Hessian-based adaptive sparse quadrature for infinite-dimensional Bayesian inverse problems
Not Available
Chen, Peng (ORCID:0000000342159901)↗
Engineering topics
Chen, Peng
Publications and source records attributed to Chen, Peng.
Femtosecond to picosecond transient effects in WSe 2 observed by pump-probe angle-resolved photoemission spectroscopy
Time-dependent responses of materials to an ultrashort optical pulse carry valuable information about the electronic and lattice dynamics; this research area has been widely studied on novel two-dimensional materials such as graphene, transition metal dichalcogenides (TMDs) and topological insulators (TIs). We report herein a time-resolved and angle-resolved photoemission spectroscopy (TRARPES) study of WSe 2 , a layered semiconductor of interest for valley electronics. The results for below-gap optical pumping reveal energy-gain and -loss Floquet replica valence bands that appear instantaneously in concert with the pump pulse. Energy shift, broadening, and complex intensity variation and oscillation at twice the phonon frequency for the valence bands are observed at time scales ranging from the femtosecond to the picosecond and beyond. Furthermore, the underlying physics is rich, including ponderomotive interaction, dressing of the electronic states, creation of coherent phonon pairs, and diffusion of charge carriers – effects operating at vastly different time domains.
36 MATERIALS SCIENCE↗
Bimetallic Effect of Single Nanocatalysts Visualized by Super-Resolution Catalysis Imaging
Not Available
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
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.
Additive Manufacturing↗
Near-infrared downconversion luminescence of SrMoO{sub 4}:Tm{sup 3+},Yb{sup 3+} phosphors
Graphical abstract: The calculated band structure of SrMoO{sub 4} and the visible and infrared emission spectra of SrMoO{sub 4}:1%Tm{sup 3+},10%Yb{sup 3+} phosphors under 283 nm excitation.▪ - Highlights: • Near-infrared downconversion luminescence of SrMoO{sub 4}:Tm{sup 3+},Yb{sup 3+} phosphors were systematically investigated. • The electronic structure of SrMoO{sub 4} was estimated by density functional theory. • The quenching concentration of Yb{sup 3+} ions approaches 10 mol%. • The energy transfer mechanism was discussed in detail. - Abstract: Tm{sup 3+} and Yb{sup 3+} codoped SrMoO{sub 4} phosphors were synthesized by the high-temperature solid-state reaction method. The structure, ultraviolet-visible diffuse reflectance spectra, photoluminescence, decay properties and theoretical energy transfer efficiency of the phosphors were investigated in detail. The electronic structure and band gap of SrMoO{sub 4} were estimated by density functional theory (DFT) calculation. The XRD results show that all the prepared phosphors can be readily indexed to scheelite-type structure. The strong visible emission around 473 nm from Tm{sup 3+} ({sup 1}G{sub 4} → {sup 3}H{sub 6}) and near-infrared (NIR) emission around 998 nm from Yb{sup 3+} ({sup 2}F{sub 5/2} → {sup 2}F{sub 7/2}) of the SrMoO{sub 4}:Tm{sup 3+},Yb{sup 3+} phosphors were observed under 283 nm excitation. The dependence of the visible and NIR emissions on Yb{sup 3+} concentration have also been investigated. The quenching concentration of Yb{sup 3+} ions approaches 10 mol%. In addition, the energy transfer processes and possible transfer routes were proposed.
36 MATERIALS SCIENCE↗
Experimental Study of Potential Heat Treatment Issues of Large Bi-2212 Coils
Not provided.
Engineering↗
X-ray study of the charge-density-wave transition in single-layer TiS e 2
Not Available
Fang, Xin-Yue↗
Elemental Topological Dirac Semimetal: α -Sn on InSb(111)
Three-dimensional (3D) topological Dirac semimetals (TDSs) are rare but important as a versatile platform for exploring exotic electronic properties and topological phase transitions. A quintessential feature of TDSs is 3D Dirac fermions associated with bulk electronic states near the Fermi level. We have observed such bulk Dirac cones in epitaxially grown α-Sn films on InSb(111), the first such TDS system realized in an elemental form, using angle-resolved photoemission spectroscopy. First-principles calculations confirm that epitaxial strain is key to the formation of the TDS phase. A phase diagram is established that connects the 3D TDS phase through a singular point of a zero-gap semimetal phase to a topological insulator phase. The nature of the Dirac cone crosses over from 3D to 2D as the film thickness is reduced.
