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Workshop on Research Collaboration FAPESP - Trinity Charge transport across ultrathin semiconducting molecular layers Carlos Cesar Bof Bufon Functional Devices and Systems Laboratory Research scope • Materials Science • Strain-Engineering • Nano/microfabrication • Self-assembly Smart Architectures Novel Functional Devices and Structures Top-Down Inorganic Materials Hybrid Organic/Inorganic Metamaterials Organic Materials Bottom-Up Research Activities on Hybrid freestanding nanomembranes Ultra-compact sensors a) b) c) Synthesis of hybrid freestanding nanomembranes. Fabrication and characterization of hybrid molecular heterojunctions. Fabrication and characterization of nanomembrane based elements. Ultra-compact capacitors Bof Bufon C.C. et.al , Nano Lett. 2010 Sharma R. et al. Adv. Energy Mater. 2014 Hybrid molecular heterojunctions Hybrid molecular heterojunctions Bof Bufon C.C. et.al , Nano Lett. 2011 Bof Bufon C.C. et.al , J. Phys. Chem. C 2014 Bendova, et. al, J. Phys. Chem. C 2016 Vervacke, C. et al. RSC Advances 2014 Grimm, D. et al. Nano Lett. 2013 Supporting Innovation Sensors and detection systems for Brazilian strategic fields Fuel quality control - production - storage - transport - end user Food quality control - processing. - storage. - transportation. - end consumer. Environmental and heath monitoring - medical and health screening. - industrial residues in rivers and lakes. - evaluation of the water contaminants by: - biological contaminants; - heavy metals; - agricultural defensives. Research Activities on Hybrid materials and devices Patterning of PPy thin films a) Synthesis of organic thin films on novel substrates. b) Micro- and nano-fabrication processes of organic thin films: i) incorporation of organic films in inorganic platforms; ii) patterning of organic thin films; iii) scaling-up. c) Fabrication of organic/inorganic hybrid functional elements. d) Characterization of organic/inorganic hybrid functional elements. PPy Schottky-Barrier FET PPy film as oxygen gas sensor - I (µA) Paper-based in-flow sensors Drain-source current (µA) In-flow acid detection T=300K Drain-source voltage (V) Time (103 s) C.C. Bof Bufon et al. Appl. Phys. Lett., 2006 C. Vervacke, et al. Anal. Chem. 2012 Patent pending, 2014 C.C. Bof Bufon et al. Phys. Rev. B., 2007 Introduction Hybrid Molecular Electronic Junctions James R. Heath and Mark A. Ratner, Physics Today 2003 Metal Metal Insulator L Semiconductor X R Semiconductor Insulator Introduction from organic to molecular electronics Bridging the gap between organic electronic devices (thicknesses of 10-100nm) and molecular electronic devices (at least 1 dimension smaller than 10nm). McCreery, Yan and Bergren, Phys Chem. Chem. Phys. 2013 Introduction from organic to molecular electronics Bridging the gap between organic electronic devices (thicknesses of 10-100nm) and molecular electronic devices (at least 1 dimension smaller than 10nm). From thin- to ultra-thin organic semiconductors Z. H. Xiong et al. Nature 427, 821 (2004) Technological challenges x x x x x x x Substrate Substrate Short-circuit via pinholes Metal interdiffusion. Haick et al., Acc. Chem. Res. 41, 359 (2008) Delicate materials require new contacting methods Vertically contacting molecular layers: some examples. Evaporation of contacts Lodha et al, J. Appl. Phys. 2006 Hg droplet Evaporation of contacts Haick and Cahen, Acc. Chem. Res. 2008 Bonifas and MacCreery, Nat. Nanotech. 