Transcript Document

Quantum Dots in the
Undergraduate Chemistry
Curriculum
Authors:
Karen S. Quaal
Chair of the Department of Chemistry and BiochemistrySiena College
Justin LaRocque, Shazmeen Mamdani, Luke Nally
Chemistry Majors-Siena College
Joshua B. Diamond
Department of Physics-Siena College
Jennifer Z. Gillies and Daniel Landry
Research Scientists
Evident Technologies
Siena College:
Background For Project:
Mid-1990:
NSF Poly-Ed Scholar
•Developed modules for incorporating polymer chemistry topics into
the undergraduate curriculum.
Modules:
•Applicable to small departments that lack the resources (time,
students and/or money) to develop an entire course devoted to
polymer chemistry.
For this project, we used a similar approach as a template for
integrating nanotechnology into the undergraduate curriculum.
Why Nanotechnology?
• Recognized that nanotechnology is a rapidly growing field in
science.
• Capital District-Tech Valley.
• Recognized that there was a need to educate our majors about the
field of nanoscience and nanotechnology.
Why cross-disciplines and cross-academic-industrial?
• Recognized the nature of the field of nanotechnology.
The Plan
Develop two 5-week modules for incorporating aspects of nanotechnology
into the typical undergraduate curriculum.
1. Chemistry Module:
* Offered as a junior-level course
* Integrated Laboratory II (1 credit)
* Laboratory using applications of Inorganic Synthesis,
Physical Chemistry II and Spectroscopy
2. Physics Module:
* Offered as a portion of a Special Topics course for
sophomores-seniors
* Course involved a collaborative effort in which the chemistry
majors synthesized the Quantum Dot samples and the
physics majors measured and analyzed some of their
optical properties
* Effects on electron-hole excitation spectrum
3. Evident Technologies:
* Served as industrial partners in the project
* Provided access to resources
* Internship sites
5 Week Chemistry Module
Week 1: Inorganic Synthesis of semiconductor quantum dots: This
segment focuses on the preparation of colloidal CdSe quantum dots.
This synthesis adapts published procedures to techniques and skills
appropriate for undergraduate students.
Week 2: Purification and Analysis of CdSe quantum dots: This segment
requires solvent extraction and centrifugation techniques to purify the
quantum dots. In addition, students will perform absorption and
fluorescence measurements to characterize the quantum dots.
Week 3: Inorganic Synthesis of ZnSe: Synthesis and comparison of
optical properties between CdSe and ZnSe. Application of Quantum
Mechanical models to results.
Week 4: Synthesis of core/shell semiconductor nanoparticles: Students
will use the quantum dots synthesized in week 1 to produce core/shell
CdSe/ZnS nanoparticles using glovebox techniques.
Week 5:
Measurement and comparison of core/shell dots to core
quantum dots: Students will measure and compare absorption and
fluorescence characteristics of the nanoparticles synthesized in this
module. Quantum yield measurements will be applied to quantum dots.
Quantum Dot Seminar
“What is a Quantum Dot” One hour lecture
presented by Mr. Daniel Landry, Vice
President of Evident Technologies
• Overview of Nanotechnology
• Description of a Quantum Dot
• Explanation of Quantum Confinement of the
exciton
Synthesis Overview
All syntheses were modified from published articles:
1. Cumberland, S; Hanif, K; Javier; Artjay; Khitrov, Gregory; Strouse, Geoffrey, Woessner;
Yun, S. Inorganic Clusters as Single-Source Precursors for Preparation of CdSe,
ZnSe, and CdSe/ZnS Nanomaterials. Chem. Mater. 2002, 14, 1576-1584.
2. Dance, I; Choy, Anna; Scudder, Marcia. Synthesis, Properties and Molecular and Crystal
Structures of (Me4N)4 [E4M10(SPh)16] (E=S, M=Zn, Cd) Molecular
Supertetrahedral Fragments of the Cubic Metal Chalcogenide Lattice. J. Am.Chem.
Soc. 1984, 106, 6285-6295.
3. Hines, Margaret A., and Philippe Guyot-Sionnest. Bright UV-Blue Luminescent Colloidal
ZnSe Nanocrystals. The Journal of Physical Chemistry B, 1998, 102, 19.
