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1.
Nano Lett ; 2020 Apr 27.
Artigo em Inglês | MEDLINE | ID: mdl-32324409

RESUMO

Metal halide perovskites are emerging as attractive materials for light-emitting diode (LED) applications. The external quantum efficiency (EQE) has experienced a rapid progress and reached over 21%, comparable to the state of the art organic and quantum dot LEDs. For metal halide perovskites, their simple solution-processing preparation, facile band gap tunability, and narrow emission line width provide another attractive route to harness their superior optoelectronic properties for multicolor display applications. In this work, we demonstrate a high-resolution, large-scale photolithographic method to pattern multicolor perovskite films. This approach is based on a dry lift-off process which involves the use of parylene as an intermediary and the easy mechanical peeling-off of parylene films on various substrates. Using this approach, we successfully fabricated multicolor patterns with red and green perovskite pixels on a single substrate, which could be further applied in liquid crystal displays (LCDs) with blue backlight. Besides, a prototype green perovskite micro-LED display under current driving has been demonstrated.

2.
Micromachines (Basel) ; 10(2)2019 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-30704097

RESUMO

This review focuses on self-cleaning surfaces, from passive bio-inspired surface modification including superhydrophobic, superomniphobic, and superhydrophilic surfaces, to active micro-electro-mechanical systems (MEMS) and digital microfluidic systems. We describe models and designs for nature-inspired self-cleaning schemes as well as novel engineering approaches, and we discuss examples of how MEMS/microfluidic systems integrate with functional surfaces to dislodge dust or undesired liquid residues. Meanwhile, we also examine "waterless" surface cleaning systems including electrodynamic screens and gecko seta-inspired tapes. The paper summarizes the state of the art in self-cleaning surfaces, introduces available cleaning mechanisms, describes established fabrication processes and provides practical application examples.

3.
Micromachines (Basel) ; 10(1)2019 Jan 19.
Artigo em Inglês | MEDLINE | ID: mdl-30669447

RESUMO

The droplet response to vibrations has been well characterized on open substrates, but microfluidic applications for droplets on open systems are limited by rapid evaporation rates and prone to environmental contamination. However, the response of enclosed droplets to vibration is less understood. Here, we investigate the effects of a dual-plate enclosure on droplet transport for the anisotropic ratchet conveyor system. This system uses an asymmetric pattern of hydrophilic rungs to transport droplets with an applied vibration. Through this work, we discovered that the addition of a substrate on top of the droplet, held in place with a 3D printed fixture, extends the functional frequency range for droplet transport and normalizes the device performance for droplets of different volumes. Furthermore, we found that the edge movements are anti-phasic between top and bottom substrates, providing a velocity profile that is correlated to vibration frequency, unlike the resonance-dependent profiles observed on open systems. These results expand the capabilities of this system, providing avenues for new applications and innovation, but also new insights for droplet mechanics in response to applied vibration.

4.
Adv Colloid Interface Sci ; 255: 18-25, 2018 May.
Artigo em Inglês | MEDLINE | ID: mdl-28927830

RESUMO

Anisotropic ratchet conveyors (ARC) are a type of digital microfluidic system. Unlike electrowetting based systems, ARCs transport droplets through a passive, micro-patterned surface and applied orthogonal vibrations. The mechanics of droplet transport on ARC devices has yet to be as well characterized and understood as on electrowetting systems. In this work, we investigate how the design of the ARC substrate affects the droplet response to vibrations and perform the first characterization of transport velocity on ARC devices. We discovered that the design of the ARC device has a significant effect on both the transport efficiency and velocity of actuated droplets, and that the amplitude of the applied vibration can modulate the velocity of transported droplets. Finally, we show that the movement of droplet edges is not continuous but rather the sum of quantized steps between features of the ARC device. These results provide new insights into the behavior of droplets vibrated on asymmetric surface patterns and will serve as the foundation for the design and development of future lab-on-a-chip systems.

