Analysis of photothermally induced vibration in metal coated AFM cantilever

NASA Astrophysics Data System (ADS)

Kadri, Shahrul; Fujiwara, Hideki; Sasaki, Keiji

2010-05-01

We report the vibration reduction in the optically driven V-shaped AFM cantilever with 70 nm gold surface coating. The driving laser at 780 nm is intensity modulated at 1 kHz to 100 kHz and focused on the AFM cantilever surface. The cantilever vibration amplitude is monitored by HeNe probe laser. Two features are observed: high vibration amplitude of the cantilever (1) at several kHz modulation frequencies regime and (2) at around its mechanical resonance. In addition, we found that vibration at the resonance peak increases when the excitation spot is positioned farther from the free end of the cantilever.

Noncontact Viscoelastic Imaging of Living Cells Using a Long-Needle Atomic Force Microscope with Dual-Frequency Modulation

NASA Astrophysics Data System (ADS)

Guan, Dongshi; Charlaix, Elisabeth; Qi, Robert Z.; Tong, Penger

2017-10-01

Imaging of surface topography and elasticity of living cells can provide insight into the roles played by the cells' volumetric and mechanical properties and their response to external forces in regulating the essential cellular events and functions. Here, we report a unique technique of noncontact viscoelastic imaging of live cells using atomic force microscopy (AFM) with a long-needle glass probe. Because only the probe tip is placed in a liquid medium near the cell surface, the AFM cantilever in air functions well under dual-frequency modulation, retaining its high-quality resonant modes. The probe tip interacts with the cell surface through a minute hydrodynamic flow in the nanometer-thin gap region between them without physical contact. Quantitative measurements of the cell height, volume, and Young's modulus are conducted simultaneously. The experiment demonstrates that the long-needle AFM has a wide range of applications in the study of cell mechanics.

Revealing molecular-level surface structure of amyloid fibrils in liquid by means of frequency modulation atomic force microscopy

NASA Astrophysics Data System (ADS)

Fukuma, Takeshi; Mostaert, Anika S.; Serpell, Louise C.; Jarvis, Suzanne P.

2008-09-01

We have investigated the surface structure of islet amyloid polypeptide (IAPP) fibrils and α-synuclein protofibrils in liquid by means of frequency modulation atomic force microscopy (FM-AFM). Ångström-resolution FM-AFM imaging of isolated macromolecules in liquid is demonstrated for the first time. Individual β-strands aligned perpendicular to the fibril axis with a spacing of 0.5 nm are resolved in FM-AFM images, which confirms cross-β structure of IAPP fibrils in real space. FM-AFM images also reveal the existence of 4 nm periodic domains along the axis of IAPP fibrils. Stripe features with 0.5 nm spacing are also found in images of α-synuclein protofibrils. However, in contrast to the case for IAPP fibrils, the stripes are oriented 30° from the axis, suggesting the possibility of β-strand alignment in protofibrils different from that in mature fibrils or the regular arrangement of thioflavin T molecules present during the fibril preparation aligned at the surface of the protofibrils.

Quartz tuning fork-based frequency modulation atomic force spectroscopy and microscopy with all digital phase-locked loop

NASA Astrophysics Data System (ADS)

An, Sangmin; Hong, Mun-heon; Kim, Jongwoo; Kwon, Soyoung; Lee, Kunyoung; Lee, Manhee; Jhe, Wonho

2012-11-01

We present a platform for the quartz tuning fork (QTF)-based, frequency modulation atomic force microscopy (FM-AFM) system for quantitative study of the mechanical or topographical properties of nanoscale materials, such as the nano-sized water bridge formed between the quartz tip (˜100 nm curvature) and the mica substrate. A thermally stable, all digital phase-locked loop is used to detect the small frequency shift of the QTF signal resulting from the nanomaterial-mediated interactions. The proposed and demonstrated novel FM-AFM technique provides high experimental sensitivity in the measurement of the viscoelastic forces associated with the confined nano-water meniscus, short response time, and insensitivity to amplitude noise, which are essential for precision dynamic force spectroscopy and microscopy.

Quartz tuning fork-based frequency modulation atomic force spectroscopy and microscopy with all digital phase-locked loop.

PubMed

An, Sangmin; Hong, Mun-heon; Kim, Jongwoo; Kwon, Soyoung; Lee, Kunyoung; Lee, Manhee; Jhe, Wonho

2012-11-01

We present a platform for the quartz tuning fork (QTF)-based, frequency modulation atomic force microscopy (FM-AFM) system for quantitative study of the mechanical or topographical properties of nanoscale materials, such as the nano-sized water bridge formed between the quartz tip (~100 nm curvature) and the mica substrate. A thermally stable, all digital phase-locked loop is used to detect the small frequency shift of the QTF signal resulting from the nanomaterial-mediated interactions. The proposed and demonstrated novel FM-AFM technique provides high experimental sensitivity in the measurement of the viscoelastic forces associated with the confined nano-water meniscus, short response time, and insensitivity to amplitude noise, which are essential for precision dynamic force spectroscopy and microscopy.

Dissolution Processes at Step Edges of Calcite in Water Investigated by High-Speed Frequency Modulation Atomic Force Microscopy and Simulation.

PubMed

Miyata, Kazuki; Tracey, John; Miyazawa, Keisuke; Haapasilta, Ville; Spijker, Peter; Kawagoe, Yuta; Foster, Adam S; Tsukamoto, Katsuo; Fukuma, Takeshi

2017-07-12

The microscopic understanding of the crystal growth and dissolution processes have been greatly advanced by the direct imaging of nanoscale step flows by atomic force microscopy (AFM), optical interferometry, and X-ray microscopy. However, one of the most fundamental events that govern their kinetics, namely, atomistic events at the step edges, have not been well understood. In this study, we have developed high-speed frequency modulation AFM (FM-AFM) and enabled true atomic-resolution imaging in liquid at ∼1 s/frame, which is ∼50 times faster than the conventional FM-AFM. With the developed AFM, we have directly imaged subnanometer-scale surface structures around the moving step edges of calcite during its dissolution in water. The obtained images reveal that the transition region with typical width of a few nanometers is formed along the step edges. Building upon insight in previous studies, our simulations suggest that the transition region is most likely to be a Ca(OH) 2 monolayer formed as an intermediate state in the dissolution process. On the basis of this finding, we improve our understanding of the atomistic dissolution model of calcite in water. These results open up a wide range of future applications of the high-speed FM-AFM to the studies on various dynamic processes at solid-liquid interfaces with true atomic resolution.

Challenges and complexities of multifrequency atomic force microscopy in liquid environments

PubMed Central

2014-01-01

Summary This paper illustrates through numerical simulation the complexities encountered in high-damping AFM imaging, as in liquid enviroments, within the specific context of multifrequency atomic force microscopy (AFM). The focus is primarily on (i) the amplitude and phase relaxation of driven higher eigenmodes between successive tip–sample impacts, (ii) the momentary excitation of non-driven higher eigenmodes and (iii) base excitation artifacts. The results and discussion are mostly applicable to the cases where higher eigenmodes are driven in open loop and frequency modulation within bimodal schemes, but some concepts are also applicable to other types of multifrequency operations and to single-eigenmode amplitude and frequency modulation methods. PMID:24778952

A low-noise measurement system for scanning thermal microscopy resistive nanoprobes based on a transformer ratio-arm bridge

NASA Astrophysics Data System (ADS)

Świątkowski, Michał; Wojtuś, Arkadiusz; Wielgoszewski, Grzegorz; Rudek, Maciej; Piasecki, Tomasz; Jóźwiak, Grzegorz; Gotszalk, Teodor

2018-04-01

Atomic force microscopy (AFM) is a widely used technology for the investigation and characterization of nanomaterials. Its functionality can be easily expanded by applying dedicated extension modules, which can measure the electrical conductivity or temperature of a sample. In this paper, we introduce a transformer ratio-arm bridge setup dedicated to AFM-based thermal imaging. One of the key features of the thermal module is the use of a low-power driving signal that prevents undesirable tip heating during resistance measurement, while the other is the sensor location in a ratio-arm transformer bridge working in the audio frequency range and ensuring galvanic isolation of the tip, enabling contact-mode scanning of electronic circuits. The proposed expansion module is compact and it can be integrated onto the AFM head close to the cantilever. The calibration process and the resolution of 11 mK of the proposed setup are shown.

Biological Applications of FM-AFM in Liquid Environment

NASA Astrophysics Data System (ADS)

Fukuma, Takeshi; Jarvis, Suzanne P.

Atomic force microscopy (AFM) was noted for its potential to study biological materials shortly after its first development in 1986 due to its ability to image insulators in liquid environments. The subsequent application of AFM to biology has included lateral characterization via imaging, unraveling of molecules under a tensile load and application of a force either to measure mechanical properties under the tip or to instigate a biochemical response in living cells. To date, the application of frequency modulation AFM (FM-AFM) specifically to biological materials has been limited to relatively few research groups when compared to the extensive application of AFM to biological materials. This is probably due to the perceived complexity of the technique both by researchers in the life sciences and those manufacturing liquid AFMs for biological research. In this chapter, we aim to highlight the advantages of applying the technique to biological materials.

Atomic force microscope based on vertical silicon probes

NASA Astrophysics Data System (ADS)

Walter, Benjamin; Mairiaux, Estelle; Faucher, Marc

2017-06-01

A family of silicon micro-sensors for Atomic Force Microscope (AFM) is presented that allows to operate with integrated transducers from medium to high frequencies together with moderate stiffness constants. The sensors are based on Micro-Electro-Mechanical-Systems technology. The vertical design specifically enables a long tip to oscillate perpendicularly to the surface to be imaged. The tip is part of a resonator including quasi-flexural composite beams, and symmetrical transducers that can be used as piezoresistive detector and/or electro-thermal actuator. Two vertical probes (Vprobes) were operated up to 4.3 MHz with stiffness constants 150 N/m to 500 N/m and the capability to oscillate from 10 pm to 90 nm. AFM images of several samples both in amplitude modulation (tapping-mode) and in frequency modulation were obtained.

