what happens if we make materials smaller?

Transcription

1 what happens if we make materials smaller? IAP VI/10 ummer chool 2007 Couvin Prof. ns

2 outline Introduction making materials smaller? ynthesis how do you make nanomaterials? Properties why would you make nanomaterials? Processing how do you handle nanomaterials?

3 introduction an example: colloidal gold

4 introduction an example: colloidal Cde

5 1 m 1 mm 1 µev 1 µm 1 ev 1 nm the nanoscale X UV IR micro electron energy size foton energy 1 K 1000 K 1 mev 1 ev 1 mev 1 kev introduction temperature

6 introduction the nanoscale do more with less Moore s law ENIAC, Pentium IV, 2002

7 introduction the nanoscale do things differently with less temperature electron energy size 1 m foton energy quantum nature of matter turns up at room temperature 1 K 1000 K 1 mm 1 nm X UV IR micro 1 mev 1 µev 1 µm 1 ev 1 mev 1 ev 1 kev discrete nature of quantities turns up at room temperature charge, conductance, where unique phenomena enable novel applications

8 introduction the nanoscale do things differently with less Confining electrons in a particle Charging a spherical particle a ε = 1s 2 π h 2 2mea 2 (ev) a e ε C = (ev) 8πεε0 a E (ev) ε 1p E (ev) ε 1s a (nm) a (nm)

9 introduction building blocks top down approach trength: Weakness: Highly complicated structures possible Does not scale down to the nanometer range

10 introduction building blocks bottom-up approach atoms & molecules nanoscale building blocks nanostructures trength: Weakness: Nanometer range easily accessible How to make complex nanostructures?

11 introduction quantum dots: top down vs. bottom up metal electrode quantum dots are created by electrostatic potential barriers GaAs AlGaAs Highly doped GaAs highly complex architectures possible dimensions: 100 nm and more temperature of operation: 4 K or less

12 introduction quantum dots: top down vs. bottom up Pbe Qdot (TEM) quantum dots are synthesized by chemical means dimensions: 1-20 nm temperature of operation: 293 K and more making complex architectures not straightforward

13 synthesis colloidal nanocrystals colloidal Pbe quantum dots dispersed in (liquid) solution need for stabilization: ligands monodisperse polydisperse 60 nm

14 colloidal Qdots properties Pbe quantum dots the absorption spectrum InP quantum dots

15 colloidal Qdots properties quantum confinement ψ k k r = e i uk (r) ψ ( r ) = 0 for the x-direction of a cube: ψ k = sin( k x x ) u x k x ( r) π k x = n Na π a 0 π a

16 colloidal Qdots properties quantum confinement Confining electrons in a particle a ε = 1s 2 π h 2 2mea 2 (ev) E (ev) ε 1p 0.2 ε 1s a (nm)

17 colloidal Qdots properties quantum confinement ψ k k r = e i uk (r) strong confinement effects: semiconductors low effective mass high dielectric constant π a 0 π a

18 colloidal Qdots properties quantum confinement ψ k k r = e i uk (r) strong confinement effects: semiconductors low effective mass high dielectric constant π a 0 π a

19 colloidal Qdots properties quantum confinement ψ k k r = e i uk (r) strong confinement effects: semiconductors low effective mass high dielectric constant π a 0 π a

20 colloidal Qdots properties quantum confinement ψ k k r = e i uk (r) strong confinement effects: semiconductors low effective mass high dielectric constant π a 0 π a

21 colloidal Qdots properties quantum confinement ψ k k r = e i uk (r) strong confinement effects: semiconductors low effective mass high dielectric constant π a 0 π a

22 colloidal Qdots properties quantum confinement example: Q-Pbe bulk 4800 nm strong confinement effects: semiconductors low effective mass high dielectric constant

23 colloidal Qdots properties colloidal quantum dot luminescence CdTe in heptane appropriate ligands passivate surface traps highly efficient luminescence Absorbance (a.u.) Wavelength (nm) nm (a.u.)

