ajinkya thesis defense
TRANSCRIPT
Spray Pyrolysis synthesis of Mn doped ZnS Nanoparticles
Ajinkya DigheM. S. Thesis Defense
Department of Chemical and Biological Engineering
Advisor: Prof. Mark T. SwihartCommittee Member: Prof. Marina
Tsianou
Outline Introduction
Semiconductor nanoparticles
Quantum confinement
Surface defects and surface to volume ratio
Mn doped ZnS
Spray pyrolysis
Mechanism of particle formation
Materials and experimental parameters
Results and Discussion
X-Ray diffraction(XRD)
Photoluminescence
Transmission Electron Microscopy
Energy dispersive X-Ray (EDX)Analysis
Conclusion
Semiconductor nanoparticles“0” D structures with scales in the nanometer range are
called Nanoparticles.
Interest in nanoparticles:
Drastic change in optical and electronic properties w.r.t. bulk
materials
Shift to higher band-gap energy.
Changes are due to
Quantum confinement effects,
High surface to volume ratio of atoms
Surface defectsAlivisatos, A.P., Semiconductor clusters, nanocrystals, and quantum dots. Science, 1996. 271(5215): P.933-937
Quantum confinementThe restricted movement of the electron in
certain permissible energy states is termed
as quantum confinement.
Surface to volume ratio and surface defects
Size (nm) Atoms Percentage of atoms at surface
10 3 × 104 20
4 4 × 103 40
2 2.5 × 102 80
1 30 >90
• Imperfect
surfaces posses
bonds and
defects.
• These act as
traps for
electrons and
holes
•Bleaches the
exciton
absorption
Hu, H.; Zhang, W., Synthesis and properties of transition metals and rare-earth metals doped ZnS nanoparticles. Optical Materials 2006, 28 (5), 536-550.
Electron Wave function
Hole Wave
function
Defectsstates
Defectsstates
ExcitationBlue
Emission
Orange
Emission
Mn d-states
Mn d-states
Radiation Less Decay
Conduction Band
Valence Band
Activated
Mn2+ activated ZnS
Doped
ZnS:Mn
= Zn2+
= Mn 2+
= S2-
Mn doped ZnS nanoparticles
• ZnS has wide band gap of 3.72-3.77 eV
• Important semiconductor in the near-UV region with
applications in electronics and as biological sensors
• Electroluminescent material with applications in flat
panel displays.
• 18% increase in Photoluminescence(PL) efficiency.
• PL lifetime shortening by about 5 orders due to
quick relaxation of the electron.Hu, H.; Zhang, W., Synthesis and properties of transition metals and rare-earth metals doped ZnS nanoparticles. Optical Materials 2006, 28 (5), 536-550.
Schematic showing the Mn2+ and Zn2+ atoms tetrahedrally coordinated with the S atoms in doped form.Energy Dissipation pathways in Mn doped ZnS
nanoparticles
Spray Pyrolysis
3-zone tube furnaceCold water
Cold waterDiffusion
Dryer
Atomizer
Precursor solution
Nitrogen
Flowmeter
Collection Filter
Pump
To hood
Schematic Drawing of the reactor system for the synthesis of Mn doped ZnS nanoparticles by spray pyrolysis.
Materials
Zinc diethyl dithiocarbamate
Dimanganese decacarbonyl
Manganese ethylene
bis(dithiocarbamate)
Tricarbonylcyclopentadienyl manganese
Mn acetate
Experimental parametersToluene was used as a primary solvent
Pyridine was used to increase the solubility of the
Mn ethylene bis(dithiocarbamate)
Dimethyl formamide(DMF) was used to dissolve Mn
acetate.
Temperature of the furnace: 500 oC to 800 oC
Conc. of the Mn precursor: 5% of the conc. of
Zn precursor
Zn Precursor conc. : 0.005 – 0.01 mol/ L
Capping leads to homogeneous dispersion of
the particles in the solvent
To study the effect of capping, various
capping agents were tested.
Trioctylphosphine oxide(TOPO)
Dodecanethiol and
Oleylamine
Results and DiscussionYield and production:
The yield of the particles as compared to the
amount of precursor is low.
~ 0.27% of the theoretical yield
Possible reasons for low yield:
Deposition of films via chemical vapor deposition
Deposition of particles via thermophoresis and
diffusion on the walls of the furnace.
Modified process to increase the yield
Particles were collected in solution phase
Recovered the particles using reverse
solubility and centrifugation
90% of the theoretical yield
However, particles show organic
contamination
V-8
3-zone tube furnaceCold water
Cold waterDiffusion
Dryer
Atomizer
Precursor solution
Nitrogen
Flowmeter
Collection Filter
Pump
To Hood
Liquid Nitrogen Bath
Cold Trap
XRD studies of structure
20 25 30 35 40 45 50 55 60
2θ (degrees)
Inte
nsi
ty
XRD result for the particles produced using different Mn precursors at 700 °C
111
220
311
101: ZnO
Mn acetate
Mn2(CO)5
C5H5Mn(CO)3
Mn ethylene bis(dithiocarbamate)
Photoluminescence
Intensity of emission varies considerably
depending on the Mn precursor.