Development of a Hybrid Atomic Force Microscopic Measurement System Combined with White Light Scanning Interferometry

PubMed Central

Guo, Tong; Wang, Siming; Dorantes-Gonzalez, Dante J.; Chen, Jinping; Fu, Xing; Hu, Xiaotang

2012-01-01

A hybrid atomic force microscopic (AFM) measurement system combined with white light scanning interferometry for micro/nanometer dimensional measurement is developed. The system is based on a high precision large-range positioning platform with nanometer accuracy on which a white light scanning interferometric module and an AFM head are built. A compact AFM head is developed using a self-sensing tuning fork probe. The head need no external optical sensors to detect the deflection of the cantilever, which saves room on the head, and it can be directly fixed under an optical microscopic interferometric system. To enhance the system’s dynamic response, the frequency modulation (FM) mode is adopted for the AFM head. The measuring data can be traceable through three laser interferometers in the system. The lateral scanning range can reach 25 mm × 25 mm by using a large-range positioning platform. A hybrid method combining AFM and white light scanning interferometry is proposed to improve the AFM measurement efficiency. In this method, the sample is measured firstly by white light scanning interferometry to get an overall coarse morphology, and then, further measured with higher resolution by AFM. Several measuring experiments on standard samples demonstrate the system’s good measurement performance and feasibility of the hybrid measurement method. PMID:22368463

Development of a hybrid atomic force microscopic measurement system combined with white light scanning interferometry.

PubMed

Guo, Tong; Wang, Siming; Dorantes-Gonzalez, Dante J; Chen, Jinping; Fu, Xing; Hu, Xiaotang

2012-01-01

A hybrid atomic force microscopic (AFM) measurement system combined with white light scanning interferometry for micro/nanometer dimensional measurement is developed. The system is based on a high precision large-range positioning platform with nanometer accuracy on which a white light scanning interferometric module and an AFM head are built. A compact AFM head is developed using a self-sensing tuning fork probe. The head need no external optical sensors to detect the deflection of the cantilever, which saves room on the head, and it can be directly fixed under an optical microscopic interferometric system. To enhance the system's dynamic response, the frequency modulation (FM) mode is adopted for the AFM head. The measuring data can be traceable through three laser interferometers in the system. The lateral scanning range can reach 25 mm × 25 mm by using a large-range positioning platform. A hybrid method combining AFM and white light scanning interferometry is proposed to improve the AFM measurement efficiency. In this method, the sample is measured firstly by white light scanning interferometry to get an overall coarse morphology, and then, further measured with higher resolution by AFM. Several measuring experiments on standard samples demonstrate the system's good measurement performance and feasibility of the hybrid measurement method.

Measurement of Intramolecular Energy Dissipation and Stiffness of a Single Peptide Molecule by Magnetically Modulated Atomic Force Microscopy

NASA Astrophysics Data System (ADS)

Kageshima, Masami; Takeda, Seiji; Ptak, Arkadiusz; Nakamura, Chikashi; Jarvis, Suzanne P.; Tokumoto, Hiroshi; Miyake, Jun

2004-12-01

A method for measuring intramolecular energy dissipation as well as stiffness variation in a single biomolecule in situ by atomic force microscopy (AFM) is presented. An AFM cantilever is magnetically modulated at an off-resonance frequency while it elongates a single peptide molecule in buffer solution. The molecular stiffness and the energy dissipation are measured via the amplitude and phase lag in the response signal. Data showing a peculiar feature in both profiles of stiffness and dissipation is presented. This suggests that the present method is more sensitive to the state of the molecule than the conventional force-elongation measurement is.

Radiation pressure excitation of Low Temperature Atomic Force & Magnetic Force Microscope (LT-AFM/MFM) for Imaging

NASA Astrophysics Data System (ADS)

Karci, Ozgur; Celik, Umit; Oral, Ahmet; NanoMagnetics Instruments Ltd. Team; Middle East Tech Univ Team

2015-03-01

We describe a novel method for excitation of Atomic Force Microscope (AFM) cantilevers by means of radiation pressure for imaging in an AFM for the first time. Piezo excitation is the most common method for cantilever excitation, but it may cause spurious resonance peaks. A fiber optic interferometer with 1310 nm laser was used both to measure the deflection of cantilever and apply a force to the cantilever in a LT-AFM/MFM from NanoMagnetics Instruments. The laser power was modulated at the cantilever`s resonance frequency by a digital Phase Lock Loop (PLL). The force exerted by the radiation pressure on a perfectly reflecting surface by a laser beam of power P is F = 2P/c. We typically modulate the laser beam by ~ 800 μW and obtain 10nm oscillation amplitude with Q ~ 8,000 at 2.5x10-4 mbar. The cantilever's stiffness can be accurately calibrated by using the radiation pressure. We have demonstrated performance of the radiation pressure excitation in AFM/MFM by imaging a hard disk sample between 4-300K and Abrikosov vortex lattice in BSCCO single crystal at 4K to for the first time.

Accurate formula for dissipative interaction in frequency modulation atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suzuki, Kazuhiro; Matsushige, Kazumi; Yamada, Hirofumi

2014-12-08

Much interest has recently focused on the viscosity of nano-confined liquids. Frequency modulation atomic force microscopy (FM-AFM) is a powerful technique that can detect variations in the conservative and dissipative forces between a nanometer-scale tip and a sample surface. We now present an accurate formula to convert the dissipation power of the cantilever measured during the experiment to damping of the tip-sample system. We demonstrated the conversion of the dissipation power versus tip-sample separation curve measured using a colloidal probe cantilever on a mica surface in water to the damping curve, which showed a good agreement with the theoretical curve.more » Moreover, we obtained the damping curve from the dissipation power curve measured on the hydration layers on the mica surface using a nanometer-scale tip, demonstrating that the formula allows us to quantitatively measure the viscosity of a nano-confined liquid using FM-AFM.« less

Tip induced mechanical deformation of epitaxial graphene grown on reconstructed 6H-SiC(0001) surface during scanning tunneling and atomic force microscopy studies.

PubMed

Meza, José Antonio Morán; Lubin, Christophe; Thoyer, François; Cousty, Jacques

2015-01-26

The structural and mechanical properties of an epitaxial graphene (EG) monolayer thermally grown on top of a 6H-SiC(0001) surface were studied by combined dynamic scanning tunneling microscopy (STM) and frequency modulation atomic force microscopy (FM-AFM). Experimental STM, dynamic STM and AFM images of EG on 6H-SiC(0001) show a lattice with a 1.9 nm period corresponding to the (6 × 6) quasi-cell of the SiC surface. The corrugation amplitude of this (6 × 6) quasi-cell, measured from AFM topographies, increases with the setpoint value of the frequency shift Δf (15-20 Hz, repulsive interaction). Excitation variations map obtained simultaneously with the AFM topography shows that larger dissipation values are measured in between the topographical bumps of the (6 × 6) quasi-cell. These results demonstrate that the AFM tip deforms the graphene monolayer. During recording in dynamic STM mode, a frequency shift (Δf) map is obtained in which Δf values range from 41 to 47 Hz (repulsive interaction). As a result, we deduced that the STM tip, also, provokes local mechanical distortions of the graphene monolayer. The origin of these tip-induced distortions is discussed in terms of electronic and mechanical properties of EG on 6H-SiC(0001).

Radiation pressure excitation of a low temperature atomic force/magnetic force microscope for imaging in 4-300 K temperature range

NASA Astrophysics Data System (ADS)

Ćelik, Ümit; Karcı, Özgür; Uysallı, Yiǧit; Özer, H. Özgür; Oral, Ahmet

2017-01-01

We describe a novel radiation pressure based cantilever excitation method for imaging in dynamic mode atomic force microscopy (AFM) for the first time. Piezo-excitation is the most common method for cantilever excitation, however it may cause spurious resonance peaks. Therefore, the direct excitation of the cantilever plays a crucial role in AFM imaging. A fiber optic interferometer with a 1310 nm laser was used both for the excitation of the cantilever at the resonance and the deflection measurement of the cantilever in a commercial low temperature atomic force microscope/magnetic force microscope (AFM/MFM) from NanoMagnetics Instruments. The laser power was modulated at the cantilever's resonance frequency by a digital Phase Locked Loop (PLL). The laser beam is typically modulated by ˜500 μW, and ˜141.8 nmpp oscillation amplitude is obtained in moderate vacuum levels between 4 and 300 K. We have demonstrated the performance of the radiation pressure excitation in AFM/MFM by imaging atomic steps in graphite, magnetic domains in CoPt multilayers between 4 and 300 K and Abrikosov vortex lattice in BSCCO(2212) single crystal at 4 K for the first time.

Radiation pressure excitation of a low temperature atomic force/magnetic force microscope for imaging in 4-300 K temperature range.

PubMed

Çelik, Ümit; Karcı, Özgür; Uysallı, Yiğit; Özer, H Özgür; Oral, Ahmet

2017-01-01

We describe a novel radiation pressure based cantilever excitation method for imaging in dynamic mode atomic force microscopy (AFM) for the first time. Piezo-excitation is the most common method for cantilever excitation, however it may cause spurious resonance peaks. Therefore, the direct excitation of the cantilever plays a crucial role in AFM imaging. A fiber optic interferometer with a 1310 nm laser was used both for the excitation of the cantilever at the resonance and the deflection measurement of the cantilever in a commercial low temperature atomic force microscope/magnetic force microscope (AFM/MFM) from NanoMagnetics Instruments. The laser power was modulated at the cantilever's resonance frequency by a digital Phase Locked Loop (PLL). The laser beam is typically modulated by ∼500 μW, and ∼141.8 nm pp oscillation amplitude is obtained in moderate vacuum levels between 4 and 300 K. We have demonstrated the performance of the radiation pressure excitation in AFM/MFM by imaging atomic steps in graphite, magnetic domains in CoPt multilayers between 4 and 300 K and Abrikosov vortex lattice in BSCCO(2212) single crystal at 4 K for the first time.

Imaging surface nanobubbles at graphite-water interfaces with different atomic force microscopy modes.

