Tunable Height Research Articles

Height‐Gradiently‐Tunable Nanostructure Arrays by Grayscale Assembly Nanofabrication for Ultra‐realistic Imaging

AbstractDue to the limitation of nanofabrication technology, nanostructured arrays and devices are usually of equal height, and it is difficult to change simultaneously its height in the Z direction at X–Y direction regulation. However, the tunable height as an indispensable part of structural spatial freedom control is very conducive to the functional expansion and innovation of nanodevices. Here, a grayscale assembled fabrication method is developed by combining e‐beam lithography with atomic layer deposition and transfer technology, and a wide range of the height gradient of nanostructures can be realized in the same array and then applied in high‐quality images. Following this strategy, ultra‐realistic relief‐nanostructured images with 256 grayscale levels are demonstrated, consisting of height‐varying nanopillars with 100 nm in pixel size and 6.4×1010 dpi in resolution. Especially, multi‐dimensional structural color based on metasurfaces with C4 symmetric pixels is designed and prepared by height regulation nanofabrication, enabling a strong multi‐dimensional control ability in hue, saturation, and brightness of the structural color display with the single pixel of 1.5 µm in size. The as‐developed grayscale nanoconfigurations open a new approach for multidimensionally structural regulations, showing great applied potential not only in high‐resolution imaging but also in more advancednanophotonic devices.

Energy Absorption of 3D Printed ABS and TPU Multimaterial Honeycomb Structures.

Advances in multimaterial 3D printing are enabling the construction of advantageous engineering structures that benefit from material synergies. Cellular structures, such as honeycombs, provide high-energy absorption to weight ratios that could benefit from multimaterial strategies to improve the safety and performance of engineered systems. In this study, we investigate the energy absorption for honeycombs with square and hexagonal unit cells constructed from acrylonitrile butadiene styrene (ABS) and thermoplastic polyurethane (TPU). Honeycombs were fabricated and tested for out-of-plane and in-plane compression using ABS, TPU, and a combination of ABS with a central TPU band of tunable height. Out-of-plane energy absorption for square honeycombs increased from 2.2 kN·mm for TPU samples to 11.5 kN·mm for ABS samples and energy absorption of hexagonal honeycombs increased from 2.9 to 15.1 kN·mm as proportions of TPU/ABS were altered. In-plane loading demonstrated a sequential collapse of unit cell rows in square honeycombs with energy absorption of 0.1 to 2.6 kN·mm and a gradual failure of hexagonal honeycombs with energy absorption of 0.6 to 2.0 kN·mm. These results demonstrate how multimaterial combinations affect honeycomb compressive response by highlighting their benefits for controlled energy absorption and deformation for tunable performance in diverse engineering applications.

The multi-frequency vibration metastructure for three-dimensional containerless attractor of particles

Constructing morphologies of particles is essential for material, biomedical, and chemical handling. Conventionally, the ordered morphologies are constructed either by internal or external force, such as optical, magnetic, electrical, and acoustic field. Existing manipulation of particles has been limited to the two-dimensional patterns due to gravity. It is challenging to construct various three-dimensional morphologies of particles. In this work, the multi-frequency vibration metastructure design for three-dimensional morphologies manipulation of particles is investigated. Tunable containerless morphologies are further achieved by altering the vibration modes of the metastructure. Firstly, the programmable vibration modes are realized by the vibration metastructure. Tunable vibration modes are generated through switching the excitation frequencies for the resonant labyrinth-type structures at different directions. Then, the three-dimensional morphologies of particles are realized near the vibration anti-node. Particles are driven by the high-intensity acoustic field, wherein gravity is overcome, including the combined effect of acoustic streaming, acoustic radiation force, and collision force. Further, the trapping of granular particles exhibits multiple morphologies assemblages with tunable height, rotation, and dynamic oscillation through parametric excitation. Finally, the directions of various attractor walls can be tunable by demultiplexing the multi-frequency vibration metastructure. This work paves a way for control of vibration modes by the metastructure, thereby enabling tunable three-dimensional morphologies manipulation of particles.

Mechanical Beam Steering Array Antenna With Tunable Height

This letter presents a mechanical beam steering array antenna (MBSA) with tunable height elements. Each antenna element is composed of a U-slot radiation patch and a stepper motor supported by the three-dimensional-printed structure. By controlling the height of each antenna element using a stepper motor, an arbitrary phase shift value in the range of 0°∼360° can be achieved. In addition, steering high-gain beams can be generated by flexibly adjusting the height of each antenna element. A prototype of 8 × 8 MBSA was designed and fabricated to realize beam scanning in the pitch angle range from −40° to 40° in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xoz-</i> plane and near-field focusing. The measured gain of MBSA is 23.3 dBi with an aperture efficiency of 85.7% at 10 GHz. The proposed MBSA has the advantages of simple structure, low cost and high stability, which can be applied in satellite communication systems.

