wet? Wet molecular junctions SONS National Center of Competence in Research Nanoscale Science

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1 ational Center of Competence in Research anoscale cience Wet molecular junctions By Christian chönenberger Transport through ingle Molecules Lorentz Center, March 7-12, 2005 wet?

2 liquid-ion gating (T=300 K) conventional back -gating liquid ion gating Electrochemical Tube-FET M. Krüger et al. Appl. Rev. Lett. 78, 1291 (2001). due to large C electrolyte-t E F U g gating = shift of e-chem-pot charge-neutrality E F

ion-sensitivity M. Krüger et al. ew Journal of Physics 5, 138.1-138.

3 ion-sensitivity M. Krüger et al. ew Journal of Physics 5, (2003) application (sensors) with T no T D. Keller,. Ifadir and M. Calame

4 do the same with real molecules real molecules are really tiny! break junctions in liquid for molecular electronics ational Center of Competence in Research anoscale cience L. Grüter, R. Huber, M. T. González, M. Calame & Ch. chönenberger University of Basel and CCR 'anoscale cience

5 break junction technique (MCBJ: mechanically controllable break junction) suspended metallic bridge z 24mm elongation: e= 6thz/L 2 reduction factor: e/z 1/100'000 2 µm microfabricated junctions: UV + e-beam (polished phosphorus-bronze/polyimide/au; -plasma underetched) set-up motorized (large gear reduction)

solvent, aqueous medium) - chemical, photochemical reactions possible, -

6 set-up Liquid cell (250 µl) rod controlled by a stepper motor - molecules in solution (org. solvent, aqueous medium) - chemical, photochemical reactions possible, - electrochemical gating measurement of conductance V bias 1 kω Conductance: G:=I/V I measured current UP: pening (breaking) the junction DW: Closing the junction

high conductance regime G 0 2e 2 /h = (12.9 kω) -1 G/G 0 6 5 4 3 2 1 DM toluene counts (arb.u.) vacuum air H 2 DM octane toluene 0 1 2 3 4 5 0 20 30 40 50 60 z (µm) opening G/G 0 o significant differences between enviroments tunneling regime from open to tunneling regime, i.

7 high conductance regime G 0 2e 2 /h = (12.9 kω) -1 G/G DM toluene counts (arb.u.) vacuum air H 2 DM octane toluene z (µm) opening G/G 0 o significant differences between enviroments tunneling regime from open to tunneling regime, i.e. G << G 0 regime of interest to contact molecules I (A) 10-9 Tunneling: ln(i) = const - Bz 10-7 Junction 83a vacuum V = 0.1 V toluene DM 10-8 air DCM octane z (µm) closing at low G, i.e. in tunneling regime, the solvent matters!

8 molecules ext: molecules H - H H H H H 2 a+ - H DMAAB (bis-acetamidothiol) chbdt (bis-dithiocarbamates) - J. Wessels H H H H H 2 a+ - DMAAcH (bis-acetamidothiol) PBDT (bis-dithiocarbamates) Ac Ac Pfalz et al. / Basel. Martin et al. / Madrid

9 molecules F. Diederich et al. Fuyong Cheng (ETHZ) I H H H Ac Ac Ac Ac molecules F. Diederich et al. Fuyong Cheng (ETHZ) AcH 2 C Zn CH 2 Ac AcH 2 C Zn Zn CH 2 Ac AcH 2 C Zn CH 2 Ac 4 Zn Zn Zn Zn Zn Zn Zn

10 triply fused diporphyrin Meso-meso-linked dimer Monomer Triply fused dimer In THF Eight reversible redox couples. mall HM-LUM gap (~1.2 ev). In CH 2 Cl 2 D. Bonifazi, et al. Angew. Chem. Int. Ed. 2003, 42, CH 2 Cl 2 molecules Ac CH 3 Ac Ac CH 3 Ac TTF1 TTF3 C 5 H 11 C 5 H 11 C 5 H 11 C 5 H 11 Ac CH 3 Ac J. Becher et al. / dense J. Jeppesen / Gopee... TTF2 C 5 H 11 C 5 H 11 UCM-FG-172. Martin, F. Giacalone / Madrid

11 molecules C C C C M. Bryce at al. / Durham

C60 first test molecule literature: C. Joachim, J. K.

74 2102 (1995). H. Park, J. Park, A. K. L. Lim, E. H. Anderson, A.

Champagne, A.. Pasupathy, D. C. Ralph Cond-mat/0409134 A.

K. Donev, P. L. McEuen, D. C. Ralph cience 306 86 (2004). L. H.

ature, 407, 57 (2000) Electromigration technique C 60 lowest

12 C60 first test molecule literature: C. Joachim, J. K. Gimzewski, R. R. chlittler, C. Chavy Phys. Rev. Lett (1995). H. Park, J. Park, A. K. L. Lim, E. H. Anderson, A. P. Alivisatos, P. L. McEuen ature (2000). A. R. Champagne, A.. Pasupathy, D. C. Ralph Cond-mat/ A.. Pasupathy, R. C. Bialczak, J. Martinek, J. E. Grose, L. A. K. Donev, P. L. McEuen, D. C. Ralph cience (2004). L. H. Yu, D. atelson anoletters 4 79 (2004). ature, 407, 57 (2000) Electromigration technique C 60 lowest intrinsic energy mode: 33 mev Molecule-surface binding oscillation: f k 1/ 2π ( ) M 1 2 = hf = 5meV T= 1.5 K

