Engineering topics
Chen, Peng
Publications and source records attributed to Chen, Peng.
Direct-Write Printing on Three-Dimensional Geometries for Miniaturized Detector and Electronic Assemblies
Aerosol Jet Printing (AJP) and other additive electronics technologies will enable new detector assemblies that were not previously possible with traditional assembly processes. This technology has the potential to reduce mass and volume for fabrication and assembly of detector, instrument and electronics concepts by reducing trace widths down to 10 microns, printing on complex geometries, and allowing new concept production. This poster summarizes development efforts of printed interconnects for space applications.
Super-resolution imaging of non-fluorescent reactions via competition
Super-resolved fluorescence microscopy techniques have enabled substantial advances in the chemical and biological sciences. However, they can only interrogate entities that fluoresce, and most chemical or biological processes do not involve fluorescent species. Here we report a competition-enabled imaging technique with super-resolution (COMPEITS) (a COMPetition-Enabled Imaging Technique with Super-resolution) that enables quantitative super-resolution imaging of non-fluorescent processes. It is based on the incorporation of competition into a single-molecule fluorescence-detection scheme. We demonstrate COMPEITS by investigating a photoelectrocatalytic reaction; we map, with nanometre precision, a non-fluorescent surface reaction that is important for water decontamination on single photocatalyst particles. The subparticle-level quantitative information of reactant adsorption affinities unambiguously decouples size- and shape-scaling laws on specific particle facets and uncovers a surprising biphasic shape dependence, leading to catalyst design principles for optimal reactant adsorption efficacy. With its ability to provide spatially resolved information on the behaviours of unlabelled, non-fluorescent entities under operando conditions, COMPEITS could interrogate a variety of surface processes in fields ranging from heterogeneous catalysis and materials engineering to nanotechnology and energy sciences.
Comment on “Chiral Phase Transition in Charge Ordered 1 T - TiSe 2 ”
A previous report of the emergence of chirality for the ( 2 × 2 × 2 ) charge density wave (CDW) in TiSe 2 has attracted much interest; the drastic symmetry breaking is highly unusual with few precedents. In that study, key evidence was provided by x-ray diffraction measurements of two superlattice reflections, (1.5 1.5 0.5) and (2.5 1 0). The (2.5 1 0) reflection appeared to show an anomalously large intensity and a transition onset at ~7 K below that of the (1.5 1.5 0.5) reflection. These observations, aided by modeling, were cited as evidence for a separate chiral transition. Here, we show that the prior conclusions based on x-ray diffraction are erroneous. There is just one transition, and it is achiral.
Taylor approximation and variance reduction for PDE-constrained optimal control under uncertainty
Not provided.
Analogy between Enzyme and Nanoparticle Catalysis: A Single-Molecule Perspective
Catalysis as a field is classically divided into three areas: homogeneous, heterogeneous, and biological catalysis.1 For the latter two, i.e., biological catalysis and heterogeneous catalysis, their dissimilarity can be apparent intuitively, from the scenes of fruit fermentation in a rural winery to make wine and oil refining in a process plant to produce gasoline. In addition to the practical differences, technological terms common in both areas show divergences in meaning. Here, a highly relevant example is the term turnover number.2 It refers to the maximum number of substrate molecules converted to products per enzyme molecule per second, often written as k cat in enzyme catalysis; while the same term means the number of moles of reactants that a mole of catalyst converts before deactivation, usually abbreviated as TON in heterogeneous catalysis.
Quantifying Photocurrent Loss of a Single Particle–Particle Interface in Nanostructured Photoelectrodes
Particle–particle interfaces are ubiquitous in nanostructured photoelectrodes and photovoltaics, which are important devices for solar energy conversion. Furthermore, these interfaces are expected to cause performance losses in these devices, but how much loss they would incur is poorly defined. Here we use a subparticle photoelectrochemical current measurement, in combination with specific photoelectrode configurations, to quantify the current losses from single particle–particle interfaces formed between individual TiO 2 nanorods operating as photoanodes in aqueous electrolytes. We find that a single interface leads to ~20% photocurrent loss (i.e., ~80% retention of the original current). Such quantitative, first-of-its-kind, information provides a metric for guiding the optimization and design of nanostructured photoelectrodes and photovoltaics.