2010 Holmlin et al. J. Am. Chem. Soc. 2001 Lift-off Float-on Cahen et al, Nature 2000 Haick and Cahen, Acc. Chem. Res. 2008 Nanomembranes: the third wave of works on nanomaterials Nanomembranes are structures with thicknesses of less than a few hundred nanometers and with minimum lateral dimensions at least two orders of magnitude larger than the thickness. Thin Flexible Strain engineered Geim, Nat. Mater. 2007 Kim, Science 2008 Zhang, Nano Lett. 2006 Deneke, Appl.Phys.Lett. 2007 Patternable 500µm Thurmer, Nano Lett. 2010 Sun, Nat. Nanotechnol. 2006 Bof Bufon, 2010 Rolled-up nanomembranes Some features of interest. a) Mechanical flexibility (transition 2D – 3D): Impact on the device’s footprint area. b) Quasi-2D nature: Sensors with improved performance and novel functionalities. c) Patterning and integration capabilities: Allows the creation of a variety of 3D devices and hybrid organic/inorganic heterojunctions. Nanomembrane technology: strain engineering selective removal Strained Layer Sacrificial Layer Substrate Patterning of regular arrays of rolled-up nanomembranes 500µm Bof Bufon, 2010 Experimental conditions: 1) Substrate: Si/SiO2 2) Sacrificial layer: GeO2 3) Strained bilayer: Ti/Cr 4) Rolling media: H2O Ø = 5µm-100µm Concept of hybrid capacitor based on nanomembranes Max. 50nm C.C. Bof Bufon, Nano Lett. 10, 2506 (2010) @DSF-LNNano 2016 Zooming in and out STEM-EDS map R. Sharma, Adv. Energy Mat. 4 (2014) C.C. Bof Bufon, Nano Lett. 10, 2506 (2010) Design, yield and dielectric material Sharma R. et al., Large-area Rolled-up nanomembrane capacitor arrays for electrostatic energy storage”. Advanced Energy Materials - Volume 4, Issue 9, June 24, 2014 Capacitance of the rolled-up capacitor RC C 3D 1 2 C 2D N Capacitance per foot print area ~220 µF/cm2 C.C. Bof Bufon et al., Nano Lett. 10, 2506 (2010) State-of-the-art for Al2O3: ~100 µF/cm2 Barnerjee et al., Nat. Nanotech. (2009) Hybrid organic/inorganic capacitor by SAM incorporation Current and capacitance dependence on the chain length C.C. Bof Bufon, Nano Lett. 10, 2506 (2010) Soft but robust electrodes based on nanomembranes “crossbar-like” structure • Pinhole-proof; • Soft contact: low damage to film (SAM, etc) • “Large scale” production and integration; • Versatile material composition; • Self-adjusting gap. • Geometrical contact area < 1µm2 Soft mechanical contacting method: Self-adjusting contacts. Haick et al., Acc. Chem. Res. 41, 359 (2008) Contacting ultra-thin CuPc layers (Au/CuPc/Au) Releasing of the nanomembrane in H2O Submittend J. Phys. Chem. C, 2014, 118 (14), pp 7272–7279 Electrode gap ~ 3nm to 110nm CuPc model molecular system Water-gated CuPc transistor DST calculation: Nita, P. et al., Nanoscale, 2014. X-Ray: Hoshino, A, et al. Acta Crystallogr. Sect. B: Struct Sci, 2003. Furlan, Merces, Vello and Bof Bufon, Organic Electronics 31, 2016 Organic Electronics, 2017 10.1016/j.orgel.2017.06.041 Knupfer, M. and Peisert, H., phys. Stat. sol.