NEXAFS investigations of transition metal oxides, nitrides, carbides, sulfides and other interstitial compounds

The paper examines geometries employing position-dependent charge partitioning to obtain a two-dimensional position signal from each detected photon or particle. Requiring three or four anode electrodes and signal paths, images have little distortion and resolution is not limited by thermal noise. An analysis of the geometrical image nonlinearity between event centroid location and the charge partition ratios is presented. In addition, fabrication and testing of two wedge-and-strip anode systems are discussed. Images obtained with EUV radiation and microchannel plates verify the predicted performance, with further resolution improvements achieved by adopting low noise signal circuitry. Also discussed are the designs of practical X-ray, EUV, and charged particle image systems.

/pdf/wedge-and-strip-anodes-for-centroid-finding-position-4u0j8836p5.pdf

Wedge-and-strip anodes for centroid-finding position-sensitive photon and particle detectors.

The physical architecture and the performance of a quantitative three‐dimensional atom probe recently constructed are described. The development of such an instrument relies on the design of a multi‐impact position sensitive detector. The multidetection system that we have developed is based on the use of a 10×10 anode array placed behind a two microchannel plate assembly in a chevron arrangement. The spread of charge between the microchannel plate and the multianode is used to derive the position of ion striking the detector. Spatial coordinates can be calculated for multiple and simultaneous time‐of‐flight events. The procedure used for the derivation of ion positions from charge measurements is given. Specific experiments were carried out in order to determine the intrinsic spatial resolution of the multidetector. Three‐dimensional reconstruction of two‐phase materials are provided and illustrate the performance of this new apparatus. The reconstructed images demonstrate that atoms are positioned with a precision of a few tenths of a nanometer. The mass resolution M/ΔM (FWHM) of the apparatus is close to 200.

The tomographic atom probe: A quantitative three‐dimensional nanoanalytical instrument on an atomic scale

The fabrication and characterization of a glass containing a regular parallel array of submicrometer channels or capillaries are described. The capillaries are arranged in a two-dimensional hexagonal close packing configuration with channel diameters as small as 33 nanometers and packing densities as high as 3 x 10(10) channels per square centimeter. The high-temperature stability of the nanochannel glass array is well suited as a host or template for the formation of quantum confined semiconductor structures or as a mask for massively parallel patterned lithographic applications.

http://science.sciencemag.org/content/sci/258/5083/783.full.pdf

Nanochannel Array Glass

We demonstrate time-resolved counting of single atoms extracted from a weakly interacting Bose-Einstein condensate of 87Rb atoms. The atoms are detected with a high-finesse optical cavity and single atom transits are identified. An atom laser beam is formed by continuously output coupling atoms from the Bose-Einstein condensate. We investigate the full counting statistics of this beam and measure its second order correlation function g((2))(tau) in a Hanbury Brown-Twiss type experiment. For the monoenergetic atom laser we observe a constant correlation function g((2))(tau)=1.00 +/- 0.01 and an atom number distribution close to a Poissonian statistics. A pseudothermal atomic beam shows a bunching behavior and a Bose distributed counting statistics.

/pdf/correlations-and-counting-statistics-of-an-atom-laser-3qkpmys2p1.pdf

Correlations and counting statistics of an atom laser.

https://psec.uchicago.edu/Papers/mcpwiza.PDF

Joseph Ladislas Wiza

Papers

Microchannel plate detectors