Bérengère Lebental

Synthesis of conducting transparent few-layer graphene directly on glass at 450??C

Post-growth transfer and high growth temperature are two major hurdles that research has to overcome to get graphene out of research laboratories. Here, using a plasma-enhanced chemical vapour deposition process, we demonstrate the large-area formation of continuous transparent graphene layers at temperatures as low as 450 °C. Our few-layer graphene grows at the interface between a pre-deposited 200 nm Ni catalytic film and an insulating glass substrate. After nickel etching, we are able to measure the optical transmittance of the layers without any transfer. We also measure their sheet resistance directly and after inkjet printing of electrical contacts: sheet resistance is locally as low as 500 Ω sq⁻¹. Finally the samples equipped with printed contacts appear to be efficient humidity sensors.

Electrostatic method to estimate the mechanical properties of suspended membranes applied to nickel-coated graphene oxide

We propose a method to estimate the bending rigidity and Youngs modulus of thin conducting suspended membranes based on measuring the deflection of the membranes submitted to an electrostatic force. Our electrostatic method appears easier to implement and more reliable than AFM-based localized force-displacement measurements to estimate the bending rigidity and Youngs modulus of slightly inhomogeneous materials. We apply the method on suspended graphene oxide (GO) sheets coated with a 5 nm thick Ni layer, providing a demonstration of electrostatic actuation for GO sheets. For a 7.7 nm thick membrane, a Young modulus of 360 GPa is found.

Aligned carbon nanotube based ultrasonic microtransducers for durability monitoring in civil engineering

Structural health monitoring of porous materials such as concrete is becoming a major component in our resource-limited economy, as it conditions durable exploitation of existing facilities. Durability in porous materials depends on nanoscale features which need to be monitored in situ with nanometric resolution. To address this problem, we put forward an approach based on the development of a new nanosensor, namely a capacitive micrometric ultrasonic transducer whose vibrating membrane is made of aligned single-walled carbon nanotubes (SWNT). Such sensors are meant to be embedded in large numbers within a porous material in order to provide information on its durability by monitoring in situ neighboring individual micropores. In the present paper, we report on the feasibility of the key building block of the proposed sensor: we have fabricated well-aligned, ultra-thin, dense SWNT membranes that show above-nanometer amplitudes of vibration over a large range of frequencies spanning from 100 kHz to 5 MHz.

Oxidation-Based Continuous Laser Writing in Vertical Nano-Crystalline Graphite Thin Films

Nano and femtosecond laser writing are becoming very popular techniques for patterning carbon-based materials, as they are single-step processes enabling the drawing of complex shapes without photoresist. However, pulsed laser writing requires costly laser sources and is known to cause damages to the surrounding material. By comparison, continuous-wave lasers are cheap, stable and provide energy at a more moderate rate. Here, we show that a continuous-wave laser may be used to pattern vertical nano-crystalline graphite thin films with very few macroscale defects. Moreover, a spatially resolved study of the impact of the annealing to the crystalline structure and to the oxygen ingress in the film is provided: amorphization, matter removal and high oxygen content at the center of the beam; sp2 clustering and low oxygen content at its periphery. These data strongly suggest that amorphization and matter removal are controlled by carbon oxidation. The simultaneous occurrence of oxidation and amorphization results in a unique evolution of the Raman spectra as a function of annealing time, with a decrease of the I(D)/I(G) values but an upshift of the G peak frequency.

Capacitive ultrasonic micro-transducer made of carbon nanotubes: Prospects for the in-situ embedded non-destructive testing of durability in cementitious materials

ABSTRACT We put forward an innovative method for the non-destructive testing of durability in cementitious material. It is based on microporosity probing by high-frequency ultrasonic micro-transducers. We present elements of the realisation and the characterization of such challenging devices. Their design relies on the exceptional mechanical performances of carbon nanotubes. Modelling of the devices in a fluid environment provides a preliminary validation of their suitability for durability monitoring.

Controlled, Low-Temperature Nanogap Propagation in Graphene Using Femtosecond Laser Patterning

Graphene nanogap systems are promising research tools for molecular electronics, memories, and nanodevices. Here, a way to control the propagation of nanogaps in monolayer graphene during electroburning is demonstrated. A tightly focused femtosecond laser beam is used to induce defects in graphene according to selected patterns. It is shown that, contrary to the pristine graphene devices where nanogap position and shape are uncontrolled, the nanogaps in prepatterned devices propagate along the defect line created by the femtosecond laser. Using passive voltage contrast combined with atomic force microscopy, the reproducibility of the process with a 92% success rate over 26 devices is confirmed. Coupling in situ infrared thermography and finite element analysis yields a real-time estimation of the device temperature during electrical loading. The controlled nanogap formation occurs well below 50 °C when the defect density is high enough. In the perspective of graphene-based circuit fabrication, the availability of a cold electroburning process is critical to preserve the full circuit from thermal damage.

Robust multi-parameter sensing probe for water monitoring based on ALD-coated metallic micro-patterns

We report on a multi-sensing probe for water network monitoring enabling simultaneous measurements of water electrical conductivity, flow-rate and temperature. A very simple fabrication process is used where all physical sensors are obtained only from micro-patterning of glass, combining platinum, gold. Further coating using Atomic Layer Deposition (ALD) is achieved for the purpose of reducing both electro-erosion and biofouling, while keeping the sensors electrical and thermal functionalities. This is critical for long-term reliability of sensors immersed in water. The lateral size of each sensing elements does not exceed a few 100μm. This small footprint allowed implementing a redundancy strategy on the chip, not only for reliability purposes but also to accommodate for different measurement ranges based on scalable designs.

Nanosensors for Embedded Monitoring of Construction Materials: The “2D Conformable” Route

We propose an approach to embedded monitoring of construction materials relying on 2D, conformable architectures that are expected to be lower cost and more robust than their 3D counterparts. In this article, we present two examples: a RFID-enabled carbon nanotube strain sensor on plastic for microcrack monitoring in concrete and a nanoparticle-asphalt sandwich for weigh-in-motion applications.

Wireless nanosensors for embedded measurement in concrete structures

In this work we propose a wireless architecture for embedded monitoring in concrete. The modular structure of the system allows it to be adapted to different types of sensors. We present the application of such architecture for the detection of microcracks in concrete. A carbon nanotube strain sensor recently developed by the group is used to track mechanical deformations. Full temperature compensation is achieved by a specific conditioning circuit.