1. February 14-18, Downtown Nashville,
Tennessee, Music City Center
Morphological, structural and optical characterization of
bottom up growth of Ag-WO3 core shell nano-cube
heterostructures
Muhammad A. Imam1
William Benton1
Ramana Reddy1
Nitin Chopra1
Department of Metallurgical and Materials Engineering1
The University of Alabama
Tuscaloosa, Alabama 35487
Presented by
Muhammad Ali Imam

2. February 14-18, Downtown Nashville,
Tennessee, Music City Center
Outline
• Background
• Motivation
• Experimental Details
• Results
I. Characterization (XRD,SEM,EDS)
II. Optical Properties (UV-vis spectra)
• Discussions
• Conclusions

3. February 14-18, Downtown Nashville,
Tennessee, Music City Center
Background
• Transition metal oxides are known as
semiconducting materials having a
wide band gap, which can be tuned
while being used as heterostructures.
• To tune the band gap facilitates rapid
charge transport [1] and unique
photonic[2] properties which is not
possible with single component or
homogenous structures.
Valence band
Conduction band
Band gap
Energy
Density of State

4. February 14-18, Downtown Nashville,
Tennessee, Music City Center
Motivation
• In literature[3], it has been reported
that the Au nano-particles could
reduce the band gap of TiO2
• It has been reported in another
literature that band gap of TiO2 was
reduced 3.7eV to 2.75eV by Ag[4]
• Another literature [5] shown that
the band gap of WO3 was tuned
using SnO2

5. February 14-18, Downtown Nashville,
Tennessee, Music City Center
Experimental procedure
• Materials and Method
• Growth of WO3 Nano-
cubes
• Sputtering of Ag onto
WO3 Nano-cubes
Silicon (111) wafers
WO3 and Ag targets
AJA International orion 3 sputtering system
Box furnace (GMF-110)
Schematic representation of step-by-step fabrication of Ag-WO3 CSNH

6. February 14-18, Downtown Nashville,
Tennessee, Music City Center
Growth of WO3 Nano-cubes
Operating condition
•A high base vacuum pressure of 2×10-7
torr
•RF power source at 50 W
•150 V working potential
• 6.54×10-3
torr working pressure
•25.1 sccm Ar flow rate,
•25 rpm substrate rotation speed
•Deposition rate of 0.2 A°/s (300nm thicknes)
•Air annealed at ~900°C for 180 min, 240 min
and 300 min in a box furnace

7. February 14-18, Downtown Nashville,
Tennessee, Music City Center
Growth of Core Shell Nano
Heterostructures (CSNH)
• WO3 nanocube on Si wafer was
loaded in the sputtering chamber
• A high base vacuum pressure of
2×10-7
torr
• DC power source at 15 W
• 750 V working potential
• 6.54×10-3
torr working pressure
• 25.1 sccm Ar flow rate,
• 25 rpm substrate rotation speed
• Deposition rate of 0.6 A°/s
(~90nm thickness)

8. February 14-18, Downtown Nashville,
Tennessee, Music City Center
Characterization
• FESEM, JEOL-7000, equipped with
an Oxford EDX detector was used
for morphological characterization
and energy- dispersive X-ray
spectroscopy (EDX).
• Philips X`Pert-MPD X-ray Diffraction
(XRD) system was used for phase
and crystal structure analysis.
• UV–vis spectroscopy was
implemented (absorbance spectra)
using an Ocean Optics USB 4000
spectrometer (Dunedin, FL)
equipped with DH-2000 UV-vis-NIR
light source.
Approximately, 2×2 cm
2
area of silicon wafer
containing WO3 nano-cubes/Ag@WO3 nano-
cubes was ultra-sonicated using hexane as a
solvent to prepare solution for UV-vis.

