Switching of K-Q intervalley trions fine structure and their dynamics in n-doped monolayer WS_(2)

Monolayer group VI transition metal dichalcogenides(TMDs)have recently emerged as promising candidates for photonic and opto-valleytronic applications.The optoelectronic properties of these atomically-thin semiconducting crystals are strongly governed by the tightly bound electron-hole pairs such as excitons and trions(charged excitons).The anomalous spin and valley configurations at the conduction band edges in monolayer WS_(2)give rise to even more fascinating valley many-body complexes.Here we find that the indirect Q valley in the first Brillouin zone of monolayer WS_(2)plays a critical role in the formation of a new excitonic state,which has not been well studied.By employing a high-quality h-BN encapsulated WS_(2)field-effect transistor,we are able to switch the electron concentration within K-Q valleys at conduction band edges.Consequently,a distinct emission feature could be excited at the high electron doping region.Such feature has a competing population with the K valley trion,and experiences nonlinear power-law response and lifetime dynamics under doping.Our findings open up a new avenue for the study of valley many-body physics and quantum optics in semiconducting 2D materials,as well as provide a promising way of valley manipulation for next-generation entangled photonic devices.

一种简便快速的制备水稻基因组DNA PCR模板的方法

目的:发展一种简便快速的制备水稻基因组DNA PCR模板的方法。方法:用枪头捣碎水稻叶片代替液氮研磨法提取水稻基因组DNA作PCR模板,在去污剂SDS和表面活性剂TrionX-100的存在下在沸水中煮沸10min,然后取上清扩增微管蛋白(TubA1)基因内含子。结果:发现在利用煮沸法提取水稻基因组DNA的过程中,用枪头捣碎叶片可代替液氮碾磨,加入0.1%表面活性剂TrionX-100煮沸叶片对制备模板有促进效果,得到了预期的PCR片断。结论:该方法快速、简便、经济,具有良好的重复性与特异性,便于自动化。

电子-电子相互作用对trion静态性质的影响

基于一维紧束缚SSH模型和扩展的Hubbard模型,采用非绝热分子动力学方法,在非限制性Hartree-Fock(HF)平均场近似下,研究了三粒子复合体trion的静态性质.trion比极化子、双极化子具有更大的束缚能、稳定性和有效质量;电子-声子耦合和电子间相互作用均增强trion的局域度,并导致其有效质量增大,稳定性增强.

New Organic Montmorillonite Preparation: Anion-Nonionic Surfactants Modified Montmorillonites

Montmorillonites (MMT) was modified with nonionic surfactant Trion X-100 (OP-10) and anionic surfactants sodium stearate (SSTA) and sodium dodecyl benzene sulfonate (SDBS) respectively. In this study, the effects of anionic surfactant types and MMT types on modification montmorillonite were investigated. XRD analysis results showed that SSTA/OP-10/MMT and SDBS/OP-10/MMT were successfully obtained. The basal spacing of SSTA/OP-10/MMT reached 5.07nm and the SSTA intercalation reaction was relatively stable. Different types of MMT (Xinjiang natural sodium montmorillonite(MMT-1), Jianping sodium montmorillonite (MMT-2) and artificial sodium montmorillonite(MMT-3)) were modified with SSTA/OP-10. XRD test results showed that MMT-1, MMT-2 and MMT-3 can be modified by SSTA/OP-10. Anion-nonionic organic montmorillonite (SSTA/OP-10/MMT-1, SSTA/OP-10/MMT-2 and SSTA/OP-10/MMT-3 were successfully obtained respectively. The higher expansion capacity was found to be beneficial to organic modification.

Long-lived Single Excitons, Trions, and Biexcitons in CdSe/CdTe Type-II Colloidal Quantum Wells

