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Outline
 Influence of the deposition technique
on the properties of CsI photocathodes
(PCs)
 Preliminary results on diamond PCs
 Concluding remarks
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
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Deposition technique
Thermal evaporation (Joule effect)
more utilised technique for the CsI
thin film deposition
Electron beam evaporation
technique used at TUM for HADES
Ion beam sputtering (IBS)
technique explored in our laboratory for
the first time for the CsI thin film
deposition
Best parameters for the CsI film deposition
by means of IBS are:
Current beam of
50 mA
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
Energy beam of
700 eV
3
Sample stability against aging
due to humid air exposure
Comparison between the QE (%) of CsI
photocathodes grown with two different
techniques: thermal evaporation and IBS in
our laboratories, without post-deposition
thermal annealing
QE (%)
RQE 
QEafter 24 h in humid
IBS
< QE (%) thermal evaporation
air
QEas deposited
CsI photocathodes deposited by IBS seem
to be more stable after 24 h air exposure
than the evaporated ones.
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
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Crystalline structure (XRD)
3000
2750
2500
2250
2000
1750
1500
1250
1000
750
500
250
0
20
(110)
Ti/Au
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
20
(50 mA, 700 eV) Sputtered
(110)
Counts (a.u.)
Counts (a.u.)
(50 mA, 350 eV) Sputtered
(220)
25
30
35
40
45
50
55
60
65
70
Ti/Au
(220)
25
30
35
40
2(°)
45
60
65
70
Evaporated CsI film
(200)
Ti/Au
3000
55
2(°)
(50 mA, 700 eV)
Sputtered with assistance ion-beam
3500
50
Counts (a.u.)
Counts (a.u.)
2500
2000
1500
(200)
1000
500
0
20
(110)
25
30
(310)
35
40
45 50
2 (°)
55
60
65
Ti/Au substrate
70
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20
25
30
35
40
45
50
(°)
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55
60
65
70
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Deposition parameters
Deposition
mode
Beam
current
(mA)
Beam
energy
(eV)
Growth
rate
(nm/s)
QE (%)
( = 160 nm)
(A)
Grain size
(nm)
(B)
Grain size
(nm)
ION BEAM
SPUTTERING
50
350
0.08
11.2
334.15
n.d.
ION BEAM
SPUTTERING
50
700
0.28
14.7
509.38
n.d.
ION BEAM
ASSISTED
SPUTTERING
50
700
0.23
7.8
287.5
144.96
1
26.4
n.d.
201.2
THERMAL EVAPORATION
n.d.: not detected
(A)
(B)
crystallographic orientation (110)
crystallographic orientation (200)
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
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3D AFM images of CsI films deposited with
two different technique on Ti/Au substrate
Quartz substrate covered with a Ti/Au layer
Ra = 1.29 nm
Ra = 1.29 nm
3D AFM image
Film deposited by thermal evaporation
Film deposited by IBS
Ra = 12.9 nm
Ra = 14.8 nm
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3D AFMWorkshop
imageon RICH, Playa del Carmen, Mexico
1st December, 2004
3D AFM image
3D AFM images of substrates
with different roughness Ra
Quartz substrate covered with an Al layer
PCB substrate
Ra = 4.55 nm
3D AFM image
Ra = 12.48 nm
3D AFM image
Peened quartz substrate covered with an Au layer
Ra = 350 nm
AFM
image
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Playa del
Carmen, Mexico
1st December, 2004
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QE (a.u.) vs. the
substrate roughness
The QE (a.u.) of CsI PCs deposited
by IBS follows the surface average
roughness Ra of substrates
The QE (a.u.) of CsI PCs deposited
by thermal evaporation seems to be
independent from the surface
average roughness Ra of substrates,
but………………………
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
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3D AFM images of CsI films deposited with
two different technique on
Peened quartz substrate
Peened quartz substrate covered with an Au layer
Ra = 350 nm
3D AFM image
Film deposited by IBS
Film deposited by thermal evaporation
Ra = 283.90 nm
Ra = 103.04 nm
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3D
AFM image
1st December, 2004
3D AFM images of CsI films deposited with
two different technique on Al substrate
Quartz substrate covered with an Al layer
Ra = 4.55 nm
3D AFM image
Film deposited by thermal evaporation
Film deposited by IBS
Ra = 39.82 nm
Ra = 67.49 nm
3D AFM
image
5th International
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December, 2004
3D AFM1stimage
3D AFM images of CsI films deposited by
two different technique on PCB substrate
Quartz substrate covered with a PCB layer
Ra = 12.48 nm
3D AFM image
Film deposited by thermal evaporation
Film deposited by IBS
Ra = 24.09 nm
Ra = 13.54 nm
3D AFM
imageon RICH, Playa del Carmen, Mexico
5th International
Workshop
3D AFM image
1st December, 2004
Model of a CsI film morphology deposited on the same
substrate by the two different techniques
hv
hv
hv

UV
Photons
hv
hv
Electron
photoexcitement
regions
FILM
SUBSTRATO
SUBSTRATE
(a)
Film deposited by
thermal evaporation
Effective reduction factor of the absorption length:
FILM
SUBSTRATE
(b)
Film deposited by
IBS
F  1
cos2
n2
n is the refractive index of CsI
 is the angle between the surface and the direction of the incident radiation
In case (a) there is an enhancement of the maximum efficiency of photoemission
for reflective PCs :
QER max  QT
L
L
QER max  QT
L
L  F
Q = intrinsic QE
T = probability that an electron that reach the surface can escape (T  1)
L = escape length
 = optical absorption length
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
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Polymer material: PET
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
Progress in diamond films for the
realization of UV photocathodes
PHOTOCATHODE = key element of many detection systems
Since many years the scientific research has been devoted to the
study of materials for the PC production, depending on the spectral
range of detection.
