Elsevier

Nano Energy

Volume 88, October 2021, 106231
Nano Energy

Shape-dependent in-plane piezoelectric response of SnSe nanowall/microspheres

https://doi.org/10.1016/j.nanoen.2021.106231Get rights and content

Highlights

  • Large-scale, crystalline SnSe nanowall/µ-spheres grown on flexible conductive wires.

  • Robust piezoelectricity (19.9 pm V-1) of SnSe nanowall overcomes the monolayer limit.

  • Shape, position, frequency-dependent piezoelectric response shows antiparallel domains.

  • Switchable polar domains, butterfly amplitude curves confirm ferroelectricity of SnSe.

  • WT-SnSe nanowall-PNG device used to harness, monitor biomechanical human finger force.

Abstract

Group-IV monochalcogenides (MCs) belong to a noncentrosymmetric C2v point group, have gained immense interest due to their semiconducting-electromechanical coupling behavior. Large polarization predicted in the armchair, zigzag directions of monolayer MCs leads to giant piezoelectricity than the other two-dimensional MX2 (M = metal, and X = S, Se, Te) compounds. Herein, we report the discovery of shape, size-dependent piezoelectric response of SnSe nanowall (NWs)/µ-spheres using a driving frequency-dependent piezoelectric force microscopy approach. The robust, high in-plane piezoelectric coefficient of ≈ 19.9 pm V-1 achieved for few-layered SnSe NWs (average width ≈35 nm), which overcomes the monolayer piezoelectricity limit in SnSe and odd/even layer combinations. The NWs/µ-spheres exhibited traditional butterfly-shaped amplitude curves, polar domains with a 180° phase shift confirmed the in-plane ferroelectric nature. Energy conversion, monitoring of human finger bending angles (30°, 60°, and 90°) was demonstrated by wire-type SnSe NW-based piezoelectric nanogenerator. Overall, the current study shows a large-scale homogeneous growth of highly crystalline MCs on flexible conductive wires by a one-pot solution-mediated process. This process will facilitate the fabrication of nanoscale piezoelectric/ferroelectric devices for neuromorphic computing, field-effect transistors, micro-power sources, and flexible medical electronic systems.

Graphical Abstract

Probing the shape-dependent piezoelectricity, switchable polar domains of radially grown SnSe for utilizing the energy conversion process and sensor applications.

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Introduction

Exploration of concealed inherent properties of transition metal chalcogenides (TMCs) according to their shape- and size-dependent nanostructure, compositional variation, crystal-structure modulation, and cost-effective synthetic route is of increasing interest [1], [2], [3], [4], [5], [6]. Recent advancements in TMCs revealed semiconducting [2], [7], optical [5], piezoelectric (PE) [4], [6], ferroelectric (FE) [1], [2], thermoelectric [8], and magnetic [9] properties by reducing the material size from the bulk to nanoscale level. The ability to form ultrathin layers conveying superior mechanical flexibility and moderate PE/FE properties to TMCs makes them an alternative material for conventional PE/FE material-based electronic devices [1], [2], [3], [4], [5], [6]. Moreover, growth in the miniaturization of interface-assembling conventional electronic devices is slow due to severe material limitations, which include the critical thickness limit, lattice imparity between the substrate and grown layer, large bandgap, surface defects, and the post-metallization annealing process [10], [11], [12]. Additionally, the devices suffer from poor toughness, high stiffness, low durability, and high density [12]. Therefore, the development of novel functional materials at the nanoscale or atomic level is necessary for their commercial application in optoelectronic, military, medical, and security fields [1], [2], [3], [4], [5], [6]. The 0.63-nm step height of SnTe [13], multilayer In2Se3 [14], 0.6-nm-thick monolayer MoS2 [15], 1.4-nm-thick two-layered WTe2 [16], and 0.8-nm-thin single-layered MoTe2 [17] have demonstrated the FE/PE properties at room temperature. These materials show better PE/FE properties compared with wurtzite structures (e.g., ZnO, GaN, and InN) but not with conventional materials [18], [19], [20], [21], [22]. Several theoretical predictions of the PE/FE nature of TMCs at the monolayer and multilayer levels, and various nanostructure shapes, have been reported but still lack experimental evidence. Also, the chemical structure stability, polarization directions, and intrinsic properties of TMCs are under investigation. High PE/FE performance of a TMC material has not yet been achieved experimentally, and thus continued research investigation is warranted [23], [24], [25].

