Recent Submissions

  • Ultraviolet-to-blue color-converting scintillating-fibers photoreceiver for 375-nm laser-based underwater wireless optical communication

    Kang, Chun Hong; Trichili, Abderrahmen; Alkhazragi, Omar; Zhang, Huafan; Subedi, Ram Chandra; Guo, Yujian; Mitra, Somak; Shen, Chao; Roqan, Iman S.; Ng, Tien Khee; Alouini, Mohamed-Slim; Ooi, Boon S. (Optics Express, The Optical Society, 2019-10-08) [Article]
    Underwater wireless optical communication (UWOC) can offer reliable and secure connectivity for enabling future internet-of-underwater-things (IoUT), owing to its unlicensed spectrum and high transmission speed. However, a critical bottleneck lies in the strict requirement of pointing, acquisition, and tracking (PAT), for effective recovery of modulated optical signals at the receiver end. A large-area, high bandwidth, and wide-angle-of-view photoreceiver is therefore crucial for establishing a high-speed yet reliable communication link under non-directional pointing in a turbulent underwater environment. In this work, we demonstrated a large-area, of up to a few tens of cm2, photoreceiver design based on ultraviolet(UV)-to-blue color-converting plastic scintillating fibers, and yet offering high 3-dB bandwidth of up to 86.13 MHz. Tapping on the large modulation bandwidth, we demonstrated a high data rate of 250 Mbps at bit-error ratio (BER) of 2.2 × 10−3 using non-return-to-zero on-off keying (NRZ-OOK) pseudorandom binary sequence (PRBS) 210-1 data stream, a 375-nm laser-based communication link over the 1.15-m water channel. This proof-of-concept demonstration opens the pathway for revolutionizing the photodetection scheme in UWOC, and for non-line-of-sight (NLOS) free-space optical communication.
  • New Insight on the Role of Electrolyte Additives in Rechargeable Lithium Ion Batteries

    Ming, Jun; Cao, Zhen; Wu, Yingqiang; Wahyudi, Wandi; Wang, Wenxi; Guo, Xianrong; Cavallo, Luigi; Hwang, Jang-Yeon; Shamim, Atif; Li, Lain-Jong; Sun, Yang-Kook; Alshareef, Husam N. (ACS Energy Letters, American Chemical Society (ACS), 2019-10-08) [Article]
    Solid electrolyte interphase (SEI)-forming agents such as vinylene carbonate, sulfone, and cyclic sulfate are commonly believed to be film-forming additives in lithium-ion batteries that help to enhance graphite anode stability. However, we find that the film-forming effect and the resultant SEI may not be the only reasons for the enhanced graphite stability. This is because the as-formed SEI cannot inhibit Li+–solvent co-intercalation once the additive is removed from the electrolyte. Instead, we show that the Li+ solvation structure, which is modified by these additives, plays a critical role in achieving reversible Li+ (de)intercalation within graphite. This discovery is confirmed in both carbonate and ether-based electrolytes. We show that the problem of graphite exfoliation caused by Li+–solvent co-intercalation can be mitigated by adding ethene sulfate to tune the Li+ coordination structure. This work brings new insight into the role of additives in electrolytes, expanding the prevailing thinking over the past 2 decades. In addition, this finding can guide the design of more versatile electrolytes for advanced rechargeable metal-ion batteries.
  • Understanding Ostwald Ripening and Surface Charging Effects in Solvothermally-Prepared Metal Oxide–Carbon Anodes for High Performance Rechargeable Batteries

