Tips and Calibration of Nearfield Scanning Microscope Johannes

Tips and Calibration of Nearfield Scanning Microscope Johannes Hoffmann#1, Toai Le. Quang#1, Denis Vasyukov#1, Markus Zeier#1 #1 RF & Microwave Lab, Federal Institute of Metrology METAS Johannes. Hoffmann@metas. ch

Outline • Introduction to SMM • Standard Operating Procedure • Calibration • Coaxial Tip

Introduction to SMM RF VNA Impedance Match Tuning Fork Probe Sample • Tuning fork is sensor force tipsample • Impedance match transfers high Z to 50 Ohm • Reflection coeficient measured by VNA depends on material under tip

Introduction to SMM Subsurface imaging Plassard et al. , PRB 83 (2011) 121409(R)

Introduction to SMM Magnetic Domain Wall Imaging Ma et al. , Science 350 (2009) 538

Standard Operating Procedure General: • Lab environment stable • No vibrations, no sound • Dry atmosphere • Clean HF connectors • Short cables • No cable movement

Standard Operating Procedure Measurement • Switch on equipment for long time before measurement • Inspect sample under SEM or microscope • Check tip status SEM Photo: IEMN

Standard Operating Procedure Measurement • Test electrical sensitivity on known sample • Log metadata (sample name, measurement freq, …)

Standard Operating Procedure Data • Uncalibrated reflection in real and imaginary • Topography • Phase, disipation, excitation amplitude • Check cross talk topography - electrical signal Topography Phase(S 11)

Calibration S 11 m e 01 1 Connection e 00 VNA e 11 SMM tip S 11 Sample, Ztip •

Calibration problems: • Small impedance space for typical samples • Valid only on sample because of stray field E-field

Calibration Metas Calibration Sample b

Calibration Metas Calibration sample production Required clean room activities: • • • Material deposition E-beam+laser lithography Dry+wet etching

Calibration Metas Cal sample customization

Coaxial Tip Advantages of coaxial tip Coaxial tip log 10 ( V/m ) Full metal tip Field concentrated under the tip, measurement unaffected by the sample geometry

Coaxial Tip METAS Tip fab 1. 2 mm quartz capillary Au coating 25 µm Pt wire Tip production steps 1. Pull capillary with wire inside 2. Check tip with SEM 3. Coat outside with Au

Coaxial Tip METAS Tip holder Sketch Tip+TF bottom RF Tip+TF

Coaxial Tip First results approach

Conclusion • SMM technique is becoming more mature and standardized measurement technique is now available • Calibration can be achieved through calibration samples but restricts measurements to sample • Transferable calibration can be achieved with coaxial tip