Recent Submissions

  • Cellular automata imbedded memristor-based recirculated logic in-memory computing

    Liu, Yanming; Tian, He; Wu, Fan; Liu, Anhan; Li, Yihao; Sun, Hao; Lanza, Mario; Ren, Tian-Ling (Research Square Platform LLC, 2022-08-05) [Preprint]
    Cellular automata is an important tool to study the emergent properties of complex systems based on its well-known parallel, bio-inspired, computational characteristics. However, running cellular automata on conventional chips suffer from low parallelism, and high hardware cost. Establish dedicated hardware for cellular automata remains elusive. Here, we propose a recirculate logic operations scheme (RLOS) based on memristive hardware combined with 2D transistors to realize cellular automata evolution. The scheme utilizes the storage and calculation characteristics of memristive devices, which greatly reduces hardware complexity. The versatility of the RLOS scheme allows implementing multiple different cellular automata algorithms on the same circuitry. The entire rule (rule 1-254) of elementary cellular automata and more complicated 1D CA model majority classification algorithm have been verified to be applicable to this circuitry. Further, the edge detection algorithm based on 2D cellular automata has been authenticated through RLOS. The experimental and evaluation results reveal that the scheme reduces the hardware cost up to 79 times comparing to the Field Programmable Gate Array (FPGA) approach. To our best knowledge, RLOS has the lowest hardware cost (6 components/per cell) among state-of-art hardware implementations. This work can pave the road towards high-efficiency and low-cost cellular automata hardware realization, and also facilitates the exploration of memristive applications.
  • Single-step post-production treatment of lead acetate precursor-based perovskite using alkylamine salts for reduced grain-boundary related film defects

    Gebremichael, Zekarias Teklu; Alam, Shahidul; Stumpf, Steffi; Diegel, Marco; Schubert, Ulrich S.; Hoppe, Harald (Nano Select, Wiley, 2022-08-04) [Article]
    Powered by the worldwide efforts of research groups experienced in dye-sensitized, and thin-film solar cells, perovskite solar cells (PSCs) reached a power conversion efficiency of 25.7% within 10 years. However, the presence of defects and trap density within the active layer's grain boundaries commonly operates as non-radiative recombination centers. Hence, intensive efforts have been reported to passivate the inevitable bulk and interface defects of the active layer using additives or post-treatment processing to enhance the efficiency and stability of PSCs. Herein, a facile post-treatment strategy based on wet processing methylammonium lead triiodide, MAPbI3 (prepared from lead acetate and methylammonium iodide precursors) films with organic amine salts (FABr and FAI) is demonstrated. As a result, high-quality films of mixed perovskites (FAxMA1-xPbI3-xBrx and FAxMA1-xPbI3) were obtained. The surface treatment has efficiently passivate the defects in the host film, suppressing the non-radiative carrier recombination. Compared to the control device, the increased open-circuit voltage (from 0.5 V to 1 V) and fill factor (FF) values of the optimized device based on FAxMA1-xPbI3 showed a PCE of 16.13%. And our findings revealed that post-treatment is possible on wet perovskite film aged for a few minutes prior to its post-treatment, which saved the energy used for pre-annealing.
  • Aggregation-Induced Fluorescence Enhancement for Efficient X-ray Imaging Scintillators and High-Speed Optical Wireless Communication

    Wang, Jian-Xin; Wang, Yue; Nadinov, Issatay; Yin, Jun; Gutierrez Arzaluz, Luis; Alkhazragi, Omar; He, Tengyue; Ng, Tien Khee; Eddaoudi, Mohamed; Alshareef, Husam N.; Bakr, Osman; Ooi, Boon S.; Mohammed, Omar F. (ACS Materials Letters, American Chemical Society (ACS), 2022-07-29) [Article]
    Aggregation of some chromophores generates very strong fluorescence signals due to the tight molecular packing and highly restricted vibrational motions in the electronically excited states. Such an aggregation-induced emission enhancement enables great strides in biomedical imaging, security screening, sensing, and light communication applications. Here, we realized efficient utilization of a series of aggregation-induced emission luminogens (AIEgens) in X-ray imaging scintillators and optical wireless communication (OWC) technology. Ultrafast time-resolved laser spectroscopic experiments and high-level density functional theory (DFT) calculations clearly demonstrate that a significant increase in the rotational energy barrier in the aggregated state of AIEgens is observed, leading to highly restricted molecular vibrations and suppressed nonradiative processes. AIEgen-based scintillators exhibit a high X-ray imaging resolution of 16.3 lp mm–1, making them excellent candidates for X-ray radiography and security inspections. In addition, these AIEgens show a broad -3-dB modulation bandwidth of ∼110 MHz and high net data rates of ∼600 Mb/s, demonstrating their high potential for application in the field of high-speed OWC.
  • Electrical manipulation of magnetization in magnetic heterostructures with perpendicular anisotropy

