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Reference Module in Chemistry, Molecular Sciences and Chemical Engineering || Electronic Structure of Oxide Ultrathin Layers on Metal Surfaces
摘要： Since about 35 years ago, the development of the electron microscopy and spectroscopy techniques has pushed the scienti?c community toward the fabrication of physical systems with a reduced “vertical” dimension, down to nanometer size and ultimately to the monolayer (ML) or single-atom thickness. Especially at the beginning, a requirement for these ultra-thin systems was that these should be grown on metallic or at least semiconducting substrates in order to exploit the enhanced resolution of surface science techniques available when working with conductive systems. Oxide systems were no exception to this trend, and systems made by one or very few oxide layers grown onto metallic substrates were indeed achieved and started to be thoroughly characterized.1,2 Another push to research on oxide ultra-thin ?lms was provided by semiconductor device technology, in which silicon chips are covered by a nanometer-size ?lm of amorphous silica, by the efforts in understanding metal corrosion, by the study of thin insulating oxide ?lms in storage devices, and by the study of oxide supports in heterogeneous catalysis. The ?eld however evolved independently of these initial drives especially as it became clear that the properties of these materials, such as transport and electronic structure, were strongly in?uenced by their detailed and unusual structure. Quite soon, in fact, it was realized that these systems in most cases were not a mere reproduction of the bulk oxides on a reduced scale, but represented completely new hybrid metal/oxide systems with novel structural and electronic properties, often with no counterpart in the bulk. This was unequivocally demonstrated when the atomistic structure of some of these phases was unveiled via the combined use of microscopy and computational characterization,3–5 which allowed researchers to investigate not only the novel structures thus produced, but also the corresponding electronic and spectroscopic properties in great detail. It was the birth of the ?eld of UltraThin Oxides (UTOx) on metal surfaces, whose theoretical or electronic structure description is the topic of this essay.
关键词： Oxide Ultrathin Layers,Electronic Structure,UltraThin Oxides,Metal Surfaces,UTOx
更新于2025-09-23 15:21:01
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Observation and implications of the Franza??Keldysh effect in ultrathin GaAs solar cells
摘要： Voltage-dependencies were observed in the external quantum efficiency (EQE) spectra of ultrathin GaAs solar cells. The subbandgap tail was shown to increase going from forward to reverse bias, while at energies above the bandgap, voltage-dependent oscillations in the EQE were measured. Using optical simulations, it is irrefutably shown that the voltage-dependencies are caused by the Franz-Keldysh effect, that is, an electric field-dependent absorption coefficient near the bandgap. The dependency on voltage of the subbandgap tail is demonstrated to be strongest in thin-film cells with a textured rear mirror, since the absorptivity below the bandgap is enhanced by light trapping. The voltage-dependent subbandgap tail has important implications for the use of the reciprocity relation between photovoltaic quantum efficiency and electroluminescence. It is shown that the radiative limit for the open-circuit voltage of thin-film cells integrated with light management schemes can be underestimated by more than 25 mV. Consequently, these cells may be assumed to be closer to the radiative limit than they really are.
关键词： Urbach tail,Franz-Keldysh effect,reciprocity,textured solar cells,ultrathin gaas
更新于2025-09-23 15:21:01
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Selective Activation of Benzyl Alcohol Coupled with Photoelectrochemical Water Oxidation via a Radical Relay Strategy
摘要： Selective oxidation to produce target chemicals usually need activation of O2 at high temperature and/or pressure, which have largely restricted its practical operation and application. Here, we put forward a radical-relay strategy coupling photoelectrochemical (PEC) water oxidation towards efficiently selective conversion of benzyl alcohol (BA) to benzaldehyde (BAD). An illuminated BiVO4 (BVO) photoanode covered with an ultrathin (~3 nm) hydrothermally synthesized layered double hydroxide (U-LDH) catalyst and graphene (G) exhibited >99% selectivity to BAD (1.2 V vs. RHE). Mechanistic studies and DFT calculation verified that the hydroxyl radicals (?OH) generated from the oxidation of water are bound to the surface of U-LDH through hydrogen-bonding interactions and the energy is lowered. Fourier transform infrared spectroscopy showed that BA is adsorbed to the U-LDH catalyst, but BAD is not. Thus, the selectivity is not only favored by the controlled oxidation capacity of ?OH radicals, but the desorption of the desired product from the catalyst before further oxidation occurs. This work introduces an alternative PEC way to achieve mild and selective oxidation of BA derivatives based on ternary G@U-LDH@BVO catalysts.
