Glancing Angle Deposition
Glancing angle deposition (GLAD) is a physical vapor deposition process where the deposition flux is incident at a large angle with respect to the surface normal and the substrate is rotating. In GLAD, the substrate is rotated in the polar and azimuthal directions by two stepper motors programmed by a computer. During the deposition, the angle between the incoming vapor from the source and the surface normal to the substrate is set between 0 to 90 degree, and the substrate can rotate azimuthally. The main mechanisms that control the growth are the shadowing effect and surface diffusion.
Setup for GLAD
GLAD produces columnar structures through the effect of shadowing during film growth, while substrate rotation controls the shape of the columns. In this technique, there are three basic parameters that determine the morphology of the columns: the incident angle, the growth rate, and the substrate rotational speed. By changing the angle of incidence, the columns can be sculptured into a C-shape, S-shape, and zigzag shape, while by changing the ratio of the deposition rate to the rotational rate (which is defined as the pitch), the column morphology can be varied between matchstick, helical, and vertical columns. Since GLAD is a physical vapor deposition technique, it has many advantages in terms of controlling the growth of nanostructured thin films: 1. It can form a nano-column array naturally. 2. The porosity of the film can be controlled by changing the incident angle. 3. There is almost no restriction on materials since the growth process is a thermal evaporation. 4. The shape and in-plane alignment of columns can be easily modified. 5. It has the advantage of self-alignment due to the shadowing effect. 6. It can also generate three-dimensional nanostructures. These advantages make the GLAD technique very promising for nanostructure fabrications.
Suggested references for GLAD
An excellent book to understand GLAD method and the growth behavior is "Glancing Angle Deposition of Thin Films: Engineering the Nanoscale" by Matthew M. Hawkeye, Michael T. Taschuk, Michael J. Brett, published by Wiley in 2014.
To look into hetero- and composite nanostructure fabrication strategies, our 2011 review paper is a very good source: Y.-P. He and Y.-P. Zhao, "Advanced multi-component nanostructures designed by dynamic shadowing growth," Nanoscale 3, 2361-2375 (2011).
For ordered nanostructure fabrication using a template or a shadow mask, our 2018 review paper can be a good start: Bin Ai and Yiping Zhao, "Glancing angle deposition meets colloidal lithography: a new evolution in the design of nanostructures," Nanophotonics, DOI: https://doi.org/10.1515/nanoph-2018-0105 (2018).
For GLAD structure based applications, a comprehensive review is given by: Angel Barranco, Ana Borras, Agustin R.Gonzalez-Elipe, and Alberto Palmero, "Perspectives on oblique angle deposition of thin films: From fundamentals to devices," Progress in Materials Science 76, 59-153 (2016).