Abstract
Nanotips made of metal and semiconductor have been widely utilized in versatile applications to strengthen the electric field through lightning rod effect and localized surface plasmon resonance (LSPR) effect. Here, we present the utilization of ferroelectric nanotips to assist photoreduction of silver nanostructures for surface enhanced Raman scattering (SERS). Ferroelectric nanotips with spontaneous polarization posses the unique feature of producing the permanent electrostatic field without requiring external excitation, which differs from the present nanotips requiring electrical and optical excitation. The enhanced electrostatic field promotes the formation of silver nanoparticles by reducing the effect of Stern layer and accelerating the movement of photoelectrons and silver ions to the template surface. Experimental results show that sharp ferroelectric nanotips facilitate the formation of large-diameter nanoparticles with strong LSPR action. Compared to the conventional ferroelectric templates, the SERS substrates using nanotip-equipped ferroelectric templates produce 5.51 times larger Raman intensity, which can be further increased by >10.76 times by increasing the reaction time. The proposed SERS substrate owns the limit of detection <10−8 M and the enhancement factor of 2.3 × 109. The presented ferroelectric nanotips with permanent electrostatic field would open promising applications in the versatile areas, such as nanomaterial fabrication and optoelectronic devices.
Highlights
Ferroelectric lithography is an emerging technique to produce micro-/nano-scale patterns correlating with the polarization distribution on the ferroelectric templates[1]
Because the electrostatic force microscopy (EFM) output signal intensity is proportional to the gradient of electrostatic field intensity, the enhancement degree of electrostatic field produced by ferroelectric nanotips can not be measured directly
We have demonstrated the nanotip-assisted photoreduction of silver nanoparticles using ferroelectric nanotips with the permanent electrostatic field for surface enhanced Raman scattering
Summary
Ferroelectric lithography is an emerging technique to produce micro-/nano-scale patterns correlating with the polarization distribution on the ferroelectric templates[1]. Nanotips made of metal and semiconductor have been produced on the substrates and star nanoparticles by various fabrication methods, such as micro-electrodischarge[18], focused ion beam (FIB) milling[19], electron cyclotron resonance (ECR) etching[20], electrochemical etching[21], chemical reduction[22], vapor phase epitaxy[23] and so on They have been utilized in the diverse applications, such as scanning probing measurement[24], nanoscale manipulation[25], field emission devices[26], tip enhanced Raman spectroscopy[27], and surface enhanced Raman scattering[22]. The proportionality of EF to the fourth power of the localized electric field intensity greatly enhances the SERS signal intensity
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