Signal and noise evolution in electron detectors are analysed using a cascade model. For each cascade, the required parameters can be obtained experimentally or by simulation. The model allows predicting the noise properties of a detector, in order to identify and improve the most important stages in the signal formation chain, or in return to evaluate the performance of unknown stage. Experimental results from Raith ionLINE tool are presented, demonstrating good agreement with the model.

A comparative study of cathodoluminescence ultraviolet photon yields and decay times of large area GaN and zinc oxide (ZnO) layers grown for scintillator applications by metalorganic vapor phase epitaxy is presented. Silicon-doped GaN and non-intentionally-doped ZnO yield up to 1.4±0.2 photons/kVe− and 1.3±0.2 photons/kVe– at room-temperature, respectively. For GaN the decay times scatter between 0.4 and 0.9ns, and for ZnO between 2.5 and 3.0ns. The GaN and the ZnO absorption coefficients, α, internal efficiencies, ηi, and radiative constants, B, are determined. The characteristics of thin-film scintillators based on these materials are compared with commercially available granular scintillators.

Radiative efficiency, band gap narrowing, and band filling are studied in Si-doped GaN films as a function of carrier concentration (n), using room and low temperature cathodoluminescence (CL). Using the Kane model, a band gap narrowing ΔEg of −(3.6±0.6)×10−8 and −(2.6±0.6)×10−8n1/3 eVn1/3 is obtained for epitaxially strained and relaxed material, respectively. Band-edge CL time response and absolute external photon yield are measured. The internal radiation efficiency is deduced. Its monotonic increase as n increases is explained by the increase in the spontaneous radiative rate with a radiative free carrier band-to-band recombination coefficient B=(1.2±0.3)×10−11 cm3 s−1.

A newly developed experimental system enables measurements of IIEE at a very low ion flux (10(5) ions/s cm(2)) avoiding the fast emission degradation caused by high ion fluxes (usually applied 10(10)-10(13) ions/s cm(2)). The method overcomes the difficulty of measurement of reliable ion-induced secondary electron emission (IIEE) yield, associated with fast degradation of the IIEE yield. We report on the investigation of the IIEE from hydrogenated undoped and B-doped diamond films as a function of (i) moderate heating in vacuum prior to the measurements, (ii) H+ and Ar+ energy in the range of 1-10 KeV, and (iii) film thickness and microstructure. An IIEE yield ((gamma)) enhancement was typically detected when the films were heated to 300 degrees C in vacuum. In the B-doped diamond film heated to 300 degrees C, T rose nearly linearly from similar to 20 to similar to 100 electrons/ion, for 1 to 10 KeV Ar+ ions, respectively. The values of T obtained with H+ showed a more moderate, nonlinear increase from similar to 8 electrons/ion at I KeV up to similar to 90 electrons/ion at 10 KeV. In heated undoped diamond films of different thicknesses the measured values of T were similar for all the studied films and somewhat lower than in B -doped film: from similar to 10-16 to 60-70 electrons per 1 to 10 KeV Ar+ respectively, and from 14-26 to 50-60 electrons per 1 to10 KeV H+, respectively. The experimental results were interpreted using TRIM calculations. (C) 2006 Elsevier B.V. All rights reserved.

A new mathematical method of measuring electron emission induced by low energy ions from solids is described and used to calculate secondary electron emission according to the recorded pulse-height spectra of ions and ultraviolet (UV) photons. Using the UV single secondary electron spectra, we predict the shape of many secondary electron distributions under consideration of detection efficiency of MCP detector. These calculated distributions allow us to characterize the secondary electrons yield, and to give a secondary electron distribution for measured data. It seems rather feasible to determine secondary electron yield emitted by low energy ions at very low ion fluxes.

The present work shows that the field electron emission (FEE) properties of polycrystalline diamond films can be enhanced by control over the film thickness. The FEE properties of undoped, continuous, and smooth submicron-thick diamond films with initial nucleation densities of ∼5×1010particles∕cm2 were investigated as a function of diamond film thickness. A set of films with thickness ranging from 70–100to830nm yielded turn-on field values of 6–8V∕μm and threshold field values of 8.5–17.5V∕μm (for 0.3μA∕cm2), respectively, without any conditioning. It was found that the films of thickness up to ∼370nm can sustain stable current density as high as 0.1A∕cm2 without morphological modification. The thicker films, however, suffer from a strong degradation of the film and breakdown. The best FEE (lower turn-on and threshold fields and morphological stability) was obtained for a thin (100nm) continuous diamond film. This result is suggested to be attributed mainly to the efficient electron conduction from the back contact to the surface.