    Chen, Aitian; Zheng, Dongxing; Fang, Bin; Wen, Yan; Li, Yan; Zhang, Xixiang (Journal of Magnetism and Magnetic Materials, Elsevier BV, 2022-07-28) [Article]
    Magnetic materials with perpendicular magnetic anisotropy are significant for spintronics due to their potential to develop high-density magnetic memory with high thermal stability. Many methods have developed to manipulate perpendicular magnetization by electric current or electric field rather than magnetic field for realizing energy-efficient spintronics. In this review, we primarily focus on recent progress on electrical manipulation of perpendicular magnetization through spin-orbit torque and strain-mediated magnetoelectric coupling. We aim to summarize field-free switching of perpendicular magnetization and exchange bias induced by spin-orbit torque in the metallic magnetic heterostructures, spin-orbit torque switching of magnetization in the perovskite oxides, and magnetoelectric control of perpendicular magnetization mediated by piezostrain in multiferroic heterostructures. Finally, our perspectives on electrical manipulation of perpendicular magnetization by spin-orbit torque and magnetoelectric coupling are given to realize practical energy-efficient spintronic devices.
  • Lead-Carbon Batteries toward Future Energy Storage: From Mechanism and Materials to Applications

    Yin, Jian; Lin, Haibo; Shi, Jun; Lin, Zheqi; Bao, Jinpeng; Wang, Yue; Lin, Xuliang; Qin, Yanlin; Qiu, Xueqing; Zhang, Wenli (Electrochemical Energy Reviews, Springer Science and Business Media LLC, 2022-07-27) [Article]
    The lead acid battery has been a dominant device in large-scale energy storage systems since its invention in 1859. It has been the most successful commercialized aqueous electrochemical energy storage system ever since. In addition, this type of battery has witnessed the emergence and development of modern electricity-powered society. Nevertheless, lead acid batteries have technologically evolved since their invention. Over the past two decades, engineers and scientists have been exploring the applications of lead acid batteries in emerging devices such as hybrid electric vehicles and renewable energy storage; these applications necessitate operation under partial state of charge. Considerable endeavors have been devoted to the development of advanced carbon-enhanced lead acid battery (i.e., lead-carbon battery) technologies. Achievements have been made in developing advanced lead-carbon negative electrodes. Additionally, there has been significant progress in developing commercially available lead-carbon battery products. Therefore, exploring a durable, long-life, corrosion-resistive lead dioxide positive electrode is of significance. In this review, the possible design strategies for advanced maintenance-free lead-carbon batteries and new rechargeable battery configurations based on lead acid battery technology are critically reviewed. Moreover, a synopsis of the lead-carbon battery is provided from the mechanism, additive manufacturing, electrode fabrication, and full cell evaluation to practical applications.
  • Correlating acceptor structure and blend nanostructure with the photostability of nonfullerene organic solar cells

    Paleti, Sri Harish Kumar; Hultmark, Sandra; Ramos, Nicolas; Gasparini, Nicola; Emwas, Abdul-Hamid M.; Martin, Jaime; Müller, Christian; Baran, Derya (Solar RRL, Wiley, 2022-07-26) [Article]
    The formation of photo-induced traps resulting in the loss of electron mobility deteriorates the performance of organic solar cells under continuous light soaking. The genesis of these loss mechanisms is elucidated by examining the structural stability of halogenated ITIC derivative films and the phase behavior of the respective binary systems by blending with the donor polymer PBDBT-2F. Under constant illumination, ITIC-4Cl is found to maintain its structural integrity, whereas fluorine on the peripheral moieties of ITIC-4F undergo chemical substitution to form a mixture of ITIC and ITIC-4F. Thermal analysis of the light soaked binary films reveals that ITIC-4Cl loses its crystalline phase while the crystallinity of ITIC-4F does not undergo changes. Further, we show that the addition of a small amount of ITIC-4F as a third component hinders the loss of ITIC-4Cl crystalline phase in bulk-heterojunction blends through the formation of co-crystals. These results suggest that long-range ordering of NFAs does not necessarily improve the photo-stability of organic solar cells and that the addition of a third component, irrespective of the crystalline nature, can prevent changes in bulk-heterojunction blend nanostructure.
  • High-Performance Copper-Doped Perovskite-Related Silver Halide X-ray Imaging Scintillator

