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“Size-Independent” Single Electron Tunneling Jianli Zhao, Shasha Sun, Logan A Swartz, Shawn L Riechers, Peiguang Hu, Shaowei Chen, Jie Zheng, and Gang-yu Liu J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.5b02323 • Publication Date (Web): 30 Nov 2015 Downloaded from http://pubs.acs.org on December 1, 2015
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“Size-Independent” Single Electron Tunneling Jianli Zhao,1 Shasha Sun,2 Logan Swartz,3 Shawn Riechers,1 Peiguang Hu,4 Shaowei Chen,4 Jie Zheng,*2 Gang-yu Liu*1,3
1
Department of Chemistry, University of California, Davis, California 95616, United States Department of Chemistry, The University of Texas at Dallas, Texas 75080, United States 3 Biophysics Graduate Group, University of California, Davis, California 95616, United States 4 Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064, United States 2
*To whom correspondence should be addressed. Prof. Gang-yu Liu, Tel: (530) 754-9678, Fax: (530) 754-8557, E-mail:
[email protected]. Prof. Jie Zheng, Tel: (972) 883 5768, Email:
[email protected].
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ABSTRACT: Incorporating single electron tunneling (SET) of metallic nanoparticles (NPs) into modern electronic devices offers great promise to enable new properties, however it is technically very challenging, due to the necessity to integrate ultra-small particles (nanometers) into the devices. The nanosize requirements are intrinsic for NPs to exhibit quantum or SET behaviors, e.g. 10 nm or smaller, at room temperature. This work represents the first observation of SET that defies the well-known size restriction. Using polycrystalline Au NPs synthesized via our newly developed solid-state glycine matrices method, a Coulomb Blockade was observed for particles as large as tens of nanometers, and the blockade voltage exhibited little dependence on the size of the NPs. These observations are counter-intuitive at first glance. Further investigations reveal that each observed SET arises from the ultra-small single crystalline grain(s) within the polycrystal NP, which is (are) sufficiently isolated from the nearest neighbor grains. This work demonstrates the concept and feasibility to overcome orthodox spatial confinement requirements to achieve quantum effects.
Keywords: Single Electron Tunneling, Metallic Nanoparticle, Polycrystalline Gold Nanoparticles, Scanning Tunneling Microscopy, Scanning Tunneling Spectroscopy
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Single electron tunneling (SET), correlated one-by-one transfer of electrons through a Coulomb Island such as a metallic nanoparticle, offers a unique property for future single-electron devices.1-8 Coulomb Blockade (CB) and Coulomb Staircase (CS) are the two most well-known characteristics of SET.9,10 Scanning tunneling microscopy (STM) and spectroscopy (STS) have proven to be accurate test platforms for SET and conductance/capacitance measurements3,10-15 where the two electrodes and tunneling junction are shown in Figure 1B. SET is only found for nanoparticles satisfying two necessary conditions: (a) EC > kBT; the charging energy, EC = e2/2C, associated with the addition of one electron to an island with capacitance C, must exceed the thermal energy, kBT, to surpass thermally activated electron tunneling; and (b) R > 6.5 kΩ; the tunneling resistances (R) of the junctions must be larger than the quantum resistance, h/4e2 (~6.5 kΩ), in order to reach the required signal to noise ratio with respect to quantum fluctuations of electrons.6,16 At room temperature kBT = 26 meV, and thus C must be on the order of 10-18 F or smaller to fulfill EC > kBT. Considering metallic nanoparticles, the capacitance is correlated with particle size, C = 2πdɛ0ϵ, where ɛ is the dielectric constant of the coating,
represents particle
diameter, and ɛ0 is the vacuum permittivity constant.6,17 Therefore, it must be d
