[Show abstract][Hide abstract] ABSTRACT: This paper reports on advances toward quantitative non-destructive nanoscale subsurface investigation of a nanofabricated sample based on mode synthesizing atomic force microscopy with heterodyne detection, addressing the need to correlate the role of actuation frequencies of the probe fp and the sample fs with depth resolution for 3D tomography reconstruction. Here, by developing a simple model and validating the approach experimentally through the study of the nanofabricated calibration depth samples consisting of buried metallic patterns, we demonstrate avenues for quantitative nanoscale subsurface imaging. Our findings enable the reconstruction of the sample depth profile and allow high fidelity resolution of the buried nanostructures. Non-destructive quantitative nanoscale subsurface imaging offers great promise in the study of the structures and properties of complex systems at the nanoscale.
[Show abstract][Hide abstract] ABSTRACT: Among the enduring challenges in nanoscience, subsurface characterization of living cells holds major stakes. Developments in nanometrology for soft matter thriving on the sensitivity and high resolution benefits of atomic force microscopy have enabled detection of subsurface structures at the nanoscale. However, measurements in liquid environments remain complex, in particular in the subsurface domain. Here we introduce liquid-mode synthesizing atomic force microscopy (l-MSAFM) to study both the inner structures and the chemically induced intracellular impairments of living cells. Specifically, we visualize the intracellular stress effects of glyphosate on living keratinocytes skin cells. This new approach, l-MSAFM, for nanoscale imaging of living cell in their physiological environment or in presence of a chemical stress agent could resolve the loss of inner structures induced by glyphosate, the main component of a well-known pesticide (RoundUp™). This firsthand ability to monitor the cell's inner response to external stimuli non-destructively and in liquid, has the potential to unveil critical nanoscale mechanisms of life science.
[Show abstract][Hide abstract] ABSTRACT: With the availability of tunable broadband coherent sources that emit mid-infrared radiation with well-defined beam characteristics, spectroscopies that were traditionally not practical for standoff detection1 or for development of miniaturized infrared detectors2, 3 have renewed interest. While obtaining compositional information for objects from a distance remains a major challenge in chemical and biological sensing, recently we demonstrated that capitalizing on mid-infrared excitation of target molecules by using quantum cascade lasers and invoking a pump probe scheme can provide spectral fingerprints of substances from a variable standoff distance.3 However, the standoff data is typically associated with random fluctuations that can corrupt the fine spectral features and useful data. To process the data from standoff experiments toward better recognition we consider and apply two types of denoising techniques, namely, spectral analysis and Karhunen-Loeve Transform (KLT). Using these techniques, infrared spectral data have been effectively improved. The result of the analysis illustrates that KLT can be adapted as a powerful data denoising tool for the presented pump-probe infrared standoff spectroscopy.
[Show abstract][Hide abstract] ABSTRACT: Single-particle interactions hold the promise of nanometer-scale devices in areas such as data communications and storage, nanolithography, waveguides, renewable energy and therapeutics. We propose that the collective electronic properties possessed by noble metal nanoparticles may be exploited for device actuation via the unapparent mechanism of plasmon-assisted heat generation and flux. The temperature dependence of the dielectric function and the thermal transport properties of the particles play the central role in the feasibility of the thermally-actuated system, however the behavior of these thermoplasmonic processes is unclear. We experimentally and computationally analyzed modulation via thermoplasmonic processes on a test system of gold (Au) nano-islands. Modulation and energy transport in discontinuous domains exhibited quantitatively different characteristics compared to thin films. The results have implications for all surface plasmon based nano-devices where inevitable small-scale thermal processes are present.
[Show abstract][Hide abstract] ABSTRACT: This comment on the paper "A comprehensive modeling and vibration analysis of AFM microcantilevers subjected to nonlinear tip-sample interaction forces" by Sohrab Eslami and Jalili (2012)  aims to: (1) discuss and elucidate the concept of "virtual resonance" and thus (2) avert a misinterpretation of the experimental results and findings reported in the Tetard et al. Physical Review Letters 106, 180801 (2011) .
[Show abstract][Hide abstract] ABSTRACT: The stability of food and water supplies is widely recognized as a global issue of fundamental importance. Sensor development for food and water safety by nonconventional assays continues to overcome technological challenges. The delicate balance between attaining adequate limits of detection, chemical fingerprinting of the target species, dealing with the complex food matrix, and operating in difficult environments are still the focus of current efforts. While the traditional pursuit of robust recognition methods remains important, emerging engineered nanomaterials and nanotechnology promise better sensor performance but also bring about new challenges. Both advanced receptor-based sensors and emerging non-receptor-based physical sensors are evaluated for their critical challenges toward out-of-laboratory applications.