24 metal nanocrystals properties the absorption spectrum colloidal gold colloidal silver

25 metal nanocrystals properties the plasmon resonance ionic lattice free electron cloud E x

26 metal nanocrystals properties the plasmon resonance ionic lattice free electron cloud

27 metal nanocrystals properties the plasmon resonance ionic lattice free electron cloud E x

28 metal nanocrystals properties the plasmon resonance ionic lattice free electron cloud m e 2 d x = 2 dt ee = 2 e nx ε 0 ω p, bulk = 2 e n m ε e 0 ε(, ) = ω p bulk 0

29 metal nanocrystals properties what about a small sphere? E

30 metal nanocrystals properties what about a small sphere?

31 metal nanocrystals properties what about a small sphere? m e 2 d x = 2 dt ee = 2 e nx 3ε 0 ω ω = p, sphere p, bulk 3 E ε( ω 2 + p, sphere ε m ) = 0

32 metal nanocrystals properties examples

33 colloidal Qdots processing processing individual quantum dots self assembly G = H T thiols on gold glue Q-dots to functionalized surface H H H H H functionalize Q-dots H H H H H 4.97 A 62º-64º H H H H H H H

34 colloidal Qdots processing processing quantum dot architectures self assembly G = H T thiols on gold γ Fe 2 O 3 + Pbe 62º-64º 4.97 A

35 colloidal Qdots processing processing quantum dot architectures Langmuir-Blodgett deposition

36 colloidal Qdots processing processing quantum dot architectures Langmuir-Blodgett deposition combined with photolithography

37 and why is it of interest for photonics? IAP VI/10 ummer chool 2007 Couvin Prof. ns

38 colloidal Qdots applications light amplification with colloidal Qdots τ IR probe Ti/saffier pulse detector

39 colloidal Qdots applications light amplification with colloidal Qdots α 0 α

40 colloidal Qdots applications light amplification with colloidal Qdots

41 colloidal Qdots applications exciton storage Quantum dot heterostructures Type I vs. type II Cde Cd heterorods Cde core Cd rod highly polarizable excited state

42 colloidal Qdots applications exciton storage Cde Cd heterorods Radiative decay Under an E-field E e e e Cde Cd Cde Cd Cde Cd + h + h + h delocalized electron localized hole determined by electron/hole overlap strongly affects electron and hole wavefunction

43 colloidal Qdots applications exciton storage Cde Cd heterorods Radiative decay affected by E-fields Under an E-field E e e Cde Cd Cde Cd + h + h delocalized electron localized hole strongly affects electron and hole wavefunction

44 colloidal Qdots applications exciton storage Cde Cd heterorods but the exciton is not lost! Under an E-field E e e Cde Cd Cde Cd + h + h delocalized electron localized hole strongly affects electron and hole wavefunction

45 colloidal Qdots applications exciton storage

46 metal nanocrystal applications sensing ε( ω p, ) = 2ε sphere m local environment determines absorption spectrum

47 metal nanocrystal applications sensing

48 metal nanocrystal applications sensing biomolecule (fibrinogen) absorption ligand-receptor binding

49 colloidal quantum dots epilogue ynthesis nearly perfect Properties exciting Processing flexible, application driven, reliable? Applications how do we get beyond proof of principle?

50 colloidal Qdots properties the nanochemist in action NMR spectroscopy of Q-Pbe suspensions oleic acid surface density: 3.9 nm -2

51 colloidal Qdots properties the nanochemist in action ICP-M analysis of digested Q-Pbe oleic acid surface density: 3.9 nm -2 excess Pb surface density: 3.8 nm -2

52 colloidal Qdots properties the nanochemist in action oleic acid surface density: 3.9 nm -2 excess Pb surface density: 3.8 nm -2

53 colloidal Qdots applications putting electrons on colloidal Q-dots TM tip Au di /dv Γin Γout V I e µ source e µ drain I µ

54 colloidal Qdots applications putting electrons on colloidal Q-dots Q-Cde on Au(111) 1,4-dithiane µ (ev) f s' d p s -1.4 science: spectrum of dot energy levels technology: bias dependent conductivity di/d µ (na/ev)

55 colloidal Qdots applications putting electrons on colloidal Q-dots Γin << Γ out Γin >> Γ out Q-Cde on Au(111) 1.5 s 2 s' s 2 d µ (ev) 1.0 s 2 p p s 2 s 2J s-p J s-s 0.5 science: electrons tunnel one at the time technology: ultimate resolution in current measurement di/d µ (na/ev)

56 colloidal Qdots applications a single electron transistor paper won t blush but in practice

57 colloidal Qdots applications a single electron transistor but in practice