Large quantity of ZnO present in the sample.
Conclusion: Mn has not substituted the Zn in
the crystal lattice 350 400 450 500 550 600
0
100
200
300
400
500
600
700
800
900
1000
Wavelength
Inte
nsi
ty
Photoluminescence spectra for particles produced from different Mn precursors
ZnO
Surface defects: ZnS
Zn vacancies: ZnS
Mn acetate
Mn2(CO)5
C5H5Mn(CO)3
Mn ethylene bis(dithiocarbamate)
PL spectra showing the effect of Mn precursor concentration
Mn precursor: C5H5Mn(CO)5
Mn conc. : 1% to 5% atomic.
350 400 450 500 550 6000
100
200
300
400
500
600
700
800
900
1000
Wavelength
Intensity
1.0% Mn
2.5 % Mn
5.o% Mn
Effect of capping agent on the PL spectra
Mn precursor: Mn ethylene
bis(dithiocarbamate)
400 450 500 550 600 6500
50
100
150
200
250
300
Wavelength
Intensity
Oleylamine
Trioctylphosphine oxideDodecanethiol
Mn ethylene bis(dithiocarbamate)
TEM analysis of size and morphology
Crystalline NP are prepared as seen from the
lattice fringes.
Size of the particles: 2 to 5 nm.
Particles are irregular in shape and not
perfect spheres.
EDX studies of composition3 types of Mn microstructures could be
formed
Mn atoms substitutionally occupying Zn sites
Mn clusters and
MnS and Mn oxides.
No Mn substitution- as there is no peak for
Mn in the PL spectra.
XRD result does not give any peak for MnS.
Element Atomic%
O K 33.67
S K 29.03
Mn K 1.43
Zn K 32.75
Element Atomic%
O K 29.65
S K 34.72
Mn K 7.43
Zn K 26.38
Zinc diethyl dithiocarbamate and Mn ethylene bis(dithiocarbamate)
Zinc diethyl dithiocarbamate and
tricarbonylcyclopentadienyl Mn
Form of Mn presentMn ethylene bis(dithiocarbamate)
N2 (99.8% pure) acts a source of O2
MnS formed reacts with O2 to give MnO
MnS + 3/2 O2 MnO +
SO2
ΔHrxn = -469.2 KJ mol-1
Decomposition of C5H5Mn-(CO)3 and (CO)5Mn-
Mn(CO)5 give Mn
Mechanism of Mn precursor decomposition
Mn ethylene bis(dithiocarbamate) and Zn diethyl
dithiocarbamate
Scheme for the decomposition of Zn Precursor
Zn(S2CN(C2H5) 2) 2 ZnS + C2H5NCS + (C2H5)
2NH +
CS2 + C2H4
A similar decomposition mechanism for the Mn
precursor gives MnS
Different chemical reactivities.Thermogravimetric Analysis (TGA) of Manganese ethylene bis(dithiocarbamate)
Thermogravimetric Analysis (TGA) of Zinc diethyl dithiocarbamate
Zinc diethyl dithiocarbamate and tricarbonylcyclopentadienyl manganese
C5H5Mn C2H2+MnC
• Bond dissociation energy
for the Mn-CO bond: 230 KJ
mol-1
•Deposition of Mn heavily
contaminated with carbon
First bond to break
Russell, D. K.; Davidson, I. M. T.; Ellis, A. M.; Mills, G. P.; Pennington, M.; Povey, I. M.; Raynor, J. B.; Saydam, S.; Workman, A. D., Mechanisms of pyrolysis of tricarbonylcyclopentadienyl manganese and tricarbonyl(methylcyclopentadienyl) manganese. Organometallics 1995, 14 (8), 3717-3723.
• BDE for the (CO) 5Mn-Mn(CO)5 bond is 185 KJ mol-1
• BDE for the Mn-CO bond can be assumed to be 230
KJ mol-1
Zinc diethyl dithiocarbamate and dimanganese decacarbonyl
2 Mn + 10 CO
ConclusionMn is present on the surface of the particles or
present as other compounds but not in
incorporated form as is confirmed by the PL
spectra.
Mn precursor decompose before the decomposition
of the ZnS precursor leading to non-incorporation.
Crystalline nanoparticles were produced without
Mn incorporation.
AcknowledgementsI would like to thank my major advisor, Dr. Swihart, for his guidance,
encouragement, suggestions and patience throughout my
graduate study at UB
I also owe my thanks to Dr. Tsianou for being on my committee and
her suggestions and her constant support and enquiry about the
project.
I would also like to thank to Sha Liu for her great help to get me
started on the project and the numerous meaningful discussions.
I would like to also thank my other group members
Folarin Erogbogbo, William Scharmach, (Ashley) Ching-wen
Chang, (Roger) Chen-An Tien, Nitin and Xin Liu for their help and
friendship.