关键词： radical relay,ultrathin LDH,aromatic alcohols,PEC water oxidation,selective activation
更新于2025-09-23 15:21:01
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Photonic Crystal Enhanced SERS Detection of Analytes Separated by Ultrathin Layer Chromatography Using a Diatom Frustule Monolayer
摘要： Diatoms are single-celled algae that biologically fabricate nanostructured silica shells with ordered pore arrays called frustules that resemble a 2D photonic crystal. A monolayer of Pinnularia frustules isolated from cell culture is deposited on a glass substrate and then conformally coated with silver nanoparticles (AgNPs) to serve as a nanostructured thin film for ultrathin layer chromatography (UTLC). Malachite green and Nile red are resolved in toluene mobile phase and the separated analytes are profiled micro-Raman spectroscopy, where plasmonic AgNPs provide surface-enhanced Raman scattering (SERS). The AgNP-diatom frustule monolayer improves SERS detection of malachite green by an average factor of 1.8 ± 0.1 over the plasmonic AgNP layer on glass. Analysis of hot spots on the AgNP-diatom frustule monolayer reveals that nearly 20% of the SERS active area intensifies the SERS signal at least tenfold over the SERS signal for AgNP on glass. Diatom-SERS enhancement is attributed to guided-mode resonances of the Raman laser source, which in turn further enhances the localized surface plasmonic resonance from AgNPs. Overall, the AgNP-diatom frustule monolayer thin film is a new functional material that uniquely enables separation of analytes by UTLC, quantitative SERS detection of separated analytes, and photonic enhancement of the SERS signals.
关键词： ultrathin layer chromatography,Raman,diatoms,surface-enhanced Raman scattering (SERS),photonic crystals
更新于2025-09-23 15:21:01
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Performance and stability enhancement of Cu(InGa)Se2 solar cells on ultrathin glass by potassium incorporation
摘要： Flexible Cu(InGa)Se2 solar cells fabricated on metal foils and plastics have achieved high conversion efficiency so far. However, metal impurities and low temperature tolerance hinder them from further considerable development. Here, 150 lm-thick ultrathin glass with desirable advantages was applied as substrate for Cu(InGa)Se2 solar cell. Potassium element was doped by a simple method during the post-selenization process. The results showed that the KInSe2 phase existed in K-doped Cu(InGa)Se2 films. The K-doped CIGS films were more compact than the pristine one due to the fact that K incorporated in films could form quasi-liquid alkali-metal-Se compounds and improve the compactness of films. K-incorporated CIGS films exhibited enhanced p-type conductivity and different surface energy level. Consequently, K-doped Cu(InGa)Se2 solar cell achieved an optimal efficiency of 8.3%, which was relatively 43% higher than that of pristine solar cell. Investigation of performance and stability of solar cells manifested that the K incorporation retarded the performance degradation of device during cyclic bending.
关键词： Potassium incorporation,Ultrathin glass,Cu(InGa)Se2,Thin films,Solar energy materials
更新于2025-09-23 15:21:01
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Ultrathin films of L1 <sub/>0</sub> -MnAl on GaAs (001): A hard magnetic MnAl layer onto a soft Mn-Ga-As-Al interface
摘要： Ferromagnetic MnAl (L10-MnAl phase) ultrathin films with thickness varying from 1 to 5 nm have been epitaxially grown on a GaAs (001) substrate. A coercivity above 8 kOe has been obtained with no need of a buffer layer by tuning the sample preparation and the growth parameters. Surface and interface analysis carried out by in situ characterization techniques (x-ray photoelectron spectroscopy and low energy electron diffraction), available in the molecular beam epitaxy chamber, has shown the formation of a ferromagnetic interface consisting of Mn-Ga-As-Al, which contribution competes with the MnAl alloyed film. The appearance of this interface provides important information to understand the growth mechanism of MnAl-based films reported in the literature.
