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In situ Raman spectroscopic evidence for oxygen reduction reaction intermediates at platinum single-crystal surfaces
摘要： Developing an understanding of structure–activity relationships and reaction mechanisms of catalytic processes is critical to the successful design of highly efficient catalysts. As a fundamental reaction in fuel cells, elucidation of the oxygen reduction reaction (ORR) mechanism at Pt(hkl) surfaces has remained a significant challenge for researchers. Here, we employ in situ electrochemical surface-enhanced Raman spectroscopy (SERS) and density functional theory (DFT) calculation techniques to examine the ORR process at Pt(hkl) surfaces. Direct spectroscopic evidence for ORR intermediates indicates that, under acidic conditions, the pathway of ORR at Pt(111) occurs through the formation of HO2*, whereas at Pt(110) and Pt(100) it occurs via the generation of OH*. However, we propose that the pathway of the ORR under alkaline conditions at Pt(hkl) surfaces mainly occurs through the formation of O2?. Notably, these results demonstrate that the SERS technique offers an effective and reliable way for real-time investigation of catalytic processes at atomically flat surfaces not normally amenable to study with Raman spectroscopy.
关键词： density functional theory,in situ Raman spectroscopy,electrochemical surface-enhanced Raman spectroscopy,oxygen reduction reaction,platinum single-crystal surfaces
更新于2025-09-10 09:29:36
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Mapping urban impervious surfaces from an airborne hyperspectral imagery using the object-oriented classification approach
摘要： The objective of this research is to explore the capabilities of the hyperspectral imagery in mapping the urban impervious objects and identifying the surface materials using an object-oriented approach. The application is conducted to Toulouse city (France) within the HYEP research project in charge of using hyperspectral imagery for the environmental urban planning. The method uses the multi-resolution segmentation and classification algorithms. The first results highlight a high potential of the hyperspectral imagery in land cover mapping of the urban environment, especially the extraction of impervious surfaces. They, also, illustrate, that the object-oriented approach by means of the fuzzy logic classifier yields promising results in distinguishing the mean roofing materials based only on the spectral information. Conversely to the red clay tiles and metal roofs, which are easily identified, the concrete, gravel and asphalt roofs are still confused with roads.
关键词： urban impervious surfaces,object-oriented classification,environmental urban planning,hyperspectral imagery
更新于2025-09-10 09:29:36
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A Novel Faraday-Cage Inspired FSS Shield for Stable Resonance Performance Characteristics
摘要： In this latter, a novel Faraday cage inspired frequency selective surface (FSS) array is illustrated to patch-type periodic element. A metallic via has been used to stow the two patch conducting arrays printed on either side of the substrate. The intended application of the proposed electromagnetic (EM) structure is at microwave frequencies for improved bandwidth characteristics and stable resonance response. The structure shows a very stable resonance performance up to 60o oblique incident angle and 11.52% improvement in its fractional bandwidth. In addition, the simulation results of proposed design prove the validity of proposed structure for high microwave powers. Finally, the fabricated prototype along with experimental results of the Faraday cage array show the efficacy of proposed structural design.
关键词： Faraday cage,High power handling,Electromagnetic (EM) performance,Frequency Selective Surfaces (FSS),Substrate Integrated Waveguide (SIW)
更新于2025-09-10 09:29:36
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Surface triads with optical properties
摘要： A geometric model of formation of surfaces comprising an interconnected triple of emitter, reflector and receiver is presented in the paper. The model is based on cyclographic mapping of a spatial curve to the plane. In such map any given point (x, y, z) of the curve corresponds to a cycle with center (x, y) and radius equal to z applicate. The entire curve corresponds to a directed envelope of cycles consisting, in the general case, of two branches. It is shown that the triad of curves consisting of two branches of the envelope and the orthogonal projection of the original curve within the plane (xy) corresponds to a triad of developable surfaces. The triad of curves in the plane (xy) and the original curve together form a triad of ruled surfaces. Both triads have an optical property. Any ray of light emerging from the point of the emitter surface along the normal to it and falling on the surface of the reflector afterwards is directed along the normal vector to the surface of the receiver. The direct and inverse problems of formation of the triad of surfaces are solved. In the first case, a one-parameter set of triads of surfaces is defined from a given spatial curve. In the second case, a single triad of surfaces is defined from a pair of curves "emitter-receiver" defined on the plane (xy). Numerical examples of solutions of the direct and inverse problems are considered and the corresponding visualizations are given. The results of the work can be used in the design of reflector antennas in radar systems and systems for converting solar energy into electric and thermal energy.