    Zhou, Lin; Zhang, Jiao; Wu, Yingqiang; Wang, Wenxi; Ming, Hai; Sun, Qujiang; Wang, Limin; Ming, Jun; Alshareef, Husam N. (Advanced Energy Materials, Wiley, 2019-10-08) [Article]
    Metal oxides synthesized by the solvothermal approach have widespread applications, while their nanostructure control remains challenging because their reaction mechanism is still not fully understood. Herein, it is demonstrated how the competitive relation between Ostwald ripening and surface charging during solvothermal synthesis is crucial to engineering high-quality metal (oxide)–carbon nanomaterials. Using SnO2 as a case study, a new type of hollow SnO2–C hybrid nanoparticles is synthesized consisting of core–shell structured SnO2@C nanodots (which has not been previously reported). This new anode material exhibits extremely high lithium storage capacity of 1225 and 955 mAh g−1 at 200 and 500 mA g−1, respectively, and excellent cycling stability. In addition, full-battery cells are constructed combining SnO2–C anode with Ni-rich cathode, which can be charged to a higher voltage compared to commercial graphite anode and still demonstrate extraordinary rate performance. This study provides significant insight into the largely unexplored reaction mechanism during solvothermal synthesis, and demonstrates how such understanding can be used to achieve high-performance metal (oxide)–C anodes for rechargeable batteries.
  • Deciphering photocarrier dynamics for tuneable high-performance perovskite-organic semiconductor heterojunction phototransistors

    Lin, Yen-Hung; Huang, Wentao; Pattanasattayavong, Pichaya; Lim, Jongchul; Li, Ruipeng; Sakai, Nobuya; Panidi, Julianna; Hong, Min Ji; Ma, Chun; Wei, Nini; Wehbe, Nimer; Fei, Zhuping; Heeney, Martin; Labram, John G.; Anthopoulos, Thomas D.; Snaith, Henry J. (Nature Communications, Springer Science and Business Media LLC, 2019-10-02) [Article]
    Looking beyond energy harvesting, metal-halide perovskites offer great opportunities to revolutionise large-area photodetection technologies due to their high absorption coefficients, long diffusion lengths, low trap densities and simple processability. However, successful extraction of photocarriers from perovskites and their conversion to electrical signals remain challenging due to the interdependency of photogain and dark current density. Here we report hybrid hetero-phototransistors by integrating perovskites with organic semiconductor transistor channels to form either “straddling-gap” type-I or “staggered-gap” type-II heterojunctions. Our results show that gradual transforming from type-II to type-I heterojunctions leads to increasing and tuneable photoresponsivity with high photogain. Importantly, with a preferential edge-on molecular orientation, the type-I heterostructure results in efficient photocarrier cycling through the channel. Additionally, we propose the use of a photo-inverter circuitry to assess the phototransistors’ functionality and amplification. Our study provides important insights into photocarrier dynamics and can help realise advanced device designs with “on-demand” optoelectronic properties.
  • Tuning the Electrochemical Performance of Titanium Carbide MXene by Controllable in situ Anodic Oxidation.

    Tang, Jun; Mathis, Tyler; Kurra, Narendra; Sarycheva, Asia; Xiao, Xu; Hedhili, Mohamed N.; Jiang, Qiu; Alshareef, Husam N.; Xu, Baomin; Pan, Feng; Gogotsi, Yury (Angewandte Chemie (International ed. in English), Wiley, 2019-10-02) [Article]
    MXenes are a class of two-dimensional (2D) transition metal carbides, nitrides and carbonitrides that have shown promise for high-rate pseudocapacitive energy storage. However, the effects that irreversible oxidation have on the surface chemistry and electrochemical properties of MXenes are still not understood. Here we report on a controlled anodic oxidation method which improves the rate performance of titanium carbide MXene (Ti 3 C 2 T x, T x refers to -F, =O, -Cl and -OH) electrodes in acidic electrolytes. The capacitance retention at 2000 mV/s (with respect to the lowest scan rate of 5 mV/s) increases gradually from 38% to 66% by tuning the degree of anodic oxidation. At the same time, a loss in the redox behavior of Ti 3 C 2 is evident at high anodic potentials after oxidation. Several analysis methods were employed to reveal that preserving the structure and surface chemistry while simultaneously introducing defects, without compromising electrochemically active sites, are key factors for improving the rate performance of Ti 3 C 2 T x . This study demonstrates improvement of the electrochemical performance of MXene electrodes by controlling the surface chemistry and transition metal stoichiometry.
  • Poly(2-alkyl-2-oxazoline) electrode interlayers for improved n-type organic field effect transistor performance

