Surface Science 605 (2011) 1607–1610 Contents lists available at ScienceDirect Surface Science journal homepage: www.elsevier.com/ locate/susc Graphene — The ultimate surface material 1. Introduction extremely large densities of transistors in computer chips and to produce many other high-power high-frequency electronic devices. Discoveries of carbon allotropes have punctuated scientificand Flexible conductive coatings can be used to manufacture bendable technological advances at the interface of the 2nd and 3rd millennia. touch-screen displays and paints that would change color by One can argue that nanoscale science as a field has emerged at the end application of weak electric currents. Graphene can lead to new of the 20th century largely as a result of these discoveries. Every decade generations of solar cells [10], electric batteries [11] and capacitors over the past 30 years saw a new form of carbon created in a lab, giving [12]. In these systems the accessible surface area is particularly birth to an exponentially growing number of studies. In 1985 Kroto, important, because it defines the interface for charge separation and Heath, O'Brien, Curl, and Smalley obtained fullerenes [1].Then,in1991 storage. Graphene is an ideal material in this case, since all atoms are Sumio Iijima clearly identified carbon nanotubes within the prepared located on the surface. material [2]. Finally, in 2004 Novoselov, Geim, Morozov, Jiang, Zhang, Graphene-based sensors can detect molecules. Nanoscale open- Dubonos, Grigorieva and Firsov prepared electrically isolated, single- ings in graphene sheets and nanoribbons may provide new tech- layer graphene [3]. Within extraordinary short periods of time the niques for rapid DNA sequencing [13,14] that will achieve an seminal importance of these works was awarded with two Nobel extremely fine resolution of individual nucleotides due to the single prizes. The 1996 Nobel Prize in Chemistry was awarded jointly to atom thickness of the detector [15]. Artificial membranes made of Robert F. Curl, Jr., Sir Harold W. Kroto, and Richard E. Smalley “for their graphene [16] can be particularly efficient in separating liquids and discovery of fullerenes”. The 2010 Nobel Prize in Physics was given to gasses. Plastic containers based on graphene can keep food fresh for Andre Geim and Konstantin Novoselov “for groundbreaking experi- weeks. The superb mechanical properties of graphene [17,18] can be ments regarding the two-dimensional material graphene”. utilized to produce longer-lasting medical implants, stronger wind Only one atomic layer thick, graphene is the ultimate surface turbines, lighter aircraft and better sports equipment. The possibilities material. It can be considered as an infinitely large aromatic molecule for these fascinating applications, which can revolutionize our lives, and the limiting case of the family of flat polycyclic aromatic arise due to the unique chemical structure of graphene, which allows hydrocarbons. The term graphene was introduced by Boehm, Setton, maximal surface area per mole of the material. and Stumpp as a combination of graphite and the suffix, -ene[4]. For The experimental technique used by Geim and Novoselov to decades graphene remained solely a topic of theoretical investigation, obtain graphene flakes is amazingly simple [3]. While investigating as experimental characterization was considered difficult if not the electrical properties of graphite, they peeled layers off the surface impossible. In the 1930s Landau [5] and later Mermin [6] argued of graphite with Scotch tape. Eventually, single-atom-thick crystallites that two-dimensional crystals should be thermodynamically unstable. were extracted and transferred onto thin silicon dioxide on a silicon The theory behind graphene was first explored in detail in 1947 by wafer. The silicon electrode beneath SiO2 could be used to vary the Philip Wallace, who pointed out its unusual electronic properties [7]. graphene charge density over a wide range. At the same time, the SiO2 At that time, the substance was viewed as a starting point for research layer electrically isolated graphene, providing nearly charge-neutral on the more complex, three-dimensional graphite. material. Earlier, single layers of graphite were grown epitaxially on The two-dimensional nature of graphene combined with versatile top of other materials. However, there was a significant charge electronic states afforded by carbon's valence structure gives rise to a transfer from the substrate onto graphene. In many cases, hybridiza- variety of novel physical, chemical and mechanical properties that can tion between the orbitals of the substrate atoms and the π orbitals of revolutionize modern world. Graphene's most renowned properties graphene significantly altered the electronic structure of epitaxial include extremely large electrical and thermal conductivities. Graphene graphene. The electro-neutral graphene sheets produced by Geim and conducts electricity as well as copper. As a conductor of heat, it Novoselov led to the first observation of the anomalous quantum Hall outperforms most known materials. Graphene is so thin that it is almost effect, which proved that electrons in graphene behaved as massless completely transparent, yet at the same time not even helium, the particles. This behavior is characteristic of photons and is extremely smallest gas atom, can permeate it. Graphene, the thinnest material unusual for electrons. The thrilling simplicity of generating high ever produced, is extremely flexible and strong, about 200 times quality graphene created an explosion of research activities. stronger than steel. The special issue of Surface Science devoted to graphene provides Graphene holds a great potential for profoundly transforming a snapshot of current activities in this exciting and rapidly evolving materials and surface science. It can replace silicon in electronics field. The goal is to exemplify the state-of-the-art in fundamental applications [8] and aid in production of electricity conducting plastics research on graphene carried out both theoretically and experimen- [9]. The single atom thickness can allow engineers to achieve tally. Since graphene was first investigated theoretically, many 0039-6028/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2011.05.009 1608 decades prior to its experimental discovery, we start with theoretical simulations of self-assembly of graphene fragments in water. Here, and computational studies. The focus migrates from fundamental the computational challenges involve both the large number of properties of graphene, to graphene doping and chemical derivatives, atoms needed to describe the process (tens of thousands) and the to graphene self-assembly and interactions with other materials. Then long timescale of the self-assembly (nanoseconds). Molecular self- we turn our attention to experimental work, covering a number of assembly draws significant attention in nanotechnology, as it techniques used for functionalization and characterization of gra- provides a tool for designing complex materials and biological phene and its derivatives aimed at a variety of applications. structures [22,23]. The authors find that parallel self-assembly of graphene sheets is initiated by entropic contributions to the 2. Theoretical studies of graphene thermodynamic potential. Then, as the sheets approach each other, capillary evaporation of water confined between the sheets The unique physical properties of graphene in combination with takes place. The entropic driving force becomes much stronger and the extremely rich chemistry of the carbon atom create a number of the sheets collapse onto each other. The enthalpic term, including theoretical challenges, making graphene one of the most exciting the potential energy of the interaction, remains weakly repulsive materials for a theoretical research. Theoretical characterization of the throughout the simulation. The results reported by Park and Aluru physical and chemical properties of any material typically starts with establish the dominant mechanism for self-assembly of nanoscale adefinition of an interatomic potential. This electronic potential systems containing graphene and provide a guideline for building ultimately determines and reconciles observed variations in a complex carbon-based nanostructures. material's structure and associated dynamics and thermodynamics The origin of the attractive forces between graphene and other properties. Reliable interatomic potentials involving carbon are nanoscale objects is investigated in detail in the paper by Dobson[24], difficult to derive given that carbon can exist in electronic states who presents a detailed analytic examination of the ab initio with different orbital hybridizations, including those leading to techniques used to compute such forces. He points out that the extended π-electron systems. The carbon atoms of graphene are unusual nature of graphene is revealed not only in electronic sp2-hybridized and include easily polarizable π-electrons. In addition, transport, e.g. the anomalous quantum Hall effect [3], but also in the defects and graphene derivatives can involve both sp and sp3 long-range interactions. Graphene is unusual from this point of view hybridizations. Long-range dispersive effects are particularly impor- due to the gapless semi-metallic nature of its electronic excitations, tant for interlayer coupling and interactions of graphene with resulting in a qualitatively different behavior