PubMed

Yang, Chih-Wen; Lu, Yi-Hsien; Hwang, Ing-Shouh

2013-05-08

We have imaged nanobubbles on highly ordered pyrolytic graphite (HOPG) surfaces in pure water with different atomic force microscopy (AFM) modes, including the frequency-modulation, the tapping, and the PeakForce techniques. We have compared the performance of these modes in obtaining the surface profiles of nanobubbles. The frequency-modulation mode yields a larger height value than the other two modes and can provide more accurate measurement of the surface profiles of nanobubbles. Imaging with PeakForce mode shows that a nanobubble appears smaller and shorter with increasing peak force and disappears above a certain peak force, but the size returns to the original value when the peak force is reduced. This indicates that imaging with high peak forces does not cause gas removal from the nanobubbles. Based on the presented findings and previous AFM observations, the existing models for nanobubbles are reviewed and discussed. The model of gas aggregate inside nanobubbles provides a better explanation for the puzzles of the high stability and the contact angle of surface nanobubbles.

Development of liquid-environment frequency modulation atomic force microscope with low noise deflection sensor for cantilevers of various dimensions

NASA Astrophysics Data System (ADS)

Fukuma, Takeshi; Jarvis, Suzanne P.

2006-04-01

We have developed a liquid-environment frequency modulation atomic force microscope (FM-AFM) with a low noise deflection sensor for a wide range of cantilevers with different dimensions. A simple yet accurate equation describing the theoretical limit of the optical beam deflection method in air and liquid is presented. Based on the equation, we have designed a low noise deflection sensor. Replaceable microscope objective lenses are utilized for providing a high magnification optical view (resolution: <3μm) as well as for focusing a laser beam (laser spot size: ˜10μm). Even for a broad range of cantilevers with lengths from 35to125μm, the sensor provides deflection noise densities of less than 11fm/√Hz in air and 16fm/√Hz in water. In particular, a cantilever with a length of 50μm gives the minimum deflection noise density of 5.7fm/√Hz in air and 7.3fm/√Hz in water. True atomic resolution of the developed FM-AFM is demonstrated by imaging mica in water.

Manipulating Si(100) at 5 K using qPlus frequency modulated atomic force microscopy: Role of defects and dynamics in the mechanical switching of atoms

NASA Astrophysics Data System (ADS)

Sweetman, A.; Jarvis, S.; Danza, R.; Bamidele, J.; Kantorovich, L.; Moriarty, P.

2011-08-01

We use small-amplitude qPlus frequency modulated atomic force microscopy (FM-AFM), at 5 K, to investigate the atomic-scale mechanical stability of the Si(100) surface. By operating at zero applied bias the effect of tunneling electrons is eliminated, demonstrating that surface manipulation can be performed by solely mechanical means. Striking differences in surface response are observed between different regions of the surface, most likely due to variations in strain associated with the presence of surface defects. We investigate the variation in local energy surface by ab initio simulation, and comment on the dynamics observed during force spectroscopy.

Cross-Sectional Imaging of Boundary Lubrication Layer Formed by Fatty Acid by Means of Frequency-Modulation Atomic Force Microscopy.

PubMed

Hirayama, Tomoko; Kawamura, Ryota; Fujino, Keita; Matsuoka, Takashi; Komiya, Hiroshi; Onishi, Hiroshi

2017-10-10

To observe in situ the adsorption of fatty acid onto metal surfaces, cross-sectional images of the adsorption layer were acquired by frequency-modulation atomic force microscopy (FM-AFM). Hexadecane and palmitic acid were used as the base oil and typical fatty acid, respectively. A Cu-coated silicon wafer was prepared as the target substrate. The solvation structure formed by hexadecane molecules at the interface between the Cu substrate and the hexadecane was observed, and the layer pitch was found to be about 0.6 nm, which corresponds to the height of hexadecane molecules. This demonstrates that hexadecane molecules physically adsorbed onto the surface due to van der Waals forces with lying orientation because hexadecane is a nonpolar hydrocarbon. When hexadecane with palmitic acid was put on the Cu substrate instead of pure hexadecane, an adsorption layer of palmitic acid was observed at the interface. The layer pitch was about 2.5-2.8 nm, which matches the chain length of palmitic acid molecules well. This indicates that the original adsorption layer was monolayer or single bilayer in the local area. In addition, a cross-sectional image captured 1 h after observation started to reveal that the adsorbed additive layer gradually grew up to be thicker than about 20 nm due to an external stimulus, such as cantilever oscillation. This is the first report of in situ observation of an adsorbed layer by FM-AFM in the tribology field and demonstrates that FM-AFM is useful for clarifying the actual boundary lubrication mechanism.

Gaining insight into the physics of dynamic atomic force microscopy in complex environments using the VEDA simulator

NASA Astrophysics Data System (ADS)

Kiracofe, Daniel; Melcher, John; Raman, Arvind

2012-01-01

Dynamic atomic force microscopy (dAFM) continues to grow in popularity among scientists in many different fields, and research on new methods and operating modes continues to expand the resolution, capabilities, and types of samples that can be studied. But many promising increases in capability are accompanied by increases in complexity. Indeed, interpreting modern dAFM data can be challenging, especially on complicated material systems, or in liquid environments where the behavior is often contrary to what is known in air or vacuum environments. Mathematical simulations have proven to be an effective tool in providing physical insight into these non-intuitive systems. In this article we describe recent developments in the VEDA (virtual environment for dynamic AFM) simulator, which is a suite of freely available, open-source simulation tools that are delivered through the cloud computing cyber-infrastructure of nanoHUB (www.nanohub.org). Here we describe three major developments. First, simulations in liquid environments are improved by enhancements in the modeling of cantilever dynamics, excitation methods, and solvation shell forces. Second, VEDA is now able to simulate many new advanced modes of operation (bimodal, phase-modulation, frequency-modulation, etc.). Finally, nineteen different tip-sample models are available to simulate the surface physics of a wide variety different material systems including capillary, specific adhesion, van der Waals, electrostatic, viscoelasticity, and hydration forces. These features are demonstrated through example simulations and validated against experimental data, in order to provide insight into practical problems in dynamic AFM.

Gaining insight into the physics of dynamic atomic force microscopy in complex environments using the VEDA simulator.

PubMed

Kiracofe, Daniel; Melcher, John; Raman, Arvind

2012-01-01

Dynamic atomic force microscopy (dAFM) continues to grow in popularity among scientists in many different fields, and research on new methods and operating modes continues to expand the resolution, capabilities, and types of samples that can be studied. But many promising increases in capability are accompanied by increases in complexity. Indeed, interpreting modern dAFM data can be challenging, especially on complicated material systems, or in liquid environments where the behavior is often contrary to what is known in air or vacuum environments. Mathematical simulations have proven to be an effective tool in providing physical insight into these non-intuitive systems. In this article we describe recent developments in the VEDA (virtual environment for dynamic AFM) simulator, which is a suite of freely available, open-source simulation tools that are delivered through the cloud computing cyber-infrastructure of nanoHUB (www.nanohub.org). Here we describe three major developments. First, simulations in liquid environments are improved by enhancements in the modeling of cantilever dynamics, excitation methods, and solvation shell forces. Second, VEDA is now able to simulate many new advanced modes of operation (bimodal, phase-modulation, frequency-modulation, etc.). Finally, nineteen different tip-sample models are available to simulate the surface physics of a wide variety different material systems including capillary, specific adhesion, van der Waals, electrostatic, viscoelasticity, and hydration forces. These features are demonstrated through example simulations and validated against experimental data, in order to provide insight into practical problems in dynamic AFM.

Three-electrode self-actuating self-sensing quartz cantilever: design, analysis, and experimental verification.

PubMed

Chen, C Julian; Schwarz, Alex; Wiesendanger, Roland; Horn, Oliver; Müller, Jörg

2010-05-01

We present a novel quartz cantilever for frequency-modulation atomic force microscopy (FM-AFM) which has three electrodes: an actuating electrode, a sensing electrode, and a ground electrode. By applying an ac signal on the actuating electrode, the cantilever is set to vibrate. If the frequency of actuation voltage closely matches one of the characteristic frequencies of the cantilever, a sharp resonance should be observed. The vibration of the cantilever in turn generates a current on the sensing electrode. The arrangement of the electrodes is such that the cross-talk capacitance between the actuating electrode and the sensing electrode is less than 10(-16) F, thus the direct coupling is negligible. To verify the principle, a number of samples were made. Direct measurements with a Nanosurf easyPPL controller and detector showed that for each cantilever, one or more vibrational modes can be excited and detected. Using classical theory of elasticity, it is shown that such novel cantilevers with proper dimensions can provide optimized performance and sensitivity in FM-AFM with very simple electronics.

Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current.

PubMed

Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A; Slavin, Andrei

2017-03-06

The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1-2.0 THz with the driving current in the Pt layer from 10 8  A/cm 2 to 10 9  A/cm 2 . The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy.

Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current

NASA Astrophysics Data System (ADS)

Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A.; Slavin, Andrei

2017-03-01

The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1-2.0 THz with the driving current in the Pt layer from 108 A/cm2 to 109 A/cm2. The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy.

Investigation on nanoscale processes on the BaF{sub 2}(111) surface in various solutions by frequency modulation atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kobayashi, Naritaka, E-mail: naritaka@mail.saitama-u.ac.jp; Kawamura, Ryuzo; Yoshikawa, Hiroshi Y.

2016-06-07

In this study, we have directly observed nanoscale processes that occur on BaF{sub 2}(111) surfaces in various solutions using liquid-environment frequency modulation atomic force microscopy (FM-AFM) with a true atomic resolution. In addition, to investigate atomic-scale mechanisms of crystal growth process of BaF{sub 2}, we determined a suitable solution for atomic-resolution FM-AFM imaging of the BaF{sub 2}(111) surface. For undersaturated solutions, the surface is roughened by barium hydroxo complexes in the case of high pH, whereas by dissolution and proton or water molecule adsorption throughout the surface in the case of low pH. On the other hand, for supersaturated solutions,more » the surface shows two-dimensional nucleation and growth (σ = 0.1) and three-dimensional crystal growth with tetrahedral structures (σ = 1), where σ is the degree of supersaturation. The atomic-resolution imaging of the BaF{sub 2}(111) surface has been demonstrated in potassium fluoride (KF) and the supersaturated (σ = 0.1 and 1) solutions, wherein atomically flat terraces are shown at least for about 30 min.« less

Localization of cesium on montmorillonite surface investigated by frequency modulation atomic force microscopy

NASA Astrophysics Data System (ADS)

Araki, Yuki; Satoh, Hisao; Okumura, Masahiko; Onishi, Hiroshi

2017-11-01

Cation exchange of clay mineral is typically analyzed without microscopic study of the clay surfaces. In order to reveal the distribution of exchangeable cations at the clay surface, we performed in situ atomic-scale observations of the surface changes in Na-rich montmorillonite due to exchange with Cs cations using frequency modulation atomic force microscopy (FM-AFM). Lines of protrusion were observed on the surface in aqueous CsCl solution. The amount of Cs of the montmorillonite particles analyzed by energy dispersive X-ray spectrometry was consistent with the ratio of the number of linear protrusions to all protrusions in the FM-AFM images. The results showed that the protrusions represent adsorbed Cs cations. The images indicated that Cs cations at the surface were immobile, and their occupancy remained constant at 10% of the cation sites at the surface with different immersion times in the CsCl solution. This suggests that the mobility and the number of Cs cations at the surface are controlled by the permanent charge of montmorillonite; however, the Cs distribution at the surface is independent of the charge distribution of the inner silicate layer. Our atomic-scale observations demonstrate that surface cations are distributed in different ways in montmorillonite and mica.