36 MATERIALS SCIENCE↗
Magnetochromic sensing and size-dependent collective excitations in iron oxide nanoparticles
We combine optical and magneto-optical spectroscopies with complementary vibrational and magnetic property measurements to reveal finite length scale effects in nanoscale α–Fe 2 O 3 . Analysis of the d-to-d on-site excitations uncovers enhanced color contrast at particle sizes below approximately 75 nm due to size-induced changes in spin-charge coupling that are suppressed again below the superparamagnetic limit. These findings provide a general strategy for amplifying magnetochromism in α–Fe 2 O 3 and other iron-containing nanomaterials that may be useful for advanced sensing applications. Lastly, we also unravel the size dependence of collective excitations in this iconic antiferromagnet.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
High expression of CREPT promotes tumor growth and is correlated with poor prognosis in colorectal cancer
CREPT (cell cycle-related and expression elevated protein in tumor) is highly expressed in many kinds of cancer, and has been shown to be prognostic in certain cancers. However, the clinical significance of CREPT in colorectal cancer (CRC) has not been sufficiently investigated. In this study, we examined the CREPT expression in 225 clinical CRC tissues and paired adjacent normal tissues, and analyzed the correlation between CREPT expression and other clinicopathological features. We also evaluated the biological function of CREPT both in vitro and in vivo using knockdown or overexpressing CRC cells. Our results showed that CREPT expressed in 175 of 225 (77.8%) CRC patients and the CREPT expression was significantly associated with tumor differentiation (P = 0.000), Dukes' stages (P = 0.013) and metastasis (P = 0.038). Patients with high CREPT expression tended to have shorter survival time. Multivariate analysis showed that positive CREPT expression can be used as an independent predictor for CRC prognosis. CREPT knockdown cells showed inhibited cell proliferation and arrested cell cycle, while CREPT overexpressing cells showed increased proliferation and promoted cell cycle. In addition, CREPT overexpression significantly promoted tumor growth in vivo. Mechanism study showed that CREPT may regulate cell proliferation and cell cycle through the regulation on cyclin D3, CDK4 and CDK6. - Highlights: • CREPT expression was associated with decreased overall survival in CRC. • CREPT expression is correlated with tumor progression in CRC. • Overexpression of CREPT promoted tumor growth both in vitro and in vivo.
60 APPLIED LIFE SCIENCES↗
Patterning monolayer graphene with zigzag edges on hexagonal boron nitride by anisotropic etching
Graphene nanostructures are potential building blocks for nanoelectronic and spintronic devices. However, the production of monolayer graphene nanostructures with well-defined zigzag edges remains a challenge. In this paper, we report the patterning of monolayer graphene nanostructures with zigzag edges on hexagonal boron nitride (h-BN) substrates by an anisotropic etching technique. We found that hydrogen plasma etching of monolayer graphene on h-BN is highly anisotropic due to the inert and ultra-flat nature of the h-BN surface, resulting in zigzag edge formation. The as-fabricated zigzag-edged monolayer graphene nanoribbons (Z-GNRs) with widths below 30 nm show high carrier mobility and width-dependent energy gaps at liquid helium temperature. These high quality Z-GNRs are thus ideal structures for exploring their valleytronic or spintronic properties.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Sparse-grid, reduced-basis Bayesian inversion: Nonaffine-parametric nonlinear equations
We extend the reduced basis (RB) accelerated Bayesian inversion methods for affine-parametric, linear operator equations which are considered in [16,17] to non-affine, nonlinear parametric operator equations. We generalize the analysis of sparsity of parametric forward solution maps in [20] and of Bayesian inversion in [48,49] to the fully discrete setting, including Petrov–Galerkin high-fidelity (“HiFi”) discretization of the forward maps. We develop adaptive, stochastic collocation based reduction methods for the efficient computation of reduced bases on the parametric solution manifold. The nonaffinity and nonlinearity with respect to (w.r.t.) the distributed, uncertain parameters and the unknown solution is collocated; specifically, by the so-called Empirical Interpolation Method (EIM). For the corresponding Bayesian inversion problems, computational efficiency is enhanced in two ways: first, expectations w.r.t. the posterior are computed by adaptive quadratures with dimension-independent convergence rates proposed in [49]; the present work generalizes [49] to account for the impact of the PG discretization in the forward maps on the convergence rates of the Quantities of Interest (QoI for short). Second, we propose to perform the Bayesian estimation only w.r.t. a parsimonious, RB approximation of the posterior density. Based on the approximation results in [49], the infinite-dimensional parametric, deterministic forward map and operator admit N-term RB and EIM approximations which converge at rates which depend only on the sparsity of the parametric forward map. In several numerical experiments, the proposed algorithms exhibit dimension-independent convergence rates which equal, at least, the currently known rate estimates for N-term approximation. We propose to accelerate Bayesian estimation by first offline construction of reduced basis surrogates of the Bayesian posterior density. The parsimonious surrogates can then be employed for online data assimilation and for Bayesian estimation. They also open a perspective for optimal experimental design.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Graphene nanoribbons epitaxy on boron nitride
