nano-ftir: Material Characterization with Nanoscale Spatial Resolution

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1 neaspec presents: neasnom microscope nano-ftir: Material Characterization with Nanoscale Spatial Resolution AMC Workshop th of June Dr Tobias Gokus

2 Company neaspec GmbH leading experts of nanoscale near-field microscopy Spin-off in 2007 from Max-Planck-Institute of Biochemistry in Martinsried (Munich, Germany) Founded by the pioneers of infrared spectroscopy: Dr. Fritz Keilmann (LMU Munich) Prof. Rainer Hillenbrand (Nanogune, San Sebastian) 03/2013: attocube systems AG acquires majority of neaspec GmbH Cutting-edge solutions for nanoscale optical imaging and spectroscopy Highly experienced employees supporting >80 installed systems worldwide Patented near-field background suppression technologies for outstanding performance

3 neasnom enables optical imaging and spectroscopy at the nanoscale in a diverse array of applications neasnom OH nano-ftir Ultrabroadband Plasmonics Time-domain spectroscopy Ultrafast Pump-probe Low temperature vacuum THz fs

4 Technology Optical (Infrared) spectroscopy is a highly sensitive too for materials research IR is highly sensitive to: Molecular vibrations Chemical composition Crystal lattice vibrations Structural properties Plasmons in doped semiconductors Electron properties but in conventional microscopy techniques the spatial resolution is limited to /2 (IR ~ 5-10µm)

5 scattering-type Scanning Near-field Optical Microscopy employs a nanofocus for near-field measurements Technology A focused laser-beam illuminates a commercially available AFM tip 1 The tip confines the incident light to a nm-large nanofocus 2 1 The near-field interaction between the tip and the sample modifies the elasticallyscattered light 3 nanowire By scanning the sample surface with the tip, an optical image with 10 nm spatial resolution is recorded

6 scattering-type Scanning Near-field Optical Microscopy employs a nanofocus for near-field measurements Technology A focused laser-beam illuminates a commercially available AFM tip nanowire 2 The tip confines the incident light to a nm-large nanofocus 2 The near-field interaction between the tip and the sample modifies the elasticallyscattered light 3 By scanning the sample surface with the tip, an optical image with 10 nm spatial resolution is recorded

7 scattering-type Scanning Near-field Optical Microscopy employs a nanofocus for near-field measurements Technology A focused laser-beam illuminates a commercially available AFM tip nanowire 2 The tip confines the incident light to a nm-large nanofocus 2 The near-field interaction between the tip and the sample modifies the elasticallyscattered light 3 By scanning the sample surface with the tip, an optical image with 10 nm spatial resolution is recorded s-snom measures the near-field optical interaction between tip and sample which is determined by the refractive index of the sample

8 Technology Tip-scattered near-field contains information about the local dielectric properties of the sample material E scat scat E in Scattering coefficient contains material specific information about the sample: E in Tip Dipole p scat w E E scat in ( w) 1 ( w) 1 (w) = complex valued dielectric function of the sample Image Dipole p' 1 p 1 s-snom signal is highly sensitive to B. Knoll, F. Keilmann, Nature 399, (1999) R. Hillenbrand, F. Keilmann, Phys. Rev. Lett. 85, (2000) A. Cvitkovic et al., Opt. Exp. 15, 8550 (2007) changes of the dielectric properties

9 Interferometric detection of scattered light enables high-performance near-field imaging and spectroscopy (nano-ftir) Technology Interferometric detection and analysis enables amplitude and phase resolved optical measurements (reflection and absorption) Single frequency laser (cw, pulsed) a) near-field imaging - vis/nir (diode lasers) - MIR (QCLs) - THz (gas laser, QCLs) b) spectroscopy by laser tuning - point spectroscopy (s-snom) - Photo Thermal Expansion (PTE+) spectra* *PTE+ not available in the USA nano-ftir (broadband light sources) a) supercontinuum (vis, NIR) b) mid-ir broadband laser c) THz-TDS d) IR beamlines of synchrotrons S. Amarie, F. Keilmann, Phys. Rev. B 83, (2011) F. Huth, et al., Nature Mater. 10, 352 (2011)

10 Technology neasnom employs interferometric near-field detection for near-field spectroscopy (nano-ftir) nw Interferogram I(d) Mid-IR broadband laser Detector BS AFM- Cantilever W d RM mid-ir laser output spectra Reflection & Absorption spectra Amplitude s n FFT nano-ftir spectra of PMMA Reflection Phase j n Absorption

11 Technology neasnom enables 2D near-field imaging (chemical mapping) with reflection & absorption information Interferometric detection Topography 53nm W 1µm 0nm Daylight solutions Reflection PS max PMMA min Absorption max Scan parameters: w=1740cm -1 (λ=5.75µm) Time constant (Lock-In): 0.52ms min

12 Application nano-ftir measures material-specific spectroscopic signatures of PS and LDPE Topography 1µm 40nm 0nm WL image x x x max min nano-ftir Reflectivity [a.u.] PS Spectrally integrated image (White Light image, WL) exhibits ponounced contrast between Polystyrene (PS) and LD- Polytethylene (LDPE) Note: spectra are offset for clarity LDPE nano-ftir absorption spectrum on matrix shows characteristic PS signature with 1460cm -1, 1500cm -1 and 1600cm -1 lines nano-ftir Absorption [ ] PS LDPE absorption line at ~ 1480cm cm -1 demonstrates <1 phase sensitivity of nano-ftir Note: spectra are offset for clarity LDPE

