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Robust Photocathode for Use in the Visible Spectrum

IP.com Disclosure Number: IPCOM000099678D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 77K

Publishing Venue

IBM

Related People

Harper, JME: AUTHOR [+4]

Abstract

Photocathodes with work functions in the visible spectrum are typically caesiated, and consequently do not survive exposure to atmosphere, or indeed anything other than an UHV environment. This restricts their use in many applications. A novel photocathode material is described herein that can be excited in the visible spectrum where high power continuous lasers are available, e.g., gas lasers such as Ar+ and at the same time does not permanently deteriorate in poor vacuum or atmospheric conditions. One particularly useful configuration is shown in Fig. 1. The Lanthanum Hexaboride is deposited in polycrystalline form by RF sputtering of a LaB6 target. Preferential orientation of low work function planes (100), (110) is achieved with suitable deposition conditions.

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Robust Photocathode for Use in the Visible Spectrum

       Photocathodes with work functions in the visible spectrum
are typically caesiated, and consequently do not survive exposure to
atmosphere, or indeed anything other than an UHV environment.  This
restricts their use in many applications. A novel photocathode
material is described herein that can be excited in the visible
spectrum where high power continuous lasers are available, e.g., gas
lasers such as Ar+ and at the same time does not permanently
deteriorate in poor vacuum or atmospheric conditions.  One
particularly useful configuration is shown in Fig. 1.  The Lanthanum
Hexaboride is deposited in polycrystalline form by RF sputtering of a
LaB6 target.  Preferential orientation of low work function planes
(100), (110) is achieved with suitable deposition conditions.
Typical sputtering conditions included an Argon pressure of 25 mTorr
and a target potential of 2.0 - 2.6 kV.  Titanium sublimation was
used to minimize the partial pressure of oxygen.  Films of
predominantly (100) orientation were fabricated by sputtering onto a
fused quartz substrate held at 500oC.

      In initial studies using a He Cd laser (442 nm, 2.8 eV) as an
exciting source, the efficiency for a preferentially oriented film
was 0.4 10-3 .  For 50 keV acceleration fields, and 20W input laser
power (488 nm/2.55 eV and 514nm/2.4 eV lines of Ar+ laser) focussed
to a 5 mm spot size this gives a brightness b = 5 108 A/cm2
. steradian (assume photoelectron energy spread of 100 meV).  For a
shaped cathode (e.g., a tapered fiber optic) space charge effects are
avoided.  A cathode with...