    Nam, Sungho; de la Rosa, Victor R.; Cho, Yuljae; Hamilton, Rick; Cha, SeungNam; Hoogenboom, Richard; Bradley, Donal (Applied Physics Letters, AIP Publishing, 2019-10-01) [Article]
    Thin film interlayer materials inserted at the metal/semiconductor interface provide an effective means to improve charge injection and reduce the threshold voltage for organic field-effect transistors. Here, we report the use of poly(2-alkyl-2-oxazoline) interlayers for gold electrodes within n-type poly[[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)] field-effect transistors. We specifically show that the use of poly(2-ethyl-2-oxazoline) yields a reduction in the work function from 5.07 to 4.73 eV (ΔE = 0.34 eV), an increase in the electron mobility from 0.04 to 0.15 cm2/V s (3.75 times), and a reduction in the threshold voltage from 27.5 to 16.5 V (ΔV = 11 V) relative to bare gold. The alkyl side chain of the poly(2-alkyl-2-oxazoline) has a significant influence on the film microstructure and, as a consequence, also device performance.
  • 17% Efficient Organic Solar Cells Based on Liquid Exfoliated WS2 as a Replacement for PEDOT:PSS

    Lin, Yuanbao; Adilbekova, Begimai; Firdaus, Yuliar; Yengel, Emre; Faber, Hendrik; Sajjad, Muhammad; Zheng, Xiaopeng; Yarali, Emre; Seitkhan, Akmaral; Bakr, Osman; El Labban, Abdulrahman; Schwingenschlögl, Udo; Tung, Vincent; McCulloch, Iain; Laquai, Frédéric; Anthopoulos, Thomas D. (Advanced Materials, Wiley, 2019-10-01) [Article]
    The application of liquid-exfoliated 2D transition metal disulfides (TMDs) as the hole transport layers (HTLs) in nonfullerene-based organic solar cells is reported. It is shown that solution processing of few-layer WS2 or MoS2 suspensions directly onto transparent indium tin oxide (ITO) electrodes changes their work function without the need for any further treatment. HTLs comprising WS2 are found to exhibit higher uniformity on ITO than those of MoS2 and consistently yield solar cells with superior power conversion efficiency (PCE), improved fill factor (FF), enhanced short-circuit current (JSC), and lower series resistance than devices based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and MoS2. Cells based on the ternary bulk-heterojunction PBDB-T-2F:Y6:PC71BM with WS2 as the HTL exhibit the highest PCE of 17%, with an FF of 78%, open-circuit voltage of 0.84 V, and a JSC of 26 mA cm−2. Analysis of the cells' optical and carrier recombination characteristics indicates that the enhanced performance is most likely attributed to a combination of favorable photonic structure and reduced bimolecular recombination losses in WS2-based cells. The achieved PCE is the highest reported to date for organic solar cells comprised of 2D charge transport interlayers and highlights the potential of TMDs as inexpensive HTLs for high-efficiency organic photovoltaics.
  • MAPbI3 Single Crystals Free from Hole-Trapping Centers for Enhanced Photodetectivity

    Yang, Chen; El Demellawi, Jehad K.; Yin, Jun; Velusamy, Dhinesh; Emwas, Abdul-Hamid M.; El-Zohry, Ahmed M.; Gereige, Issam; AlSaggaf, Ahmed; Bakr, Osman; Alshareef, Husam N.; Mohammed, Omar F. (ACS Energy Letters, American Chemical Society (ACS), 2019-10-01) [Article]
    Perovskite single crystals (PSCs) are considered the next breakthrough in optoelectronics research due to their free-grain boundary and much lower density of trap states compared to those of their polycrystalline counterparts. However, the inevitable formation of triiodide-based intrinsic defects during high-temperature crystal growth is one of the major challenges impeding the further development of optoelectronic devices based on PSCs. Here, we not only identified the existence of these triiodide ions as hole-trapping centers and their tremendous negative impact on the performance of PSCs, but more importantly, we used a reduction treatment to prevent their formation during crystal growth. The removal of such defect centers resulted in much higher charge carrier mobility and longer carrier lifetime than the untreated counterparts, leading to enhanced photodetection properties. The I3–-free MAPbI3 single crystal (MSC) devices consistently generated a more than 100 times higher photocurrent than that generated by I3–-rich devices under the same light intensity.
  • Use of the Phen-NaDPO:Sn(SCN) 2 Blend as Electron Transport Layer Results to Consistent Efficiency Improvements in Organic and Hybrid Perovskite Solar Cells