关键词： triad of surfaces,optical property,cyclographic mapping,geometric model
更新于2025-09-10 09:29:36
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Insights into different photocatalytic oxidation activities of anatase, brookite, and rutile single crystal facets
摘要： For the understanding of the activity of TiO2 photocatalysts knowledge of the activities of different crystal facets is necessary. This information can be achieved by the investigation of well-defined single crystalline TiO2 surfaces. In this study, the photocatalytic activity of different anatase, brookite, and rutile single crystal wafers with only one exposed surface has been investigated via the oxidation of methanol and the hydroxylation of terephthalic acid, respectively. XRD and SEM measurements have shown that all surfaces are clearly defined and possess a smooth surface, which allows a reliable comparison of the photocatalytic activities. The investigated anatase surfaces show a higher activity than the rutile surfaces, while the brookite surface is interestingly the least active one. To the best of our knowledge, there are no other reports based on the investigation and comparison of well-defined TiO2 anatase (100), anatase (001), and brookite (100) single crystalline surfaces concerning their photocatalytic activity. Furthermore, the influence of the coordination of the titanium and the oxygen ions on the photocatalytic activity is discussed.
关键词： rutile,terephthalic acid hydroxylation,anatase,TiO2 modifications,photocatalytic methanol oxidation,TiO2 surfaces,brookite,single crystalline surfaces
更新于2025-09-09 09:28:46
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Second and third order nonlinear optical studies of a novel thiophene substituted chalcone derivative
摘要： A noncentrosymmetric chalcone derivative (E)-1-(thiophen-2-yl)-3-(3, 4, 5-trimethoxyphenyl) prop-2-en-1-one (TTMP) was synthesized using Claisen Schmidt condensation approach and single crystals were grown using slow evaporation method. The grown TTMP crystals crystallises in orthorhombic structure with Pna21 space group. The intermolecular interactions of the TTMP crystals were envisioned by Hirshfeld surface analysis (HSA). Further, the structural conformations of the crystal were carried out by using 1H NMR, FTIR and FT-Raman spectral analysis. The UV-Vis-NIR spectrum of the sample clearly shows the prime transparency in the entire visible and near infrared region. Thermal studies (TG/DTA/DSC) of the TTMP sample shows excellent thermal stability and phase transition and also noticed that crystal was most stable up to 152.65 0C. The second harmonic generation efficiency was obtained for the crystals using Nd:YAG laser and is to be 1.93 times that of urea . The third order nonlinear absorption coefficient (β), nonlinear refractive index (n2), third-order nonlinear susceptibilities (χ (3)), second order hyper polarizability (γh) and optical limiting thresholds were determined by Z-scan technique using the Diode-Pumped Solid State (DPSS) Continuous Wave (CW) laser. The results suggest that the TTMP molecules are promising materials for optoelectronic device applications.
关键词： Hirshfeld surfaces,Optical limiting,SHG,Z-scan,Single crystal,Chalcones
更新于2025-09-09 09:28:46
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Dissociation dynamics of the water dication following one-photon double ionization. I. Theory
摘要： The measurement of the triple differential cross section in the body frame for double photoionization of a molecule can be made in principle by detecting the ionic fragments and the two photoelectrons in coincidence—but only if the dynamics and geometry of dissociation of the doubly charged molecular ion are known. A classical trajectory study of the nine lowest states of the water dication is presented using high quality ab initio potential-energy surfaces. Sampling from a semiclassical initial distribution of positions and momenta is used to approximate ionization from the Frank-Condon region of the ground vibrational state of neutral H2O. Excellent agreement in comparison with preliminary experimental momentum imaging measurements of double photoionization of water show that eight dication states can be unambiguously identified in the experiment with the aid of theory. The theoretical trajectory results allow body frame measurements of double photoionization to yield all eight states even though the usual assumption of direct dissociation, the “axial recoil” approximation, breaks down for three of the dication electronic states seen in the experiment.
