Low energy ion scattering from surfaces is an established technique, which gives unique information from the first two atomic layers of a surface. A high flux of ions employed in such technique will change the nature of the surface in a number of ways, such as preferential sputtering, chemical damage and charging effects, particularly in insulating and semiconducting samples. A time-of-flight fast atom spectrometer with a pulsed ion/fast atom source (energy range of 100-5000 eV) has been developed to overcome these disadvantages. In this study, spectra of He scattered from both 'ion-cleaned' and 'ion-cleaned and heated' polycrystalline copper surfaces, bombarded with either ions or fast atoms were monitored for incident angles ranging from 5°-80° with a constant scattering angle of 90°. For the 'ion-cleaned' surfaces, spectra of both ion and neutral projectiles show that the technique is sensitive to the outermost surface atomic layer, but that fast atom bombardment seems the more surface specific. For the 'ion-cleaned and heated' surface, spectra of both projectiles are qualitatively identical. But small differences of peak energy were observed and may be explained in terms of an electronic stopping process.

宁生 许;J. L. Sullivan

Vacuum

1989

宁生 许

IVNC and IFES 2006 - Technical Digest - l9th International Vacuum Nanoelectronics Conference and 50th International Field Emission Symposium

2006

The reliable insulation of high voltages by vacuum remains a major challenge for many key technologies, not least for the development of present and future space-based power systems. As discussed in the following review, considerable progress has been made during the past decade in both the physical understanding of the parasitic 'cold cathode' electron emission process that limits the performance of hv devices, and the development of reliable technological procedures for preparing and commissioning hv electrodes. Details are also given as to how this same emission process may be used constructively as an alternative basis for producing arrays of 'cold cathode' micro electron sources.

R. V. Latham;宁生 许

Vacuum

1991

An experimental study has established that correlations exist between the pre-breakdown electron emission characteristics and the associated breakdown events that occur in a high-voltage vacuum gap formed by OFHC Cu electrodes. A tin-oxide-coated ‘transparent anode’ imaging technique was employed to display the spatial distribution of pre-breakdown emission sites and the locations of subsequent direct current breakdown events. By using a real-time video recording technique, it has been possible to demonstrate that a correlation exists between the spatial location of a pre-breakdown emission site and a subsequent direct current breakdown event, and to investigate the time evolution of the two processes. The pre-breakdown electrical characteristics of emission sites, namely their switch-on fields and B values, are also correlated with the threshold field for direct current breakdown. A new breakdown-initiating mechanism is considered, and subsequently used to explain the findings that emerged from this study.

宁生 许;R. V. Latham

Journal Physics D: Applied Physics

1994-12-14

Novel experiments were carried out during which it was possible to observe in situ and record the process of transition from cold to hot electron emission. A newly etched tungsten (W) tip was mounted in a system with a base pressure of 3x10^-7mbar. In this system, experiments were previously carried out to investigate polymerization of tetracyanoethylene (TCNE) gas on a field cathode metal tip by negative field ion microscopy (NFIM). The process of in situ coating the metallic tips with the carbonic layer in vacuum from the background of the residual TCNE gas during emission might prove to be of crucial importance in terms of technological applications. This produced a more powerful electron source emitting higher currents at much lower applied field. Emitted currents from each coated tip of higher than 50μA was recorded. Even after tip explosion it was always possible to obtain emission again after additional TCNE coating. The duration of ~6s for transfer of the cold to hot electron emission process was determined from video recording. Few seconds after the switch-on process, the electron emission indicated chemical reactions (e.g. pyrolysis) in the polymer layer which lead to a change of the electric properties of the coating. Thus, chemical aspects have to be considered to explain the hot electron emission mechanism involved. Copyright (C) 1999 Elsevier Science B.V.

