Journal of Vacuum Science & Technology B emphasizes processing, measurement and phenomena associated with micrometer and nanometer structures and devices. Processing may include vacuum processing, plasma processing and microlithography among others, while measurement refers to a wide range of materials and device characterization methods for understanding the physics and chemistry of submicron and nanometer structures and devices.
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This paper presents a novel mirror-tunable laser interference system for the wafer-scale patterning (>4-in.) of submicron grating structures with a flexible periodicity (200–1000 nm) in a compact and cost-effective manner. The proposed system guides and splits the laser beam into two expanded light beams propagating in a downward direction to be reflected by rotatable ultraviolet mirrors to produce interference patterns. The incident angle of two light beams can be controlled by rotating the mirrors until they match the targeted periodicity of the grating, without the need to reconfigure the optical paths. The fact that light polarization changes with the rotation angle of the mirrors necessitates the use of a half-wave plate along each optical path to adjust the direction of polarization perpendicular to the plane of incident light. The proposed system enables large-area fabrication and wide-range grating tunability, making it highly useful for applications that require wafer-scale patterning of submicron periodic structures, such as flexible wire-grid polarizers for displays, patterned sapphire substrates for light-emitting diodes, and Bragg gratings for distributed feedback lasers.
In this work, low-energy electron microscopy is employed to probe structural as well as electronic information in few-layer WSe2 on epitaxial graphene on SiC. The emergence of unoccupied states in the WSe2–graphene heterostructures is studied using spectroscopic low-energy electron reflectivity. Reflectivity minima corresponding to specific WSe2 states that are localized between the monolayers of each vertical heterostructure are shown to reveal the number of layers for each point on the surface. A theory for the origin of these states is developed and utilized to explain the experimentally observed featured in the WSe2 electron reflectivity. This method allows for unambiguous counting of WSe2 layers, and furthermore may be applied to other two-dimensional transition metal dichalcogenide materials.
The authors describe recent experimental efforts to perform polarization-resolved optical spectroscopy of monolayer transition-metal dichalcogenide semiconductors in very large pulsed magnetic fields to 65 T. The experimental setup and technical challenges are discussed in detail, and temperature-dependent magnetoreflection spectra from atomically thin tungsten disulphide are presented. The data clearly reveal not only the valley Zeeman effect in these two-dimensional semiconductors but also the small quadratic excitondiamagnetic shift from which the very small exciton size can be directly inferred. Finally, the authors present model calculations that demonstrate how the measured diamagnetic shifts can be used to constrain estimates of the exciton