Topic: Oblique Angle Deposition Technique and Its Application in Optical Nanomaterials
Speaker: Associate Professor Dexian Ye from Virginia Commonwealth University
Event date: 7/2/2019
Event time: 9:30 am
Venue: Academic LectureHall, 4th Floor, Building 7
Sponsor: School of Physics and Electronic Engineering, Jiangsu Collaborative Innovation Center of Advanced Laser Technology and Emerging Industry, Jiangsu Key Laboratory of Advanced Laser Material and Devices, Institute of Science and Technology
Abstract: Oblique angledeposition (OAD) is a facile and versatile nanofabrication technique, which is based on a common vacuum physical vapor deposition system. It manipulates the arrangement of substrates to allow the light-of-sight vapor beam approaching the surface of the substrate at a large incident angle. The atoms are first self-assembled into islands on the surface controlled by thermal dynamics. Since the atoms incident at an angle, they only land on the protrusions and areprohibited to reach certain regions on the surface behind the islands due to the shadowing effect. As such, nanowires with similar structures are formed. They slant toward the PVD source with a same angle, and have uniform sizes and lengths. If the substrate rotates along its normal axis in OAD, the techniqueis specifically called dynamic OAD or glancing angle deposition (GLAD). The nanostructures can be designed and controlled to form complex shapes, such as nanosprings and nanospheres, by using GLAD technique. General speaking, OAD and GLAD can be used to fabricate nanostructures of a large variety of materials including semiconductors, metals, metal oxides, metal nitrides, polymers, etc. as long as they can be vaporized in PVD systems.
In recent years, combining experiments and computer simulations, we investigated the fabricationof nanostructures made of silicon, metal, titanium nitrides, and transitionmetal oxides using OAD and GLAD, and studied their growth mechanisms andphysical properties. We found that long range capturing of incident atoms through ballistic sticking, non-unity sticking and surface re-emission mechanismsplay equally important roles as the shadowing effect and surface diffusion inthe growth of nanostructures. In simulations and experiments, we introduced templates to the flat substrates as the seeds to control the arrangement of nanostructures on the surface. The resulted regularly spaced nanostructures have unique optical properties such as the photonic band gaps and plasmonicresonance.
As mentioned above, OAD and GLAD techniques are focused on the manipulation of substrates in commonpractice. Nevertheless, the control of PVD source is not investigated.Recently, we introduced the partial ionization method to OAD and GLAD. The evaporated atoms are partially ionized through the electron bombardment and accelerated to gain certain amount of kinetic energy. When the ions depositedon the surface with other neutral atoms, the surface diffusion and other thermal dynamics can be enhanced by transferring the kinetic energy of ions tolocal surface. Under certain conditions, it is possible to promote the crystalgrowth without substantial substrate heating. We chose tungsten oxide (WO3) asthe material to demonstrate this new approach. Single crystal WO3 nanowires canbe grown at room temperature with 3 keV kinetic energy of the ions. WO3 is animportant optical material with a band gap in the visible region, which can be used as photocatalysts for water splitting.