Volume 33, Issue 3, May 2015
Index of content:
- 27th International Vacuum Nanoelectronics Conference (27th IVNC 2014)
33(2015); http://dx.doi.org/10.1116/1.4902016View Description Hide Description
The authors report on the first experimental characterization of a fiber tip-based electron source, where electron emission can be triggered by both electric field and optical excitation. Our approach consists of coating the open aperture of a commercial 100 nm apex size near-field scanning optical microscopy fiber tip with a 10 nm thick tungsten (W) layer, which is back-illuminated by a 405 nm continuous-wave laser beam in the presence of an extraction electric field. Despite the very low optical transmission of the fiber due to the subwavelength aperture size, measurements show a clearly enhanced emission when photoexciting the W layer with respect to pure field emission. The emission response time is slower than the optical trigger time, suggesting that thermal effects are predominant in the studied regime. To back up this hypothesis, the authors fabricated a nanometric thermocouple probe based on a Pt/Au junction and measured the temporal response of the tip temperature. The measured switch-on time for the tip temperature is consistent with the switch-on time of the optically enhanced electron emission.
33(2015); http://dx.doi.org/10.1116/1.4903229View Description Hide Description
To clarify the origin of the superior field emission characteristics of carbon-coated emitters, the authors investigated the field enhancement and the work function of model systems calculated by numerical simulations. They propose that the field enhancement is due to the triple junctions, which are distributed on the surface of the carbon film consisting of sp3 (diamond-like) insulating and sp2 (graphite-like) conducting nanometer-sized grains. The electric field around the triple junction is one order of magnitude higher than at other places. Based on ab initio density functional theory calculations, the authors found that (1) the work functions of diamond and graphite dramatically decrease down to 3–3.6 eV upon hydrogen termination, and (2) the effective work functions of these models decrease to 2–2.5 eV by applying an external electric field of 2.57 × 107 V/cm. They also estimated the field emission current from the potential distribution and the local density of states under the external electric field applied. As a result, the authors found that hydrogen termination significantly increases the field emission current. The results suggest that the triple junction and hydrogen termination are promising candidates as the mechanism of improving the emission of the carbon-coated emitters.
33(2015); http://dx.doi.org/10.1116/1.4903448View Description Hide Description
The paper concerns the problems associated with the generation and measurement of vacuum in small-volume microelectromechanical (MEMS) devices. A concept of equipping vacuum MEMS with miniature vacuum pump and gauge has been presented. The ion-sorption vacuum micropump developed by the authors has been integrated with two “external” miniature pressure sensors: a specially developed miniature Bayard-Alpert gauge and a MEMS-type Pirani sensor. The pressure during the pumping process was in-situ measured and co-work of vacuum micropump and sensors has been investigated. The experimental results confirmed good pumping properties of the micropump, but indicated that the work of micropump significantly affects the operation of vacuum sensors and vice versa.