    He, Tengyue; Zhou, Yang; Wang, Xiaojia; Yin, Jun; Gutierrez Arzaluz, Luis; Wang, Jian-Xin; Zhang, Yuhai; Bakr, Osman; Mohammed, Omar F. (ACS Energy Letters, American Chemical Society (ACS), 2022-07-26) [Article]
    Scintillators are critical for high-energy radiation detection across a wide array of potential applications, from medical radiography and safety inspections all the way to space exploration. However, constrained by their current shortcomings, including high-temperature and complex fabrication as well as inherent brittleness and fragility among thick films and bulk crystals, traditional scintillators are finding it difficult to meet the rising demand for cost-effective, ecofriendly, and flexible X-ray detection. Here, we describe the development of high-performance and flexible X-ray scintillators based on films of Cu-doped Cs2AgI3 that exhibit ultrahigh X-ray sensitivity. The materials exhibit a high scintillation light yield of up to 82 900 photons/MeV and a low detection limit of 77.8 nGy/s, which is approximately 70 times lower than the dosage for a standard medical examination. Moreover, richly detailed X-ray images of biological tissue and electronic components with a high spatial resolution of 16.2 lp/mm were obtained using flexible, large-area, solution-processed scintillation screens.
  • Releasing Plating Induced Stress for Highly Reversible Aqueous Zn Metal Anodes

    Chen, Jianyu; Qiao, Xin; Han, Xuran; Zhang, Jinghao; Wu, Hanbo; He, Qian; Chen, Zibo; Shi, Li; Wang, Yizhou; Xie, Yannan; Ma, Yanwen; Zhao, Jin (Elsevier BV, 2022-07-22) [Preprint]
    Rechargeable aqueous zinc-ion batteries (ZIBs) have become one of the most potential technology for grid-scale energy storage. But their commercialization has been severely plagued by the uncontrollable dendrite growth and side reactions on planar-structured anodes. Hence developing efficient methods to stabilize Zn anodes is of vital importance. Herein, we reveal that the Zn dendrite growth is strongly associated with the internal stress accumulation during Zn plating. We demonstrate that the patterned micro-grooves on planar Zn metal can effectively release the plating-induced stress and inhibit the dendrite growth. By coupling with Nafion film coating to depress the side reaction, the groove-patterned Zn anodes present ultra-stable cycling over 1200 h at a high current density of 10 mA cm-2, a low electrochemical polarization for the rate performance range from 1 to 20 mA cm-2, and stable voltage hysteresis in deep discharge/charge performance at 10 mA cm-2 and 10 mAh cm-2. The feasibility of our strategy was further exhibited in the Zn|MnO2 flexible cell, which delivers an impressive capacity of 186 mAh g-1, high electrochemical stability, and outstanding mechanical flexibility. The finding of this study is expected to provide a deep insight into the design of highly reversible aqueous Zn-ion batteries.
  • Large Spin Coherence Length and High Photovoltaic Efficiency of the Room Temperature Ferrimagnet Ca2FeOsO6 by Strain Engineering

    Rout, Paresh Chandra; Schwingenschlögl, Udo (Advanced Science, Wiley, 2022-07-21) [Article]
    The influence of epitaxial strain on the electronic, magnetic, and optical properties of the distorted double perovskite Ca2FeOsO6 is studied. These calculations show that the compound realizes a monoclinic structure with P21/n space group from −6% to +6% strain. While it retains ferrimagnetic ordering with a net magnetic moment of 2 μB per formula unit at low strain, it undergoes transitions into E-antiferromagnetic and C-antiferromagnetic phases at −5% and +5% strain, respectively. It is shown that spin frustration reduces the critical temperature of the ferrimagnetic ordering from the mean field value of 600–350 K, in excellent agreement with the experimental value of 320 K. It is also shown that the critical temperature can be tuned efficiently through strain and that the spin coherence length surpasses that of Sr2FeMoO6 under tensile strain. An indirect-to-direct bandgap transition is observed at +5% strain. Localization of the valence and conduction states on different transition metal sublattices enables efficient electron–hole separation upon photoexcitation. The calculated spectroscopic limited maximum efficiency of up to 33% points to excellent potential of Ca2FeOsO6 in solar cell applications.
  • Direct Band Gap in Multilayer Transition Metal Dichalcogenide Nanoscrolls with Enhanced Photoluminescence

