Microscopie a scansione (SPM, E-SEM, E

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1 Scuola Nazionale di Mineralogia Otranto, giugno 2004 Microscopie a scansione (SPM, E-SEM, E DB-FIB) Giovanni Valdrè Università di Bologna

2 New developments in microscopy Applications in nano-mineral sciences SCANNING PROBE MICROSCOPY SCANNING FORCE MICROSCOPY VARIABLE PRESSURE AND ENVIRONMENTAL SEM FOCUSED ION BEAMS DUAL BEAMS LOW VOLTAGE/LOW ENERGY ELECTRON MICROSCOPY ADVANCES IN X-RAY SPECTROMETRY INSTRUMENTATION AND TECHNIQUE ELECTRON ENERGY LOSS SPECTROSCOPY AND IMAGING ELECTRON LENSES AND ABERRATION CORRECTION QUANTITATIVE HIGH RESOLUTION TEM (HRTEM) ENERGY FILTERED TEM ELECTRON HOLOGRAPHY

3 Spectra from the Microcalorimeter Energy Dispersive X-Ray Spectrometer of a layered semple using 5kV excitation voltage (From DEL REDFERN et al. 2002)

4 (From DEL REDFERN et al. 2002) Spectra of a BN sample acquired using the Microcalorimeter EDS system

5 (From C. MITTERBAUER et al. 2002) The experimental spectra of the Ti L2,3 edge in rutile a: CM20 (200 kv, LaB6); b: STEM-PEELS-system (60 kv, FEG);

6 Fe L 23 edges from the pyroxene solid solutions hedenbergite-acmite, hd-ac. The spectra have been normalised to the integral Fe L 23 white-line intensity, and some of the spectra have been shifted vertically for clarity. The Fe L 23 white-line maxima are located at ev and ev for Fe 2+ (hd 100 ) and Fe 3+ (ac 100 ), respectively. The Fe 3+ /ΣFe ratios are data from literature. (From P.A. VAN AKEN 2002)

7 SE images of the same area of a contaminated Si wafer obtained with an electron landing energy of: 500 ev SE images of the same area of a cleaved HOPG sample obtained with an electron landing energy of: 500 ev 11 ev 7 ev 3 ev 3 ev (From JINGYUE LIU 2002)

8 SPM-SEM SEM

9 Characteristics of Common Microscopic Techniques for Imaging and Measuring Surface Morphology

10 SPM GENEALOGIC TREE

11 History : young technique Invention of Scanning Tunneling Microscopy (STM) Developped in 1982 by Binnig, Rohrer,Gerber, et Weibel at IBM, Zurich Binnig & Rohrer have received Nobel in 1986 Invention of Atomic Force Microscopy (AFM) : - Developped in 1986 by Binnig, Quate, et Gerber in between IBM and Standford University

12 AFM Principio di funzionamento simile a quello di un profilometro op amp fotorivelatore V ref diodo laser computer campione cantilever piezoelettrico la forza tra la punta e la superficie del campione varia tra 10-5 e N

13 AFM AFM measures interactions between probe and surface Topography is obtained by keeping constant interaction Applicable to both non and conductor samples Applicable in vacuum, air, controlled atmosphere or liquid Lateral resolution: tip dependant (few nanometer) or up to «atomic resolution» Vertical resolution: noise limited ~ 0.03 nm RMS

14 AFM I vantaggi: Elevata risoluzione spaziale Possibilità di lavorare: -inaria - in liquido - sotto vuoto Osservazione di campioni biologici in ambiente fisiologico senza alterazione della struttura

15 AFM I vantaggi: elevata risoluzione spaziale Muscovite Risoluzione atomica del piano basale degli ossigeni Immagine della muscovite dopo attacco acido in HF al 50% per 4 ore; si noti la presenza di gradini di 1 nm in corrispondenza della periodicità interstrato lungo z. La risoluzione in z è di frazioni di Angstrom