关键词： x-ray photoelectron spectroscopy,ferromagnetic,GaAs,molecular beam epitaxy,low energy electron diffraction,ultrathin films,L10-MnAl
更新于2025-09-23 15:21:01
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Synthesis of BiOCl Nanosheets by a Simple Ultrasonic Route
摘要： Ternary bismuth oxyhalide (BiOX, X = F, Cl, Br, I) with layered structure have emerged as promising photocatalysts for water splitting and environmental remediation. Ultrathin BiOCl nanosheets were achieved by a simple ultrasound way. The product was characterized by XRD, SEM and TEM.
关键词： Ultrathin,Nanosheets,BiOX,Ultrasonic
更新于2025-09-23 15:21:01
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Ultrathin InP annular nanohole arrays for efficient light absorption solar cells
摘要： This Letter proposes ultrathin InP films consisting of annular nanohole arrays (ANAs) for highly efficient solar cells. By tailoring the inner and outer radii of ANAs properly and combining antireflection coating (ZnO) and back-reflector (Ag), the photocurrent generated in the InP based dielectric-semiconductor-metal (DSM) configuration can be increased dramatically by 124.6% with respect to the planar solar cell of equal geometric thickness (100 nm). The fact that the DSM-ANA structure is able to harvest broadband and wide-angle incident light can be attributed to the excitation of leaky waveguide modes, Bloch modes, and surface plasmon polariton modes. This work provides a promising and feasible way to design and fabricate efficient ultrathin InP photovoltaic and other optoelectronic devices.
关键词： light absorption,ultrathin InP films,dielectric-semiconductor-metal configuration,annular nanohole arrays,surface plasmon polariton modes,solar cells
更新于2025-09-23 15:19:57
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Energy band alignment in molybdenum oxide/ Cu(In,Ga)Se2 interface for high efficiency ultrathin Cu(In,Ga)Se2 solar cells from low-temperature growth
摘要： In this work, the molybdenum oxide (MoOx) was employed as a back contact layer to improve the device performance of ultrathin Cu(In,Ga)Se2 (CIGS) solar cells with CIGS absorber synthesized through the low-temperature three-stage co-evaporation process. This contribution focuses on the investigation of the inherent mechanisms and the improved device performance in detail. Our research shows that the energy band of the CIGS/Mo interface can be tuned and the Schottky barrier can be reduced. Compared with the reference sample without MoOx, the back barrier height of the new device with 10 nm MoOx enjoys a significant decrease from 43.83 meV to 15.98 meV because of the improvement of energy band structure. Meanwhile, the results of wxAMPS simulation corroborate that the energy band bends upward in the devices with appropriate thickness of MoOx films, which facilitates the carrier transportation and suppresses the recombination of charge carriers at the MoOx/Cu(In,Ga)Se2 interface. Moreover, the carriers can transport through the MoOx/CIGS interface by tunneling when the MoOx film is thin enough. Finally, by controlling the thicknesses of MoOx films, an efficiency of 10.38 % is achieved in 0.5 μm CIGS solar cells by optimizing the MoOx thickness under the low-temperature three-stage co-evaporation process.
关键词： ultrathin,Cu(In,Ga)Se2,MoOx,low-temperature,energy band
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Equivalent Circuit For AC Response of Cu(In,Ga)Se <sub/>2</sub> Thin Film Solar Cells
摘要： Ultrathin Cu(In,Ga)Se2 (CIGS) is desired to reduce production costs of CIGS solar cells. The present work aims to study the AC electrical response of standard-thick, ultrathin and passivated ultrathin devices. Admittance measurements allow to choose the AC equivalent circuit for each type of CIGS device. It is of utmost importance to understand the AC electrical behavior of each device, as the differences between reference thick, reference ultrathin and passivated ultrathin CIGS solar cells are yet to be fully understood. The analyses show a simpler AC equivalent circuit for the reference ultrathin device, which is explained by the lowered bulk recombination for thin film CIGS solar cells when compared with thick ones. The importance of shunts mitigation by the use of a passivation layer is also demonstrated, with a shunt resistance increase for the passivation device compared to both reference devices.
关键词： admittance,Cu(In,Ga)Se2,recombination,ultrathin solar cells
更新于2025-09-23 15:19:57