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Bone is a hierarchical material primarily composed of collagen, water, and mineral that is organized into discrete molecular, nano-, micro-, and macroscale structural components. In contrast to the structural knowledge of the collagen and mineral domains, the nanoscale porosity of bone is poorly understood. In this study, we introduce a well-established pore characterization technique, positron annihilation lifetime spectroscopy (PALS), to probe the nanoscale size and distribution of each component domain by analyzing pore sizes inherent to hydrated bone together with pores generated by successive removal of water and then organic matrix (including collagen and noncollagenous proteins) from samples of cortical bovine femur. Combining the PALS results with simulated pore size distribution (PSD) results from collagen molecule and microfibril structure, we identify pores with diameter of 0.6 nm that suggest porosity within the collagen molecule regardless of the presence of mineral and water. We find that water occupies three larger domain size regions with nominal mean diameters of 1.1, 1.9, and 4.0 nm—spaces that are hypothesized to associate with intercollagen molecular spaces, terminal segments (d-spacing) within collagen microfibrils, and interface spacing between collagen and mineral structure, respectively. Subsequent removal of the organic matrix determines a structural pore size of 5–6 nm for deproteinized bone—suggesting the average spacing between mineral lamella. An independent method to deduce the average mineral spacing from specific surface area (SSA) measurements of the deproteinized sample is presented and compared with the PALS results. Together, the combined PALS and SSA results set a range on the mean mineral lamella thickness of 4–8 nm.

Swarms of micro- and milli-sized robots have the potential to advance biological micro-manipulation, micro- assembly and manufacturing, and provide an ideal platform for studying large swarm behaviors and control. Due to their small size and low cost, tens to hundreds of micro/milli robots can function in parallel to perform a task that otherwise would be too cumbersome or costly for a larger macroscopic robot. Here, we demonstrate a scalable system and modular circuit architecture for controlling and coordinating the motion of $ >$ 10's of magnetic micro/milli robots. By modifying the concepts of safety barrier certificates to our magnetic robot hardware, we achieve minimally invasive, collision-free, 2D position control (x, y) of up to N = 16 robots in a low-cost tabletop ( $\text{288 mm} \times \text{288 mm}$ ) magnetic milli-robot platform with up to 288 degrees of freedom. We show that the introduction of random dithering can achieve a $100\%$ success rate (i.e., no deadlocking), enabling the system to serve as a platform for the study of various swarm-like behaviors or multi-agent robotic coordination.

Metal organic framework (MOF) materials have emerged as the adsorbent materials with the highest H2 storage densities on both a volumetric and gravimetric basis. While measurements of hydrogen storage at the material level (primarily at 77 K) have been published for hundreds of MOFs, estimates of the system-level hydrogen storage capacity are not readily available. In this study, hydrogen storage capacities are estimated at the system-level for MOFs with the highest demonstrated volumetric and gravimetric H2 storage densities. System estimates are based on a single tank cryo-adsorbent system that utilizes a type-1 tank, multi-layer vacuum insulation, liquid N2 cooling channels, in-tank heat exchanger, and a packed MOF powder inside the tank. It is found that with this powder-based system configuration, MOFs with ultra-high gravimetric surface areas and hydrogen adsorption amounts do not necessarily provide correspondingly high volumetric or gravimetric storage capacities at the system-level. Meanwhile, attributes such as powder packing efficiency and system cool-down temperature are shown to have a large impact on the system capacity. These results should shed light on the material properties that must to be optimized, as well as highlight the important design challenges for cryo-adsorbent hydrogen storage systems.

Microbiological environments are a clear application area for microscale robotics, but targeted delivery of biochemical cues to particular cells or tissues remains a significant challenge. This challenge is compounded by the sheer number of cells that compose tissues. Multirobot system development has been limited due to challenges in discrete operation of several robots in a confined space. Here, we demonstrate the use of multiple diamagnetically levitated robots for delivering biochemicals dissolved in liquid in a manner compatible with light microscopy. Specifically, we show loading, transport, and diffusive release of fluorescent molecules in hydrogels with microscale precision, as well as induction of synthetically engineered bacterial cells with signaling molecules. This platform holds potential for impact and utility in fields, such as developmental biology, tissue engineering, and synthetic biology.

The process of activation, an essential step to reveal the porosity of metal–organic frameworks (MOFs), was examined for materials that produce surface areas in accord with prediction as well as for those failing to meet expectations. In situ two-dimensional powder X-ray diffraction, in combination with surface area measurements, was used to classify the structural outcomes of a variety of MOF activations. By modulation of activation solvent as well as linker length and flexibility, a variety of structural outcomes were obtained. In addition to pristine and amorphous products, MOFs that exhibit intermediate activation success were observed. Such MOFs were found to undergo reductions in crystallite size while varying in total amorphous content, which leads to vastly different product surface areas. Models to explain different activation outcomes are presented.

