Search for: All records

Interfacial adhesion energy is a fundamental property of two-dimensional (2D) layered materials and van der Waals heterostructures due to their intrinsic ultrahigh surface to volume ratio, making adhesion forces very strong in many processes related to fabrication, integration and performance of devices incorporating 2D crystals. However, direct quantitative characterization of adhesion behavior of fresh and aged homo/heterointerfaces at nanoscale has remained elusive. Here, we use an atomic force microscopy technique to report precise adhesion measurements in ambient air through well-defined interactions of tip-attached 2D crystal nanomesas with 2D crystal and SiO_xsubstrates. We quantify how different levels of short-range dispersive and long-range electrostatic interactions respond to airborne contaminants and humidity upon thermal annealing. We show that a simple but very effective precooling treatment can protect 2D crystal substrates against the airborne contaminants and thus boost the adhesion level at the interface of similar and dissimilar van der Waals heterostructures. Our combined experimental and computational analysis also reveals a distinctive interfacial behavior in transition metal dichalcogenides and graphite/SiO_xheterostructures beyond the widely accepted van der Waals interaction.

 

Along with the increasing interest in MoS 2 as a promising electronic material, there is also an increasing demand for nanofabrication technologies that are compatible with this material and other relevant layered materials. In addition, the development of scalable nanofabrication approaches capable of directly producing MoS 2 device arrays is an imperative task to speed up the design and commercialize various functional MoS 2 -based devices. The desired fabrication methods need to meet two critical requirements. First, they should minimize the involvement of resist-based lithography and plasma etching processes, which introduce unremovable contaminations to MoS 2 structures. Second, they should be able to produce MoS 2 structures with in-plane or out-of-plane edges in a controlled way, which is key to increase the usability of MoS 2 for various device applications. Here, we introduce an inkjet-defined site-selective (IDSS) method that meets these requirements. IDSS includes two main steps: (i) inkjet printing of microscale liquid droplets that define the designated sites for MoS 2 growth, and (ii) site-selective growth of MoS 2 at droplet-defined sites. Moreover, IDSS is capable of generating MoS 2 with different structures. Specifically, an IDSS process using deionized (DI) water droplets mainly produces in-plane MoS 2 features, whereas the processes using graphene ink droplets mainly produce out-of-plane MoS 2 features rich in exposed edges. Using out-of-plane MoS 2 structures, we have demonstrated the fabrication of miniaturized on-chip lithium ion batteries, which exhibit reversible lithiation/delithiation capacity. This IDSS method could be further expanded as a scalable and reliable nanomanufacturing method for generating miniaturized on-chip energy storage devices. 

Detrimental nanoscale gas bubble defects seriously hinder the practical applications of nanoimprint lithography in manufacturing of nanoelectronic devices. Here, we present a nanofluidics study on the formation and evolution mechanisms of nanoscale bubble defects in dispensing-based UV-curable nanoimprint lithography processes. Our work indicates that the formation of nanoscale bubble defects is mainly attributed to the pinning of resist spreading edges at the nanostructures or contaminants on the mold/substrate surfaces. Such pinning-induced nanoscale gas bubbles undergo an evolution process governed by the combinational effect of surface pinning and gas dissolution into resist. Such an evolution process results in a prominent drop of the gas pressure inside bubbles and therefore prevents nanoscale gas bubble defects from the complete dissolution into resists. This work identifies the critical mechanisms responsible for the formation of detrimental nanoscale bubble defects and provides important insights for the ultimate elimination of such defects