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Optical systems typically use galvanometers (galvos) and scanners. Galvos move, quasi-statically, from one static position to another. Scanners move in an oscillatory fashion, typically at the device resonant frequency. MEMS devices, which have many advantages and are often used in optical systems, are typically high Q devices. Moving from one position to another for a galvo or one amplitude to another for scanners, can take many periods to settle following the ring down. During these transitions, the optical system is inactive. Here, we show how precisely timed pulses can be used (in an open loop manner) to begin or end scanner motion without ring up/ring down time. The size of pulse required is found to depend on the Q of the device, and relationships are derived. The pulse can also be separated into multiple pulse spaced one period apart if pulses of the necessary size are not possible due to constraints of the physical device. For finite Q scanners, the amplitude decreases after the initial pulse due to damping. This can be eliminated by applying an excitation at the frequency of the scanner. The necessary amplitude for this excitation is derived. Finally, by combining this open loop control algorithm with an open loop control algorithm for galvo motion the device can seamlessly move between scanner and galvo functioning. These control algorithms are demonstrated using computer simulations, analytical models and a commercially available MEMS mirror (Mirrorcle Technologies, A8L2.2). [2020-0238]

Plastic recycling is limited due to the immiscibility of most polymers and the weakness of the corresponding interface. Here, a method to synthesize block nanotubes in a scalable manner is describe...

In this article, we present a nanoelectromechanical system (NEMS) designed to detect changes in the Casimir energy. The Casimir effect is a result of the appearance of quantum fluctuations in an electromagnetic vacuum. Previous experiments have used nano- or microscale parallel plate capacitors to detect the Casimir force by measuring the small attractive force these fluctuations exert between the two surfaces. In this new set of experiments, we aim to directly detect the shifts in the Casimir energy in a vacuum due to the presence of the metallic parallel plates, one of which is a superconductor. A change in the Casimir energy of this configuration is predicted to shift the superconducting transition temperature (Tc) because of the interaction between it and the superconducting condensation energy. In our experiment, we take a superconducting film, carefully measure its transition temperature, bring a conducting plate close to the film, create a Casimir cavity, and then measure the transition temperature again. The expected shifts are smaller than the normal shifts one sees in cycling superconducting films to cryogenic temperatures, so using a NEMS resonator in situ is the only practical way to obtain accurate, reproducible data. Using a thin Pb film and opposing Au surface, we observe no shift in Tc >12 µK down to a minimum spacing of ~70 nm at zero applied magnetic field., Measuring quantum fluctuations with NEMS A nano-electromechanical system (NEMS) allows for the direct measurement of Casimir energy. The Casimir effect relates to the fluctuation of electromagnetic waves between two plates in a vacuum. Previous studies used plate capacitors that function by detecting small Casimir forces exerted on the plates by the electromagnetic fluctuations. Now, a team from the United States and Switzerland led by David Bishop, of Boston University, Massachusetts, and Vladimir Aksyuk of the National institute of Standards and Technology, have developed a technique in which a thin lead superconductor film is placed parallel to a gold surface. This allows direct measurements as the plate and film are brought close together and the actual Casimir energy in the cavity changes. The team measured the Casimir energy via its effect on the superconductor’s “transition temperature”, finding changes no more than 12 micro-Kelvin. The team says their paper “opens a novel experimental window” that future studies should exploit.

Inductive circuits and devices are ubiquitous and important design elements in many applications, such as magnetic drives, galvanometers, magnetic scanners, applying direct current (DC) magnetic fields to systems, radio frequency coils in nuclear magnetic resonance (NMR) systems, and a vast array of other applications. They are widely used to generate both DC and alternating current (AC) magnetic fields. Many of these applications require a rapid step and settling time, turning the DC or AC magnetic field on and off quickly. The inductive response normally makes this a challenging thing to do. In this article, we discuss open loop control algorithms for achieving rapid step and settling times in four general categories of applications: DC and AC systems where the system is either under- or over-damped. Each of these four categories requires a different algorithm, which we describe here. We show the operation of these drive methods using Simulink and Simscape modeling tools, analytical solutions to the underlying differential equations, and experimental results using an inductive magnetic coil and a Hall sensor. Finally, we demonstrate the application of these techniques to significantly reduce ringing in a standard NMR circuit. We intend this article to be practical, with useful, easy-to-apply algorithms and helpful tuning tricks.