In this article, we demonstrate diamagnetically levitated milli-robots performing 3D heterogeneous micro-assembly of silicon micro-machined parts and polymer microspheres. Diamagnetically levitated milli-robots, in conjunction with controlled magnetic fields from printed circuit boards, can enable very precise, low cost, high density, and an easily scalable approach to massively parallel micro-assembly. By using an eddy-current dampening layer to suppress ambient external forces, we measured an open-loop in-plane equilibrium motion repeatability of 28.6 nm rms over cm’s of travel and a total vertical range of 50–70 μm. To perform micro-assembly, light-weight end effectors and force compatible micro-processes (i.e. micro-grasping and liquid handling) were integrated with the diamagnetic levitated milli-robots. Various tele-operated micro-assembly tasks were demonstrated such as joining polymer micro-spheres, interlocking silicon micro-parts, and printing electrical interconnects. Multiple specialized milli-robots, each taking up only 31 mm2, are used to perform each individual micro-task. In the future, by developing more sophisticated milli-robots and operating many more of these milli-robots in parallel, a dense, automated, rapid milli-robot assembly may be possible.

This paper describes the systematic study of metal–organic framework (MOF) catalysts for the reaction of propylene oxide (PO) with carbon dioxide (CO2) to generate propylene carbonate (PC). These studies began with the evaluation of MIL-101(Cr) as catalyst in a flow reactor. Under the developed flow conditions, MIL-101(Cr) was found to effectively catalyze PO carbonation in the absence of a halide co-catalyst. A systematic study of catalyst performance was then undertaken as a function of MOF synthesis technique, activation conditions, metal center, and node architecture. Ultimately, these investigations led to the identification of MIL-100(Sc) as a new, active, and stable catalyst for PO carbonation.

Exploratory research into the critical steps in metal-organic framework (MOF) activation involving solvent exchange and solvent evacuation are reported. It is discovered that solvent exchange kinetics are extremely fast, and minutes rather days are appropriate for solvent exchange in many MOFs. It is also demonstrated that choice of a very low surface tension solvent is critical in successfully activating challenging MOFs. MOFs that have failed to be activated previously can achieve predicted surface areas provided that lower surface tension solvents, such as n-hexane and perfluoropentane, are applied. The insights herein aid in the efficient activation of MOFs in both laboratory and industrial settings and provide best practices for avoiding structural collapse.

Magnetic micro-robots have a variety of potential applications for biomedical manipulation and microassembly. However, providing independent degrees of freedom to individual magnetic micro-robots can be hindered by the large numbers of local coils or traces required to achieve all degrees of freedom. In this paper, we explore the use of novel control strategies and mechanical constraints to provide additional rotational degrees of freedom to underactuated multipole magnetic robots originally designed with only translational degrees of freedom. By carefully applying repulsive impulse forces and changing the center of rotation, we show that a dynamic in-plane rotation of 3500 deg/s can be achieved. By using other geometries of mechanical constraints such as a wheel on axle, we can also demonstrate 1800 deg/s out-of-plane rotation.

Metal organic frameworks (MOFs) are promising materials for the storage of hydrogen fuel due to their high surface areas, tunable properties, and reversible gas adsorption. Although several MOFs are known to exhibit high hydrogen densities on a gravimetric basis, realizing high volumetric capacities – a critical attribute for maximizing the driving range of fuel cell vehicles – remains a challenge. Here, MOFs that achieve high gravimetric and volumetric H2 densities simultaneously are identified computationally, and demonstrated experimentally. The hydrogen capacities of 5309 MOFs drawn from databases of known compounds were predicted using empirical (Chahine rule) correlations and direct atomistic simulations. A critical assessment of correlations between these methods, and with experimental data, identified pseudo-Feynman–Hibbs-based grand canonical Monte Carlo calculations as the most accurate predictive method. Based on these predictions, promising MOF candidates were synthesized and evaluated with respect to their usable H2 capacities. Several MOFs predicted to exhibit high capacities displayed low surface areas upon activation, highlighting the need to understand the factors that control stability. Consistent with the computational predictions, IRMOF-20 was experimentally demonstrated to exhibit an uncommon combination of high usable volumetric and gravimetric capacities. Importantly, the measured capacities exceed those of the benchmark compound MOF-5, the record-holder for combined volumetric/gravimetric performance. Our study illustrates the value of computational screening in pinpointing materials that optimize overall storage performance.

