Generation and detection of photo-thermal and photo-acoustic waves in solids for advanced near-field IR imaging

WP1: Environmental Sensing

Recruiting Host
Technische Universität Wien

Vienna, Austria


Dr. Georg Ramer

Cork Institute of Technology

Cork, Ireland


Dr. Stephen Hegarty

Proposed Secondments
Anton Paar GmbH


AVL List GmbH


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.

Expected Results

  • 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


M0 M12 M24 M36 Time at Recruiting Host Time at Co-Host Time on Secondment

* N.B. Secondments and timings shown are indicative only, and may be subject to change.