Outline

55thth International Workshop on RICH, Playa del Carmen, Mexico International Workshop on RICH, Playa del Carmen, Mexico 11stst December, 2004 December, 2004

OutlineOutline

Influence of the deposition deposition techniquetechnique

on the properties of CsICsI photocathodes photocathodes

(PCs)(PCs)

Preliminary results on diamonddiamond PCsPCs

Concluding remarks22


Deposition techniqueDeposition techniqueThermal 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 depositionby means of IBS are:

Current beam of Energy beam of 50 mA50 mA 700 eV 700 eV

0

5

10

15

20

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30

35

150 160 170 180 190 200 210

AS DEPOSITED

CsI film deposited by IBS (50 mA, 700 eV)CsI film deposited by IBS (50 mA, 700 eV) with assistance ion-beamCsI film deposited by IBS (50 mA, 350 eV)

(nm)

33


Sample stability against Sample stability against aging aging

due to humid air exposuredue to humid air exposure

CsI photocathodes deposited by IBS seem to be more stablestable after 24 h air exposure than the evaporated ones.

QE (%) IBS < QE (%) thermal evaporation

Comparison between the QE (%) of CsI photocathodes grown with two different techniques: thermal evaporation and IBS in our laboratories, without post-depositionthermal annealing

0

5

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15

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30

35

150 160 170 180 190 200 210

AS DEPOSITED

CsI film deposited by THERMAL EVAPORATION

CsI film deposited by IBS (50 mA, 700 eV)

(nm)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

CsI film deposited by IBS (50 mA, 700 eV)

CsI film deposited by THERMAL EVAPORATION

150 155 160 165 170 175 180 185 190

(nm)

depositedas

airhumidinhafter

QE

QERQE 24

44


Crystalline structure Crystalline structure (XRD)(XRD)

20 25 30 35 40 45 50 55 60 65 70

(200)

Ti/Au substrate

Evaporated CsI film

Co

un

ts (

a.u

.)

2(°)

20 25 30 35 40 45 50 55 60 65 700

250500750

100012501500175020002250250027503000

(220)

Ti/Au

(50 mA, 350 eV) Sputtered

Co

un

ts (

a.u

.)

2(°)

(110)

20 25 30 35 40 45 50 55 60 65 700

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000(50 mA, 700 eV) Sputtered

(220)

Ti/Au

Co

un

ts (

a.u

.)

2(°)

(110)

20 25 30 35 40 45 50 55 60 65 700

500

1000

1500

2000

2500

3000

3500

(50 mA, 700 eV) Sputtered with assistance ion-beam

(200)

Cou

nts

(a.u

.)

2 (°)

(310)(110)

Ti/Au

55


Deposition parametersDeposition parameters

Depositionmode

Beamcurren

t(mA)

Beamenergy

(eV)

Growthrate

(nm/s)

QE (%)( = 160

nm)

(A)Grain size

(nm)

(B)Grain size

(nm)

ION BEAMSPUTTERING

50 350 0.08 11.2 334.15 n.d.

ION BEAMSPUTTERING

50 700 0.28 14.7 509.38 n.d.

ION BEAMASSISTED

SPUTTERING50 700 0.23 7.8 287.5 144.96

THERMAL EVAPORATION 1 26.4 n.d. 201.2

n.d.: not detectedn.d.: not detected (A)(A) crystallographic orientationcrystallographic orientation (110)(110)

(B)(B) crystallographic orientationcrystallographic orientation (200)(200)66


3D AFM images of CsI films deposited 3D AFM images of CsI films deposited with two different technique on Ti/Au with two different technique on Ti/Au

substratesubstrate

3D AFM image

Film deposited by thermal evaporation

3D AFM image

RRaa = 1.29 nm = 1.29 nm

RRaa = 12.9 nm = 12.9 nmFilm deposited by IBS

RRaa = 14.8 = 14.8 nmnm

QuartzQuartz substrate covered with a Ti/Au Ti/Au layer RRaa = 1.29 = 1.29

nmnm

3D AFM image


3D AFM images of 3D AFM images of substrates substrates with different roughness Rwith different roughness Raa

RRaa = 12.48 nm = 12.48 nm

RRaa = 350 nm = 350 nm

RRaa = 4.55 = 4.55 nmnm

Quartz Quartz substrate covered withsubstrate covered with an an Al Al layerlayer PCBPCB substrate

PeenedPeened quartz quartz substrate covered withsubstrate covered with an an Au Au layerlayer