13 functionalized C60 Diederich et al. I Ionic C60 compound without anchor-to-au end group H with a thiol end group Fuyong Cheng, ETHZ with two metylsulfid end groups contacting molecules add molecules in solution apply voltage (~ 0.1 V), open a 3 nm gap in the junction (molecule + end group ~ 1.5 nm) bring the electrodes near, without closing completely Current (µa) DM z (µm) closing counts (arb. units) H DM G/G 0

14 contacting molecules add molecules in solution apply voltage (~ 0.1 V), open a 3 nm gap in the junction (molecule + end group ~ 1.5 nm) bring the electrodes near, without closing completely Current (µa) 1.0 DM z (µm) closing counts (arb. units) H DM G/G 0 solvent dependence H (V=0.2 V) I [µa] In DM C H 3 CH z [µm] 1.0 H 0.8 I (µa) In toluene CH z [µm]

15 peak in addition to plateau V Current [µa] 0.4 tolune only TTF1 in tolune what about a peak? vertical distance [µm] a plateau, which is typical (at least this is what we understand from others) I (µa) nm position series resistor model x R L = const R R = A exp(-xκ) R tot = R L + R R Classical approximation: G x

16 resonant tunneling Γ 1 Γ 2 (d) we define Γ 2 = Γ 2 e κd with d = 0 at the peak, i.e. Γ 2 (peak) = Γ 2 E F ε It then follows that: d Γ? 2 = p 4ε 2 + Γ 2 1 T = 2 4 ε 4Γ1 Γ2 + ( Γ + Γ 1 2 ) 2 There are two limits: a) Γ 1 >> ε and b) Γ 1 << ε resonant tunneling (Breit Wigner) T = 2 4 ε 4Γ1 Γ2 + ( Γ + Γ 1 2 ) 2 G (2e 2 /h)γ 1 /ε 2e 2 Γ 1 h ² Γ 2/ε =2 Γ 2 (d) =Γ 2e κd Γ 2/ε Γ 2 /ε d = r s

17 I (A) calibrate 10-7 Junction 83a vacuum V = 0.1 V toluene DM 10-8 air DCM octane 10-9 we use our old work as reference G/G d[å] 10 0 (a) G/G d[å] z (µm) recall the importance of callibration r (reduction factor) set with respect to solvent alone solvent is set with respect to vacuum G/G (b) d[å] 5 0 G/G d[å] Comparison (DM)

18 Comparison (toluene) what do we learn at this point? ote: all is scale-invariant! G (2e 2 /h)γ 1 /ε 2e 2 h Γ 1 ² Γ 2 /ε = Γ 2/ε Γ 2 /ε Are there bounds, upper and lower ones?

19 finite bias ev b (0.2 V) >> kt 10 G (10-2 2e 2 /h) γ 1 :=Γ 1 /ev b = Breit-Wigner ε/ev b γ 2 :=Γ 2 /ev b Comparison (DM) ε & 0.2V

20 Comparison (toluene) ε & 0.12 V upper bound 10 G (10-2 2e 2 /h) γ 1 :=Γ 1 /ev b =0.02 Breit-Wigner ε/ev b γ 2 :=Γ 2 /ev b

21 Comparison Γ 1 Γ 2 - C 60 C 60 E F LUM ~ 1 ev ε HM ~ 2 ev Comparison G/G H d (Å) Γ 1 = meV

22 electrochem. gating cience 301, 1221 (2003) ; ano Lett. 4, 267 (2004)

24 TTF compounds Jan Becher et al. University of ourthern Denmark Ac CH 3 Ac TTF1 C 44 H C 5H 11 C 5H 11 Acetyl protection group TTF2 C 60 H Deprotection with Tetrabutylammonium hydroxid (TBAH) Ac CH 3 Ac C 5 H 11 C 5 H 11 Conductance of the molecule is expected to change when the TTF group is oxidized

25 test on gating in TTF1 IV curves at different gate voltages: CH 3 CH TTF1 in toluene with MgCl C 5H 11 C 5H 11 C 5H 11 C 5H 11 I (µa) V (V) -0.50V -0.25V 0.0 V 0.5 V 1.0 V 0.75 V 0.25 V I (µa) Adding Fe(Cl 4 ) 3 (Ironpercloride) 0.9 TTF2 in toluene only in toluene 0.6 adding Fe(Cl 4 ) V (V) test on gating in TTF2 Ac CH 3 Ac H 11 C 5 C 5 H 11 8 File:91bliq4, iv20, 21_up.dat, TTF I (µa) TTF2 before adding MgCl 2 TTF2 after adding MgCl V (V)

26 test on gating in FG172 FG172 (0.3 mm) in CH 2 Cl 2 TTF3 with 0.1 M TBAPF 6 in Tol/A (5:1) Gate voltage varied 0.2 File: 104BLIQ2IV13-20_DW I (µa) V (V) 0 V -0.6 V +0.6 V Current (µa) V bias =0.6V Gate voltage (V) acknowledgment Lucia Grüter Laetitia Bernard Roman Huber Jianhui Liao Teresa Gonzalez Michel Calame Tero Heikkilä J. Wessels H. Riehl, E. Lörtscher M. Mayor et al.

Break junctions in liquid for molecular electronics

Break junctions in liquid for molecular electronics L. Grüter, R. Huber,, M. Calame & Ch. chönenberger University of Basel and CCR 'anoscale cience (witzerland) anopain, March 2005, Barcelona, pain Financial