Extremely large ion-induced electron emission (IIEE) yields, γ, defined as the number of emitted electrons per incident projectile, were previously reported by us for impingement of sub-mega electron volt light (H) and heavy (N and Ar) ions onto hydrogenated, boron-doped diamond surfaces. γ was found to decrease rapidly with increasing ion dose, presumably because of ion-damage related modification of the emitting material. In this work, we compare γ for molecular impingement (H2+, N2+) to that of the atom ion impingement (H+, N+) with the individual species having the same velocity. It is found that (i) the maximal IIEE yields (extrapolated to 0 dose) per atom for molecular impingement is smaller by 15–20% than that measured for the corresponding single ions. Yet they are still extremely large. (ii) The decay rates of γ per atom for molecular impingement are faster than those measured for the corresponding single ions, yet they still saturate at very high γ values. The present results bear on the physics of ion–solid interactions and on the applicability of diamond for the detection and counting of single ion and molecule.

The number of electrons emitted per impinging ion is known to be very high for hydrogenated B-doped diamond films. However, following ion bombardment the yield of emitted electrons rapidly decreases due to structural and chemical changes induced by the irradiation process. These changes eventually result in negative electron affinity loss and graphitization of the diamond film. Here we report results on ion-induced electron emission (IIEE) from undoped, sub-micron thick and hydrogenated diamond films. We found that the IIEE properties of these films are more stable upon similar bombardment conditions as compared to those of micron and sub-micron thick B-doped films. The enhanced IIEE properties of the sub-micron films are most likely associated with a reduced charging.

Extremely high ion-induced electron emission (IIEE) yields-γ-(exceeding 400) are measured for boron-doped hydrogenated diamond, bombarded with sub-MeV Ar ions. These high values are found to rapidly diminish with an increasing number of ions impinging on the diamond surface, eventually reaching the low values of IIEE (of the order of 5) found for graphite and most materials. This reduction is shown to be caused by two processes: One, which affects a very large area around each ion-impingement point (and thus causes the rapid reduction in γ), may be either due to electron transport limitations caused by point defects introduced by the ion during their slowing down in the diamond or to surface hydrogen loss induced by the outgoing electrons; the second, more gradual loss process, is attributed to local graphitization around each ion track. A material with such a high electron-emission yield as the presently studied B-doped hydrogenated diamond, may find an application in the detection and counting of single ions or molecules, as needed mainly for biological applications.

Extremely high ion-induced electron emission yields (γ) from B-doped diamond films induced by impingement of 200-keV protons and 140-keV Ar ions (γ=150 and γ=180, respectively) are reported. The dependence of γ on target temperature, on total accumulated ion-dose and on surface termination (hydrogen- or oxygen-terminated) were studied. Very large γ were found with fresh surfaces at elevated temperatures possibly due to removal of surface contaminants. Progressive ion bombardment severely deteriorated emission properties, presumably due to material modification (graphitization) in the case of Ar, but much less so for hydrogen ion bombardment. Heating the target (up to 500°C) strongly inhibited degradation of γ after some initial degradation, but did not stop it completely. Oxygen-terminated diamond surfaces emitted approximately 30% less efficiently than hydrogen-terminated surfaces. Theoretical and practical implications of these findings are discussed.

A new detection system for extreme ultraviolet (XUV) and vacuum ultraviolet (VUV) spectroscopic measurements, in the energy range of 7–2500 eV, is demonstrated. A photonstimulated luminescence mechanism in BaFBr:Eu2+, previously used in image plates (IPs) for hard x rays and particle beam detection, is used for detecting the XUV–VUV spectra. The IP detection system proved to be one to two orders of magnitude more sensitive than conventional photographic glass plates. The measured dynamic range of the IP system (four to five orders of magnitude) is wider than any other available XUV recording media. The internal resolution of the IP system (50 μm) is slightly lower than photographic glass plate resolution, restricted by scattering processes in the IP during their readout procedure. Theoretically, much higher resolution (∼5 μm) could be obtained in the XUV–VUV region by using thinner IPs with better scanning systems. Image plates are flexible, easy to handle, and reusable. No dark room loading and developing conditions are needed and good reproducibility is obtained. All these characteristics make the image plate a very suitable recording medium for XUV–VUV spectroscopy.

AbstractAn efficient, broadband polarizing beam splitter based on birefringence of liquid crystals suitable for projection and communication systems was developed. Large aperture (about 2″), broad band (450nm–800nm or 1,000nm–1,800nm), wide acceptance angle (±10°), high splitting efficiency (contrast better than of 3,000:1 for the transmitted channel and 200:1–2,000:1 for the reflected one) with polarization axes matching the prism entrance and exit were achieved. Specially designed beveled edges contribute to beam splitter mechanical stability and manufacturability. The contrast remains better than 200:1 over the visible range at 45°C. Enhanced contrast for s‐polarization is obtained in a version that incorporates two reflecting surfaces within the prism. The device, used simultaneously as polarizer, analyzer, and combiner, is suitable for compact efficient high intensity image projector.