For the UV range, PCs manufactured with alternative materials with
respect to CsI have to present the following properties:
– quantum efficiency comparable to that of CsI PCs;
– high stability for
exposure to high photon or ion flux
exposure in air
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
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Comparison diamond-CsI
Properties
Diamond
CsI
Density (g/cm3)
3.51
4.51
Bandgap EG (eV)
5.5
6.2
Electron affinity  (eV)
< 1 eV
(or negative)
0.1
Resistivity ( cm)
1013-1016
1010-1011
Optical transparency
Broad from
the deep (225
nm) UV to the
far IR region
From UV to
far IR
Elevate
Elevate
Scarce
Scarce
Stability for:
- Air exposure
- UV photon exposure
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
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Electron affinity (PEA, NEA)
Band energy for:
F. J. Himpsel e al., Phys.Rev.B 20 (1979) 624
a) Positive electron affinity (PEA)
b) “Effective” negative electron affinity (NEA) due to Cs layer and its dipole layer
c) “True” negative electron affinity (NEA) systems, typical of boron-doped natural
diamond
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
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QE (%) of an amourphous diamond
film deposited by means of IBS
Our results (IBS diamond film – Bari -)
@  = 150 nm
QE (%) = 0.7 %
Ion Beam Sputtered DLC
QE (%)
1
0.1
0.01
150
160
170
180
190
200
A.S. Tremsin* and O.H.W. Siegmund
210
Proceedings SPIE, vol. 4139, San Diego, California (2000)
(nm)
Literature (POLYCRYSTALLINE film)
@  = 1500 Å
QE (%) = 0.2 %
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
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Substrates used
Silicon (Si) substrates were used for the diamand film deposition because of their cubic crystalline
structure, as that of diamond.
Before proceeding to the deposition of diamond film, it is important to treat the surface of Si
substrate with diamond powder in ultrasonic bath.
Si not treated, in fact, presents:
 low density of nucleation centres (104 cm-2) due to the high surface energy of diamond, the big
mismatch between Si and diamond and the low probability of nucleation precursor sticking.
Si traited with diamond powder presents:
 high density of nucleation centres (1011 cm-2)
(a) Si substrate not traited
(b) Si substrate traited
with Al2O3 powder
(c) Si substrate traited
with SiC powder
(d) Si substrate traited
with diamaond polwder
At the LIMHP of Paris, nanocrystalline diamand films with different percentage of
graphite were deposited by MPECVD on quartz substrate too.
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
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Techniques of deposition for
diamond films
Poly and nanocrystalline diamond films were prepared by MPECVD, at the LIMHP
(Laboratoire d’Ingénierie des Materiaux et des Hautes Pressions) - CNRS-UPR- Paris.
CH4/H2 plasma discharge conditions,
adopted in experiment of diamond deposition are:
1. reactor UHV coupled to a microwave generator
(2.45 GHz)
2. CH4 highly diluited in H2 (CH4 < 4%)
3. high deposition temperature (750-900 °C)
4. high microwave input power (0.45-2.5 kW)
5. high pressure (10-200 mbar)
Amorphous diamond films were prepared by
IBS, at the Thin Film Laboratory of Bari,
starting from a carbon target.
MPECVD: microwave plasma enhanced
chemical vapour deposition
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
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AFM images of poly and nanocrystalline
diamond films (MPECVD - LIMHP)
NANOCRYSTALLINE
POLYCRYSTALLINE
Ra = 16.44 nm
Ra = 48.83 nm
Average GRAIN size
≤ 250-500 nm
5th International Workshop on RICH, Playa del Carmen, Mexico
Average GRAIN size
≥ 0.5-1 m
1st December, 2004
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Comparison with literature
Our results (MPECVD diamond film – Paris-)
@  = 150 nm
Literature
@  = 1500 Å
QE (%) = 0.2 %
5th International Workshop on RICH, Playa del Carmen, Mexico
QE (%) = 5  30 %
A.S. Tremsin* and O.H.W. Siegmund
Proceedings SPIE, vol. 4139, San Diego, California (2000)
1st December, 2004
18
Aging due to air exposure
Comparison between the RQE of a CsI PC, deposited by thermal evaporation, and
a nanographitic (NG) diamond PC, deposited by MPECVD.
The diamond PC presents a lower aging with respect to the CsI one.
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
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Concluding remarks
 The study of the deposition technique influence on
morphological, structural and photoemissive properties of CsI
PCs, indicates that the evaporated ones have a higher QE, and
suggests to increase the substrate microroughness in order to
enhance the photoyield of sputtered ones.
 A model of surface morphology has been also presented in
order to explain the higher photoemission of evaporated PCs
than that of PCs grown by IBS.
 On the basis of the preliminary results on diamond PCs
we look forward to applying them to UV photon detectors,
because of their higher stability in air with respect to that of
the detectors based on CsI PCs.
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
Thank you
for your attention
and
see YOU at
RICH 2006
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
5th International Workshop on RICH, Playa del Carmen, Mexico
1st December, 2004
Photon-aging
(UV flux : 107 photons/mm2sec)
Before exposure
After
exposure
Photoelectron
UV photon
Grains
Substrate
5th International Workshop on RICH, Playa del Carmen, Mexico
1st Channeling
December, 2004 mechanism