Exploring glass surface with high-resolution XPSExploring glass surface with high-resolution XPS and LEIS:

E l f F d t l St di d A li tiExamples of Fundamental Studies and Applications

Andriy KovalskiyAndriy KovalskiyMaterials Science & Engineering Department

Lehigh University, PA

Co-authors: Himanshu Jain, Bruce Koel, Alfred Miller, Miroslav Vlcek,Roman Golovchak, Keisha Antoine, Maria Mitkova

“The surface was invented by the devil”Wolfgang Pauli

Glass structure – lack of translational symmetry

iquidVA

Liqu

Supercooled

liquid

V

E

B

Crystal

Glass

G

F

TTg range

D

TcrystTgmaxTgminTroom

C

High-resolution XPS:

one of the fundamental structural methods in glass science Other methods:

Raman/FTIR spectroscopy, EXAFS, NMR

State of the art high resolution XPS vs “normal” XPS

25000

30000

Se 3d

Se

Se-S

e-S

e

25000As40Se60

Se 3d 12000

14000As40Se60

As 3d

0

5000

10000

15000

20000

Cou

nts

5000

10000

15000

20000

Cou

nts

Se 3d

2000

4000

6000

8000

10000

12000

Cou

nts

58 57 56 55 54 53 52 510

Binding energy , eV 58 57 56 55 54 53 520

Binding energy , eV45 44 43 42 41 40

0

Binding energy , eV

21000As2S3 bulkS 2 l l 12000

14000 As2S3 bulkAs3d core level

Structure of fresh cut of glass vs freshly deposited thin film

9000

12000

15000

18000 S 2p core level

Cou

nts

4000

6000

8000

10000

12000

Cou

nts

165 164 163 162 161 1600

3000

6000

Binding energy, eV

46 45 44 43 42 410

2000

Binding energy, eV

10000

Bulk As2S3

7000

6000

8000S2p

84 % AsS3/2

16 % within S-S

ount

s 4000

5000

6000 As 3d

85 % AsS3/2

unts

2000

4000

Co

1000

2000

3000 15 % As-AsCou

165 164 163 162 1612000

Binding energy (eV)45 44 43 42 41

0

Binding energy (eV)

Freshly deposited As2S3 film

Thin films: photostructural transformations by XPS

Array of Fresnel lenses with focal point ~300 μm

Fresnel lens with focal point ~5.38 mm

IR laser beam (1.55 μm) focused by Fresnel lens on Si substrate

Photooxidation on the surface of ChG

Oxidation in air strongly depends on Ge content

500

600

/sec

)

Ge2Se3 thin film

Ge 3d core level400

500

/sec

)

Ge within GeSe4Ge 3d core level

Ge3Se7 thin film exposed to air

200

300

400

sity

(cou

nts/ Ge within

ethane-like unitsdistributed Ge-O bonds 200

300

sity

(cou

nts

36 34 32 30 280

100

200

Inte

ns Ge oxide

33 32 31 30 290

100

Inte

n36 3 3 30 8

Binding energy (eV) Binding energy (eV)

Strong oxidation in air No oxidation in air

E-beam Patterning of Chalcogenide Glasses

What is the resolution limit for ChG?

17 nm

7 nm ~20 nm

Finest structural features on l

Direct observation of separate e-beam spots

Wet Etching in Amine Solutionglasses beam spots

Structural Origin of E-beam Patterning of Chalcogenide Glasses

10S3p(lp)As4p(b)As4s(nb)

As35S65

glass substrate + Cr

10As4s(nb)

As35S65

glass substrate + Cr

6

8

10 ( p)S3p(b)

( )

S3s(nb)O2s(c)

glass substrate + Cr

CPS

a)

4

6

8

CPS

b)

30 25 20 15 10 5 00

2

4 fresh light-irradiated

C

30 25 20 15 10 5 00

2 fresh electron-irradiation (dose I)

Binding energy (eV)Binding energy (eV)

Binding energy (eV)

300

350

400

As35S65

glass substrate + Cr

d)8

10

As4s(nb)

As35S65

glass substrate + Cr

c)

100

150

200

250

300

fresh

CP

S2

4

6

fresh

CPS

25 20 15 10 5 00

50fresh electron-irradiation (dose III)

Binding energy (eV)30 25 20 15 10 5 0

0

2 electron-irradiation (dose II)

Binding energy (eV)

Gray Scale Lithography based on Ag Photodiffusion in Chalcogenide Glass Thin Films

Motivation: 3-D profiles in photoresist film for development of microturbine compressor with smooth blades

Example of complex shape structure on the surface– negative dry etching

Si substrate to ChG thickness transfer ratio of > 10 is achieved

Gray Scale Lithography based on Ag Photodissolution into Chalcogenide Glass Thin Films

20000

25000

30000

93 % AsS

S2p- Ag dissolves into As-S glass in step like mode- depth of dissolution - function of exposure dose

5000

10000

15000

7 % Ag-S

93 % AsS3/2

Cou

ntsdepth of dissolution function of exposure dose

165 164 163 162 161 160Binding energy (eV)

Control of composition

30

35

40

45Ag (7 nm)/As2S3 (50 nm) bi-layer,films deposited and irradiated at UHV,no contact with air

at. %

Kinetics of X-ray-induced silver dissolution from the surface of a-As2S3 thin film by high-resolution XPS

Profilogram demonstrating the change of etching depth with gradual variation of transparency of mask fragments.

