Resonant imaging mode

In our tip-enhanced near-field CARS microscopy, two mode-locked pulsed lasers (pulse duration 5ps, spectral width 4cm ) were used for excitation of CARS polarization [21]. The sample was a DNA network nanostructure of poly(dA-dT)-poly(dA-dT) [24]. The frequency difference of the two excitation lasers (cOi — CO2) was set at 1337 cm, corresponding to the ring stretching mode of diazole. After the on-resonant imaging, CO2 was changed such that the frequency difference corresponded to none of the Raman-active vibration of the sample ( off-resonant ). The CARS images at the on- and off- resonant frequencies are illustrated in Figure 2.8a and b, respectively. 

The dynamic imaging mode can be further classified into two subcategories intermittent contact mode (also known as tapping mode) and noncontact mode. In both techniques, the AFM tip is attached to the end of an oscillating cantilever. For the intermittent contact technique, the cantilever is vibrated near its resonance frequency. The amplitude of the oscillation is typically 100-200 nm with the tip intermittently contacting... 

K.B. Ghaghada, et al.. New dual mode gadolinium nanoparticle contrast agent for magnetic resonance imaging, PLoS One 4 (10) (2009) e7628. 

To circumnavigate the problem of dragging poorly immobilized specimens across the substrate and/or the potential damage of debcate samples, alternative imaging modes were subsequently developed. The first of these was termed non-contact mode. In this mode the cantilever is oscillated above the surface at its resonant frequency, with... 

The AFM imaging mode that holds out greatest hope for seeing such differences in local properties is phase imaging, in which the change in phase of the tapping cantilever s response relative to the drive phase is monitored. Unfortunately, as the cantilever is driven at resonance, the contact with the sample surface is intermittent, the shape of the AFM tip and hence the con-... 

A popularly employed imaging mode for biological samples is the intermittent contact mode (also oscillating or tapping mode). In this mode, lateral force components are eliminated by oscillating the AFM tip above the sample surface, so that the tip only directly touches the surface vertically and at the minimum of its oscillation amplitude. Oscillation is mediated via piezo contacts and is applied close to the resonance... 

The three-dimensional nature of the helical pattern was studied by Manz et al. using magnetic resonance imaging (MRI) [102]. Pojman etal. observed zigzag modes in square reactors [103] and bistability in conical reactors [104]. 

Static deflection AFM can be used to measure local mechanical properties of polymer surfaces, but only after consideration of the relative stiffness of the cantilever and the surface under study. Cantilevers with stiffness in excess of 50 N/m are necessary to indent materials with a bulk modulus in excess of 1 GPa (10 N/m ). Soft levers with a spring constant less than 1 N/m are sufficient to indent elastomers. Conventional staining techniques used in electron microscopy provide a viable way to harden unsaturated, hydrocarbon elastomers for imaging with soft cantilevers. Alternatively, low bulk modulus polymers (E < 1 MPa or 10 N/m ) require resonant imaging techniques such as Tapping Mode for direct imaging. 

Figure 5.2 Examples of mass spectra collected under high-mass resolution conditions over (a) the 55.90-56.10 miq range from a Silicon wafer on a Time-of-Flight (TOF)-based SIMS instrument (Supplied by Physical Electronics), (b) the 39.962-39.966 mIq range from an Adularia mineral sample on two different IMS-1280 Magnetic Sector-based SIMS instruments (care of Cameca), and (c) the 368-372 m/q range from a rat brain section on a TOF-based SIMS instrument in imaging mode (this affects mass resolution as covered in Section 5.3.2.1.2) overlaid with that from a Fourier Transform-Ion Cyclotron Resonance (FT-ICR)-based SIMS instrument. Reproduced with permission from Smith et al. (2013) Copyright 2013 Springer.

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