Ion-Sieving Carbon Nanoshells for Deeply Rechargeable Zn-Based Aqueous Batteries
As an alternative to lithium-ion batteries, Zn-based aqueous batteries feature nonflammable electrolytes, high theoretical energy density, and abundant materials. However, a deeply rechargeable Zn anode in lean electrolyte configuration is still lacking. Different from the solid-to-solid reaction mechanism in lithium-ion batteries, Zn anodes in alkaline electrolytes go through a solid-solute-solid mechanism (Zn-Zn(OH) 4 2- -ZnO), which introduces two problems. First, discharge product ZnO on the surface prevents further reaction of Zn underneath, which leads to low utilization of active material and poor rechargeability. Second, soluble intermediates change Zn anode morphology over cycling. In this work, an ion-sieving carbon nanoshell coated ZnO nanoparticle anode is reported, synthesized in a scalable way with controllable shell thickness, to solve the problems of passivation and dissolution simultaneously. The nanosized ZnO prevents passivation, while microporous carbon shell slows down Zn species dissolution. Under extremely harsh testing conditions (closed cell, lean electrolyte, no ZnO saturation), this Zn anode shows significantly improved performance compared to Zn foil and bare ZnO nanoparticles. The deeply rechargeable Zn anode reported is an important step toward practical high-energy rechargeable aqueous batteries (e.g., Zn-air batteries). And the ion-sieving nanoshell concept demonstrated is potentially beneficial to other electrodes such as sulfur cathode for Li-S batteries.
Solution-processable 2D semiconductors for high-performance large-area electronics
Not provided.
Frustration and Glasslike Character in RIn 1–x Mn x O 3 (R = Tb, Dy, Gd)
Here, we bring together ac susceptibility and dc magnetization to uncover the rich magnetic field-temperature behavior of a series of rare earth indium oxides, RInO 3 (R = Tb, Dy, and Gd). The degree of frustration is much larger than expected, particularly in TbInO 3 , and the ground states are glasslike with antiferromagnetic tendencies. The activation energy for spin reorientation is low. Chemical substitution with Mn 3+ ions to form TbIn 1–x Mn x O 3 (x ≤ 0.01) relieves much of the frustration that characterizes the parent compound and slightly enhances the short-range antiferromagnetic order. The phase diagrams developed from this work reveal the rich competition between spin orders and provide an opportunity to compare the dynamics in the RInO 3 and Mn-substituted systems. Finally, these structure–property relations may be useful for understanding magnetism in other geometrically frustrated multiferroics.
Metal-to-Semiconductor Transition and Electronic Dimensionality Reduction of Ca 2 N Electride under Pressure
Abstract not provided
Direct-Write Printing on Three-Dimensional Geometries for Miniaturized Detector and Electronic Assemblies
Direct-write printing techniques will enable new detector assemblies that were not previously possible with traditional assembly processes. Detector concepts were manufactured using this technology to validate repeatability. Additional detector applications and printed wires on a 3-dimensional magnetometer bobbin will be designed for print. This effort focuses on evaluating performance for direct-write manufacturing techniques on 3-dimensional surfaces. Direct-write manufacturing has the potential to reduce mass and volume for fabrication and assembly of advanced detector concepts by reducing trace widths down to 10 microns, printing on complex geometries, allowing new electronic concept production, and reduced production times of complex those electronics.
In Situ Strain Tuning of the Dirac Surface States in Bi 2 Se 3 Films
Elastic strain has the potential for a controlled manipulation of the band gap and spin-polarized Dirac states of topological materials, which can lead to pseudomagnetic field effects, helical flat bands, and topological phase transitions. However, practical realization of these exotic phenomena is challenging and yet to be achieved. Here we show that the Dirac surface states of the topological insulator Bi 2 Se 3 can be reversibly tuned by an externally applied elastic strain. Performing in situ X-ray diffraction and in situ angle-resolved photoemission spectroscopy measurements during tensile testing of epitaxial Bi 2 Se 3 films bonded onto a flexible substrate, we demonstrate elastic strains of up to 2.1% and quantify the resulting changes in the topological surface state. Our study establishes the functional relationship between the lattice and electronic structures of Bi 2 Se 3 and, more generally, demonstrates a new route toward momentum-resolved mapping of strain-induced band structure changes.