(a), 2004 4 µm J. Phys. Chem. C, 2014, 118 (14), pp 7272–7279 Transport properties of CuPc thin films: IV and It traces Yan, H et al, PNAS 2013 The Journal of Physical Chemistry C, 2017 10.1021/acs.jpcc.7b02528 Transport properties of CuPc thin films: IV and IT traces for t = 6.5nm 1) For V < 0.15V and T > 100 - 140 K, hopping conduction dominates; 2) At T = T1: transition from thermally activated transport to tunneling; 3) Strong temperature dependence for T > T1 associated to impurity/defect (ID) sites; For T > T1: Ea Submittend I V exp kT J. Phys. Chem. C, 2014, 118 (14), pp 7272–7279 Physisorbed vs. chemisorbed molecules Au/CuPc/Au Yoram Selzer et al. J. Am. Chem. Soc. 2004, 126, 4052 Transport properties of CuPc thin films: Activation energy for T > T1 - Ea < EF - EHOMO: hopping into the molecular layer; - Impurity/defect sites work as charge localization centers where: temperature enhances the hopping process. applied bias lowers the potential barrier between such sites. Region B q3 Ea E0 V r 0 d *in accordance with the in-plane ε calculated for CuPc thin layers: Shi, N.; Ramprasad, R. Phys. Rev. B 2007, 75, 155429. Ramprasad, R.; Shi, N. Appl. Phys. Lett. 2006, 88, 222903. Shi, N.; Ramprasad, R. Appl. Phys. Lett. 2006, 89, 102904. εr = 13* Low temperature transport For T < T1: • the charge carriers are trapped into the ID sites; • the transport across the CuPc layer occurs either: via the molecular levels or; by a non-resonant tunneling across the thin barrier. V < 0.26 V: non-resonant direct tunneling (DT) across the CuPc barrier. 2d 2meΦ I V exp V ~ 0.40 V: “resonant tunneling” V > 0.75 V: Fowler-Nordheim tunneling (FN). 4d 2m 3 e 2 I V exp 3qV Summarizing Au/CuPc/Au • We precisely set/map the transport properties of a model molecular system (CuPc) controlling the external parameters (temperatures and voltage) over a wide range. • The contributions to the conductance related to the impurity/defect states and those due to the CuPc molecular levels were isolated. • At low temperatures the sequential transitions from DT to resonant-tunneling to FN tunneling was observed. • The Au/CuPc/Au heterojunctions can mimic the behaviour of molecular wires over a certain temperature/voltage range. Submittend J. Phys. Chem. C, 2014, 118 (14), pp 7272–7279 Acknowledgements TU-Chemnitz Dietrich R. T. Zahn Georgeta Salvan Michael Fronk Iulia Korodi IFF, IFW-Dresden Martin Knupfer Susi Lindner IIN, IFW-Dresden Celine Vervacke Dominic Thurmer Martin Bauer Oliver G. Schmidt LNNano/ CNPEM Jeferson Bettini Christoph Deneke Angelo Gobbi DSF/ LNNano /CNPEM Davi Henrique de Camargo Cátia Crispilho Corrêa Murilo Santhiago Leirson Daniel Palermo Leandro das Mercês Silva Tatiana Parra Vello Paula Andreia Petrini Mariane Peres Pereira Isabel Emperatriz Loayza Andreia da Silva Chagas Rafael Furlan de Oliveira Geovana dos Santos Priscila G. da Costa Kleyton Torikai Ricardo M. L. Silva Thank you for your attention 2014/25979-2 [email protected] Au/SAM/Au heterojunctions Contacting sulfur terminated alkanes Non-resonant tunneling transport C.C.Bof Bufon et al., Nano Lett. 11, 3727 (2011) Au/nanoparticles/Au STM tip Dorogi et al. Phys. Rev. B. 1995 Andreas et al. Science 1996 n-dodecanethiol Au nanorparticles (2-5nm) Sato et al. J. Appl. Phys. 1997 Au/NPs/Au heterojunction J. Phys. Chem. C, 2016, just accepted Summarizing 1) Rolled-up nanomembranes can gently contact ultra-thin (3 - 110nm) hybrid organic-inorganic layers from the top; 2) No interdiffusion of metallic atoms was detected. 