M. S. Mousa;Karl Lorenz;宁生 许

Ultramicroscopy

1999-9

Field electron emission from diamond and related films has been a popular topic of both experimental and theoretical research since the beginning of 1990s. Because of their low surface electron affinity, chemical inertness and high thermal conductivity, this type of films is considered a strong candidate for cold-cathode materials. The field-emission properties of various types of diamond film are reviewed, and the milestone developments are identified. Current theoretical models are compared. Potential applications of the diamond based cold-cathode emitters are predicted. Copyright (C) 1999 Elsevier Science B.V.

宁生 许

Ultramicroscopy

1999-9

Collision of water molecule ions with solid surfaces can result in neutralization and fragmentation of the molecule. The energy distribution of total scattered yield was measured with a time‐of‐flight mass spectrometer. The major spectral peak energy is close to the value expected for a binary collision of OH with a copper atom, and the energy distribution can be accounted for by the existing dissociation models. Comparisons are made between the scattering of water molecule ions and that of He⁺ and Ne⁺ ions in terms of the spectral full width at half‐maximum, shape and the scattered yield. It is found that significant water vapour neutral peaks appear in the spectra of scattered Ne. This implies that strong non‐resonance charge exchange mechanisms occur in the projectile beams. The spectral peak heights of the water ion and neutral scattered at different incident angles are compared to those of Ne.

宁生 许;C. G. Pearce;J. L. Sullivan

Surface and Interface Analysis

1990-7

Low‐energy ion scattering from surfaces is an established technique that gives unique information from the first one or two atomic layers on a surface. The standard technique employing an electostatic analyser, however, has some disadvantages. It detects only scattered ions whose yield from surfaces is relatively low and thus high incident ion fluxes must be used. A high flux of ions will change the nature of the surface in a number of ways. It will lead to significant preferential sputtering and to charging effects, particularly in insulating and semiconducting samples. It has been shown also that ions produce more chemical damage in surfaces that do neutrals of the same energy and species. Many of these disadvantages may be overcome if neutrals are used as the bombarding particles instead of ions. Conventional electrostatic methods cannot be employed to detect neutral sacttered spectra. Hence, a time‐of‐flight mass spectrometer with a pulsed ion/fast atom source (energy range 100–5000 eV) has been developed. This instrument has been used to measure the energy of particles scattered from a polycrystalline copper surface bombarded with either ions or fast atoms. In this study, spectra of He scattered from both ‘ion‐cleaned’ and ‘ion‐cleaned and heated’ copper surfaces were monitored for incident angles ranging from 5° to 75° with a constant scattering angle of 90°. For the ‘ion‐cleaned’ surfaces, spectra of both ion and neutral projectiles show that the technique is sensitive to the outermost surface atomic layer, but that fast atom bombardment seems the more surface specific. For the ‘ion‐cleaned and heated’ surface, spectra for both projectiles are qualitatively identical and first‐order effects can be accounted for by the single binary collision model; however, small but significant differences in peak energy were observed and these may be explained in terms of inelastic collision processes.

宁生 许;J. L. Sullivan

Surface and Interface Analysis

1990-7

A high area density of field-induced electron emission sites has been observed on broad-area (12 mm in diameter) CVD diamond films deposited on molybdenum substrates. Furthermore, it was found that the density increased with the electric field applied to the surface of the films. These findings indicate that the CVD diamond film has to be seen as a potentially favoured candidate among electronic materials for the development of new types of cold cathode electron source.

宁生 许;R. V. Latham;Y. Tzeng

Electronics Letters

1993-9

The details are given of an experimental study of the growth process of aligned Cu₂S nanowire arrays with anodic aluminum oxide (AAO) template by a gas-solid reaction. It was found that the template played an important role in the control growth with good alignment. The nanowire arrays had similar diameter (about 100 nm) and height (about 1 μ m). Their electron field emission property was also measured. A turn-on field of 2.2MV/m and a threshold-field of 8MV/m were observed, respectively.

Q. B. Wu;山 任;少芝 邓;军 陈;宁生 许

2003