The use of microporous coordination polymers with coordinatively unsaturated metal centers in the removal of dimethyl ether from chloromethane via flow was explored as an alternative to current industrial methods. Three different materials examined, Co/DOBDC, MIL-100(Fe), and HKUST-1, were able to efficiently purify chloromethane through selective adsorption of dimethyl ether. The recyclability of Co/DOBDC after separation was also examined, and little loss of capacity for dimethyl ether over the course of multiple regeneration cycles was observed.

The cationic rhodium complexes (dppe)Rh(COD)BF4 and (MeCN)2Rh(COD)BF4 have been supported in metal–organic frameworks bearing anionic nodes (ZJU-28) and anionic linkers (MIL-101-SO3) via ion exchange. These MOF-supported Rh species serve as recyclable catalysts for the hydrogenation of both the terminal alkene substrate 1-octene and the internal alkene substrate 2,3-dimethylbutene. The nature of the MOF support impacts various aspects of catalysis, including: (i) the rate of 1-octene hydrogenation, (ii) the activity and recyclability of the catalyst in 2,3-dimethylbutene hydrogenation, and (iii) the size selectivity of hydrogenation with alkene substrates appended to calixarenes.

In this article, we study the use of ferrofluids for levitating magnetic micro/milli-robots. With the addition of a ferrofluid, the robots improved their weight-carrying ability (xI2, >12 grams) and precision (x2 ~5 um) without any associated increase in actuation power of the robot relative to sliding versions without the ferrofluid. To better understand the longterm stability of a ferrofluid on the micro/milli-robot, we perform motion cycle testing on two different surfaces (graphite and Teflon), ultimately achieving a motion repeatability and pose angular stability of 5 um and 0.05 °, close to the limits of our measurement setup. The underdamped motion of the ferrofluid robot showed a natural resonance of ~58–60 Hz. Through careful control of the evaporation of the ferrofluid, we show long-term stability of a ferrofluid micro/milli-robot over the course of >11 hours. While the performance of the robot does change due to evaporation of the particular ferrofluid used, we also show that robots can easily be replenished with new ferrofluid after mechanically cleaning away the remaining ferrofluid. Overall, the application of ferrofluids toward magnetically actuated micro/milli-robots can enable low-cost and high-precision motion for future high-precision micro-manipulation or positioning tasks.

The development of high-capacity methane adsorbents would accelerate the adoption of natural gas as a vehicular fuel, thereby lowering CO2 emissions from the combustion of gasoline. In this regard metal–organic frameworks (MOFs) have emerged as promising methane storage materials due to their high capacities and tunable properties. Within this class, HKUST-1 ([Cu3(BTC)2]n, BTC = 1,3,5-benzenetricarboxylate) is an important benchmark, as it exhibits methane densities that are among the highest reported. Furthermore, uptake in HKUST-1 can potentially be tuned by altering the methane–MOF interaction through metal substitution on coordinatively unsaturated sites (CUS). Predicting the impact of metal substitution remains a challenge, however, because general interatomic potentials commonly used in calculating uptake do not properly describe interactions involving CUS. Here, a new interatomic potential that explicitly accounts for these interactions is derived from quantum-mechanical calculations. The potential...

A strategy that allows the tuning of pore size in microporous coordination polymers (MCPs) through modification of their organic linkers is presented. When large substituents are introduced onto the linker, these pendent groups partially occupy the pores, thus reducing pore size while serving as additional adsorption sites for gases. The approach takes advantage of the fact that, for methane storage materials, small pores (0.4-0.8 nm in diameter) are more desirable than large pores since small pores promote optimal volumetric capacity. This method was demonstrated with IRMOF-8, a MCP constructed from Zn4O metal clusters and 2,6-naphthalenedicarboxylate (NDC) linkers. The NDC was functionalized through the addition of substituents including tert-butylethynyl or phenylethynyl groups. High pressure methane uptake demonstrates that the IRMOF-8 derivatives have significantly better performance than the unfunctionalized material in terms of both excess volumetric uptake and deliverable capacity. Moreover, IRMOF-8 derivatives also give rise to stronger interactions with methane molecules as shown by higher heat of adsorption values.

This paper describes the systematic study of metal-organic framework (MOF) catalysts for the reaction of propylene oxide (PO) with carbon dioxide (CO

Examination of the microstructure of metal–organic frameworks (MOFs) after postsynthetic exchange (PSE) reveals that the exchanged ligand is concentrated at the edges of the crystal and decreases in concentration with crystal depth, resulting in a core–shell arrangement. Diffusion studies of the carboxylate ligand into MOF-5 indicate that diffusion is limiting to the exchange process and may ultimately be responsible for the observed core–shell structure. Examination of PSE in UMCM-8 and single crystals of UiO-66 shows a similar trend, illustrating the applicability of PSE as a method for the creation of core–shell MOFs.

