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Zhang, Chuang

Publications and source records attributed to Zhang, Chuang.

9 records
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DOE OSTI2023

Dark Exciton in 2D Hybrid Halide Perovskite Films Revealed by Magneto-Photoluminescence at High Magnetic Field

Here, a comprehensive study of the exciton fine structure (EFS) is presented in 2D-phenethylammonium lead iodide films using magnetic field-induced polarization of photoluminescence (PL) in both Faraday and Voigt configurations at fields up to 25 Tesla. Three exciton bands are identified in the PL spectrum associated with bound, dark, and bright excitons, respectively. Under a high magnetic field in Faraday/Voigt configuration, large field-induced circular/linear polarization is observed in the PL band related to the dark exciton, which is magnetically activated. Furthermore, it is found that the dark exciton has an anomalous field-induced circular polarization, which cannot be explained by the classical Boltzmann distribution of spin-polarized species. These findings are well explained by an effective mass model that includes exchange terms unique to the monoclinic symmetry as a perturbation of the EFS in the approximate tetragonal symmetry. It is also confirmed that the field-induced linear polarization is sensitive to the monoclinic exchange term, whereas the field-induced circular polarization is immune to such term.

14 SOLAR ENERGY↗
DOE OSTI2019

Surface-enhanced spin current to charge current conversion efficiency in CH3NH3PbBr3-based devices

Hybrid organic-inorganic perovskites have shown great promise for spintronic applications due to their large spin-orbit coupling induced by the Pb and halogen atoms. Particularly, the large observed surface-induced Rashba splitting in CH3NH3PbBr3 indicates efficient spin-current-to-charge-current (StC) conversion, which, however, has not been demonstrated yet. In this work, the StC conversion efficiency in ferromagnet/CH3NH3PbBr3-based devices is studied using the pulsed spin-pumping technique measured by the inverse spin Hall effect. We found that the StC conversion efficiency is anomalous in that it increases at small perovskite layer thickness. This indicates the existence of a surface-dominated StC mechanism such as the inverse Rashba-Edelstein effect. By inserting a thin LiF layer between the ferromagnet and the perovskite film, the StC conversion efficiency is greatly suppressed, validating the existence of a Rashba surface in the CH3NH3PbBr3 film.

Sun, Dali (ORCID:0000000346623265)↗
DOE OSTI2019

Tunable Spin Characteristic Properties in Spin Valve Devices Based on Hybrid Organic–Inorganic Perovskites

The hybrid organic–inorganic perovskites (HOIPs) form a new class of semiconductors which show promising optoelectronic device applications. Remarkably, the optoelectronic properties of HOIP are tunable by changing the chemical components of their building blocks. Recently, the HOIP spintronic properties and their applications in spintronic devices have attracted substantial interest. Here the impact of the chemical component diversity in HOIPs on their spintronic properties is studied. Additionally, spin valve devices based on HOIPs with different organic cations and halogen atoms are fabricated. The spin diffusion length is obtained in the various HOIPs by measuring the giant magnetoresistance (GMR) response in spin valve devices with different perovskite interlayer thicknesses. In addition spin lifetime is also measured from the Hanle response. It is found that the spintronic properties of HOIPs are mainly determined by the halogen atoms, rather than the organic cations. The study provides a clear avenue for engineering spintronic devices based on HOIPs.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Spin-optoelectronic devices based on hybrid organic-inorganic trihalide perovskites

Recently the hybrid organic-inorganic trihalide perovskites have shown remarkable performance as active layers in photovoltaic and other optoelectronic devices. However, their spin characteristic properties have not been fully studied, although due to the relatively large spin-orbit coupling these materials may show great promise for spintronic applications. Here we demonstrate spin-polarized carrier injection into methylammonium lead bromide films from metallic ferromagnetic electrodes in two spintronic-based devices: a ‘spin light emitting diode’ that results in circularly polarized electroluminescence emission; and a ‘vertical spin valve’ that shows giant magnetoresistance. In addition, we also apply a magnetic field perpendicular to the injected spins orientation for measuring the ‘Hanle effect’, from which we obtain a relatively long spin lifetime for the electrically injected carriers. Our measurements initiate the field of hybrid perovskites spin-related optoelectronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Optical Properties of Two-Dimensional Perovskite Films of (C 6 H 5 C 2 H 4 NH 3 ) 2 [PbI 4 ] and (C 6 H 5 C 2 H 4 NH 3 ) 2 (CH 3 NH 3 ) 2 [Pb 3 I 10 ]

The temperature dependence of absorption and photoluminescence (PL) spectroscopies were used to study the optical properties of 2D perovskite films, including n = 1 and 3 of (PEA) 2 (CH 3 NH 3 ) n-1 [Pb n I 3n+1 ] (PEA = C 6 H 5 (CH 2 ) 2 NH 3 ). In (PEA) 2 [Pb 1 I 4 ] (PEPI), excitons coupling to optical phonons with an average energy of ~30 meV dominate the photophysics of absorption and PL. (PEA) 2 (CH 3 NH 3 ) 2 [Pb 3 I 10 ] (shortened as PMPI 3 ), nominally prepared as n = 3, actually was a mixture of multiple layered perovskites with various n. In absorption, a PMPI 3 film presents respective n materials' excitonic features, coupling to phonons with an average energy of ~30 meV; in analyzing PL peaked singly at ~1.6 eV and its width as a function of temperature, we found that PMPI 3 behaves like PEPI at around 80 K but like 3D perovskite near room temperature, with three times larger electron-phonon interaction strength compared to that in PEPI.

14 SOLAR ENERGY↗
DOE OSTI2017

CEPC booster design study

In September 2012, Chinese scientists proposed a Circular Electron Positron Collider (CEPC) in China at 240 GeV center-of-mass energy for Higgs studies. The booster provides 120 GeV electron and positron beams to the CEPC collider for top-up injection at 0.1 Hz. The design of the full energy booster ring of the CEPC is a challenge. The ejected beam energy is 120 GeV and the injected beam energy is 6 GeV. Here in this paper we describe two alternative schemes, the wiggler bend scheme and the normal bend scheme. For the wiggler bend scheme, we propose to operate the booster ring as a large wiggler at low energy and as a normal ring at high energy to avoid the problem of very low dipole magnet fields. Finally, for the normal bend scheme, we implement the orbit correction to correct the earth field.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