Nanoimprint-induced strain engineering of two-dimensional materials

The high stretchability of two-dimensional(2D)materials has facilitated the possibility of using external strain to manipulate their properties.Hence,strain engineering has emerged as a promising technique for tailoring the performance of 2D materials by controlling the applied elastic strain field.Although various types of strain engineering methods have been proposed,deterministic and controllable generation of the strain in 2D materials remains a challenging task.Here,we report a nanoimprint-induced strain engineering(NISE)strategy for introducing controllable periodic strain profiles on 2D materials.A three-dimensional(3D)tunable strain is generated in a molybdenum disulfide(MoS_(2))sheet by pressing and conforming to the topography of an imprint mold.Different strain profiles generated in MoS_(2)are demonstrated and verified by Raman and photoluminescence(PL)spectroscopy.The strain modulation capability of NISE is investigated by changing the imprint pressure and the patterns of the imprint molds,which enables precise control of the strain magnitudes and distributions in MoS_(2).Furthermore,a finite element model is developed to simulate the NISE process and reveal the straining behavior of MoS_(2).This deterministic and effective strain engineering technique can be easily extended to other materials and is also compatible with common semiconductor fabrication processes;therefore,it provides prospects for advances in broad nanoelectronic and optoelectronic devices.

Spatial modulation of nanopattern dimensions by combining interference lithography and grayscale-patterned secondary exposure

Functional nanostructures are exploited for a variety of cutting-edge fields including plasmonics,metasurfaces,and biosensors,just to name a few.Some applications require nanostructures with uniform feature sizes while others rely on spatially varying morphologies.However,fine manipulation of the feature size over a large area remains a substantial challenge because mainstream approaches to precise nanopatterning are based on low-throughput pixel-by-pixel processing,such as those utilizing focused beams of photons,electrons,or ions.In this work,we provide a solution toward wafer-scale,arbitrary modulation of feature size distribution by introducing a lithographic portfolio combining interference lithography(IL)and grayscale-patterned secondary exposure(SE).Employed after the high-throughput IL,a SE with patterned intensity distribution spatially modulates the dimensions of photoresist nanostructures.Based on this approach,we successfully fabricated 4-inch wafer-scale nanogratings with uniform linewidths of<5%variation,using grayscale-patterned SE to compensate for the linewidth difference caused by the Gaussian distribution of the laser beams in the IL.Besides,we also demonstrated a wafer-scale structural color painting by spatially modulating the filling ratio to achieve gradient grayscale color using SE.

Gradient wettability induced by deterministically patterned nanostructures

We report a large-scale surface with continuously varying wettability induced by ordered gradient nanostructures.The gradient pattern is generated from nonuniform interference lithography by utilizing the Gaussian-shaped intensity distribution of two coherent laser beams.We also develop a facile fabrication method to directly transfer a photoresist pattern into an ultraviolet(UV)-cured high-strength replication molding material,which eliminates the need for high-cost reactive ion etching and e-beam evaporation during the mold fabrication process.This facile mold is then used for the reproducible production of surfaces with gradient wettability using thermal-nanoimprint lithography(NIL).In addition,the wetting behavior of water droplets on the surface with the gradient nanostructures and therefore gradient wettability is investigated.A hybrid wetting model is proposed and theoretically captures the contact angle measurement results,shedding light on the wetting behavior of a liquid on structures patterned at the nanoscale.