[Show abstract][Hide abstract] ABSTRACT: Obtaining compositional information for objects from a distance remains a major challenge in chemical and biological sensing. Capitalizing on mid-infrared (IR) excitation of molecules by using quantum cascade lasers (QCLs) and invoking a pump–probe technique, we present a variation of the photothermal process that can provide spectral fingerprints of substances from a variable standoff distance. We have evaluated the modal variations of the QCL beam that must be taken into account when applying QCLs for photothermal measurements. The results compare well with spectra obtained from conventional IR spectroscopy. Guided by the results, the potential of the measurements to be extended such that each point within a target region may be spectrally interrogated to form a hyperspectral image is discussed.
Journal of Physics D Applied Physics 03/2012; 45(12):125101. · 2.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The polarization dependence of the optical scattering properties of two-dimensional arrays of metal nanostructures with sub-wavelength dimensions (nanoantennas) has been investigated. Arrays of 500 nm × 100 nm gold nanorods covering a 100 × 100 µm(2) area were fabricated with varying orientations on an electrically conductive substrate. The experimental and computational analysis of the angularly organized nanorods suggest potential use toward the development of an integrated polarimeter. Using the gold nanorods on a transparent substrate as a preliminary system, we show that in the proper spectral range the scattering properties of the structures may be tuned for such an application.
[Show abstract][Hide abstract] ABSTRACT: Exploring the interior of a cell is of tremendous importance in order to assess the effects of nanomaterials on biological systems. Outside of a controlled laboratory environment, nanomaterials will most likely not be conveniently labeled or tagged so that their translocation within a biological system cannot be easily identified and quantified. Ideally, the characterization of nanomaterials within a cell requires a nondestructive, label-free, and subsurface approach. Subsurface nanoscale imaging represents a real challenge for instrumentation. Indeed the tools available for high resolution characterization, including optical, electron or scanning probe microscopies, mainly provide topography images or require taggants that fluoresce. Although the intercellular environment holds a great deal of information, subsurface visualization remains a poorly explored area. Recently, it was discovered that by mechanically perturbing a sample, it was possible to observe its response in time with nanoscale resolution by probing the surface with a micro-resonator such as a microcantilever probe. Microcantilevers are used as the force-sensing probes in atomic force microscopy (AFM), where the nanometer-scale probe tip on the microcantilever interacts with the sample in a highly controlled manner to produce high-resolution raster-scanned information of the sample surface. Taking advantage of the existing capabilities of AFM, we present a novel technique, mode synthesizing atomic force microscopy (MSAFM), which has the ability to probe subsurface structures such as non-labeled nanoparticles embedded in a cell. In MSAFM mechanical actuators (PZTs) excite the probe and the sample at different frequencies as depicted in the first figure of this chapter. The nonlinear nature of the tip-sample interaction, at the point of contact of the probe and the surface of the sample, in the contact mode AFM configuration permits the mixing of the elastic waves. The new dynamic system comprises new synthesized imaging modes, resulting from sum- and difference-frequency generation of the driving frequencies. The specific electronics of MSAFM allows the selection of individual modes and the monitoring of their amplitude and phase. From these quantities of various synthesized modes a series of images can be acquired. The new images contain subsurface information, thus revealing the presence of nanoparticles inside the cells.
[Show abstract][Hide abstract] ABSTRACT: The study of the spatially resolved physical and compositional properties of materials at the nanoscale is increasingly challenging due to the level of complexity of biological specimens such as those of interest in bioenergy production. Mode synthesizing atomic force microscopy (MSAFM) has emerged as a promising metrology tool for such studies. It is shown that, by tuning the mechanical excitation of the probe-sample system, MSAFM can be used to dynamically investigate the multifaceted complexity of plant cells. The results are argued to be of importance both for the characteristics of the invoked synthesized modes and for accessing new features of the samples. As a specific system to investigate, we present images of Populus, before and after a holopulping treatment, a crucial step in the biomass delignification process.
[Show abstract][Hide abstract] ABSTRACT: Micro- and nanocantilevers, which have traditionally played a vital role in the development of force microscopy, and more recently a special role in biological, chemical and physical sensing and detection, have received comparatively little attention in optical spectroscopy. We present an investigation of the optical response of microcantilevers towards their utilization in integrated spectrometers in a broad part of the spectrum. By discussing the overall actuation mechanism we describe how surface modes may effectively contribute to the final signal. Using Fourier transform infrared (FTIR) spectroscopy, a series of multilayered microcantilevers are characterized for their spectral response in the range from 7800 to 400 cm−1. Transmission FTIR and FTIR photothermal spectroscopy are carried out using polystyrene with well-established infrared spectra.