In this article, we demonstrate the application of diamagnetically levitated milli-robots for the 2D micro-assembly of 10-μm polymer microspheres and other silicon microfabricated parts. By using an optical microscope for feedback (imaged at 27 Hz), we are able to demonstrate long-term open-loop stability (up to 78 hr) and sub-micron stability of the levitated micro-robots. Furthermore, due to the low hysteresis and high compliance in the magnetic drive of the milli-robots, we are able to directly use the milli-robots in conjunction with machine vision as a force sensor. Soft polymer-based end effectors are used for the micromanipulation of parts and show modest reliability of pick (>70%) and high reliability of place (>99%) that is insensitive to the pick surface material. Finally, we implement autonomous micro-assembly from randomly deposited microspheres into ordered arrays.

Multi-agent robotic systems on small scales typically use, or envision using, small mobile robots. This paper takes a broad-brush look at a relatively recent development in milli and micro robots, Diamagnetic Micro Manipulation (DM3) systems, in a multi-agent context. We report various multi-agent operations, such as multi-agent part manipulation, robots-acting-on-other-robots for enhanced functionality, and robot-supplied local feed, to assess the state of the art of this new type of system. In addition, we explore and analyze the multi-agent implications of known DM3 properties and earlier single-agent results to motivate future research in this area. As reported here, some of these multi-agent implications include mobile high-precision sensor transducers, near-field communications channels using robots as both transmitters and receivers, and novel swarm architectures.

Air drying is a widespread and critical industrial process. Removal of water from air is commonly accomplished by passage through a desiccant such as alumina; modest water capacity and energy intensive regeneration are limitations of currently used sorbents. Microporous coordination polymers (MCPs) are demonstrated here to be efficient desiccants for the dehumidification of air, and a comparison of their capacity, regenerability, and efficiency with commercial activated alumina is conducted. Complete regeneration using dry air with mild heating is achieved. The attainment of high capacity for the adsorption of water coupled to facile regeneration indicates that gas dehumidification may be an important application for MCPs.

Because of their high surface areas, crystallinity, and tunable properties, metal–organic frameworks (MOFs) have attracted intense interest as next-generation materials for gas capture and storage. While much effort has been devoted to the discovery of new MOFs, a vast catalog of existing MOFs resides within the Cambridge Structural Database (CSD), many of whose gas uptake properties have not been assessed. Here we employ data mining and automated structure analysis to identify, “cleanup,” and rapidly predict the hydrogen storage properties of these compounds. Approximately 20 000 candidate compounds were generated from the CSD using an algorithm that removes solvent/guest molecules. These compounds were then characterized with respect to their surface area and porosity. Employing the empirical relationship between excess H2 uptake and surface area, we predict the theoretical total hydrogen storage capacity for the subset of ∼4000 compounds exhibiting nontrivial internal porosity. Our screening identifies...

Microporous coordination polymers (MCPs) have emerged as strong contenders for adsorption-based fuel storage and delivery in large part because of their high specific surface areas. The strategy of increasing surface area by increasing organic linker length has shown only sporadic success; as demonstrated by many members of the iconic Zn4O-based IRMOF series, for example, accessible porosity is often limited by interpenetration or pore collapse upon guest removal. In this work, we focus on Zn4O(ndc)3 (IRMOF-8, ndc = 2,6-naphthalene dicarboxylate), which exhibits typical surface areas of only 1000-2000 m(2)/g even though a surface area of more than 4000 m(2)/g is expected from geometric analysis of the originally reported crystal structure. We recently showed that a high surface area could be produced with zinc and ndc by room-temperature synthesis followed by activation with flowing supercritical CO2. In this work, we investigate in detail the porosity of both the low- and high-surface-area materials. Positron annihilation lifetime spectroscopy (PALS) is used to show that the low-surface-area material suffers from near-complete interpenetration, explaining why traditional synthetic routes have failed to yield materials with the expected porosity. Furthermore, the high-pressure hydrogen and methane sorption properties of noninterpenetrated Zn4O(ndc)3 are examined, and PALS is used to show that pore filling is not operative during room-temperature CH4 sorption even at pressures approaching 100 bar. These results provide insight into how gas adsorbs in high-surface-area materials at high pressure and reinforce previous contentions that increasing surface area alone is not sufficient for the simultaneous optimization of deliverable gravimetric and volumetric gas uptake in MCPs.

