Tailoring the Grain Size of Bi-Layer Graphene by Pulsed Laser Deposition

Abstract

Improving the thermoelectric efficiency of a material requires a suitable ratio between electrical and thermal conductivity. Nanostructured graphene provides a possible route to improving thermoelectric efficiency. Bi-layer graphene was successfully prepared using pulsed laser deposition in this study. The size of graphene grains was controlled by adjusting the number of pulses. Raman spectra indicated that the graphene was bi-layer. Scanning electron microscopy (SEM) images clearly show that graphene changes from nanostructured to continuous films when more pulses are used during fabrication. Those results indicate that the size of the grains can be controlled between 39 and 182 nm. A detailed analysis of X-ray photoelectron spectra reveals that the sp2 hybrid state is the main chemical state in carbon. The mobility is significantly affected by the grain size in graphene, and there exists a relatively stable region between 500 and 800 pulses. The observed phenomena originate from competition between decreasing resistance and increasing carrier concentration. These studies should be valuable for regulating grains sizes for thermoelectric applications of graphene.

A Controllability Investigation of Magnetic Properties for FePt Alloy Nanocomposite Thin Films

“…By adjusting the ratio of Fe and Pt in the nanocomposite films, the saturation magnetization and coercivity can be tuned at high values. Thus the saturation magnetization values can be controlled without sacrificing much coercivity, which can provide advanced magnets for future applications in high density power and date storage [30,31,32].…”

Pulsed Laser Deposition of Carbon-Based Materials: A Focused Review of Methods and Results

“…Two main approaches have been tested for PLD of graphene: one that involves the use of metallic catalysts deposited on the substrate in different phases of the film growth, and one that proceeds without catalysts. The latter approach is particularly attractive as it eliminates the need to transfer the deposited graphene film and to grow it, in principle, directly on any desired substrate (e.g., pure and doped Si, SiO 2 and fused silica [121][122][123][124][125][126][127][128][129], sapphire [130], copper [131][132][133], glass [134]). In fact, considerations such as substrate-film lattice mismatch and film-substrate adhesion should, as usual with thin-film deposition techniques, always be considered when producing usable films for specific applications is the goal.…”

“…Recent research on PLD of graphene has also largely explored UV laser sources; in particular, KrF excimer lasers at 248 nm [123,124,126,127,131,132,[137][138][139]141,153] and, occasionally, the higher harmonics of Nd:YAG lasers (355 nm [129], 266 nm [133]). The reports of graphene films grown with femtosecond lasers, mostly Ti:Sapphire at 800 nm, are also sporadic [140,148], as they do not appear to provide significant advantages with respect to longer-pulse sources, while remaining generally more expensive and less user-friendly.…”

“…Parameters such as laser fluence and repetition rate are optimized in each experiment and with the specific employed setup, but some general trends can be inferred as to how some experimental parameters can affect the graphene film. As mentioned in the previous section, evidence has emerged that controlling the number of laser pulses reaching the target (by acting on the laser repetition rate and the ablation time) can affect the C-to-metal thickness ratio and is therefore key to obtaining few-layer graphene films [131,136].…”

Laser processing of graphene and related materials for energy storage: State of the art and future prospects

“…The PLD growth of graphene onto different types of substrates has been accomplished by ablation of pyrolytic carbon, graphite and HOPG targets (with or without metal catalysts) [199,200]. Mostly, few-layer and multi-layer graphene deposits have been obtained, though single layers and bilayers have also been recently reported [201][202][203]. Different laser sources (excimer lasers, Nd:YAG, CO2) have been used, and the substrate is typically maintained at RT or a few hundred degrees during deposition.…”