Technology and applications of microassembly using elastomer stamps

The microelectronics industry benefits from reduced costs and improved performance afforded by miniaturization of components. Advanced lithographic methods provide the greatest levels of miniaturization in a high-throughput (parallel), high-precision (deterministic) manner, but the same methods are limited in their ability to integrate multiple, diverse heterogeneous materials in a miniaturized system. In contrast, joining diverse materials together into a system typically happens in packaging, using assembly techniques that usually involve serial operations and impose constraints on the sizes and shapes of the components to be assembled. As a result, the benefits of miniaturization are not fully accessible to systems that require the combined properties of diverse heterogeneous materials. Microassembly technologies make the benefits of miniaturization accessible to heterogeneous materials systems and can provide cost savings, performance improvements, and in some cases totally new capabilities. Microtransfer printing, a microassembly technology developed in the John Rogers research group at UIUC, uses elastomer stamps to deterministically manipulate objects that are too small, numerous, fragile, or otherwise difficult to handle in a practical way. The material properties of the stamps provide robust mechanisms of manipulation, controllably retrieving objects from their native substrates and placing them on non-native substrates. Commercially relevant implementations of microtransfer printing include small solar cells for electricity generation, lasers for data storage, and light emitting diodes and integrated circuits for information display and illumination. Pilot-scale manufacturing that uses microtransfer printing produces commercially available, high-efficiency (? \u3e 33–35%) solar modules and demonstrates some of the benefits of miniaturized, microassembled devices. Microtransfer printing technology and applications. (a) Illustration of transfer printing with an elastomer stamp. (b) Small, transfer printed display driver integrated circuit. (c) 90 m2 concentrator photovoltaic tracker that uses transfer-printed cells

High Fidelity Tape Transfer Printing Based On Chemically Induced Adhesive Strength Modulation

Transfer printing, a two-step process (i.e. picking up and printing) for heterogeneous integration, has been widely exploited for the fabrication of functional electronics system. To ensure a reliable process, strong adhesion for picking up and weak or no adhesion for printing are required. However, it is challenging to meet the requirements of switchable stamp adhesion. Here we introduce a simple, high fidelity process, namely tape transfer printing(TTP), enabled by chemically induced dramatic modulation in tape adhesive strength. We describe the working mechanism of the adhesion modulation that governs this process and demonstrate the method by high fidelity tape transfer printing several types of materials and devices, including Si pellets arrays, photodetector arrays, and electromyography (EMG) sensors, from their preparation substrates to various alien substrates. High fidelity tape transfer printing of components onto curvilinear surfaces is also illustrated

Elastic properties of freely suspended MoS2 nanosheets

We study the elastic deformation of few layers (5 to 25) thick freely suspended MoS2 nanosheets by means of a nanoscopic version of a bending test experiment, carried out with the tip of an atomic force microscope. The Young's modulus of these nanosheets is extremely high (E = 0.33 TPa), comparable to that of graphene oxide, and the deflections are reversible up to tens of nanometers.Comment: 11 pages, 7 figures (including supplementary information

The ‘porin-cytochrome’ model for microbe-to-mineral electron transfer

Many species of bacteria can couple anaerobic growth to the respiratory reduction of insoluble minerals containing Fe(III) or Mn(III/IV). It has been suggested that in Shewanella species electrons cross the outer membrane to extracellular substrates via ‘porin–cytochrome’ electron transport modules. The molecular structure of an outer-membrane extracellular-facing deca-haem terminus for such a module has recently been resolved. It is debated how, once outside the cells, electrons are transferred from outer-membrane cytochromes to insoluble electron sinks. This may occur directly or by assemblies of cytochromes, perhaps functioning as ‘nanowires’, or via electron shuttles. Here we review recent work in this field and explore whether it allows for unification of the electron transport mechanisms supporting extracellular mineral respiration in Shewanella that may extend into other genera of Gram-negative bacteria

A Re-evaluation of Electron-Transfer Mechanisms in Microbial Electrochemistry: Shewanella Releases Iron that Mediates Extracellular Electron Transfer

