Micro/Nano Manufacturing

Micro- and nano-scale manufacturing has been the subject of ever more research and industrial focus over the past 10 years. Traditional lithography-based technology forms the basis of micro-electro-mechanical systems (MEMS) manufacturing, but also precision manufacturing technologies have been developed to cover micro-scale dimensions and accuracies. Furthermore, these fundamentally different technology platforms are currently combined in order to exploit the strengths of both platforms. One example is the use of lithography-based technologies to establish nanostructures that are subsequently transferred to 3D geometries via injection molding. Manufacturing processes at the micro-scale are the key-enabling technologies to bridge the gap between the nano- and the macro-worlds to increase the accuracy of micro/nano-precision production technologies, and to integrate different dimensional scales in mass-manufacturing processes. Accordingly, this Special Issue seeks to showcase research papers, short communications, and review articles that focus on novel methodological developments in micro- and nano-scale manufacturing, i.e., on novel process chains including process optimization, quality assurance approaches and metrology

Roughness, wetting, and optical properties of functional surfaces

Funktionale Oberflächen mit einstellbaren Benetzungseigenschaften sind von enormem Interesse für hochwertige optische Komponenten sowie für Massenprodukte mit ästhetischen Anforderungen (z.B. easy-to-clean Brillengläser, Fenster oder beschlagfreie Visiere und Badezimmerspiegel). Gegenstand der vorliegenden Arbeit war die Entwicklung einer Mess- und Auswertemethodologie zur komplexen Charakterisierung der Struktur-Eigenschaftsbeziehung hydrophober und hydrophiler Funktionsflächen bis hin zur Superhydrophobie und zu Anti-Beschlageffekten. Dazu wurden bestehende Verfahren der Rauheits- und Benetzungsanalyse hinsichtlich ihrer Eignung für Benetzungssysteme mit unterschiedlich stochastisch rauen Oberflächen und intrinsischen Materialeigenschaften ausgewählt, angepasst und um neu eingeführte Methoden erweitert

Roughness, wetting, and optical properties of functional surfaces

Funktionale Oberflächen mit einstellbaren Benetzungseigenschaften sind von enormem Interesse für hochwertige optische Komponenten sowie für Massenprodukte mit ästhetischen Anforderungen (z.B. easy-to-clean Brillengläser, Fenster oder beschlagfreie Visiere und Badezimmerspiegel). Gegenstand der vorliegenden Arbeit war die Entwicklung einer Mess- und Auswertemethodologie zur komplexen Charakterisierung der Struktur-Eigenschaftsbeziehung hydrophober und hydrophiler Funktionsflächen bis hin zur Superhydrophobie und zu Anti-Beschlageffekten. Dazu wurden bestehende Verfahren der Rauheits- und Benetzungsanalyse hinsichtlich ihrer Eignung für Benetzungssysteme mit unterschiedlich stochastisch rauen Oberflächen und intrinsischen Materialeigenschaften ausgewählt, angepasst und um neu eingeführte Methoden erweitert

Droplet motion on miniaturized ratchets

The main objective of this study is to evaluate the feasibility of using miniaturized asymmetric structures to move liquid droplets and understand the driving mechanism. We developed the fabrication process for large area topological ratchets with the period ranging from millimeter down to sub-micrometer using micromachining techniques. Non-wetting superhydrophobic surfaces were successfully fabricated using soft UV or thermal nanoimprint lithography, reactive ion etching by oxygen plasma, and chemical surface modification by fluorinated silane vapor deposition. An accurate and reproducible experimental setup equipped with high speed camera and automatic injection system was established. Image processing tools allowed us to obtain various critical information related droplet motion and behavior along the ratchets surface. Various influences on the motion such as the surface temperature, ratchets dimension, surface wettability, droplet volume, kind of liquid, initial impact speed of droplet, polymer additive, and surface slope were systematically investigated for miniaturized non-wetting asymmetric ratchets. It is observed that the droplet motion on the ratchets is strongly dependent on the ratchets dimensions as well as the surface temperature. Extremely fast water droplet motion was achieved from the sub-micrometer ratchets near the Leidenfrost temperature. Even though the Leidenfrost-miniaturized ratchets system can be considered as an efficient pumping and cooling component, further intensive study to reduce the operating temperature and drive the liquid motion within microchannel is required for the broad range of applications

