672 Advanced Solid State PhysicsScanning Tunneling MicroscopyBiao Hu2. STM principle & working modesIn the classically forbidden region:3. STM application & extension(b) DNA4.STM in our group672 Advanced Solid State PhysicsScanning Tunneling MicroscopyBiao HuOutline:1. Introduction to STM 2. STM principle & working modes3. STM application & extension4. STM in our group1. Introduction to STMI. Invented by G.Binnig & H.Rohrer in 1982II. Richard Feynman’s address: “There’s Plenty of Room at the Bottom” at Caltech in 1959Red blood cells(~7-8 µm) DNA~2-1/2 nm diameterThings NaturalThings NaturalFly ash~ 10-20 µmAtoms of siliconspacing ~tenths of nmHuman hair~ 60-120 µm wideAnt~ 5 mmDust mite200 µmATP synthase~10 nm diameterMicroworld10-2m10-3m10-4m10-5m10-6m10-7m10-8m10-9m10-10mNanoworld0.1 nm1 nanometer (nm)0.01 µm10 nm0.1 µm100 nm1 micrometer (µm)0.01 mm10 µm0.1 mm100 µm1 millimeter (mm)1 cm10 mmVisible1,000 nanometers = InfraredUltravioletSoft x-rayMicrowave1,000,000 nanometers = Office of Basic Energy SciencesThe Scale of ThingsThe Scale of ThingsThings ManmadeThings ManmadeHead of a pin1-2 mmQuantum corral of 48 iron atoms on copper surfacepositioned one at a time with an STM tipCorral diameter 14 nmNanotube electrodeZone plate x-ray “lens”Outer ring spacing ~35 nmMicroElectroMechanical(MEMS) devices10 -100 µm wideCarbon nanotube~1.3 nm diameterCarbon buckyball~1 nm diameterSelf-assembled,Nature-inspired structureMany 10s of nmScanning Tunneling MicroscopyScanning Tunneling MicroscopyOpen Open ““doordoor””for for nanosciencenanoscienceNobel PrizeNobel Prize2. STM principle & working modesi: Principle:Fig.1The wave function of tip and sample overlap.In the classically forbidden region:() ()()⎥⎥⎦⎤⎢⎢⎣⎡−−=hzEmzφψψ2exp0(1)The tunneling current: ()()()zFsFsteEVzEmEVIφρφρ025.122exp−∝⎥⎥⎦⎤⎢⎢⎣⎡−−∝h(2)eV5=φIn gold, , current drops an order of magnitude, gap is changed by one Åii: Working modes:••idea for STM, like idea for STM, like ““fingerfinger””, to , to ““touchtouch””the atomsthe atoms(a) Constant current modeSuited tip; Actuator; Controller.Vibrational isolation;Fig. 2Atomic sharp Atomic sharp tiptipelectronelectrontunnelingtunnelingpiezoelectricspiezoelectrics::move with voltagemove with voltageSTM can image individual atoms!(b) Constant height mode Measure the tunneling current while scanning on a given, smooth x-y-z contour.The z-position (output of feedback loop) is measured at discrete (x, y)-positions.line-scan image, grey-scale image or color encoded image.Observe dynamical processes, but increase the risk of crashing the tip3. STM application & extension(a) Reconstruction in Si(111)The rhombohedral surface unit cell are the corner hole and the 12 maxima, the adatoms. G. Binnig, H. Rohrer, Ch. Gerber, and E. Weibel, Phys. Rev. Lett. 50, 120 (1983)Si(111) surfaceSi(111) surface--7x7 reconstruction7x7 reconstruction(b) DNAFig. a, Unsmoothed, unfiltered plane-subtracted STM image of DNA ~80x120 Åb. Model of the Van der Waals surface of A-DNA derived from X-ray crystallographic data, scaled to a. Robert J. Driscoll, Michael G. Youngquist & John D. Baldeschwieler Nature 346294-296 (1990)(c) Atom Manipulation and Surface Standing Wave(c) Atom Manipulation and Surface Standing WaveQuantum Corral of 48 iron atoms on copper surfaceQuantum Corral of 48 iron atoms on copper surfacepositioned one at a time with an STM tip (positioned one at a time with an STM tip (corral diameter 14 nm)corral diameter 14 nm)G. Binnig, H. Rohrer Rev. Mod. Phys. 71, 324 (1999)(d) STM extensionscanning near-field optical microscope (SNOM), atomic force microscope (AFM), Maxwell stress microscopy, scanning electrochemical microscopy et. al.4.STM in our groupRecent work:Surface reconstruction of TiO2 (110) by Ti interstitialsSTM image of a strand (1.2V; 0.5nA) with the height profiles across (left, dotted line) and along (right) the line defect. K. T. Park, M. H. Pan, V. Meunier, and E. W. Plummer, Phys. Rev. Lett. 96, 226105 (2006)• Sr2RuO4: layered perovskite without copper that exhibits superconductivity (A)STM image of a 4 by 4 surface area showing extremely large terraces and steps. (B)Height along the line scan shown in the STM image. (C)Ball model of the bulk unit cell of Sr2RuO4. Red, strontium; blue, oxygen; and green, ruthenium (in the center of the octahedron).R. Matzdorf, Z. Fang, Ismail, Jiandi Zhang, T. Kimura, Y. Tokura, K. Terakura, and E. W. Plummer, Science 289, 746 (2000)UT STM (SERF 101-E)mµScan range:xy :12 x12z: 1.5Resolution:xy: 0.1nmz: 0.01nmmµmµmµFrontviewSample stageElectronicsSTM scannerApplications Single atom or molecule spectroscopy.  Atomic resolved spectroscopy maps.  The temperature and magnetic field range to study the quantum response of nano-objects.  Optical access to the sample in the magnetic field for probing and exciting atoms or molecules.Low Temperature, High Field STMScanning Tunneling Microscope with extreme stability under extreme conditionsIsolated concrete block with pitAcoustic isolation roomDewar / MagnetActive vibrationisolationGrowth ChamberManipulatorAnalysis chamberTransfer ChamberSingle molecule vibrational spectroscopy: CC22HH22, C, C22DD22Science 280, 1732 (1998)------Stipe and Ho1 K Stage300 mKStageSample CleaverSTM HeadRotation StageHe3 PotHe3 CondensorHe4 PotHeat SwitchesTipTriangular sapphire rodSample HolderTube scannerShear stacksSampleA CNMS partner instrument built by ORNL, The University of Tennessee, and The University of HoustonTransfer chamber300 mKstage1 K stageRotating STMSamplecleaverScientific Drivers¾ Atomically-resolved topographyand spectroscopy maps¾ Quantum response at low T and High B¾ Real Space---K spaceCapabilities¾ Low T - 300 mK¾ High B - 9 Tesla¾ STM rotates in magnetic field¾ Cryogenic UHV cleaving¾ Sample Fabrication in UHVNature 415, 412 (2002)– Lang and DavisElectronic