88

3D AFM image

3D AFM image

3D AFM image


0

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150 160 170 180 190 200 210

CsI films deposited by thermal evaporation

Qz + Al (Ra = 4.55 nm)

Qz + Ti/Au (Ra = 1.29 nm)

Peened Qz + Au ((Ra = 350 nm)

Cern PCB (Ra = 12.48 nm)

(nm)

QE (a.u.) vs. the QE (a.u.) vs. the substrate roughnesssubstrate 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………………………

0

1

2

3

4

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6

7

8

150 160 170 180 190 200 210

CsI film deposited by IBS

Qz + Ti/Au (Ra = 1.29 nm)

Qz + Al (Ra = 4.55 nm)

Peened Qz + Au (Ra= 350 nm)

Cern PCB (Ra = 12.48 nm)

(nm)

99



RRaa = 103.04 = 103.04 nmnm

3D AFM image

3D AFM images of CsI films deposited 3D AFM images of CsI films deposited with two different technique on with two different technique on

Peened quartz substratePeened quartz substratePeenedPeened quartz quartz substrate covered withsubstrate covered with an an Au Au layerlayer

RRaa = 350 nm = 350 nm

3D AFM image 3D AFM image



3D AFM images of CsI films deposited 3D AFM images of CsI films deposited with two different technique on Al with two different technique on Al

substratesubstrate

RRaa = 4.55 = 4.55 nmnm

Quartz Quartz substrate covered withsubstrate covered with an an Al Al layerlayer

RRaa = 39.82 nm = 39.82 nmFilm deposited by IBS RRaa = 67.49 = 67.49

nmnm

3D AFM image




3D AFM images of CsI films deposited 3D AFM images of CsI films deposited by two different technique on PCB by two different technique on PCB

substratesubstrate


RRaa = 13.54 = 13.54 nmnm

QuartzQuartz substrate covered with a PCBPCB layer

3D AFM imageFilm deposited by thermal evaporation

RRaa = 12.48 nm = 12.48 nm



Model of a CsI film morphology deposited on the Model of a CsI film morphology deposited on the same substrate by the two different techniquessame substrate by the two different techniques

(a)(a)Film deposited by

thermal evaporationthermal evaporation

(b)(b)Film deposited by

IBSIBS

Electron photoexcitement

regions

FILM

SUBSTRATO

hv hv

FILM

hvhv UV

Photons

SUBSTRATE SUBSTRATE

hv

2

2cos1

nF

Effective reduction factor of the absorptionabsorption lengthlength:

nn is the refractive index of CsI is the angle between the surface and the direction of the incident radiation

In case (a)(a) there is an enhancement of the maximum efficiency of photoemission for reflectivereflective PCs :

L

LQTQER max FL

LQTQER

max

Q = intrinsic QE T = probability that an electron that reach the surface can escape (T 1)L = escape length = optical absorptionabsorption lengthlength

1010


Polymer material: PET


Progress in diamond films for the Progress in diamond films for the realization of UV photocathodesrealization of UV photocathodes

PHOTOCATHODEPHOTOCATHODE = key element of many detectiondetection systems

Since many years the scientific research has been devoted to the study of materialsmaterials for the PCPC production, depending on the spectral rangespectral range of detection.

For the UV UV range, PCsPCs manufactured with alternativealternative materials with respect to CsI have to present the following properties:

– quantum efficiency comparablecomparable to that of CsICsI PCsPCs;

exposure to high photon or ion flux– high stability stability for exposure in air

1212


Comparison diamond-CsIComparison diamond-CsI

PropertiesProperties DiamonDiamondd

CsICsI

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

Stability for:- Air exposure

- UV photon exposureElevateElevate

ScarceScarce

1313


Electron affinity (PEA, NEA)Electron affinity (PEA, NEA)

Band energy for: a) Positive electron affinity (PEA)(PEA) b) “Effective“Effective”” negative electron affinity (NEA) (NEA) due to Cs layer and its dipole

layer c) “True”“True” negative electron affinity (NEA(NEA) systems, typical of boron-doped natural diamond

F. J. Himpsel e al., Phys.Rev.B 20 (1979) 624

1414


QE (%) of an amourphous QE (%) of an amourphous diamonddiamond

film deposited by means of IBSfilm deposited by means of IBS

Proceedings SPIE, vol. 4139, San Diego, California (2000)

A.S. Tremsin* and O.H.W. Siegmund0.01

0.1

1

150 160 170 180 190 200 210

Ion Beam Sputtered DLC

QE

(%)

(nm)

Literature (Literature (POLYPOLYCRYSTALLINE CRYSTALLINE film)film)@ = 1500 Å QE (%) = 0.2

%

Our results (Our results (IBSIBS diamonddiamond filmfilm – – Bari Bari --))@ = 150 nm QE (%) = 0.7 %

1919


Substrates usedSubstrates used

Silicon (Si) substrates were used for the diamand film deposition because of their cubic crystalline

structure, as that of diamond.