    Seitkhan, Akmaral; Neophytou, Marios; Kirkus, Mindaugas; Abou-Hamad, Edy; Hedhili, Mohamed N.; Yengel, Emre; Firdaus, Yuliar; Faber, Hendrik; Lin, Yuanbao; Tsetseris, Leonidas; McCulloch, Iain; Anthopoulos, Thomas D. (Advanced Functional Materials, Wiley, 2019-09-27) [Article]
    A simple approach that enables a consistent enhancement of the electron extracting properties of the widely used small-molecule Phen-NaDPO and its application in organic solar cells (OSCs) is reported. It is shown that addition of minute amounts of the inorganic molecule Sn(SCN)2 into Phen-NaDPO improves both the electron transport and its film-forming properties. Use of Phen-NaDPO:Sn(SCN)2 blend as the electron transport layer (ETL) in binary PM6:IT-4F OSCs leads to a remarkable increase in the cells' power conversion efficiency (PCE) from 12.6% (Phen-NaDPO) to 13.5% (Phen-NaDPO:Sn(SCN)2). Combining the hybrid ETL with the best-in-class organic ternary PM6:Y6:PC70BM systems results to a similarly remarkable PCE increase from 14.2% (Phen-NaDPO) to 15.6% (Phen-NaDPO:Sn(SCN)2). The consistent PCE enhancement is attributed to reduced trap-assisted carrier recombination at the bulk-heterojunction/ETL interface due to the presence of new energy states formed upon chemical interaction of Phen-NaDPO with Sn(SCN)2. The versatility of this hybrid ETL is further demonstrated with its application in perovskite solar cells for which an increase in the PCE from 16.6% to 18.2% is also demonstrated.
  • Terahertz metamaterial beam splitters based on untraditional coding scheme

    Xing, Xiaohua; Li, Yanfeng; Lu, Yongchang; Zhang, Wentao; Zhang, Xixiang; Han, Jiaguang; Zhang, Weili (Optics Express, The Optical Society, 2019-09-25) [Article]
    Terahertz waves have attracted considerable research interest in recent years because of their potential applications in diverse fields. As an important device to control terahertz waves, beam splitters with greater flexibility and higher degrees of freedom are highly desirable. In order to obtain higher degrees of freedom in beam splitting, 2-bit or higher-bit coding elements are usually introduced into metamaterial beam splitters based on the coding theory. In this work, a new “offset” coding scheme using only the 1-bit coding elements of “0” and “1” is presented, and the period of coding for beam splitting can be a non-integer multiple of the length of a single unit rather than only its integer multiples. Therefore, more beam-splitting degrees of freedom can be obtained, and the design strategy is experimentally verified. We believe that the new coding scheme will also be of significance in radar cross section reduction and flexible wave control.
  • Magnetoelectric coupling in γ′ -Fe4N/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 multiferroic heterostructures

    Lai, Zhengxun; Li, Peng; Mi, Wenbo (Journal of Applied Physics, AIP Publishing, 2019-09-21) [Article]
    Epitaxial γ′-Fe4N films with different thicknesses were fabricated on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) substrates by facing-target reactive sputtering. The magnetoelectric coupling (MEC) in the samples was systematically investigated. Firstly, the magnetization along different in-plane directions is tunable by the electric field. It was found that MEC in the films on PMN-PT(011) is stronger than that on PMN-PT(001) due to the different in-plane magnetic anisotropy. Moreover, the magnetoelectric coupling is strongly related to the γ′-Fe4N film thickness, which can be ascribed to the competition between the strain and spin-dependent screening effect induced MEC. Additionally, the electric-field tailored remanent magnetization of the samples gradually increases with temperature due to the thermal agitation. Besides, the electric-field effect on the out-of-plane magnetic hysteresis loops is consistent with the in-plane cases. The results are of benefit to the development of the electric-field controlled spintronic devices.
  • Halogen Vacancies Enable Ligand-Assisted Self-Assembly of Perovskite Quantum Dots into Nanowires.

