Cost-Effective Laboratory Matrix Projection Micro-Lithography System.

This paper presents a home-built projection lithographer designed to transfer the image from a DLP (digital light processing) projector MEMS matrix onto the microscope objective's field of view, where a photoresist-covered substrate is placed. The photoresist is exposed using blue light with a wavelength of 450 nm. To calibrate the device and adjust focal lengths, we utilize a red light that does not affect the photoresist. The substrate is located on a movable platform, allowing the exposure field to be shifted, enabling the exposure of designs with lateral sizes of 1 × 1 cm2 at a resolution of a few micrometers. Our setup showcases a 2 µm resolution for the single frame 200 × 100 µm2, and a 5 µm resolution for 1 × 1 cm2 with field stitching. The exposure speed, approximately 1 mm2/100 s, proves to be sufficient for a variety of laboratory prototyping needs. This system offers a significant advantage due to its utilization of easily accessible and budget-friendly components, thereby enhancing its accessibility for a broader user base. The exposure speed and resolution meet the requirements for laboratory prototyping in the fields of 2D materials, quantum optics, superconducting microelectronics, microfluidics, and biology.

3D Hypersound Microscopy of van der Waals Heterostructures.

The mechanical properties of the layered crystals in the few layer limit are largely unexplored. We employ a picosecond ultrasonic technique to access the corresponding mechanical parameters. Temporal variation of the reflection coefficient of the Al film that covers hBN/WSe2/hBN (where hBN is hexagonal boron nitride) heterostructures on a sapphire substrate after the femtosecond laser pulse excitation is carefully measured using an interferometric technique with spatial resolution. The laser pulse generates a broadband sound wave packet propagating perpendicularly to the Al plane and partially reflecting from the heterostructural interfaces. The demonstrated technique allows one to resolve a WSe2 monolayer embedded in hBN. We apply a multilayered model of the optoacoustical response to evaluate the mechanical parameters, in particular, the rigidity of the interfaces. Mapping of the Fourier spectra of the response visualizes different composition regions and may serve as an acoustic tomography tool. Almost zero phonon dissipation below 150 GHz demonstrates the van der Waals heterostructures' potential for nanoacoustical applications.

Superconductivity in Cu Co-Doped SrxBi2Se3 Single Crystals.

In this study, we grew Cu co-doped single crystals of a topological superconductor candidate Sr x Bi 2 Se 3 , and studied their structural and transport properties. We reveal that the addition of even as small an amount of Cu co-dopant as 0.6 atomic %, completely suppresses superconductivity in Sr x Bi 2 Se 3 . Critical temperature (∼2.7 K) is rather robust with respect to co-doping. We show that Cu systematically increases the electron density and lattice parameters a and c. Our results demonstrate that superconductivity in Sr x Bi 2 Se 3 -based materials is induced by significantly lower Sr doping level x < 0.02 than commonly accepted x ∼ 0.06 , and it strongly depends on the specific arrangement of Sr atoms in the host matrix. The critical temperature in superconductive Sr-doped Bi 2 Se 3 is shown to be insensitive to carrier density.