Ultrathin high-resolution flexographic printing using nanoporous stamps

Since its invention in ancient times, relief printing, commonly called flexography, has been used to mass-produce artifacts ranging from decorative graphics to printed media. Now, higher-resolution flexography is essential to manufacturing low-cost, large-area printed electronics. However, because of contact-mediated liquid instabilities and spreading, the resolution of flexographic printing using elastomeric stamps is limited to tens of micrometers. We introduce engineered nanoporous microstructures, comprising polymer-coated aligned carbon nanotubes (CNTs), as a next-generation stamp material. We design and engineer the highly porous microstructures to be wetted by colloidal inks and to transfer a thin layer to a target substrate upon brief contact. We demonstrate printing of diverse micrometer-scale patterns of a variety of functional nanoparticle inks, including Ag, ZnO, WO[subscript 3], and CdSe/ZnS, onto both rigid and compliant substrates. The printed patterns have highly uniform nanoscale thickness (5 to 50 nm) and match the stamp features with high fidelity (edge roughness, ~0.2 μm). We derive conditions for uniform printing based on nanoscale contact mechanics, characterize printed Ag lines and transparent conductors, and achieve continuous printing at a speed of 0.2 m/s. The latter represents a combination of resolution and throughput that far surpasses industrial printing technologies.Massachusetts Institute of Technology. Department of Mechanical EngineeringNational Science Foundation (U.S.) (Grant CMMI-1463181)United States. Air Force Office of Scientific Research. Young Investigator Program (Grant FA9550-11-1-0089)National Institutes of Health (U.S.) (Grant 1R21HL114011-01A1

