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.
Nitrogen‐containing carbons (NC) are a class of sustainable materials for selective CO2 adsorption. A versatile concept is introduced to fabricate flexible NC‐based sensor architectures for room‐temperature sensing of CO2 in a one‐step laser conversion of primary films cast from abundant precursors. By the unidirectional energy impact in conjunction with depth‐dependent attenuation of the laser beam, a layered sensor heterostructure with a porous transducer and active sensor layer is formed. Comprehensive microscopic and spectroscopic cross‐sectional analyses confirm the preservation of the high content of imidazolic nitrogen in the sensor. The performance is optimized in terms of material morphology, chemical composition, and surface chemistry to achieve a linear relative resistive response of up to ΔR/R0 = −14.3% (10% of CO2). Thermodynamic analysis yields ΔadsH values of −35.6 and 34.1 kJ·mol−1 for H2O and CO2, respectively. The sensor is operable even in humid environments (e.g., ∆R/R0,RH = 80% = 0.53%) and shows good performance upon strong mechanical deformation.
The development of mobile, noninvasive, and portable
sensor technologies
for diagnostics and emission control is highly demanded. For that
purpose, laser carbonization is studied as a tool to produce responsive
carbon materials from inexpensive organic precursors for the room-temperature
selective detection of volatile organic compounds (VOCs) applicable
in future sensor array-based devices. To increase the response of
intrinsically low-responsive laser-patterned carbons (LP-C) to analytes
in the gas phase, we tested carbonization in the presence of nanoscale
ZnO precursors in primary inks. Following the addition of a zinc salt,
Zn(NO3)2, a noticeable 43-fold increase in the
sensor response (ΔR/R
0 = −21.5% toward 2.5% acetone) was achieved. This effect
is explained by a significant increase in the measurable surface area
up to ∼700 m2·g–1 due to
the carbothermic reduction supported by the in situ formation of ZnO
nanoparticles. Varying Zn concentrations or the addition of as-prepared
ZnO nanorods lead to different surface properties like the surface
area, porosity, and polarity of LP-C. A predominant effect of the
surface polarity on the selectivity toward different analytes of the
sensors during physisorption, e.g., acetone vs toluene, was identified
and tested. The best-performing LP-C sensors were finely characterized
by transmission/scanning electron microscopies and X-ray photoelectron/energy-dispersive
X-ray/Raman spectroscopies.
Electrochemically
exfoliated graphene (e-G) thin films on Nafion
membranes exhibit a selective barrier effect against undesirable fuel
crossover. This approach combines the high proton conductivity of
state-of-the-art Nafion and the ability of e-G layers to effectively
block the transport of methanol and hydrogen. Nafion membranes are
coated with aqueous dispersions of e-G on the anode side, making use
of a facile and scalable spray process. Scanning transmission electron
microscopy and electron energy-loss spectroscopy confirm the formation
of a dense percolated graphene flake network, which acts as a diffusion
barrier. The maximum power density in direct methanol fuel cell (DMFC)
operation with e-G-coated Nafion N115 is 3.9 times higher than that
of the Nafion N115 reference (39 vs 10 mW cm–2@0.3
V) at a 5M methanol feed concentration. This suggests the application
of e-G-coated Nafion membranes for portable DMFCs, where the use of
highly concentrated methanol is desirable.
We investigate the optical properties of polycrystalline diamond membranes containing silicon-vacancy (SiV) color centers in combination with other nano-analytical techniques. We analyze the correlation between the Raman signal, the SiV emission, and the background luminescence in the crystalline grains and in the grain boundaries, identifying conditions for the addressability of single SiV centers. Moreover, we perform a scanning transmission electron microscopy (STEM) analysis, which associates the microscopic structure of the membranes and the evolution of the diamond crystals along the growth direction with the photoluminescence properties, as well as a time-of-flight secondary ion mass spectrometry (ToF-SIMS) to address the distribution of Si in implanted and un-implanted membranes. The results of the STEM and ToF-SIMS studies are consistent with the outcome of the optical measurements and provide useful insight into the preparation of polycrystalline samples for quantum nano-optics.
Nitrogen-doped carbons (NC) are a class of sustainable materials for selective CO2 adsorption. We introduce a versatile concept to fabricate flexible NC-based sensor architectures for room-temperature sensing of CO2 in a one-step laser conversion of primary coatings cast from abundant precursors. By the unidirectional energy impact in conjunction with depth-dependent attenuation of the laser beam, a layered sensor heterostructure with porous transducer and active sensor layer is formed. Comprehensive microscopic and spectroscopic cross-sectional analyses confirm the preservation of a high content of imidazolic nitrogen in the sensor. The performance was optimized in terms of material morphology, chemical composition, and surface chemistry to achieve a linear relative resistive response of up to ∆R/R0 = -14.3% (10% of CO2). Thermodynamic analysis yields ΔadsH values of -35.6 kJ·mol-1 and 34.1 kJ·mol 1 for H2O and CO2, respectively. The sensor is operable even in humid environments (e.g., ∆R/R0,RH=80% = 0.53%) and shows good performance upon strong mechanical deformation.
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