16 AFM Il cantilever nitruro di silicio lungo 115 µm / 193 µm, largo 20 µm spesso 0,6 µm K (spring constant N/m) stretto largo 6 µm per contact mode

17 AFM Il cantilever per tapping mode 750 µmlung. 200 µmlarg. 5 µm spess. Immagine al SEM di un cantilever in silicio frequenza di risonanza 300 khz costante di forza 40 N/m

18 AFM La punta 20 µm r θ h (h) altezza (r) raggio di curvatura apicale valori tipici: nm (θ) valore di metà angolo di apertura definisce la possibilità di osservare campioni con pareti quasi verticali

19 AFM La punta IBM super cone Olympus Monocristalline silicon probes and cantilevers Conic or pyramidal shape with apex radius emcompassed between 5-10 nm Cantilever length : µm Resonance frequency : 50 et 400 khz Various probe for specific application BUT really fragile

20 ELECTRON BEAM DEPOSITED TIP Raggio di curvatura 5 nm

21 r 5 nm a r 50 nm b b R C1 R C2 2R m r 10 nm W 1 Schema delle dimensioni apparenti di un cilindro (supposto incompressibile) ottenute con due punte di diverso raggio di curvatura apicale. W 2 Immagini SEM di un cantilever in nitruro di silicio con punta integrata (a), e di una punta in silicio integrata su un cantilever in silicio (b).

22 Funzionalizzazione delle punte

23 AFM Funzionalizzazione può essere: - FISICA cambia la geometria della punta - CHIMICA legame di gruppi chimici (gruppi funzionali, idrofobicità, idrofilicità) - BIOLOGICA Ligando-Recettore (es. Antig./Antic.) MOLECOLA-CELLULA CELLULA-CELLULA FORZE INTRAMOLECOLARI

24 R C1 R C2 2R m W 1 W 2

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26 Realizzazione di un monolayer 1 mm 1-HEXADECANETHIOL -CH3 o Soluzione di: 1 mm 11-MERCAPTOUNDECANOIC ac -COOH In etanolo puro Per 24 ore

27 -COOH -CH 3 -NH 2

28 AFM Imaging Modes Contact Mode Intermittent Mode Non Contact Mode

29 AFM Contact Mode Constant Force Mode piezo t Constant Height Mode piezo t

30 AFM Contact mode Applications: Atomic and molecular résolution Force curves Friction measurement (Lateral Force Microscopy) Electrochemistry

31 AFM

32 AFM Deformazione del cantilever Longitudinal deflection Longitudinal torsion Transversal torsion Laser diode A C B D Photodetector B A Deflection (A+B) - (C+D) Torsion (A+C) - (B+D) cantilever

33 AFM Friction Friction causes twist of cantilever causing lateral deflection Twist is proportionnal to friction force. Scanning at 90, vertical deflexion (A+B)-(C+D) ensures topography description and constant force while torsion is recorded in mean time thanks to (A+C)-(B+D).

34 AFM Friction Mixe of natural ealstomer and EDPM

35 Cella liquida AFMLa CELLA LIQUIDA

36 AFM Contact mode under liquid

37 AFM Calcium Hydro Silicate growth and evolution under liquid Equilibrium - long time equilibrium gives rise to recrystallization - atomically flat domains

38 AFM Force curves XY motion is shut down while Z undergoes regular oscillations Deflection versus Z motion of piezo Applications : measure of force applied, adhesion, surface chemistry, colloïdal science, hardness.

