Publications (51)244.41 Total impact
- [Show abstract] [Hide abstract] ABSTRACT: Atomic force microscope infrared spectroscopy (AFM-IR) can perform IR spectroscopic chemical identification with sub-100 nm spatial resolution, but is relatively slow due to its low signal-to-noise ratio (SNR). In AFM-IR, tunable IR laser light is incident upon a sample, which results in a rise in temperature and thermomechanical expansion of the sample. An AFM tip in contact with the sample senses this nanometer-scale photothermal expansion. The tip motion induces cantilever vibrations, which are measured either in terms of the peak-to-peak amplitude of time-domain data or the integrated magnitude of frequency-domain data. Using a continuous Morlet wavelet transform to the cantilever dynamic response, we show that the cantilever dynamics during AFM-IR vary as a function of both time and frequency. Based on the observed cantilever response, we tailor a time-frequency-domain filter to identify the region of highest vibrational energy. This approach can increase the SNR of the AFM cantilever signal, such that the throughput is increased 32-fold compared to state-of-the art procedures. We further demonstrate significant increases in AFM-IR imaging speed and chemical identification of nanometer-scale domains in polymer films.
- [Show abstract] [Hide abstract] ABSTRACT: The widely used dynamic mode atomic force microscopy (AFM) suffers severe sensitivity degradation and noise increase when operated in liquid. The large hydrodynamic drag between the oscillating AFM cantilever and the surrounding liquid overwhelms the dissipative tip-sample interaction forces that are employed for nanomechanical imaging. In this article, we show that the recently developed Trolling-Mode AFM based on a nanoneedle probe can resolve nanomechanical properties on soft samples in liquid, enabled by the significantly reduced hydrodynamic drag between the cantilever and the liquid. The performance of the method was demonstrated by mapping mechanical properties of the membrane of living HeLa cells.
- [Show abstract] [Hide abstract] ABSTRACT: Nonlinear mechanical systems promise broadband resonance and instantaneous hysteretic switching that can be used for high sensitivity sensing. However, to introduce nonlinear resonances in widely used microcantilever systems, such as AFM probes, requires driving the cantilever to too large amplitude for any practical applications. We introduce a novel design for a microcantilever with a strong nonlinearity at small cantilever oscillation amplitude arising from the geometrical integration of a single BN nanotube. The dynamics of the system was modeled theoretically and confirmed experimentally. The system, besides providing a practical design of a nonlinear microcantilever-based probe, demonstrates also an effective method of studying the nonlinear damping properties of the attached nanotube. Beyond the typical linear mechanical damping, the nonlinear damping contribution from the attached nanotube was found to be essential for understanding the dynamical behavior of the designed system. Experimental results obtained through laser microvibrometry validated the developed model incorporating the nonlinear damping contribution.
- [Show abstract] [Hide abstract] ABSTRACT: We measure the infrared spectra of polyethylene nanostructures of height 15 nm using atomic force microscope infrared spectroscopy (AFM-IR), which is about an order of magnitude improvement over state of the art. In AFM-IR, infrared light incident upon a sample induces photothermal expansion, which is measured by an AFM tip. The thermomechanical response of the sample-tip-cantilever system results in cantilever vibrations that vary in time and frequency. A time-frequency domain analysis of the cantilever vibration signal reveals how sample thermomechanical response and cantilever dynamics affect the AFM-IR signal. By appropriately filtering the cantilever vibration signal in both the time domain and the frequency domain, it is possible to measure infrared absorption spectra on polyethylene nanostructures as small as 15 nm.
- [Show abstract] [Hide abstract] ABSTRACT: We explore the use of a nonlinear cantilever system integrating geometric nonlinearity for AFM imaging, in contrast from the traditional linear cantilever system. The intrinsically nonlinear AFM cantilever system exhibits broadband resonance over a bandwidth several times of its linear resonant frequency and possesses an intrinsic stability that virtually eliminates the instability induced by the tip–sample interactions involved in a linear AFM system, thus the artifact of image contrast reversal. The ability to realize broadband operation may extend the application of AFM to spectral analysis of tip–sample interactions across a broad frequency range at the nanoscale.
- [Show abstract] [Hide abstract] ABSTRACT: Atomic force microscope (AFM) probe with a long and rigid needle tip was fabricated and studied for high Q factor dynamic (tapping mode) AFM imaging of samples submersed in liquid. The extended needle tip over a regular commercially available tapping-mode AFM cantilever was sufficiently long to keep the AFM cantilever from submersed in liquid, which significantly minimized the hydrodynamic damping involved in dynamic AFM imaging of samples in liquid. Dynamic AFM imaging of samples in liquid at an intrinsic Q factor of over 100 and an operational frequency of over 200 kHz was demonstrated. The method has the potential to be extended to acquire viscoelastic material properties and provide truly gentle imaging of soft biological samples in physiological environments.