Today, trends in manufacturing automation favor high levels of adaptability and flexibility for rapid product change, customization, and new process integration. This paper looks at a new technology, diamagnetic micro manipulation (DM3), for taking adaptability of automation to a higher level. Experiments reported here show a path to automation systems that can self-assemble their own robotic manipulators, fabricate tools-on-demand to execute new processes, optimize existing processes, and/or replace or repair tools. These printed circuit board (PCB) systems can control very large numbers of milli-scale robots. Hence, as described in this paper and in contrast to conventional robotic systems, only a small percentage of DM3 system resources, approximately 5–10% of system area and robot numbers, are needed to achieve on-board self-assembly and tool-on-demand functions. This paper describes the key step of self-assembly of self-levitating magnet arrays using 1 mm × 1 mm × 0.4 mm magnets, with self-assembly times of less than 10 s. We also report experiments showing how milli-robots can build simple end effector tools (a straight probe tip, a forked tip, and a hook tip) on other milli-robots for on-board, tool-on-demand functions.

This paper reports early results of optimal control using diamagnetically levitated robot (DLR) systems. Levitated robots, typically 1–4 mm in size, are driven locally by printed circuit boards (PCBs) with zero friction and near-zero hysteresis. As previously reported [1, 2], these properties give the levitated system excellent repeatability at the micron and submicron levels for both positioning and trajectories. Highly repeatable systems are generally good candidates for optimal control because variability in identifying and exploiting optimized control parameters are minimized. In the data reported here, levitated milli robots are characterized, and we present experiments showing a 5× reduction in oscillations using a debouncing routine that is manually optimized in time. Manual optimization is effective in some cases, but due to the multi-degree-of-freedom (DOF) aspects of levitated robots, a more robust self-tuning method is desirable. Toward this goal, we describe experiments using automatic optimization of robot motion using a computerized search-and-test routine that varies PCB trace currents and selects optimal currents based on automatic measurement of motion error. The automatic optimization using this method has shown settling times to micron and submicron levels that are 20–40 times faster than simple bang-bang control of equilibrium currents. In one test reported here, 150-µm moves were demonstrated at 90-nm rms error with 15-ms move times.

Using diamagnetic micro-manipulation, micro-robots (∼10 mm in size) with specialized end-effectors are able to grasp and manipulate small light weight (∼mg) carbon fiber elements to construct macroscopic cubic carbon fiber trusses (∼1000 parts and 300 mm long) that can achieve mechanical crush performances surpassing those of commercially available aluminum honey combs. Employing low cost micro-robots and end-effectors allows the implementation of both parallelization and new functionality without the need for expensive fixed tooling. We demonstrate this concept by modifying the micro-robot end effectors to build carbon fiber octet trusses and carbon fiber trusses with integrated electronics.

Stretchable electronics can go beyond what might commonly be considered “electronics.” They can exploit their inherent elasticity to enable new types of transducers that convert between electrical energy and mechanical energy. Dielectric elastomer actuators are “stretchable capacitors” that can offer muscle-like strain and force response to an applied voltage. As generators, dielectric elastomers offer the promise of energy harvesting with few moving parts. Power can be produced simply by stretching and contracting a relatively low-cost rubbery material. This simplicity, combined with demonstrated high energy density and high efficiency, suggests that dielectric elastomers are promising for a wide range of energy-harvesting applications. Indeed, dielectric elastomers have been demonstrated to harvest energy from human walking, ocean waves, flowing water, blowing wind, pushing buttons, and heat engines. While the technology is promising and advances are being made, there are challenges that must be addressed if dielectric elastomers are to be a successful and economically viable energy-harvesting technology. These challenges include developing materials and packaging that sustain a long lifetime over a range of environmental conditions, designing the devices that stretch the elastomer material uniformly, and system issues such as practical and efficient energy-harvesting circuits.

The application of a core-shell architecture allows the formation of a polymer-coated metal-organic framework (MOF) maintaining high surface area (2289-2857 m(2) g(-1)). The growth of a MOF shell from a MOF core was used to spatially localize initiators by post-synthetic modification. The confinement of initiators ensures that polymerization is restricted to the outer shell of the MOF.

Random copolymerization is a core strategy of the polymer industry, enabling broad tuning of materials properties through mixing monomers with similar reactivities. In coordination polymers, analogous results have recently been achieved using combinations of isomorphic linkers copolymerized by appropriate metals; in general, the properties of the resultant coordination copolymers can be described as a linear combination of the properties of the constituent building blocks. Here we demonstrate that this need not be the case: coordination copolymerization is a powerful strategy for directing phase formation. For example, reaction of 1,4-benzenedicarboxylic acid with Zn2+ typically affords phase-impure material in N,N-dimethylformamide whereas using an amino functionalized linker leads to pure high surface area material with the structure of MOF-5. However, mixed-linker copolymers derived from a combination of both linkers display surface areas comparable to that of MOF-5 synthesized in N,N-diethylformamide,...

