NOVELTY - Method (M1) for preparing a carbon film involves: treating a carbon nanostructure with at least one dispersing agent; filtering the carbon nanostructure through a filter membrane to form the carbon film; releasing the carbon film from the filter membrane; and transferring the carbon film onto a substrate, where the method occurs without use of sonication.    USE - For preparing carbon film, such as on transmission electron microscopy (TEM) grid substrate (claimed). The carbon films are further useful in variety of applications such as transparent conductive films for touch screens, display technologies, solid state lighting; electrodes for fuel cells, solar cells, batteries, electromagnetic shields, and smart windows; and filters for water filtration and sterilization.    ADVANTAGE - The method provides more efficient and effective approach for fabricating carbon films, useful such as on transmission electron microscopy (TEM) grid; as compared to prior art methods. The method presents simple and highly reproducible technique for fabricating electron microscopy imaging supports from readily available commercial carbon nanotubes (CNT)s and graphite. The resulting carbon supports are mechanically stable and have high electrical and thermal conductivity and chemical inertness. The method achieves key requirement of individualized dispersion of nanotubes without compromising their length and aspect ratio. Single walled nanotube (SWNT) carbon films have been fabricated from surfactant and organic solvent/SWNT dispersions by using sonication, which reduces the tube length, compromising film mechanical stability. Carbon films (transparency above 90%) formed from surfactant and organic solvent dispersions broke at the air water interface during transfer process. The method facilitates fabrication of carbon films that are several micrometer long using carbon nanotubes of arbitrarily long lengths (several microns and above, such as more than 500 nm), without inducing any cuffing, functionalization or other kind of damage to nanotubes. Hence the formed films exhibit better properties. The method also produces final film in free floating form, which allows easy transfer to any substrate. By utilizing super acids, such as chlorsulfonic acid, the method can individualize and dissolve CNTs, graphene and fullerenes without employing sonication or functionalization, or use of additives, so that the nanotubes formed are not shortened nor damaged. The method results in monolayers of carbon films, such as monolayers of CNTs, and/or graphene, and produces carbon films that that are just few layers in thickness. The acid-carbon nanostructure solution can also be used for controlled, efficient and homogenous functionalization of carbon nanostructures for formation of thin carbon films with specially tailored properties. The films manufactured are substantially free of any additional polymers, surfactants or other dispersing agents and include primarily carbon nanostructure. Further, as polymers or surfactants are absent in carbon film (which negatively affect properties of CNT films made by other methods), carbon films are substantially free of residual material. The properties of carbon films are thus significantly better than current state-of the art carbon films and can be readily extended to large areas by using large filters that can be rolled onto cylindrical screens. The manufactured carbon films possess enough mechanical strength so that films can be recovered in free floating form that allows them to be easily transferred to any substrate of interest. The ability to make such thin films in uniform and reproducible way, and flexibility of substrates, opens up wide range of new potential applications. Results also demonstrate optimal performance of grid produced to visualize small nanoparticles as well as to prepare TEM grids from reactive fluids, such as acids. The chemical inertness, thermal stability, electrical conductivity and porous microstructures of grids can enable novel sample preparation and optimal imaging compared to standard TEM grids.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a carbon film (F1) prepared by the method (M1); and    (2) a carbon film (F1') having a thickness of less than 20 nm, and is substantially free of polymers, surfactants, and dispersing agents.