Terahertz-Frequency Spin Hall Auto-oscillator Based on a Canted Antiferromagnet

NASA Astrophysics Data System (ADS)

Sulymenko, O. R.; Prokopenko, O. V.; Tiberkevich, V. S.; Slavin, A. N.; Ivanov, B. A.; Khymyn, R. S.

2017-12-01

We propose a design of a terahertz-frequency signal generator based on a layered structure consisting of a current-driven platinum (Pt) layer and a layer of an antiferromagnet (AFM) with easy-plane anisotropy, where the magnetization vectors of the AFM sublattices are canted inside the easy plane by the Dzyaloshinskii-Moriya interaction (DMI). The dc electric current flowing in the Pt layer creates due to the spin Hall effect, a perpendicular spin current that, being injected in the AFM layer, tilts the DMI-canted AFM sublattices out of the easy plane, thus exposing them to the action of a strong internal exchange magnetic field of the AFM. The sublattice magnetizations, along with the small net magnetization vector mDMI of the canted AFM, start to rotate about the hard anisotropy axis of the AFM with the terahertz frequency proportional to the injected spin current and the AFM exchange field. The rotation of the small net magnetization mDMI results in the terahertz-frequency dipolar radiation that can be directly received by an adjacent (e.g., dielectric) resonator. We demonstrate theoretically that the radiation frequencies in the range f =0.05 - 2 THz are possible at the experimentally reachable magnitudes of the driving current density, and we evaluate the power of the signal radiated into different types of resonators. This power increases with the increase of frequency f , and it can exceed 1 μ W at f ˜0.5 THz for a typical dielectric resonator of the electric permittivity ɛ ˜10 and a quality factor Q ˜750 .

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verbiest, G. J., E-mail: Verbiest@physik.rwth-aachen.de; Zalm, D. J. van der; Oosterkamp, T. H.

The application of ultrasound in an Atomic Force Microscope (AFM) gives access to subsurface information. However, no commercially AFM exists that is equipped with this technique. The main problems are the electronic crosstalk in the AFM setup and the insufficiently strong excitation of the cantilever at ultrasonic (MHz) frequencies. In this paper, we describe the development of an add-on that provides a solution to these problems by using a special piezo element with a lowest resonance frequency of 2.5 MHz and by separating the electronic connection for this high frequency piezo element from all other connections. In this sense, wemore » support researches with the possibility to perform subsurface measurements with their existing AFMs and hopefully pave also the way for the development of a commercial AFM that is capable of imaging subsurface features with nanometer resolution.« less

[AFM fishing of proteins under impulse electric field].

PubMed

Ivanov, Yu D; Pleshakova, T O; Malsagova, K A; Kaysheva, A L; Kopylov, A T; Izotov, A A; Tatur, V Yu; Vesnin, S G; Ivanova, N D; Ziborov, V S; Archakov, A I

2016-05-01

A combination of (atomic force microscopy)-based fishing (AFM-fishing) and mass spectrometry allows to capture protein molecules from solutions, concentrate and visualize them on an atomically flat surface of the AFM chip and identify by subsequent mass spectrometric analysis. In order to increase the AFM-fishing efficiency we have applied pulsed voltage with the rise time of the front of about 1 ns to the AFM chip. The AFM-chip was made using a conductive material, highly oriented pyrolytic graphite (HOPG). The increased efficiency of AFM-fishing has been demonstrated using detection of cytochrome b5 protein. Selection of the stimulating pulse with a rise time of 1 ns, corresponding to the GHz frequency range, by the effect of intrinsic emission from water observed in this frequency range during water injection into the cell.

Electrical control of antiferromagnetic metal up to 15 nm

NASA Astrophysics Data System (ADS)

Zhang, PengXiang; Yin, GuFan; Wang, YuYan; Cui, Bin; Pan, Feng; Song, Cheng

2016-08-01

Manipulation of antiferromagnetic (AFM) spins by electrical means is on great demand to develop the AFM spintronics with low power consumption. Here we report a reversible electrical control of antiferromagnetic moments of FeMn up to 15 nm, using an ionic liquid to exert a substantial electric-field effect. The manipulation is demonstrated by the modulation of exchange spring in [Co/Pt]/FeMn system, where AFM moments in FeMn pin the magnetization rotation of Co/Pt. By carrier injection or extraction, the magnetic anisotropy of the top layer in FeMn is modulated to influence the whole exchange spring and then passes its influence to the [Co/Pt]/FeMn interface, through a distance up to the length of exchange spring that fully screens electric field. Comparing FeMn to IrMn, despite the opposite dependence of exchange bias on gate voltages, the same correlation between carrier density and exchange spring stiffness is demonstrated. Besides the fundamental significance of modulating the spin structures in metallic AFM via all-electrical fashion, the present finding would advance the development of low-power-consumption AFM spintronics.

Exploratory Study of RNA Polymerase II Using Dynamic Atomic Force Microscopy

NASA Astrophysics Data System (ADS)

Rhodin, Thor; Umemura, Kazuo; Gad, Mohammed; Jarvis, Suzanne; Ishikawa, Mitsuru; Fu, Jianhua

2002-03-01

An exploratory study of the microtopological dimensions and shape features of yeast RNA polymerase II (y-poly II) on freshly cleaved mica was made in phosphate aqueous buffer solution at room temperature following previous work by Hansma and others. The molecules were imaged by stabilization on freshly cleaved mica at a limiting resolution of 10 Å and scanned using dynamical atomic force microscopy with a 10 nm multi-wall carbon nanotube in the resonance frequency modulation mode. They indicated microtopological shape and dimensional features similar to those predicted by electron density plots derived from the X-ray crystallographic model. It is concluded that this is considered primarily a feasibility study with definitive conclusions subject to more detailed systematic measurements of the 3D microtopology. These measurements appear to establish validity of the noncontact atomic force microscopy (nc-AFM) approach into defining the primary microtopology and biochemical functionality of RNA polymerase II. Further nc-AFM studies at higher resolution using dynamical nc-AFM will be required to clearly define the detailed 3D microtopology of RNA polymerase II in anaerobic aqueous environments for both static and dynamic conditions.

Atomic force microscopy of red-light photoreceptors using peakforce quantitative nanomechanical property mapping.

PubMed

Kroeger, Marie E; Sorenson, Blaire A; Thomas, J Santoro; Stojković, Emina A; Tsonchev, Stefan; Nicholson, Kenneth T

2014-10-24

Atomic force microscopy (AFM) uses a pyramidal tip attached to a cantilever to probe the force response of a surface. The deflections of the tip can be measured to ~10 pN by a laser and sectored detector, which can be converted to image topography. Amplitude modulation or "tapping mode" AFM involves the probe making intermittent contact with the surface while oscillating at its resonant frequency to produce an image. Used in conjunction with a fluid cell, tapping-mode AFM enables the imaging of biological macromolecules such as proteins in physiologically relevant conditions. Tapping-mode AFM requires manual tuning of the probe and frequent adjustments of a multitude of scanning parameters which can be challenging for inexperienced users. To obtain high-quality images, these adjustments are the most time consuming. PeakForce Quantitative Nanomechanical Property Mapping (PF-QNM) produces an image by measuring a force response curve for every point of contact with the sample. With ScanAsyst software, PF-QNM can be automated. This software adjusts the set-point, drive frequency, scan rate, gains, and other important scanning parameters automatically for a given sample. Not only does this process protect both fragile probes and samples, it significantly reduces the time required to obtain high resolution images. PF-QNM is compatible for AFM imaging in fluid; therefore, it has extensive application for imaging biologically relevant materials. The method presented in this paper describes the application of PF-QNM to obtain images of a bacterial red-light photoreceptor, RpBphP3 (P3), from photosynthetic R. palustris in its light-adapted state. Using this method, individual protein dimers of P3 and aggregates of dimers have been observed on a mica surface in the presence of an imaging buffer. With appropriate adjustments to surface and/or solution concentration, this method may be generally applied to other biologically relevant macromolecules and soft materials.

Minimising the effect of nanoparticle deformation in intermittent contact amplitude modulation atomic force microscopy measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Babic, Bakir, E-mail: bakir.babic@measurement.gov.au; Lawn, Malcolm A.; Coleman, Victoria A.

The results of systematic height measurements of polystyrene (PS) nanoparticles using intermittent contact amplitude modulation atomic force microscopy (IC-AM-AFM) are presented. The experimental findings demonstrate that PS nanoparticles deform during AFM imaging, as indicated by a reduction in the measured particle height. This deformation depends on the IC-AM-AFM imaging parameters, material composition, and dimensional properties of the nanoparticles. A model for nanoparticle deformation occurring during IC-AM-AFM imaging is developed as a function of the peak force which can be calculated for a particular set of experimental conditions. The undeformed nanoparticle height can be estimated from the model by extrapolation tomore » zero peak force. A procedure is proposed to quantify and minimise nanoparticle deformation during IC-AM-AFM imaging, based on appropriate adjustments of the experimental control parameters.« less

Nonlinear Dynamics of Cantilever-Sample Interactions in Atomic Force Microscopy

NASA Technical Reports Server (NTRS)

Cantrell, John H.; Cantrell, Sean A.