The CO(2)-capture performance of microporous coordination polymers of the M/DOBDC series (where M = Zn, Ni, Co, and Mg; DOBDC = 2,5-dioxidobenzene-1,4-dicarboxylate) was evaluated under flow-through conditions with dry surrogate flue gas (5/1 N(2)/CO(2)). The CO(2) capacities were found to track with static CO(2) sorption capacities at room temperature, with Mg/DOBDC demonstrating an exceptional capacity for CO(2) (23.6 wt %). The effect of humidity on the performance of Mg/DOBDC was investigated by collecting N(2)/CO(2)/H(2)O breakthrough curves at relative humidities (RHs) in the feed of 9, 36, and 70%. After exposure at 70% RH and subsequent thermal regeneration, only about 16% of the initial CO(2) capacity of Mg/DOBDC was recovered. However, in the case of Ni/DOBDC and Co/DOBDC, approximately 60 and 85%, respectively, of the initial capacities were recovered after the same treatment. These data indicate that although Mg/DOBDC has the highest capacity for CO(2), under the conditions used in this study, Co/DOBDC may be a more desirable material for deployment in CO(2) capture systems because of the added costs associated with flue gas dehumidification.

Isolated successes of coordination copolymerization for the production of microporous coordination polymers (MCPs) have been reported recently; the logic for this synthetic approach has not been established nor have the key features of the synthetic conditions needed to generalize the method. Here, we establish guidelines for application of the copolymerization technique by exploring coordination modes and report, in addition to details on two previous coordination copolymers with exceptional properties, three new MCPs: UMCM-3 (Zn(4)O(2,5-thiophenedicaboxylate)(1.2)(1,3,5-tris(4-carboxyphenyl)benzene)(1.2)), UMCM-4 (Zn(4)O(1,4-benzenedicarboxylate)((3)/(2))(4,4',4''-tricarboxytriphenylamine)), and UMCM-5 (Zn(4)O(1,4-naphthalenedicarboxylate)(1,3,5-tris(4-carboxyphenyl)benzene)((4)/(3))). The MCPs prepared by the copolymerization technique demonstrate Brunauer-Emmett-Teller (BET) surface areas between 3500-5200 m(2)/g and high pore volumes (1.64-2.37 cm(3)/g). In addition, the alignment of poly(3-hexylthiophene) within mesoporous channels of UMCM-1 is reported as a demonstration of the unique properties of these hosts.

Five non-interpenetrated microporous coordination polymers (MCPs) are derived by vertex desymmetrization using linkers with symmetry inequivalent coordinating groups, and these MCPs include properties such as rare metal clusters, new network topologies, and supramolecular isomerism. Gas sorption in polymorphic frameworks, UMCM-152 and UMCM-153 (based upon a copper-coordinated tetracarboxylated triphenylbenzene linker), reveals nearly identical properties with BET surface areas in the range of 3300-3500 m(2)/g and excess hydrogen uptake of 5.7 and 5.8 wt % at 77 K. In contrast, adsorption of organosulfur compounds dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) shows remarkably different capacities, providing direct evidence that liquid-phase adsorption is not solely dependent on surface area or linker/metal cluster identity. Structural features present in MCPs derived from these reduced symmetry linkers include the presence of more than one type of Cu-paddlewheel in a structure derived from a terphenyl tricarboxylate (UMCM-151) and a three-bladed zinc paddlewheel metal cluster in an MCP derived from a pentacarboxylated triphenylbenzene linker (UMCM-154).

[*] Prof. A. J. Matzger, Dr. A. G. Wong-Foy, J. K. Schnobrich Department of Chemistry, University of Michigan 930N. University St., Ann Arbor, MI 48109 (USA) E-mail: matzger@umich.edu Prof. D. W. Gidley, Dr. M. Liu, Dr. W. E. Frieze Department of Physics, University of Michigan 450 Church St. Ann Arbor, MI 48109 (USA) E-mail: gidley@umich.edu Prof. R. S. Vallery Department of Physics, Grand Valley State University 151 Padnos Hall, Allendale, MI 49401 (USA)

We present experimental investigations of the dynamical properties of semiconductor optical amplifiers (SOAs) and their impacts in all-optical signal processing using SOAs. We introduce ultrafast optical signal characterization techniques to fully characterize the gain and phase dynamics of SOAs. We elucidate a consequence of the slow carrier recovery as pattern-dependent phase fluctuation in wavelength conversion of on-off -keyed signals. We also analyze the conversion of the phase fluctuation into amplitude fluctuation limiting the performance of all-optical xor operation. Finally, the performance of all-optical wavelength conversion of differential phase-shift-keyed signals is presented with emphasis on regeneration of the phase information.

