Electron emission from MOS electron emitters with clean and cesium covered gold surface

MOS (metal-oxide-semiconductor) electron emitters consisting of a Si substrate, a SiO₂ tunnel barrier and a Ti (1 nm)/Au(7 nm) top-electrode, with an active area of 1 cm² have been produced and studied with surface science techniques under UHV (ultra high vacuum) conditions and their emission characteristics have been investigated. It is known, that deposition of an alkali metal on the emitting surface lowers the work function and increases the emission efficiency. For increasing Cs coverages the surface has been characterized by X-ray Photoelectron Spectroscopy (XPS), Ion Scattering Spectroscopy (ISS) and work function measurements. Energy spectra of electron emission from the devices under an applied bias voltage have been recorded for the clean Au surface and for two Cs coverages and simultaneous work function curves have been obtained. The electron emission onset is seen to appear at the surface work function. A method for cleaning the ex situ deposited Au top electrodes to a degree satisfactory to surface science studies has been developed, and a threshold for oxide damage by low-energy ion exposure between 0.5 and 1 keV has been determined.     

Photoelectron angular distributions from gold

Angular distributions of electrons photoemitted from evaporated gold have been measured for 21.2 eV and 40.8 eV photons by varying the acceptance angle of a spherical, electrostatic, electron energy analyzer. The results for primary (unscattered) electrons are shown to be consistent with the three-step model of photoelectron emission.     

Photoelectron emission from thin overlayers

Photoelectron signal intensities calculated for a thin overlayer from theoretical models taking elastic photoelectron collisions into account are shown to be very weakly dependent on the substrate material. This result has been obtained for photoelectrons analyzed in XPS spectrometers equipped with typical X-ray sources, i.e. sources of Mg Kα and Al Kα radiation. Low sensitivity to the substrate material is due to the fact that trajectories of photoelectrons emitted in the overlayer and entering the substrate have a low probability to reach the analyzer without energy loss. On the other hand, the signal intensity of photoelectrons emitted in the overlayer is found to be distinctly affected by elastic photoelectron scattering. Consequently, a theoretical model that can accurately describe the photoelectron intensity from an overlayer deposited on any material (e.g. on a substrate of the same material as the overlayer) can be a useful basis for a universal and convenient method for determination of the overlayer thickness. It is shown that the formalism derived from the kinetic Boltzmann equation within the so-called transport approximation satisfies these requirements. This formalism is postulated for use in overlayer-thickness measurements to avoid time-consuming Monte Carlo simulations of photoelectron transport, and also to circumvent problems with determining the effective attenuation lengths for overlayer/substrate systems.     

Photoelectron emission from island metallic sodium films during the excitation of localized plasmon resonances

The photoelectron emission from island sodium films is studied under the action of radiation that is resonant to the collective electron excitations in the nanoparticles forming a film. Noticeable deviations from the Fowler law and an increase in the photoelectron yield are detected. The dependences of the photoeffect efficiency from these films on their structural parameters, the polarization vector, and the angle of radiation incidence are obtained.     

Electron-stimulated desorption of cesium atoms from cesium layers adsorbed on tungsten coated by a gold film

Physics of the Solid State - The yield and energy distributions of cesium atoms escaping in electron-stimulated desorption (ESD) from cesium layers adsorbed on tungsten coated by a gold film have...     

Photoelectron emission from implanted SiO2: Se+ films

Silica films implanted with selenium ions (330 keV, 5 × 10¹⁶ cm⁻²) were studied. The method of optically stimulated electron emission (OSEE) was used to analyze features specific to disordering of the film structure. Spectrum dependences of the OSEE are described in terms of the formalism of Urbach’s emission rule. It was found that the discrete-continuum disturbances arising upon implantation considerably distort the spectrum of the electronic and vibrational states of the SiO₂ matrix. Results of the experiment and the numerical simulation provide evidence for the activation tunneling of electrons from optically excited surface states of SiO₂ to a vacuum.     

Photoelectron emission from semiconductors with low valence band dispersion

In application to the group of compounds under consideration, a simple analytical expression is obtained for the quantum yield. Electron scattering processes of both elastic and inelastic nature are taken into account. The influence of such scattering processes on the structure of the spectral dependence of the quantum yield is discussed. It is shown that they can be responsible for the appearance of a number of features in this spectral dependence.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 68–72, April, 1982.     

Field electron emission and field desorption of cesium from graphene

Field electron emission and field desorption of cesium ions from a monatomic graphene film on Ir and graphene clusters in amorphous carbon are investigated using field electron microscopy and continuous-mode field desorption microscopy. The deposition of cesium on amorphous carbon with graphite clusters leads to inversion of the emission (i.e., emission from the emission centers disappears against the back-ground of uniform emission from the previously nonemitting surface). In both systems, ion current pulses are observed during field desorption in a stationary electric field. During field desorption from the graphene film, current pulses of Cs⁺ ions with a duration shorter than 0.1 s appear from the plane faces of the iridium point. During desorption from graphite clusters, ion current pulses form a pattern of “collapsing rings” on the screen. Possible mechanisms of the observed processes are considered using the model of cesium intercalation by graphite and by the graphene layer and the desorption of Cs atoms under the action of the electric field, as well as the “flip” of the dipole moment during the cesium intercalation.     