Experimental and theoretical electronic structure and symmetry effects in ultrathin NbSe2 films
Layered quasi-two-dimensional transition-metal dichalcogenides (TMDCs), which can be readily made in ultrathin films, offer excellent opportunities for studying how dimensionality affects electronic structure and physical properties. Among all TMDCs, NbSe2 is of special interest; bulk NbSe2 hosts a charge-density-wave phase at low temperatures and has the highest known superconducting transition temperature, and these properties can be substantially modified in the ultrathin film limit. Motivated by these effects, we report herein a study of few-layer NbSe2 films, with a well-defined single-domain orientation, epitaxially grown on GaAs. Angle-resolved photoemission spectroscopy was used to determine the electronic band structure and the Fermi surface as a function of layer thickness; first-principles band-structure calculations were performed for comparison. The results show interesting changes as the film thickness increases from a monolayer (ML) to several layers. The most notable changes occur between a ML and a bilayer, where the inversion symmetry in bulk NbSe2 is preserved in the bilayer but not in the ML. Finally, the results illustrate some basic dimensional effects and provide a basis for further exploring and understanding the properties of NbSe2.
Charge Carrier Activity on Single-Particle Photo(electro)catalysts: Toward Function in Solar Energy Conversion
Understanding the fundamental properties of charge carriers on the surface of semiconductor photo(electro)catalysts is key to the rational design of efficient photo(electro)catalytic devices for sunlight-driven energy conversion. Here high spatial resolution information is always desirable because of the ubiquitous heterogeneity in semiconductor particles. In this Perspective, we review the latest advances in nanoscale imaging and quantitative analysis of charge carrier activities on individual semiconductor particles down to subparticle resolution, covering the approaches of single-molecule super-resolution fluorescence imaging, scanning electron microscopy, and photoluminescence microscopy. We further highlight direct, operando functional assessments of their performances toward the targeted photo(electro)-catalytic processes through single- and subparticle photocurrent measurements. Here, we also discuss the significance of establishing quantitative relations between the desired functions of photo(electro)catalysts and their surface charge carrier activities. These fundamental relations can provide guiding principles for rationally engineering photo(electro)catalytic systems, for example with cocatalysts, for a broad range of applications.
Structural basis for recognition of frizzled proteins by Clostridium difficile toxin B
Clostridium difficile infection is the most common cause of antibiotic-associated diarrhea in developed countries. The major virulence factor, C. difficile toxin B (TcdB), targets colonic epithelia by binding to the frizzled (FZD) family of Wnt receptors, but how TcdB recognizes FZDs is unclear. Here, we present the crystal structure of a TcdB fragment in complex with the cysteine-rich domain of human FZD2 at 2.5-angstrom resolution, which reveals an endogenous FZD-bound fatty acid acting as a co-receptor for TcdB binding. This lipid occupies the binding site for Wnt-adducted palmitoleic acid in FZDs. TcdB binding locks the lipid in place, preventing Wnt from engaging FZDs and signaling. Finally, our findings establish a central role of fatty acids in FZD-mediated TcdB pathogenesis and suggest strategies to modulate Wnt signaling.
Gapped electronic structure of epitaxial stanene on InSb(111)
We report that stanene (single-layer gray tin), with an electronic structure akin to that of graphene but exhibiting a much larger spin-orbit gap, offers a promising platform for room-temperature electronics based on the quantum spin Hall (QSH) effect. This material has received much theoretical attention, but a suitable substrate for stanene growth that results in an overall gapped electronic structure has been elusive; a sizable gap is necessary for room-temperature applications. Here, we report a study of stanene, epitaxially grown on the (111)B-face of indium antimonide (InSb). Angle-resolved photoemission spectroscopy measurements reveal a gap of 0.44 eV, in agreement with our first-principles calculations. Lastly, the results indicate that stanene on InSb(111) is a strong contender for electronic QSH applications.