Journal of Physics D Applied Physics 10/2011; 44(44):445102. · 2.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The spectral tunability of semiconductor-metal multilayer structures can provide a channel for the conversion of light into useful mechanical actuation. Responses of suspended silicon, silicon nitride, chromium, gold, and aluminum microstructures are shown to be utilized as a detector for visible and IR spectroscopy. Both dispersive and interferometric approaches are investigated to delineate the potential use of the structures in spatially resolved spectroscopy and spectrally resolved microscopy. The thermoplasmonic, spectral absorption, interference effects, and the associated energy deposition that contributes to the mechanical response are discussed to describe the potential of optomechanical detection in future integrated spectrometers.
[Show abstract][Hide abstract] ABSTRACT: The ability to explore the interior of materials for the presence of inhomogeneities was recently demonstrated by mode synthesizing atomic force microscopy [L. Tetard, A. Passian, and T. Thundat, Nature Nanotech. 5, 105 (2009).]. Proposing a semiempirical nonlinear force, we show that difference frequency ω_ generation, regarded as the simplest synthesized mode, occurs optimally when the force is tuned to van der Waals form. From a parametric study of the probe-sample excitation, we show that the predicted ω_ oscillation agrees well with experiments. We then introduce the concept of virtual resonance to show that probe oscillations at ω_ can efficiently be enhanced.
[Show abstract][Hide abstract] ABSTRACT: Optical and electronic phenomena associated with excitation of plasmons in metal-dielectric interfaces of nanoparticles and nanostructures are central to many emerging applications. We present ongoing efforts in utilizing excitation and decay energy of optically excited surface plasmons toward applications in solar energy conversion and biomedical investigations.
[Show abstract][Hide abstract] ABSTRACT: The understanding of material nanosystems necessitates the development of tools that can capture their spatial and temporal behavior with minimum disturbance. Atomic force microscopy has emerged as a powerful tool for such measurements. As many forms of nanoparticles are emerging, a better understanding of their physical properties and response in various environments is of great importance. We used a variation of force microscopy that utilizes elastic excitations to determine if mice that have been exposed to nanoparticles by inhalation possess cells invaded by manufactured particles. We demonstrate that the high resolution non-invasive imaging is also of potential for characterizing extensive as well as intensive material properties of nano-bio systems. Distributions of single-walled carbon nanohorns, and silica nanoparticles located within macrophages from the mice lungs were imaged with a resolution of a few nanometers.
[Show abstract][Hide abstract] ABSTRACT: Scanning probe microscopy has emerged as a powerful approach to a broader understanding of the molecular architecture of cell walls, which may shed light on the challenge of efficient cellulosic ethanol production. We have obtained preliminary images of both Populus and switchgrass samples using atomic force microscopy (AFM). The results show distinctive features that are shared by switchgrass and Populus. These features may be attributable to the lignocellulosic cell wall composition, as the collected images exhibit the characteristic macromolecular globule structures attributable to the lignocellulosic systems. Using both AFM and a single case of mode synthesizing atomic force microscopy (MSAFM) to characterize Populus, we obtained images that clearly show the cell wall structure. The results are of importance in providing a better understanding of the characteristic features of both mature cells as well as developing plant cells. In addition, we present spectroscopic investigation of the same samples.
[Show abstract][Hide abstract] ABSTRACT: The emerging interest in understanding the interactions of nanomaterial with biological systems necessitates imaging tools that capture the spatial and temporal distributions and attributes of the resulting nano-bio amalgam. Studies targeting organ specific response and/or nanoparticle-specific system toxicity would be profoundly benefited from tools that would allow imaging and tracking of in-vivo or in-vitro processes and particle-fate studies. Recently we demonstrated that mode synthesizing atomic force microscopy (MSAFM) can provide subsurface nanoscale information on the mechanical properties of materials at the nanoscale. However, the underlying mechanism of this imaging methodology is currently subject to theoretical and experimental investigation. In this paper we present further analysis by investigating tip-sample excitation forces associated with nanomechanical image formation. Images and force curves acquired under various operational frequencies and amplitudes are presented. We examine samples of mouse cells, where buried distributions of single-walled carbon nanohorns and silica nanoparticles are visualized.
[Show abstract][Hide abstract] ABSTRACT: Non-destructive, nanoscale characterization techniques are needed to understand both synthetic and biological materials. The atomic force microscope uses a force-sensing cantilever with a sharp tip to measure the topography and other properties of surfaces. As the tip is scanned over the surface it experiences attractive and repulsive forces that depend on the chemical and mechanical properties of the sample. Here we show that an atomic force microscope can obtain a range of surface and subsurface information by making use of the nonlinear nanomechanical coupling between the probe and the sample. This technique, which is called mode-synthesizing atomic force microscopy, relies on multi-harmonic forcing of the sample and the probe. A rich spectrum of first- and higher-order couplings is discovered, providing a multitude of new operational modes for force microscopy, and the capabilities of the technique are demonstrated by examining nanofabricated samples and plant cells.