Development and characterization of micro/nano structured surfaces for enhanced condensation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (pages 159-168).Micro/nanostructures have long been recognized to have potential for heat transfer enhancement in phase-change processes by achieving extreme wetting properties, which is of great importance in a wide range of applications including thermal management, building environment control, water harvesting, desalination, and industrial power generation. This thesis focuses on the fundamental understanding of water vapor condensation on superhydrophobic surfaces, as well as the demonstration of such surfaces for enhanced condensation heat transfer performance. We first studied droplet-surface interactions during condensation on superhydrophobic surfaces to understand the emergent droplet wetting morphology. We demonstrated the importance of considering local energy barriers to understand the condensed droplet morphologies and showed nucleation-mediated droplet-droplet interactions can overcome these barriers to develop wetting states not predicted by global thermodynamic analysis. To minimize these droplet-droplet interactions and ensure the formation of favorable morphologies for enhanced condensation heat transfer, we show that the structure length scale needs to be minimized while ensuring the local energy barriers satisfy the morphology dependent criteria. This mechanistic understanding offers insight into the role of surface-structure length scale and provides a quantitative basis for designing surfaces optimized for condensation in engineered systems. Using our understanding of emergent droplet wetting morphology, we experimentally and numerically investigated the morphology dependent individual droplet growth rates. By taking advantage of well-controlled functionalized silicon nanopillars, the growth and shedding behavior of both suspended and partially wetting droplets on the same surface during condensation was observed. Environmental scanning electron microscopy was used to demonstrate that initial droplet growth rates of partially wetting droplets were 6 times larger than that of suspended droplets. A droplet growth model was developed to explain the experimental results and showed that partially wetting droplets had 4-6 times higher heat transfer rates than that of suspended droplets. Based on these findings, the overall performance enhancement created by surface nanostructuring was examined in comparison to a flat hydrophobic surface. These nanostructured surfaces had 56% heat flux enhancement for partially wetting droplet morphologies, and 71% heat flux degradation for suspended morphologies in comparison to flat hydrophobic surfaces. This study provides fundamental insights into the previously unidentified role of droplet wetting morphology on growth rate, as well as the need to design nanostructured surfaces with tailored droplet morphologies to achieve enhanced heat and mass transfer during dropwise condensation. To create a unified model for condensation capable of predicting the surface heat transfer for a variety of surface length scales, geometries, and condensation conditions, we incorporated the emergent droplet wetting morphology, individual droplet heat transfer, and size distribution. The model results showed a specific range of characteristic length scales (0.5 - 2 ptm) allowing for the formation of coalescence-induced jumping droplets with a 190% overall surface heat flux enhancement over conventional flat dropwise condensing surfaces. This work provided a unified model for dropwise condensation on micro/nanostructured superhydrophobic surfaces and offered guidelines for the selection of ideal structured surfaces to maximize heat transfer. Using the insights gained from the developed model and optimization, a scalable synthesis technique was developed to produce functionalized oxide nanostructures on copper surfaces capable of sustaining superhydrophobic condensation. Nanostructured copper oxide (CuO) films were formed via chemical oxidation in an alkaline solution resulting in dense arrays of sharp CuO nanostructures with characteristic heights and widths of -1 pm and -300 nm, respectively. Condensation on these surfaces was characterized using optical microscopy and environmental scanning electron microscopy to quantify the distribution of nucleation sites and elucidate the growth behavior of individual droplets with characteristic radii of -1 to 10 pm at supersaturations < 1.5. Comparison of the measured individual droplet growth behavior showed good agreement with our developed heat transfer model. We subsequently studied the macroscopic heat transfer performance during water condensation on superhydrophobic CuO tube surfaces in a custom built experimental chamber. The results experimentally demonstrated for the first time a 25% higher overall heat flux and 30% higher condensation heat transfer coefficient compared to state-of-the-art hydrophobic condensing surfaces at low supersaturations (<1.12). This work not only shows significant condensation heat transfer enhancement, but promises a low cost and scalable approach to increase efficiency for applications such as atmospheric water harvesting and dehumidification. Furthermore, the results offer insights and an avenue to achieve high flux superhydrophobic condensation. In addition to demonstrating enhanced heat transfer performance, we discovered electrostatic charging of jumping droplets on CuO. With the aid of electric fields, the charge on the droplets was quantified, and the mechanism for the charge accumulation was studied. We demonstrated that droplet charging was associated with the formation of the electric double layer at the droplet-surface interface, and subsequent separation during coalescence and jumping. The observation of droplet charge accumulation and electric double layer charge separation provides important insight into jumping droplet physics. Furthermore, this work is a starting point for more advanced approaches for enhancing jumping droplet surface performance by using external electric fields to control droplet jumping. Finally, we demonstrated electric-field-enhanced (EFE) condensation, whereby an external electric field was used to force charged departing droplets away from the surface and limit their return. With the CuO surfaces, we studied EFE condensation heat transfer performance during water condensation. The results experimentally demonstrated a 50% higher overall heat transfer coefficient compared to the no-field jumping surface at low supersaturations (<1.12). This work not only shows significant condensation heat transfer enhancement, it offers insights into new avenues for improving the performance of self-cleaning and anti-icing surfaces, as well as thermal diodes. This thesis presents improved fundamental understanding of wetting and condensation on micro/nanostructures as well as practical implementation of these structures for enhanced condensation heat transfer. The insights gained demonstrate the potential of new surface engineering approaches to improve the performance of various thermal management and energy production applications.by Nenad Miljkovic.Ph.D