Field-electron emission from polyimide-ablated films

Polyimide-ablated film was deposited by using pulsed laser ablation of a polyimide target, and field-electron emission from the film was observed for the first time. The turn-on field of the polyimide-ablated film is 12 V/μm. The current density is 0.725 mA/cm², and the emission sites density is on the order of 10⁶/cm² at the applied field of 24 V/μm. The field-electron emission measurements indicate that this kind of film could be a new cold cathode material. It is suggested that the graphite-like clusters contained in the film play an important role in the field-electron emission. Received: 2 February 2000 / Accepted: 13 March 2000 / Published online: 9 August 2000     

Effect of deposition of samarium atoms on the electron-stimulated desorption of cesium and samarium atoms from the surface of tungsten coated by gold and cesium

It has been shown that deposition of Sm atoms on W(100) surface coated by several monolayers of gold and cesium affects noticeably the yield of Cs atoms in electron-stimulated desorption (ESD) from this surface. The measurements have been performed by the time-of-flight method with a surface-ionization detector. The paper reports on the first observation of ESD of Sm atoms from the tungsten surface coated by layers of gold and cesium. The ESD threshold for Sm atoms, E _e = 57 eV, coincides with that for Cs atoms and corresponds to the energy of the Au 5p _3/2 core level. The dependence of the ESD yield of Sm atoms on the bombarding electron energy E _e follows a resonance pattern in the form of a narrow peak located in the range 57 ≤ E _e ≤ 66 eV. Deposition of Sm atoms at room temperature (～300 K) reduces (by a factor of about two) the ESD yield of Cs atoms for 600 s, and deposition of Sm atoms at 160 K reduces the ESD of Cs atoms down to zero already for 270 s. This difference finds explanation in the study of the change the structure of the top layer of the (Au + Cs)/W surface coating undergoes under cooling of the surface from 300 to 160 K.     

Light emission from Ag cluster films excited by conduction current

The light emission spectra obtained for a silver cluster film, excited by the passage of electrical current through it, were measured by the charge‐coupled device (CCD) combined with a monochromator in the spectral range 200 ≑ 1050 nm (6.2 ≑ 1.18 eV). This film is a two‐dimensional ensemble of Ag clusters linked by tunneling on a dielectric substrate. It was shown that the light emission spectra had a number of features, and the shape of spectrum depends on a voltage applied to the film. With increasing the voltage the spectrum starts to extend to high energies. The light emission in the visible spectral region was observed already at 1 V applied to the film, i.e., the photon energy can exceed the excitation energy. It means that this phenomenon is not trivial. In order to explain these results, an assumption about the electron gas heating in metal clusters may be used.     

Excimer emission from evaporated pyrene films

Emission spectra and decay times of fluorescence of pyrene thin films prepared by evaporation onto glass substrate at low temperatures were measured. The band positions of the excimer emission from the films evaporated onto substrates at temperatures below about 200 K, are found to the lower energy side of those of the crystal. The decay time of excimer emission in a film prepared by evaporation onto a substrate cooled with liquid nitrogen is about 100 ns at 85 K and is shorter than that of the crystal. These results are discussed in relation to an amorphous structure in the pyrene evaporated thin films. The energy transfer was also studied in evaporated pyrene films containing perylene as a dopant. The results are explained in terms of excimer exciton diffusion through the crystalline structure in the film.     

Preparation of gold films by plasma-CVD

ThemetalorganicplasmaenhancedChemicalVapourDeposition (MOPECVD) of gold films at room temperature using dimethyl(2,4-pentane-dionato)gold(III) as starting material is reported. By adding oxygen or propene to the rf glow discharge, films of Au oxide and of a composite gold polymer, respectively, were obtained.     

Continuum emission from recombining oxygen and nitrogen plasmas

The quantum defect method is used to obtain photoionization cross-sections for some 40(55) levels of OI (NI) over a range of electron energies from threshold to one Rydberg. These cross-sections are then incorporated into a model that predicts the total radiative emission resulting from radiative recombination and bremsstrahlung in the presence of singly ionized oxygen (nitrogen) atoms. Modified emission coefficients are presented for the wavelength region extending from the visible to the long wave infrared for a variety of temperatures.     

Optical emission spectra from microwave oxygen plasma produced by surfatron discharge

This paper is devoted to a systematic study of the production of molecular and atomic ions and excited atoms in a microwave oxygen plasma generated by surfatron in a quartz tube (i.d. 6 mm). The content of O ₂ ⁺ , O⁺ and O is measured, using the optical emission spectroscopy, in a wide range of oxygen pressures (from 3.5 Pa to 10² Pa) and microwaves powers (from about 30 W to 300 W) delivered into the plasma. It is shown that the content of individual species O2⁺, O⁺ and O strongly depends on the conditions, particularly operating pressurep and the microwave powerP, under which plasma is created. It means that the chemical reactivity of microwave plasma also strongly depends onp andP. It is of great importance for many practical applications, e.g. for a reproducible production of thin films with prescribed properties.The authors wish to express their thanks to the Grant Agency of Academy of Sciences of the Czech Republic for the support of this research. This work was done under Academy of Sciences Grant No. 11020.     

Secondary electron emission from thin carbon films

For the purpose of investigating how secondary electrons are produced in carbon, the correlation between energy-loss events and secondary electrons was studied experimentally by using the coincidence method. If a secondary electron is detected in coincidence with an electron transmitted through a thin film which has lost an amount of energy E, then the process causing this energy loss results in the production of secondary electrons. We established the existence of these coincidences and have taken inelastic and coincidence spectra for films of different thickness. We found that in carbon secondary electrons are predominantly produced as a result of energy losses of about 20 eV, with an efficiency of about 5%. The escape depth of secondary electrons was also estimated to be approximately 30 Å.