Jyi-Tsong Lo

Enhanced Electron Field Emission Characteristics of Carbon Nanoflakes Prepared by Modified RF Sputtering

Carbon films with flakelike geometry, exhibiting excellent electron field emission (EFE) properties were synthesized by a modified RF sputtering process, which used an Ar:CH4:H2 gas mixture, instead of a conventional Ar:H2 mixture. These films contain nanosized diamonds and allotropic phases (i-carbons and graphites) embedded in amorphous carbon films. The EFE process can be turned on at E0 = 4.83 V/µm, achieving an EFE current density of Je = 280 µA/cm2 at an 8 V/µm applied field. The EFE properties of these flakelike carbon films essentially do not change with processing parameters, indicating that these carbon films are more process-reliable and hence have better potential for application as electron field emitters.

Synthesis of Carbon Nanoflakes by Radio-Frequency Sputtering and Their Field Emission Characteristics

The growth, structure and field emission properties of the two-dimensional carbon nanoflakes (CNFs) produced by radio-frequency (RF) sputtering without any catalyst or special substrate treatment have been investigated. The effects of deposition parameters (such as deposition time, sputtering gas composition, substrate temperature and RF power) on the structure and properties of the CNFs were also studied. Possible growth mechanism of the CNFs has been discussed with time evolution of surface microstructure. These films contain nanosized diamonds and allotropic phases (i-carbons and graphites) embedded in amorphous carbon films. The electron field emission (EFE) process can be turned on at E0=2.8 V/µm, achieving an EFE current density of Je = 1 mA/cm2 at a 5 V/µm applied field. The low turn-on field of 2.8 V/µm for electron field emission suggests that the CNFs could be used as a potential edge emitter.

Fabrication of vertical graphitic nano-partitions for anti-reflection function of silicon solar cells

Vertical standing, thin graphitic nano-partitions were fabricated on quartz and silicon substrates using a reactive plasma sputtering system. These nano-sized partitions act as light reflectors, enhancing the solar absorption of omni-directional incident light. The structure of nano-partitions doubles the output power of the solar cell when illuminated from a 30° to 150° angle of incidence. Such nano-partitions also enhance solar efficiency when reflected light is used to produce more photon absorption. Measurement of reflectance has shown a minimum of 0.49% at a wavelength of 580 nm when nano-partitions are used. The average reflectance of the entire visible regime is 0.85%, which is equivalent to the conventional multi-layer anti-reflection coatings. We also found that this nano-partition system has superior anti-reflection efficiency in a UV regime. This 3D anti-reflection structure provides a promising route to the fabrication of high-efficiency solar cells.