Electron energy distribution function in a collisional plasma heated by an electron beam

The electron energy distribution function for the non-resonant electrons in a collisional weakly ionized plasma is found, provided that the intensity of the Langmuir oscillation is spatially dependent. It is assumed that electron-electron collisions are responsible for energy loss.     

High-detective-quantum-efficiency fast-electron detector for electron energy loss spectroscopy

In order to increase the sensitivity of the parallel electron detector used in electron energy loss spectroscopy (EELS), we have developed a direct electron exposed detector, based on a photodiode array (PDA). This work investigates the performance of this detector at 100 keV incident electrons in terms of the detective quantum efficiency (DQE), the modulation transfer function (MTF) and radiation damage.     

Electron energy spectra from intense laser double ionization of helium

The double ionization of helium in the strong-field limit has been studied using an electron-ion coincidence technique. The observed double ionization electron energy spectra differ significantly from the single ionization distributions. This gives new support to the rescattering model of double ionization and explicitly reveals the role of backward electron emission following the e-2e ionizing collision.     

Interband transitions in ZnO observed in low energy electron spectroscopy

Using a high resolution two-axis-spectrometer energy loss spectra of electrons specularly reflected from (1¯100) ZnO-surfaces have been investigated. The electron impact energy was varied between 25 and 60 eV. The spectra show a strong dependence on the orientation of thec-axis with respect to the plane of incidence. The dependence of the loss intensities on the angle of incidence and the shape of the spectra can be qualitatively described by the “Dielectric Theory”. Contrary to optical reflection measurements the excitation of excitons could not be observed in agreement with the existence of a surface barrier for excitons.     

Surface and bulk plasmon coupling observed in reflection electron energy loss spectra

Reflection electron energy loss spectra have been measured for a semiconductor and some metals (Si, Cu, Ag and Au). A novel procedure is presented to rigorously decompose the spectra into contributions corresponding to surface and volume excitations. The resulting distributions of energy losses in an individual surface loss are in good agreement with theory. In particular, the begrenzungs effect occurring at the boundary of a solid state plasma, i.e. the reduction of the intensity of bulk modes due to the coupling with surface modes, can be clearly observed in the retrieved energy loss distribution.     

Background subtraction in electron spectroscopy by use of reflection electron energy loss spectra

The use of reflected electron energy loss spectra (REELS) in deconvoluting the inelastic background signal from XPS and AES spectra from homogeneous samples is studied. It is demonstrated that under certain assumptions, the cross section for inelastic electron scattering can be extracted from a REELS spectrum. This cross section is applied to deconvolute an experimental XPS spectrum of aluminium. The method, its limitations and its relation to other methods are discussed.     

Measurement of collisional multiphoton energy deposition by a new optothermal detector

The infrared multiphoton absorption of SF₆ under collisional condition has been measured by a new optothermal detector which is based on measuring the change of resistance of a platinum filament. The optothermal signal, i.e., the absorbance of CO₂ laser energy by SF₆, was enhanced by the addition of Ar or NH₃. But the increase of optothermal signal caused by adding NH₃ is much greater than that caused by adding Ar, mainly due to the energy siphoning from excited SF₆ molecules to NH₃ molecules.     

Electron temperature measurements in low-density plasmas by helium spectroscopy

Methods of measuring the electron temperature in low-density plasmas by He spectroscopy are examined. These utilize either the relative intensities of singlet and triplet lines or the absolute intensities of single lines. Calculations from measured and theoretical data show that both methods are seriously influenced by secondary processes, the most important of which are excitation from the metastable levels 2¹S and 2³S, and excitation transfer in electron-atom collisions combined with imprisonment of resonance radiation. The calculations give parameter limits for the validity of different methods and combinations of lines. Due to the secondary processes, the determination of T_e from relative line intensities is restricted to low-density, short-duration plasmas (typically n_e < 2 × 10¹⁶ m^-3, t_ex < 5 × 10^-6 s) or to even lower densities that depend on the apparatus dimensions (typically n_e < 3 × 10¹⁵ m^-3, L ≈ 0.1 m). For the determination of T_e from absolute line intensities, the situation is more favourable and, with a suitable choice of lines, typical restrictions on n_e and t_ex are n_e < 5 × 10¹⁷ m^-3, t_ex < 10^-5 s or n_e < 10¹⁷ m^-3, L ≈ 0.1 m for electron temperatures above 10 eV. For temperatures below 10 eV and degrees of imprisonment below 7% measurements are possible for electron densities up to 10¹⁹–10²⁰ m^-3, without any limits on t_ex or L.     

Electron emission spectra in low energy positron-atom collisions

Energy spectra of electrons ejected from an Ar target, in the forward direction, by a low energy positron beam have been measured and compared with theory. Structures are present in these spectra at energies compatible with electron capture to continuum states of the scattered positron (ECC) and with binary collisions.     