    Lin, Ci; Cai, Liang; Fu, Jui-Han; Sattar, Shahid; Wang, Qingxiao; Wan, Yi; Tseng, Chien-Chih; Yang, Chih-Wen; Aljarb, Areej; Jiang, Ke; Huang, Kuo-Wei; Li, Lain-Jong; Canali, Carlo Maria; Shi, Yumeng; Tung, Vincent (ACS Materials Letters, American Chemical Society (ACS), 2022-07-20) [Article]
    A direct band gap that solely exists in monolayer semiconducting transition metal dichalcogenides (TMDs) endows strong photoluminescence (PL) features, whereas multilayer TMD structures exhibit quenched PL due to the direct-to-indirect band gap transition. We demonstrate multilayer TMD (such as MoS2 and WS2) nanoscrolls with a preserved direct band gap fabricated by an effective and facile method of solvent-driven self-assembly. The resultant multilayer nanoscrolls, exhibiting up to 11 times higher PL intensity than the remanent monolayer, are carefully characterized using PL spectroscopy. Significantly enlarged interlayer distances and modulated interlayer coupling in the fabricated nanostructures are unveiled by cross-sectional scanning transmission electron microscopy, atomic force microscopy, and Raman spectroscopy. The preservation of direct band gap features is further evidenced by density functional theory calculations using the simplified bilayer model with an experimentally obtained 15 Å interlayer distance. The modulation of the PL intensity as an indicator of the band gap crossover in the TMD nanoscrolls is demonstrated by removing the acetone molecules trapped inside the interlayer space. The general applicability of the method presents an opportunity for large-scale fabrication of a plethora of multilayer TMD nanoscrolls with direct band gaps.
  • Bifacial perovskite/silicon tandem solar cells

    de Bastiani, Michele; Subbiah, Anand Selvin; Babics, Maxime; Ugur, Esma; Xu, Lujia; Liu, Jiang; Allen, Thomas; Aydin, Erkan; De Wolf, Stefaan (Joule, Elsevier BV, 2022-07-20) [Article]
    Perovskite/silicon tandem solar cells are a rapidly emerging class of high-efficiency photovoltaic (PV) devices that have demonstrated excellent power conversion efficiencies (PCEs) while promising low-cost manufacturing. In recent years, this technology has been pushed increasingly closer to market entrance. Yet, for true commercial success, PCEs also need to be stable, in line with the warranty certificates of commercial crystalline-silicon (c-Si) PV modules. Bifacial tandem solar cells that collect light at both their sunward and rear side by exploiting the albedo—the scattered and reflected photons from the ground—offer a promising pathway toward a greater stability and energy yield. Thanks to the additional photons arising from the albedo, bifacial solar cells may generate a current larger than their conventional monofacial counterparts, enabling a higher performance. For bifacial monolithic tandems, exploiting such current enhancement requires current matching between top and bottom cells, which mandates the use of a bromide-lean, narrow-band-gap perovskite that is known to suppress halide segregation, thereby significantly improving device stability. In this perspective, we discuss bifacial perovskite/silicon tandem technology in depth, highlighting its great appeal, thanks to its combination of enhanced performance and improved stability with promising low costs, thereby representing a key future technology at the utility scale that can contribute to the formation of a carbon-neutral sustainable economy.
  • Spin canting of Ni/CoO/Fe films grown on curved MgO(0 0 1) substrate