- [Show abstract] [Hide abstract] ABSTRACT: Hierarchical surface morphologies form when thin films are deposited onto preexisting templates of vertically aligned wires using a line-of-sight deposition method, providing a facile path to experimental battery electrodes with high surface-to-volume ratios. To demonstrate this, we fabricate and electrochemically cycle highly textured thin film electrodes of LixMn2−yO4 with large surface-to-volume ratios and low impedance. The active surface area of the electrodes exceeds the area of the substrate by at least a factor of five. This factor is due in part to the textured template, and in part to the effects of local shadowing during line-of-sight film deposition, resulting in a hierarchical surface morphology. The textured electrodes maintain their structural integrity for at least 30 cycles, as shown through microstructural characterization and reversible cycling against metallic lithium over the range of 2.0–4.4 V. In comparison to planar thin film electrodes of equal mass, they also offer a lasting reduction in internal impedance. Overall, textured thin film electrodes of any material are readily fabricated through this templating technique and can be used to improve three-dimensional battery architectures or to simply probe electrochemical surface effects.
- [Show abstract] [Hide abstract] ABSTRACT: a b s t r a c t Micro/nanomechanical resonators often exhibit nonlinear behaviors due to their small size and their ease to realize relatively large amplitude oscillation. In this work, we design a nonlinear micromechanical can-tilever system with intentionally integrated geometric nonlinearity realized through a nanotube cou-pling. Multiple scales analysis was applied to study the nonlinear dynamics which was compared favorably with experimental results. The geometrically positioned nanotube introduced nonlinearity effi-ciently into the otherwise linear micromechanical cantilever oscillator, evident from the acquired responses showing the representative hysteresis loop of a nonlinear dynamic system. It was further shown that a small change in the geometry parameters of the system produced a complete transition of the nonlinear behavior from hardening to softening resonance.
- [Show abstract] [Hide abstract] ABSTRACT: It is a well-known fact that a sphere offers less surface area, and thus less surface energy, than any other arrangement of the same volume. From this perspective, all other shapes are metastable objects. In this paper, we present and discuss a manifestation of this metastability: the spontaneous alignment of free-standing amorphous nanowires towards, and ultimately parallel to, a flux of directional ion irradiation. The behavior expected from surface energy reduction is the opposite of that predicted by both theory and experiment regarding defect generation in crystalline nanowires, but is consistent with other observations on non-crystalline materials. We verify our expectations by bending and aligning finely stranded amorphous silica nanowires, noting that such nanostructures are particularly susceptible to bending through ion-induced surface energy reduction. We offer support for this mechanism through bending rate studies, thermal annealing experiments and mathematical modeling. Experimentally, we also demonstrate selective reorientation of nanowires in patterned areas, as well as conformal coating of reoriented arrays with functional materials. These capabilities offer the prospect of exploiting engineered surface anisotropies in optical, fluidic and micromechanical applications.
- [Show abstract] [Hide abstract] ABSTRACT: In this chapter nanoscale characterization techniques for piezoelectric materials are discussed, with a focus on nanomechanical and electromechanical methods for one-dimensional nanomaterials. One-dimensional nanostructures have been the focus of recent nanoscale research due to their potential application in future nanoelectronics and nanodevices. However, their small size and special geometry impose a challenge especially from experimental point of view and renders their characterization nontrivial. In this chapter, the common methods of nanomechanical and electromechanical characterization of these nanostructures are discussed, with an emphasis on piezoelectric one-dimensional materials. Advantages and limitations of each method are discussed and the relevant literature is presented.
- [Show abstract] [Hide abstract] ABSTRACT: A rich research history exists for crystalline growth by vapor–liquid–solid (VLS) methods, but not for amorphous growth. Yet VLS growth in the absence of crystallographic influences provides an ideal laboratory for exploring surface energy effects, including the role of line tension. We discuss the growth of amorphous silica nanowires from indium droplets by a modified VLS method. Multiple strands issue from each droplet, each strand having <1% (i.e., < 5 nm) of the radius of the droplet. We analyze the surface forces for this system, including line tension, and combine data in a novel way to estimate the surface energy of silica, the interfacial energy of liquid indium on silica, and the line tension at the three-phase boundary. The results suggest that the growth of these silica strands would be impossible without the presence of a negative line tension that also serves to stabilize the strand radii against perturbation.
- [Show abstract] [Hide abstract] ABSTRACT: A direct-write nanofabrication technique was applied to fabricate high aspect ratio Pt needle electrodes for site specific electrochemistry and electrophysiology. Non-passivated and passivated (with a 10 nm thin insulating film) Pt needles having uniform radii as small as 100 nm and lengths over 30 μm were deposited on the exposed conductive ends of ultramicroelectrodes to form extended needle electrodes. Diffusion limited current and its dependence on the radius of the Pt needle were measured with linear sweep voltammetry. Model fittings validated the function of such needle electrodes for effective microscale electrochemical studies and potentially electrophysiological applications.
