Quantifying the Growth of Individual Graphene Layers by In Situ Environmental Transmission Electron Microscopy

ABSTRACT: The  bottom-up approach where materials are built atom by atom are becoming more and more common to create next generation of electric and optical devices. For instance, heterostructured semiconductor nanowires, carbon nanotubes and graphene those with excellent electron mobility and band gap structure, are the examples of materials synthesized via a bottom up approach. The atom-by-atom building scheme is highly dependent on synthesis parameters such as temperature, precursors, and time of synthesis. The resulted structures finally determines the macroscopic properties, such as strength, brittleness, electric, magnetic, optical properties and catalytic performance, etc. In order to tailor materials for specific applications, control of the synthesis parameters for obtaining the desired materials structure is necessary.
Achieving in situ TEM observation of chemical synthesis process enables chemical reaction kinetics and mechanisms to be followed at the nanoscale, even at atomic scale. The insights provided by in situ TEM observations can be exploited to facilitate robust scaling of nanoscale synthesis processes to the manufacturing scale

Figure left: Growing layered carbon structures on a nickel catalyst using acetylene (C2H2) as precursor: Ni is firstly heated in situ in the ETEM to the growth temperature 650°C in the presence of hydrogen (H2). Switching C2H2 into the microscope at this temperature results in the formation of carbon layers on the Ni surfaces. Image series (a)-(d) with 0.61s time intervals indicate the in-plane growth of the carbon (see arrows). The images are acquired approximately 100s after introduction of C2H2.  T= 650⁰C, P(C2H2)= 3×10-2Pa.

Video left: Images from in situ growth experiments performed at 600°C in C2H2. (a) and (b) shows two different characteristic areas after growth. The carbon layers appear less defined in most of the areas. T= 600⁰C, (C2H2)= 3×10-2Pa.

DENSsolutions Comments:

Understanding gas–solid interaction involved in materials synthesis and their functioning is central to the ability to control them. However, it has been clear that measurements performed on reactants and products are often not sufficient to determine the dynamic state of materials/samples ‘in operation’. Therefore, direct observations of chemical reactions down to atomic scale are of utmost importance.
DENSsolutions Heating System provides a unique platform for the detailed study of chemical synthesis/process at environmental TEM (ETEM).  DENSsolutions has a fast feedback control system that stabilizes the sample immediately when changing parameters such as pressure and temperature, opening the possibility of HREM imaging of a transient event. Furthermore, the system provides accurate temperature readout at various gas environments (composition & pressure) and even during the change of the environment such that optimization of the growth parameters can be achieved in a reliable and efficient way