Narrow Results

A broad general interest in the process of affecting the energetic deposition of flying nanoparticles has prompted a new opportunity to consider the medium-energy region in which the nanoparticles maintain their integrity and must respond to the energetic shock caused by collisions. We herein report our experimental results on the structural transition of the carbon nanoparticles induced by such energetic collisions. The beam energy was varied from 0 keV to 30 keV for a nanoparticle with over 5000 carbon atoms. Electron energy loss spectroscopy, X-ray photoemission spectroscopy, and Raman spectroscopy were carried out on the samples using a series of beam energies. These tests revealed that some graphitic sheets were formed at the higher beam energy while the sp³ ratio was unexpectedly higher for a medium beam energy.

Microscale to nanoscale carbon and carbon nitride particles and films were synthesized by using plasma discharge sputtering deposition techniques. Experimental results indicated that sizes and distributions of the particles were directly determined by both discharge voltage and bias voltage. Sputtering deposition at high discharge voltages yielded large sizes (micrometer order) of particles with a high disorder of distribution. Whereas sputtering deposition at low discharge voltages yielded nanoscale of particles that uniformly distributed on the surface of the substrate. Ar laser beam in combination with an optical microscope has been used, enabling one to remove these particles and to achieve preferred distributions of the particles. Low growth rate of the films was found at the low voltage discharge sputtering deposition. Bias voltage was employed during the experiments in order to speed up the growth rate and increase nitrogen content inside the carbon nitride film. With an increase of the bias voltage up to 5 kV, nanoparticles appeared in two-dimensional, sunflower type of cluster distributions. Typical G, D, and C=N bands in the Raman spectra of the samples were identified.

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 fluences (3.6, 5.4, 10.6, and 14.6J/cm²) were utilized to irradiate the target. XRD measurements demonstrated the presence of the two carbon phases (002, 111) except for the sample prepared at 3.6J/cm² laser fluence; it showed disappearance of (002) phase. This result can be an indication of changing the phase of carbon nanomaterials when prepared at this fluence. TEM revealed that carbon nanoparticles had a spherical shape and were 10–90nm in size, while nanostructure carbon prepared at 3.6J/cm² has nanosheets 45mm in width and 275mm in length. The absorption of CNPs indicated the appearance of the absorption peak at about 305nm, which is attributed to the $\pi$–$\pi$* transition of the C $=$ O band. PL emission was decreased at the higher laser fluence (14.6J/cm²) due to the quenching of the carbon nanoparticles luminescence.

In this study, thin sheets like carbon nanostructures and carbon nanoparticles have been effectively synthesized with CH₄ and Ar as precursors at low temperature (< 400°C) by inductively coupled radio frequency plasma enhanced chemical vapor deposition on silicon and glass substrates. The surface morphology and chemical composition were studied by atomic force microscopy (AFM), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analysis. AFM studies show that the nanoparticles roughly about 70 to 80 nm in diameter surrounded by nanosheets. Nanosheets are about 100 nm in thickness, which attain approximately 1.75 μm lengths. EDS results revealed that the atomic percentage of carbon in the particle like structure is more than that in the nanosheet like structures.

Fluorescent nanoparticles have received much attention for their potential applications in biology and medicine, such as uses as fluorescence markers or imaging agents. Recently, surface-passivated carbon nanoparticles or "carbon dots" were demonstrated to be brightly fluorescent, thus representing a new platform for nanoscale fluorescent agents. For targeted bioapplications of carbon dots, an understanding of their toxicity behavior is necessary, including issues on potential defunctionalization of the dots in biological systems that might result in the exposure of the nanoscale carbon core. In this work, we performed cytotoxicity evaluations on both precursor carbon nanoparticles and carbon dots, from which the results suggested no significant cytotoxic effects.

Nanotechnology has become a distinctive field of research, aimed to modernize the way scientists have addressed urgent needs and sophisticated problems, towards the achievement of unprecedented discoveries. Amidst the myriad of materials extensively used in the modern society, carbon-based systems seem to embody a significant role especially where endurance and strength are required: carbon nanoparticles, nanotubes, graphite, diamonds and fullerenes et al. In addition to the above advantages, this review also emphasizes some concerns on the carbonnanosystems and which are mainly attributable to the lack of an exhaustive characterization and to the potential hazardous effects deriving from their potential accumulation in the environment and inside the body.