T. Hironaka

Bio: T. Hironaka is an academic researcher from Keio University. The author has contributed to research in topics: Thin film & Graphite. The author has an hindex of 2, co-authored 2 publications receiving 19 citations.

Size Effects in the In-plane Electrical Resistivity of Very Thin Graphite Crystals (特集 炭素材料と次元性)

Abstract: According to the Slonczewski-Weiss-McClure (SWMcC) energy band model, the three dimensional graphite should be semimetal because the valence band overlaps slightly to the conduction band1),2) , while the two dimensional graphite should be zero band gap semi-conductor because the valence band and the conduction band touch together just at the Fermi leve13) Moreover, the graphite dilayer density of state at the Fermi level has been predicted to be much smaller than that for the bulk crystal4) .Therefore, the electron energy band structure of very thin graphite crystals is expected to be different from that of bulk crystals, that is, the degree of the overlap of these two bands will depend on the film thickness. Moreover, the bands overlap should be reflected in the carrier concentrations. In fact, some kinds of carbon fibers have been treated as quasi-two dimensional carbon materials. The electrical properties of these materials were measured under the various conditions5)-8) . Especially, the temperature dependence of the electric resistivity was discussed in relation to the effect of heat treatment temperature (HTT)5),7),8) . HTT, however, has an influence on both basal plane stackings and the crystalline growth along the basal plane, simultaneously. Therefore, it will be necessary to measure the electrical properties of thin graphite films with good crystal perfection, only by changing the thickness. The measurements of the electrical resistivity have already been carried out for kish graphite (KG) films with various thicknesses, and it has been reported that the carrier concentrations of very thin crystals are different from those of bulk crystals9),10) However, two subjects were found to be improved. In the first place it was pointed out that the thin films cemented on the substrates with the epoxy resin might be distorted by changing the temperature and this distortion should have an effect on their electric resistivity. In the second place the residual resistivity ratio (rrr) values of the bulk KG crystals had not been measured before cleaving. The value of rrr is the ratio of the resistivity measured at room temperature to that at 4.2K. The quality of the graphite materials is evaluated by the rrr value. In this study, we prepared the graphite specimens of thickness ranging from 290A to 1110A by cleaving a KG crystal with high crystallinity improving on two points mentioned above. The temperature dependence of the electric resistivity was measured in the temperature range between 4.2K and room temperature. A simple two band (STB) model11) and the effect of the lattice vibration'2) were applied to the experimental results, and then the values of the band overlap energy were estimated for the thin graphite crystals with various film thicknesses.

The rise of graphene

Abstract: Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.

Graphene-based semiconductor nanostructures

Abstract: One of the current priorities in the physics and chemistry of graphene is the study of its semiconducting derivatives. This review summarizes the state of the art in this area of research. The structure and electronic properties of materials as such graphene ribbons, partially hydrogenated and fluorinated graphene, graphane, fluorographene, and diamane are discussed in detail.

The 2010 Nobel Prize in physics—ground-breaking experiments on graphene

Abstract: The 2010 Nobel Prize in physics was awarded to Professors Andre Geim and Konstantin Novoselov for their ground-breaking experiments on graphene, a single atomic layer of carbon, and more generally, for their pioneering work in uncovering a new class of materials, namely two-dimensional atomic crystals. This paper gives an accessible account and review of the story of graphene; from its first description in the literature, to the realization and confirmation of its remarkable properties, through to its impressive potential for broad-reaching applications. The story of graphene is written within the context of the enormous impact that Geim and Novoselovs' work has had on this field of research, and recounts their personal pathways of discovery, which ultimately led to their award of the 2010 Nobel Prize.

The evolution of graphene-based electronic devices

Abstract: Successful isolation of single-layer graphene, the two-dimensional allotrope of carbon from graphite, has fuelled a lot of interest in exploring the feasibility of using it for fabrication of various electronic devices, particularly because of its exceptional electronic properties. Graphene is poised to save Moore's law by acting as a successor of silicon-based electronics. This article reviews the success story of this allotrope with a focus on the structure, properties and preparation of graphene as well as its various device applications.