Generation and detection of photo-thermal and photo-acoustic waves in solids for advanced near-field IR imaging
The objective of this project is to gain a deeper understanding of the process of emergence and propagation of photothermal and photoacoustic signal waves and using this knowledge for sensor optimisation. In particular, new transducers for near-field IR imaging based on using an atomic force microscope (AFM) coupled to a pulsed tunable mid-IR laser shall be designed and produced at CIT and tested at TU-WIEN. This ESR will use the techniques of integrated photonics to build a nanophotonic AFM transducer for use in combined atomic force microscopy and infrared spectroscopy (AFM-IR), enabling nanoscale spatial resolution chemical imaging. In AFM-IR, when the sample absorbs a light pulse it heats up and expands inducing vibrations in the AFM cantilever (like a struck tuning fork) with amplitudes directly proportional to the absorption coefficient of the sample.
The AFM-IR system at TU-WIEN will be operated in the photothermal induced resonance mode for generating and detecting thermal and acoustic waves. The details of the process by which photothermal and photo-acoustic waves are generated and propagate is, surprisingly, not yet well understood in the literature. This understanding is crucial for further development of the technique and the ESR will make a numerical treatment of the process by which pressure and thermal waves are produced in gases, liquids and solids.
Recent advances in AFM tip design have enabled monolayer sensitivity AFM-IR spectroscopy as well as nanoscale thermal conductivity analysis. However, these tips have several draw backs that are detrimental to their routine use: 1. low lateral stiffness leading to sub-par imaging; 2. low dynamic range making destruction through normal use likely; 3. IR absorbing tip restricting the use to bottom illumination attenuated total reflection mode imaging.
This project aims to improve on all these parameters, through a new design paradigm based on integrated optics for highly sensitive AFM tips. The tip will have sub 1 N/m spring constant to enable contact mode imaging, as well as a high first resonance frequency in contact (>1 MHz). At TU-WIEN, a high speed data acquisition system will be used to perform AFM-IR chemical spectroscopy and imaging of heat conductivity as well as spectroscopy.
- Formulation of equations
- Numerical modelling of thermal and acoustic waves
- Realisation of a nanophotonic transducer for AFM-IR
- Validation of the model using experiment
- Validation of the new tips on a Bruker NanoIR3s system with dedicated fast readout electronics
* N.B. Secondments and timings shown are indicative only, and may be subject to change.