DIY electrodynamic trap for physics education

We present a simple and affordable method for making a surface electrodynamic trap for microparticles. The principles of electrodynamic trapping of charged particles are discussed and step-by-step instructions on how to make a surface trap are given. In addition to the electrodynamic trap implementation and operation process, options for its further use are proposed. The work may be of interest to physics teachers as a material for practical work, for the formation of students’ skills in performing a physical experiment.

Efficient Infrared Emission of Colloidal PbSe Nanoplatelets by Lateral Size Control

Colloidal two-dimensional (2D) lead chalcogenide nanoplatelets (NPLs) represent highly interesting materials for near- and short wave-infrared applications including innovative glass fiber optics exhibiting negligible attenuation. In this work, we demonstrate a direct synthesis route for 2D PbSe NPLs with cubic rock salt crystal structure at low reaction temperatures of 0 °C and room temperature. A lateral size tuning of the PbSe NPLs by controlling the temper-ature and by adding small amounts of octylamine to the reaction leads to excitonic absorption features in the range of 800 – 1000 nm (1.6 – 1.3 eV) and narrow photoluminescence (PL) seamlessly covering the broadband infrared spec-tral window of 900 – 1450 nm (1.4 – 0.9 eV). The PL quantum yield of the as-synthesized PbSe NPLs is more than doubled by a postsynthetic treatment with CdCl2 (e.g. from 14.7 % to 37.4 % for NPLs emitting at 980 nm with a FWHM of 214 meV). An analysis of the slightly asymmetric PL line shape of the PbSe NPLs and their characterization by ultrafast transient absorption and time-resolved PL spectroscopy reveal a surface trap related PL contribution which is successfully reduced by the CdCl2 treatment from 40 % to 15 %. Our results open up new pathways for a direct synthesis and straightforward incorporation of colloidal PbSe NPLs as efficient infrared emitters at technologi-cally relevant telecommunication wavelengths.

Mitigating the charge trapping effects of D-sorbitol/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) polymer blend contacts to crystalline silicon

Solution-processable conductive polymers are advantageous materials for making inexpensive, electrical junctions to crystalline semiconductors. We have investigated methods to improve the device performance of hybrid solar cells made from n-type silicon and a conductive polymer glue based on a blend of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and D-sorbitol. The PEDOT:PSS blend behaves like a high work function metal creating a Schottky-type junction. The addition of D-sorbitol increases PEDOT:PSS conductivity and provides adhesive properties, allowing the top contact of the solar cell to be laminated onto the silicon substrate. Unfortunately, the addition of the D-sorbitol to the PEDOT:PSS significantly alters the shape of the measured current-voltage performance curve of a crystalline silicon (n-Si)/PEDOT:PSS junction. Under illumination, this results in a decline in the fill factor (FF) and a drop in photocurrent density (J sc) compared to PEDOT:PSS-only devices. We have discovered that the decline in device performance is likely due to surface trap states caused by D-sorbitol/silicon interaction and/or silicon oxidation. X-ray photoelectron spectroscopic (XPS) analysis shows that surface oxidation quickens, and possible silicon surface functionalization with D-sorbitol occurs while processing the D-sorbitol/PEDOT:PSS contact on H-terminated surfaces. To overcome these interface issues, the silicon surface was chemically modified using surface methylation, making it insensitive to D-sorbitol/silicon interactions and surface oxidation during the processing of the PEDOT:PSS polymer blend contact. This also enabled the crystalline silicon (n-Si)/s-PEDOT:PSS device performance to be maintained for longer periods. Using a silicon surface methylation strategy, good device performance could be achieved without changing the adhesive properties of D-sorbitol/PEDOT:PSS polymer blend.

Air-Resistant Lead Halide Perovskite Nanocrystals Embedded into Polyimide of Intrinsic Microporosity

Although cesium lead halide perovskite (CsPbX3, X = Cl, Br, or I) nanocrystals (PNCs) have been rapidly developed for multiple optoelectronic applications due to their outstanding optical and transport properties, their device fabrication and commercialization have been limited by their low structural stability, especially under environmental conditions. In this work, a new approach has been developed to protect the surface of these nanocrystals, which results in enhanced chemical stability and optical properties. This method is based on the encapsulation of CsPbX3 NCs into a polyimide with intrinsic microporosity (PIM-PI), 4,4′-(hexafluoroisopropylidene)diphthalic anhydride reacted with 2,4,6-trimethyl-m-phenylenediamine (6FDA-TrMPD). The presence of 6FDA-TrMPD as a protective layer can efficiently isolate NCs from an air environment and subsequently enhance their optical and photoluminescence stability. More specifically, comparing NCs treated with a polymer to as-synthesized nanocrystals after 168 h, we observe that the PL intensity decreased by 70% and 20% for the NCs before and after polymer treatment. In addition, the PNC film with a polymer shows a much longer excited-state lifetime than the as-synthesized nanocrystals, indicating that the surface trap states are significantly reduced in the treated PNCs. The enhancement in chemical and air stability, as well as optical behavior, will further improve the performance of CsPbBr3 PNCs yielding promising optical devices and paving the way for their production and implementation at a large scale.

Dimensional Roadmap for Maximizing the Piezoelectrical Response of ZnO Nanowire-Based Transducers: Impact of Growth Method

ZnO nanowires are excellent candidates for energy harvesters, mechanical sensors, piezotronic and piezophototronic devices. The key parameters governing the general performance of the integrated devices include the dimensions of the ZnO nanowires used, their doping level, and surface trap density. However, although the method used to grow these nanowires has a strong impact on these parameters, its influence on the performance of the devices has been neither elucidated nor optimized yet. In this paper, we implement numerical simulations based on the finite element method combining the mechanical, piezoelectric, and semiconducting characteristic of the devices to reveal the influence of the growth method of ZnO nanowires. The electrical response of vertically integrated piezoelectric nanogenerators (VING) based on ZnO nanowire arrays operating in compression mode is investigated in detail. The properties of ZnO nanowires grown by the most widely used methods are taken into account on the basis of a thorough and comprehensive analysis of the experimental data found in the literature. Our results show that the performance of VING devices should be drastically affected by growth method. Important optimization guidelines are found. In particular, the optimal nanowire radius that would lead to best device performance is deduced for each growth method.

Investigating in novel CdZnSe/CdSe/CdZnSe quantum well with 97% PLQY

Thick-shell not only provides colloidal quantum dots (QDs) stability and workability, but also plays a significant role in passivation of QDs surface defects and change of electron transport characteristics of QDs. Here, the dedicated design and synthesis of high luminescence CdZnSe/CdSe/CdZnSe quantum wells are reported by precisely controlled shell growth. By tuning the thicknesses of the CdSe and CdZnSe layers, photoluminescence quantum yields (PLQY) can be attained a maximum of 97% as the CdSe shell thickness is 4 monolayers and the CdZnSe shell thickness is 10 monolayers. These gradient thick shell CdZnSe/CdSe/CdZnSe quantum wells confirm the suppression of surface trap-state emission in gradient core/shell structures. Superior optical properties render CdZnSe/CdSe/CdZnSe quantum wells suitable for use in solid-state lightings.