1. Electrical Characterization of GUMBOS Using Conductive-Probe Atomic Force Microscopy NAVEEN JAGADISH, SERGIO DE ROOY, ATIYA JORDAN, ASHLEIGH WRIGHT, SUSMITA DAS, BILAL EL-ZAHAB, ISIAH M. WARNER, AND THEDA DANIELS-RACE LOUISIANA STATE UNIVERSITY, Nanoscale Electronic Materials Characterization Group Electronic Materials and Devices Laboratory Department of Electrical & Computer Engineering

2. OUTLINE Motivation Introduction to NanoGUMBOS Mechanism of Atomic Force Microscopy Conductive Probe - Atomic Force Microscopy (CP-AFM) Different types of NanoGUMBOS Experimental Results: – Topographies – I-V plots of each type of NanoGUMBOS Conclusion Acknowledgements

3. Motivation Measurement of electrical properties of a contemporary nanomaterial. To provide enough evidence to qualify these materials as Hybrid Electronic Materials (HEMs)

4. Characteristics of (Traditional) Ionic Liquids ● Organic salts with melting points ≤ 100 o C; two main types: -RTIL (room temperature ionic liquids) -Frozen (solid state) ionic liquids ● High ionic conductivity ● Non-volatile ● High thermal stability/Low vapor pressure ● Highly solvating -For organic and inorganic compounds -For hydrophobic and hydrophilic materials ● Recyclable (also known as “green solvents”) ● Broadly tunable (i.e.-solubility, melting point, viscosity) What Are and Why Nano GUMBOS? ● GUMBOS = Group of Uniform Materials Based on Organic Salts ● Frozen ionic liquids; Melting points between 25 o C and 250 o C ● Size and properties mimic traditional nanoparticles ● Functionalizable (“designer nanoparticles”) for task specific properties – e.g.- fluorescence, magnetism, antimicrobial, chirality, and electrical properties ● Paradigm shift in nanoparticle construction and applications Introduction to NanoGUMBOS 10μm SEM image of NanoGUMBOS

5. Atomic Force Microscopy (AFM) Schematic representation of conductive probe AFM Laser beam is focused on the head of the cantilever. The tip (very small and sharp) is scanned over the surface. The reflected light intensity varies with the vibrations of the cantilever. The detected light is converted to an image. Using AFM it is possible to obtain the image of a few atoms. Surface Detector Cantilever LASER Tip

6. Conductive Probe-Atomic Force Microscopy (CP-AFM) GOAL: To measure electrical properties of NanoGUMBOS- A conductive Pt-coated Silicon tip is used instead of a regular tip. The AFM is operated in contact mode. The tip acts as one of the electrodes and the gold surface being the other. Closed circuit is formed when tip is brought in contact with the nanoparticle on the surface. The voltage is swept from -1V to +1V and current is measured using Semiconductor Characterization System. Advantages of using CP-AFM - The dimensions of the tip are comparable to the size of the nanoparticles – precise measurements. Contact resistance at one end is minimized. Topography and electrical properties of nanoparticles can be measured simultaneously - making it easier to identify the nanoparticles on the surface. CP-AFM EXPERIMENTAL SETUP

7. Different types of NanoGUMBOS measured The I-V curves of following types of GUMBOS were obtained using conductive probe atomic force microscopy: Sample-1 : Rhodamine 6G tetraphenylborate (R6G [TPB]). Sample-2 : Dimethylpyrollidinium bistrifluoromethanesulfonimide (Py 11 Tf 2 N) Sample-3 : Pseudoisocyanine bistrifluoromethanesulfonamide (PIC [NTF2]) Sample-4 : Pseudoisocyanine bis(perfluoroethylsulfonyl)imide (PIC [BETI]) Sample-5 : PicopropylSH tetraphenylborate (PicopropylSH [TPB])

8. Sample 1 : Rhodamine 6G tetraphenylborate (R6G [TPB]) Current (A) Voltage(V) Chemical Structure of R6G [TPB] AFM image of R6G [TPB] nanoparticles I-V curve of R6G [TPB] obtained using CP-AFM

9. Sample 2 : Dimethylpyrollidinium bistrifluoromethanesulfonimide (Py 11 Tf 2 N) AFM image of (Py 11 Tf 2 N) nanoparticles Chemical Structure of (Py 11 Tf 2 N ) I-V curve of Py11Tf2N obtained using CP-AFM

10. Sample 3 : Pseudoisocyanine bistrifluoromethanesulfonamide (PIC [NTF2]) AFM image of diamond-shaped NTF2 nanoparticles I-V curve of PIC [NTF2] obtained using CP-AFM Chemical Structure of PIC [NTF2]

11. Sample 4: Pseudoisocyanine BETI (PIC [BETI]) I-V curve of PIC [BETI] obtained using CP-AFM AFM image of PIC BETI nanorods Chemical Structure of PIC [BETI]

12. Sample 5 : PicopropylSH TPB nanorods (before & after coating with gold) I-V of PicopropylSH [TPB] nanorods before gold coating Current (A) Voltage(V) Increase in current observed after coating the nanorods with gold AFM image of PicopropylSH TPB nanoparticles Chemical Structure of PicopropylSH [TPB]

13. Conclusion Observed conductivity in this new material. Successfully measured Current vs. Voltage (I-V) characteristics of different types of NanoGUMBOS using conductive probe-AFM. Dimensions of nanoparticles also determined. Other electrical properties like resistivity and conductivity can be deduced using the dimensions and I-V plots.

14. Acknowledgements Golden Hwuang, Research Associate, Electronic Material and Device Laboratory (EMDL), LSU Department of Electrical & Computer Engineering Kalyan Kanakamedla, Graduate Assistant, Electronic Material and Device Laboratory (EMDL), LSU Department of Electrical & Computer Engineering This work was supported by the Louisiana Board of Regents (LEQSF(2011-14)-RD-A-07 and National Science Foundation (2010)-PFUND-172) and NASA ( DART-44). Thanks to Dr. A. Kelley for assistance with the CP-AFM measurements and the LSU Electronic Materials and Devices Laboratory (EMDL) for use of this shared facility.

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