2 research outputs found
Pitch Control of Hexagonal Non-Close-Packed Nanosphere Arrays Using Isotropic Deformation of an Elastomer
Self-assembly
of colloidal nanospheres combined with various nanofabrication
techniques produces an ever-increasing range of two-dimensional (2D)
ordered nanostructures, although the pattern periodicity is typically
bound to the original interparticle spacing. Deformable soft lithography
using controlled deformation of elastomeric substrates and subsequent
contact printing transfer offer a versatile method to systematically
control the lattice spacing and arrangements of the 2D nanosphere
array. However, the anisotropic nature of uniaxial and biaxial stretching
as well as the strain limit of solvent swelling makes it difficult
to create well-separated, ordered 2D nanosphere arrays with large-area
hexagonal arrangements. In this paper, we report a simple, facile
approach to fabricate such arrays of polystyrene nanospheres using
a custom-made radial stretching apparatus. The maximum stretchability
and spatial uniformity of the polyÂ(dimethylsiloxane) (PDMS) elastomeric
substrate is systematically investigated. A pitch increase as large
as 213% is demonstrated using a single stretching-and-transfer process,
which is at least 3 times larger than the maximum pitch increase achievable
using a single swelling-and-transfer process. Unlike the colloidal
arrays generated by the uniaxial and biaxial stretching, the isotropic
expansion of radial stretching allows the hexagonal array to retain
its original structure across the entire substrate. Upon radial strain
applied to the PDMS sheet, the nanosphere array with modified pitch
is transferred to a variety of target substrates, exhibiting different
optical behaviors and serving as an etch mask or a template for molding
Air-Stable Humidity Sensor Using Few-Layer Black Phosphorus
As
a new family member of two-dimensional layered materials, black
phosphorus (BP) has attracted significant attention for chemical sensing
applications due to its exceptional electrical, mechanical, and surface
properties. However, producing air-stable BP sensors is extremely
challenging because BP atomic layers degrade rapidly in ambient conditions.
In this study, we explored the humidity sensing properties of BP field-effect
transistors fully encapsulated by a 6 nm-thick Al<sub>2</sub>O<sub>3</sub> encapsulation layer deposited by atomic layer deposition.
The encapsulated BP sensors exhibited superior ambient stability with
no noticeable degradation in sensing response after being stored in
air for more than a week. Compared with the bare BP devices, the encapsulated
ones offered long-term stability with a trade-off in slightly reduced
sensitivity. Capacitance–voltage measurement results further
reveal that instead of direct charge transfer, the electrostatic gating
effect on BP flakes arising from the dipole moment of adsorbed water
molecules is the basic mechanism governing the humidity sensing behavior
of both bare and encapsulated BP sensors. This work demonstrates a
viable approach for achieving air-stable BP-based humidity or chemical
sensors for practical applications