Quantum Dots in the Undergraduate Chemistry

Curriculum Authors:

Karen S. QuaalChair of the Department of Chemistry and

Biochemistry- Siena CollegeJustin LaRocque, Shazmeen Mamdani, Luke Nally

Chemistry Majors-Siena College Joshua B. Diamond

Department of Physics-Siena College Jennifer Z. Gillies and Daniel Landry

Research ScientistsEvident Technologies

Siena College:

Background For Project: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 Spectroscopy2. 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 spectrum3. 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 OverviewAll 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

DotsSample # Max (nm) Absorbanc

eObserved 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 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.

Quantum Mechanical DataSeveral 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 DataTemp. (°C)

128138148158168178188198208218

Lambda Max (nm)453473501510521522530538546555

Energy (J)4.38E-194.20E-193.97E-193.90E-193.81E-193.81E-193.75E-193.69E-193.64E-193.58E-19

radius (nm)1.972.112.332.412.512.522.612.702.792.91

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/dotDensity 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 + dCORE4) (mg Cd divided by mg Zn) = (mg CdSe/dot divided by mg ZnS/dot)

Determination of Number of ZnS Shells - UV methodDetermination of concentration of CdSe using UV spectroscopyDetermination of ZnS using constant mass

Posters1. “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

AcknowledgementsNSF 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