NJU research group realized material synthesis lab on the device

NJU research group realized material synthesis lab on the device

Low-dimensional materials will play an increasingly important role in future developments in the fields of physics, chemistry, biology and electronics. Different applications rely on materials with different properties, which presents customizable requirements for the materials synthesis. In particular, developing a preparation method for low-dimensional materials that can perform electrical tests in situ is crucial for the study of condensed matter physics, electronics and electrochemistry. However, traditional material synthesis usually relies on vast experimental space and lengthy waiting time, which makes it incompatible with in-situ electrical measurements and device applications. This thus leads to high technical barriers between material synthesis and application. Therefore, the exploration of a new paradigm for the synthesis of low-dimensional materials has become an important issue in the field of materials science.

Recently, the research team led by Shi-Jun Liang and Feng Miao from the School of Physics at Nanjing University, in collaboration with teams from the Southern University of Science and Technology and Sun Yat-Sen University, reported an on-device phase engineering based material synthesis paradigm, which allows forin-situ realizing various lattice phases with distinct stoichiometries andimplementingversatilefunctions, thus opening a new pathway for next-generation technology of low-dimensional material synthesis. The relevant work titled "On-device phase engineering" has been published on Nature Materials, with Xiaowei Liu, Dr. Junjie Shan, Tianjun Cao, Liang Zhu and Jiayu Ma as the co-first authors, and Prof. Xin Luo, Prof. Junhao Lin,Prof. Shi-Jun Liangand Prof. Feng Miao as corresponding authors. (https://www.nature.com/articles/s41563-024-01888-y).

The abstract of the paper is as following:

In situ tailoring of two-dimensional materials' phases under external stimulus facilitates the manipulation of their properties for electronic, quantum and energy applications. However, current methods are mainly limited to the transitions among phases with unchanged chemical stoichiometry. Here we propose on-device phase engineering that allows us to realize various lattice phases with distinct chemical stoichiometries. Using palladium and selenide as a model system, we show that a PdSe₂ channel with prepatterned Pd electrodes can be transformed into Pd₁₇Se₁₅ and Pd₄Se by thermally tailoring the chemical composition ratio of the channel. Different phase configurations can be obtained by precisely controlling the thickness and spacing of the electrodes. The device can be thus engineered to implement versatile functions in situ, such as exhibiting superconducting behavior and achieving ultralow-contact resistance, as well as customizing the synthesis of electrocatalysts. The proposed on-device phase engineering approach exhibits a universal mechanism and can be expanded to 29 element combinations between a metal and chalcogen. Our work highlights on-device phase engineering as a promising research approach through which to exploit fundamental properties as well as their applications.

Fig. 1 | The concept of on-device phase engineering.a, Schematic illustration of on-device phase engineering under thermal treatment. b, The device top view showing atomic structures before and after phase engineering. Region I is PdSe₂ and regions II and III are other phases of Pd-Se. c, Optical images of PdSe₂ field-effect device before and after thermal treatment, onto which metal electrodes (60 nm Pd/20 nm Au) were deposited. Region I represents the pristine PdSe₂ phase while regions II and III exhibit color contrasts different from region I, indicating the generation of new phases. d, The Raman spectra for regions I, II and III in the bottom panel of c. The Raman spectrum measured in region I corresponds to the pristine PdSe₂ phase, whereas regions II and III exhibit different Raman spectra, verifying the creation of new phases.

Fig. 2 | Atomic STEM characterization of the on-device polymorphic Pd_xSe_y crystal.a, Low-magnification HAADF-STEM image of the device after phase engineering. Brighter contrast is induced by phase transition. b, EDS spectrum of the brighter region near the electrode. Pd/Se ratio is estimated to be 1.1:1. c, Quantitative EDS analysis of the Pd/Se ratio across the interface labelled by the blue square in a. d,e, HAADF-STEM images (left side) of the pristine PdSe₂ along the [001] zone axis (d), and a representative Pd₁₇Se₁₅ domain along the [221] zone axis (e). The corresponding simulated images and the atomic models are shown in the upper and bottom right panels, respectively. f, Atomic-resolution HAADF image of the phase boundary between PdSe₂ and Pd₁₇Se₁₅. g, Low-magnification HAADF-STEM image of the device after phase engineering. h, HAADF-STEM image of a representative Pd₄Se domain along the [201] zone axis. Simulated image and the atomic model are shown in the upper and bottom right panels, respectively. i, The corresponding fast Fourier transform image of Pd₄Se in h.

Fig. 3 | On-device multiphase engineering for fundamental studies and versatile applications.a, Phase diagram for electrode spacings and relative thickness of Pd electrode and PdSe₂ (T_Pd/T_PdSe2). b, Optical images of PdSe₂ device used for implementing multiphase engineering; the top and bottom panels show optical images of before and after phase engineering, respectively. c,d, The electrical transport measurement of the R-T curves of the Pd₄Se phase and Pd₁₇Se₁₅ phase. The inset in c shows the I-V characteristics at different temperatures, while the inset in d shows the I-V characteristics at room temperature. e, The contact resistance (R_c) of PdSe₂ field-effect transistors before and after phase engineering plotted against channel length. The inset in e is the optical image of the device. f, Schematic of the micro-electrochemical cell for HER measurement. High-purity graphite and Ag/AgCl electrodes serve as counter and reference electrodes, respectively. The entire device is completely covered with polymethyl methacrylate (PMMA), except for the window at the top of the Pd₁₇Se₁₅ phase (with phase engineering) or PdSe₂ phase (without phase engineering). Only the exposed basal planes are in contact with the electrolyte (0.5 M H₂SO₄). g, Electrocatalytic performance (polarization curves and Tafel slopes (inset in g)) of the basal planes with and without phase engineering.

Fig. 4 | Universal mechanism for other 2D layered materials.a, Migration barriers of Pd atoms of different diffusion paths, including the vertical diffusion of Pd atoms through the van der Waals interface between Pd and PdSe₂, the lateral diffusion of Pd atoms along the van der Waals gap of PdSe₂ and the lateral diffusion of Pd atoms on the top surface of PdSe₂. b, Calculated formation energies of Pd_xSe_y as a function of the chemical potential of palladium. c, HAADF-STEM images of PdTe₂ and Pd₉Te₄ (emerging phase). d, HAADF-STEM images of SnSe₂ and SnSe (emerging phase). The insets in c and d show the fast Fourier transform images. e, Periodic table showing the metal (purple) and chalcogen (orange) combinations that can be used for on-device phase engineering according to the DFT predictions. The asterisk labels on the chalcogens in the purple region represent the systems that were experimentally realized.