2010-01-01

The interaction of the cantilever tip of an atomic force microscope (AFM) with the sample surface is obtained by treating the cantilever and sample as independent systems coupled by a nonlinear force acting between the cantilever tip and a volume element of the sample surface. The volume element is subjected to a restoring force from the remainder of the sample that provides dynamical equilibrium for the combined systems. The model accounts for the positions on the cantilever of the cantilever tip, laser probe, and excitation force (if any) via a basis set of set of orthogonal functions that may be generalized to account for arbitrary cantilever shapes. The basis set is extended to include nonlinear cantilever modes. The model leads to a pair of coupled nonlinear differential equations that are solved analytically using a matrix iteration procedure. The effects of oscillatory excitation forces applied either to the cantilever or to the sample surface (or to both) are obtained from the solution set and applied to the to the assessment of phase and amplitude signals generated by various acoustic-atomic force microscope (A-AFM) modalities. The influence of bistable cantilever modes of on AFM signal generation is discussed. The effects on the cantilever-sample surface dynamics of subsurface features embedded in the sample that are perturbed by surface-generated oscillatory excitation forces and carried to the cantilever via wave propagation are accounted by the Bolef-Miller propagating wave model. Expressions pertaining to signal generation and image contrast in A-AFM are obtained and applied to amplitude modulation (intermittent contact) atomic force microscopy and resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM). The influence of phase accumulation in A-AFM on image contrast is discussed, as is the effect of hard contact and maximum nonlinearity regimes of A-AFM operation.

Dissipative and electrostatic force spectroscopy of indium arsenide quantum dots by non-contact atomic force microscopy

NASA Astrophysics Data System (ADS)

Stomp, Romain-Pierre

This thesis is devoted to the studies of self-assembled InAs quantum dots (QD) by low-temperature Atomic Force Microscopy (AFM) in frequency modulation mode. Several spectroscopic methods are developed to investigate single electron charging from a two-dimensional electron gas (2DEG) to an individual InAs QD. Furthermore, a new technique to measure the absolute tip-sample capacitance is also demonstrated. The main observables are the electrostatic force between the metal-coated AFM tip and sample as well as the sample-induced energy dissipation, and therefore no tunneling current has to be collected at the AFM tip. Measurements were performed by recording simultaneously the shift in the resonant frequency and the Q-factor degradation of the oscillating cantilever either as a function of tip-sample voltage or distance. The signature of single electron charging was detected as an abrupt change in the frequency shift as well as corresponding peaks in the dissipation. The main experimental features in the force agree well with the semi-classical theory of Coulomb blockade by considering the free energy of the system. The observed dissipation peaks can be understood as a back-action effect on the oscillating cantilever beam due to the fluctuation in time of electrons tunneling back and forth between the 2DEG and the QD. It was also possible to extract the absolute value of the tip-sample capacitance, as a consequence of the spectroscopic analysis of the electrostic force as a function of tip-sample distance for different values of the applied voltage. At the same time, the contact potential difference and the residual non-capacitive force could also be determined as a function of tip-sample distance.

Subsurface imaging of carbon nanotube networks in polymers with DC-biased multifrequency dynamic atomic force microscopy.

PubMed

Thompson, Hank T; Barroso-Bujans, Fabienne; Herrero, Julio Gomez; Reifenberger, Ron; Raman, Arvind

2013-04-05

The characterization of dispersion and connectivity of carbon nanotube (CNT) networks inside polymers is of great interest in polymer nanocomposites in new material systems, organic photovoltaics, and in electrodes for batteries and supercapacitors. We focus on a technique using amplitude modulation atomic force microscopy (AM-AFM) in the attractive regime of operation, using both single and dual mode excitation, which upon the application of a DC tip bias voltage allows, via the phase channel, the in situ, nanoscale, subsurface imaging of CNT networks dispersed in a polymer matrix at depths of 10-100 nm. We present an in-depth study of the origins of phase contrast in this technique and demonstrate that an electrical energy dissipation mechanism in the Coulomb attractive regime is key to the formation of the phase contrast which maps the spatial variations in the local capacitance and resistance due to the CNT network. We also note that dual frequency excitation can, under some conditions, improve the contrast for such samples. These methods open up the possibility for DC-biased amplitude modulation AFM to be used for mapping the variations in local capacitance and resistance in nanocomposites with conducting networks.

Note: Design of FPGA based system identification module with application to atomic force microscopy

NASA Astrophysics Data System (ADS)

Ghosal, Sayan; Pradhan, Sourav; Salapaka, Murti

2018-05-01

The science of system identification is widely utilized in modeling input-output relationships of diverse systems. In this article, we report field programmable gate array (FPGA) based implementation of a real-time system identification algorithm which employs forgetting factors and bias compensation techniques. The FPGA module is employed to estimate the mechanical properties of surfaces of materials at the nano-scale with an atomic force microscope (AFM). The FPGA module is user friendly which can be interfaced with commercially available AFMs. Extensive simulation and experimental results validate the design.

Near-field deformation of a liquid interface by atomic force microscopy.

PubMed

Mortagne, C; Chireux, V; Ledesma-Alonso, R; Ogier, M; Risso, F; Ondarçuhu, T; Legendre, D; Tordjeman, Ph

2017-07-01

We experiment the interaction between a liquid puddle and a spherical probe by Atomic Force Microscopy (AFM) for a probe radius R ranging from 10 nm to 30 μm. We have developed a new experimental setup by coupling an AFM with a high-speed camera and an inverted optical microscope. Interaction force-distance curves (in contact mode) and frequency shift-distance curves (in frequency modulation mode) are measured for different bulk model liquids for which the probe-liquid Hamaker constant H_{pl} is known. The experimental results, analyzed in the frame of the theoretical model developed in Phys. Rev. Lett. 108, 106104 (2012)PRLTAO0031-900710.1103/PhysRevLett.108.106104 and Phys. Rev. E 85, 061602 (2012)PLEEE81539-375510.1103/PhysRevE.85.061602, allow to determine the "jump-to-contact" critical distance d_{min} below which the liquid jumps and wets the probe. Comparison between theory and experiments shows that the probe-liquid interaction at nanoscale is controlled by the liquid interface deformation. This work shows a very good agreement between the theoretical model and the experiments and paves the way to experimental studies of liquids at the nanoscale.

Near-field deformation of a liquid interface by atomic force microscopy

NASA Astrophysics Data System (ADS)

Mortagne, C.; Chireux, V.; Ledesma-Alonso, R.; Ogier, M.; Risso, F.; Ondarçuhu, T.; Legendre, D.; Tordjeman, Ph.

2017-07-01

We experiment the interaction between a liquid puddle and a spherical probe by Atomic Force Microscopy (AFM) for a probe radius R ranging from 10 nm to 30 μ m . We have developed a new experimental setup by coupling an AFM with a high-speed camera and an inverted optical microscope. Interaction force-distance curves (in contact mode) and frequency shift-distance curves (in frequency modulation mode) are measured for different bulk model liquids for which the probe-liquid Hamaker constant Hp l is known. The experimental results, analyzed in the frame of the theoretical model developed in Phys. Rev. Lett. 108, 106104 (2012), 10.1103/PhysRevLett.108.106104 and Phys. Rev. E 85, 061602 (2012), 10.1103/PhysRevE.85.061602, allow to determine the "jump-to-contact" critical distance dmin below which the liquid jumps and wets the probe. Comparison between theory and experiments shows that the probe-liquid interaction at nanoscale is controlled by the liquid interface deformation. This work shows a very good agreement between the theoretical model and the experiments and paves the way to experimental studies of liquids at the nanoscale.

On the nonlinear dynamics of trolling-mode AFM: Analytical solution using multiple time scales method

NASA Astrophysics Data System (ADS)

Sajjadi, Mohammadreza; Pishkenari, Hossein Nejat; Vossoughi, Gholamreza

2018-06-01

Trolling mode atomic force microscopy (TR-AFM) has resolved many imaging problems by a considerable reduction of the liquid-resonator interaction forces in liquid environments. The present study develops a nonlinear model of the meniscus force exerted to the nanoneedle of TR-AFM and presents an analytical solution to the distributed-parameter model of TR-AFM resonator utilizing multiple time scales (MTS) method. Based on the developed analytical solution, the frequency-response curves of the resonator operation in air and liquid (for different penetration length of the nanoneedle) are obtained. The closed-form analytical solution and the frequency-response curves are validated by the comparison with both the finite element solution of the main partial differential equations and the experimental observations. The effect of excitation angle of the resonator on horizontal oscillation of the probe tip and the effect of different parameters on the frequency-response of the system are investigated.

Analytical Model of the Nonlinear Dynamics of Cantilever Tip-Sample Surface Interactions for Various Acoustic-Atomic Force Microscopies

NASA Technical Reports Server (NTRS)

Cantrell, John H., Jr.; Cantrell, Sean A.

2008-01-01

A comprehensive analytical model of the interaction of the cantilever tip of the atomic force microscope (AFM) with the sample surface is developed that accounts for the nonlinearity of the tip-surface interaction force. The interaction is modeled as a nonlinear spring coupled at opposite ends to linear springs representing cantilever and sample surface oscillators. The model leads to a pair of coupled nonlinear differential equations that are solved analytically using a standard iteration procedure. Solutions are obtained for the phase and amplitude signals generated by various acoustic-atomic force microscope (A-AFM) techniques including force modulation microscopy, atomic force acoustic microscopy, ultrasonic force microscopy, heterodyne force microscopy, resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM), and the commonly used intermittent contact mode (TappingMode) generally available on AFMs. The solutions are used to obtain a quantitative measure of image contrast resulting from variations in the Young modulus of the sample for the amplitude and phase images generated by the A-AFM techniques. Application of the model to RDF-AFUM and intermittent soft contact phase images of LaRC-cp2 polyimide polymer is discussed. The model predicts variations in the Young modulus of the material of 24 percent from the RDF-AFUM image and 18 percent from the intermittent soft contact image. Both predictions are in good agreement with the literature value of 21 percent obtained from independent, macroscopic measurements of sheet polymer material.