Tempalte-induced interfacial construction of mesoporous CuS hollow spherical caps with tunable height, light receiving region and photocatalytic activities

A new micro/nano-structured material, mesoporous CuS hollow spherical cap (HSC), was fabricated on the surface of a solution by template-induced interfacial reaction. The Cu2(OH)2CO3 microspheres modified with vinyl trimethoxy silane were floated on the mixed aqueous solution of ethanol and thioacetamide, and acted as the template and the copper source. At the solid-liquid interface thioacetamide reacted with Cu2(OH)2CO3 to produce CuS shells around the immersed part of the template, and then the mesoporous CuS HSC was obtain by removal of the template. Controlling the content of ethanol could systemically tune the immersed depth and the HSC height. Such HSCs displayed increased photocatalytic activity in degradation of methyl blue with the decrease of the HSC height. In addition to the conventional specific surface area, the activity regions accessible by light (light receiving region) were analyzed by optical simulation for the first time and considered an important factor in enhancing the photocatalytic activity of HSC structure. The present study not only shows a facile strategy to fabricate activity-tunable CuS HSC photocatalyst, but also establishes a relationship between the geometry of morphology and photocatalytic performance.

Deterministic Modification of CVD Grown Monolayer MoS2 with Optical Pulses

AbstractTransition metal dichalcogenide monolayers have demonstrated a number of exquisite optical and electrical properties. Here, the authors report the optical modification of topographical and optical properties of monolayer MoS2 with femtosecond pulses under an inert atmosphere. A formation of three‐dimensional structures on monolayer MoS2 with tunable height up to ≈20 nm is demonstrated. In contrast to unmodified monolayer MoS2, these optically modified structures show significantly different optical properties, such as lower photoluminescence intensity and longer fluorescence lifetime. The results suggest a novel way to modify transition metal dichalcogenide materials for mechanic, electronic and photonic applications.

Observation of rogue events in non-Markovian light

Efforts to understand the physics of rogue waves have motivated the study of mechanisms that produce rare, extreme events, often through analogous optical setups. As many studies have reported nonlinear generation mechanisms, recent work has explored whether optical rogue events can be produced in linear systems. Here we report the observation of linear rogue events with tunable height, generated from light imprinted with a non-Markovian wavefront. Moreover, if the non-Markovian wavefront is allowed to propagate through a nonlinear medium, extraordinarily long-tailed intensity distributions are produced, which do not conform to the statistics previously observed in optical rogue wave experiments.

Fabrication of Biomimetic Micropatterned Surfaces by Sol–Gel Dewetting

AbstractDewetting of thin polymer films has been extensively investigated as a way to generate patterned surfaces. In this paper, the controlled dewetting of sol–gel thin films induced by solvent annealing is reported. The key factors that control the dewetting process are identified and patterns with tunable diameter between 5 and 80 µm and tunable height between 1 and 10 µm are fabricated on a large scale. By changing the chemistry of the sol–gel system, patterns with wetting contrast, consisting of hydrophilic bumps on a hydrophobic layer, are realized. These surfaces are inspired by the exoskeleton of the Namib desert beetle and are amenable to application in atmospheric water capture, as they facilitate condensation and allow for water droplets to roll off at low critical volumes (6–8 µL), similar to the value predicted for the Namib desert beetle. The approach presented is simple, scalable, and can be applied to a wide range of substrates including glass. Transparent micropatterns are realized with high transmittance in the visible range, suitable for fabrication of coatings on windows or microlens arrays.

Gate-Controlled Transmission of Quantum Hall Edge States in Bilayer Graphene.

The edge states of the quantum Hall and fractional quantum Hall effect of a two-dimensional electron gas carry key information of the bulk excitations. Here we demonstrate gate-controlled transmission of edge states in bilayer graphene through a potential barrier with tunable height. The backscattering rate is continuously varied from 0 to close to 1, with fractional quantized values corresponding to the sequential complete backscattering of individual modes. Our experiments demonstrate the feasibility to controllably manipulate edge states in bilayer graphene, thus opening the door to more complex experiments.

Performance study of humidification–dehumidification system operating on the principle of an airlift pump with tunable height

Abstract A new experimental set up for humidification–dehumidification operating on the principle of an air lift pump was experimented. Experimental work investigates the main operating parameters of a proposed desalination process working with an air humidification–dehumidification method. The principal objective of this investigation was the determination of the humid air behavior through single stage of an airlift humidification–dehumidification system. The experimental work studied the influence of the operating conditions such as the water temperature, the submerged ratio and the airflow rate on the performance of the setup. The experimental results show that the production rate of the system increases with the both increase of the brackish water temperature and the airflow rate. The productivity of the system is strongly affected by the brackish water temperature, airflow rate and slightly affected by the submerged ratio. Within the studied ranges, the maximum productivity of the system reached to 4.035 kg/h, at water temperature (Tw) = 85 °C and m ˙ a = 5 kg/h. A good agreement was achieved with productivity calculations.

