Secondary-electron emission from hydrogen-terminated diamond Page: 3 of 7
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SECONDARY-ELECTRON EMISSION FROM HYDROGEN-
Erdong Wang#, Ilan Ben-Zvi, Triveni Rao, Qiong Wu, Brookhaven National
Laboratory, Upton, NY 11973, USA
D.A.Dimitrov Tech-X Corp., Boulder, CO 80303, USA
Tianmu Xin Physics and Astronomy Department, Stony Brook University, Stony
Brook, NY11974, USA
Diamond amplifiers demonstrably are an electron
source with the potential to support high-brightness, high-
average-current emission into a vacuum. We recently
developed a reliable hydrogenation procedure for the
diamond amplifier. The systematic study of
hydrogenation resulted in the reproducible fabrication of
high gain diamond amplifier. Furthermore, we measured
the emission probability of diamond amplifier as a
function of the external field and modelled the process
with resulting changes in the vacuum level due to the
Schottky effect. We demonstrated that the decrease in the
secondary electrons' average emission gain was a
function of the pulse width and related this to the trapping
of electrons by the effective NEA surface. The findings
from the model agree well with our experimental
measurements. As an application of the model, the energy
spread of secondary electrons inside the diamond was
estimated from the measured emission.
Assuring a high-brightness, high average current and
low emittance electron beam is required by new light
source based on energy recovery linac. The diamond
demonstrably is a stable electron source that potentially
meets the request of energy recovery linac.
The diamond, functioning as a secondary emitter,
amplifies the primary current. Primary electrons with
energy of a few keV penetrate the diamond through the
metal coating, and excite electron-hole pairs. A fraction
of secondary electrons drift across the diamond under the
electric field and reach the hydrogen-terminated surface.
Except the electrons are emitted, the rest are trapped and
accumulate on the surface until the external electric field
is shielded totally. Therefore, the field inside the
diamond, transmitted charge and emitted charge are time
dependent. The probability of the emission of an electron
that arrives at the emission surface is depending on
diamond surface condition, hydrogenation quality and
external field. In this article, we describe our optimization
of the hydrogenation process which results in high quality
diamond amplifiers being reproducible. To understand the
*Work supported by Brookhaven Science Associates, LLC under
Contract No. DE-AC02-98CH10886 and at Stony Brook University
under grant DE-5C0005713 with the U.S. DOE.
mechanism for electrons trapping and its external
conditions dependent, we measured the emission
probability of four diamond amplifiers as a function of the
external field and modelled the process with the resulting
changes in the vacuum level due to the Schottky effect.
We carried out the hydrogenation experiments in a
UHV chamber. Our set-up for hydrogenation, details is
published elsewhere. To fabricate a diamond amplifier,
we Pt-coated one side of high purity 4*4mm2, 300um-
thick single-crystal diamond samples, grown by chemical
deposition (CVD); the other side was hydrogenated.
We compared four diamonds hydrogenated at room
temperature with four others treated at high temperatures.
For the latter, after temperature of the diamond reached
800 0C, the heater was turned off; hydrogenation was
started, and continued as the sample's temperature
decreased gradually to 3200C. For room-temperature
hydrogenation, the sample was allowed to cool down to
230C before starting hydrogenation. For both the
hydrogen partial pressure was 1.3*10-%Pa. Figure 1
shows a typical curve for photocurrent yield from the
hydrogenated surface of sample treated at 8000C (dark
curve) and at 230C (gray curve).
0 10 20 30 40 50
Figure 1: The trend in the photocurrent during the
hydrogenation process. Dark curve represents the trend
during high-temperature hydrogenation, and the gray
curve is that at room temperature.
As Figure 1 shows, the photocurrent took 30 minutes to
reach a peak when the diamond was hydrogenated at high
temperature; in contrast, during hydrogenation at 23 0C,
the photocurrent peaked in 10 minutes. The speed of
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E., Wang; Ben-Zvi, I.; Rao, T.; Wu, Q.; Dimitrov, D.A. & T. Xin, T. Secondary-electron emission from hydrogen-terminated diamond, article, May 20, 2012; United States. (digital.library.unt.edu/ark:/67531/metadc840766/m1/3/: accessed June 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.