Large spontaneous polarization predicted for Group-IV monochalcogenides (MCs; SnS, GeSe, GeS, and SnSe) may generate very large PE coefficients of up to 75–251 mV–1, which are several fold higher than those attainable by dichalcogenides and other two-dimensional (2D) materials [24]. These MC materials possess an orthorhombic crystal structure with a noncentrosymmetric C2v point group. The flexible puckered structure along the armchair direction induces a remarkable electric dipole moment under applied electrical/mechanical field stress. In recent times, the monolayer PE/FE properties of SnS have been experimentally measured using piezoresponse force microscopy (PFM) [2]. Multilayer (< 15 layers) SnS exhibits robust FE behavior and overcomes the FE limit in monolayer SnS and the even/odd layer effect [3]. Like SnS, the naturally abundant SnSe semiconductor is of significant interest due to its use in thermoelectric, photoelectric, memory, and Li-ion battery applications [8], [26]. A wide variety of SnSe structures, including nanosheets, nanoflowers, nanoplates, textured thin films, and nanorod arrays, have been synthesized for thermoelectric applications. Furthermore, the anisotropic crystalline nature of SnSe (noncentrosymmetric point group in an orthorhombic crystal structure of space group Pnma) favors the possibility of the PE property, similar to other Group-IV MCs [24], [26]. But no experimental evidence has been reported until now because of the lack of measurement techniques and sufficient understanding of the intrinsic properties at the atomic or nanoscale level. PFM and scanning tunneling microscopy techniques open up the possibility of measuring PE behavior at the atomic or nanoscale level [2], [14], [17], [27], [28]. However, the role of shape, size-dependent, multilayer intrinsic PE properties of materials has not been explored systematically.

Herein, the shape- and size-dependent PE/FE properties of Group-IV MC SnSe nanowalls/microspheres (NWs/µ-spheres) at room temperature are reported for the first time. Significant SnSe morphological changes were observed during growth on Sn wire in a solvent-assisted one-pot solution-mediated (SM) method. We observed homogeneous nucleation, high crystalline quality, and large-scale uniform growth of SnSe on a flexible Sn wire (diameter: ~800 µm). The SnSe NWs, having an average width of ~35 nm, generated a much higher PE coefficient (19.9 pm V–1) than the outward grown nanoparticles (NPs) composed of SnSe µ-spheres (6.8 pm V–1). The average lateral length of the NPs within a µ-sphere was ~168 nm. The direction of FE polarization, 180° polar nanodomain switching, and localized position/frequency-dependent in-plane PE coefficient of SnSe were investigated systematically. We also evaluated the formation of bias voltage-dependent polarized domains of SnSe with a clear 180° phase shift. This work confirms that modern MCs are candidates for replacing conventional PE/FE materials in the development of advanced smart electronic devices.

Section snippets

Results and discussion

Fig. 1a schematically illustrates the growth of SnSe micro/nanostructures on a flexible conductive wire at 200 °C/24 h via the SM growth technique; the detailed synthetic procedure is given in the Supporting Information. The purity of the solvent medium affected the surface morphology of growing SnSe; i.e., NWs were generated in ethanol (> 94.5% ethanol, < 0.02% methanol, and < 2 ppm heavy metals), whereas µ-spheres were formed in absolute ethanol (> 99.9% ethanol, < 0.025% methanol, 0.05% <

Conclusions

Large-scale, homogeneous, high crystalline SnSe NWs/µ-spheres were grown on a flexible Sn wire via the cost-effective one-pot SM growth approach, which is superior to vapor deposition (physical, chemical) techniques, hydrothermal, and others. The SnSe NWs/µ-spheres exhibited typical butterfly-shaped amplitude curves, and polar domains showing a 180° phase shift confirmed intrinsic PE and FE behavior. The calculated in-plane PE coefficient (19.9 pm V-1) of few-layer SnSe NWs is several-fold

Supplementary material

  • (1)

    Experimental section: Synthesis of SnSe nanowall (NW) and µ-spheres, Fabrication of wire-type SnSe NW piezoelectric Nanogenerator (WT-SnSe NW-PNG), and Characterization techniques.