    Yang, M.; Li, Q.; N'Diaye, A. T.; Shafer, P.; Klewe, C.; Wang, T. Y.; Wu, Y. Z.; Zhang, Xixiang; Hwang, C.; Qiu, Z. Q. (Journal of Magnetism and Magnetic Materials, Elsevier BV, 2022-07-19) [Article]
    Using element-resolved x-ray magnetic circular dichroism (XMCD) and x-ray magnetic linear dichroism (XMLD) measurements, we determined the spin orientations of Ni, CoO and Fe films in Ni/CoO/Fe films grown on a curved MgO(0 0 1) substrate. We find that the vicinal surface of MgO(0 0 1) substrate results in a spin canting towards out-of-plane direction in the Ni and CoO films as a result of the interfacial coupling. The Ni spin canting angle increases monotonically with the vicinal angle in the studied range of 0–17° and the CoO spin canting angle increases more rapidly towards saturation only at a few degrees of the vicinal angle. The uniaxial magnetic anisotropy induced in the Ni layer by the Ni/CoO interfacial coupling is quantitatively determined and is shown to increase monotonically with the vicinal angle. Our result provides a new pathway for tailoring the spin orientation by modifying the substrate surface symmetry in combining with the ferromagnetic/antiferromagnetic interfacial interaction in thin-film based spintronic devices.
  • Low-defect-density WS2 by hydroxide vapor phase deposition

    Wan, Yi; Li, En; Yu, Zhihao; Huang, Jing-Kai; Li, Ming-yang; Chou, Ang-Sheng; Lee, Yi-Te; Lee, Chien-Ju; Hsu, Hung-Chang; Zhan, Qin; Aljarb, Areej; Fu, Jui-Han; Chiu, Shao-Pin; Wang, Xinran; Lin, Juhn-Jong; Chiu, Ya-Ping; Chang, Wen-Hao; Wang, Han; Shi, Yumeng; Lin, Nian; Cheng, Yingchun; Tung, Vincent; Li, Lain-Jong (Nature Communications, Springer Science and Business Media LLC, 2022-07-18) [Article]
    Two-dimensional (2D) semiconducting monolayers such as transition metal dichalcogenides (TMDs) are promising channel materials to extend Moore’s Law in advanced electronics. Synthetic TMD layers from chemical vapor deposition (CVD) are scalable for fabrication but notorious for their high defect densities. Therefore, innovative endeavors on growth reaction to enhance their quality are urgently needed. Here, we report that the hydroxide W species, an extremely pure vapor phase metal precursor form, is very efficient for sulfurization, leading to about one order of magnitude lower defect density compared to those from conventional CVD methods. The field-effect transistor (FET) devices based on the proposed growth reach a peak electron mobility ~200 cm2/Vs (~800 cm2/Vs) at room temperature (15 K), comparable to those from exfoliated flakes. The FET device with a channel length of 100 nm displays a high on-state current of ~400 µA/µm, encouraging the industrialization of 2D materials.
  • Charge transfer mediated triplet excited state formation in donor-acceptor-donor BODIPY: Application for recording of holographic structures in photopolymerizable glass

    Mikulchyk, Tatsiana; Karuthedath, Safakath; De Castro, Catherine S. P.; Buglak, Andrey A.; Sheehan, Aimee; Wieder, Aaron; Laquai, Frédéric; Naydenova, Izabela; Filatov, Mikhail A. (JOURNAL OF MATERIALS CHEMISTRY C, Royal Society of Chemistry (RSC), 2022-07-18) [Article]
    Donor–acceptor–donor BODIPY triads bearing anthracene or pyrene as electron donating subunits were prepared through a stepwise synthesis. Photoinduced electron transfer and formation of long-lived triplet excited states via spin–orbit charge transfer intersystem crossing (SOCT-ISC) was studied by steady-state and ultrafast pump-probe spectroscopy and further supported by DFT computations. New BODIPYs were found to form triplet states and sensitize singlet oxygen in both polar and non-polar solvents which is unusual for photosensitizers operating via SOCT-ISC. BODIPY-anthracene triad (ABA) was used as a photosensitizer component in a photopolymerizable glass that was prepared by a four-step sol–gel process. ABA in combination with N-phenylglycin (NPG) showed the ability to initiate a free-radical polymerization of methacrylate monomers under 532 nm irradiation thus allowing for holographic recording of diffractive structures. High diffraction efficiency (up to 87%) obtained for ABA-NPG containing glass as compared to a reference diiodo-BODIPY (I2BDP) demonstrates for the first time that heavy-atom-free SOCT-ISC photosensitizers can efficiently operate in the solid state.
  • Addition of Diquat Enhances the Electron Mobility in Various Non-Fullerene Acceptor Molecules

