Modeling and Numerical Simulation of Material Science, 2012, 2, 76-84 doi:10.4236/mnsms.2012.24009 Published Online October 2012 (http://www.SciRP.org/journal/mnsms) A First Principles Investigation of the Mechanical Properties of g-TlN Qing Peng * , Chao Liang, Wei Ji, Suvranu De Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, USA Email: * qpeng.org@gmail.com Received September 3, 2012; revised October 5, 2012; accepted October 16, 2012 ABSTRACT We investigate the structure and mechanical properties of proposed graphene-like hexagonal thallium nitride monolayer (g-TlN) using first-principles calculations based on density-functional theory. Compared to graphene-like hexagonal boron nitride monolayer (g-BN), g-TlN is much softer, with 12% in-plane stiffness, 25%, 22%, and 20% ultimate strengths in armchair, zigzag, and biaxial strains respectively. However, g-TlN has a larger Poisson’s ratio, 0.69, about 3.1 times that of g-BN. It was found that the g-TlN also sustains much smaller strains before rupture. We obtained the second, third, fourth, and fifth order elastic constants for a rigorous continuum description of the elastic response of g-TlN. The second order elastic constants, including in-plane stiffness, are predicted to monotonically increase with pressure while the Poisson’s ratio monotonically decreases with increasing pressure. Keywords: g-TlN; Mechanical Properties; High Order Elastic Constants; Density Functional Theory; 2D Materials 1. Introduction Fruitful studies and applications of graphene triggered the new era of the two-dimensional (2D) nanomaterials [1-10]. Graphene analogues of BN (g-BN), an insulating material that serves as an excellent dielectric substrate for graphene electronics, was exfoliated recently and subjected to extensive studies with promising applica- tions in electronics and energy storage [11-17]. Besides the nanosheet, tremendous researches were carried on other nanostructures of g-BN, such as nanotubes [18-24], nanoshells [25], antidotes [26], bilayer of graphene and g-BN [10,27-29], quantum dots and nanorods of gra- phene embedded in g-BN [30], hybrid graphene/g-BN monolayer [30-33], and graphyne BN analog [34]. As a consequence, other III-nitrides have raised a lot of atten- tion [35-39]. Hexagonal thallium nitride monolayer (g-TlN) is a proposed graphene-like 2D material, which is only monoatomically thick (Figure 1). Although g-TlN has not been fabricated currently, the theoretical study of the g-TlN could expand the range of possible applications of III-nitrides, and open new perspectives for miniaturiza- tion in engineering functional nano-devices and inter- connects by a chemical modification. The bulk thallium nitride (TlN) was predicted to have a small energy gap, indicating a semi-metallic character [40,41]. The combi- Figure 1. g-TlN: graphene-like hexagonal thallium nitride monolayer. nation of thallium with other group III atoms which has wide gap in III-nitrides yields promising semiconductors for optical communication systems (laser diodes, detec- tors) with small band gap, down to the infrared energy region [42-47]. Structural stability [48], defects [49], * Corresponding author. Copyright © 2012 SciRes. MNSMS