Electron energy loss spectra of dye vapors

Electron energy loss studies of POPOP andp-terphenyl in the vapor phase at an incident electron energy of 25 eV have been performed. The spectra covering an energy loss between 0 and 9 eV revealed a considerable initial triplet population under electron impact excitation. The implications for electron-beam pumped vapor phase dye lasers are discussed.     

Electron energy loss processes in X-ray photoelectron spectroscopy

A technique is established in X-ray photoelectron spectroscopy (XPS), using spectra emitted from successively evaporated metallic films, to distinguish between electron energy loss mechanisms identified as, respectively, extrinsic and intrinsic to the photoelectron excitation process. It is demonstrated that tailing on the high kinetic energy side of many XPS peaks is due to intrinsic processes, while the background emission at energies generally some 30 eV below the peaks arises from extrinsic processes. Plasmon energy-loss peaks are believed to contain contributions from both intrinsic and extrinsic processes.     

Rydberg states of HCN observed by electron impact spectroscopy

The electron energy loss spectrum of HCN has been determined in the energy region 8–13.6 eV at impact energies of 100, 50 and 30 eV. It is shown that energy loss spectra of HCN at intermediate impact energies can be satisfactorily analysed unlike the diffuse unassigned optical absorption spectra that have previously been reported. Rydberg series have been assigned using term values and quantum defects together with ionization potentials obtained by photoelectron spectroscopy.     

Characteristic electron energy loss spectra for diamond

The complete set of optical fundamental functions is determined for diamond in the range from 4 to 32 eV. The features of the bulk and surface characteristic energy loss spectra are elucidated and the functions n _eff(E) and ?_eff(E) are calculated. The energies of volume and surface plasmons are established.     

Simulated electron energy loss spectra from a C70 crystal

Electron energy loss spectra are simulated for a C70 crystalline structure. It is found that the simulated spectrum is similar to the unoccupied density of states of a C70 molecule, indicating that the crystalline structure has only a small effect on the spectrum. Unlike the case of a single molecule, however, the main contribution to the second peak in the spectrum cannot be ascribed as being due to the equatorial atoms.     

Single electron on a nanodot in a double-barrier tunneling structure observed by noncontact atomic-force spectroscopy

A single electron has been observed on a nanodot in a double-barrier tunneling structure by noncontact atomic-force microscopy at fixed separation. Frequency shift-voltage dependence of an Au-coated cantilever/vacuum/1-decanethiol protected Au nanodot/1-octanethiol self-assembled monolayer/Au substrate structure deviates from the theoretical parabolic curve, which is attributed to the change in the number of quantized electrons on the Au nanodot caused by the Coulomb blockade phenomena.     

The energy of thermal electrons in electron beam created helium discharges

We have measured the electron energy of the thermal group of electrons in both longitudinal and transverse electron beam created helium glow discharges. The measurement technique employs the ratio of intensities of spectral lines in the 2s³S?np³P He I series. Values of kT_e between 0.07 and 0.11 eV were obtained. These energies are typical of the beam-generated electric field free plasmas. The competitive loss of helium ions by recombination and by charge transfer in a He?Hg electron beam created plasma is calculated. The results are applied to the Hg⁺ laser pumping scheme using a electron beam created He?Hg plasma.     

Low energy alpha particle spectroscopy using CR-39 detector

The possibility of using CR-39 to measure the depth profile of ¹⁰B in Si is analysed. The measuring technique exploits the ¹⁰B(n, )⁷Li nuclear reaction. For this reason the track parameters (size, optical properties) of low energy alpha-particles (<1.47 MeV) were studied. The results showed that an energy resolution of about 100 keV could be obtained by an appropriate selection of etching conditions. The profile of ¹⁰B in Si at a depth as small as 1 μm can be measured.     

Monitoring the energy variation of an electron linac using a Cerenkov detector

A new method to monitor the energy variation of a multi-energy electron linac by combining a Cerenkov detector and a CsI（Tl） detector is reported. The signals in the Cerenkov detector show an appreciable but different dependence on the energy of the electron linac from the traditional CsI（Tl） detector due to the particular response of the former to charged electrons with high velocity above threshold. The method is more convenient than the HVL （half-value layer） method which is commonly employed to calibrate the energy of an electron linac for real time monitoring. The preliminary validity of the method is verified in a dual-energy electron linac with 6 MeV and 3 MeV gears. Moreover, the method combining the Cerenkov detector and the CsI（Tl） detector is applicable to probe the X-ray spectrum hardened by the inspected material and may serve as a novel tool for material discrimination with effective atomic number in radiation imaging.