Noncontact viscoelastic measurement of polymer thin films in a liquid medium using a long-needle AFM

NASA Astrophysics Data System (ADS)

Guan, Dongshi; Barraud, Chloe; Charlaix, Elisabeth; Tong, Penger

We report noncontact measurement of the viscoelastic property of polymer thin films in a liquid medium using frequency-modulation atomic force microscopy (FM-AFM) with a newly developed long-needle probe. The probe contains a long vertical glass fiber with one end adhered to a cantilever beam and the other end with a sharp tip placed near the liquid-film interface. The nanoscale flow generated by the resonant oscillation of the needle tip provides a precise hydrodynamic force acting on the soft surface of the thin film. By accurately measuring the mechanical response of the thin film, we obtain the elastic and loss moduli of the thin film using the linear response theory of elasto-hydrodynamics. The experiment verifies the theory and demonstrates its applications. The technique can be used to accurately measure the viscoelastic property of soft surfaces, such as those made of polymers, nano-bubbles, live cells and tissues. This work was supported by the Research Grants Council of Hong Kong SAR.

Immunoactive two-dimensional self-assembly of monoclonal antibodies in aqueous solution revealed by atomic force microscopy

NASA Astrophysics Data System (ADS)

Ido, Shinichiro; Kimiya, Hirokazu; Kobayashi, Kei; Kominami, Hiroaki; Matsushige, Kazumi; Yamada, Hirofumi

2014-03-01

The conformational flexibility of antibodies in solution directly affects their immune function. Namely, the flexible hinge regions of immunoglobulin G (IgG) antibodies are essential in epitope-specific antigen recognition and biological effector function. The antibody structure, which is strongly related to its functions, has been partially revealed by electron microscopy and X-ray crystallography, but only under non-physiological conditions. Here we observed monoclonal IgG antibodies in aqueous solution by high-resolution frequency modulation atomic force microscopy (FM-AFM). We found that monoclonal antibodies self-assemble into hexamers, which form two-dimensional crystals in aqueous solution. Furthermore, by directly observing antibody-antigen interactions using FM-AFM, we revealed that IgG molecules in the crystal retain immunoactivity. As the self-assembled monolayer crystal of antibodies retains immunoactivity at a neutral pH and is functionally stable at a wide range of pH and temperature, the antibody crystal is applicable to new biotechnological platforms for biosensors or bioassays.

Direct Imaging of Individual Intrinsic Hydration Layers on Lipid Bilayers at Ångstrom Resolution

PubMed Central

Fukuma, Takeshi; Higgins, Michael J.; Jarvis, Suzanne P.

2007-01-01

The interactions between water and biological molecules have the potential to influence the structure, dynamics, and function of biological systems, hence the importance of revealing the nature of these interactions in relation to the local biochemical environment. We have investigated the structuring of water at the interface of supported dipalmitoylphosphatidylcholine bilayers in the gel phase in phosphate buffer solution using frequency modulation atomic force microscopy (FM-AFM). We present experimental results supporting the existence of intrinsic (i.e., surface-induced) hydration layers adjacent to the bilayer. The force versus distance curves measured between the bilayer and the AFM tip show oscillatory force profiles with a peak spacing of 0.28 nm, indicative of the existence of up to two hydration layers next to the membrane surface. These oscillatory force profiles reveal the molecular-scale origin of the hydration force that has been observed between two apposing lipid bilayers. Furthermore, FM-AFM imaging at the water/lipid interface visualizes individual hydration layers in three dimensions, with molecular-scale corrugations corresponding to the lipid headgroups. The results demonstrate that the intrinsic hydration layers are stable enough to present multiple energy barriers to approaching nanoscale objects, such as proteins and solvated ions, and are expected to affect membrane permeability and transport. PMID:17325013

Automated force controller for amplitude modulation atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miyagi, Atsushi, E-mail: atsushi.miyagi@inserm.fr, E-mail: simon.scheuring@inserm.fr; Scheuring, Simon, E-mail: atsushi.miyagi@inserm.fr, E-mail: simon.scheuring@inserm.fr

Atomic Force Microscopy (AFM) is widely used in physics, chemistry, and biology to analyze the topography of a sample at nanometer resolution. Controlling precisely the force applied by the AFM tip to the sample is a prerequisite for faithful and reproducible imaging. In amplitude modulation (oscillating) mode AFM, the applied force depends on the free and the setpoint amplitudes of the cantilever oscillation. Therefore, for keeping the applied force constant, not only the setpoint amplitude but also the free amplitude must be kept constant. While the AFM user defines the setpoint amplitude, the free amplitude is typically subject to uncontrollablemore » drift, and hence, unfortunately, the real applied force is permanently drifting during an experiment. This is particularly harmful in biological sciences where increased force destroys the soft biological matter. Here, we have developed a strategy and an electronic circuit that analyzes permanently the free amplitude of oscillation and readjusts the excitation to maintain the free amplitude constant. As a consequence, the real applied force is permanently and automatically controlled with picoNewton precision. With this circuit associated to a high-speed AFM, we illustrate the power of the development through imaging over long-duration and at various forces. The development is applicable for all AFMs and will widen the applicability of AFM to a larger range of samples and to a larger range of (non-specialist) users. Furthermore, from controlled force imaging experiments, the interaction strength between biomolecules can be analyzed.« less

Communication: atomic force detection of single-molecule nonlinear optical vibrational spectroscopy.

PubMed

Saurabh, Prasoon; Mukamel, Shaul

2014-04-28

Atomic Force Microscopy (AFM) allows for a highly sensitive detection of spectroscopic signals. This has been first demonstrated for NMR of a single molecule and recently extended to stimulated Raman in the optical regime. We theoretically investigate the use of optical forces to detect time and frequency domain nonlinear optical signals. We show that, with proper phase matching, the AFM-detected signals closely resemble coherent heterodyne-detected signals. Applications are made to AFM-detected and heterodyne-detected vibrational resonances in Coherent Anti-Stokes Raman Spectroscopy (χ((3))) and sum or difference frequency generation (χ((2))).

Quench of paramagnetic orbital selective Mott phase and appearance of antiferromagnetic orbital selective slater phase in multiorbital correlated systems

NASA Astrophysics Data System (ADS)

Quan, Ya-Min; Liu, Da-Yong; Lin, Hai-Qing; Zou, Liang-Jian

2018-06-01

We present the modulation of magnetic order on the orbital selective Mott phases (OSMP) and the metal-insulator transitions (MIT) of multi-orbital Hubbard models by employing the rotationally invariant slave-boson methods. We show that at half filling, the well-known paramagnetic (PM) OSMP is completely covered by an antiferromagnetic (AFM) Slater insulator, and the PM Mott phase by an AFM Mott insulator when electron correlation strength varies from intermediate to strong both in two- and three-orbitals Hubbard systems. Away from half-filling, we find that a partial-polarized AFM orbital-selective Slater phase appears in the intermediate correlation regime, and an almost full-polarized AFM OSMP fully covers the paramagnetic OSMP. In addition, the ferromagnetic phase in the three-orbital case is more robust than that in the two-orbital case. These results demonstrate that the modulation of magnetic correlation to the quasiparticle spectra leads to much rich and more interesting MIT scenario in multiorbital correlated systems.

Optical detection of ultrasound using an apertureless near-field scanning optical microscopy system

NASA Astrophysics Data System (ADS)

Ahn, Phillip; Zhang, Zhen; Sun, Cheng; Balogun, Oluwaseyi

2013-01-01

Laser ultrasonics techniques are power approaches for non-contact generation and detection of high frequency ultrasound on a local scale. In these techniques, optical diffraction limits the spatial information that can be accessed from a measurement. In order to improve the lateral spatial resolution, we incorporate an apertureless near-field scanning optical microscope (aNSOM) into laser ultrasonics setup for local detection of laser generated ultrasound. The aNSOM technique relies on the measurement of a weak backscattered near-field light intensity resulting from the oblique illumination of a nanoscale probe-tip positioned close to a sample surface. We enhance the optical near-field intensity by coupling light to surface plasmon polaritons (SPPs) on the shaft of an atomic force microscopy (AFM) cantilever. The SPPs propagate down the AFM shaft, localize at the tip apex, and are backscattered to the far-field when the separation distance between the probe tip and the sample surface is comparable to the probe-tip radius. The backscattered near-field intensity is dynamically modulated when an ultrasonic wave arrives at the sample surface leading to a transient change in the tip-sample separation distance. We present experimental results detailing measurement of broadband and narrowband laser generated ultrasound in solids with frequencies reaching up to 180 MHz range.

High quality-factor quartz tuning fork glass probe used in tapping mode atomic force microscopy for surface profile measurement

NASA Astrophysics Data System (ADS)

Chen, Yuan-Liu; Xu, Yanhao; Shimizu, Yuki; Matsukuma, Hiraku; Gao, Wei

2018-06-01

This paper presents a high quality-factor (Q-factor) quartz tuning fork (QTF) with a glass probe attached, used in frequency modulation tapping mode atomic force microscopy (AFM) for the surface profile metrology of micro and nanostructures. Unlike conventionally used QTFs, which have tungsten or platinum probes for tapping mode AFM, and suffer from a low Q-factor influenced by the relatively large mass of the probe, the glass probe, which has a lower density, increases the Q-factor of the QTF probe unit allowing it to obtain better measurement sensitivity. In addition, the process of attaching the probe to the QTF with epoxy resin, which is necessary for tapping mode AFM, is also optimized to further improve the Q-factor of the QTF glass probe. The Q-factor of the optimized QTF glass probe unit is demonstrated to be very close to that of a bare QTF without a probe attached. To verify the effectiveness and the advantages of the optimized QTF glass probe unit, the probe unit is integrated into a home-built tapping mode AFM for conducting surface profile measurements of micro and nanostructures. A blazed grating with fine tool marks of 100 nm, a microprism sheet with a vertical amplitude of 25 µm and a Fresnel lens with a steep slope of 90 degrees are used as measurement specimens. From the measurement results, it is demonstrated that the optimized QTF glass probe unit can achieve higher sensitivity as well as better stability than conventional probes in the measurement of micro and nanostructures.

Atomic force microscopy capable of vibration isolation with low-stiffness Z-axis actuation.