39 AFM Colloidal science: Calcium hydro silicate

40 AFM Nanoindentation Topography of polyethylene HD et LD Section along indents made by diamond probe

41 AFM Tapping Mode

42 AFM Advantages: Intermittent contact = quite no adhesion nor friction (compare to ShFM) High lateral resolution thanks to sharp tip analyze soft matter (polymers, biological samples) Precise control of tip/surface interactions Most popular mode in AFM

43 Force Volume Phase imaging Lift Mode Various examples and applications

44 Deflessione Deflessione del cantilever C B A Curva di forza A B C D E D E Distanza Z Posizione z A- Il cantilever non tocca la superficie del campione e non sente alcuna forza per cui non c è alcuna deflessione. B- Avvicinando la punta al campione, essa salta a contatto con il campione stesso quando sente una sufficiente forza attrattiva. C- Una volta che la punta è in contatto con il campione aumenta la deflessione del cantilever di pari passo con gli spostamenti del piezoelettrico. D- Dopo aver raggiunto una forza stabilita il processo viene invertito. Durante l allontanamento l adesione o i legami formati durante il contatto fanno sì che la punta aderisca al campione fino ad una distanza superiore al precedente punto di contatto (isteresi). E- A questo punto viene rotta l adesione e il cantilever si trova libero dalla superficie. La misura di questa distanza di rottura è un elemento molto importante nelle curve Forza-Distanza.

45 AFM Force Volume

46 Consideriamo lo spazio al di sopra della superficie come una regione, detta VOLUME DI FORZA, attraverso la quale la sonda si muove ed interagisce con il campione FORCE VOLUME è una tecnica che permette di determinare la distribuzione spaziale di tali forze: consiste nel registrare una serie di curve di forza in una matrice bidimensionale di punti su una superficie Ciclo di avvicinamento-allontanamento effettuato per ogni punto Deflessione del cantilever C B A D E Posizione z

47 Un insieme di dati di una immagine in mappe di forze è rappresentato da una raccolta di curve di forza per ogni punto della superficie su cui si effettua la scansione. Tutti i dati sono quindi raccolti in una matrice 3x3.

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49 64 pixel x 64 line 64 pixel x 64 line N porzione nucleare, più soffice (4 kpa circa) P zona di maggior concentrazione di microtubuli Fibroblasto vivente (NIH3T3) da H. Haga 2000

50 AFM Phase imaging Tapping mode operation Recording of both topography and phase Phase imaging permits to get information on local dissipation properties (viscoelasticity, friction, adhesion ) Phase signal is sensitive toward any tip/surface interaction

51 AFM Lift Mode Main pass permits to record topography Second pass permits to maintain constant tip/surface separation During this second pass, tip is only sensitive to long distance force like electrical or magnetic force It permits to detects electric or magnetic fields thanks to phase signal

52 AFM Lift Mode: EFM Electric Field Microscopy: measures the electric fields at the surface Example : piezoelectric ceramic Before manipulation after DC = +7V after DC = -7V in central area in small central area

53 AFM Electrical characterization: : SCM AFM (Scanning Capacitance Microscopy) While probe is scanning in contact mode, local capacitance is recorded. Information on dopant concentration (10e15 to 10e20 dopants/cm3) with lateral resolution around nm.

54 AFM (Scanning Capacitance Microscopy) C-V & Polarization spectra can be obtained by integration of the SCM dc/dv dv spectrum

55 AFM Electrical characterization: : TUNA AFM (Tunneling AFM) While probe is scanning in contact mode, local tunneling current is recorded. Information on dielectric thikness.

56 AFM TUNA on Oxidized Zirconium TUNA current (3 pa scale) Topography (20 nm scale)

57 EFM (lift mode) biased aluminium strips

58 EFM of RuO2 in glass matrix

59 MFM and TEM of Co nanocrystals

60 MFM of Co magnetic cross-ties

61 MFM (a) and TEM-Lorentz (b) of Magnetization ripples from the same magnetic domain of nanocrystalline Cobalt

62 Funzionalizzazione della mica

63 ESEMPI di ALTA RISOLUZIONE in CONTACT MODE Phlogopite

64 Clintonite

65 Shear Force Microscopy

66 SHFM Shear Force Microscope Schematic diagram of the TDFM. The optical head contains the vertical probe (9), two orthogonal piezoelectric elements (5) and two optical detection systems (diode laser (1), polarizer (2) focusing lens (3), split photodetector (4)). To avoid cross talking between the detectors cross-polarizers (2) are employed. The sample (8) is mounted on the piezotube (6) in the microscope base and can be accurately positioned with respect to the probe by using an XY translation stage (7). Three screws (not shown) adjust the vertical position of the optical head. Two digital lock-in amplifiers excite and detect the oscillation of the probe and provide the true amplitude to the controller for the electronic feedback loop.