    Nugraha, Mohamad; Gedda, Murali; Firdaus, Yuliar; Scaccabarozzi, Alberto D.; Zhang, Weimin; Alshammari, Sanaa Hayel Nazil; Aniés, Filip; Adilbekova, Begimai; Emwas, Abdul-Hamid; McCulloch, Iain; Heeney, Martin; Tsetseris, Leonidas; Anthopoulos, Thomas D. (Advanced Functional Materials, Wiley, 2022-07-15) [Article]
    Molecular doping of organic semiconductors is often used to enhance their charge transport characteristics. Despite its success, however, most studies to date concern p-doping with considerably fewer reports involving n-dopants. Here, n-doping of organic thin-film transistors (OTFTs) based on several non-fullerene acceptor (NFA) molecules using the recently developed diquat (DQ) as a soluble molecular dopant is reported. The low ionization potential of DQ facilitates efficient electron transfer and subsequent n-doping of the NFAs, resulting in a consistent increase in the electron field-effect mobility. Solution-processed BTP-eC9 and N3-based OTFTs exhibit significant increase in the electron mobility upon DQ doping, with values increasing from 0.02 to 0.17 cm2 V–1 s–1 and from 0.2 to 0.57 cm2 V–1 s–1, respectively. A remarkable electron mobility of >1 cm2 V–1 s–1 is achieved for O-IDTBR transistors upon optimal doping with DQ. The enhanced performance originates primarily from synergistic effects on electronic transport and changes in morphology, including: i) significant reduction of contact resistances, ii) formation of larger crystalline domains, iii) change of preferred crystal orientation, and iv) alteration in molecular packing motif. This work demonstrates the universality of DQ as an electronic additive for improving electron transport in OTFTs.
  • Lecithin Capping Ligands Enable Ultrastable Perovskite-Phase CsPbI3 Quantum Dots for Rec. 2020 Bright-Red Light-Emitting Diodes

    Mir, Wasim Jeelani; Alamoudi, Ahmed; Yin, Jun; Yorov, Khursand E.; Maity, Partha; Naphade, Rounak; Shao, Bingyao; Wang, Jiayi; Lintangpradipto, Muhammad Naufal; Nematulloev, Saidkhodzha; Emwas, Abdul-Hamid M.; Genovese, Alessandro; Mohammed, Omar F.; Bakr, Osman (Journal of the American Chemical Society, American Chemical Society (ACS), 2022-07-14) [Article]
    Bright-red light-emitting diodes (LEDs) with a narrow emission line width that emit between 620 and 635 nm are needed to meet the latest industry color standard for wide color gamut displays, Rec. 2020. CsPbI3 perovskite quantum dots (QDs) are one of the few known materials that are ideally suited to meet these criteria. Unfortunately, CsPbI3 perovskite QDs are prone to transform into a non-red-emitting phase and are subject to further degradation mechanisms when their luminescence wavelength is tuned to match that of the Rec. 2020 standard. Here, we show that zwitterionic lecithin ligands can stabilize the perovskite phase of CsPbI3 QDs for long periods in air for at least 6 months compared to a few days for control samples. LEDs fabricated with our ultrastable lecithin-capped CsPbI3 QDs exhibit an external quantum efficiency (EQE) of 7.1% for electroluminescence centered at 634 nm─a record for all-inorganic perovskite nanocrystals in Rec. 2020 red. Our devices achieve a maximum luminance of 1391 cd/m2 at 7.5 V, and their operational half-life is 33 min (T50) at 200 cd/m2─a 10-fold enhancement compared to control samples. Density functional theory results suggest that the surface strain in CsPbI3 QDs capped with the conventional ligands, oleic acid and oleylamine, contributes to the instability of the perovskite structural phase. On the other hand, lecithin binding induces virtually no surface strain and shows a stronger binding tendency for the CsPbI3 surface. Our study highlights the tremendous potential of zwitterionic ligands in stabilizing the perovskite phase and particle size of CsPbI3 QDs for various optoelectronic applications.
  • Recent Advances in Chemistry/Materials (Saudi Arabia)

    Aziz, Md. Abdul; Hossain, M. Mozahar; Mohammed, Omar F. (The Chemical Record, Wiley, 2022-07-08) [Article]
    Saudi Arabia in recent years has made considerable progress in the field of chemistry and material science, especially in topics, such as nanotechnology, energy storage, and photovoltaics. This special issue comprises high-quality contributions by researchers in the country.
  • Photophysics of Defect-Passivated Quasi-2D (PEA)2PbBr4 Perovskite Using an Organic Small Molecule