13 Topography Application AFM phase neasnom near-field imaging at selected frequencies verifies pure optical contrast for detected phase separation 40nm Near-field phase Near-field amplitude 1467cm cm cm -1 max 2µm 0nm min max min Near-field imaging at 1600cm -1 shows strong contrast between matrix and inclusions unmatched material contrast and S/N for ~1 absorption line of PS Off-resoncance image at 1710cm -1 does not reveal any amplitude and phase contrast for measured polymers

14 IR Absorption Nano-FTIR Absorption Comparing nano-ftir and conventional far-field IR Application Im [ ] C-O C=O nano-ftir (60nm PUR film) 20 nm radius area PUR E sca = σ(w)e inc E inc Si Far-field IR-Microscopy E inc 10 mm radius area ATR Microscopy E det PUR nano-ftir absorbance directly correlates with far-field absorbance

15 position [nm] Application nano-ftir spectroscopy along an ultrasharp polymer interface verifies nanoscale resolved FTIR spectroscopy Topography nano-ftir Absorption 500nm PMMA PC PMMA PC 40nm 0nm 100nm Spectral linescan across PMMA/PC interface nano-ftir spectra reveal characteristic signature of PMMA and PC Spatial resolution: Transition from PMMA (1730cm -1 ) to PC (1506 and 1780cm -1 ) occurs within less than 50nm spatial extension

16 Application Integrated optical microscope outlines sample area on a human hair Internal brightfield microscope allows do identify suitable sample locations at spatial resolution < 1µm Characteristic surface structure of hair cuticles is clearly visible 20µm Important note: small focal depth of integrated microscope allows to focus only smaller regions on hair surface and cantilver appears blurred.

17 Application nano-ftir reveal local changes of characteristic hair IR absorption spectrum at selected locations µm 80 Nano-FTIR Absorption [ ] 10cm -1 spectral res., 5 spec. averaging, no filtering, < 2 min/spec Amide II Amide I Topography 10µm 0nm 5 Integr. near-field amplitude max min nano-ftir spectra show chararacteristic absorption signatures (Amide I +II) similar to farfield FTIR Excellent reproducability (spectra 1+2); Small variation at selected locations (spectra 3+4) Red spectrum indicates additional lipid signature FTIR Absorption* [a.u.] Wavenumber [cm -1 ] * representative literature spectrum

18 Application nano-ftir hyperspectral imaging of hair cross section reveals micron-sized melanin inclusions Hair cross section: Hair cross section: nanoscale IR imaging at 1660cm -1 reveals isolated ca. d=300nm dark islands at 1660cm -1 in cortex region 1µm nano-ftir verifies inclusions as melanin-rich areas Hair cross section: nanoscale IR imaging at 1660cm -1 reveals disk shaped ca. d=300nm dark areas at 1660cm -1 in cortex region nano-ftir verifies inclusions as melanin-rich areas I. Amenabar, et al., Nature Comm. 8, (2017)

19 Application nano-ftir hyperspectral imaging of hair cross section reveals micron-sized melanin inclusions nano-ftir hyperspectral imaging with full spectroscopic signature at every pixel of imaged area Analysis of spectral signatures enables to identify - pure cortex/keratin areas (C) - pure melanin areas (A) - mixed phase (B,D) Mulitvariate data analysis reveals three clusters of materials (segmentation map) Melanin (M) c 1 *M + c 2 *K Keratin (K) I. Amenabar, et al., Nature Comm. 8, (2017)

20 Application IR undoped W P1 n-type Near-field amplitude A B Au s-snom can directly measure the local carrier densities in nanoparticles/-wires =11.2 µm B * C P2 1 µm Topography Near-field phase P1 A B B * C P2 InP nanowires with modulation in doping concentration Center segment features highly conductive properties at 11.2µm wavelength Detection of doping gradient between adjacent sections Contact-free determination of doping concentration from near-field scans Mid-IR s-snom is sensitive to free charge carrier concentrations between ca cm -1 J. M. Stiegler et al., Nano Lett. 10, 1387 (2010)

21 Application Direct observation of propagating surface plasmon polaritons on graphene First-time, real-space observation of propagating surface plasmon poloraitons (SPP) on graphene using the neasnom microscope Plasmon interference detection enables direct read-out of plasmon wavelength and dispersion Extraction of local material properties, e.g. conductivity, intrinsic doping, defects, λ 0 = 9.68 mm Direct control of propagating surface plasmons on graphene via refractive index of substrate, gate voltage and excitation wavelength λ 0 = mm J. Chen et al., Nature 487, 77 (2012) Z. Fei et al., Nature 487, 82 (2012)

22 Application neasnom enables screening of graphene quality via plasmon interference mapping Visualizing defects: Reflection of propagating plasmons at grain boundaries, substrate edge, wrinkles, etc. => characteristic interference pattern identifies graphene defects Analysis of SPP interference allows quantification of Graphene properties at defect (i.e. mobility, Fermi level, etc.) Large area characterization of graphene crystal quality Z. Fei et al., Nature Nano. (2012) 8, 821 J. Chen et al., Nano Lett. (2013) 13, 6210

23 Recent Highlights nano-ftir is a powerful optical microscopy technique for nanoscale material characterization Nanowires Nanoparticles Mineralogy Plasmonics Semiconductors Polymers 2D Materials Life Sciences Catalysis Composites

24 Recent Highlights nano-ftir is a powerful optical microscopy technique for nanoscale material characterization Nanowires Nanoparticles Mineralogy Plasmonics Semiconductors Thank you for Polymers 2D Materials your attention! Life Sciences Catalysis Composites

25 Visit the neaspec homepage for more information about applications and a continuously up-dated list of customer publications neaspec GmbH Bunsenstr Martinsried (Munich) Germany phone: fax: