Publications by authors named "Maokun Wu"

5 Publications

  • Page 1 of 1

Dehydration of Electrochemically Protonated Oxide: SrCoO with Square Spin Tubes.

J Am Chem Soc 2021 Oct 14;143(42):17517-17525. Epub 2021 Oct 14.

Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan.

Controlling oxygen deficiencies is essential for the development of novel chemical and physical properties such as high- superconductivity and low-dimensional magnetic phenomena. Among reduction methods, topochemical reactions using metal hydrides (e.g., CaH) are known as the most powerful method to obtain highly reduced oxides including NdSrNiO superconductor, though there are some limitations such as competition with oxyhydrides. Here we demonstrate that electrochemical protonation combined with thermal dehydration can yield highly reduced oxides: SrCoO thin films are converted to SrCoO by dehydration of HSrCoO at 350 °C. SrCoO forms square (or four-legged) spin tubes composed of tetrahedra, in contrast to the conventional infinite-layer structure. Detailed analyses suggest the importance of the destabilization of the SrCoO precursor by electrochemical protonation that can greatly alter reaction energy landscape and its gradual dehydration (HSrCoO) for the SrCoO formation. Given the applicability of electrochemical protonation to a variety of transition metal oxides, this simple process widens possibilities to explore novel functional oxides.
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http://dx.doi.org/10.1021/jacs.1c07043DOI Listing
October 2021

Electronic structures and anisotropic carrier mobilities of monolayer ternary metal iodides MLaI(M=Mg, Ca, Sr, Ba).

J Phys Condens Matter 2021 Jul 5;33(35). Epub 2021 Jul 5.

Department of Electronic Science and Engineering, and Tianjin Key Laboratory of Photo-Electronic Thin Film Device and Technology, Nankai University, Tianjin 300350, People's Republic of China.

Exploiting two-dimensional (2D) materials with natural band gaps and anisotropic quasi-one-dimensional (quasi-1D) carrier transport character is essential in high-performance nanoscale transistors and photodetectors. Herein, the stabilities, electronic structures and carrier mobilities of 2D monolayer ternary metal iodides MLaI(M = Mg, Ca, Sr, Ba) have been explored by utilizing first-principles calculations combined with numerical calculations. It is found that exfoliating MLaImonolayers are feasible owing to low cleavage energy of 0.19-0.21 J mand MLaImonolayers are thermodynamically stable based on phonon spectra. MLaImonolayers are semiconductors with band gaps ranging from 2.08 eV for MgLaIto 2.51 eV for BaLaI. The carrier mobility is reasonably examined considering both acoustic deformation potential scattering and polar optical phonon scattering mechanisms. All MLaImonolayers demonstrate superior anisotropic and quasi-1D carrier transport character due to the striped structures. In particular, the anisotropic ratios of electron and hole mobilities along different directions reach hundreds and tens for MLaImonolayers, respectively. Thus, the effective electron-hole spatial separation could be actually achieved. Moreover, the absolute locations of band edges of MLaImonolayers have been aligned. These results would provide fundamental insights for MLaImonolayers applying in nano-electronic and optoelectronic devices.
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http://dx.doi.org/10.1088/1361-648X/ac0c3dDOI Listing
July 2021

Ideal two-dimensional solid electrolytes for fast ion transport: metal trihalides MX with intrinsic atomic pores.

Nanoscale 2020 Apr;12(13):7188-7195

Department of Electronic Science and Engineering, Key Laboratory of Photo-Electronic Thin Film Device and Technology of Tianjin, Nankai University, Tianjin, 300350, China.

Exploring ultrathin two-dimensional (2D) solid electrolytes with fast ion transport is highly desirable in nanoelectronics, ionic devices and various energy storage systems, following the rapid scaling of devices to the nanometer scale. Herein, two-dimensional (2D) metal trihalides MX3 (ScCl3, ScBr3, AsI3, ScI3, YBr3, SbI3, YI3 and BiI3) with intrinsic atomic pore structures have been examined and found to be promising as realistic 2D solid electrolytes. Through examining the binding interactions and the diffusion barriers of monolayer MX3-ion (Li+, Na+, K+, Mg2+, and Ca2+) systems by utilizing first principles calculations, it is found that MX3-ion complexes are energetically favorable and the energy barriers of some MX3-ion systems are comparable to or even smaller than those of the conventional solid electrolyte systems. More significantly, the short diffusion time of Na+ and K+ ions in some monolayers MX3 at the nanosecond (ns) or even at the sub-ns scale indicates fast ion transport. In terms of practical applications, ultrafast Li+ travelling in the timescale of sub-ns to ns and Na+ in several tens ns in few-layer MX3 is achieved. In addition, the insulating nature of wide band gaps for MX3 is maintained during the ion transport, which is essential for solid electrolytes. These theoretical results provide fundamental guidance that MX3 materials with natural atomic pores are realistic candidates for 2D solid electrolytes with broad applications in ionic devices and energy storage devices.
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http://dx.doi.org/10.1039/c9nr08719bDOI Listing
April 2020

Molecularly Thin Electrolyte for All Solid-State Nonvolatile Two-Dimensional Crystal Memory.

Nano Lett 2019 12 11;19(12):8911-8919. Epub 2019 Nov 11.

Department of Chemical and Petroleum Engineering , University of Pittsburgh , Pittsburgh , Pennsylvania 15260 , United States.

A molecularly thin electrolyte is developed to demonstrate a nonvolatile, solid-state, one-transistor (1T) memory based on an electric-double-layer (EDL) gated WSe field-effect transistor (FET). The custom-designed monolayer electrolyte consists of cobalt crown ether phthalocyanine and lithium ions, which are positioned by field-effect at either the surface of the WSe channel or an h-BN capping layer to achieve "1" or "0", respectively. Bistability in the monolayer electrolyte memory is significantly improved by the h-BN cap with density functional theory (DFT) calculations showing enhanced trapping of Li near h-BN due to a ∼1.34 eV increase in the absolute value of the adsorption energy compared to vacuum. The threshold voltage shift between the two states corresponds to a change in charge density of ∼2.5 × 10 cm, and an On/Off ratio exceeding 10 at a back gate voltage of 0 V. The On/Off ratio remains stable after 1000 cycles and the retention time for each state exceeds 6 h (max measured). When the write time approaches 1 ms, the On/Off ratio remains >10, showing that the monolayer electrolyte-gated FET can respond on time scales similar to existing flash memory. The data suggest that faster switching times and lower switching voltages could be feasible by top gating.
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http://dx.doi.org/10.1021/acs.nanolett.9b03792DOI Listing
December 2019

First-Principle Prediction on STM Tip Manipulation of Ti Adatom on Two-Dimensional Monolayer YBr.

Scanning 2019 4;2019:5434935. Epub 2019 Feb 4.

Department of Electronic Science and Engineering and Tianjin Key Laboratory of Photo-Electronic Thin Film Device and Technology, Nankai University, Tianjin 300071, China.

Scanning tunneling microscopy (STM) is an important tool in surface science on atomic scale characterization and manipulation. In this work, Ti adatom manipulation is theoretically simulated by using a tungsten tip (W-tip) in STM based on first-principle calculations. The results demonstrate the possibility of inserting Ti adatoms into the atomic pores of monolayer YBr, which is thermodynamically stable at room temperature. In this process, the energy barriers of vertical and lateral movements of Ti are 0.38 eV and 0.64 eV, respectively, and the Ti atoms are stably placed within YBr by >1.2 eV binding energy. These theoretical predictions provide an insight that it is experimentally promising to manipulate Ti adatom and form artificially designed 2D magnetic materials.
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http://dx.doi.org/10.1155/2019/5434935DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6378768PMC
March 2019
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