Trained laser-patterned carbon as high-performance mechanical sensors

Abstract

We describe the mechanical properties of turbostratically graphitized carbon films obtained by carbon laser-patterning (CLaP) and their application as bending or mechanical pressure sensors. Stable conductive carbonized films were imprinted on a flexible polyethylene terephthalate (PET) substrate by laser-induced carbonization. After initial gentle bending, i.e. training, these sponge-like porous films show a quantitative and reversible change in resistance upon bending or application of pressure in normal loading direction. Maximum response values of ΔR/R0 = 388% upon positive bending (tensile stress) and −22.9% upon negative bending (compression) are implicit for their high sensitivity towards mechanical deformation. Normal mechanical loading in a range between 0 and 500 kPa causes a response between ΔR/R0 = 0 and −15%. The reversible increase or decrease in resistance is attributed to compression or tension of the turbostratically graphitized domains, respectively. This mechanism is supported by a detailed microstructural and chemical high-resolution transmission electron microscopic analysis of the cross-section of the laser-patterned carbon.

Laser-Patterned Porous Carbon/ZnO Nanostructure Composites for Selective Room-Temperature Sensing of Volatile Organic Compounds

“…As demonstrated in previous studies, due to the direct exposure to the laser beam, the upper layer consists of porous turbostratic graphite with a highly crystalline structure (Figure 3c−e) and it is free of Zn. 38 In the lower layers, significant amounts of Zn were detected (Figure 3b). Scanning transmission electron microscopy− electron energy-loss spectroscopy (STEM-EELS) further confirmed the clear chemical and structural delineation between the highly graphitized top layer and the Zn/Ncontaining bottom layer (Figure 3c, right).…”

“…To this end, the porous LP-C/Zn(5) sensor films were infiltrated and embedded in an epoxy resin and cut with a microtome into thin slices of ∼50 nm thickness. 38 An optical micrograph of the block face is presented in Figure 3a. Across the entire section, the films show a distinct porosity with visible pore sizes on the order of 5−10 μm represented in the scanning electron micrograph in Figure 3b.…”

Flexible CO2 Sensor Architecture with Selective Nitrogen Functionalities by One‐Step Laser‐Induced Conversion of Versatile Organic Ink

“…It is reversible and comparable to previously analyzed LP‐Cs. [ 32 ] In order to simulate the bending of the sensor film on the finger (Figure S23, Supporting Information), we placed a flexible hose with a diameter of ≈6 mm under the sensor film resulting in a curvature of 0.25 mm −1 determined by translating the shapes from photographs into x‐y data using the freeware Engauge Digitizer. Then the sensor performance in the bent state was analyzed in the gas‐sensing cell (Figure 4E,F) (1000 s, 24 cycles).…”

“…The observed baseline change by a factor of around two for the curvature of 0.25 mm −1 is in agreement with previous results about mechanical LP‐(N)C sensors. [ 32 ] Moreover, the response and recovery times, t res and t rec , are the same. From the proposed functions of the transducer and sensor layers, such behavior has to be expected because both, the efficiency/density of the chemical binding sites for CO 2 as well as their accessibility through the still highly porous transducer layer, are hardly altered by such a degree of deformation.…”

“…Here, we present a complete architecture for CO 2 sensing on polyethylenetherephthalate (PET). [ 32 ] The flexible nitrogen‐containing LP‐C (LP‐NC) sensors exhibit high sensitivity to CO 2 and a decent degree of selectivity even in humid environments in conjunction with good cycling stability and excellent mechanical properties. Adenine was used as the major precursor due to its rich nitrogen functionalities; glucose and sodium iodide were employed as foaming agents and porogen, respectively.…”