    Pan, Jun; Li, Xiyan; Gong, Xiwen; Yin, Jun; Zhou, Dianli; Sinatra, Lutfan; Huang, Renwu; Liu, Jiakai; Chen, Jie; Dursun, Ibrahim; El-Zohry, Ahmed M.; Saidaminov, Makhsud I.; Sun, Hong-Tao; Mohammed, Omar F.; Ye, Changhui; Sargent, E.; Bakr, Osman (Angewandte Chemie (International ed. in English), Wiley, 2019-09-19) [Article]
    Interest has been growing in defects of halide perovskites in view of their intimate connection with key material optoelectronic properties. In perovskite quantum dots (PQDs), the influence of defects is even more apparent than in their bulk counterparts. By combining experiment and theory, we report herein a halide-vacancy-driven, ligand-directed self-assembly process of CsPbBr3 PQDs. With the assistance of oleic acid and didodecyldimethylammonium sulfide, surface-Br-vacancy-rich CsPbBr3 PQDs self-assemble into nanowires (NWs) that are 20-60 nm in width and several millimeters in length. The NWs exhibit a sharp photoluminescence profile (≈18 nm full-width at-half-maximum) that peaks at 525 nm. Our findings provide insight into the defect-correlated dynamics of PQDs and defect-assisted fabrication of perovskite materials and devices.
  • Ultrathin channels make transistors go faster

    Anthopoulos, Thomas D. (Nature Materials, Springer Science and Business Media LLC, 2019-09-19) [Article]
    Reducing the thickness of an amorphous conductive indium tin oxide layer down to a few nanometres has enabled the realization of 40-nm-long channel transistors with remarkable operating characteristics.
  • Passivating contacts for crystalline silicon solar cells

    Allen, Thomas; Bullock, James; Yang, Xinbo; Javey, Ali; De Wolf, Stefaan (Nature Energy, Springer Science and Business Media LLC, 2019-09-16) [Article]
    The global photovoltaic (PV) market is dominated by crystalline silicon (c-Si) based technologies with heavily doped, directly metallized contacts. Recombination of photo-generated electrons and holes at the contact regions is increasingly constraining the power conversion efficiencies of these devices as other performance-limiting energy losses are overcome. To move forward, c-Si PV technologies must implement alternative contacting approaches. Passivating contacts, which incorporate thin films within the contact structure that simultaneously supress recombination and promote charge-carrier selectivity, are a promising next step for the mainstream c-Si PV industry. In this work, we review the fundamental physical processes governing contact formation in c-Si. In doing so we identify the role passivating contacts play in increasing c-Si solar cell efficiencies beyond the limitations imposed by heavy doping and direct metallization. Strategies towards the implementation of passivating contacts in industrial environments are discussed.
  • Solar-Blind Self-Powered Photodetector Using Solution-Processed Amorphous Core-Shell Gallium Oxide Nanoparticles.

    Mitra, Somak; Pak, Yusin; Xin, Bin; Almalawi, Dhaifallah R; Wehbe, Nimer; Roqan, Iman S. (ACS applied materials & interfaces, American Chemical Society (ACS), 2019-09-10) [Article]
    Solution-processed deep ultraviolet (DUV) photodetectors based on wide band gap oxide semiconductors (WBGS) working in the <280 nm wavelength range are drawing increasing attention of the research community because of their cost-effective production and potential use in diverse applications. Here, we report on the synthesis of novel core-shell amorphous gallium oxide nanoparticles (NPs) (a-Ga2Ox/GaOx NPs) that have not been previously obtained. The amorphous gallium oxide NPs were synthesized from gallium nitride using the femtosecond laser ablation in liquid technique. Transmission electron microscopy and electron energy-loss spectroscopy measurements revealed the amorphous NP nature with a Ga-rich core and oxide-rich shell. Optical properties of these core-shell amorphous gallium oxide NPs were investigated by time-resolved spectroscopy and photoluminescence. As a proof of concept, the amorphous gallium oxide NPs were used as an active layer in a solar-blind DUV photodetector with high responsivity (778 mA/W) at 244 nm, which is the highest responsivity recorded to date for any solution-processed DUV photodetector. This work on a high-performance solution-processed device paves the way for large-scale industrial application of the WBGS.
  • Interfacial Engineering at the 2D/3D Heterojunction for High-Performance Perovskite Solar Cells.