Design and application of flexible insert for microinjection compression molding polymer microlens arrays with tunable height

A flexible insert is assembled using easily available porous plate and flexible polymer film. Then, applying microinjection compression molding technology, a fast and efficient method is proposed for successive, mass and one‐step replication of polymer microlens arrays (MLAs). Orderly MLAs with convex microlenses are successfully prepared without a given micro‐feature on the insert corresponding to that on the MLAs. Interestingly, the flexible films are deformed to arc‐like profiles that match with the shape of the microlenses with different curvatures under the action of different mold compression forces. Hence, by only changing the compression force, a series of high quality MLAs with tunable height and so geometrical‐morphology are molded by one flexible insert. The molded MLAs exhibit average heights of 61.61–86.28 µm by varying the compression force from 90 to 120 kN. The molded MLAs exhibit favorable geometrical‐morphology uniformity and optical properties. The proposed method is an accessible approach to avoid expensive equipment and complicated procedure for manufacturing the mold microfeature. POLYM. ENG. SCI., 58:213–219, 2018. © 2017 Society of Plastics Engineers

Scanning gate imaging in confined geometries

This article reports on tunable electron backscattering investigated with the biased tip of a scanning force microscope. Using a channel defined by a pair of Schottky gates, the branched electron flow of ballistic electrons injected from a quantum point contact is guided by potentials of a tunable height well below the Fermi energy. The transition from injection into an open two-dimensional electron gas to a strongly confined channel exhibits three experimentally distinct regimes: one in which branches spread unrestrictedly, one in which branches are confined but the background conductance is affected very little, and one where the branches have disappeared and the conductance is strongly modified. Classical trajectory-based simulations explain these regimes at the microscopic level. These experiments allow us to understand under which conditions branches observed in scanning gate experiments do or do not reflect the flow of electrons.

Entropically Controlled Nanomechanical DNA Origami Devices

Structural DNA nanotechnology is a rapidly emerging field with immense potential for applications such as single molecule sensing, drug delivery, and manipulating molecular components. Major advances in the last decade have enabled the precise design and fabrication of DNA nanostructures with unprecedented geometric complexity; however, relative to natural biomolecular machines, the functional scope of DNA nanotechnology is limited by an inability to design dynamic mechanical behavior such as complex motion, conformational dynamics, or force generation. Inspired by approaches used in macroscopic machine design, we have recently developed methods to design structures with controllable 1D, 2D, or 3D motion. Moving beyond design of geometry or motion paths, we have recently developed structures with multiple thermally accessible states separated by well-defined energy barriers with tunable height. In particular, we have design a two-state device that transitions between compact and open states driven by thermal energy. We directly measured the dynamic behavior via single molecule fluorescence experiments, which show both the equilibrium distribution of states and the kinetics of switching between states can be tuned via design parameters that regulate the relative configurational space, or equivalently the entropy change, between states. Finally, we show that these dynamic structures can be used to probe local molecular scale forces, specifically depletion forces that result from entropic interactions with a crowding reagent. This work is the first demonstration of an ability to control the kinetics of DNA origami nanostructures down to the second scale and establishes a foundation for exploiting dynamic behavior of these devices to study physical interactions at the molecular scale.

Micromolding Surface‐Initiated Polymerization: A Versatile Route for Fabrication of Coatings with Microscale Surface Features of Tunable Height

This article introduces a process termed micromolding surface‐initiated polymerization (μMSIP) as a versatile route to provide surface‐bound, partially fluorinated polymer coatings with a homogeneous array of microscale surface features. The process employs hard‐polydimethylsiloxane (h‐PDMS) to mold the surface structure of master substrates exhibiting patterned microscale features. Upon filling the mold with the monomer 5‐(perfluorooctyl)norbornene (NBF8) and placing against a surface that is pre‐activated for surface‐initiated ring‐opening metathesis polymerization (SI‐ROMP), a partially fluorinated polymer film propagates from the surface with features that grow into the recesses of the mold to produce the final microtextured coating. The heights of these features can be tuned from 20–100% of the full height of the mold features based on the amount of initiator employed as well as the polymerization time and temperature. Reproduced topographies include pyramidal and inverted pyramidal structures. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images show that the final polymer film exhibits a homogeneously microstructured surface that resembles that of its corresponding master.

Nonlinear beam splitter in Bose-Einstein-condensate interferometers

A beam splitter is an important component of an atomic/optical Mach-Zehnder interferometer. Here we study a Bose Einstein Condensate beam splitter, realized with a double well potential of tunable height. We analyze how the sensitivity of a Mach Zehnder interferometer is degraded by the non-linear particle-particle interaction during the splitting dynamics. We distinguish three regimes, Rabi, Josephson and Fock, and associate to them a different scaling of the phase sensitivity with the total number of particles.