3) The charge transport across hybrid heterojunctions can be investigated. Additional possibilities Submittend Transport across the hybrid junctions Simmons model for conductance [1] : Field-emission [2] : VT=160mV [1] Simmons, J. G. Journal of Applied Physics 1963, 34, (1), 238 -239. [2] Gadzuk, J. W.; Plummer, E. W. Reviews of Modern Physics 1973, 45, (3), 487-548. C.C.Bof Bufon et al., Nano Lett. 11, 3727 (2011) SAMPLE: Ag tube/Organic Semiconductor/Au electrode D#S7#JM4@F1_Ag_11 nm (AFM) dI/dV (6K) dI/dV (8K) dI//dV (10K) dI/dV (13K) dI/dV (15K) dI/dV (20K) dI/dV (25K) dI/dV (30K) dI/dV (40K) dI_dV versus V for different T_CB 15:47:42 03/03/2016 0.6 5.0 10 K 4.0 0.4 4.0 0 2.0 dI/dV (nS) 3.0 dI/dV (nS) I (nA) 0.2 3.0 2.0 -0.2 1.0 1.0 -0.4 -0.6 -0.4 -0.2 0 0.2 0.4 0 0 -0.4 -0.2 0 V (V) V (V) 0.2 0.4 differential resistance around V= 0V According to Mesoscopic Electronics in Solid State Nanostructures, by Thomas Heinzel: “The Coulomb gap manifest itself in an increased differential resistance around V= 0 V, compared to that observed at larger voltages” D#S7#JM4@F1_Ag_11 nm (AFM) 3 10 12 2.5 10 12 2 10 12 1.5 10 12 1 10 12 i) 𝐸𝐶 = 2𝐶 > 𝑘𝐵 𝑇 ii) RTunnel >> RQuantum (25.8 kΩ) At 10K (the temperature we’ve observed a gap in the conductance) the thermal energy is 0.86 meV, so: C < 9.3 x 10-17 F (at 10K) The gap from the conductance plot is ~ 100 mV, thus, considering the Coulomb blockade energy (EC), we have: 10 K dV/dI (Ohm) The requirements for observing Coulomb blockade are: 𝑒2 𝑒2 𝐸𝐶 = 2𝐶 𝑒2 𝐶= 2 . 100 𝑚𝑒𝑉 𝐶 = 8 𝑥 10−19 𝐹 Thus, from the conductance gap, the obtained capacitance satisfies (i). In addition, the measured resistance is ~1 GΩ, which satisfies (ii) as well. We can consider the charged “site” having a disk-like geometry with a self-capacitance given by: C0 = 8εra, whereas εr is the dielectric constant of CuPc and a the disk radius. 9 500 10 According to the literature εr of CuPc varies from 2.1 – 7¹ (for polycrystalline layers), thus a = 5.3 – 1.6 nm 0 -1 -0.5 0 V (V) 0.5 1 If εr = 13² (in-plane dielectric constant), then a = 0.87 nm ¹ Jarosz, G. et al, Thin Solid Films (514), 2006, 287 - 291 ² Bof Bufon, C. C. et al, Journal of Physical Chemistry (118), 2014, 7272 - 7279 IxV (T) IxV (T) 13:22:27 12/02/2016 0.6 10 -7 10 -9 ABS (6K) ABS (10K) ABS (15K) ABS (20K) ABS (30K) ABS (40K) ABS (50K) ABS (60K) ABS (80K) ABS (100K) ABS (120K) ABS (140K) ABS (160K) ABS (180K) ABS (220K) ABS (240K) ABS (260K) ABS (280K) ABS (300K) 0.4 -11 I (10K) 0 I (A) I (A) 0.2 I (13K) 10 I (15K) -13 I (20K) -0.2 10 I (25K) I (30K) -0.4 -0.6 I (40K) -15 10 -0.4 -0.2 0 V (V) 0.2 0.4 -17 10 -1.5 -1 -0.5 0 V (V) 0.5 1 1.5 +0.16 V ± 12% V (peak) +50 mV ± 12% V +500 mV ± 12% V -0.16 V ± 12% V (peak) -50 mV ± 12% V -500 mV ± 12% V G vs T for peaks in the forward scan -9 1 10 -6 -9 100 10 -9 10 10 1 10 10 10 -9 -9 1 10 -9 Mean G (S) Mean G (S) G vs T for peaks in the forward scan 100 10 -12 100 10 -12 10 10 -12 100 10 -12 10 10 -12 1 10 -12 1 10 -15 100 10 350 -15 300 250 200 150 T (K) 100 50 0 100 10 350 300 250 200 150 T (K) 100 50 0