Suivie de résonance: méthodes à fréquences multiples. Romain Stomp Application Scientist, Zurich Instruments AG. ZI Applications

Transcription

1 Suivie de résonance: méthodes à fréquences multiples Romain Stomp Application Scientist, Zurich Instruments AG Slide 1

2 Sommaire 1. Un peu de traitement du signal pour le SPM Détection synchrone pour le champs proche Génération et acquisition d image à n fréquences 2. Méthode Dual Frequency Resonance Tracking (DFRT) Principe Exemple 3. Le KPFM à la mode de chez nous Variation sur le même thème Quel type de résolution temporelle? Slide 2

3 1. Un peu de traitement du signal pour le SPM Slide 3

4 Multifrequency & mutliple feedback loops in SPM LD sample Z-piezo XY-piezo PD k, Q Actuator Mechanical modes f df ts /dz, 1 excitation F ts Electrostatic drive HVA Scan engine R 1, ϕ 1 Amplitude feedback (AGC) + A 1 V DC + V AC AFM Controller with Z- Feedback Phase-locked loop (PLL) LIA with Bias feedback (KPFM) df 1 Most common AFM modes: Contact Modes (DC deflection) Tapping Modes (AC Modulation & Amplitude demodulation) Non-Contact Modes (FM-AFM, measure dissipation or drive and conservative forces or freq shift) Many variations: Electrostatic modes (EFM, KPFM, SSRM, ) Magnetic modes (MFM, MRFM) Resonance Contact modes (PFM, DFRT, ) for nanomechanics Spectroscopic modes (Force volume) Slide 4

5 NC-AFM: Phase & Amplitude feedback loops Phase setpoint Demodulator: Phase PID feedback on the phase Reference Oscillator (NCO) Freq. shift df Signal Input + Signal Output Demodulator: Amplitude PID feedback on the amplitude Drive Output Amplitude Dissipation Amplitude setpoint Slide 5

6 HF2LI Multiple detection and excitation Detection Drive Measurements From PD - Dual Input for tandem or lateral deflection Mechanical excitation (f0, f1, ) Electrostatic excitation (AC+DC) To SPM Controller Complete dynamic signal generations & detections Slide 6

7 Time and Frequency Domain Analysis All digital Solution Time domain Frequency domain t f Digitized samples A/D Oscilloscope Digitizer Function Generator Raw FFT Analyzer Frequency Tracking Demodulated signal after down conversion Multiple Demods Numerical and Plotter Tools Software Trigger Frequency Response Analyzer (FRA) Zoom FFT Slide 7

8 LabOne example: Oscilloscope and Trigger 65kSa scope memory (extendable to 20MSa) trigger on any internal or external signal ring-down of transient phenomena Slide 8

9 Slide 9

10 Mapping applications: Multichannel SW trigger Save all 8 demodulators at once HW trigger from Trigger 2 Line scan axis for data alignment Multiple phase (up to 8) Multiple Amplitude (up to 8) Data recording starts 10ms after initial shot (bwd trace) One trigged scan line (superposed fwd traces) Slide 10

11 2. Méthode Dual Frequency Resonance Tracking (DFRT) Slide 11

12 Dual Frequency Resonance Tracking (DFRT) 1. Bimodal f c +/-f m (just around the resonance) 2. Both sides of the resonance amplitude are measured simultaneously. 3. The difference of amplitude exhibits a linear dependance with a set-point of 0 at resonance. Slide 12

13 How it works in practice Slide 13

14 AM Modulation: frequency domain Amplitude Modulation can be with or without carrier suppression Slide 14

15 How it looks like Slide 17

16 3. Le KPFM à la mode de chez nous Slide 18

17 Kelvin Probe Microscopy: chose your mode Single-pass vs Mutli-pass AM-KPFM vs FM-KPFM Tandem vs Direct Sideband Slide 19

18 Feedback on bias OFF PLL or Demod BW needs to be high V DC = 1V V 300Hz Slide 20

19 Feedback on bias ON V DC = V cpd V 300Hz 2ω component not affected by cpd (as expected) Slide 21

20 FM-KPFM: benefit of using many demodulators Slide 22

21 FM-KPFM: example on Graphene flakes Slide 23

22 Why phase adjustement is important for KPFM? Slide 24

23 Combining DFRT & KPFM method? Second eigenmmode for bias modulation with mechanical frequency tracking 1. Carrier is electrostatically driven 2. Sidebands are mechanical modulated Slide 25

24 More KPFM imaging... Cu(111) on KBr - 300mV V second eigenmode (f2) Slide 26

25 AFM & laser case 1: static illumination LD PD R 1, ϕ 1 Amplitude feedback (AGC) Phase-locked loop (PLL) k, Q Actuator + A 1 df ts /dz, Mechanical modes excitation f 1 e.g. Nano IR, Photo-illuminations, TERS, sample Can be additionally modulated with mechanical chopper to increase SNR Z-piezo XY-piezo HVA Scan engine AFM Controller with Z- Feedback df 1 Slide 27

26 AFM & laser case 2 modulated laser beam LD PD R 1, ϕ 1 Amplitude feedback (AGC) Phase-locked loop (PLL) Modulated Laser beam (Frequency Domain analysis) df ts /dz, k, Q Actuator Mechanical modes excitation + A 1 f 1 Accousto-Optic Modulator (AOM or EOM) sample e.g. FDTR (Thermal Reflectance) Z-piezo XY-piezo HVA Scan engine AFM Controller with Z- Feedback df 1 Slide 28

27 AFM & laser case 3: pulsed illumination LD PD R 1, ϕ 1 Amplitude feedback (AGC) Phase-locked loop (PLL) k, Q Actuator + A 1 df ts /dz, Mechanical modes excitation f 1 Pump probe with femto-sec lasers Boxcar averager (TD analysis) sample Boxcar Averaged value from lock-in output as function of delays (FD analysis) Z-piezo XY-piezo HVA Scan engine AFM Controller with Z- Feedback df 1 Slide 29

28 Time-resolved SPM : laser pump-probe with BOX Decay curve BOX N times N times N times Laser t p +Δt t p +2Δt t p +3Δt Slide 30

29 Time resolved SPM without lasers: electrical pump&probe AWG: Arbitrary Waveform Generator LD PD R 1, ϕ 1 Down to 1ns rise time Transfer function measurements Pulse shaping after ifft k, Q Actuator Amplitude feedback (AGC) + A 1 Phase-locked loop (PLL) df ts /dz, Mechanical modes excitation f 1 AWG: Bias pulse via RF cabling sample Z-piezo XY-piezo HVA Scan engine AFM Controller with Z- Feedback df 1 Slide 31

30 Time-resolved SPM : electrical pump-probe with AWG Decay curve LIA N times N times N times AWG t p +Δt t p +2Δt t p +3Δt Slide 32

31 Concrete example: time-domain modulated frequency shift for KPFM Slide 33

32 From AWG to Boxcar Slide 34

33 Conclusion: The Benefit of Digital Zurich Instruments integrates in one box Lock-in (6/8 demodulators) Dual signal generator Oscilloscope / Digitizer FFT / Spectrum Analyzer Boxcar Integrator Frequency Sweeper PLL / PID Controller Most SPM modes available with Basic HF2LI Lock-in configuration and upgradable later with options (PLL, PID, MOD, ). Increase Demodulation Speed and reduce pixel dwell time Slide 35

34 More resources on ZI website & ZI blogs! Slide 36