tailieunhanh - Báo cáo hóa học: " From covalent bonding to coalescence of metallic nanorods"

Tuyển tập các báo cáo nghiên cứu về hóa học được đăng trên tạp chí hóa hoc quốc tế đề tài : From covalent bonding to coalescence of metallic nanorods | Lee and Huang Nanoscale Research Letters 2011 6 559 http content 6 1 559 o Nanoscale Research Letters a SpringerOpen Journal NANO EXPRESS Open Access From covalent bonding to coalescence of metallic nanorods Soohwan Lee and Hanchen Huang Abstract Growth of metallic nanorods by physical vapor deposition is a common practice and the origin of their dimensions is a characteristic length scale that depends on the three-dimensional Ehrlich-Schwoebel 3D ES barrier. For most metals the 3D ES barrier is large so the characteristic length scale is on the order of 200 nm. Using density functional theory-based ab initio calculations this paper reports that the 3D ES barrier of Al is small making it infeasible to grow Al nanorods. By analyzing electron density distributions this paper shows that the small barrier is the result of covalent bonding in Al. Beyond the infeasibility of growing Al nanorods by physical vapor deposition the results of this paper suggest a new mechanism of controlling the 3D ES barrier and thereby nanorod growth. The modification of local degree of covalent bonding for example via the introduction of surfactants can increase the 3D ES barrier and promote nanorod growth or decrease the 3D ES barrier and promote thin film growth. Keywords metal surface steps adatom diffusion covalent bonding simulation Introduction The growth of metallic nanorods by physical vapor deposition PVD is a common practice. Limited diffusion is a critical condition for nanorod growth 1 and geometrical shadowing in glancing angle deposition further promotes nanorod growth 2 3 . In addition to the diffusion of adatoms on flat surfaces when diffusing over monolayer surface steps adatoms experience a large energy barrier-he Ehrlich-Schwoebel ES barrier-which affects the resulting surface 4 5 . Adatoms diffusing over multiple-layer steps experience even larger energy barriers 6-9 this barrier is referred to as threedimensional 3D ES barrier for comparison .