Assessment of Subsampling Schemes for Compressive Nano-FTIR Imaging

Nano-Fourier transform infrared (FTIR) imaging is a powerful scanning-based technique at nanometer spatial resolution that combines FTIR spectroscopy and scattering-type scanning near-field optical microscopy (s-SNOM). Recording large spatial areas using nano-FTIR is, however, limited, because its sequential data acquisition entails long measurement times. Compressed sensing and low-rank matrix reconstruction are mathematical techniques that can reduce the number of these measurements significantly by requiring only a small fraction of randomly chosen measurements. However, choosing this small set of measurements in a random fashion poses practical challenges for scanning procedures and does not save as much time as desired. We, therefore, consider different subsampling schemes of practical relevance that ensure rapid data acquisition, much faster than random subsampling, in combination with a low-rank matrix reconstruction procedure. It is demonstrated that the quality of the results for almost all subsampling schemes considered, namely, original Lissajous, triangle Lissajous, and random reflection subsampling, is similar to that achieved for random subsampling. This implies that nano-FTIR imaging can be significantly extended to also cover samples extended over large areas while maintaining its high spatial resolution

Centrifugal LabTube platform for fully automated DNA purification and LAMP amplification based on an integrated, low-cost heating system

This paper introduces a disposable battery-driven heating system for loop-mediated isothermal DNA amplification (LAMP) inside a centrifugally-driven DNA purification platform (LabTube). We demonstrate LabTube-based fully automated DNA purification of as low as 100 cell-equivalents of verotoxin-producing Escherichia coli (VTEC) in water, milk and apple juice in a laboratory centrifuge, followed by integrated and automated LAMP amplification with a reduction of hands-on time from 45 to 1 min. The heating system consists of two parallel SMD thick film resistors and a NTC as heating and temperature sensing elements. They are driven by a 3 V battery and controlled by a microcontroller. The LAMP reagents are stored in the elution chamber and the amplification starts immediately after the eluate is purged into the chamber. The LabTube, including a microcontroller-based heating system, demonstrates contamination-free and automated sample-to-answer nucleic acid testing within a laboratory centrifuge. The heating system can be easily parallelized within one LabTube and it is deployable for a variety of heating and electrical applications

Thermoelectric nanospectroscopy for the imaging of molecular fingerprints

We present a nanospectroscopic device platform allowing simple and spatially resolved thermoelectric detection of molecular fingerprints of soft materials. Our technique makes use of a locally generated thermal gradient converted into a thermoelectric photocurrent that is read out in the underlying device. The thermal gradient is generated by an illuminated atomic force microscope tip that localizes power absorption onto the sample surface. The detection principle is illustrated using a concept device that contains a nanostructured strip of polymethyl methacrylate (PMMA) defined by electron beam lithography. The platform's capabilities are demonstrated through a comparison between the spectrum obtained by on-chip thermoelectric nanospectroscopy with a nano-FTIR spectrum recorded by scattering-type scanning near-field optical microscopy at the same position. The subwavelength spatial resolution is demonstrated by a spectral line scan across the edge of the PMMA layer

Nanoscale plasmonic phenomena in CVD-grown MoS2 monolayer revealed by ultra- broadband synchrotron radiation based nano-FTIR spectroscopy and near-field microscopy

Nanoscale plasmonic phenomena observed in single and bi-layers of molybdenum disulfide (MoS2) on silicon dioxide (SiO2) are reported. A scattering type scanning near-field optical microscope (s-SNOM) with a broadband synchrotron radiation (SR) infrared source was used. We also present complementary optical mapping using tunable CO2-laser radiation. Specifically, there is a correlation of the topography of well-defined MoS2 islands grown by chemical vapor deposition, as determined by atomic force microscopy, with the infrared (IR) signature of MoS2. The influence of MoS2 islands on the SiO2 phonon resonance is discussed. The results reveal the plasmonic character of the MoS2 structures and their interaction with the SiO2 phonons leading to an enhancement of the hybridized surface plasmon-phonon mode. A theoretical analysis shows that, in the case of monolayer islands, the coupling of the MoS2 optical plasmon mode to the SiO2 surface phonons does not affect the infrared spectrum significantly. For two-layer MoS2, the coupling of the extra inter-plane acoustic plasmon mode with the SiO2 surface transverse phonon leads to a remarkable increase of the surface phonon peak at 794 cm−1. This is in agreement with the experimental data. These results show the capability of the s-SNOM technique to study local multiple excitations in complex non- homogeneous structures

Compressed sensing FTIR nano-spectroscopy and nano-imaging.

Infrared scattering scanning near-field optical microscopy (IR s-SNOM) provides for spectroscopic imaging with nanometer spatial resolution, yet full spatio-spectral imaging is constrained by long measurement times. Here, we demonstrate the application of compressed sensing algorithms to achieve hyperspectral FTIR-based nano-imaging at an order of magnitude faster imaging speed to achieve the same spectral content compared to conventional approaches. At the example of the spectroscopy of a single vibrational resonance, we discuss the relationship of prior knowledge of sparseness of the employed Fourier base functions and sub-sampling. Compressed sensing nano-FTIR spectroscopy promises both rapid and sensitive chemical nano-imaging which is highly relevant in academic and industrial settings for fundamental and applied nano- and bio-materials research

Terahertz pump-probe experiment at the synchrotron light source MLS

We have developed a pump-probe experiment utilizing broad-band coherent terahertz synchrotron radiation provided by the Metrology Light Source (MLS). The design, performance and first results obtained with the setup are presented

Determination of the Timing Jitter of THz-Synchrotron Radiation by a Cross-Correlation Technique

The objective of this study is to determine the timing jitter of THz synchrotron radiation. The jitter at the beamline is a composition of several instabilities related to the electron beam and the beam optics. By comparing pulses through correlation techniques it is possible to determine the jitter without the need for direct pulse timing measurements

THz autocorrelation measurements at the Metrology Light Source

We have developed a flexible Martin-Puplett Interferometer setup utilizing broad band coherent terahertz (THz) synchrotron radiation provided by the Metrology Light Source (MLS). In order to obtain frequency resolved measurements we combined the Martin-Puplett setup with a Fourier transform spectrometer (FTS). Frequency resolved autocorrelation measurements for beam diagnostics will be presented

Characterization of semiconductor materials using synchrotron radiation-based near-field infrared microscopy and nano-FTIR spectroscopy

We describe the application of scattering-type near-field optical microscopy to characterize various semiconducting materials using the electron storage ring Metrology Light Source (MLS) as a broadband synchrotron radiation source. For verifying high-resolution imaging and nano-FTIR spectroscopy we performed scans across nanoscale Si-based surface structures. The obtained results demonstrate that a spatial resolution below 40 nm can be achieved, despite the use of a radiation source with an extremely broad emission spectrum. This approach allows not only for the collection of optical information but also enables the acquisition of near-field spectral data in the mid-infrared range. The high sensitivity for spectroscopic material discrimination using synchrotron radiation is presented by recording near-field spectra from thin films composed of different materials used in semiconductor technology, such as SiO2, SiC, SixNy, and TiO2