MPI Stuttgart Max-Planck-Institut fuer Festkoerperforschung Stuttgart, Germany R. Sordan, K. Balasubramanian, M. Burghard WP2(A): Single fullerene transistor assisted single spin detection

MPI Stuttgart Method for contacting the molecules Ultra-small sandwich junctions in crossed-wire geometry Schematic device structure: advantage: ferromagnetic metals can be used as contact(s) disadvantages: cross section of junction: ~40 x 40nm 2  dilution of molecules shielding of electric field (back gate) bottom top How to attach the molecules?

MPI Stuttgart Molecule deposition onto bottom nanowire Langmuir-Blodgett (LB) monolayers H2OH2O H2OH2O compression C60 in toluene transfer onto substrate area per C60: ~1nm 2 required area on LB trough: ~100cm 2 ~10 16 molecules (~10µg)

MPI Stuttgart LB monolayers of C60 Horizontally deposited onto Si/SiO 2 wafer low surface pressure high surface pressure 14µm

MPI Stuttgart Molecule deposition onto bottom nanowire Electrochemical Method approach no.1: Pure C60 Pt pseudo- reference electrode Pt counter electrode probe needle electrolyte solution deposition conditions: -0.9V vs. Pt sec + N(CH 2 CH 2 CH 2 CH 3 ) 4 BF 4 - CH 2 Cl 2 TBA-BF 4 :

MPI Stuttgart Electrodeposited C60 molecules major problem: low adhesion of top wire (6 samples tested) continuous films obtained for thickness > 2nm electropolymerisation(?) Height increase ~ 2nm

MPI Stuttgart Electrodeposition of molecules onto bottom nanowire approach no.2: C60 in matrix SH matrix = benzene-1,3-dithiol SS S SS oxidation ( -H +, -e - ) conditions: +0.7V vs. Pt in toluene/acetonitrile ( sec); C60 : matrix = 1 : 10. continuous films for thickness >4nm film structure and extent of C60 inclusion to be determined

MPI Stuttgart electrodeposition Fabrication of crossed-wire junctions 2nd e-beam lithography Bottom wire defined by e-beam lithography, Ti/AuPd (1/12nm) n + -Si SiO 2 (100nm) Top wire, Ti/AuPd (0.5/15nm)

MPI Stuttgart 5  m Crossed-wire junction bottom wire

MPI Stuttgart Electrical behaviour of pure matrix sandwich junctions gap widths: V type I : “ohmic” (thinner films) type II : with gap (thicker films)

MPI Stuttgart I/V characteristics of C60/matrix- sandwich junctions Sample no.1 (of 10) ~0.3V

MPI Stuttgart I/V characteristics of C60/matrix- sandwich junctions Sample no.2 (of 10) ~50mV

MPI Stuttgart Features in the I/V of C60/matrix- junctions C60 in nanogap (1) (1): H. Park et al., Nature 407 (2000), 57. (2): Y. Noguchi et al., Thin Solid Films (2003), meV excitation from nano- mechanical oscillation features with small separation: internal vibrational modes (several 10meV) C60 embedded in polymer film (macroscopic junction area) (2)

MPI Stuttgart Investigation of gate dependence for C60/matrix- sandwich junctions T=2K Sample no.2 (of 10)

MPI Stuttgart Investigation of B field-dependence for C60/matrix-sandwich junctions Sample no.2 (of 10)

MPI Stuttgart Mn 12 -cluster for comparison synthesis electrodeposition: matrix method deposition: self-assembly Spin ground state: S=10 AuPd [Mn 12 O 12 (O 2 CMe) 16 (H 2 O) 4 ] S COO OOC

MPI Stuttgart I/V traces of Mn 12 sandwich junction for increasing B field

MPI Stuttgart Next steps cobalt or dysprosium bottom top Sandwich junctions with ferromagnetic metal (top) contact Incorporation of molecules Top electrode (e.g., Co) AuPd bottom electode  effect on features in I/V spin polarised tunneling

MPI Stuttgart Nano-gaps via electromigration-induced breaking of nanowires ion beam etching V 2 O 5 nanowire Ti/AuPd (1/6 nm) layer SiO 2 (100 nm) layer n + -Si substrate nm cross-section of ~100nm 2 (7nm x 15nm) gap size  1nm for breaking at 4K (R RT < M  ) after breaking via electro-migration: advantages: allows for single molecule contacts possibly smaller gate shielding disadvantage: possible with ferromagnetic metal wires ?

MPI Stuttgart Electrical behaviour of pure matrix sandwich junctions B = 0 T, 2 T, 5 T, 10 T, -10 T T = 2 K type I - “ohmic”