Modifications were made for several reasons:
•
•
•
•
To adapt procedures to the junior-level skill set
To adapt procedures for a typical 4-hour laboratory
To require equipment typically available to junior-level laboratory
course
To take into account safety issues
Apparatus
and bubbler
Synthesis of Cadmium Selenide
(Temperature Dependent Growth)
Reference:
Cumberland, S; Hanif, K; Javier; Artjay; Khitrov, Gregory; Strouse,
Geoffrey, Woessner; Yun, S. Inorganic Clusters as Single-Source
Precursors for Preparation of CdSe, ZnSe, and CdSe/ZnS
Nanomaterials. Chem. Mater. 2002, 14, 1576-1584.
Modifications:
• Precursor: Synthesized by instructor
• Temperature: Hexadecylamine was degassed at 60°C (as opposed to
120°C)
• Time: Hexadecylamine was degassed for 30 minutes (as opposed to
an unspecified time)
• Temperature controller: 5°C/minute temperature interval
• Sample aliquots quenched in room temperature toluene
• Bulk sample isolation by precipitation in methanol for x-ray
diffraction for Physics module
Spectral Properties of a Series of
CdSe Quantum Dots
Sample #
Max (nm)
Absorbance
Observed Color
1
453
9.03E-02
Butterscotch
2
473
0.22753
Orange-Yellow
3
501
0.23844
Bright Orange
4
510
0.91365
Light Cherry
5
521
0.22921
Cherry "Koolaid"
6
522
0.83224
Strawberry Jolly
Rancher
7
530
0.46623
Red Candy Apple
8
538
0.55526
Rose Red
9
546
0.69466
Blood Red
Synthesis of Zinc Selenide
(Temperature Dependent Growth)
Reference:
Cumberland, S; Hanif, K; Javier; Artjay; Khitrov, Gregory; Strouse,
Geoffrey, Woessner; Yun, S. Inorganic Clusters as Single-Source
Precursors for Preparation of CdSe, ZnSe, and CdSe/ZnS
Nanomaterials. Chem. Mater. 2002, 14, 1576-1584.
Modifications:
• Precursor: Synthesized by instructor
• Temperature: Hexadecylamine was degassed under vacuum at 60°C
(as opposed to 120°C)
• Time: Hexadecylamine was degassed for 30 minutes (as opposed to
2 hours)
• Temperature controller: 5°/minute temperature interval
• Sample aliquots quenched in room temperature toluene
Synthesis of Zinc Selenide
(Time Dependent Growth)
Reference:
Hines, Margaret A., and Philippe Guyot-Sionnest. Bright UV-Blue
Luminescent
Colloidal ZnSe Nanocrystals. The Journal of Physical Chemistry B, 1998, 102; 19.
Modifications:
• Time: Aliquots were removed at 5 minute time intervals
• Temperature:
-During freeze thaw cycle: H.D.A was heated to melting, placed under
reduced pressure at 65oC, and cooled under vacuum to 40oC
-After freeze and thaw cycles, system placed under vacuum at 60o.
-Under Nitrogen, system heated to 320oC and injection of Zn/Se/TOP
solution was introduced
-Nanoparticles were grown at 270oC
• Temperature Controller: 5o/minute temperature intervals
• Sample Aliquots: quenched in 1 mL toluene at room temperature
Quantum Mechanical
Applications
“Quantum Mechanics”
One Hour lecture given by Dr. Jason Hofstein,
Assistant Professor of Physical ChemistrySiena College
Models Used
• 1-D Particle in a Box
• Particle in a Spherical well using the mass of an electron and the reduced mass
of an electron
• Strong Confinement Approximation
– Gaponenko, S.V. Optical Properties of Semiconductor Nanocrystals. New York:
Cambridge University Press, 1998.
– Yu, W. William, Lianhua Qu, Wenzhuo Guo, Xiaogang Peng. Experimental
Determination of the Extinction Coefficient of CdTe, CdSe, and CdS Nanocrystals.
Chemical Mater. 20 Feb. 2003.
Quantum Mechanical Data
Several quantum mechanical models were used to predict the size of the Q.D. The
best agreement with TEM values was found with the strong confinement model.
