The role of positive gaseous ions in the formation of secondary electron images in low vacuum scanning electron microscopes is discussed. This paper describes the charging processes and related effects that occur during high vacuum imaging of insulators and then discusses the influence of ions on those processes. The ions are responsible for a number of phenomena, including distortion of the electric field above and below the specimen surface due to space charge, removal of excess negative charge from the specimen, alteration of the specimen surface barrier, and scavenging/filtering of the secondary electron emission. The resulting electron-specimen-ion interactions can give rise to interesting contrast effects that are unique to this class of instruments. 相似文献
The structure I clathrate hydrate of carbon monoxide has been studied using dielectric measurements and13C NMR spectroscopy. Broad, weak dielectric absorption curves with maxima at 2.2–3.8 K yieldEa = 0.14 kJ mol–1 for the average Arrhenius activation energy associated with the reorientation of the low polarity guest. Except for H2S this represents the fastest reorienting polar guest known among the clathrate hydrates. The low temperature dielectric absorption curves can best be fitted with a Cole-Davidson asymmetric distribution of relaxation times and activation energies (with = 0.06 at 4 × 106 Hz), which at 107 Hz has been resolved into a double symmetric distribution of discrete relaxation times for CO in the small and large cages. The cross-polarization magic angle spinning13C NMR spectra indicate identical chemical shifts for CO in the small and large cages, in contrast to other hydrates. The static spectra show that the CO molecules undergo anisotropic reorientation in the large cages and that there is still considerable mobility at 77 K. One possible model for the anisotropic motion has the CO rapidly moving among sites over each of the 14 faces of the cage with the CO axis orientated towards the cage centre. The cage occupancy ratio at 220 K,
s/
L = 1.11, indicates slightly greater preference of CO for the small cage.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena. 相似文献
A low-operating voltage and high performance polymeric field effect transistors using octadecylphosphonic acid-treated high-k AlOx and HfO2 hybrid dielectrics were demonstrated. High-k metal oxide hybrid dielectrics were prepared by oxygen plasma treatment of deposited Al film for AlOx and by spin coating of solution-processable HfO2 sol-gel solution for HfO2 in combination with phosphoric acid-based self-assembled monolayer (SAM), resulting in high capacitance (10 nF/cm2 for SiO2, 600 nF/cm2 for AlOx and 580 nF/cm2 for HfO2). With phosphoric acid-based SAM on high-k metal oxide and thermal annealing of thieno[3,2-b]thiophene-based conducting polymer, the device performance was significantly enhanced. The highest mobility of the transistors using ODPA-treated AlOx as a gate dielectric is 2.3 × 10?2 cm2 V?1 s?1 in the saturation region with the source-drain of ?2 V. In ODPA-treated HfO2 hybrid dielectric, the saturated mobility is 1.1 × 10?2 cm2 V?1 s?1 and the threshold voltage was measured to be ?0.31 V, which is at least one order lower than SiO2 hybrid dielectric (?3 V). 相似文献
In this study, GaAs metal–oxide–semiconductor (MOS) capacitors using Y‐incorporated TaON as gate dielectric have been investigated. Experimental results show that the sample with a Y/(Y + Ta) atomic ratio of 27.6% exhibits the best device characteristics: high k value (22.9), low interfacestate density (9.0 × 1011 cm–2 eV–1), small flatband voltage (1.05 V), small frequency dispersion and low gate leakage current (1.3 × 10–5A/cm2 at Vfb + 1 V). These merits should be attributed to the complementary properties of Y2O3 and Ta2O5:Y can effectively passivate the large amount of oxygen vacancies in Ta2O5, while the positively‐charged oxygen vacancies in Ta2O5 are capable of neutralizing the effects of the negative oxide charges in Y2O3. This work demonstrates that an appropriate doping of Y content in TaON gate dielectric can effectively improve the electrical performance for GaAs MOS devices.
Capacitance–voltage characteristic of the GaAs MOS capacitor with TaYON gate dielectric (Y content = 27.6%) proposed in this work with the cross sectional structure and dielectric surface morphology as insets. 相似文献
This paper describes the structural properties and electrical characteristics of thin Dy2O3 dielectrics deposited on silicon substrates by means of reactive sputtering. The structural and morphological features of these films after postdeposition annealing were studied by X-ray diffraction and X-ray photoelectron spectroscopy. It is found that Dy2O3 dielectrics annealed at 700 °C exhibit a thinner capacitance equivalent thickness and better electrical properties, including the interface trap density and the hysteresis in the capacitance-voltage curves. Under constant current stress, the Weibull slope of the charge-to-breakdown of the 700 °C-annealed films is about 1.6. These results are attributed to the formation of well-crystallized Dy2O3 structure and the reduction of the interfacial SiO2 layer. 相似文献