PubMed

Ito, Shingo; Schitter, Georg

2018-03-01

For high-resolution imaging without bulky external vibration isolation, this paper presents an atomic force microscope (AFM) capable of vibration isolation with its internal Z-axis (vertical) actuators moving the AFM probe. Lorentz actuators (voice coil actuators) are used for the Z-axis actuation, and flexures guiding the motion are designed to have a low stiffness between the mover and the base. The low stiffness enables a large Z-axis actuation of more than 700 µm and mechanically isolates the probe from floor vibrations at high frequencies. To reject the residual vibrations, the probe tracks the sample by using a displacement sensor for feedback control. Unlike conventional AFMs, the Z-axis actuation attains a closed-loop control bandwidth that is 35 times higher than the first mechanical resonant frequency. The closed-loop AFM system has robustness against the flexures' nonlinearity and uses the first resonance for better sample tracking. For further improvement, feedforward control with a vibration sensor is combined, and the resulting system rejects 98.4% of vibrations by turning on the controllers. The AFM system is demonstrated by successful AFM imaging in a vibrational environment. Copyright © 2017 Elsevier B.V. All rights reserved.

Trade-offs in sensitivity and sampling depth in bimodal atomic force microscopy and comparison to the trimodal case

PubMed Central

Eslami, Babak; Ebeling, Daniel

2014-01-01

Summary This paper presents experiments on Nafion® proton exchange membranes and numerical simulations illustrating the trade-offs between the optimization of compositional contrast and the modulation of tip indentation depth in bimodal atomic force microscopy (AFM). We focus on the original bimodal AFM method, which uses amplitude modulation to acquire the topography through the first cantilever eigenmode, and drives a higher eigenmode in open-loop to perform compositional mapping. This method is attractive due to its relative simplicity, robustness and commercial availability. We show that this technique offers the capability to modulate tip indentation depth, in addition to providing sample topography and material property contrast, although there are important competing effects between the optimization of sensitivity and the control of indentation depth, both of which strongly influence the contrast quality. Furthermore, we demonstrate that the two eigenmodes can be highly coupled in practice, especially when highly repulsive imaging conditions are used. Finally, we also offer a comparison with a previously reported trimodal AFM method, where the above competing effects are minimized. PMID:25161847

Noise in NC-AFM measurements with significant tip–sample interaction

PubMed Central

Lübbe, Jannis; Temmen, Matthias

2016-01-01

The frequency shift noise in non-contact atomic force microscopy (NC-AFM) imaging and spectroscopy consists of thermal noise and detection system noise with an additional contribution from amplitude noise if there are significant tip–sample interactions. The total noise power spectral density D Δ f(f m) is, however, not just the sum of these noise contributions. Instead its magnitude and spectral characteristics are determined by the strongly non-linear tip–sample interaction, by the coupling between the amplitude and tip–sample distance control loops of the NC-AFM system as well as by the characteristics of the phase locked loop (PLL) detector used for frequency demodulation. Here, we measure D Δ f(f m) for various NC-AFM parameter settings representing realistic measurement conditions and compare experimental data to simulations based on a model of the NC-AFM system that includes the tip–sample interaction. The good agreement between predicted and measured noise spectra confirms that the model covers the relevant noise contributions and interactions. Results yield a general understanding of noise generation and propagation in the NC-AFM and provide a quantitative prediction of noise for given experimental parameters. We derive strategies for noise-optimised imaging and spectroscopy and outline a full optimisation procedure for the instrumentation and control loops. PMID:28144538

Noise in NC-AFM measurements with significant tip-sample interaction.

PubMed

Lübbe, Jannis; Temmen, Matthias; Rahe, Philipp; Reichling, Michael

2016-01-01

The frequency shift noise in non-contact atomic force microscopy (NC-AFM) imaging and spectroscopy consists of thermal noise and detection system noise with an additional contribution from amplitude noise if there are significant tip-sample interactions. The total noise power spectral density D Δ f ( f m ) is, however, not just the sum of these noise contributions. Instead its magnitude and spectral characteristics are determined by the strongly non-linear tip-sample interaction, by the coupling between the amplitude and tip-sample distance control loops of the NC-AFM system as well as by the characteristics of the phase locked loop (PLL) detector used for frequency demodulation. Here, we measure D Δ f ( f m ) for various NC-AFM parameter settings representing realistic measurement conditions and compare experimental data to simulations based on a model of the NC-AFM system that includes the tip-sample interaction. The good agreement between predicted and measured noise spectra confirms that the model covers the relevant noise contributions and interactions. Results yield a general understanding of noise generation and propagation in the NC-AFM and provide a quantitative prediction of noise for given experimental parameters. We derive strategies for noise-optimised imaging and spectroscopy and outline a full optimisation procedure for the instrumentation and control loops.

Finite element modeling of trolling-mode AFM.

PubMed

Sajjadi, Mohammadreza; Pishkenari, Hossein Nejat; Vossoughi, Gholamreza

2018-06-01

Trolling mode atomic force microscopy (TR-AFM) has overcome many imaging problems in liquid environments by considerably reducing the liquid-resonator interaction forces. The finite element model of the TR-AFM resonator considering the effects of fluid and nanoneedle flexibility is presented in this research, for the first time. The model is verified by ABAQUS software. The effect of installation angle of the microbeam relative to the horizon and the effect of fluid on the system behavior are investigated. Using the finite element model, frequency response curve of the system is obtained and validated around the frequency of the operating mode by the available experimental results, in air and liquid. The changes in the natural frequencies in the presence of liquid are studied. The effects of tip-sample interaction on the excitation of higher order modes of the system are also investigated in air and liquid environments. Copyright © 2018 Elsevier B.V. All rights reserved.

Atomic force microscopy characterization of Zerodur mirror substrates for the extreme ultraviolet telescopes aboard NASA's Solar Dynamics Observatory.

PubMed

Soufli, Regina; Baker, Sherry L; Windt, David L; Gullikson, Eric M; Robinson, Jeff C; Podgorski, William A; Golub, Leon

2007-06-01

The high-spatial frequency roughness of a mirror operating at extreme ultraviolet (EUV) wavelengths is crucial for the reflective performance and is subject to very stringent specifications. To understand and predict mirror performance, precision metrology is required for measuring the surface roughness. Zerodur mirror substrates made by two different polishing vendors for a suite of EUV telescopes for solar physics were characterized by atomic force microscopy (AFM). The AFM measurements revealed features in the topography of each substrate that are associated with specific polishing techniques. Theoretical predictions of the mirror performance based on the AFM-measured high-spatial-frequency roughness are in good agreement with EUV reflectance measurements of the mirrors after multilayer coating.

Scanning hall probe microscopy (SHPM) using quartz crystal AFM feedback.

PubMed

Dede, M; Urkmen, K; Girişen, O; Atabak, M; Oral, A; Farrer, I; Ritchie, D

2008-02-01

Scanning Hall Probe Microscopy (SHPM) is a quantitative and non-invasive technique for imaging localized surface magnetic field fluctuations such as ferromagnetic domains with high spatial and magnetic field resolution of approximately 50 nm and 7 mG/Hz(1/2) at room temperature. In the SHPM technique, scanning tunneling microscope (STM) or atomic force microscope (AFM) feedback is used to keep the Hall sensor in close proximity of the sample surface. However, STM tracking SHPM requires conductive samples; therefore the insulating substrates have to be coated with a thin layer of gold. This constraint can be eliminated with the AFM feedback using sophisticated Hall probes that are integrated with AFM cantilevers. However it is very difficult to micro fabricate these sensors. In this work, we have eliminated the difficulty in the cantilever-Hall probe integration process, just by gluing a Hall Probe chip to a quartz crystal tuning fork force sensor. The Hall sensor chip is simply glued at the end of a 32.768 kHz or 100 kHz Quartz crystal, which is used as force sensor. An LT-SHPM system is used to scan the samples. The sensor assembly is dithered at the resonance frequency using a digital Phase Locked Loop circuit and frequency shifts are used for AFM tracking. SHPM electronics is modified to detect AFM topography and the frequency shift, along with the magnetic field image. Magnetic domains and topography of an Iron Garnet thin film crystal, NdFeB demagnetised magnet and hard disk samples are presented at room temperature. The performance is found to be comparable with the SHPM using STM feedback.

Contact resonances of U-shaped atomic force microscope probes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rezaei, E.; Turner, J. A., E-mail: jaturner@unl.edu

Recent approaches used to characterize the elastic or viscoelastic properties of materials with nanoscale resolution have focused on the contact resonances of atomic force microscope (CR-AFM) probes. The experiments for these CR-AFM methods involve measurement of several contact resonances from which the resonant frequency and peak width are found. The contact resonance values are then compared with the noncontact values in order for the sample properties to be evaluated. The data analysis requires vibration models associated with the probe during contact in order for the beam response to be deconvolved from the measured spectra. To date, the majority of CR-AFMmore » research has used rectangular probes that have a relatively simple vibration response. Recently, U-shaped AFM probes have created much interest because they allow local sample heating. However, the vibration response of these probes is much more complex such that CR-AFM is still in its infancy. In this article, a simplified analytical model of U-shaped probes is evaluated for contact resonance applications relative to a more complex finite element (FE) computational model. The tip-sample contact is modeled using three orthogonal Kelvin-Voigt elements such that the resonant frequency and peak width of each mode are functions of the contact conditions. For the purely elastic case, the frequency results of the simple model are within 8% of the FE model for the lowest six modes over a wide range of contact stiffness values. Results for the viscoelastic contact problem for which the quality factor of the lowest six modes is compared show agreement to within 13%. These results suggest that this simple model can be used effectively to evaluate CR-AFM experimental results during AFM scanning such that quantitative mapping of viscoelastic properties may be possible using U-shaped probes.« less

The description of friction of silicon MEMS with surface roughness: virtues and limitations of a stochastic Prandtl-Tomlinson model and the simulation of vibration-induced friction reduction.

PubMed

van Spengen, W Merlijn; Turq, Viviane; Frenken, Joost W M

2010-01-01

We have replaced the periodic Prandtl-Tomlinson model with an atomic-scale friction model with a random roughness term describing the surface roughness of micro-electromechanical systems (MEMS) devices with sliding surfaces. This new model is shown to exhibit the same features as previously reported experimental MEMS friction loop data. The correlation function of the surface roughness is shown to play a critical role in the modelling. It is experimentally obtained by probing the sidewall surfaces of a MEMS device flipped upright in on-chip hinges with an AFM (atomic force microscope). The addition of a modulation term to the model allows us to also simulate the effect of vibration-induced friction reduction (normal-force modulation), as a function of both vibration amplitude and frequency. The results obtained agree very well with measurement data reported previously.