- [Show abstract] [Hide abstract] ABSTRACT: Accessing the interior of live cells with minimal intrusiveness for visualizing, probing, and interrogating biological processes has been the ultimate goal of much of the biological experimental development. The recent development and use of the biofunctionalized nanoneedles for local and spatially controlled intracellular delivery brings in exciting new opportunities in accessing the interior of living cells. Here we review the technical aspect of this relatively new intracellular delivery method and the related demonstrations and studies and provide our perspectives on the potential wide applications of this new nanotechnology-based tool in the biological field, especially on its use for high-resolution studies of biological processes in living cells. Different from the traditional micropipette-based needles for intracellular injection, a nanoneedle deploys a sub-100-nm-diameter solid nanowire as a needle to penetrate a cell membrane and to transfer and deliver the biological cargo conjugated onto its surface to the target regions inside a cell. Although the traditional micropipette-based needles can be more efficient in delivery biological cargoes, a nanoneedle-based delivery system offers an efficient introduction of biomolecules into living cells with high spatiotemporal resolution but minimal intrusion and damage. It offers a potential solution to quantitatively address biological processes at the nanoscale. The nanoneedle-based cell delivery system provides new possibilities for efficient, specific, and precise introduction of biomolecules into living cells for high-resolution studies of biological processes, and it has potential application in addressing broad biological questions. This article is part of a Special Issue entitled Nanotechnologies - Emerging Applications in Biomedicine.
- [Show abstract] [Hide abstract] ABSTRACT: Recent demonstration of shear piezoelectricity in an isolated collagen fibril, which is the origin of piezoelectricity in bone, necessitates investigation of shear piezoelectric behavior in bone at the nanoscale. Using high resolution lateral piezoresponse force microcopy (PFM), shear piezoelectricity in a cortical bone sample was studied at the nanoscale. Subfibrillar structure of individual collagen fibrils with a periodicity of 60–70 nm were revealed in PFM map, indicating the direct contribution of collagen fibrils to the shear piezoelectricity of bone.
- [Show abstract] [Hide abstract] ABSTRACT: A membrane-penetrating nanoneedle (also serving as a nanoelectrode) is developed for carrying and rapidly releasing individual quantum dots into the nucleus of a living cell via an electrochemical reaction activated by an electrical pulse. Direct delivery of biological probes into the nucleus with high spatial and temporal precision offers new strategies for the study of biological activity in a living cell.
- [Show abstract] [Hide abstract] ABSTRACT: Continued progress in the electronics industry depends on downsizing, to a few micrometers, the wire bonds required for wiring integrated chips into circuit boards. We developed an electrodeposition method that exploits the thermodynamic stability of a microscale or nanoscale liquid meniscus to “write” pure copper and platinum three-dimensional structures of designed shapes and sizes in an ambient air environment. We demonstrated an automated wire-bonding process that enabled wire diameters of less than 1 micrometer and bond sizes of less than 3 micrometers, with a breakdown current density of more than 1011 amperes per square meter for the wire bonds. The technology was used to fabricate high-density and high-quality interconnects, as well as complex three-dimensional microscale and even nanoscale metallic structures.
- [Show abstract] [Hide abstract] ABSTRACT: A nanomechanical resonator incorporating intrinsically geometric nonlinearity and operated in a highly nonlinear regime is modeled and developed. The nanoresonator is capable of extreme broadband resonance, with tunable resonance bandwidth up to many times its natural frequency. Its resonance bandwidth and drop frequency (the upper jump-down frequency) are found to be very sensitive to added mass and energy dissipation due to damping. We demonstrate a prototype nonlinear mechanical nanoresonator integrating a doubly clamped carbon nanotube and show its broadband resonance over tens of MHz (over 3 times its natural resonance frequency) and its sensitivity to femtogram added mass at room temperature.
- [Show abstract] [Hide abstract] ABSTRACT: Recent advance has seen the development of nanomechanical resonators operated in the linear regime that are capable of detecting extremely small physical quantities and even quantum interactions. However, the reduced device size reduces its dynamic range (down to nanometer) for linear operation, which makes developing the required measurement system difficult and accordingly limits their sensitivity, especially in ambient and room temperature environments. We design and develop a conceptually new nanomechanical resonator integrating an essential nonlinearity, which consists of a simple doubly clamped carbon nanotube driven with an oscillating concentrated force. We demonstrate the RF broadband nanoresonator that realizes a tunable bandwidth over three times its natural frequency and a room temperature mass sensitivity up to 0.1 zg/ Hz, over two orders of magnitude better than the corresponding linear nanoresonator. This intrinsically nonlinear design can be readily integrated into the ongoing development of nanoscale electromechanical systems to extend their practical operation for ultrahigh sensitivity sensing.
- [Show abstract] [Hide abstract] ABSTRACT: Studying biology in living cells is methodologically challenging but highly beneficial. Recent advances in nanobiotechnology offer exciting new opportunities to address this challenge. The nanoneedle technology, as an emerging technology that uses a cell membrane-penetrating nanoneedle to probe and manipulate biological processes in living cells, is expected to play an important role in this endeavor. Here we review the recent development and future direction of the nanoneedle technology for biological studies in living cells. The nanoneedle technology is shown to be powerful and versatile, and can offer numerous new ways to explore biological processes and biophysical properties of living cells with high spatial and temporal precision potentially reaching molecular resolution.
University of Illinois, Urbana-Champaign
Urbana, Illinois, United States
- Department of Mechanical Science and Engineering