N L Tran J Z Sexton T J

N. L. Tran, J. Z. Sexton, T. J. Grassman, B. Fruhberger, A. C. Kummel University of California, San Diego S. V. Patel, T. E. Mlsna Seacoast Science AFOSR MURI# F 49620 -02 -1 -0288 Determination of Material Growth and Analyte Interaction Goal Develop Instruments to: (a) Fabricate Metallo-Phthalocyanine (MPC) Chemically Sensitive Field Effect Transistor (Chem. Fet) DFT Computation DEbinding of Cl 2 using GGA-DFT Binding Site 1. 2. 3. Current Capabilities: (b) Test MPC Chem. FETs 1 2 Room temperature STM (c) Image Sensor Materials [e. V] -1. 40 -1. 05 -1. 41 Computation suggest multiple possible binding sites for Cl 2 (Cu and the organic ligand) • Filled state image of Cu. Pc on Au(111) at monolayer coverage • Metal center of adsorbed Cu. Pc appears dark, consistent with unfilled Cu-dz 2 orbitals • Conditions: -1 V sample bias, 0. 3 n. A tunneling current Phthalocyanine Deposition • Custom designed MBE cell for MPc deposition Low T effusion cell In Preparation: Low Temperature STM for Single Molecule Studies: funded by NSF Plate valve mechanics: Cu cooling shield braised onto SS can Effusion cell shutter Plate valve Temperature Controlled Enclosure • Scanner: Beetle type with x-, y-coarse movement • Cooling: Liquid He bath cryostat; Scanner 100% surrounded by a 4 K shield • Vibration isolation: Internal spring system with eddy current damping and external isolation with pneumatic isolation leg • Additional shutter to control in-situ gas dosing at low temperature onto STM mounted sample • Temperature variation either by heating the complete STM scanner or just the sample Carrier Gas High Resolution Images of Complex Molecules At Low Temperature due to Extremely Stable Environment rotary feedtrough (transfer shutter) Cu spacers for heat transfer – also act as hard stops - Additional He gas cooled radiation shield in between to improve thermal isolation Closed to UHV Open to UHV And for deposition LN 2 dewar (14 l) LHe dewar (4 l) STM-contacts (37 -pin plug) (a) 8 K STM image of TBPP (porphyrin) on Cu(100), (b) STM simulation of TBPP/Cu(100); (c) structure of TBPP on Cu(100). Note the excellent submolecular resolution at the good agreement with the simulation. From Moresco et al Temperature Controlled Bubblers 4 -Way Valve Heat Exchanger Exhaust Test Chamber Flow Meter • 50 electrical feedthroughs • Closed-loop temperature control: 0 - 100 ± 0. 05° C; 20 minute response time • Closed-loop relative humidity control: 0 - 100% ± 2% RH; 10 minute response time • Open-loop permanent gas concentration control: 0 - 40000 ± 4 ppm; 4 minute response time; or, • Open-loop volatile organics concentration control: up to 8 volatile organics from temperature-controlled bubblers in any one experiment, 4 minute response time • Temperature and humidity sensors inside chamber • Outer enclosure with closed-loop temperature control: 25 ± 0. 5°C • Test runs are fully automated baffles - Eddy current vibration damping of the pendulum motion of the inner cryostat - STM is completely isolated (thermally and electrically) when tunneling electrical feedtroughs Cabling (stainless steel) Instrument Features: Linear feedthrough Viton o-ring for sealing Data Acquisition And Control PC The Createc STM-SY-014 -2 combines a low-temperature STM (LT-STM) with three chambers: load-lock, sample preparation, and analysis. Two side ports for mounting turbo pump and ion gauge • MBE cell capabilities include: • fast introduction of different MPcs • differential pumping • H 2 O cooled Cu heat shield to minimize heat transfer and protect UHV instrumentation • plate valve allowing separation between MBE cell and UHV chamber Evaluation of Sensor Performance Mass Flow Control Two mounted tees to connect shafts to feedthroughs Linear/rotary feedthrough DFT simulations can aid in the assignment of observed STM features 60 Å x 60 Å Linear & Linear/Rotary feedthroughs control plate valve Cu plate 3 shutter for sample & tip transfer linear feedtrough 4” (to pull down the STM) He gas cooled radiation shields (LN 2, LHe) STM head eddy current damping for the LHe cryostat Future Plans • Use STM to image growth modes and analyte binding sites for Metallo-Phthalocyanines • Test sensors for ppb sensitivity and selectivity to Chemical Warfare Agent (CWA) simulants