The electron emission yields (γ) from conductive (B doped) and undoped chemical vapor deposited diamond caused by light (protons) and heavy (argon) ion impact were measured as functions of ion dose and energy (40–300 keV). Very large values of γ are obtained for the case of B doped diamond for both ions. Whereas the emission due to Ar is found to decay very rapidly towards the low γ value measured for graphite, it remains persistently very high (γ∼25) for the case of protons, indicating possible application of diamond as a sensitive detector for light ions.

The mass and velocity distributions of ions from a pulsed titanium-deuteride arc plasma source in vacuum were measured by a time-of-flight mass spectrometer. The arc source consisted of a thin deuterium-loaded titanium layer between two electrodes on an alumina substrate with a narrow groove across the center. Operation of the plasma source by 0.25, 0.75, and 2.1 /spl mu/s 100 A pulses eroded the cathode side of the groove. The deuterium ions were found to have mean velocities only 20% higher than the /sup ++/Ti ions. Almost all the deuterium ions were emitted during the first 0.75 /spl mu/s of the pulse. The titanium ions had charge states of 1+, 2+, and 3+, with 2+ predominating. Their mean energy-per charge state decreased slightly with increasing charge state. The findings are interpreted as arising from a dense cathode spot in which acceleration of the ions occurs and in which ion-ion and ion-atom collisions slow down the very light ions.

The influence of a surface layer of implanted nitrogen on the properties of titanium hydride further implanted by He was investigated. Samples were implanted with 45 keV N2+ ions cm−2 to a total dose of 1.25 × 1017 ions cm−2 at room temperature. These samples, as well as identical samples not irradiated by N2 ions, were implanted with He ions at energies of 25 keV and 45 keV to doses ranging from 2 × 1017 to 5.5 × 1017 ions cm−2. Helium release from the implanted samples was increased by a factor of 2–4 in nitrogen implanted samples. Nitrogen implantation also induced surface erosion and blistering at lower He fluences than in samples not irradiated by N2. It seems that radiation damaged caused by N2 implantation suppresses the possible enhancement of the irradiation resistance due to surface nitrogenation.

Lifetimes in the range 10−11 to 10−9 s of prompt γ rays emitted from the fission fragments of 252Cf were measured using a recoil distance method. A 252Cf source was deposited on a stretched Ni foil and placed in a plunger device, the recoil direction of the studied fragments being determined by the detection of the complementary fragment. The lifetime was determined by the change in the non-Doppler-shifted peak intensities of prompt γ rays as a function of the source-plunger distance. The 2+ → 0+ half-life in 112Pd and 4+ → 0+ halflives in 104, 106Mo, 108,110Ru and 142Ba were determined for the first time. Several other measurements of longer lived 2+ → 0+ transitions were repeated as well. The experimental results are discussed within the framework of the rotational and the IBA-2 models.

A combination of post-implantation, room temperature, He release measurements and surface erosion investigation by scanning electron microscopy was used for the study of the possible mechanisms of He release from implanted samples. He release was greatly accelerated at fluences exceeding a critical value. The critical fluence for fast He release was found to be smaller than that needed for the onset of surface erosion and was independent of surface erosion, (i.e. different samples with markedly different amounts of surface erosion exhibited the same He release). Post-implantation He release could be explained in terms of atomic diffusion processes. It was suggested that at high He concentrations this diffusion takes place via micro-channels created by micro-erosion processes that are independent of the known macro-erosion processes (such as flaking, cracking and blistering).

Room temperature postimplantation He release from implanted titanium hydride films was investigated. The release decreased with time obeying the equation log(dN/dt)=−m log t+A, where 0.5

Titanium hydride films of various grain sizes and surface roughnesses were prepared. Helium ions with energies of 25 and 45 keV were implanted at room temperature in doses ranging from 1 × 1017 to 9 × 1017 ions cm−2. The surface morphology prior to and post implantation was investigated by scanning electron microscopy. Helium release rates from implanted samples were also measured. Some of the samples were specially chosen so that there was a mixture of smooth and rough areas which appeared as dark and light patches under low magnifications. After irradiation with the helium ions the resulting surface erosion was found to be dependent on the amount of surface roughness. Smooth areas showed marked erosion, whereas surface erosion was totally suppressed in rough areas of the same sample. Other uniformly rough samples with smaller asperities exhibited marked surface erosion. It was concluded that surface roughness does indeed reduce erosion, but other factors such as the helium distribution (both the projected range and the standard deviation of the distribution) and the magnitude of the roughness (average height of single asperities) also have an effect. The helium release rates of all samples showed the same dose dependence regardless of the marked surface erosion differences between samples. This implies that the helium release is not directly related to surface erosion.