Molecular Doping of Graphene

Abstract

Graphene, a one-atom thick zero gap semiconductor [1,2], has been attracting an increasing interest due to its remarkable physical properties ranging from an electron spectrum resembling relativistic dynamics [3,4,5,6,7,8,9,10,11,12] to ballistic transport under ambient conditions [1,2,3,4]. The latter makes graphene a promising material for future electronics and the recently demonstrated possibility of chemical doping without significant change in mobility has improved graphene's prospects further [13]. However, to find optimal dopants and, more generally, to progress towards graphene-based electronics requires understanding the physical mechanism behind the chemical doping, which has been lacking so far. Here, we present the first joint experimental and theoretical investigation of adsorbates on graphene. We elucidate a general relation between the doping strength and whether or not adsorbates have a magnetic moment: The paramagnetic single NO 2 molecule is found to be a strong acceptor, whereas its diamagnetic dimer N 2 O 4 causes only weak doping. This effect is related to the peculiar density of states of graphene, which provides an ideal situation for model studies of doping effects in semiconductors. Furthermore, we explain recent results on its "chemical sensor" properties, in particular, the possibility to detect a single NO 2 molecule [13].Controlling the type and the concentration of charge carriers is at the heart of modern electronics: It is the ability of combining gate voltages and impurities for locally changing the density of electrons or holes that allows for the variety of nowadays available semiconductor based devices. However, the conventional Si-based electronics is expected to encounter fundamental limitations at the spatial scale below 10 nm, according to the semiconductor industry roadmap, and this calls for novel materials that might substitute or complement Si. Being only one atomic layer thick, graphene exhibits ballistic transport on a submicron scale and can be doped heavily -either by gate voltages or molecular adsorbateswithout significant loss of mobility [1]. In addition, later experiments [13] demonstrated its potential for solid state gas sensors and even the possibility of single molecule detection.We show, that in graphene, aside from the donoracceptor distinction, there are in general two different classes of dopants -paramagnetic and nonmagnetic. In contrast to ordinary semiconductors, the latter type of impurities act generally as rather weak dopants, whereas the paramagnetic impurities cause strong doping: Due to the linearly vanishing, electron-hole symmetric density of states (DOS) near the Dirac point of graphene, localised impurity states without spin polarisation are pinned to the centre of the pseudogap. Thus impurity states in graphene distinguish strongly from their counterparts in usual semiconductors, where the DOS in the valence and conduction bands are very different and impurity levels lie generally far away from the middle of the gap. Impurity effects on t...

Structural Defects in Graphene

“…5 Thus we will only briefly summarize the influence of structural defects on the electronic structure and transport properties. We do not consider the effects originating from weakly attached organic 102,103 or inorganic 104 surface species on perfect graphene, because these are no structural defects, nor discuss the effects of ripples in free-standing or substrate-supported graphene.…”

Charge Transfer-Induced Molecular Hole Doping into Thin Film of Metal–Organic Frameworks

“…3 All calculations were performed using the local density approximation (LDA) 4 , which is feasible to model adsorption of molecules with charge transfer. 5,6 Other alternative approach for the modeling of weakly bonded layered systems is GGA+vdW 7-9 is proper only for the systems without charge transfer and lack in description of systems with charge transfer. 10 Crystal structure parameters are taken from the Ref.…”

“…[1][2][3][4][5][6][7][8][9] For most of these applications, MOFs are used in the form of bulk powder. One of the interesting and challenging future issues in the field of MOFs is their material investigation for making thin film, and study their electronic properties.…”

Tuning the Electronic Structure of Graphene by an Organic Molecule

“…14 The single, open-shell NO 2 molecule is found to be a strong acceptor, whereas its equilibrium gaseous state N 2 O 4 acts as a weak dopant and does not result in any significant doping effect. 15 Boron or nitrogen substitutional doping is also not reliable and always induces defects that destroy the promising electronic property of graphene. Thus, it is desirable and crucial to develop new methods to precisely control the carrier type and concentration in graphene for further development of graphene-based nanoelectronics.…”