Quantum Dots (DQ) Imaging for Thermal flow studies

Transcription

1 AerE 545 class notes #43 Quantum Dots (DQ) Imaging for Thermal flow studies Hui Hu Department of Aerospace Engineering, Iowa State University Ames, Iowa 511, U.S.A

2 Quantum Dots Quantum dots are chemically synthesized semiconductor nanoparticles that can exhibit unique quantum confinement behavior. Size dependent emission: Smaller particles emit high-energy (shorter wavelength) radiation Larger particles emit low-energy (longer wavelength) radiation. Adjustable hydrophilic or hydrophobic properties: The surface layer can be designed to be either hydrophilic or hydrophobic allowing the nanoparticles to be solubilized in a variety of liquids (i.e. polar and nonpolar). The structure of a (CdSe)ZnS quantum dot 2.3nm 5.5nm

3 Introduction The propose of the present study is to explore the possibility of Quantum dots (QDs)) for thermofluid diagnostics. Compared to commonly-used fluorescent dyes such as Fluorescein and Rhodamine B, the photophysical properties of (CdSe)ZnS( QDs will be investigated: Absorption and emission spectra. Stability against photobleaching under different laser excitations. Temperature sensitivity under different laser excitations. The applications of QDs for thermofluid diagnostics Individual QDs as particle tracers for velocimetry in micro flows: Single Quantum Dot (QD) Velocimetry by Pouya et al. Experiments in Fluids, 26. QDs as fluorescent tracers: Flow visualization and concentration c measurements in a pulsed jet flow. Temperature distribution mapping in a stratified flow.

4 Absorption and Emission Spectra of (CdSe)ZnS Quantum Dots Absorption spectrum: wide range of absorption various laser can be used as excitation source Emission spectrum: emission peak wavelength is adjustable by controlling the size of QDs emission spectrum is symmetrical to the emission peak emission concentrates near emission peak with FWHM only 3~4 nmn Quantum Dots QD-1 QD-2 QD-3 QD-4 Emission Peak 57 nm 593 nm 63 nm 65 nm Emission Full-Width Half-Maximum 33 nm 34 nm 36 nm 4 nm absorption (relative intensity) absorption QD-1 emission QD-2 QD wavelength (nm) QD emission (relative intensity)

5 QD imaging for flow velocity measurements Image of 6 nm (CdSe)ZnS( quantum dots in aqueous solution within 1 nm of the surface. Field of view is 153 lm 93 lm Taken from Single quantum dot (QD) imaging of fluid flow near surfaces By Shahram Pouya Æ Manoochehr Koochesfahani Preston Snee, Moungi Bawendi, Daniel Nocera, Experiments in Fluids (25) 39: Superposition of four consecutive frames showing the movement of two single QDs appearing in three frames. Mean flow is from left to right. Field of view is 37 lm 37 lm

6 Photophysical stability against photobleaching Same volume (2ml) of QD, Fluorescein and Rhodamine B solutions were prepared. Concentration of the Fluorescein and Rhodamine B aqueous solution is M. The solvent of QD is Hexane. The absolute molar concentration of QD is unknown, but it has the e same initial fluorescence emission intensity as the Rohdamine B M solution. mirror optics laser beam CCD camera stirring rod excitation laser test solution digital delay generator (SRS DG535) host computer Experimental setup for the photoluminescence p stability test

7 Photoluminescence stability against photobleaching (Comparison of QD with Fluorescein and Rhodamine B) excitation laser source: pulsed excimer UV laser (38nm ) Normalized fluorescence intensity QD 4 - laser energy: 2mJ/pulse QD 4 - laser enrgy: 15mJ/pulse Rhodamine B - laser energy: 2mJ/pulse Rhodamine B - laser energy: 15mJ/pulse Rhodamine B - laser energy 1mJ/ulse Fluorescein - laser energy: 2mJ/pulse Fluorescein - laser energy 15mJ/pulse Fluorescein - laser energy 1mJ/pulse Number of laser pulse Normalized Fluorescence intensity QD 4 (laser power 2mJ/pulse) QD 4 (laser power 15mJ/pluse) Flourescein (laser power 2mJ/pulse) Fluorescein (laser power 15mJ/pulse) Fluorescein ( laser pulser 1mJ/pulse) Rhodamine B( laser power 2mJ/pluse) Rhodamine B (Laser power 15mJ/pulse) Rhodamine B (laser Power 1mJ/pulse) Total enegy input from the exicitation laser (J)