Exoelectrogenic bacteria can couple their metabolism to extracellular electron acceptors, including macroscopic electrodes, and this has applications in energy production, bioremediation and biosensing. Optimisation of these technologies relies on a detailed molecular understanding of extracellular electron-transfer (EET) mechanisms, and Shewanella oneidensis MR-1 (MR-1) has become a model organism for such fundamental studies. Here, cyclic voltammetry was used to determine the relationship between the surface chemistry of electrodes (modified gold, ITO and carbon electrodes) and the EET mechanism. On ultra-smooth gold electrodes modified with self-assembled monolayers containing carboxylic-acid-terminated thiols, an EET pathway dominates with an oxidative catalytic onset at 0.1V versus SHE. Addition of iron(II)chloride enhances the catalytic current, whereas the siderophore deferoxamine abolishes this signal, leading us to conclude that this pathway proceeds via an iron mediated electron transfer mechanism. The same EET pathway is observed at other electrodes, but the onset potential is dependent on the electrolyte composition and electrode surface chemistry. EET pathways with onset potentials above -0.1V versus SHE have previously been ascribed to direct electron-transfer (DET) mechanisms through the surface exposed decaheme cytochromes (MtrC/OmcA) of MR-1. In light of the results reported here, we propose that the previously identified DET mechanism of MR-1 needs to be re-evaluated

Interview with Juliana Knopp

An interview with Juliana regarding her experiences in a one-room school house.https://scholars.fhsu.edu/ors/1156/thumbnail.jp

Ultrathin compound semiconductor on insulator layers for high performance nanoscale transistors

Over the past several years, the inherent scaling limitations of electron devices have fueled the exploration of high carrier mobility semiconductors as a Si replacement to further enhance the device performance. In particular, compound semiconductors heterogeneously integrated on Si substrates have been actively studied, combining the high mobility of III-V semiconductors and the well-established, low cost processing of Si technology. This integration, however, presents significant challenges. Conventionally, heteroepitaxial growth of complex multilayers on Si has been explored. Besides complexity, high defect densities and junction leakage currents present limitations in the approach. Motivated by this challenge, here we utilize an epitaxial transfer method for the integration of ultrathin layers of single-crystalline InAs on Si/SiO2 substrates. As a parallel to silicon-on-insulator (SOI) technology14,we use the abbreviation "XOI" to represent our compound semiconductor-on-insulator platform. Through experiments and simulation, the electrical properties of InAs XOI transistors are explored, elucidating the critical role of quantum confinement in the transport properties of ultrathin XOI layers. Importantly, a high quality InAs/dielectric interface is obtained by the use of a novel thermally grown interfacial InAsOx layer (~1 nm thick). The fabricated FETs exhibit an impressive peak transconductance of ~1.6 mS/{\mu}m at VDS=0.5V with ON/OFF current ratio of greater than 10,000 and a subthreshold swing of 107-150 mV/decade for a channel length of ~0.5 {\mu}m

Mechanical properties of freely suspended atomically thin dielectric layers of mica

We have studied the elastic deformation of freely suspended atomically thin sheets of muscovite mica, a widely used electrical insulator in its bulk form. Using an atomic force microscope, we carried out bending test experiments to determine the Young's modulus and the initial pre-tension of mica nanosheets with thicknesses ranging from 14 layers down to just one bilayer. We found that their Young's modulus is high (190 GPa), in agreement with the bulk value, which indicates that the exfoliation procedure employed to fabricate these nanolayers does not introduce a noticeable amount of defects. Additionally, ultrathin mica shows low pre-strain and can withstand reversible deformations up to tens of nanometers without breaking. The low pre-tension and high Young's modulus and breaking force found in these ultrathin mica layers demonstrates their prospective use as a complement for graphene in applications requiring flexible insulating materials or as reinforcement in nanocomposites.Comment: 9 pages, 5 figures, selected as cover of Nano Research, Volume 5, Number 8 (2012

Annual energy consumption of reciprocating refrigeration systems for humidity control

Call number: LD2668 .T4 1985 M44Master of Scienc

Graduate teaching assistant (GTA) development in the college classroom

The graduate student population has been traditionally overlooked within higher education. However, within recent decades, much research has been devoted to addressing the multiple facets of the graduate student experience, including that of the graduate teaching assistant (GTA) position. This thesis seeks to explore in depth the experiences of GTAs in the classroom. A summary and critique of the literature that exists surrounding GTAs is provided, including literature related to national graduate student demographics, the history of GTA/GRA positions, salient issues surrounding the GTA position, and models of GTA development. The goal of this thesis is to share results from a quantitative study that analyzes how graduate students self-identify into a three-stage model of GTA development proposed by Nyquist and Sprague (1998). Within this particular study, an online survey questionnaire was developed to support a quantitative research design. An independent chi-square analysis was conducted on the data derived from this questionnaire. The results from this study will be discussed, and further implications of this research for both researchers and practitioners will be explored