Furanics are produced in high abundance from the decomposition of biomass. The thermal and chemical instability of these species leads to the formation of humins upon condensation. The ring rearrangement of furfural to form 2-cyclopentenone and cyclopentanone is known to occur in the condensed aqueous phase, but this requires operation in condensed acidic media where humin formation readily occurs. High hydrogen pressures are typically used to offset rapid polymerization reactions, limiting the yields of stable unsaturated products that result. Here we report that furfural can be selectively converted to 2-cyclopentenone and cyclopentanone in a single step over supported TiO2 catalysts with both model compounds and real biomass-derived streams in the vapor phase. Selectivity for ring rearrangement vs. C O cleavage over TiO2 supported Ru and Pd catalysts can be tuned by manipulating the water partial pressure. The formation of these products in the absence of a condensed acidic stream also enables the tuning of reaction environments to favor the selective formation of unsaturated ketones, which could be valuable diolefin precursors. The incorporation of a TiO2 support in the catalysts tested leads to the suppression of C C hydrogenolysis/decarbonylation and enhancement of ring rearrangement reactions. The nature of the active sites for selective C O cleavage as well as vapor phase ring rearrangement are discussed.

Optical systems typically use galvanometers (aka galvos) and scanners. Galvos move optical elements such as mirrors, quasi-statically, from one static position to another, and an important figure of merit is their step-settle relaxation time. Scanners move in an oscillatory fashion, typically at the device resonant frequency. MEMS devices, which have many advantages and are often used in such optical systems, are typically high Q devices. Moving from one position to another for a galvo or one frequency/amplitude to another for scanners, can take many periods to settle following the ring down. During these transitions, the optical system is inactive and the time is not being efficiently used. In this article we show how a novel class of open loop control algorithms can be used to rapidly change position, frequency and amplitude, typically in well under the period of the device. We show how the MEMS designer can excite, with complete, high-speed control, a vibrational mode of the system. We call this modal engineering, the ability to control the modes of the system in a practical, fast way. This control of the modes is accomplished with open loop control algorithms.

Standard physical vapor deposition systems are large, expensive, and slow. As part of an on-going effort to build a fab-on-a-chip, we have developed a chip-scale, low cost, fast physical vapor deposition system designed to be used with atomic calligraphy or dynamic stencil lithography to direct write nanostructures. The system comprises two MEMS devices: a chip-scale thermal evaporator and a mass sensor that serves as a film thickness monitor. Here, we demonstrate the functionality of both devices by depositing Pb thin-films. The thermal evaporator was made by fabless manufacturing using the SOIMUMPs processs (MEMSCAP, inc). It turns on in 1:46 s and reaches deposition rates as high as 7.2A s−1 with ~1 mm separation from the target. The mass sensor is a re-purposed quartz oscillator (JTX210) that is commercially available for less than one dollar. Its resolution was measured to be 2.65 fg or 7.79E-5 monolayers of Pb. [2020-0237]

Catalysts consisting of metal particles supported on reducible oxides exhibit promising activity and selectivity for a variety of current and emerging industrial processes. Enhanced catalytic activity can arise from direct contact between the support and the metal or from metal-induced promoter effects on the oxide. Discovering the source of enhanced catalytic activity and selectivity is challenging, with conflicting arguments often presented based on indirect evidence. Here, we separate the metal from the support by a controlled distance while maintaining the ability to promote defects via the use of carbon nanotube hydrogen highways. As illustrative cases, we use this approach to show that the selective transformation of furfural to methylfuran over Pd/TiO2 occurs at the Pd-TiO2 interface while anisole conversion to phenol and cresol over Cu/TiO2 is facilitated by exposed Ti3+ cations on the support. This approach can be used to clarify many conflicting arguments in the literature.

The fabrication of metallic electromagnetic meta-atoms on a soft microstructured polymer scaffold using a MEMS-based stencil lithography technique is demonstrated. Using this technique, complex metasurfaces that are generally impossible to fabricate with traditional photolithographic techniques are created. By engineering the mechanical deformation of the polymer scaffold, the metasurface reflectivity in the mid-infrared can be tuned by the application of moderate strains.