5.
Langmuir ; 33(40): 10745-10752, 2017 10 10.
Artigo em Inglês | MEDLINE | ID: mdl-28929766

RESUMO

An anisotropic ratchet conveyor is an asymmetric, periodic, micropatterned surface that propels droplets when vibrated with a sinusoidal signal at certain frequencies and amplitudes. For each input frequency, there is a threshold amplitude beyond which the droplet starts to move. In this paper, we study the parameters that initiate droplet motion and the relationship between the input frequency and threshold amplitude among droplets with different volume, density, viscosity, and surface tension. Through this investigation we demonstrate how nondimensionalization reveals consistent behavior for droplets of different volumes. Finally, we propose a compact model that captures the essential features of the system to describe how a pure vertical vibration results in horizontal droplet motion. This model provides an intuitive understanding of the underlying physics and explains how the surface asymmetry is the key for lateral droplet motion.

6.
Micromachines (Basel) ; 8(12)2017 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-30400553

RESUMO

Anisotropic ratchet conveyors (ARCs) are a recently developed microfluidic platform that transports liquid droplets through a passive, microfabricated surface pattern and applied orthogonal vibrations. In this work, three new functionalities are presented for controlling droplet transport on the ARC system. These devices can pause droplet transport (ARC gate), decide between two pathways of droplet transport (ARC switch), and pass droplets between transport tracks (ARC delivery junction). All devices function solely through the modification of pinning forces acting on the transported droplet and are the first reported devices that can selectively control droplet timing and directionality without active (e.g., thermal, electrical, or magnetic) surface components.

7.
Opt Express ; 22 Suppl 2: A276-81, 2014 Mar 10.
Artigo em Inglês | MEDLINE | ID: mdl-24922236

RESUMO

We demonstrate red-emitting silicon quantum dot (SiQD) phosphors as a low-cost and environment-friendly alternative to rare-earth element phosphors or CdSe quantum dots. After surface passivation, the SiQD-phosphors achieve high photoluminescence quantum yield = 51% with 365-nm excitation. The phosphors also have a peak photoluminescence wavelength at 630 nm and a full-width-at-half-maximum of 145 nm. The relatively broadband red emission is ideal for forming the basis of a warm white spectrum. With 365-nm or 405-nm LED pumping and the addition of green- and/or blue-emitting rare-earth element phosphors, warm white LEDs with color rendering index ~95 have been achieved.

8.
Opt Express ; 22(5): A276-81, 2014 Mar 10.
Artigo em Inglês | MEDLINE | ID: mdl-24800283

RESUMO

We demonstrate red-emitting silicon quantum dot (SiQD) phosphors as a low-cost and environment-friendly alternative to rare-earth element phosphors or CdSe quantum dots. After surface passivation, the SiQD-phosphors achieve high photoluminescence quantum yield = 51% with 365-nm excitation. The phosphors also have a peak photoluminescence wavelength at 630 nm and a full-width-at-half-maximum of 145 nm. The relatively broadband red emission is ideal for forming the basis of a warm white spectrum. With 365-nm or 405-nm LED pumping and the addition of green- and/or blue-emitting rare-earth element phosphors, warm white LEDs with color rendering index ~95 have been achieved.

9.
Opt Lett ; 37(22): 4771-3, 2012 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-23164908

RESUMO

We demonstrate wavelength-tunable, air-stable and nontoxic phosphor materials based on silicon quantum dots (SiQDs). The phosphors, which are composed of micrometer-size silicon particles with attached SiQDs, are synthesized by an electrochemical etching method under ambient conditions. The photoluminescence (PL) peak wavelength can be controlled by the SiQD size due to quantum confinement effect, as well as the surface passivation chemistry of SiQDs. The red-emitting phosphors have PL quantum yield equal to 17%. The SiQD-phosphors can be embedded in polymers and efficiently excited by 405 nm light-emitting diodes for potential general lighting applications.

10.
Langmuir ; 28(38): 13765-70, 2012 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-22934529

RESUMO

We introduce the wetting barrier ratchet, a digital microfluidic technology for directed drop transport in an open air environment. Cyclic drop footprint oscillations initiated by orthogonal vibrations as low as 37 µm in amplitude at 82 Hz are rectified into fast (mm/s) and controlled transport along a fabricated ratchet design. The ratchet is made from a simple wettability pattern atop a microscopically flat surface consisting of periodic semi-circular hydrophilic features on a hydrophobic background. The microfluidic ratchet capitalizes on the asymmetric contact angle hysteresis induced by the curved features to drive transport. In comparison to the previously reported texture ratchets, wetting barrier ratchets require 3-fold lower actuation amplitudes for a 10 µL drop, have a simplified fabrication, and can be made optically flat for applications where transparency is paramount.


