TimeResolved XPS Analysis of the SiSO2 System in the Millisecond Range

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Time-Resolved XPS Analysis of the Si/SO2 System
in the Millisecond Range

• U. Korcan Demirok
• Supervisor Prof.Dr. Sefik Süzer
• Bilkent University / Ankara / Turkey

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Contents

• Photoelectron Spectroscopy
• XPS Principles
• Surface Charging
• Charging under External Bias
• Early Work
• Our Work
• Application of Voltage Pulses
• Acquisition of Time-resolved XPS spectra
• Investigation of Various Si/SiO2/Au Systems in
  Time-Resolved mode
• Future Work and Applications

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Photoelectron SpectroscopyXPS
Radiation
photo-electrons
BE h? - KE
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Photoelectron SpectroscopyXPS

• Highly Surface Sensitive
• Down to 1nm
• Chemical and Elemental Information
• Quantitative / Qualitative Analysis
• All Elements Except H and He
• Chemical States
• Identification of Oxidation States of the
  Elements via Chemical Shift Analysis

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Surface Charging

• Conducting Samples
• The lack of electrons is compensated from the
• ground immediately

Radiation
photo-electrons
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Surface Charging

• Non-Conducting Materials
• Positive charge develops due to the faster rate
  of loss of electrons

Radiation
photo-electrons

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Surface Charging Potential
Grounded Sample (No Surface Charge)
Sample is Grounded via a Resistor Slowing down
the rate of e- flow to the sample (Positive
Surface Charge)
Bombardment with Low Energy Electrons (Negative
Surface Charge)
W.M. Lau, J. Appl. Phys. 67 (3), 1 Feb. 1990
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Charging under External Bias
x-ray
e-
e-
e-
SiO2
Si
BE Difference between Si4 and Si0 is dependent
on External Bias
B. Ülgüt and S. Süzer, J. Phys. Chem. B 107,
2939-43 (2003)
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Early Work
Takakuwa et al.
Real-time monitoring of the growth of SiO2 Layers
by AES
Time Scale of the Order of 3000s.
Fig. 1. Time evolutions of O KLL Auger electron
intensity taken in situ as a function of the
temperature during thermal oxidation of 27a
Si(001) surface with O of 2310 Torr. The thermal
oxidation changes from passive oxidation (SiO
growth) to active oxidation (etching due to SiO
desorption) at about 750.8C as indicated
by arrows. The passive oxidation is divided into
two regions of Langmuir-type adsorption and
two-dimensional island growth at about 630.8C.
The short bars represent an origin for the O
KLL Auger electron intensity.
Takakuwa et al., J. Electron Spectroscopy and
Rel. Phen, 114-116 (2001),401-407
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Questions
Aspect I Time Dependent Information

• Minimum Time Required to Acquire an XPS Spectrum
  3-5minutes
• Most of the Atomic Phenomena Take Place in
  Smaller Time Scales
• How Can We Bring The Period of Data Collection
  Down?
• What is the Dynamics of Charge Flow?

(Depending on the Parameters)
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Our Work

• Application of Voltage Pulses by Making Use of
  External Bias
• Measuring the Intensity of an Energy with 5ms
  Intervals
• Scanning the Energy Region with Desired Energy
  Resolution
• Collection of Consequent XPS Spectra

U. K. Demirok, G. Ertas, S. Suzer, J. Phys. Chem.
B, 2004, vol.108, Iss.17, 5179 (Cover)
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Time Resolved XPS

• The Result
• Addition of a
• Third Dimension
• (Time)
• to a 40-year-old Spectroscopic Technique

U. K. Demirok, G. Ertas, S. Suzer, J. Phys. Chem.
B, 2004, vol.108, Iss.17, 5179 (Cover)
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Time Resolved XPS
System I
System II
x-ray
x-ray
Gold
SiO2
Gold Nano-Clusters
SiO2
Si
Si
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Time Resolved XPS
System I

• Time Evolution of the Charging of a 400nm thick
  SiO2 layer
• Most of the Charges are Built-up within
  a second
• Bulk Gold Does not Exhibit any Charging Behavior
  in the Same Period

U. K. Demirok, G. Ertas, S. Suzer, J. Phys. Chem.
B, 2004, vol.108, Iss.17, 5179 (Cover)
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Time Resolved XPS
System II

• Charging of C12-thiol-capped Gold Nano-clusters
  together with SiO2 is Observed.
• Au Nano-clusters also display a charging behavior
  in time.
• Slight difference in the charging behavior of
  SiO2 and Au-nano-clusters, i.e., difference in
  time constants is observed.

U. K. Demirok, G. Ertas, S. Suzer, J. Phys. Chem.
B, 2004, vol.108, Iss.17, 5179 (Cover)
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Time Resolved XPS
System III

• Bulk Gold and Gold nano-clusters are combined
• Is it possible to observe two different charging
  behavior for two types?

Filament
e-
x-ray
Bulk Gold
Gold Nano-Clusters
Si
SiO2
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Time Resolved XPS
System III
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Time Resolved XPS
System III

• Two Different signals coming from two different
  types gold are observed!
• Going from -10V to 10V, time dependent splitting
  of the Au4f photoemission of gold nano-clusters
  from bulk gold due charging of thiol-capped gold
  nano-clusters is displayed in time.

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Our Work
What other information can be derived from
Time-Resolved XPS data?
Time Constant
t
R
C
Resistance
Capacitance
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Resistance-Capacitance
T. Ohgi, D. Fujita
Capacitance Measurements, Core level Shifts in
Supported Gold Nano-clusters
Dependency of Binding Energy Shifts on Cluster
Size
Schematic diagram and equivalent circuit for
photoelectron spectroscopy on Au-cluster/octanedit
hiol/Au(111) sample
T. Ohgi, D. Fujita,Physical Review B
66,115410(2002)
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Aspect II Material Properties

• Can We Measure the Capacitance of Layers and
  Clusters?
• Can other Material Properties, i.e. Resistance,
  of Layers and Clusters be Measured too?
• Can All These be Done in-situ, with non-contact
  measurements?

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Resistance Measurements
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Material Properties

• Monitoring the charging of the SiO2 overlayer
• Obtaining the Time Constant of the charging
  process

• All the measurements are in-situ
• Extracting information on the Resistance and
  Capacitance of the layers in question

U. K. Demirok, G. Ertas, S. Suzer, J. Phys. Chem.
B, 2004, vol.108, Iss.17, 5179 (Cover)
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Future Work and Applications
Material Properties
Time Resolved XPS

• Understanding the Dynamics and Nature of Surface
  Charging
• Possibility of Monitoring/Probing Various
  Charging/Discharging Phenomena at the Nanometer
  Scale

• In-situ, non-contact Measurements to reveal
  important material properties
• Resistance
• Capacitance
• Dielectric Constants
• of Various Nano-Structures
• Investigation of Layered Nanostructures (i.e.
  Organic, Polymer, Semiconductor Layers)

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Thank You