In this letter, we report a pilot study on epitaxy of monolayer graphene nanoribbons (GNRs) on hexagonal boron nitride (h-BN). We found that GNRs grow preferentially from the atomic steps of h-BN, forming in-plane heterostructures. GNRs with well-defined widths ranging from ∼15 nm to ∼150 nm can be obtained reliably. As-grown GNRs on h-BN have high quality with a carrier mobility of ∼20 000 cm{sup 2} V{sup −1} s{sup −1} for ∼100-nm-wide GNRs at a temperature of 1.7 K. Besides, a moiré pattern induced quasi-one-dimensional superlattice with a periodicity of ∼15 nm for GNR/h-BN was also observed, indicating zero crystallographic twisting angle between GNRs and h-BN substrate. The superlattice induced band structure modification is confirmed by our transport results. These epitaxial GNRs/h-BN with clean surfaces/interfaces and tailored widths provide an ideal platform for high-performance GNR devices.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
High-quality graphene grown on polycrystalline PtRh{sub 20} alloy foils by low pressure chemical vapor deposition and its electrical transport properties
High-quality continuous uniform monolayer graphene was grown on polycrystalline PtRh{sub 20} alloy foils by low pressure chemical vapor deposition. The morphology of graphene was investigated by Raman spectroscopy, scanning electron microscopy, and atomic force microscopy. Analysis results confirm that high quality single-layer graphene was fabricated on PtRh{sub 20} foil at 1050 °C using a lower flux of methane under low pressure. Graphene films were transferred onto the SiO{sub 2}/Si substrate by the bubbling transfer method. The mobility of a test field effect transistor made of the graphene grown on PtRh{sub 20} was measured and reckoned at room temperature, showing that the carrier mobility was about 4000 cm{sup 2} V{sup −1} s{sup −1}. The results indicate that desired quality of single-layer graphene grown on PtRh{sub 20} foils can be obtained by tuning reaction conditions.
36 MATERIALS SCIENCE↗
Sub-particle reaction and photocurrent mapping to optimize catalyst-modified photoanodes
The splitting of water photoelectrochemically into hydrogen and oxygen represents a promising technology for converting solar energy to fuel. The main challenge is to ensure that photogenerated holes efficiently oxidize water, which generally requires modification of the photoanode with an oxygen evolution catalyst (OEC) to increase the photocurrent and reduce the onset potential. However, because excess OEC material can hinder light absorption and decrease photoanode performance, its deposition needs to be carefully controlled—yet it is unclear which semiconductor surface sites give optimal improvement if targeted for OEC deposition, and whether sites catalysing water oxidation also contribute to competing charge-carrier recombination with photogenerated electrons. Surface heterogeneity exacerbates these uncertainties, especially for nanostructured photoanodes benefiting from small charge-carrier transport distances. In this study, we use super-resolution imaging, operated in a chargecarrier- selective manner and with a spatiotemporal resolution of approximately 30 nanometres and 15 milliseconds, to map both the electron- and hole-driven photoelectrocatalytic activities on single titanium oxide nanorods. We then map, with sub-particle resolution (about 390 nanometres), the photocurrent associated with water oxidation, and find that the most active sites for water oxidation are also the most important sites for charge-carrier recombination. Site-selective deposition of an OEC, guided by the activity maps, improves the overall performance of a given nanorod—even though more improvement in photocurrent efficiency correlates with less reduction in onset potential (and vice versa) at the subparticle level. Moreover, the optimal catalyst deposition sites for photocurrent enhancement are the lower-activity sites, and for onset potential reduction the optimal sites are the sites with more positive onset potential, contrary to what is obtainable under typical deposition conditions. These findings allow us to suggest an activity-based strategy for rationally engineering catalyst-improved photoelectrodes, which should be widely applicable because our measurements can be performed for many different semiconductor and catalyst materials.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Generation of arbitrary vector beams with liquid crystal polarization converters and vector-photoaligned q-plates
Arbitrary vector beams (VBs) are realized by the designed polarization converters and corresponding vector-photoaligned q-plates. The polarization converter is a specific twisted nematic cell with one substrate homogeneously aligned and the other space-variantly aligned. By combining a polarization-sensitive alignment agent with a dynamic micro-lithography system, various categories of liquid crystal polarization converters are demonstrated. Besides, traditional radially/azimuthally polarized light, high-order and multi-ringed VBs, and a VB array with different orders are generated. The obtained converters are further utilized as polarization masks to implement vector-photoaligning. The technique facilitates both the volume duplication of these converters and the generation of another promising optical element, the q-plate, which is suitable for the generation of VBs for coherent lasers. The combination of proposed polarization converters and correspondingly fabricated q-plates would drastically enhance the capability of polarization control and may bring more possibilities for the design of photonic devices.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