Device and strategy for surface energy measurement

In this Ph.D. Thesis, we have developed a new measurement method to measure the contact angle and the surface energy in hydrophobic samples with a device based on confocal technology. This new measurement method incorporates the correction of the effect of the roughness of the surface in the contact angle measurement. The developed measurement method includes the measurement with the confocal device of the Developed Interfacial Area Ratio (Sdr) of the surface under study as well as several parameters of a liquid drop placed on the surface, such as the height and the apparent diameter of the drop. On the other hand, the developed measurement method also includes three mathematical models to calculate the contact angle from a combination of the height (h) and the apparent diameter (L) of the drop measured by the confocal device, and the volume of the dispensed drop (V) indicated by the liquid dispenser. We have verified the validity of each mathematical model by evaluating the introduced error in the calculation of the contact angle. A validation study has also been performed by comparing the calculated contact angles by means of the developed mathematical model that uses exclusively the height and the apparent width of the drop measured with the confocal device with the contact angles measured by a current commercial contact angle meter applying the height-width fitting method. This allowed us to verify the developed measurement method to calculate contact angles on different hydrophobic samples. Furthermore, we have corrected the effect of the surface roughness of a subset of hydrophobic samples on the calculated contact angles according to Wenzel’s model. Our method uses the Sdr parameter measured with the confocal device to calculate the roughness ratio factor required to correct the calculated contact angle with the effect of the roughness. Finally, by doing the measurement with water and diiodomethane, we have evaluated the total surface energy as well as its dispersive and polar components according to OWRK’s method from the previously corrected contact angles, obtaining accurate surface energy values. Therefore, we can conclude that the work reported in this Ph.D. Thesis has been able to demonstrate the validity of the developed measurement methodology for evaluating the contact angle and the surface energy on hydrophobic samples with a confocal device. The advantage of this new technique is that it allows to take into account and correct the effect of the roughness in the evaluation of the surface energy, using a single device.En esta Tesis doctoral hemos desarrollado un nuevo método de medida para medir el ángulo de contacto y la energía superficial en muestras hidrofóbicas con un equipo basado en tecnología confocal. Este nuevo método de medida incorpora la corrección del efecto de la rugosidad de la superficie en la medida del ángulo de contacto. El método de medida desarrollado incluye la medida con el equipo confocal de un parámetro que mide el área real que se está midiendo, por lo que incluye la rugosidad y es conocido como Sdr por sus siglas en inglés, y además diversos parámetros de una gota que es depositada sobre la superficie a medir, tal como son la altura y el diámetro aparente de la gota. Por otro lado, el método de medida desarrollado también incluye tres modelos matemáticos que permiten calcular el ángulo de contacto a partir de la combinación de la altura (h) y el diámetro aparente (L) de la gota medidos con el equipo confocal, y también el volumen de la gota dispensada (V) indicado por el dispensador de líquidos. Hemos verificado la validez de cada uno de los modelos matemáticos mediante la evaluación del error introducido por esto parámetros en el cálculo del ángulo de contacto. También hemos realizado un estudio de validación comparando los ángulos de contacto calculados mediante el modelo matemático que únicamente utiliza h y L medidos con el equipo confocal, con los ángulos de contacto medidos por un medidor de ángulos de contacto comercial que se puede encontrar actualmente en el mercado, aplicando el método de ajuste conocido como altura-anchura (height-width). Esto nos permitió verificar el método de medida desarrollado para calcular ángulos de contacto en diferentes muestras hidrofóbicas. Además, hemos corregido el efecto de la rugosidad de la superficie según el modelo de Wenzel en los ángulos de contacto calculados para un subconjunto de muestras hidrofóbicas. Nuestro método utiliza el parámetro Sdr medido con el equipo confocal para calcular el factor de rugosidad requerido para corregir el efecto de la rugosidad de la superficie en el ángulo de contacto calculado. Finalmente, midiendo con agua y diyodometano, hemos podido evaluar la energía superficial total, así como también sus componentes dispersiva y polar de acuerdo con el método de OWRK a partir de los ángulos de contacto corregidos anteriormente, obteniendo como resultado valores de la energía superficial muy preciosos. Por lo tanto, podemos concluir que con el trabajo presentado en esta Tesis doctoral hemos sido capaces de demostrar la validez del método de medida desarrollado para evaluar el ángulo de contacto y la energía superficial en muestras hidrofóbicas con un equipo confocal. La ventaja de esta nueva técnica es que permite tener en cuenta y corregir el efecto de la rugosidad de una superficie en la evaluación de su energía superficial utilizando un único equipo de medidaPostprint (published version