关键词： potential-energy surfaces,double photoionization,dissociation dynamics,classical trajectory study,water dication
更新于2025-09-09 09:28:46
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Prediction of Fundamental Properties of Semiconductors and Materials Exploration Using First-Principles Calculations
摘要： 昨今の資源?環境問題やエネルギー情勢を背景に，卓越した機能だけでなく，地球上に豊富に存在する元素により構成され，安価で高い環境調和性を示す新材料が望まれている．社会に役立つ「材料」へと昇華できる新物質を見いだすためには，的確に設計?探索の指針を立てることが重要であることは言うまでもない．そして次の関門が，いかに広い探索空間をカバーするか，その中からどのように有望な物質を絞り込むかである．最近では計算科学の進展とスーパーコンピュータの演算能力の向上により，第一原理計算等の計算科学手法を用いることで物質の安定性や特性を高精度かつ網羅的に予測できるようになってきた．これにデータ科学手法，更にはコンビナトリアル合成?評価等を連携させることで，新物質?新材料の開発を加速し，同時に膨大なデータの解析から設計?探索指針を得ようとする試みが世界各国で盛んになっている．いわゆる「マテリアルズ?インフォマティクス」によるアプローチである．
关键词： surfaces,point defects,interfaces,materials exploration,semiconductors,first-principles calculations
更新于2025-09-09 09:28:46
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Facile Preparation of Functional Group Gradient Surfaces by Desorption and <i>Re</i> -Adsorption of Alkanethiols on Gold
摘要： Many organisms live in various stimuli-responsive milieus of signaling components in gradient forms which are known to be closely related to biological phenomena including embryonic development, wound repair, and tumor metastasis. In addition, the physicochemical properties of gradient surfaces, i.e., a continuous spatial variation of gradient components, enable various types of biological/biochemical research such as cell proliferation/migration and tissue engineering. Various techniques have been reported for the preparation of gradient surfaces, including laminar flow mixing in microfluidic channels, cross-diffusion of alkanethiols, microfluidic permeation printing, oblique deposition and template coating, controlled polymerization on substrates, and controlled UV irradiation on photo-responsive substrates. Previously, we reported a simple method for the generation of multi-component gradient surfaces on self-assembled monolayers (SAMs) on gold. The monolayers consisted of quinone derivatives which reacted with reducing agents in a predictable manner to produce amine gradient surfaces. Recently, desorption and re-adsorption-based methods on SAMs have gained attention, in which alkanethiolates on gold surfaces were desorbed in order to provide an empty space gradient, following which other types of alkanethiols filled up the empty space, leading to an end group gradient of alkanethiolates. For example, Kim et al. reported a simple and flexible method for preparing cell adhesion ligand patterns on SAMs by using a laser beam equipped in a matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometer. Similarly, Meyyappan et al. demonstrated that a surface gradient can be achieved by irradiating a focused laser beam on SAMs with subsequent re-adsorption of a second alkanethiol. Fioravanti et al. reported on a new method to fabricate surface chemical gradients of alkanethiols through combining reductive electrochemical desorption and partial re-adsorption of alkanethiolates. Recently, we found that tetrahydrofuran (THF) highly compromises the stability of SAMs on gold, and thus induces unusually fast exchange of alkanethiolates of SAMs with other alkanethiols in the solution. In this study, we harnessed this desorption capability of THF for the preparation of functional group gradient surfaces. In our strategy, a monolayer of alkanethiolates was exposed to THF in a time-dependent manner followed by immersion in a solution of other functional group-terminated alkanethiols, leading to functional group gradient surfaces. The functional group then played a role of a chemical handle to conjugate various functional molecules for the formation of gradients of those components.
关键词： Gradient surfaces,Alkanethiols,Desorption,Self-assembled monolayers,Tetrahydrofuran
更新于2025-09-09 09:28:46
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Wave Propagation Concepts for Near-Future Telecommunication Systems || Numerical Investigation about Frequency Behaviour of Conformal FSS
摘要： Frequency selective surfaces (FSSs) are spatial filters widely employed in high-performance applications like hybrid radomes for radars and antennas. While planar geometries are widely studied, less attention has been devoted to conformal ones, where we must consider the influence of both the lattice geometry and the shape and size of the individual elements. In the planar case, periodicity first impacts on the general reflecting properties of the surface, while the shape and the size of the individual element affect its detailed both spatial and frequency filtering behaviour. In particular, the frequency response is dictated mainly by the scattering by the individual element and attains its maximum at resonance conditions. We mean to numerically investigate whether the same also occurs for non-planar surfaces and curved elements, for both cylindrical and conical surfaces. We compare the results of the general frequency behaviour of FSS both made of strips in free space and slots cut in a perfectly conducting material. The effect of the lattice geometrical parameters is also appreciated. The main conclusions are that also for curved elements a frequency selective behaviour can be appreciated and the interaction with the single elements plays an important role, when mutual coupling is not strong.
关键词： thin strips,conformal surfaces,electromagnetic scattering,slots,mutual coupling,FSS
更新于2025-09-09 09:28:46