Graphene Production by Chemical Vapor Deposition

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"Thanks to the modular CompactDAQ products, we implemented the management, control, display, and data-saving functionalities on the CVD bench easily."

- Bruno PASSILLY, Onera

The Challenge:
Developing a graphene-coating system by chemical vapor deposition (CVD).

The Solution:
Designing a turnkey graphene-coating bench based on CompactDAQ products and powered by LabVIEW software to control all the instruments of the system (flow, pressure, and temperature regulators) while actuating and monitoring all the valves of the process and the safety devices.

Author(s):
Bruno PASSILLY - Onera

Graphene is an innovative material with exceptional physical properties. Graphene comes in the form of a single-layer sheet of carbon atoms with a honeycomb structure. It is expected to be used in many areas such as electronics (flexible screens, high-frequency electronics, nanoelectronics), environment (batteries, chargers, air quality sensors, desalination of sea water), and health (targeted therapy). In the aircraft industry, graphene is intended to be part of the development of composite materials used to create lighter aircraft structures.

Graphene conducts better than copper and is more resistant, but much lighter, than steel. For all these reasons, it could be used for building lighter and less energy-intensive planes.

In order to meet this strategic demand, the French aerospace lab Onera has started to work on a CVD bench, which is a promising way to produce graphene in quantity (Figure 1).

A Multimaterial Production

Graphene production uses methane, which is a precursor gas that breaks down at 1,000 °C in a vacuum environment. Introducing hydrogen helps prepare the deposition surface and dilute the precursor gas. For silicon carbide (SiC) or boron nitride deposition, tetramethylsilane (Si(CH3)4) and borazine (B3N3H6) are used respectively. Introducing a complex set of valves into the process is critical to mix some precursor gases, purge the pipelines with argon before injecting gases, and monitor the valve operation in the pump block. Around 20 valves are actuated and displayed through a cDAQ-9178 chassis with two NI 9485 modules and three NI 9423 modules, so we can continuously read the state of all the valves in the system.

A Multi-Instrument Dialog

The process of depositing graphene includes several steps. First, we obtain the ultimate vacuum through a pump block equipped with a liquid nitrogen trap to condense the residue of the precursor gas decomposition reaction. We then set the induction furnace set point (1,000 °C) and the temperature start ramp on the regulation system before the heating process is engaged. When the set point is reached, the gas flow rate is set and the gases are injected into the vacuum housing. We maintain the working pressure through a throttle valve located at the pump block intake port. All these operations involve regulation valves, flowmeters, and temperature control, and are generated through a serial link dialog between LabVIEW software and the program. We can easily modify each setting because of the dialog between the various control tools.

When using hydrogen, safety settings are vital. In order to perform CVD deposition test, we added a set of sensors to the system. The vacuum housing overpressure sensors, oxygen deficiency detectors in the lab, gas-detecting devices, a cooling water flow sensor, a pumping detector, a furnace overheating sensor, a purge gas pressure sensor, a gas supply cabinet ventilation sensor, and a liquid nitrogen level sensor connect to the CompactDAQ modules to display the state of these safety elements. In the meantime, a safety programmable logic controller (PLC) implements the system safety measures by injecting neutral gas, stopping the heating process, and cutting off the gas with hard-wire logic.

A Powerful, Scalable System

When starting a prototype research project, the initial specifications are often subject to changes following the first manufacturing tests. These changes can be significant when additional tools, sensors, valves, or gas lines are needed. The modular CompactDAQ chassis makes it easy to perform this type of modifications by adding specific modules.

Display, Save, and Warn

The monitor screen comprises several tabs to display several windows on a single screen. The Synoptique window (Figure 2) displays all the control settings of the CVD process, as well as the state of each valve in the system. The Graphique window displays the pressure, gas flow rate and furnace temperature variations in time. Other tabs show the tools settings so the operator can access the flowmeter settings (Figure 3) and the temperature and pressure regulators.

For each test, a folder is created to save the test parameters and the data files that contain the time, pressure, gas flow rate, and furnace temperature information, as well as the binary state of all the valves and the alarm thresholds, to analyze any technical issue.

Simple Integration and Rapid Results

The test operator who uses the program and the associated tools is best placed to assess its user friendliness and simplicity of use. In this case, the test operators did not face any particular difficulty when first handling the program. This program is the heart of the system, and the graphical interface delivers easy implementation. The hardest part was to adapt and become familiar with each instrument’s dialog. The availability of drivers and example programs helped us reduce program development time, which took around two months.

Conclusion and Outlook

Thanks to the modular CompactDAQ products, we implemented the management, control, display, and data-saving functionalities on the CVD bench easily. The application led to a user friendly end product, which manages a whole set of instruments. The application is scalable and the first graphene deposition performed in our research center is paving the way for future development based on this accomplishment.

Author Information:
Bruno PASSILLY
Onera
29 avenue de la Division Leclerc
92322 Châtillon
France
Tel: +33 (0)1 46 73 45 54
bruno.passilly@onera.fr

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