The influence of surface functional groups on multi-walled carbon nanotubes (MWNT) the stability and type of Pickering emulsions in water and oil systems is reported. The strong interaction between carbon nanotubes allows for the unique ability to tune emulsion type and droplet size while producing emulsions that are stable for over a month. This behavior stands in stark contrast to what is known for other Pickering emulsion stabilizers such as colloidal silica. Emulsion droplet size displays parabolic behavior, with amphiphilic MWNTs stabilizing the smallest emulsion droplets while larger droplets are stabilized with more hydrophobic or hydrophilic MWNTs. At equivalent volumes of oil and water, water-in-oil emulsions are stabilized by hydrophobic MWNTs, while hydrophilic MWNTs result in oil-in-water emulsions. Emulsion droplet size and type vary depending on the wettability of the MWNTs when changing the oil-to-water ratio. Mixing MWNTs of different wettability results in a non-linear emulsion droplet size trend and may possibly be due to the interaction between the MWNTs of different wettability. To our knowledge, no other Pickering emulsion stabilizer allows for this range of tuning of emulsion properties while sustaining high emulsion stability, even when changing the oil-to-water ratio to induce catastrophic emulsion inversion.

The Casimir Effect is a physical manifestation of quantum fluctuations of the electromagnetic vacuum. When two metal plates are placed close together, typically much less than a micron, the long wavelength modes between them are frozen out, giving rise to a net attractive force between the plates, scaling as d−4 (or d−3 for a spherical-planar geometry) even when they are not electrically charged. In this paper, we observe the Casimir Effect in ambient conditions using a modified capacitive micro-electromechanical system (MEMS) sensor. Using a feedback-assisted pick-and-place assembly process, we are able to attach various microstructures onto the post-release MEMS, converting it from an inertial force sensor to a direct force measurement platform with pN (piconewton) resolution. With this system we are able to directly measure the Casimir force between a silver-coated microsphere and gold-coated silicon plate. This device is a step towards leveraging the Casimir Effect for cheap, sensitive, room temperature quantum metrology. The Casimir effect is a quantum fluctuation force that exists between conducting surfaces separated by hundreds of nanometers, and the effect holds promise for application as a sensing tool in conjunction with an inexpensive micro-electromechanical system (MEMS) device. A team headed by Alexander Stange in the Bishop group at Boston University, United States, observed the Casimir effect under ambient conditions using a modified off-the-shelf MEMS sensor. The authors were able to integrate a Casimir cavity with the MEMS device by attaching various microstructures onto the MEMS sensor, converting it into a customized force measurement platform. The team believes that the Casimir effect has considerable potential as a practical, controllable sensing tool and that it could be used for such purposes as temperature sensing, AC voltage measurements, and low-impedance current measurements.

The construction of a complex, 3D optical metamaterial challenges conventional nanofabrication techniques. These metamaterials require patterning of both a deformable mechanical substrate and an optically-active structure with ~200 nm resolution and precision. The soft nature of the deformable mechanical materials often precludes the use of resist-based techniques for patterning. Furthermore, FIB deposition approaches produce metallic structures with considerable disorder and impurities, impairing their optical response. In this paper we discuss a novel solution to this nanofabrication challenge -- the integration of direct laser writing and MEMS stencil patterning. We demonstrate a variety of methods that enable this integration and then show how one can produce optically-active, 3D metamaterials. We present optical characterization data on one of these metamaterials to demonstrate the viability of our nanofabrication approach.

High-aspect-ratio metallic microstructures have a variety of potential applications in sensing and actuation. However, fabrication remains a challenge. We have fabricated nickel microstructures with over 20:1 aspect ratios by electroplating patterned carbon-coated carbon-nanotube forests using a nickel chloride bath. Pulse plating allows nickel ions to diffuse into the interior of the forest during off portions of the cycle. Done properly, this solves the problem of the formation of an external crust, which otherwise blocks nickel deposition in the interior of the structures. Thus, densities of 86 ± 3% of bulk Ni for the composite structures are achieved. Cantilever structures do not yield under load, but break. Measurements of the material properties of this composite material indicate an elastic modulus of $\sim 42$ GPa and a strength of 400 MPa. We demonstrate the utility of this method with an external field magnetic actuator consisting of a proof mass and two flexures. We achieved 1-mN actuation forces. [2014-0274]

The autothermal reforming and partial oxidation of hexadecane via Pt/Ni bimetallic nanoparticles on various ceria-based supports were investigated. Nanoparticles with Pt/Ni molar ratios ranging from 0/100 to 10/90 were loaded on ceria-based supports including cerium oxide, gadolinium-doped cerium oxide and cerium-doped zirconium oxide. The effect of the Pt/Ni molar ratio and the promotional effect of the support were studied by comparing the hydrogen yield. TPR and XPS analysis showed that there was a strong interaction between Ni and the CeO 2 –ZrO 2 support, which led to the enhancement of catalyst performance when the Pt/Ni ratio was low. In the case of bimetallic catalysts loaded on Gd 2 O 3 –CeO 2 , no significant improvement of the catalytic activity of auto-thermal reforming was achieved until the Pt/Ni ratio reached 10/90.