67 SHFM The damped harmonic oscillator model gives the following relations between, oscillation amplitude (u) and phase (θ) on one side, and resonant frequency (ω 0 ) and quality factor (Q) on the other: By inverting equations it is possible to express the resonant frequency and the quality factor as a function of the two measured d u(ω 0,Q) = 0 ω 2 (ω 2 0 ω 2 ) 2 + (ω 0 ω /Q) 2 θ(ω 0,Q) = arctan ω 0ω /Q ω 2 0 ω 2 quantities u and θ. Figure 5 shows their values at different tipsample separation for the curves displayed in figure 3. In the experiment the probe was driven at a frequency and the driving amplitude d 0 was obtained by fitting the frequency spectrum of the probe when it was already in liquid and only a few nanometers away from the surface (data not shown). The spring constant of the glass probe is around 1.0 nn/nm ± 10%. The effective mass of the probe can be calculated considering that. The quality factor is related to the dissipative coefficient α by the relation. The viscous (F α ) and the elastic (F k ) forces, due to the confinement of the OMCTS, can be calculated by inserting the values of ω 0 and Q from figure 5 in the following equations: 2 F k = αω 0 u = M eff uω 0 F α = ku = M eff uω 0 ω Q G'= z F k A u G"= z F α A u where u is the oscillation amplitude of the probe at different tip-sample separations, as in figure 3. It has to be noted that, in order to isolate the contribution to the two forces of the confined molecules, the effect of the bulk liquid and the intrinsic elasticity of the probe have to be subtracted. This means that the viscous and the elastic constants will have each two components: one when the probe is far from the surface (more than 10 molecular diameters) and one due to the the confinement. A further step to characterize the elastic and viscous response of the confined liquid is the introduction of the storage modulus G and the loss modulus G. They are related to the quantities in equation (2) by the following equations:

68 SHFM Amplitude approach curve acquired in pure water over a freshly cleaved muscovite surface. The steps present in the curves are a manifestation of the molecular layering of water in the confined space between the probe and the muscovite surface. The dotted vertical lines have been drawn to guide the eyes and have a periodicity of 0.23 nm. This value is within 10% of the diameter of the water molecule.

69 SHFM Amplitude (black curve) and phase (grey curve) approach curves for OMCTS. The dashed lines are at a distance of 0.9 nm that is the diamter of the OMCTS molecule, and are drawn to emphasise the periodicity of the original data. It is interesting to notice that, close to the surface, the phase signal has a better signal-to-noise ratio than the corresponding amplitude signal.

70 SHFM Fast Fourier Transform of the amplitude curve shown in figure 3. The curve is plotted against spatial periodicity (high frequencies are on the left part of the graph) to simplify the measurement of periodic components. The peak at 0.9 nm is a confirmation that the steplike behaviour in figure 3 has indeed a periodicity very close to the diameter of the OMCTS molecule.

71 SHFM The data in figure 3 have been analysed using equation (1) and the resultant quality factor (black curve) and resonant frequency (grey curve) plotted. The step-like behaviour of the original data is maintained in these graphs but the noise level is increased due to the analysis process. The decrease of the quality factor with the confinement is a clear indication of an increased viscous interaction, whereas the increase in resonant frequency can be explained with a larger elastic force. The storage modulus G (grey curve) and the loss module G (black curve) are plotted versus tip/muscovite distance. These two quantities are used to determine intrinsic viscoelastic properties of the confined OMCTS. It is interesting to notice that the two curves cross each other when the film thickness is around three layers indicating a change from a viscous to a more elastic behaviour at high confinement.