Quantum Dots in the Undergraduate Chemistry Curriculum

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Quantum Dots in the Undergraduate Chemistry
Curriculum
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• Authors
• Karen S. Quaal
• Chair of the Department of Chemistry and
  Biochemistry- Siena 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

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• 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.

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• 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-industria
  l?
• Recognized the nature of the field of
  nanotechnology.

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The Plan
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• 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

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5 Week Chemistry Module
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• 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.

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Quantum Dot Seminar
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• 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

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Synthesis Overview
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• 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 (ES, MZn,
  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

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Apparatus
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and bubbler
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Synthesis of Cadmium Selenide(Temperature
Dependent Growth)
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• 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 60C
  (as opposed to 120C)
• Time Hexadecylamine was degassed for 30 minutes
  (as opposed to an unspecified time)
• Temperature controller 5C/minute temperature
  interval
• Sample aliquots quenched in room temperature
  toluene
• Bulk sample isolation by precipitation in
  methanol for x-ray diffraction for Physics module

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Spectral Properties of a Series of CdSe Quantum
Dots
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Synthesis of Zinc Selenide (Temperature Dependent
Growth)
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• 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 60C (as opposed to 120C)
• 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

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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

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Quantum Mechanical Applications
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• Quantum Mechanics
• One Hour lecture given by Dr. Jason Hofstein,
  Assistant Professor of Physical Chemistry-Siena
  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.

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Quantum Mechanical Data
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• 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 p2 (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

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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 5C/minute temperature
  intervals
• Sample Aliquots were quenched in 1 mL toluene at
  room temperature

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Fluorescence Spectra
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Fluorescence Spectra for CdSe core nanoparticle
(left, ?max 553 nm) and CdSe/ZnS nanoparticle
(right, ?max 557 nm)
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Quantum Yield
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• Calculation of Quantum Yield
• Quantum Yield dot QY dyeAbsdye (Idot)
• Absdot (Idye)
• Quantum Yield of CdSe (core)
• QY dot (CdSe) (0.95) 0.0034 (7.06106
  nmcount/sec)
• 0.036 (5.26107
  nmcount/sec)
• QY dot(CdSe) 0.012
• Quantum Yield of CdSe/ZnS (core/shell)
• QY dot (CdSe/ZnS) (0.95) 0.0034 (1.81107
  nmcount/sec)
• 0.040 (5.26107 nmcount/sec)
• QY dot(CdSe/ZnS) 0.028
• QY has increased by a factor of 2.3 for CdSe/ZnS
  compared to CdSe.

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Atomic Absorption
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• 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)
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• 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

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Posters
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• 1. How Big is a Quantum Dot? Quantum Mechanical
  Models for Cadmium Selenide and Zinc Selenide
  Nanoparticles-Luke Nally
• 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

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Acknowledgements
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• 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