Beam steering is essential for a variety of optical applications such as communication, LIDAR, and imaging. Microelectromechanical system (MEMS) mirrors are an effective method of achieving modest speeds and angular range at low cost. Typically there are a number of tradeoffs considered when designing a tip-tilt mirror, such as tilt angle and speed. For example, many mirrors are designed to scan at their resonant frequency to achieve large angles. This is effective for a scanning mode; however, this makes the device slow and ineffective as a galvo (quasi-static). Here, we present a magnetic MEMS mirror with extreme quasi-static mechanical tilt angles of ±60° (±120° optical) about two rotation axes. This micromirror enables full hemispheric optical coverage without compromising speed; settling in 4.5 ms using advanced drive techniques. This mirror will enable new applications for MEMS micromirrors previously thought impossible due to their limited angular range and speed.

The present paper reports the findings of a study in which the appropriateness of using two-dimensional (2D) and three-dimensional (3D) numerical modelling in order to simulate the flow in a small reach of the river Blackwater, UK, was examined. The numerical simulations were compared with data obtained from a 1 : 5 scale physical model of the reach. A variety of turbulence models were used in order to evaluate their suitability and assess their impact on the simulations. In order to enable direct comparisons, all of the simulations were undertaken using a single modelling code, Delft3D. It was shown that 3D models offer significant advantages over 2D when applied to a meandering channel and that this choice outweighs the choice of turbulence model.

Single-layer graphene has demonstrated remarkable electronic properties that are strongly influenced by interfacial bonding and break down for the lowest energy configuration of stacked graphene layers (AB Bernal). Multilayer graphene with relative rotations between carbon layers, known as turbostratic graphene, can effectively decouple the electronic states of adjacent layers, preserving properties similar to that of SLG. While the growth of AB Bernal graphene through chemical vapor deposition has been widely reported, we investigate the growth of turbostratic graphene on heteroepitaxial Ni(111) thin films utilizing physical vapor deposition. By varying the carbon deposition temperature between 800 –1100 °C, we report an increase in the graphene quality concomitant with a transition in the size of uniform thickness graphene, ranging from nanocrystallites to thousands of square microns. Combination Raman modes of as-grown graphene within the frequency range of 1650 cm−1 to 2300 cm−1, along with features of the Raman 2D mode, were employed as signatures of turbostratic graphene. Bilayer and multilayer graphene were directly identified from areas that exhibited Raman characteristics of turbostratic graphene using high-resolution TEM imaging. Raman maps of the pertinent modes reveal large regions of turbostratic graphene on Ni(111) thin films at a deposition temperature of 1100 °C.

A nanoporous carbon monolith structure has been developed for use as a scaffold for silicon anodes for lithium batteries. This scaffold was fabricated by coating vertically aligned carbon nanotubes in a highly conformal coating of nanocrystalline carbon, applied via atmospheric pressure chemical vapor deposition. The coating increases the mechanical stability of the nanotube structure, which provides electrically conductive pathways through the anode. Silicon anodes were fabricated with the monoliths by low pressure chemical vapor infiltration of silicon. This platform allows the carbon and silicon volume fractions to be independently varied in the anode. Anodes with a low silicon content (less than 5% by volume) showed high stability in cycling against lithium with a capacity retention of 89.7% between cycles 2 and 185. Anodes with a high silicon content (∼25% by volume) showed poor capacity retention when the carbon content was low (

