Template-assisted nanostructure fabrication by glancing angle deposition: a molecular dynamics study
© Zhang et al.; licensee Springer. 2013
Received: 24 May 2013
Accepted: 28 June 2013
Published: 5 July 2013
In the present work, we investigate the pre-existing template-assisted glancing angle deposition of Al columnar structures on Cu substrate by means of molecular dynamics simulations, with a focus on examining the effect of deposition-induced template deformation on the morphologies of the fabricated structures. Our simulations demonstrate that the pre-existing templates significantly intensify the shadowing effect, which thus facilitates the formation of columnar structures under small deposition flux. The underlying deformation modes of the templates under different deposition configurations are analyzed and are correlated to the geometrical characteristics of the columnar structures. It is found that the template height-dependent deformation behavior of the templates strongly influences the morphologies of the fabricated columnar structures. Our findings provide design and fabrication guidelines for the fabrication of one-dimensional nanostructures by the template-assisted deposition technique.
KeywordsGlancing angle deposition Template Deformation mechanism Molecular dynamics
One-dimensional (1D) nanostructures, including nanopillars, nanorods, nanotubes, and nanowires, are promising building blocks for constructing nanoscale electronical and optoelectronical elements and interconnects because of their unique physical properties . In addition to the characterization, the fabrication of ordered arrays of 1D nanostructures has been one of the current research focuses of nanostructures engineering. In particular, the rotational glancing angle deposition (GLAD) has been demonstrated to be one powerful nanostructuring technique for the fabrication of columnar nanostructures in an orientation- and structure-controllable, material-independent fashion [2–6]. The rotational GLAD as a physical vapor deposition is extended from the static GLAD (oblique angle deposition) by adding azimuthal and/or polar rotations of the substrate. During the rotational GLAD process, the lateral component of deposition flux with respect to the surface normal of the substrate contributes to the formation of columnar structures due to the shadowing effect, while the rotation of the substrate eliminates the preferred orientation growth, thus controls the shape of the structures. In the past few decades, there is considerable effort of both experimental investigation and atomistic simulations taken to investigate the fundamental mechanisms of the rotational GLAD [7–11].
Since nucleated islands acting as shadowing centers are essentially required for the formation of columnar structures in the initial period of the rotational GLAD, recently placing nano-sized templates on the bare substrate is proposed to replace the nucleated islands, in such a way both deposition period and deposition flux can be reduced significantly. Most importantly, by designing the geometry and the alignment of the templates, ordered arrays of columnar structures with pre-designed shapes can be fabricated under the intensified shadowing effect [12, 13]. Although the template-assisted rotational GLAD has been demonstrated to be one promising nanostructuring technique for the fabrication of 1D nanostructures, our fundamental understanding of the deposition process, particularly the deposition-induced deformation of the templates, is still limited: will the templates deform during the deposition? If yes, what are the underlying deformation mechanisms of the templates? And how does the deformation behavior of the templates influence the geometry of the fabricated columnar structures?
In this letter, we address the above questions by performing three-dimensional molecular dynamics (MD) simulations of the template-assisted rotational GLAD of 1D Al columnar structures on Cu substrate. Our simulations demonstrate that the presence of templates significantly intensifies the shadowing effect to form 1D columnar structures when deposition flux is small, as compared to the template-free rotational GLAD. Furthermore, the morphology of the fabricated columnar structures by the template-assisted rotational GLAD strongly depends on the deformation behaviors of the templates.
Parameters for the four deposition configurations
Rotational velocity (ps−1)
Template geometry (d, s, h)
0, 0, 0
6a, 10a, 14a
6a, 10a, 14a
6a, 10a, 8a
Results and discussion
Figure 2 also shows that the morphology of the columnar structures strongly depends on the parameters of the deposition configurations. Figure 2b shows that the height distribution of the columnar structures obtained through the high template-assisted rotational GLAD is not uniform, although the heights of the templates are the same. Furthermore, slight inclination of the axial of the columnar structures is observed. For the template-assisted static GLAD, the inclination is more pronounced than the template-assisted rotational GLAD, as shown in Figure 2b. In addition, the discrepancy between the heights of the columnar structures is pronounced, and the coalescence of columnar structures occurs. A comparison between Figure 2b,c shows that the template-assisted rotational GLAD leads to a lower but more uniform columnar structures than the template-assisted static GLAD, given the same height of the templates. As compared to the high template-assisted rotational GLAD, Figure 2d shows that the morphologies of the columnar structures obtained through the low template-assisted rotational GLAD are more uniform, as the structures are mainly straight and the heights are almost the same. We note that the morphology of the columnar structures may strongly depend on the rotational velocity, which determines the coverage of deposited Al atoms in conjunction with the deposition rate. It suggests that the height of the templates has strong influence on the morphology of the columnar structures obtained through the template-assisted rotational GLAD.
In summary, we perform MD simulations of the pre-existing template-assisted rotational GLAD to investigate the influence of templates on the formation of Al columnar nanostructures on Cu substrate. Our simulation results show that under small deposition flux, the presence of the templates significantly contributes to the formation of columnar structures due to the intensified shadowing effect, while there are only islands formed during template-free rotational GLAD. As compared to the template-assisted static GLAD, the azimuthal rotation of the substrate during the template-assisted rotational GLAD leads to uniform morphologies of the formed columnar structures. Our simulations reveal the two deformation modes of dislocation mechanisms and deformation twinning that operating in the plastic deformation of the templates, which strongly influence both the morphologies of the templates and the formed columnar structures. While the formation of TBs mainly causes the shape change of the templates, the presence of ISF leads to the shear of the template by an atomic step. Furthermore, the deformation modes dominating the plastic deformation of the templates change significantly with the height of the templates.
The authors greatly acknowledge finical support of the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (no. 51075088), the Doctoral Discipline Foundation for Young Teachers in the Higher Education Institutions of Ministry of Education (no. 20092302120005), the Heilongjiang Provincial Natural Science Foundation (no. E201019), and the Fundamental Research Funds for the Central Universities (grant no. HIT. NSRIF. 2014050).
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