S. E. Schnatterly

A surface recombination model applied to large features in inorganic phosphor efficiency measurements in the soft x‐ray region

The photoluminescent quantum efficiencies of the inorganic phosphors Y2O2S:Eu, Y2O3:Eu, La2O2S:Tm, Gd2O2S:Tb, and Sr5Cl(PO4)3:Eu have been measured in the range 17 to 450 eV. The optical properties of these phosphors from 2 to 160 eV have been determined from inelastic electron scattering measurements. Using a model which involves nonradiative recombination at the surface of the material, we relate photoluminescent efficiency to optical absorption properties, and find that surface recombination is the predominant source of efficiency loss for these materials in the soft x‐ray range. From the model, we obtain values for the diffusion length, surface recombination velocity, and bulk quantum efficiency of these materials.

A positron-sensitive photon detector for the UV or X-ray range

Abstract This paper describes the conversion of a light sensitive self-scanning silicon photodiode array into a soft X-ray detector. We combine a photodiode array, a UHV compatible soft X-ray sensitive phosphor and read out electronics. The detector has been tested in the soft X-ray and UV regions. The results indicate a high quantum efficiency in the soft X-ray region.

Response of photodiodes in the vacuum ultraviolet

We have measured the responses of four commercial photodiodes in the vacuum ultraviolet from 20 to 600 eV and have also measured the inelastic‐electron‐scattering spectra of the materials contained in the diodes from 0 to 260 eV. Three of the diodes are silicon: an enhanced channel device, an x‐ray‐stabilized silicon diode, and a p‐i‐n diode. The fourth is a gallium arsenide phosphide Schottky diode. The diode response has been modeled by considering absorption through the surface layer and inelastic surface recombination. The model produces an excellent description of the measured responses. From our analysis we have obtained reasonable values for the number of electrons produced per eV of incident radiation, the thicknesses of the surface layers, the surface recombination velocities, and the average diffusion lengths of the minority carriers. The highest efficiency is obtained for a silicon x‐ray‐stabilized diode followed by the gallium arsenide phosphide diode. We find that both of these diodes make ex...

A new toroidal grating spectrometer for the soft x-ray region

Abstract We have developed toroidal grating instrument using holography aberration corrected gratings to give a flat field focus and cover the wavelength region 16–625 A. The spectrometer uses four interchangeable gratings as analysers and a self scanning silicon array as detector. The sample chamber is a bakeable UHV system with LEED and Auger surface analysis equipment to characterize the sample surface.

Surface recombination effects in soft x‐ray efficiencies

We have measured the soft x‐ray efficiencies of a silicon p‐i‐n photodiode and a La2O2S:Tm phosphor over a broad energy range. We have also measured the inelastic electron scattering spectra of the constituent materials and obtained values of optical absorption coefficients versus energy. The energy dependence of the efficiencies is well explained by a model based on surface recombination of electron hole pairs, and the quality of data which can now be obtained from synchrotrons makes possible quantitative fits from which we obtain diffusion length, surface recombination velocity, and bulk quantum efficiency.

Observation of second‐order kinetic damage in sodium salicylate due to soft x rays

We have observed the dose dependence of the bulk quantum efficiency for luminescence of sodium salicylate as a function of the photon energy from 7 to 150 eV. We show that the damage is a second‐order or higher kinetic process in the number of electron‐hole pairs and is not reversible. We predict that the threshold for damage occurs at 7.2 eV, or twice the band gap of sodium salicylate.

New soft x‐ray emission spectrograph

We have built a new soft x‐ray emission spectrograph covering the photon energy range 20–800 eV. It incorporates toroidal holographic grazing incidence diffraction gratings and a position‐sensitive photodiode array as a detector. The detector electronics are remote from the array which is under vacuum at nitrogen temperature, and features a double‐correlated sampling scheme. The sample is excited with a Pierce‐type electron gun using a quadrupole focusing lens. The performance of the instrument is described.

Optical absorption measurements in the soft-x-ray range

We report measurements of optical-absorption coefficients obtained by techniques not requiring free-standing films. The results of these methods are compared with data obtained by inelastic electron scattering. We find that, as expected, absorption data obtained with smoother substrates yield results with more detail in the regions with rich structure. The spectra resulting from samples evaporated onto a Si diode vacuum-UV detector with a KCI buffer layer yield results that are quite similar to the results for inelastic electron scattering.

A low-temperature sample mount for an inelastic electron scattering spectrometer

A continuously operable low‐temperature (10–20 K) sample mount for a solid‐state inelastic electron scattering spectrometer is described. The cooling is achieved by a closed‐cycle gas phase He refrigerator. Because the entire sample chamber is at a potential of 300 kV, it must be isolated from ground, requiring computer automation for positioning, and insulating plumbing for the helium. The motion control has a detachable coupling that allows for complete thermal isolation from room temperature. Details and problems encountered in the design are described.

A Fast Soft X-Ray Spectrograph

We have developed a soft x-ray emission spectrograph for the energy region 20–800 eV. The spectrograph consists of a sample chamber, grating chamber and detector chamber connected together as a single UHV vacuum system with each chamber isola-table with gate valves. Figure 1 shows a sketch of the spectrograph.