Our work’s objective is to improve the performance of advanced battery materials through the use of structurally engineered electrodes that are designed to exploit simultaneously the benefits of both the nano- and micro- length scales. Consequently, a three- dimensional fabrication approach has been developed to enable hierarchical control over electrode structures and surface areas. Potential advantages include improved pathways for electron and ion transport, enhanced mechanical stability, and additional control over interfacial areas and compositions for improved stability and performance. Silicon is an advanced material with promise for use in next generation batteries. Among anode materials, silicon stands out because of its potential for extremely high capacities – more than ten times the specific capacity of the commercial graphite anodes. Two issues that negatively impact the usable capacity and performance of Si anodes are i) large volume changes during charging/discharging and ii) the formation of an unstable solid-electrolyte interphase (SEI). The use of nanostructured electrodes has been effective in accommodating the large volume changes that occur during cycling [1, 2]. However, nanostructuring leads to a very high surface area, which exacerbates problems associated with SEI formation and stability. This study seeks to improve the performance of Si anodes through the use of hierarchically structured electrodes to provide the nanoscale framework needed to accommodate large volume changes while controlling the interfacial area – which affects SEI formation. To accomplish this, electrodes will be fabricated from vertically aligned carbon nanotubes (VACNT) infiltrated with silicon. On the nanoscale, these electrodes allow us to adjust the surface area, porosity, and silicon layer thickness. On the microscale, we have the ability to control the electrode thickness and the incorporation of micro-sized features. For instance, microscopic patterning of the CNT matrix to form vertical holes, as shown in Figure 1, has the potential to impact transport through the electrode – as well as its interfacial area and mechanical stability. Treatment of the surface between the nano- and micro-structured areas can be used to control the size and chemistry of the interface between the electrolyte and the electrode matrix. VACNT-Si composite electrodes were prepared by first synthesizing VACNTs on Si wafers using photolithography for catalyst patterning, followed by aligned CNT growth. Nano-layers of silicon were then deposited on the aligned carbon nanotubes via LPCVD at 200mTorr and 570°C. Figure 2 shows a cross-sectional SEM image of a synthesized VACNT-Si array. A thin copper film was used as the current collector. Electrochemical testing was performed on the electrodes assembled in a CR2025 coin cell with a metallic Li foil as the counter electrode. The impact of the electrode structure on the capacity at various C-rates was investigated. Experiment results demonstrate the influence of structurally engineered electrodes on the performance of silicon electrodes for next generation batteries. References C. K. Chan, H. Peng, G. Liu, K. McIlwrath, X. F. Zhang, R. A. Huggins, and Y. Cui, Nat Nanotechnol,3 (2008), 31-35. K. Evanoff, J. Khan, A. A. Balandin, A. Magasinski, W. J. Ready, T. F. Fuller, and G. Yushin, Adv Mater, 24 (2012), 533-540.

Impacted mandibular canines are less common than impacted maxillary canines. They are often in a horizontal position and can migrate anteriorly, some crossing the midline. A canine is considered transmigrated when more than half of the tooth has crossed the midline. A study by Rohrer’ examining 3,000 patients radiographically found 62 impacted maxillary canines (2.06%) and only 3 impacted mandibular canines (O.l%), a 2O:l ratio. Nodine’ found 62 impacted canines per thousand and 44 per thousand in white men and women, respectively. His study showed a lesser frequency in Chinese men and women, with 7 per thousand in men and 9 per thousand in women. However, he did not subgroup the maxillary and mandibular canines. Kramer and Williams3 examined 3,745 patients and found 48 impacted canines; only 3 (.0X%) were impacted mandibular canines. Grover and Lorton4 studied 5,000 Army recruits and found 10,979 impacted teeth; 153 were canines, of which 11 (.l%) were in the mandible. Miranti and Levbarg5 reviewed 2,000 panoramic radiographs and found only 1 (0.05%) impacted mandibular canine, which happened to be transmigrated. The preceeding studies show that impacted mandibular canines occur in approximately 0.1% of patients examined. Among these studies, only the report by Miranti and Levbarg’ dealt with the treatment of the impacted mandibular canine. A report by Javid6 discussed 13 cases of transmigrated impacted mandibular canines, but did not discuss surgical treatment.

Here, we discuss a novel, mixed mode 3D XYZ scanner built within a single foundry process. The device has a large range of motion in X, Y, and Z ( $14.1~\mu \text{m}$ in X and Y and $97.9~\mu \text{m}$ in Z) and can also rotate about two axes (7.4°), making it a 5 degree of freedom scanner. Vertical actuation can be accomplished with both thermal actuators, which have a larger range of motion, and capacitive actuators, which are faster, responding fully up to 3.2 kHz. Although useful for many applications, including scanning probe microscopy, micrometer scale optical microscopy, and manipulation of biological objects, the device was designed to be a 3D scanner for spray-painting atoms upon a surface with nanoscale precision and resolution for nanofabrication. Demonstrating the ability to combine the device with other complicated MEMS systems, it is integrated with an XY scanner designed to serve as a shutter of atomic flux. The full system has 7 degrees of freedom and 12 actuation motors, and because it is built in a low cost commercial foundry with a robust and stable process, it is easy and inexpensive to fabricate multiple copies or integrate into other complicated systems, making a system of systems. [2018-0213]