    Niu, Tianqi; Lu, Jing; Jia, Xuguang; Xu, Zhuo; Tang, Ming-Chun; Barrit, Dounya; Yuan, Ningyi; Ding, Jianning; Zhang, Xu; Fan, Yuanyuan; Luo, Tao; Zhang, Yalan; Smilgies, Detlef-M.; Liu, Zhike; Amassian, Aram; Jin, Shengye; Zhao, Kui; Liu, Shengzhong (Frank) (Nano letters, American Chemical Society (ACS), 2019-09-04) [Article]
    Perovskite solar cells based on two-dimensional/three-dimensional (2D/3D) hierarchical structure have attracted significant attention in recent years due to their promising photovoltaic performance and stability. However, obtaining a detailed understanding of interfacial mechanism at the 2D/3D heterojunction, for example, the ligand-chemistry-dependent nature of the 2D/3D heterojunction and its influence on charge collection and the final photovoltaic outcome, is not yet fully developed. Here we demonstrate the underlying 3D phase templates growth of quantum wells (QWs) within a 2D capping layer, which is further influenced by the fluorination of spacers and compositional engineering in terms of thickness distribution and orientation. Better QW alignment and faster dynamics of charge transfer at the 2D/3D heterojunction result in higher charge mobility and lower charge recombination loss, largely explaining the significant improvements in charge collection and open-circuit voltage (VOC) in complete solar cells. As a result, 2D/3D solar cells with a power-conversion efficiency of 21.15% were achieved, significantly higher than the 3D counterpart (19.02%). This work provides key missing information on how interfacial engineering influences the desirable electronic properties of the 2D/3D hierarchical films and device performance via ligand chemistry and compositional engineering in the QW layer.
  • S-wave elastic scattering of o -Ps from H2 at low energy

    Zhang, Junyi; Wu, M. S.; Qian, Y.; Gao, X.; Yang, Y. J.; Varga, K.; Yan, Z. C.; Schwingenschlögl, Udo (Physical Review A, American Physical Society (APS), 2019-09-03) [Article]
    The confined variational method is applied to investigate the low-energy elastic scattering of orthopositronium from H2 by first-principles quantum mechanics. Describing the correlations with explicitly correlated Gaussians, we obtain accurate s-wave phase shifts and pickoff annihilation parameters for different incident momenta. By a least-squares fit of the data to the effective-range theory, we determine the s-wave scattering length AS=2.02a0 and the zero-energy value of the pickoff annihilation parameter, 1Zeff=0.1839. The obtained 1Zeff agrees well with the precise experimental value of 0.186(1) [G. L. Wright, J. Phys. B 16, 4065 (1983)10.1088/0022-3700/16/21/027] and the obtained AS agrees well with the value of 2.1(2)a0 estimated from the average experimental momentum-transfer cross section for positronium energy below 0.3 eV [F. Saito, J. Phys. B 36, 4191 (2003)10.1088/0953-4075/36/20/011].
  • Continuous production of pure liquid fuel solutions via electrocatalytic CO2 reduction using solid-electrolyte devices