0 10 20 30 40 50 60 70 80

15

20

25

30

Ag,

a

t, mint, min

Kinetics of X-ray-induced Ag dissolution

Influence of surface oxidation?

Ag Photodiffusion into As2S3

ChG Surface after PhotodiffusionChG Surface after Photodiffusion and Treatment in HNO3 solution

Spikes are due to: oxide clusters which etch differentlySpikes are due to: oxide clusters which etch differently.

Compare final productsAg Photodiffusion into ChG

/ S

3000

4000

As 3d core level

Ag/As2S3 X-ray irradiated exposed to air Ag/As2S3 X-ray irradiated in vacuum

s/se

c) 8000

10000

S 2p core level

Ag/As2S3 X-ray irradiated in vacuum Ag/As2S3 X-ray irradiated exposed to air

s/se

c)

1000

2000

nten

sity

(cou

nt

2000

4000

6000

nten

sity

(cou

nt

x 103

40

46 44 42 40 380

In

Binding energy (eV)

165 164 163 162 161 160 159 1580

In

Binding energy (eV)

A 3dFINAL PRODUCTS f A diff i i d i

15

20

25

30

35

vacuumair

Ag 3d5/2FINAL PRODUCTS of Ag diffusion in vacuum and air:

•S chemical environment is similar, except that formation of ternary is slowed down by arsenic oxidation

C asaXPS (Thi s string can be edited in CasaXPS.DEF/PrintFootNote.txt )

0

5

10

370 369 368 367 366 365Binding Energy (eV)

•As chemical environment differs drastically:- phase separation due to oxidation in air; - some clustering of As in vacuum

•Ag chemical environment slightly differs due to As

Strong Glasses for Solar Energy

Concentrated Solar Thermal (CST)(CST)

Photovoltaics: IncreasedPhotovoltaics: Increased strength to weight (thickness) to permit larger thin film modulepermit larger thin film module size

Methods: XPS, LEIS

Sodium silicate glasses – breaking path

Sample Na O Si Na/Si BO/NBO

Sodium 21 55 24 0 875 2 2disilicate, 90 21 55 24 0.875 2.2

Sodium disilicate, 25 19 59 22 0.86 2.3

Sodium disilicate heat

treated, 9020 55 25 0.80 2.3

diSodium disilicate heat

treated, 2521 54 25 0.84 2.2

Sodium Sodium trisilicate, 90 14 60 26 0.54 3.0

Sodium trisilicate, 25 24 56 20 1.20 2.4

Ion-TOF low energy ion scattering: first resultsNa O-2SiO fractured

80

100 SiO2 fracturedO

100

120

140

Na2O 2SiO2 fractured

O

Na

40

60

EIS

sygn

al (a

.u.)

Si

40

60

80

LEIS

syg

nal (

a.u.

)

Si

800 1000 1200 1400 1600 1800 20000

20

LE

800 1000 1200 1400 1600 1800 2000

0

20

L

800 1000 1200 1400 1600 1800 2000

Energy (eV)

800 000 00 00 600 800 000

Energy (eV)

Low Energy Ion Scattering: Preliminary results

Sample Si, at. % O, at. % Na, at. % Na/SiSiO2SiO2

fractured 35 65 - -

Na2O⋅2SiO2fractured 8 17 75 9.4fractured

Na2O⋅2SiO2treated 1 h

t 620 °C 5 24 71 14.2at 620 °C, fractured

Na2O⋅3SiO2 3 19 78 26 0fractured 3 19 78 26.0

ConclusionsConclusions

Surface charge energy Surface charge energy EEchch can be determined by electrically calibrating the can be determined by electrically calibrating the

Binding Energy Referencing

instrument to a spectral feature.instrument to a spectral feature.C1s at 284.8 C1s at 284.8 eVeVAu4fAu4f7/27/2 at 84.0 at 84.0 eVeV7/2 7/2

x 101

80

90

Se 3dwithout Au

50

60

70

Ge 3d

___ without Au___ with Au

30

40

50

CPS

0

10

20

CasaXPS (T his string can be edited in CasaXPS.DEF/PrintFootNote.txt)

55 50 45 40 35 30Binding Energy (eV)

Ge3Se7 – ideal referencing of Ge 3d to Au 4f7/2