Efeitos de molhabilidade e propriedades mecânicas de materiais 2D

Orientador: Douglas Soares GalvãoTese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb WataghinResumo: A área de materiais bi-dimensionais é uma área promissora em ciência dos materiais com um diverso conjunto de aplicações em várias áreas distintas. Desde a síntese do grafeno em 2004, o interesse na produção e caracterização de outros materiais monocamada tem crescido. Para compreender como as propriedades desses nanomateriais se comparam com suas verso?es bulk, novos procedimentos experimentais são usualmente necessários. Entretanto, quando experimentos não conseguem analisar estes sistemas a nível atômico e dessa forma compreender suas características principais, simulações atomísticas são úteis. Nesta tese, apresento um conjunto de trabalhos que fazem uso de simulações atomísticas para estudar molhabilidade e propriedades mecânicas de materiais 2D. Primeiramente, no capítulo 1, faço uma revisão da pesquisa em materiais 2D, especificamente molhabilidade e propriedades mecânicas, assim como os conceitos teóricos usados em simulações de dinâmica molecular. No capítulo 2, apresento trabalhos sobre como nanogotas de água interagem com superfícies dos nanomateriais grafeno e grafidino quando a velocidade de impacto estão na faixa de 1 a 15 Â/ps. Fenômenos interessantes ocorrem a medida que a velocidade aumenta, e no caso do grafidino é observada permeação parcial. Este capítulo também discute dois estudos de gotas interagindo nas superfícies de florestas de nanotubos de carbono e camadas de grafeno empilhadas. Mostro que diferentes funcionalizações podem ser usadas para ajustar como a gota penetra nos poros e fendas formadas nestas nanoestruturas, influenciando sua molhabilidade. No capítulo 3, apresento os resultados de uma série de simulações de diferentes combinações de calcogenetos metálicos: um sistema multicamada, uma heteroestrutura vertical e uma heteroestrutura planar. Os resultados das simulações refletem aqueles obtidos nos experimentos, e adicionalmente são capazes de explicar os comportamentos observados para os materiais. O capítulo 4 lista as publicações produzidas como parte do projeto e as conferências onde resultados foram apresentados. Finalmente, no capítulo 5 faço observações finais sobre os sistemas estudadosAbstract: The area of two-dimensional materials is a growing field in materials science with a diverse set of applications in many different areas. Since the synthesis of graphene in 2004, interest in other layered materials¿ production and characterization has grown. To understand how the properties of these nanomaterials compares with their bulk counterparts, novel experimental procedures are often necessary. However, when experiments cannot analyze those systems at the atomic level and thus comprehend their key characteristics, atomistic simulations are useful. In this thesis, I present a set of works that make use of atomistic simulations to study wetting and mechanical properties of 2D materials. First, in chapter 1, I review research on 2D materials, specifically their wetting and mechanical properties, as well as the theoretical concepts used in molecular dynamics simulations. In chapter 2, I present a work on how water nanodroplets interact on the surfaces of the carbon-based nanomaterials graphene and graphdiyne when the velocity of impact is in the range of 1 to 15 A?/ps. Interesting phenomena occur as the velocity increases, and for graphdiyne partial permeation of liquid is observed. This chapter also discusses two studies of the interaction of water droplets on the surfaces of carbon nanotube forests and stacked graphene layers. I found that different functionalizations can be used to tune how the droplet penetrates the pores and slits formed in those nanostructures and influences their wetting behavior. In chapter 3, I present the results of a series of simulations of different combinations of transition metal dichalcogenides: a multilayer system, a vertical heterostructure and an in-plane heterostructure.The simulation results mirrored those obtained in the experiments, and additionally were able to precisely explain the observed behaviors of those materials. Chapter 4 lists the publications produced as part of this project and the venues where results were presented. Finally, in chapter 5 I make concluding remarks about the systems studiedDoutoradoFísicaDoutor em Ciências2013/24500-2 FAPESP; 2016/12341-5FAPES