    Xia, Chuan; Zhu, Peng; Jiang, Qiu; Pan, Ying; Liang, Wentao; Stavitsk, Eli; Alshareef, Husam N.; Wang, Haotian (Nature Energy, Springer Science and Business Media LLC, 2019-09-02) [Article]
    Electrocatalytic CO2 reduction is often carried out in a solution electrolyte such as KHCO3(aq), which allows for ion conduction between electrodes. Therefore, liquid products that form are in a mixture with the dissolved salts, requiring energy-intensive downstream separation. Here, we report continuous electrocatalytic conversion of CO2 to pure liquid fuel solutions in cells that utilize solid electrolytes, where electrochemically generated cations (such as H+) and anions (such as HCOO−) are combined to form pure product solutions without mixing with other ions. Using a HCOOH-selective (Faradaic efficiencies > 90%) and easily scaled Bi catalyst at the cathode, we demonstrate production of pure HCOOH solutions with concentrations up to 12 M. We also show 100 h continuous and stable generation of 0.1 M HCOOH with negligible degradation in selectivity and activity. Production of other electrolyte-free C2+ liquid oxygenate solutions, including acetic acid, ethanol and n-propanol, are also demonstrated using a Cu catalyst. Finally, we show that our CO2 reduction cell with solid electrolytes can be modified to suit other, more complex practical applications.
  • Current-driven magnetization switching in a van der Waals ferromagnet Fe3GeTe2.

    Wang, Xiao; Tang, Jian; Xia, Xiuxin; He, Congli; Zhang, Junwei; Liu, Yizhou; Wan, Caihua; Fang, Chi; Guo, Chenyang; Yang, Wenlong; Guang, Yao; Zhang, Xiaomin; Xu, Hongjun; Wei, Jinwu; Liao, Mengzhou; Lu, Xiaobo; Feng, Jiafeng; Li, Xiaoxi; Peng, Yong; Wei, Hongxiang; Yang, Rong; Shi, Dongxia; Zhang, Xixiang; Han, Zheng; Zhang, Zhidong; Zhang, Guangyu; Yu, Guoqiang; Han, Xiufeng (Science advances, American Association for the Advancement of Science (AAAS), 2019-08-31) [Article]
    The recent discovery of ferromagnetism in two-dimensional (2D) van der Waals (vdW) materials holds promises for spintronic devices with exceptional properties. However, to use 2D vdW magnets for building spintronic nanodevices such as magnetic memories, key challenges remain in terms of effectively switching the magnetization from one state to the other electrically. Here, we devise a bilayer structure of Fe3GeTe2/Pt, in which the magnetization of few-layered Fe3GeTe2 can be effectively switched by the spin-orbit torques (SOTs) originated from the current flowing in the Pt layer. The effective magnetic fields corresponding to the SOTs are further quantitatively characterized using harmonic measurements. Our demonstration of the SOT-driven magnetization switching in a 2D vdW magnet could pave the way for implementing low-dimensional materials in the next-generation spintronic applications.
  • General Mild Reaction Creates Highly Luminescent Organic-Ligand-Lacking Halide Perovskite Nanocrystals for Efficient Light-Emitting Diodes.

    Zhang, Bin-Bin; Yuan, Shuai; Ma, Ju-Ping; Zhou, Yang; Hou, Jingshan; Chen, Xueyuan; Zheng, Wei; Shen, Huaibin; Wang, Xue-Chun; Sun, Baoquan; Bakr, Osman; Liao, Liang-Sheng; Sun, Hong-Tao (Journal of the American Chemical Society, American Chemical Society (ACS), 2019-08-31) [Article]
    The presence of labile bulky insulating hydrocarbon ligands in halide perovskite nanocrystals (NCs) passivates surface traps but concurrently makes charge transport difficult in optoelectronic devices. Early efforts routinely rely on the replacement of long-chain ligands with short-chain cousins, leading to notable changes in NC's sizes and photophysical properties and thus making it hard to obtain devices with nearly designed emissions. Here we report a general solution-phase ligand-exchange strategy to produce organic-ligand-lacking halide perovskite NCs with high photoluminescence (PL) quantum yields and good stability in ambient air. We demonstrate that the ligand exchange can be achieved by a well-controlled mild reaction of thionyl halide with the carboxylic and amine groups on the NC's surface, resulting in nearly dry NCs with well-passivated surfaces and almost unaltered emission characteristics. Consequently, we achieve exceptionally high-performance blue perovskite NC light-emitting diodes (LEDs) with an external quantum efficiency of up to 1.35% and an extremely narrow full width at half-maximum of 14.6 nm. Our work provides a systematic framework for preparing high-quality organic-ligand-lacking perovskite NC inks that can be directly cast as films featuring effective charge transport, thereby providing the foundation for further development of a wide range of efficient perovskite optoelectronic devices.

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