Search results for "vacuum"
showing 10 items of 352 documents
Dual-source vacuum deposition of pure and mixed halide 2D perovskites: thin film characterization and processing guidelines
2020
The dual-source vacuum deposition of 2D perovskite films of the type PEA2PbX4, (PEA = phenethylammonium and X = I−, Br−, or a combination of both) is presented. Low-temperature deposited 2D perovskite films showed high crystallinity with the expected trend of bandgap as a function of halide type and concentration. Importantly, we observed an unavoidable halide cross-contamination among different deposition runs, as well as a strong dependence of the material quality on the type of halide precursors used. These findings should be taken into account in the development of vacuum processing for low-dimensional mixed halide perovskites.
Efficient Wide-Bandgap Mixed-Cation and Mixed-Halide Perovskite Solar Cells by Vacuum Deposition
2021
Vacuum deposition methods are increasingly applied to the preparation of perovskite films and devices, in view of the possibility to prepare multilayer structures at low temperature. Vacuum-deposited, wide-bandgap solar cells based on mixed-cation and mixed-anion perovskites have been scarcely reported, due to the challenges associated with the multiple-source processing of perovskite thin films. In this work, we describe a four-source vacuum deposition process to prepare wide-bandgap perovskites of the type FA1-n Cs n Pb(I1-x Br x )3 with a tunable bandgap and controlled morphology, using FAI, CsI, PbI2, and PbBr2 as the precursors. The simultaneous sublimation of PbI2 and PbBr2 allows the…
Vacuum-Deposited Multication Tin-Lead Perovskite Solar Cells
2020
The use of a combination of tin and lead is the most promising approach to fabricate narrow bandgap metal halide perovskites. This work presents the development of reproducible tin and lead perovskites by vacuum co-deposition of the precursors, a solvent-free technique which can be easily implemented to form complex stacks. Crystallographic and optical characterization reveal the optimal film composition based on cesium and methylammonium monovalent cations. Device optimization makes use of the intrinsically additive nature of vacuum deposition, resulting in solar cells with 8.89% photovoltaic efficiency. The study of the devices by impedance spectroscopy identifies bulk recombination as on…
Achieving high effectiveQ-factors in ultra-high vacuum dynamic force microscopy
2010
The effective Q-factor of the cantilever is one of the most important figures-of-merit for a non-contact atomic force microscope (NC-AFM) operated in ultra-high vacuum (UHV). We provide a comprehensive discussion of all effects influencing the Q-factor and compare measured Q-factors to results from simulations based on the dimensions of the cantilevers. We introduce a methodology to investigate in detail how the effective Q-factor depends on the fixation technique of the cantilever. Fixation loss is identified as a most important contribution in addition to the hitherto discussed effects and we describe a strategy for avoiding fixation loss and obtaining high effective Q-factors in the forc…
Reduction of low-frequency 1/f noise in Al-AlOx-Al tunnel junctions by thermal annealing
2010
We report that annealing Al-AlOx-Al tunnel junctions in a vacuum chamber at temperature of 400C reduces the characteristic 1/f noise in the junctions, in some cases by an order of magnitude. Both ultra high vacuum and high vacuum fabricated samples demonstrated a significant reduction in the 1/f noise level. Temperature dependence of the noise was studied between 4.2 and 340 Kelvin, with a linear dependence below 100 K, but a faster increase above. The results are consistent with a model where the density of charge trapping two level-systems within the tunneling barrier is reduced by the annealing process.
Vacuum-ultraviolet absorption of amorphousSiO2: Intrinsic contribution and role of silanol groups
2008
We present a study on the vacuum-ultraviolet (VUV) absorption properties of amorphous ${\text{SiO}}_{2}$ $(a{\text{-SiO}}_{2})$ with high concentrations of silanol groups (Si-OH). We found that the absorption spectra are made up of a couple of exponential profiles. The first, in the range from $\ensuremath{\sim}7.5$ to $\ensuremath{\sim}8.1\text{ }\text{eV}$, was attributed to Si-OH group absorption, while the second, in the range from $\ensuremath{\sim}8.1$ to $\ensuremath{\sim}8.25\text{ }\text{eV}$, was ascribed to the intrinsic absorption. The VUV absorption cross section of Si-OH groups in $a{\text{-SiO}}_{2}$ was determined as well. The intrinsic absorption was found to be affected by…
Impact of a cryogenic baffle system on the suppression of radon-induced background in the KATRIN Pre-Spectrometer
2018
The KATRIN experiment will determine the effective electron anti-neutrino mass with a sensitivity of 200 meV/c2 at 90% CL. The energy analysis of tritium β-decay electrons will be performed by a tandem setup of electrostatic retarding spectrometers which have to be operated at very low background levels of <10−2 counts per second. This benchmark rate can be exceeded by background processes resulting from the emanation of single 219,220Rn atoms from the inner spectrometer surface and an array of non-evaporable getter strips used as main vacuum pump. Here we report on the impact of a cryogenic technique to reduce this radon-induced background in electrostatic spectrometers. It is based on ins…
Single-Source Vacuum Deposition of Mechanosynthesized Inorganic Halide Perovskites
2018
Fully inorganic cesium lead halide perovskite thin films were prepared by an easy, fast and dry process based on single-source vacuum deposition. We investigated the structural and optical characteristics of the so-formed films as a function of chemical composition (chloride, bromide and iodide films were formed), post-deposition thermal annealing, as well as previous mechanosynthesis of perovskite powders. We found out that the CsPbX3 perovskite was preferentially formed for the smaller halides and favored by previous ball-milling of CsX and PbX2 precursors. When bigger halides were used and/or CsX and PbX2 precursors were simply mixed without previous mechanosynthesis, PbX2-rich compounds…
Effects of ball-milling on the hydrogen sorption properties of LaNi5
2009
Abstract Pressure–composition isotherms of LaNi 5 alloys were studied as function of ball-milling time. Results indicate that ball-milling convert a part of the LaNi 5 to a non-absorbing state—a state which does not absorb hydrogen under conditions where un-milled LaNi 5 powders absorb and transform to LaNi 5 H 6 , in addition to particle size reduction and creation of defects. The non-absorbing fraction in the milled sample is found to grow with increase in the ball-milling time. The resistance to the hydride formation of the long-time ball-milled LaNi 5 samples is found to continue even after a 1-h high vacuum annealing at around 1000 K. This indicates that the hydrogen-absorption-resist-…
Study of Gasdynamic Electron Cyclotron Resonance Plasma Vacuum Ultraviolet Emission to Optimize Negative Hydrogen Ion Production Efficiency
2019
Negative hydrogen ion sources are used as injectors into accelerators and drive the neutral beam heating in ITER. Certain processes in low-temperature hydrogen plasmas are accompanied by the emission of vacuum ultraviolet (VUV) emission. Studying the VUV radiation therefore provides volumetric rates of plasma-chemical processes and plasma parameters. In the past we have used gasdynamic ECR discharge for volumetric negative ion production and investigated the dependencies between the extracted H$^-$ current density and various ion source parameters. It was shown that it is possible to reach up to 80 mA/cm$^2$ of negative ion current density with a two electrode extraction. We report experime…