E1s1s = Eg + π2 (ab/adot)2 Ry* - 1.786 (ab/adot) Ry* - 0.248 Ry*
Where E1S1S = Energy calculated from UV/VIS spectrum
Eg= bang gap (CdSe= 1.84 eV)
ab= exciton Bohr radius (CdSe= 4.9 nm)
adot= radius of the Q.D
Ry* = Rydberg constant (CdSe= 0.016 eV)
Table 1: CdSe Spectral Data
Temp. (°C) Lambda Max (nm)
128
453
138
473
148
501
158
510
168
521
178
522
188
530
198
538
208
546
218
555
Energy (J)
4.38E-19
4.20E-19
3.97E-19
3.90E-19
3.81E-19
3.81E-19
3.75E-19
3.69E-19
3.64E-19
3.58E-19
radius (nm)
1.97
2.11
2.33
2.41
2.51
2.52
2.61
2.70
2.79
2.91
Synthesis of ZnS Shell on CdSe Core
Reference:
Cumberland, S; Hanif, K; Javier; Artjay; Khitrov, Gregory; Strouse, Geoffrey, Woessner;
Yun, S. Inorganic Clusters as Single-Source Precursors for Preparation of CdSe, ZnSe,
and CdSe/ZnS Nanomaterials. Chem. Mater. 2002, 14, 1576-1584.
Modification:
• Precursor: Synthesized by instructor
• Time: Aliquots were removed after 30 minute time intervals
• Temperature:
TOPO was degassed at 120oC.
Solution was cooled to 70oC while under vacuum.
Solution was heated to 150oC while under nitrogen. Solution containing
TMS, dimethylzinc and TOP was added drop wise.
Solution was heated to 170oC and allowed to sit for 1 hour.
Solution was heated to 190oC and allowed to sit for 30 minutes.
•Temperature Controller: 5°C/minute temperature intervals
•Sample Aliquots were quenched in 1 mL toluene at room temperature
Fluorescence Spectra
Fluorescence Spectra for CdSe core nanoparticle (left, max =
553 nm) and CdSe/ZnS nanoparticle (right, max = 557 nm)
Quantum Yield
Calculation of Quantum Yield:
Quantum Yield dot= QY dye*Absdye * (Idot)
Absdot * (Idye)
Quantum Yield of CdSe (core):
QY dot (CdSe)= (0.95) * 0.0034 * (7.06*106 nm*count/sec)
0.036 * (5.26*107 nm*count/sec)
QY dot(CdSe) = 0.012
Quantum Yield of CdSe/ZnS (core/shell):
QY dot (CdSe/ZnS)= (0.95) * 0.0034 * (1.81*107 nm*count/sec)
0.040 * (5.26*107 nm*count/sec)
QY dot(CdSe/ZnS)= 0.028
QY has increased by a factor of 2.3 for CdSe/ZnS
compared to CdSe.
Atomic Absorption
Determination of Number of ZnS Shells – Atomic Absorption method:
Information needed:
Diameter of CdSe (nm)
# units of CdSe across diameter
# units of CdSe/dot
Density of ZnS (4.1x10-21 g/nm3)
Single ZnS shell thickness (0.31 nm)
Equations:
1) VTOTAL = (4/3) (dTOTAL/2)3
2) VTOTAL = VCORE + VSHELL
3) dTOTAL = d1 +d2 + dCORE
4) (mg Cd divided by mg Zn) = (mg CdSe/dot divided by mg ZnS/dot)
Determination of Number of ZnS Shells - UV method
Determination of concentration of CdSe using UV spectroscopy
Determination of ZnS using constant mass
Posters
“How Big is a Quantum Dot?: Quantum Mechanical Models for
Cadmium Selenide and Zinc Selenide Nanoparticles”-Luke Nally
1.
2. “Synthesis and Optical Properties of Amine-Capped Cadmium Selenide
Nanoparticles” -Kimberly Renzi
3. “Synthesis of a Zinc Sulfide Shell on Cadmium Selenide Nanocrystals”Elizabeth Quaal
4. “The Effect of Zinc Sulfide Shell Formation on the Fluorescence
Efficiency of Cadmium Selenide Nanoparticles” -Shazmeen Mamdani
5. “Synthesis and Analysis of Quantum Dots”-Karen S. Quaal1, Justin
LaRocque1, Shazmeen Mamdani1, Luke Nally1, Jennifer Z. Gillies2 and
Daniel Landry2, (1) Siena College, Loudonville, NY, (2) Evident
Technologies
Acknowledgements
NSF grant DMR-0303992
Nanotechnology Undergraduate Education (NUE)
program.
Siena College.
Evident Technologies.
Research Students: Justin LaRocque, Shazmeen
Mamdani, and Luke Nally
http://www.siena.edu/chemistry/quaal.asp