide for researchers developing desirable nanomaterials via LAL.

https://iopscience.iop.org/article/10.1088/2515-7647/ac0bfd/pdf

Laser ablation in liquids for nanomaterial synthesis: diversities of targets and liquids

Effects of laser fluence on the properties of carbon nanostructures produced by laser ablation method in liquid nitrogen have been studied experimentally. The beam of a Q-switched Nd:YAG laser of 1064-nm wavelength at 7 ns pulse width and different fluences is employed to irradiate the graphite target in liquid nitrogen. Properties of carbon nanostructures were studied using their UV–Vis–NIR spectrum, TEM images, and Raman scattering spectrum. Two categories of graphene nanosheets and carbon nanoparticles were observed due to variation of laser fluence. Results show that in our experimental condition there is a threshold fluence for producing carbon nanoparticles. With increasing the laser fluence from the threshold, the amount of carbon nanoparticles in suspensions was increased, while the amount of graphene nanosheets was decreased.

Nushin Tabatabaie

Papers

Effect of fluence on carbon nanostructures produced by laser ablation in liquid nitrogen