Nanoceanal Spectroscopy of Vibrariums and Electariums

Transcription

1 FEM-Simulationen von Feldverteilungen im elektrischen Rasterkraft-Mikroskop Falk Müller 100 nm 2,93 nm 0 nm Experimental set-up Results Results on gold Application on silicon Numerical umerical simulations Conclusion Zwickau, , 13:30 Uhr

2 TU Chemnitz Institut für Physik LS Analytik an Festkörperoberflächen Prof. M. Hietschold Melanchthonstr Oelsnitz

3 Experimental Set-Up LockIn Set point - Feedback + Preamplifier laser z X Y

4 75 nm Alqb on silicon Image size: 3 µm 3 µm Mode: DNC 47 nm Cantilever: NSC15 Sample courtesy TU Braunschweig 0 nm

5 Porous anodic alumina Image size: 2 µm 2 µm Mode: DNC Cantilever: NSC15/STING 940 nm Sample courtesy MPI f. Mikrostrukturphysik Dr. Mato Knez 0 nm

6 ITO-layer on silicon (100) Image size: 1 µm 1 µm Mode: DNC Cantilever: NSC15/HiRes Sample courtesy Dr. J. Kupfer Institut für Physik TU Chemnitz 100 nm 26 nm 0 nm

7 DNA-functionalized gold particles on Au Image size: 1 µm 1 µm Mode: DNC 32 nm Cantilever: NSC15/HiRes-W Sample courtesy University of Karlsruhe Dr. U. Plutowksi Inst. of Chemistry 100 nm 0 nm Clusters with different sizes are functionalized with different DNA sequences. The Anfatec selectivity Instruments of their AGadsorption on a functionalized gold surface is investigated with AFM.

8 Amplitude [V] Experimental Set-Up 0,01 1E-3 1E-4 1E % f ac = 10 khz Frequenz [khz] f r = 38,5 khz LockIn Preamplifier Set point - laser U ac sin(ω el t) Feedback + ~ z X Y + U ext

9 Basic Equations 1 2 Electrostatic energy W el : = CU and resulting force: 2 Total voltage: U = built in ( U + U ) + U sin(2π f t) Bias AC el Force on the cantilever caused by the voltage: = U DC Follows for the measurement results: 1. harmonic 2. harmonic Static elongation

10 Amplitude [V] Experimental Set-Up 0,01 1E-3 1E-4 1E % f ac = 10 khz Frequenz [khz] f r = 38,5 khz LockIn 2ωel LockIn ω el LockIn Preamplifier Set point - laser U ac sin(ω el t) Feedback + ~ z X Y + U ext

11 Sputtered gold surface Topography 5,59 nm 0,11 mv 50 nm 0 nm 50 nm 0,08 mv

12 Simulation for a certain gemometry: Geometry influence Geometry Potential distribution Energy density distribution Geometry variation: 4 Results Kapazität [a.u.] 3 2 R=50 R=25 R= Oberflächenprofil [Pixel]

13 Estimation of the resolution Tip sample distance: 10 nm (Van-der-Waals) Tip diameter: 100 nm C R Sphere-plate-capacitor: 2π ε z z Tip sample dc/dz-signal: 5*10-9 F/m position A position B Voltage sensitivity: 1 1 s Measured amplitude: 100 mv pf Resolution of dc/dz: 50 m Hz sample Capacitance sensitivity: C = z dc dz C = 0. 5 af Hz

14 Hydrogen-passivated Silicon(111) surfaces 2,93 nm 100 nm 0 nm Tip: CSC37/AlBS - Type A + Pt-coated

15 Equations used for numerical simulations Poisson-equation: Force r F = r EQ

16 Mesh generation for FEMLab simulations Tip radius: 100 nm Tip-sample distance: 10 nm Final mesh Initial mesh

17 V tip = - 20 V Potential distribution

18 V tip = - 20 V Energy density 20 V in W/m 3

19 Electrical force spectroscopy LockIn 2ω LockIn ω Set point LockIn - Feedback + Preamplifier laser Amplitude [V] 0,01 1E-3 1E-4 1E % f r = 38,5 khz f ac = 10 khz Frequenz [khz] + U ac sin(ω el t) ~ z X Y U dc

20 Simulated X 2f (U dc ) vs. distance 2 /δu ext [F/nm ] δq surface metal δ 2 F/δU 2 [pn/v 2 ] 1 n-si (P-dotiert) 25 C (k B T = 25 mev) E C -E F = const = 0,25 ev --> N D =1,27 * cm E-3 bias U dc [V] n-si (P-dotiert) 25 C (k B T = 25 mev) E C -E F = const = 0,25 ev --> N D =1,27 * cm -3 1E bias U dc [V] 10 nm 20 nm 30 nm 40 nm 50 nm 60 nm 70 nm 80 nm 90 nm 100 nm 10nm 20nm 30nm 40nm 50nm 60nm 70nm 80nm 90nm 100nm

21 Potential drop inside the semiconductor accumulation depletion

22 EFS spectra on hydrogen passivated n-si(111) n 1E-3 U ac = 1 V X 2f [V] 1E-4 1E-5-10 na -8 na -6 na -4 na U dc [V]

23 Conclusion EFM is a nice tool for the investigation of material properties in the nano- and micrometer range Capacitance resolution: ~ af Method opens new challenges concerning the electronic spectroscopy in dynamic non-contact-mode. Thanks to Dr. Heike Angermann, Dr. R. Scholz, Prof. M. Hietschold, B. Graffel,...