Light-harvesters with long-lived excited states are desired for efficient solar energy conversion systems. Many solar-to-fuel conversion reactions, such as H2 evolution and CO2 reduction, require multiple sequential electron transfer processes, which leads to a complicated situation that excited states involves not only excitons （electron-hole pairs） but also multi-excitons and charged excitons. While long-lived excitons can be obtained in various systems （e.g., semiconductor nanocrystals）, multi-excitons and charged excitons are typically shorted-lived due to nonradiative Auger recombination pathways whereby the recombination energy of an exciton is quickly transferred to the third carrier on a few to hundreds of picoseconds timescale. In this work, we report a study of excitons, trions （an exciton plus an additional charge）, and biexcitons in CdSe/CdTe colloidal quantum wells or nanoplatelets. The type- II band alignment effectively separates electrons and holes in space, leading to a single exciton lifetime of 340 ns which is -2 order of magnitudes longer than that in plane CdSe nanoplatelets. More importantly, the electron-hole separation also dramatically slows down Auger decay, giving rise to a trion lifetime of 70 ns and a biexciton lifetime of 11 ns, among the longest values ever reported for colloidal nanocrystals. The long-lived exciton, trion, and biexciton states, combined with the intrinsically strong light-absorption capability of two-dimensional systems, enable the CdSe/CdTe type-II nanoplatelets as promising light harvesters for efficient solar-to-fuel conversion reactions.

Thickness-dependent excitonic properties of atomically thin 2H-MoTe2

Two-dimensional(2D)2H-MoTe2 is a promising semiconductor because of its small bandgap,strong absorption,and low thermal conductivity.In this paper,we systematically study the optical and excitonic properties of atomically thin 2H-MoTe2(1–5 layers).Due to the fact that the optical contrast and Raman spectra of 2H-MoTe2 with different thicknesses exhibit distinctly different behaviors,we establish a quantitative method by using optical images and Raman spectra to directly identify the layers of 2H-MoTe2 thin films.Besides,excitonic states and binding energy in monolayer/bilayer 2H-MoTe2 are measured by temperature-dependent photoluminescence(PL)spectroscopy.At temperature T=3.3 K,we can observe an exciton emission at^1.19 eV and trion emission at^1.16 eV for monolayer 2H-MoTe2.While at room temperature,the exciton emission and trion emission both disappear for their small binding energy.We determine the exciton binding energy to be 185 meV(179 meV),trion binding energy to be 20 meV(18 me V)for the monolayer(bilayer)2H-MoTe2.The thoroughly studies of the excitonic states in atomically thin 2H-MoTe2 will provide guidance for future practical applications.

Negative Trions Trapped by a Spherical Parabolic Quantum Dot

In this paper, a negatively charged exciton trapped by a spherical parabolic quantum dot has been investigated. The energy spectra of low-lying states are calculated by means of matrix diagonalization. The important feature of the low-lying states of the negatively charged excitons in a spherical quantum dot is obtained via an analysis of the energy spectra.

印度Bodal化学收购Trion化学的全部股份

印度Bodal化学公司于2020年2月17日宣布,已收购印度Trion化学(TCPL)的全部股份。该交易以5871万印度卢比(819103美元)成交。Bodal化学公司早些时候购买了TCPL 59%的股份,使TCPL成为Bodal的全资子公司。Bodal表示,收购TCPL是为了扩大特种化学品业务。它主要生产染料中间体和染料,用于纺织、造纸、皮革等行业。2019年,TCPL的销售额达到了1.6173亿卢比。

Dynamics of Exciton Transport in Two-Dimensional Materials

In recent years,two-dimensional(2D)materials have attracted extensive interests due to the large exciton binding energy different from bulk materials.Many peculiar properties have been discovered that have farreaching perspectives in the next generation of optoelectronic devices.In this review,we introduce the forms of exciton existence in 2D materials and several promising 2D materials with good applications at first.Then,we summarize relevant contemporary tools for probing exciton dynamics and methods of regulating 2D exciton transport,for instance,electrical regulation,stress/surface wave regulation and moirépotential regulation,etc.Finally,we conclude the general development of regulation in 2D materials and propose several possible opportunities of application prospect.

Strain-induced direct-indirect bandgap transition and phonon modulation in monolayer WS2