Porous crystals constructed from the assembly of organic linking units with metal ions or metal clusters are proving to be an exciting class of materials with unprecedented properties and high potential for use in applications such as catalysis, gas storage, and separations. The underlying structure obtained from a given secondary building unit (SBU) with a multitopic ligand can be analyzed, at least with hindsight, as belonging to various nets. In some cases this approach has led to well-defined series with preserved topologies whose members vary in metrics or functionalities. At the same time, it is clear that even a single linker with a given metal under the same reaction conditions can give rise to considerable structural diversity, as is illustrated by our recent application of polymer-induced heteronucleation to the discovery of three new phases based on the simple terephthalic acid linker/zinc nitrate system. Perhaps one lesson to be learned is that there is currently no single structure-predicting design scheme but rather sets of empirically derived default behaviors that can often be used to rationalize the outcome of an experiment. In the case of employing two different linkers possessing the same coordinating functionality, experimental data are lacking, and there is no basis for answering even the most basic question of phase composition. In broad terms we can expect two different behaviors in a crystalline mixed-linker coordination polymer. The default behavior for two components combined and allowed to crystallize is segregation; this behavior forms the basis of purification by crystallization. By contrast, the default behavior when monomers of similar reactivity are combined is random copolymerization. Therefore, it is interesting to contemplate whether in a porous crystal in which strong bonds reversibly assemble the framework, copolymerization patterns will dominate or if self-sorting crystallization will prevail. The former would represent an expeditious route to discover new porous solids. To investigate this question we undertook the synthesis of porous crystals based on two organic linkers of different topologies, namely, terephthalic acid (H2BDC) and 1,3,5-tris(4-carboxyphenyl)benzene (H3BTB). H2BDC is the organic linker that, when combined with Zn, yields MOF-5, a stable cubic structure that is the best studied of the metal–organic frameworks. Using H3BTB under essentially identical synthetic conditions affords MOF177. This trigonal framework exhibits exceptional porosity and surface area and boasts the highest reported uptake of hydrogen gas in a physisorptive material. Combining H2BDC with H3BTB, two ligands possessing aryl carboxylic acid coordinating groups, in the presence of zinc nitrate incorporates both components into a completely new type of structure that can be obtained to the exclusion of materials derived from either pure linker. Figure 1 illustrates the porous crystals produced by heating various ratios of H2BDC and H3BTB in the presence of excess Zn(NO3)2·4H2O at 85 8C for 2 days. Three distinct crystalline phases are observed as the mole fraction of H3BTB is increased. At low H3BTB concentrations, only MOF-5 crystals are formed; however, at a mole ratio of 4:1 (H2BDC:H3BTB), a new needle-shaped phase is formed along with MOF-5. Increasing the H3BTB concentration leads to exclusive formation of the needleshaped phase, which according to powder X-ray diffraction (XRD) data is different from MOF-5 and MOF-177 (Figure S4 in the Supporting Information). A further increase of the H3BTB concentration results in MOF-177 forming as well. Finally, at H2BDC:H3BTB mole ratios greater than or equal to 2:3, MOF-177 is the first product to crystallize out of solution. A single-crystal X-ray diffraction study of the needleshaped crystals revealed a structure with one-dimensional hexagonal channels. The product crystallizes in the space group P63m and dramatically differs from the structures derived from the pure linkers. The framework of the material consists of Zn4O clusters linked together by two BDC and four BTB linkers arranged in an octahedral geometry (Figure 2a). Two BDC linkers are adjacent, leaving the other four positions occupied by BTB linkers, and these octahedra assemble into a structure containing both micropores and mesopores. This product is denoted as UMCM-1 (University of Michigan Crystalline Material-1). The micropores are found in cage-like structures constructed from six BDC linkers, five BTB linkers, and nine Zn4O clusters, and with an internal dimension of approximately 1.4 nm@1.7 nm (subtracting the van der Waals radii of the atoms, Figure 2b). Six such microporous cages assemble together in an edgesharing fashion to define the diameter of the mesopore, a 1D hexagonal channel 2.7 nm@ 3.2 nm (measured between pore walls, Figure 2c). When van der Waals radii of the atoms are taken into account, the mesopore is 2.4 nm@ 2.9 nm. Comparison of the bulk powder XRD pattern to that simulated [*] Dr. K. Koh, Dr. A. G. Wong-Foy, Prof. A. J. Matzger Department of Chemistry and the Macromolecular Science and Engineering Program University of Michigan 930 North University Ave, Ann Arbor, MI 48109-1055 (USA) Fax: (+1)734-6715-8853 E-mail: matzger@umich.edu

The design, synthesis, and properties of the new microporous coordination polymer UMCM-310 are described. The unique electronic character of the perylene-based linker enables selective interaction with electron-poor aromatics leading to efficient separation of nitroaromatics. UMCM-310 possesses high surface area and large pore size and thus permits the separation of large organic molecules based on adsorption rather than size exclusion.

