Variation of growth morphology with chemical composition of terraces: Ag on a twofold surface of a decagonal Al-Cu-Co quasicrystal

T. Duguet, B. Ünal, Y. Han, J. W. Evans, J. Ledieu, C. J. Jenks, J. M. Dubois, V. Fournée, and P. A. Thiel

Phys. Rev. B 82, 224204 – Published 9 December 2010

Abstract

Growth of Ag thin films on the twofold surface of a decagonal Al-Cu-Co quasicrystal is characterized by scanning tunneling microscopy, at different temperatures, and for coverages ranging from submonolayer to 11 monolayers. From prior work, three types of clean surface terraces are known to exist. By correlation with a bulk structural model, the major difference between them lies in their transition-metal (TM) content, two being aluminum-rich (0 and $15 at . %$ TM) and one being TM-rich ( $40 - 50 at . %$ TM). The present article focuses on understanding the difference between Ag film morphologies on these terminations, in terms of their chemical content. Growth is found to be smoother on the TM-rich terraces and rougher on the Al-rich ones. The first Ag atomic layer is even pseudomorphic on the TM-rich terraces. Roughness variation with temperature shows that the equilibrium morphology is two dimensional for TM-rich terraces and three dimensional for Al-rich terraces. The explanation of different growth modes in terms of different terrace compositions is supported by calculations of the adhesion energy of a Ag slab with Ag, Al, Cu, and Co slabs, using density-functional theory. For the Al-rich terraces, the roughness variation with temperature also indicates reentrant growth, i.e., anomalously smooth growth at low temperature due to kinetic effects.

Received 2 June 2010

DOI:https://doi.org/10.1103/PhysRevB.82.224204

Authors & Affiliations

T. Duguet^1,2,3, B. Ünal^1,2,*, Y. Han^4,5, J. W. Evans^4,5, J. Ledieu³, C. J. Jenks^1,2, J. M. Dubois³, V. Fournée³, and P. A. Thiel^1,2

¹Ames Laboratory, U.S. Department of Energy, Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA
²Department of Materials Sciences & Engineering, Iowa State University, Ames, Iowa 50011, USA
³Institut Jean Lamour, UMR 7198 CNRS, Nancy-Université–UPV-Metz, École des Mines de Nancy, Parc de Saurupt, CS14234, F-54042 Nancy, France
⁴Institute of Physical Research & Technology, Department of Physics & Astronomy, Iowa State University, Ames, Iowa 50011, USA
⁵Department of Mathematics, Ames Laboratory, U.S. Department of Energy, Iowa State University, Ames, Iowa 50011, USA

^*Present address: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 82, Iss. 22 — 1 December 2010

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(Color online) Summary of structural features observed on the clean twofold d-Al-Cu-Co surface. (a) Step terrace morphology $(1000 \times 1000 {nm}^{2})$ . Panels (b) and (c) show a small region $(100 \times 48 {nm}^{2})$ of the TM-rich terrace in (a), imaged at different tip biases. Panel (d) shows a $100 \times 100 {nm}^{2}$ STM images of the Al-rich #1 terrace. (b), (c), and (d) orientation corresponds to the aperiodic (A) and periodic (P) axes shown in (d). STM images were recorded at 0.5 nA tunneling current. Panel (e) shows the three $10 \times 3 {nm}^{2}$ corresponding model terminations. Blue (dark) dots represent Al atoms and orange (bright) dots represent TM atoms. The size of the dots is a function of their vertical position (larger size is closer to vacuum). Arrows indicate 0.3-nm-wide line separations that are called “low-density rows” in the text.Reuse & Permissions
Figure 2
(Color online) STM images of the TM-rich and Al-rich #1 terraces shown in Fig. 1a, after consecutive depositions of Ag at 300 K. All images are $100 \times 100 {nm}^{2}$ and are recorded with a tunneling current of 0.5 nA. Coverage and tip bias are given for each row on the left. rms roughness are given below each image. The roughness measurements were performed after low-noise filtering, using the WSXM software. Black line drawn in the left column images limits a nanodomain on the TM-rich terrace. A tip effect increases the apparent thickness of features in (b).Reuse & Permissions
Figure 3
(Color online) STM images $(100 \times 100 {nm}^{2})$ of 5 ML Ag on a TM-rich and an Al-rich #1 terrace, deposited at 365 K and annealed to 420 K and held at 420 K during scanning. Each line profile corresponds to the path indicated by the arrow within the STM image to its right. The tunneling current is 0.5 nA for all images and bias voltage is $+ 1 V$ in (a), $+ 1.5 V$ in (b), and $- 1 V$ in [(c) and (d)].Reuse & Permissions
Figure 4
rms roughness as a function of deposition temperature (except for Al-rich at 420 K, where the film is annealed to 420 K after deposition at 365 K). Roughness is obtained from images of size $100 \times 100 {nm}^{2}$ . Error bars correspond to standard deviations and are sometimes smaller than the data marker.Reuse & Permissions
Figure 5
(Color online) Clean surface terraces and 0.5 ML Ag films deposited at 300 K and at 365 K on (a) a TM-rich terrace and (c) an Al-rich #1 terrace. Panel (b) shows 1.5 ML deposited at 300 K on an Al-rich #2 terrace. Corresponding model terminations are superimposed for a better understanding of the surface features. All the STM images except the clean surface ones are $14.5 \times 14.5 {nm}^{2}$ and were recorded at $- 1 V$ and 0.5 nA. A smooth FFT filtering has been applied to the STM images in (a) and added to the same duplicate image in derivative mode. Arrows show what are referred in the text as doubled periodicity rows in panel (b) and adrows and troughs in panel $(c_{1})$ . The single-line arrow in panel $(c_{3})$ shows an elongated island and the double-line arrow shows a bright stripe covering a trough.Reuse & Permissions

Physical Review B

covering condensed matter and materials physics