In situ strain photoluminescence （PL） and Raman spectroscopy have been employed to exploit the evolutions of the electronic band structure and lattice vibrational responses of chemical vapor deposition （CVD）-grown monolayer tungsten disulphide （WS2） under uniaxial tensile strain. Observable broadening and appearance of an extra small feature at the longer-wavelength side shoulder of the PL peak occur under 2.5% strain, which could indicate the direct-indirect bandgap transition and is further confirmed by our density-functional-theory calculations. As the strain increases further, the spectral weight of the indirect transition gradually increases. Over the entire strain range, with the increase of the strain, the light emissions corresponding to each optical transition, such as the direct bandgap transition （K-K） and indirect bandgap transition （F-K, ≥2.5%）, exhibit a monotonous linear redshift. In addition, the binding energy of the indirect transition is found to be larger than that of the direct transition, and the slight lowering of the trion dissociation energy with increasing strain is observed. The strain was used to modulate not only the electronic band structure but also the lattice vibrations. The softening and splitting of the in-plane E＇ mode is observed under uniaxial tensile strain, and polarization-dependent Raman spectroscopy confirms the observed zigzag-oriented edge of WS2 grown by CVD in previous studies. These findings enrich our understanding of the strained states of monolayer transition-metal dichalcogenide （TMD） materials and lay a foundation for developing applications exploiting their strain-dependent optical properties, including the strain detection and light-emission modulation of such emerging two-dimensional TMDs.

Giant enhancement of photoluminescence emission in monolayer WS_(2)by femtosecond laser irradiation

Monolayer transition metal dichalcogenides have emerged as promising mat erials for opt oelectTonic and nanophotonic devices.However,the low photoluminescence(PL)quantum yield(QY)hinders their various potential applications.Here we engineer and enhance the PL intensity of monolayer WS_(2)by femtosecond laser irradiation.More than two orders of magnitude enhancement of PL intensity as compared to the as-prepared sample is determined.Furthermore,the engineering time is shortened by three orders of magnitude as compared to the improvement of PL intensity by continuous-wave laser irradiation.Based on the evolution of PL spectra,we attribute the giant PL enhancement to the conversion from trion emission to exciton,as well as the improvement of the QY when exciton and trion are localized to the new-formed defects.We have created microstructures on the monolayer WS_(2)based on the enhancement of PL intensity,where the engineered structures can be stably stored for more than three years.This flexible approach with the feature of excellent long-term storage stability is promising for applications in information storage,display technology,and opto electronic devices.

Local modulation of exc辻ons and trions in monolayer WS2 by carbon nanotubes

Mixed dimensional van der Waals(VdW)heterostructures constructed by one-dimensional(1D)and two-dimensional(2D)materials exhibit extra degree of freedom to modulate the electronic and optical properties due to the combination of difterent dimensionalities.The charge transfer at the intertace between 1D and 2D materials plays a crucial role in the optoelectronic properties and performance of the heterostructure-based devices.Here,we stacked single-walled carbon nanotubes(SWNTs)on monolayer WS2 for a mixed dimensional vdW heterostructure,and investigated the local modulation of excitions and trions in WS2 by SWNTs.Different directions of charge transfer between SWNTs and WSz are evidenced by the photoluminescence(PL)spectra of WS2.The PL intensity can be either enhanced or weakened by individual SWNTs.In our work,the PL intensity of WS2 is enhanced and the exciton peak position heterostructure is red-shifted about 3 meV due to the charge transfer from WS2 to an individual SWNT(SWNT#1).The change of PL by another SWNT(SWNT#2)can not be well-resolved in far fild,but scanning near field optical microscope(SNOM)measurements show that the PL intensity of WS2 is weakened by the SWNT.The peak position of exciton is blue-shifted by^1 meV while that of trion is redshifted by^1 meV due to the charge transfer from the SWNT to WS2,These results give insight into the charge transfer at the interface of SWNTWS2 heterostructure,and can be useful for design of optoelectronic devices based on mixed dimensional vdW heterostructures.

Bright trions in direct-bandgap silicon nanocrystals revealed by low-temperature single-nanocrystal spectroscopy

Strain-engineered silicon nanocrystals(SiNCs)have recently been shown to possess direct bandgap.Here,we report the observation of a rich structure in the single-nanocrystal photoluminescence spectra of strain-engineered direct-bandgap SiNCs in the temperature range of 9–300 K.The relationship between individual types of spectra is discussed,and the numerical modeling of spectral diffusion of the experimentally acquired spectra reveals a common origin for most types.The intrinsic spectral shape is shown to be a structure that contains three peaks,approximately 150 meV apart,each of which possesses a Si phonon substructure.Narrow spectral lines,reaching ≤ meV at 20 K,are detected.The observed temperature dependence of the spectral structure can be assigned to the radiative recombination of positively charged trions,in contrast to several previous reports linking a very similar shape to phonons in the surface capping layers.Our result serves as strong additional support for the direct-bandgap nature of the investigated SiNCs.