Electrical Percolation Threshold and Size Effects in Polyvinylpyrrolidone-Oxidized Single-Wall Carbon Nanohorn Nanocomposite: The Impact for Relative Humidity Resistive Sensors Design

Bogdan-Catalin Serban; Cornel Cobianu; Niculae Dumbravescu; Octavian Buiu; Marius Bumbac; Cristina Mihaela Nicolescu; Cosmin Cobianu; Mihai Brezeanu; Cristina Pachiu; Matei Serbanescu

doi:10.3390/s21041435

Electrical Percolation Threshold and Size Effects in Polyvinylpyrrolidone-Oxidized Single-Wall Carbon Nanohorn Nanocomposite: The Impact for Relative Humidity Resistive Sensors Design

Sensors (Basel). 2021 Feb 19;21(4):1435. doi: 10.3390/s21041435.

Authors

Bogdan-Catalin Serban^{1

2}, Cornel Cobianu^{1

2

3}, Niculae Dumbravescu^{1

2}, Octavian Buiu^{1

2}, Marius Bumbac^{4

5}, Cristina Mihaela Nicolescu⁵, Cosmin Cobianu⁶, Mihai Brezeanu⁷, Cristina Pachiu¹, Matei Serbanescu⁷

Affiliations

¹ National Institute for Research and Development in Microtechnologies-IMT Bucharest, 126 A Erou Iancu Nicolae Str., 077190 Voluntari, Romania.
² Research Center for Integrated System, Nanotechnologies, Carbon-Based Nanomaterials (CENASIC)-IMT, 126 A Erou Iancu Nicolae Str., 077190 Voluntari, Romania.
³ Academy of Romanian Scientists, Science, Technology of Information Section, 3 Ilfov Str., 077160 Bucharest, Romania.
⁴ Faculty of Sciences and Arts, Sciences and Advanced Technologies Department, Valahia University of Targoviste, 13 Sinaia Alley, 130004 Targoviste, Romania.
⁵ Institute of Multidisciplinary Research for Science Technology, Valahia University of Targoviste, 13 Sinaia Alley, 130004 Targoviste, Romania.
⁶ Electrical Engineering, Electronics and Information Technology Faculty, Valahia University of Targoviste, 13 Sinaia Alley, 130004 Targoviste, Romania.
⁷ Faculty of Electronics, University Politehnica of Bucharest Telecommunications and Information Technology, 1-3 Iuliu Maniu Blvd., 6th District, 061071 Bucharest, Romania.

Abstract

This paper reports, for the first time, on the electrical percolation threshold in oxidized carbon nanohorns (CNHox)-polyvinylpyrrolidone (PVP) films. We demonstrate-starting from the design and synthesis of the layers-how these films can be used as sensing layers for resistive relative humidity sensors. The morphology and the composition of the sensing layers are investigated through Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and RAMAN spectroscopy. For establishing the electrical percolation thresholds of CNHox in PVP, these nanocomposite thin films were deposited on interdigitated transducer (IDT) dual-comb structures. The IDTs were processed both on a rigid Si/SiO₂ substrate with a spacing of 10 µm between metal digits, and a flexible substrate (polyimide) with a spacing of 100 µm. The percolation thresholds of CNHox in the PVP matrix were equal to (0.05-0.1) wt% and 3.5 wt% when performed on 10 µm-IDT and 100 µm-IDT, respectively. The latter value agreed well with the percolation threshold value of about 4 wt% predicted by the aspect ratio of CNHox. In contrast, the former value was more than an order of magnitude lower than expected. We explained the percolation threshold value of (0.05-0.1) wt% by the increased probability of forming continuous conductive paths at much lower CNHox concentrations when the gap between electrodes is below a specific limit. The change in the nanocomposite's longitudinal Young modulus, as a function of the concentration of oxidized carbon nanohorns in the polymer matrix, is also evaluated. Based on these results, we identified a new parameter (i.e., the inter-electrode spacing) affecting the electrical percolation threshold in micro-nano electronic devices. The electrical percolation threshold's critical role in the resistive relative-humidity sensors' design and functioning is clearly emphasized.

Keywords: Young modulus elasticity; electrical percolation threshold; nanocomposite; oxidized carbon nanohorns (CNHox); polyvinylpyrrolidone (PVP); relative-humidity resistive sensors; size effects; swelling.

Abstract

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