Quantitative analysis of printed nanostructured networks using high-resolution 3D FIB-SEM nanotomography

Abstract

Networks of solution-processed nanomaterials are becoming increasingly important across applications in electronics, sensing and energy storage/generation. Although the physical properties of these devices are often completely dominated by network morphology, the network structure itself remains difficult to interrogate. Here, we utilise focused ion beam – scanning electron microscopy nanotomography (FIB-SEM-NT) to quantitatively characterise the morphology of printed nanostructured networks and their devices using nanometre-resolution 3D images. The influence of nanosheet/nanowire size on network structure in printed films of graphene, WS2 and silver nanosheets (AgNSs), as well as networks of silver nanowires (AgNWs), is investigated. We present a comprehensive toolkit to extract morphological characteristics including network porosity, tortuosity, specific surface area, pore dimensions and nanosheet orientation, which we link to network resistivity. By extending this technique to interrogate the structure and interfaces within printed vertical heterostacks, we demonstrate the potential of this technique for device characterisation and optimisation.

Understanding how junction resistances impact the conduction mechanism in nano-networks

“…We demonstrate this impedance approach using liquid-deposited networks of electrochemically exfoliated MoS 2 nanosheets ( l NS ≈ 1 μm, t NS ≈ 3.3 nm) with low porosity 47 and large-area junctions 19 (Fig. 4a ).…”

“…Nanosheet aspect ratio, k NS , and AgNW diameter, D NW , were measured using AFM and SEM respectively. Network porosity, P Net , values were taken from Gabbett et al 47 and Carey et al 19 . WS 2 and WSe 2 nanosheet mobilities were extracted from Kelly et al 53 , while the mobility of graphene was taken as the in-plane mobility of graphite 83 .…”

“…3d, e for LPE nanosheets, while R J / R NS = 4.4 ± 0.2, meaning it is much less junction-limited than the LPE WS 2 and WSe 2 networks presented above. We can further analyse the nanosheet resistance by converting it to nanosheet resistivity using (or directly from the network impedance spectrum as described in Supplementary Note 15 ), obtaining ρ NS = (4.4 ± 0.5) × 10 −3 Ω m. As the meso-porosities of networks of electrochemically exfoliated nanosheets are very low (≈0.02) 19 , 47 , we make the assumption that the average number of carriers per volume of network is the same as the average number of carriers per volume of nanosheet ( ) 52 . This allows us to calculate a nanosheet mobility of 37 ± 4 cm 2 V −1 s −1 , reasonable for electrochemically exfoliated MoS 2 21 , 53 .…”

Two-Dimensional MoS2 Nanosheets Derived from Cathodic Exfoliation for Lithium Storage Applications

“…Although it is not known how exactly this re-stacking occurs or how it depends on the thickness of the sheets, the fact that thicker sheets tend to be stiffer makes it reasonable to think that they will re-stack worse than the thinner ones and, therefore, tend to lose less area with respect to the case without re-stacking. Indeed, there are previous instances in the literature where a thinner, electrochemically exfoliated 2D material (e.g., graphene) is shown to lead to more compact, less porous re-stacked films than its thicker, liquid-phase exfoliated counterpart [45]. (g) Typical Raman spectra of the starting bulk MoS 2 bulk crystal (black trace) and cathodically exfoliated MoS 2 (green trace).…”

Graphene and Silver Nanoparticle-Coated Poly(vinyl) Alcohol/Graphene Oxide/Dioctyl Terephthalate: Bis(2-hydroxyethyl) Terephthalate Composite Strain Sensors

“…Such nanoparticle diffusion of AgNPs coatings on the GNP layer was recently proven by 3D FIB-SEM observations. 36 It has been reported that this increment in sheet resistance can be caused by blocking the conductive path in the coated material on polymer substrates created by the polymer lubrication effect. 37 Another reason is that polymers retain water molecules on the sensing layer by the low contact angle of the polymers.…”