We demonstrate a technique in microscopy which extends the domain of atomic force microscopy to optical spectroscopy at the nanometer scale. We show that molecular resonance of feature sizes down to the single molecular level can be detected and imaged purely by mechanical detection of the force gradient between the interaction of the optically driven molecular dipole and its mirror image in a platinum coated scanning probe tip. This microscopy and spectroscopy technique is extendable to frequencies ranging from radio to infrared and the ultraviolet.

The Raman effect is typically observed by irradiating a sample with an intense light source and detecting the minute amount of frequency shifted scattered light. We demonstrate that Raman molecular vibrational resonances can be detected directly through an entirely different mechanism-namely, a force measurement. We create a force interaction through optical parametric down conversion between stimulated, Raman excited, molecules on a surface and a cantilevered nanometer scale probe tip brought very close to it. Spectroscopy and microscopy on clusters of molecules have been performed. Single molecules within such clusters are clearly resolved in the Raman micrographs. The technique can be readily extended to perform pump probe experiments for measuring inter-and intramolecular couplings and conformational changes at the single molecule level. The Raman effect 1 is one of the most widely used phenomenon in chemical spectroscopy. Over the past 80 years, this effect has been measured by irradiating the sample with intense monochromatic light and detecting the minute amount (one part in 10 9 ) of frequency shifted scattered light. A typical Raman setup utilizes a high rejection, low insertion loss, long pass filter to reject the incident pump light. This is followed by a sensitive detector coupled to a high resolution spectrometer to record the molecular vibrational spectrum. We present initial results on an entirely different mechanism for detecting the Raman effect. It is based on the force interaction between a Raman excited molecule and a scanning probe microscope probe tip. The ability to measure the Raman effect using a non-optical channel is important because the weak Raman signal can be detected in zero optical background, providing similar sensitivity advantages to that offered by photoacoustic spectroscopy. 2 Furthermore, since we do not need a spectrometer for the measurement, the resolution of the technique can be improved by several orders of magnitude as compared with conventional techniques, since it is only limited by the spectral bandwidth of the lasers used and not by the spectrometer resolution; for diode lasers, this bandwidth can be as narrow as 100 kHz. We present images from our Raman Probe Force Microscope of molecular clusters where single molecules can be discerned within them due to their orientation differences.The concept of our scheme can be understood by referring to Figure 1. Two collinear optical beams-a pump beam at frequency m 1 and a stimulating beam at frequency m 2 -are focused to a diffraction limited spot on the sample surface to efficiently stimulate molecular vibrations at frequency (m 1 À m 2 ). The stimulating beam at frequency m 2 is tunable, allowing (m 1 À m 2 ) to be tuned through the various Raman vibrational resonances. We probe the force interaction between the excited oscillating molecules and a cantilevered, gold coated, scanning probe microscope tip approached within nm range of the sample surface as the force interaction is modulated at frequency f m . The force ...

Nonlinear dynamics underpin a vast array of physical phenomena ranging from interfacial motion to jamming transitions. In many cases, insight into the nonlinear behavior can be gleaned through exploration of higher order harmonics. Here, a method using band excitation scanning probe microscopy (SPM) to investigate higher order harmonics of the electromechanical response, with nanometer scale spatial resolution is presented. The technique is demonstrated by probing the first three harmonics of strain for a Pb(Zr1-xTix)O3 (PZT) ferroelectric capacitor. It is shown that the second order harmonic response is correlated with the first harmonic response, whereas the third harmonic is not. Additionally, measurements of the second harmonic reveal significant deviations from Rayleigh-type models in the form of a much more complicated field dependence than is observed in the spatially averaged data. These results illustrate the versatility of nth order harmonic SPM detection methods in exploring nonlinear phenomena in nanoscale materials.

We demonstrate a method for engineering substrates for surface enhanced Raman spectroscopy (SERS) by Ag− ion implantation in Si. The implantation dose and beam current density are chosen such that the Ag concentration in Si exceeds the solid solubility limit, causes aggregation of Ag and nucleates Ag nano particles. The embedded nano particles are then partially exposed by a wet etch process. Our measurements show that the so fabricated nano‐composite substrates are very effective as stable and reproducible SERS substrates. Copyright © 2013 John Wiley & Sons, Ltd.