BeforeBefore proceeding to the deposition of diamond film, it is important to treat the surface of Si

substrate with diamond powder diamond powder in ultrasonic bathultrasonic bath..

Si Si not 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 Si traitedtraited with diamond powderdiamond powder presents: high density of nucleation centres (1011 cm-2)

At the LIMHP of Paris, nanocrystalline diamand films with different percentage of graphite were deposited by MPECVD on quartz substrate too.

(a) Si substrate notnot traited (b) Si substrate traited with AlAl22OO3 3 powder

(c) Si substrate traited with SiC SiC powder

(d) Si substrate traited with diamaond diamaond

polwderpolwder

1515


Techniques of deposition for Techniques of deposition for diamond filmsdiamond films

PolyPoly and nanonanocrystallinecrystalline diamond films were prepared by MPECVDMPECVD, at the LIMHP (Laboratoire d’Ingénierie des Materiaux et des Hautes Pressions) - CNRS-UPR- Paris.

MPECVDMPECVD:: microwavemicrowave plasma plasma enhancedenhanced chemical vapour depositionchemical vapour deposition

AmorphousAmorphous diamond films were prepared by IBSIBS, at the Thin Film Laboratory of Bari, starting from a carbon target.

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)

1616


AFM images of poly and nanocrystallineAFM images of poly and nanocrystalline diamond films (MPECVD - LIMHP) diamond films (MPECVD - LIMHP)

NANONANOCRYSTALLINECRYSTALLINE POLYPOLYCRYSTALLINECRYSTALLINE

Average GRAIN size ≤ 250-500 nm

RRaa = 16.44 nm = 16.44 nm RRaa = 48.83 nm = 48.83 nm

Average GRAIN size ≥ 0.5-1 m

1717


Comparison with Comparison with literatureliterature

Proceedings SPIE, vol. 4139, San Diego, California (2000)

A.S. Tremsin* and O.H.W. Siegmund

0

5

10

15

20

25

30

150 160 170 180 190 200 210

Diamond films

Ech 4 graphitic NANO (890 ° C)Ech 3 POLY (880 ° C)Ech 2 NANO (815 ° C)Ech 1 NANO (800 ° C)

Wavelength (nm)

Our results (Our results (MPECVDMPECVD diamond diamond film – film – ParisParis--))

LiteratureLiterature

@ = 1500 Å QE (%) = 0.2 %

@ = 150 nm QE (%) = 5 30 %

1818


Aging due to air exposureAging due to air exposure

Comparison between the RQE of a CsI PC, deposited by thermal evaporation, and a nanographitic (NG) diamond PC, deposited by MPECVDMPECVD. The diamond PC presents a lower aging with respect to the CsI one.

2020

0.1

1

140 150 160 170 180 190 200 210 220

CsI film deposited by thermal evaporationEch 4 graphitic NANO (890 ° C)

Wavelength (nm)


Concluding remarksConcluding remarks The study of the depositiondeposition techniquetechnique influence on morphological, structural and photoemissive properties of CsI CsI PCsPCs, indicates that the evaporated ones have a higher QEhigher QE, and suggests to increaseincrease the substrate microroughnessmicroroughness in order to enhance the photoyield of sputtered ones. A modelmodel of surfacesurface morphology morphology has been also presented in order to explain the higher higher photoemissionphotoemission of evaporated PCs PCs than that of PCsPCs grown by IBSIBS..

On the basis of the preliminary results on diamonddiamond PCsPCs we look forward to applying them to UVUV photonphoton detectorsdetectors, because of their higherhigher stability stability in in airair with respect to that of the detectorsdetectors based on CsI CsI PCsPCs.


Thank you

for your attention

and

see YOU at

RICH 2006




Photon-agingPhoton-aging (UV flux : 10 (UV flux : 1077

photons/mmphotons/mm22sec)sec)Before exposure

After exposure

Channeling mechanism

Substrate

PhotoelectronUV

photon

Grains

1

10

100

150 160 170 180 190 200

(nm)

PHOTON AGING UNDER VACUUM

As deposited

Aged after 5 days

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