8 Photoluminescence stability against photobleaching (Comparison of QD with Fluorescein and Rhodamine B) excitation laser source: Argon-ion laser (514.5 nm ) Normalized fluorescence intensity QD-4 (laser power 1.5w) Rhodamine B (laser power 1.w) Rhodamine B (laser power 1.5w) Flourescein (laser power 1.5 W) Flourescein (laser power 1. W) Normalized fluorescence intensity QD-4 (laser power 1.5w) Rhodamine B (laser power 1.w) Rhodamine B (laser power 1.5w) Flourescein (laser power 1.5 W) Flourescein (laser power 1. W) Excitation time (second) Total input energy from the excitation laser (J)

9 Temperature Sensitivity Test mirror RTD probe laser sheet optics 12-bit gated intensified CCD camera (DiCam-Pro) stirring rod Excitation laser QD solution digital delay generator (SRS DG535) heating plate host computer Experimental setup for temperature sensitivity test

10 Temperature sensitive of QD, Fluorescein and Rhodamine B Normalized fluorescence intensity QD Rhodamine B Fluorescein QD-3 (514nm) QD-3 (488nm) QD-3 (38nm) Normalized fluorescence intensity Rhodamine B (514nm) Rhodamine B (488nm) Rhodamine B (38nm) Normalized fluorescence intensity Fluorescein (514nm) Fluorescein (488nm) Fluorescein (38nm) Temperature ( o C) Temperature ( o C) Temperature ( o C) 38nm Excimer laser 488nm Argon-ion laser 514nm Argon-ion laser QD % per C (5 C ~ 65 C) -4% per C (5 C ~ 65 C) -1.5% per C (5 C ~ 65 C) Rhodamine B -1.57% per C (5 C ~ 65 C) -% per C (5 C ~ 65 C) Kim & Khim (21) % per C (15 C ~ 4 C) -1.52% per C (5 C ~ 65 C) Coppeta & Roger(1998) % per C (2 C ~ 6 C) Fluorescein -.45% per C (5 C ~ 65 C) -.25% per C (5 C ~ 65 C) Coppeta & Roger(1998) -.16 % per C (2 C ~ 6 C) +2.25% per C (5 C ~ 65 C) Coppeta & Roger(1998) % per C (2 C ~ 6 C)

11 Applications of Quantum Dots for Thermofluid Diagnostics: (Flow visualization and quantitative concentration measurements) burette QD-3 solution mirror optics Laser sheet CCD Camera Argon-ion Laser ( wavelength = 514.4nm) Experimental setup host computer

12 Application Quantum Dots for Thermofluid Diagnostics: (Flow visualization and quantitative concentration measurements) concentration. 1. a. t = t b. t = t +.2 s c. t = t +.4 s

13 Application Quantum Dots for Thermofluid Diagnostics (Temperature measurements in a Stratified Flow) 5mm QD-3 3 solution (temperature is 23 o C at t = s) mirror optics Ambient temperature amb = 23 o C) (T amb Laser sheet Y test cell (made from glass) 1mm CCD Camera X Argon-ion Laser ( wavelength = 514.4nm) Chilled plate (T( surface =. O C) Coolant flow in Heat exchanger Coolant flow out host computer

14 Application Quantum Dots for Thermofluid Diagnostics (Temperature measurements in a Stratified Flow) Ymm Temperature ( o C) Ymm Temperature ( o C) Ymm Temperature ( o C) Xmm Xmm 1 minute later 5 minutes later 1 minutes later Xmm Ymm Temperature ( o C) Ymm Temperature ( o C) Ymm Temperature ( o C) Xmm Copyright by Dr. Hui Xmm Xmm 15 minutes later Iowa State University. All Rights Reserved! 2 minutes later 3 minutes later

15 Application Quantum Dots for Thermofluid Diagnostics (Temperature profiles in the center of the test cell) 65 Ymm Temperature ( o C) Xmm Distance away from the bottom plate (mm) t = 1 minute t = 5 minutes t = 1 minutes t = 15 minutes t = 2 minutes t = 25 minutes t = 3 minutes Temperature ( o C) Temperature profiles along the vertical line in the center of the test cell.