We report on a novel design for a colorless wavelength adding-and-dropping module. The module comprises a cyclic demultiplexer and an optical cross connect and greatly reduces the insertion loss of this functionality, in comparison to other approaches. Implementation of ultralow-power-consumption thermo-optic switches simplifies the module thermal control.

The adsorption behavior of CH4 and N2 (298 K, 30 bar) in a series of isoreticular metal−organic frameworks (IRMOFs) was investigated by Raman spectroscopy. For CH4, the ν1 vibrational mode shifted to lower frequency by 7.6, 8.4, 11.0, 10.3, and 10.1 cm-1 from 2917 cm-1 when adsorbed to IRMOF-1, -6, -8, -11, and -18, respectively. Along this same series, the adsorbed N2 stretch exhibited smaller shifts of 2.7, 3.1, 4.2, 4.1, and 3.7 cm-1. These shifts arise because of interactions within the framework pores, and not with the outer crystal surface. In all cases, Raman spectra at pressures up to 30 bar showed that saturation of the sorption sites does not occur. The observed shifts of the vibrational modes for each gas indicate different chemical environments within different IRMOFs, pointing to the important role the linkers play in the adsorption of gases.

A coordination terpolymerization strategy is introduced to alter the connectivity within layers of a pillared-layer coordination polymer. Assembling two different dicarboxylate linkers around a metal cluster in the layer suppresses interpenetration while enabling formation of a rectangular 2D grid structure.

A 2D zirconium-based microporous coordination polymer derived from the tritopic linker 1,3,5-(4-carboxylphenyl)benzene, UMCM-309a, has been synthesized. This noninterpenetrated material possesses a Zr6(μ3-O)4(μ3-OH)4(RCO2)6(OH)6(H2O)6 cluster with six hexagonal-planar-coordinated linkers. UMCM-309a is stable in an aqueous HCl solution for over 4 months. The use of different monocarboxylates as modulators leads to similar 2D structures with different layer spacings; moreover, removal of the modulator yields the parent UMCM-309a.

A novel tunable dispersion compensator (TDC) with /spl plusmn/500-ps/nm tuning range and bandwidth support for 40-Gb/s signals is described. The TDC is constructed from a waveguide grating router (WGR) that provides very high spatial dispersion and a deformable cylindrical mirror for applying quadratic spatial phase across the dispersed wavefront. The WGR's 100-GHz free-spectral range (FSR) allows the device to simultaneously apply the same dispersion to all wavelength-division multiplexing (WDM) channels.

A novel device that demodulates both quadratures of the optical differential quadrature phase-shift keying (DQPSK) format in a single interferometer by using a 4 /spl times/ 4 star coupler was demonstrated. Simultaneous measurements of both DQPSK quadratures at 42.7 Gb/s are also presented.

A compact and simple silica-waveguide 10-Gb/s tunable optical dispersion compensator (ODC) that works with uncontrolled wavelength transmitters by tracking the signal wavelength is demonstrated. Transmissions at 10.7 Gb/s over 5100 ps/nm of dispersion with a duobinary signal using a single pass of the ODC and 3825 ps/nm of dispersion with an unchirped non-return-to-zero signal using a double pass of the ODC are shown.

An endless, reset-free polarization controller implemented with planar lightwave circuits using phase shifters for tuning is proposed and demonstrated. By avoiding the need for tunable polarization mode converters, simple fabrication processes and a large range of material systems can be used, since neither the electrooptic effect nor a rotatable birefringence axis are necessary for device operation. The proof of concept is demonstrated by implementing the equivalent of a rotating waveplate using Ge-doped silica-on-silicon waveguides and thermooptic phase shifters. The polarization controller is shown to have excellent tolerance to fabrication variations. Fast thermooptic control (on the order of 10 kHz) is achieved using high-index-contrast (4%) waveguides.

We describe a wide range of reconfigurable optical add-drop multiplexer architecture designs that may be implemented in standard silica-on-silicon planar lightwave circuits. This proven, reliable technology offers high performance and cost-effective solutions for reducing complex service provisioning in reconfigurable optical networks. Recent advances enable very flexible wavelength routing devices for mesh- and ring-based networks to be implemented on a common subsystem integration platform. We show excellent system performance at 10 Gb/s.

This paper describes the demonstration of an improved eight-channel coarse wavelength-division multiplexer. The fully packaged channel losses range from 2.3 to 3.9 dB, the 1-dB bandwidth is 16.3 nm, and the crosstalk is

We integrated a wavelength-selective cross-connect, de-interleaver, interleaver, power combiner, and variable attenuators on one silica waveguide chip and a band demultiplexer, band multiplexer, and optical monitor on another. These two chips are used to create an eight-channel add-drop node that is expandable up to 80 channels with minimal traffic interruption by adding more of these chips.