  • (2)

    Supporting Figures (S1-S9): Optical images of as-grown SnSe NW/ µ-spheres on flexible conductive wire, FESME and EDS mapping analysis, Grain-size distribution analysis using the image-J software, PFM analysis of substrate, Line profile data to confirm the 180° ferroelectric polar domains, Experimental test-site to

CRediT authorship contribution statement

N. R. Alluri: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Data curation, Writing - original draft, Writing - review & editing, Visualization, Supervision, Project administration, Funding acquisition. N. P. M. J. Raj: Investigation (Sample synthesis). G. Khandelwal: Investigation (PFM analysis). S. J. Kim: Resources, Supervision, Project administration, Funding acquisition.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) grant funded by the Korea government (MIST) (2018R1D1A1B07049944, 2019R1A2C3009747, and 2021R1A4A2000934).

Dr. Nagamalleswara Rao Alluri currently working as a postdoctoral researcher at Nanomaterials & Systems Lab, Department of Mechatronics Engineering, Jeju National University (JNU). He is the recipient of a young investigator project as a principal investigator form the National Research Foundation of Korea. He received a Ph.D. degree at Applied Energy Systems (Mechanical Engineering) from JNU under the supervision of Prof. Kim Sang-Jae, Prof. Ji Hyun. He obtained his Master of Technology in

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    Dr. Nagamalleswara Rao Alluri currently working as a postdoctoral researcher at Nanomaterials & Systems Lab, Department of Mechatronics Engineering, Jeju National University (JNU). He is the recipient of a young investigator project as a principal investigator form the National Research Foundation of Korea. He received a Ph.D. degree at Applied Energy Systems (Mechanical Engineering) from JNU under the supervision of Prof. Kim Sang-Jae, Prof. Ji Hyun. He obtained his Master of Technology in Sensor Systems (VIT University) and Master of Science in Condensed Mater Physics (Andhra University). His research interests include growth of nanomaterials, micro/nanodevices, energy harvesters and self-powered sensors.

    Dr. Nirmal Prashanth Maria Joseph Raj is currently working as a postdoctoral researcher at the Department of Mechatronics Engineering in Jeju National University, Jeju, South Korea where he is a scholarship recipient from the Brain Korea Program. He has a Master of Philosophy and Master of Science in Physics from Bishop Heber college, Bharathidasan university, Tamilnadu, India and Bachelors of Science in Physics degree from St. Josephs College, Bharathidasan university, Tamilnadu, India. His research interest includes piezoelectric materials, self-powered systems and sensors, and photocatalyst applications.

    Dr. Gaurav Khandelwal is currently working as a postdoctoral researcher at the Department of Mechatronics Engineering at Jeju National University, South Korea. He holds a Bachelor and Master degree in Nanotechnology from Centre for Converging Technologies, U.O.R, India. He worked as Project Associate at Indian Institute of Technology (I.I.T), Delhi India. He also worked as a research intern in the field of “Peptide-based nanofibers” at Institute of Nano Science and Technology (I.N.S.T), India. His current research area includes Triboelectric Nanogenerators, nanomaterial synthesis, and characterization.

    Prof. Sang Jae Kim is a professor in the Department of Mechatronics Engineering and the Department of Advanced Convergence Technology and Science in Jeju National University, Republic of Korea. Also, a fellow member of Korean Academy and Science (KAST). He received his PhD degree in Electrical Communication Engineering from Tohoku University, Japan. He was a visiting research scholar in materials science department at University of Cambridge, UK and at Georgia Institute of Technology, USA as well as a senior researcher at National Institute of Materials Science. His research disciplines are based on nanomaterials and systems for energy and electronics applications, covering Josephson devices, MEMS, supercapacitors, nanogenerators and nanobiosensors.

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