    Khan, Jafar Iqbal; Gedda, Murali; Wang, Mingcong; Yengel, Emre; Kreß, Joshua A.; Vaynzof, Yana; Anthopoulos, Thomas D.; Laquai, Frédéric (ACS Energy Letters, American Chemical Society (ACS), 2022-07-07) [Article]
    2D Ruddlesden–Popper perovskites are promising candidates for energy-harvesting applications because of their tunable optical properties and ambient stability. Moreover, they are solution-processable and compatible with scalable manufacturing via various printing techniques. However, such methods often induce large degrees of heterogeneity because of poorly controlled crystallization. We address this issue by blending the well-known 2D perovskite (PEA)2PbBr4 with an organic small molecule, C8-BTBT. Terahertz (THz) absorption and temperature-dependent photoluminescence (PL) spectroscopy studies revealed changes in the photophysical properties of the perovskite without affecting its structural integrity upon adding C8-BTBT. The inclusion of trace amounts of C8-BTBT results in defect passivation both at perovskite platelet boundaries and at surfaces, as indicated by increased carrier lifetimes and substantially increased photoluminescence quantum yields (PLQY). This improves the responsivity of photodetectors using the 2D perovskite as an active layer. Our study highlights a straightforward strategy for fabricating high-quality 2D perovskites via large-area processing techniques.
  • Two-dimensional ferroelectricity and antiferroelectricity for next-generation computing paradigms

    Xue, Fei; Ma, Yinchang; Wang, Hua; Luo, Linqu; Xu, Yang; Anthopoulos, Thomas D.; Lanza, Mario; Yu, Bin; Zhang, Xixiang (Matter, Elsevier BV, 2022-07-06) [Article]
    Ferroelectricity (FE) and antiferroelectricity (AFE) are correlated physical phenomena that, in the two-dimensional (2D) limit, exhibit unprecedented rich physics in terms of polarization creation, stabilization, and switching. By modulating the proximity effect of polarization, 2D FE and AFE can unexpectedly demonstrate reversible transformations. Moreover, these fundamental physics can spur innovation in memory devices toward emerging computation paradigms, including neuromorphic computing and sensing. In this perspective, we discuss the emergent physics of 2D FE and AFE and highlight phase transitions with different approaches between them. We also outline advanced device applications for next-generation computing and provide possible future research lines.
  • Unraveling the Correlation between Raman and Photoluminescence in Monolayer MoS2 through Machine Learning Models

    Lu, Ang-Yu; Martins, Luiz Gustavo Pimenta; Shen, Pin-Chun; Chen, Zhantao; Park, Ji-Hoon; Xue, Mantian; Han, Jinchi; Mao, Nannan; Chiu, Ming-Hui; Palacios, Tomás; Tung, Vincent; Kong, Jing (Advanced Materials, Wiley, 2022-07-05) [Article]
    Two-dimensional (2D) transition metal dichalcogenides (TMDCs) with intense and tunable photoluminescence (PL) have opened up new opportunities for optoelectronic and photonic applications such as light-emitting diodes, photodetectors, and single-photon emitters. Among the standard characterization tools for 2D materials, Raman spectroscopy stands out as a fast and non-destructive technique capable of probing material crystallinities and perturbations such as doping and strain. However, a comprehensive understanding of the correlation between photoluminescence and Raman spectra in monolayer MoS2 remains elusive due to its highly nonlinear nature. Here, we systematically explore the connections between PL signatures and Raman modes, providing comprehensive insights into the physical mechanisms correlating PL and Raman features. Our analysis further disentangles the strain and doping contributions from the Raman spectra through machine learning models. First, we deploy a DenseNet to predict PL maps by spatial Raman maps. Moreover, we apply a gradient boosted trees model (XGBoost) with Shapley additive explanation (SHAP) to bridge the impact of individual Raman features in PL features, allowing us to link the strain and doping of monolayer MoS2. Last, we adopt a support vector machine (SVM) to project PL features on Raman frequencies. Our work may serve as a methodology for applying machine learning in 2D material characterizations and providing the knowledge for tuning and synthesizing 2D semiconductors for high-yield photoluminescence.

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