Assuntos
Silanos/química , Compostos de Sulfidrila/química , Compostos de Trimetilsilil/química , Técnicas Analíticas Microfluídicas , Tamanho da Partícula , Propriedades de Superfície , Vibração , Molhabilidade
11.
Nanotechnology ; 23(30): 305301, 2012 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-22751003

RESUMO

Orchestrated structure evolution is an alternative nanomanufacturing approach that combines the advantages of top-down patterning and bottom-up self-organizing growth. It relies upon tool-directed patterning to create 'seed' locations on a surface from which a subsequent deposition process produces the final, merged film. Despite its demonstrated ability to reduce patterning time by orders of magnitude, our prior reliance on mass transfer limited deposition and square seed arrays resulted in extraneous film growth along pattern edges, thereby limiting the pattern quality of the final film. Here, quality improvements are demonstrated by modeling and tuning the growth mechanism of the deposition step to include charge transfer effects. In addition, a seed positioning optimization technique derived from simulated annealing is introduced as a method for relocating the seeds to minimize film overgrowth at the pattern edges. These improvements enable OSE to maintain geometric quality while substantially reducing the time and cost compared to traditional direct-write manufacturing methods.

12.
Adv Mater ; 24(12): 1545-50, 2012 Mar 22.
Artigo em Inglês | MEDLINE | ID: mdl-22331660

RESUMO

Controlled vibration selectively propels multiple microliter-sized drops along microstructured tracks, leading to simple microfluidic systems that rectify oscillations of the three-phase contact line into asymmetric pinning forces that propel each drop in the direction of higher pinning.


Assuntos
Técnicas Analíticas Microfluídicas/métodos , Movimento (Física) , Água/química , Propriedades de Superfície , Vibração , Viscosidade
13.
Nanotechnology ; 22(16): 165303, 2011 Apr 22.
Artigo em Inglês | MEDLINE | ID: mdl-21393828

RESUMO

Orchestrated structure evolution (OSE) is a scalable manufacturing method that combines the advantages of top-down (tool-directed) and bottom-up (self-propagating) approaches. The method consists of a seed patterning step that defines where material nucleates, followed by a growth step that merges seeded islands into the final patterned thin film. We develop a model to predict the completed pattern based on a computationally efficient approximate Green's function solution of the diffusion equation plus a Voronoi diagram based approach that defines the final grain boundary structure. Experimental results rely on electron beam lithography to pattern the seeds, followed by the mass transfer limited growth of copper via electrodeposition. The seed growth model is compared with experimental results to quantify nearest neighbor seed-to-seed interactions as well as how seeds interact with the pattern boundary to impact the local growth rate. Seed-to-seed and seed-to-pattern interactions are shown to result in overgrowth of seeds on edges and corners of the shape, where seeds have fewer neighbors. We explore how local changes to the seed location can be used to improve the patterning quality without increasing the manufacturing cost. OSE is shown to enable a unique set of trade-offs between the cost, time, and quality of thin film patterning.


Assuntos
Cristalização/métodos , Modelos Químicos , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Simulação por Computador , Tamanho da Partícula
14.
Lab Chip ; 10(8): 1079-85, 2010 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-20358117

RESUMO

Protein micropatterns have applications in fundamental life sciences and clinical medicine. In this work, we present a new technique to create 2-D protein micropatterns by local activation of a thin film of thermoresponsive plasma-deposited poly(N-isopropylacrylamide) (ppNIPAM) using a computer-controlled infrared laser beam. While the whole substrate is exposed to the protein solution, protein deposition happens only at laser-activated locations. A few seconds of laser exposure is all that is required to form a pattern with resolution in the single micrometre range. Successful ligand binding after protein deposition indicates that protein function remains intact after laser-induced adsorption onto ppNIPAM. This rapid, simple technique advances currently available strategies for protein patterning by its potential to pattern proteins in an enclosed environment or onto a 3-D scaffold.


