Terahertz Time‐Domain Spectroscopy and Near‐Field Microscopy of Transparent Silver Nanowire Networks

Abstract

spin-coating to spray-coating, electrospinning, and dip coating. [3,6,7] Furthermore, large-area lithography and metal coating techniques are increasingly emerging as promising alternatives. [8][9][10] However, it is not uncommon for these deposition techniques to result in a conductance that varies spatially due to local modulations in the network thickness or connectivity. These spatial modulations of the electrical conductance are impossible to detect with standard characterization techniques such as the four-point probe method, in which the electrical impedance is measured using a pair of separated electrodes carrying a current and sensing the voltage differences. Furthermore, although microprobes have been developed to map the conductance with high spatial resolution, [11] the four-point probe technique requires electrical contact with the surface, leading to the risk of modifying the sample. These limitations highlight the need for a contact-free and high resolution technique to map electrical conductance over large areas. Broadband and phase sensitive spectroscopic techniques, such as terahertz time-domain spectroscopy (THz-TDS), have emerged as powerful alternatives for probing the complex conductivity of samples. [12][13][14][15] THz-TDS uses very short (single cycle) electromagnetic pulses as low frequency electromagnetic probes to measure the electronic properties. This probing is done by measuring the attenuation and the phase of the THz pulse as it propagates through the medium and interacts (mainly) with free charge carriers. A major advantage of THz-TDS over four-point probe techniques is that it is a contact free technique, which also enables an easy implementation of conductivity scans. The diffraction limit of electromagnetic waves (on the order of the wavelength) defines the maximum spatial resolution that can be attained for the determination of the conductivity using far-field THz techniques. The broadband character of THz-TDS and the standard focusing optics, with relatively low numerical aperture, leads to spatial resolutions on the order of 1 mm or larger.In this manuscript, we synthesize highly monodisperse AgNWs with a diameter of ≈50 nm and a length of ≈10 μm by adapting a polyol method. [16] Subsequently, transparent electrodes are prepared by spray coating the AgNWs solution on top of 25 × 25 mm 2 quartz substrates. The nanowire monodispersity allows us to draw quantitative conclusions from the measurements performed on the conductive networks. We spatially vary the thickness of the AgNWs network across the quartz substrate, and therefore its optical transmission and THz conductance, by adjusting the spray coating conditions. Transparent conductive layers are key components of optoelectronic devices. Here, a polyol method is used to synthesize large quantities of monodisperse silver nanowires (AgNWs) and these are used to fabricate transparent conducting networks over large areas. The optical extinction and terahertz (THz) conductance of these networks are simultaneously investigated,...

Transparent Heaters: A Review

“…[ 93 ] In addition, terahertz spectroscopy has been used for noncontact measurement of the conductance of AgNW networks. [ 94 ]…”

Characterization of Silver Nanowire Layers in the Terahertz Frequency Range

“…In metal nanowire networks, adjusting the length, diameter, and concentration of wires allows tuning of the optical/THz properties that may lead to improvement of the efficiency of nanowire-based antennas [ 14 , 18 , 23 , 24 ]. Metal nanowires, especially silver nanowires (AgNWs), are a prospective material for nanoelectronic circuits, transparent and conductive coatings, printable antennas, and other applications [ 22 , 25 , 26 , 27 , 28 , 29 , 30 ]. There are numerous reports on the fabrication of AgNW layers, such as vacuum filtration [ 31 , 32 ], transfer printing [ 33 , 34 , 35 ], air-spraying from suspension [ 36 , 37 ], and rod-coating technique [ 38 , 39 ].…”

Terahertz Conductivity of Silver Nanowire Layers

“…14,18,23,24 Metal nanowires, especially silver nanowires (AgNWs), are a perspective material for nanoelectronic circuits, transparent and conductive coatings, printable antennas, and other applications. 22,[25][26][27][28][29][30] There are numerous reports on the fabrication of AgNW layers, such as vacuum filtration, 31,32 transfer printing, [33][34][35] " air-spraying from suspension, 36,37 and rod-coating technique. 38,39 Nevertheless, all of these methods present several challenges related to the inability to obtain layers that would simultaneously exhibit excellent high frequency/THz properties, low surface roughness, high transparency, flexibility, and stretchability.…”