9. February 14-18, Downtown Nashville,
Tennessee, Music City Center
Results
FESEM micrograph of WO3 A. As sputtered, annealing at 900°C B.180 min C.240 min D. 300
min E. Particle size distribution F. EDX based elemental analysis of WO3
 Annealing effect directly enhances the
formation of nano-cube WO3 from the
sputtered WO3 [FESEM images B-C-D].
 This is a bottom up growth of nano
particles – the vapor-solid (VS) growth
mechanism drives this growth process
[6].
 The diameter of WO3 nano cubes was
varied from ~90nm to ~340 nm (E).
 EDS analysis of growth particle to

10. February 14-18, Downtown Nashville,
Tennessee, Music City Center
Results
FESEM micrograph of Ag-WO3 CSNH A. Before annealing B. Corresponding EDX based
elemental analysis C. After annealing (300°C for 60 min in Ar atmosphere) D. Corresponding
EDX based elemental analysis
 FESEM image of Ag-WO3
before (A) and after annealing
(C) and their corresponding
EDX spectrum (B and D)
respectively.
 From the EDX spectrum, the
presence of Ag was confirmed.

11. February 14-18, Downtown Nashville,
Tennessee, Music City Center
Results
XRD patterns for WO3 A. As sputtered, annealing at 900°C B.300 min C.240 min D. 180 min
 As sputtered WO3 (A) shows
amorphous characteristics of
WO3. Only Si peak (PDF # 80-
0018) was identified as Si was
used as a substrate.
 But after annealing at 900°C
for different time periods, the
structure started becoming
crystalline and monoclinic
WO3 (PDF # 76-1134) was
found.
 No significant change was

12. February 14-18, Downtown Nashville,
Tennessee, Music City Center
XRD patterns of the A. As sputtered WO3, B. Ag-WO3 annealed for 60 min at 300°C, C. Ag-WO3
before anneal D . Annealed WO3
Results
 A clear peak of Ag
(PDF # 76-1134) was
observed after coating
with Ag.
 The significant change
of Ag peak was
identified after
annealing because of
better crystallinity

13. February 14-18, Downtown Nashville,
Tennessee, Music City Center
UV-vis absorption spectra of WO3 (A), Ag-WO3 before (B) and after annealing (C)
Results
 A lot of changes in
major excition
absorption peaks
compared to the WO3
(~250 nm) and Ag-
WO3 (before ~275 nm
and after annealing ~
280 nm).

14. February 14-18, Downtown Nashville,
Tennessee, Music City Center
UV-Vis measurement
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2.303 × 𝐴𝑏�
�

15. February 14-18, Downtown Nashville,
Tennessee, Music City Center
Results
Band Gap (eV) Wave length(nm)
WO3 2.9 428
Ag@WO3 2.68 464
Annealed Ag@WO3 2.45 506
Summary of the band gap analysis using UV-vis absorption
 The band gap of WO3 was calculated ~ 2.9 eV which matched
with the literature[7].
 Band gap of Ag-WO3 was calculated (Table) 2.68 eV and 2.45 eV
before and after annealing respectively.
 The band gap tailoring was identified due to the morphology of
CSNH and quantum confinement effect [8]

16. February 14-18, Downtown Nashville,
Tennessee, Music City Center
 Interfaces of Ag-WO3 nano cubes
heterostructures strongly effects the
charge transfer and separation
mechanisms[6], which allows the
lowering of the band gap.
 Subsequently, this tailoring band gap
permits more visible light interaction
with the CSNH than controlled WO3.
 Tuning the band gap features, the
CSNH reflects the promise of this
heterostructures as a photocatalysis
Results
Band gap(Eg)
Conduction Band
Valence Band
Depletionlayer
WO3
Ag
Proposed mechanism for Band gap tailoring

17. February 14-18, Downtown Nashville,
Tennessee, Music City Center

18. February 14-18, Downtown Nashville,
Tennessee, Music City Center
Acknowledgements
 Dr. Ramana Reddy and Dr. Nitin Chopra for their support
 This work was sponsored by the National Science Foundation NSF-
EPSCoR RII award (#24067).
 In addition, presenter thank the Graduate Council Fellowship (GCF) by
the University of Alabama Graduate School.

19. February 14-18, Downtown Nashville,
Tennessee, Music City Center
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