Single-Nucleus Polycrystallization in Thin Film Epitaxial Growth

J. T. Sadowski, G. Sazaki, S. Nishikata, A. Al-Mahboob, Y. Fujikawa, K. Nakajima, R. M. Tromp, and T. Sakurai

Phys. Rev. Lett. 98, 046104 – Published 25 January 2007

Abstract

We have observed, by use of low-energy electron microscopy, the first direct evidence of self-driven polycrystallization evolved from a single nucleus in the case of epitaxial pentacene growth on the Si(111)-H terminated surface. In this Letter we demonstrate that such polycrystallization can develop in anisotropic systems (in terms of crystal structure and/or the intermolecular interactions) when kinetic growth conditions force the alignment of the intrinsic preferential growth directions along the density gradient of diffusing molecules. This finding gives new insight into the crystallization of complex molecular systems, elucidating the importance of nanoscale control of the growth conditions.

Received 3 February 2006

DOI:https://doi.org/10.1103/PhysRevLett.98.046104

Authors & Affiliations

J. T. Sadowski¹, G. Sazaki^1,2, S. Nishikata¹, A. Al-Mahboob¹, Y. Fujikawa¹, K. Nakajima¹, R. M. Tromp³, and T. Sakurai^1,*

¹Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
²Center for Interdisciplinary Research, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578, Japan
³IBM Research Division, T. J. Watson Research Center, 1101 Kitachawan Road, P.O. Box 218, Yorktown Heights, New York 10598, USA

^*Corresponding author. Email address: sakurai@imr.tohoku.ac.jp

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Vol. 98, Iss. 4 — 26 January 2007

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Images

Figure 1
(a) Tilted-beam LEEM image of the pentacene island grown on the H-Si(111) surface (imaging electron energy of 2.2 eV)—at these imaging conditions a complicated domain pattern is visible within the island; red circle marks the initial nucleation site of the island. (b) LEED diffraction pattern obtained from the island shown in (a); spots originating from $Si (111) − (1 \times 1)$ lattice are marked by yellow circles and a unit cell of one of the Pn rotational domains is outlined by a rectangle; magnified image of the pair of spots defining the “paired” Pn domains, rotated with respect to each other by an angle of $4.6 \pm 0.3 °$ , is shown in the inset.Reuse & Permissions
Figure 2
(a) Tilted-beam LEEM image showing tip of the one of the branches in Pn island on H-Si(111) with three distinctive contrasts (I, II, III) visible. (b) The $μ$ -LEED diffraction pattern obtained from an individual contrast segment II in (a)—spots in black circles are from the Si(111) lattice and spots marked by red solid circles are from the Pn(001) lattice. (c) A simple model outlining the epitaxial relations between Pn lattice and H-Si(111) substrate. (d) Schematic of Pn 2D crystal alignment reflecting the contrast difference in the domain structure shown in (a); shorter side of each rectangle corresponds to $a$ axis while longer side corresponds to $b$ axis of the 2D unit cell in a particular domain.Reuse & Permissions
Figure 3
(a) STM image of the compact Pn island (second layer) grown on the $Bi (0001) / Si (111)$ surface; island’s shape is very close to the equilibrium crystal shape predicted theoretically by Northrup et al. [20] (outlined in white); $μ$ -LEED pattern showing single-crystalline, bulklike structure of Pn island is shown in the inset. (b) LEEM image of the Pn island (second layer) grown on the top of the wetting layer formed on a clean $Si (111) − (7 \times 7)$ surface—the primitive vectors constituting the in-plane unit cell are outlined in the image, demonstrating that under kinetically limited growth conditions the fast growth direction aligns to the $b$ axis in this anisotropic system; $μ$ -LEED pattern evidencing the relation between island shape and Pn in-plane unit cell lattice vectors is shown in the inset.Reuse & Permissions
Figure 4
(a) Tilted-beam LEEM image showing the internal structure of the Pn island grown on the H-Si(111) surface; the arrows outline the major crystallographic directions of the substrate, which are also a direction of development of the branches. (b) Sketch illustrating the branching mechanism observed in (a); the equipotential lines of the density gradient of diffusing molecules are shown schematically (yellow arrows indicate the fast growth directions of the branches, which align to the density gradient).Reuse & Permissions

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