Assuntos
Acrilamidas/química , Membranas Artificiais , Técnicas Analíticas Microfluídicas/instrumentação , Micromanipulação/instrumentação , Análise Serial de Proteínas/instrumentação , Proteínas/química , Adsorção , Desenho de Equipamento , Análise de Falha de Equipamento , Lasers , Impressão , Ligação Proteica , Temperatura
15.
Nanotechnology ; 21(19): 195306, 2010 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-20400815

RESUMO

Direct-write nanomanufacturing with scanning beams and probes is flexible and can produce high quality products, but it is normally slow and expensive to raster point-by-point over a pattern. We demonstrate the use of an accelerated direct-write nanomanufacturing method called 'orchestrated structure evolution' (OSE), where a direct-write tool patterns a small number of growth 'seeds' that subsequently grow into the final thin film pattern. Through control of seed size and spacing, it is possible to vary the ratio of 'top-down' to 'bottom-up' character of the patterning processes, ranging from conventional top-down raster patterning to nearly pure bottom-up space-filling via seed growth. Electron beam lithography (EBL) and copper electrodeposition were used to demonstrate trade-offs between process time and product quality over nano- to microlength scales. OSE can reduce process times for high-cost EBL patterning by orders of magnitude, at the expense of longer (but inexpensive) copper electrodeposition processing times. We quantify the degradation of pattern quality that accompanies fast OSE patterning by measuring deviations from the desired patterned area and perimeter. We also show that the density of OSE-induced grain boundaries depends upon the seed separation and size. As the seed size is reduced, the uniformity of an OSE film becomes more dependent on details of seed nucleation processes than normally seen for conventionally patterned films.

16.
Anal Chem ; 80(10): 3677-83, 2008 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-18407621

RESUMO

This work presents an electrical technique called electric cell-substrate impedance sensing to measure the cell-substrate separation and the projected area of an individual adherent cell. Cell adhesion and cell spreading are fundamental processes of adherent cells. By recording changes in the cell-substrate separation, the projected area, or both properties with time, the dynamics of cell spreading and cell adhesion can be studied. The advantage of this electrical technique is that it enables a measurement of many individual cells simultaneously. This is a great benefit to the study of heterogeneity in cell populations. The research consisted of building a custom impedance sensing setup, designing an in vitro assay to record an impedance spectrum of an individual living cell, and developing a data analysis method to obtain two properties of the cell from curve-fitting of the impedance spectrum. The values of the cell-substrate separation and the projected area of an individual cell were within the expected ranges and in agreement with those obtained from optical microscopy.


Assuntos
Adesão Celular , Células Cultivadas , Eletricidade , Humanos , Queratinócitos/citologia
17.
Langmuir ; 22(14): 6161-7, 2006 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-16800671

RESUMO

Systematic variation of microscale structures has been employed to create a rough superhydrophobic surface with a contact angle gradient. Droplets are propelled down these gradients, overcoming contact angle hysteresis using energy supplied by mechanical vibration. The rough hydrophobic surfaces have been designed to maintain air traps beneath the droplet by stabilizing its Fakir state. Dimensions and spacing of the microfabricated pillars in silicon control the solid-liquid contact area and are varied to create a gradient in the apparent contact angle. This work introduces the solid-liquid contact area fraction as a new control variable in any scheme of manipulating droplets, presenting theory, fabricated structures, and experimental results that validate the approach.


Assuntos
Modelos Químicos , Transição de Fase , Interações Hidrofóbicas e Hidrofílicas , Vibração
18.
J Biomed Mater Res A ; 70(2): 159-68, 2004 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-15227660

RESUMO

A novel approach is reported for cell patterning based on addressable microheaters and a poly(N-isopropyl acrylamide) (pNIPAM) themoresponsive coating. This thermoresponsive coating is created by a radio frequency NIPAM plasma and is denoted as plasma polymerized NIPAM (ppNIPAM). Films of ppNIPAM with a good retention of monomer side-chain functionality are produced using low-power continuous plasma deposition. Cell adhesion and cell detachment tests indicate that the surface switches between adhesive and nonadhesive behaviors as a function of temperature. The use of a photolithographically fabricated microheater array allows the ppNIPAM transition to occur spatially under the control of individual heaters. This localized change in the surface adhesive behavior is used to direct site-specific cell attachment. Patterned adhesion of two types of cells has been visualized on the array through fluorescent markers. Applications for diagnostic devices, cell-based sensors, tissue engineering, and cell transfection are envisioned.


Assuntos
Materiais Biocompatíveis , Biofilmes , Resinas Acrílicas , Animais , Biofilmes/crescimento & desenvolvimento , Bovinos , Adesão Celular , Divisão Celular , Linhagem Celular , Células Cultivadas , Temperatura Alta , Humanos , Teste de Materiais , Propriedades de Superfície
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