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Description
Manganese oxide and carbon nano-materials are often incorporated into energy storage electrodes. Mn oxide stores charge electrochemically and carbon facilitates electron transport. In this study, a new dual-flame setup is constructed for the fabrication of binary-layered films (BLF) by depositing nanomaterials from two separate sources. The layered structure of nano-scale Mn oxide and carbon can potentially be optimized for energy storage electrode performance. Individual Mn oxide and carbon films are first examined in terms of the morphology of the film deposit. Nano-scale Mn oxide was deposited from a flame lightly doped (50 ppm) with metal oxide precursor. As expected, the cold surface and short growth time result in granular films in which sintering into coarser features is largely avoided. BLFs are fabricated in the new apparatus by depositing particles from two separate flames in an alternating fashion. A newly designed water-block heat exchanger interlocked with the sample stages is capable of regulating the film temperature to enable a variety of film growth conditions. Examination of a series of BLF films by SEM indicates that heat transfer is the crucial process for controlling the morphology and thickness of films deposited. Carbon is not expected to sinter in the flame environment due to its high melting point. However, the thermal and transport properties of carbon vary with synthesis conditions. In the current work, carbon served as a thermal insulator between the cooled substrate and the flame. For metal oxides, a finite time and height of any film exists before sintering or melting of the material will occur due to the accumulation of energy from the flame and the decreasing heat transfer out of the film. Factors driving growth and densification through sintering and melting may be understood in terms of two reference morphologies. An energy balance in these cases, indicates that the effective surface area of heat transfer on opposing sides of the film largely govern the temperature and growth of the film. Further work is required to model and design BLFs for precise fabrication such that the electrochemical applications of these films could be tested.
