96 research outputs found
Atomic layer deposition of HfO2 on graphene from HfCl4 and H20
Atomic layer deposition of ultrathin HfO2 on unmodified graphene from HfCl4
and H2O was investigated. Surface RMS roughness down to 0.5 nm was obtained for
amorphous, 30 nm thick hafnia film grown at 180 degrees C. HfO2 was deposited
also in a two-step temperature process where the initial growth of about 1 nm
at 170 degrees C was continued up to 10-30 nm at 300 degrees C. This process
yielded uniform, monoclinic HfO2 films with RMS roughness of 1.7 nm for 10-12
nm thick films and 2.5 nm for 30 nm thick films. Raman spectroscopy studies
revealed that the deposition process caused compressive biaxial strain in
graphene whereas no extra defects were generated. An 11 nm thick HfO2 film
deposited onto bilayer graphene reduced the electron mobility by less than 10%
at the Dirac point and by 30-40% far away from it.Comment: 4 figures, accepted by CEJ
Correlated Photon Emission from a Single II-VI Quantum Dot
We report correlation and cross-correlation measurements of photons emitted
under continuous wave excitation by a single II-VI quantum dot (QD) grown by
molecular-beam epitaxy. A standard technique of microphotoluminescence combined
with an ultrafast photon correlation set-up allowed us to see an antibunching
effect on photons emitted by excitons recombining in a single CdTe/ZnTe QD, as
well as cross-correlation within the biexciton ()-exciton ()
radiative cascade from the same dot. Fast microchannel plate photomultipliers
and a time-correlated single photon module gave us an overall temporal
resolution of 140 ps better than the typical exciton lifetime in II-VI QDs of
about 250ps.Comment: 4 pages, 3 figures, to appear in Appl. Phys. Let
Operando deconvolution of photovoltaic and electrocatalytic performance in ALD TiO2 protected water splitting photocathodes
The dual-working-electrode technique enables the deconvolution of the intrinsic properties of the buried p–n junction and the electrocatalyst on the surface for water splitting photocathodes
Coherence Length of Excitons in a Semiconductor Quantum Well
We report on the first experimental determination of the coherence length of
excitons in semiconductors using the combination of spatially resolved
photoluminescence with phonon sideband spectroscopy. The coherence length of
excitons in ZnSe quantum wells is determined to be 300 ~ 400 nm, about 25 ~ 30
times the exciton de Broglie wavelength. With increasing exciton kinetic
energy, the coherence length decreases slowly. The discrepancy between the
coherence lengths measured and calculated by only considering the acoustic
phonon scattering suggests an important influence of static disorder.Comment: 4 Pages, 4 figure
Solution phase treatments of SbSe heterojunction photocathodes for improved water splitting performance
Antimony selenide (SbSe) is an auspicious material for solar energy conversion that has seen rapid improvement over the past ten years, but the photovoltage deficit remains a challenge. Here, simple and low-temperature treatments of the p–n heterojunction interface of SbSe/TiO-based photocathodes for photoelectrochemical water splitting were explored to address this challenge. The FTO/Ti/Au/SbSe (substrate configuration) stack was treated with (NH)S as an etching solution, followed by CuCl treatment prior to deposition of the TiO by atomic layer deposition. The different treatments show different mechanisms of action compared to similar reported treatments of the back Au/SbSe interface in superstrate configuration solar cells. These treatments collectively increased the onset potential from 0.14 V to 0.28 V vs. reversible hydrogen electrode (RHE) and the photocurrent from 13 mA cm to 18 mA cm at 0 V vs. RHE as compared to the untreated SbSe films. From SEM and XPS studies, it is clear that the etching treatment induces a morphological change and removes the surface SbSe layer, which eliminates the Fermi-level pinning that the oxide layer generates. CuCl further enhances the performance due to the passivation of the surface defects, as supported by density functional theory molecular dynamics (DFT-MD) calculations, improving charge separation at the interface. The simple and low-cost semiconductor synthesis method combined with these facile, low-temperature treatments further increases the practical potential of SbSe for large-scale water splitting
Robust High-performance Dye-sensitized Solar Cells Based on Ionic Liquid-sulfolane Composite Electrolytes
Novel ionic liquid-sulfolane composite electrolytes based on the 1,2,3-triazolium family of ionic liquids were developed for dye-sensitized solar cells. The best performing device exhibited a short-circuit current density of 13.4 mA cm(-2), an open-circuit voltage of 713 mV and a fill factor of 0.65, corresponding to an overall power conversion efficiency (PCE) of 6.3%. In addition, these devices are highly stable, retaining more than 95% of the initial device PCE after 1000 hours of light-and heat-stress. These composite electrolytes show great promise for industrial application as they allow for a 14.5% improvement in PCE, compared to the solvent-free eutectic ionic liquid electrolyte system, without compromising device stability
Impedance spectroscopy of Sb<sub>2</sub>Se<sub>3</sub> photovoltaics consisting of (Sb<sub>4</sub>Se<sub>6</sub>)<sub><i>n</i></sub> nanoribbons under light illumination.
Sb2Se3, consisting of one-dimensional (Sb4Se6)n nanoribbons has drawn attention as an intriguing light absorber from the photovoltaics (PVs) research community. However, further research is required on the performance-limiting factors in Sb2Se3 PVs. In this study, we investigated the charge carrier behavior in Sb2Se3 PVs by impedance spectroscopy (IS) under light illumination. (Sb4Se6)n nanoribbons with two different orientations were used to investigate the effect of crystal orientation on the device performance. Regardless of the (Sb4Se6)n orientation, negative capacitance was observed at forward bias, representing a recombination pathway at the TiO2/Sb2Se3 interface. A comparison of the recombination resistances and lifetimes of two different Sb2Se3 PVs showed that a better interface could be formed by placing the (Sb4Se6)n ribbons parallel to the TiO2 layer. Based on these observations, an ideal structure of the Sb2Se3/TiO2 interface is proposed, which will enhance the performance of Sb2Se3 PVs toward its theoretical limit
Space GlucoseControl system for blood glucose control in intensive care patients:a European multicentre observational study
Post-Synthetic Silver Ion and Sulfurization Treatment for Enhanced Performance in Sb2Se3 Water Splitting Photocathodes
In the past decade, antimony selenide (Sb2Se3) has made significant progress as a solar energy conversion material. However, the photovoltage deficit continues to pose a challenge and is a major hurdle that must be overcome to reach its maximum solar conversion efficiency. In this study, various post-synthetic treatments are employed, of which the combination of a solution phase silver nitrate treatment and sulfurization has shown to be the most effective approach to mitigate the photovoltage deficit in this Sb2Se3-based device. A significant enhancement in the photovoltage is observed after the treatments, as evident by the increase in the onset potential from 0.18 to 0.40 V versus reversible hydrogen electrode. Multiwavelength Raman shows that combining these two treatments removes amorphous Se and metallic Sb from the surface and yields a high-quality surface layer of Sb2(S1−x, Sex)3 on the bulk Sb2Se3 photoabsorber layer. X-ray photoelectron spectroscopy with depth profiling reveals extensive incorporation of silver into the film. Density functional theory calculations suggest that silver ions can intercalate between the [Sb4Se6]n ribbons and remain in the Ag+ state. This effective treatment combination brings the practicality of the Sb2Se3 photocathode for water splitting one step closer to large-scale applications
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