Examination of humidity effects on measured thickness and interfacial phenomena of exfoliated graphene on silicon dioxide via amplitude modulation atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jinkins, K.; Farina, L.; Wu, Y., E-mail: wuy@uwplatt.edu

2015-12-14

The properties of Few-Layer Graphene (FLG) change with the number of layers and Amplitude Modulation (AM) Atomic Force Microscopy (AFM) is commonly used to determine the thickness of FLG. However, AFM measurements have been shown to be sensitive to environmental conditions such as relative humidity (RH). In the present study, AM-AFM is used to measure the thickness and loss tangent of exfoliated graphene on silicon dioxide (SiO{sub 2}) as RH is increased from 10% to 80%. We show that the measured thickness of graphene is dependent on RH. The loss tangent values of the graphene and oxide regions are bothmore » affected by humidity, with generally higher loss tangent for graphene than SiO{sub 2}. As RH increases, we observe the loss tangent of both materials approaches the same value. We hypothesize that there is a layer of water trapped between the graphene and SiO{sub 2} substrate to explain this observation. Using this interpretation, the loss tangent images also indicate movement and change in this trapped water layer as RH increases, which impacts the measured thickness of graphene using AM-AFM.« less

High-frequency effects in antiferromagnetic Sr3Ir2O7

NASA Astrophysics Data System (ADS)

Williamson, Morgan; Seinige, Heidi; Shen, Shida; Wang, Cheng; Cao, Gang; Zhou, Jianshi; Goodenough, John; Tsoi, Maxim

Antiferromagnetic (AFM) spintronics is one of many promising routes for `beyond the CMOS' technologies where unique properties of AFM materials are exploited to achieve new and improved functionalities. AFMs are especially interesting for high-speed memory applications thanks to their high natural frequencies. Here we report the effects of high-frequency (microwave) currents on transport properties of antiferromagnetic Mott insulator Sr3Ir2O7. The microwaves at 3-7 GHz were found to affect the material's current-voltage characteristic and produce resonance-like features that we tentatively associate with the dissipationless magnonics recently predicted to occur in antiferromagnetic insulators subject to ac electric fields. Our observations support the potential of antiferromagnetic materials for high-speed/high-frequency spintronic applications. This work was supported in part by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA, by NSF Grants DMR-1207577, DMR-1265162, DMR-1600057, and DMR-1122603, and by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No. OSR-2015-CRG4-2626.

Atomic force microscopy characterization of Zerodur mirror substrates for the extreme ultraviolet telescopes aboard NASA's Solar Dynamics Observatory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soufli, Regina; Baker, Sherry L.; Windt, David L.

2007-06-01

The high-spatial frequency roughness of a mirror operating at extreme ultraviolet (EUV)wavelengths is crucial for the reflective performance and is subject to very stringent specifications. To understand and predict mirror performance, precision metrology is required for measuring the surface roughness. Zerodur mirror substrates made by two different polishing vendors for a suite of EUV telescopes for solar physics were characterized by atomic force microscopy (AFM). The AFM measurements revealed features in the topography of each substrate that are associated with specific polishing techniques. Theoretical predictions of the mirror performance based on the AFM-measured high-spatial-frequency roughness are in good agreement withmore » EUV reflectance measurements of the mirrors after multilayer coating.« less

Single- and multi-frequency detection of surface displacements via scanning probe microscopy.

PubMed

Romanyuk, Konstantin; Luchkin, Sergey Yu; Ivanov, Maxim; Kalinin, Arseny; Kholkin, Andrei L

2015-02-01

Piezoresponse force microscopy (PFM) provides a novel opportunity to detect picometer-level displacements induced by an electric field applied through a conducting tip of an atomic force microscope (AFM). Recently, it was discovered that superb vertical sensitivity provided by PFM is high enough to monitor electric-field-induced ionic displacements in solids, the technique being referred to as electrochemical strain microscopy (ESM). ESM has been implemented only in multi-frequency detection modes such as dual AC resonance tracking (DART) and band excitation, where the response is recorded within a finite frequency range, typically around the first contact resonance. In this paper, we analyze and compare signal-to-noise ratios of the conventional single-frequency method with multi-frequency regimes of measuring surface displacements. Single-frequency detection ESM is demonstrated using a commercial AFM.

Method and system for near-field spectroscopy using targeted deposition of nanoparticles

NASA Technical Reports Server (NTRS)

Anderson, Mark S. (Inventor)

2012-01-01

There is provided in one embodiment of the invention a method for analyzing a sample material using surface enhanced spectroscopy. The method comprises the steps of imaging the sample material with an atomic force microscope (AFM) to select an area of interest for analysis, depositing nanoparticles onto the area of interest with an AFM tip, illuminating the deposited nanoparticles with a spectrometer excitation beam, and disengaging the AFM tip and acquiring a localized surface enhanced spectrum. The method may further comprise the step of using the AFM tip to modulate the spectrometer excitation beam above the deposited nanoparticles to obtain improved sensitivity data and higher spatial resolution data from the sample material. The invention further comprises in one embodiment a system for analyzing a sample material using surface enhanced spectroscopy.

Three-channel false colour AFM images for improved interpretation of complex surfaces: a study of filamentous cyanobacteria.

PubMed

Kurk, Toby; Adams, David G; Connell, Simon D; Thomson, Neil H

2010-05-01

Imaging signals derived from the atomic force microscope (AFM) are typically presented as separate adjacent images with greyscale or pseudo-colour palettes. We propose that information-rich false-colour composites are a useful means of presenting three-channel AFM image data. This method can aid the interpretation of complex surfaces and facilitate the perception of information that is convoluted across data channels. We illustrate this approach with images of filamentous cyanobacteria imaged in air and under aqueous buffer, using both deflection-modulation (contact) mode and amplitude-modulation (tapping) mode. Topography-dependent contrast in the error and tertiary signals aids the interpretation of the topography signal by contributing additional data, resulting in a more detailed image, and by showing variations in the probe-surface interaction. Moreover, topography-independent contrast and topography-dependent contrast in the tertiary data image (phase or friction) can be distinguished more easily as a consequence of the three dimensional colour-space.

GPIM AF-M315E Propulsion System

NASA Technical Reports Server (NTRS)

Spores, Ronald A.; Masse, Robert; Kimbrel, Scott; McLean, Chris

2014-01-01

The NASA Space Technology mission Directorate's (STMD) Green Propellant Infusion Mission (GPIM) Technology Demonstration Mission (TDM) will demonstrate an operational AF-M315E green propellant propulsion system. Aerojet-Rocketdyne is responsible for the development of the propulsion system payload. This paper statuses the propulsion system module development, including thruster design and system design; Initial test results for the 1N engineering model thruster are presented. The culmination of this program will be high-performance, green AF-M315E propulsion system technology at TRL 7+, with components demonstrated to TRL 9, ready for direct infusion to a wide range of applications for the space user community.

Nanomechanics of multidomain neuronal cell adhesion protein contactin revealed by single molecule AFM and SMD.

PubMed

Mikulska-Ruminska, Karolina; Kulik, Andrej J; Benadiba, Carine; Bahar, Ivet; Dietler, Giovanni; Nowak, Wieslaw

2017-08-18

Contactin-4 (CNTN4) is a complex cell adhesion molecule (CAM) localized at neuronal membranes, playing a key role in maintaining the mechanical integrity and signaling properties of the synapse. CNTN4 consists of six immunoglobulin C2 type (IgC2) domains and four fibronectin type III (FnIII) domains that are shared with many other CAMs. Mutations in CNTN4 gene have been linked to various psychiatric disorders. Toward elucidating the response of this modular protein to mechanical stress, we studied its force-induced unfolding using single molecule atomic force microscopy (smAFM) and steered molecular dynamics (SMD) simulations. Extensive smAFM and SMD data both indicate the distinctive mechanical behavior of the two types of modules distinguished by unique force-extension signatures. The data also reveal the heterogeneity of the response of the individual FNIII and IgC2 modules, which presumably plays a role in the adaptability of CNTN4 to maintaining cell-cell communication and adhesion properties under different conditions. Results show that extensive sampling of force spectra, facilitated by robot-enhanced AFM, can help reveal the existence of weak stabilizing interactions between the domains of multidomain proteins, and provide insights into the nanomechanics of such multidomain or heteromeric proteins.

True non-contact atomic force microscopy imaging of heterogeneous biological samples in liquids: topography and material contrast.

PubMed

Almonte, Lisa; Colchero, Jaime

2017-02-23

The present work analyses how the tip-sample interaction signals critically determine the operation of an Atomic Force Microscope (AFM) set-up immersed in liquid. On heterogeneous samples, the conservative tip-sample interaction may vary significantly from point to point - in particular from attractive to repulsive - rendering correct feedback very challenging. Lipid membranes prepared on a mica substrate are analyzed as reference samples which are locally heterogeneous (material contrast). The AFM set-up is operated dynamically at low oscillation amplitude and all available experimental data signals - the normal force, as well as the amplitude and frequency - are recorded simultaneously. From the analysis of how the dissipation (oscillation amplitude) and the conservative interaction (normal force and resonance frequency) vary with the tip-sample distance we conclude that dissipation is the only appropriate feedback source for stable and correct topographic imaging. The normal force and phase then carry information about the sample composition ("chemical contrast"). Dynamic AFM allows imaging in a non-contact regime where essentially no forces are applied, rendering dynamic AFM a truly non-invasive technique.

High-speed AFM and the reduction of tip-sample forces

NASA Astrophysics Data System (ADS)

Miles, Mervyn; Sharma, Ravi; Picco, Loren

High-speed DC-mode AFM has been shown to be routinely capable of imaging at video rate, and, if required, at over 1000 frames per second. At sufficiently high tip-sample velocities in ambient conditions, the tip lifts off the sample surface in a superlubricity process which reduces the level of shear forces imposed on the sample by the tip and therefore reduces the potential damage and distortion of the sample being imaged. High-frequency mechanical oscillations, both lateral and vertical, have been reported to reduced the tip-sample frictional forces. We have investigated the effect of combining linear high-speed scanning with these small amplitude high-frequency oscillations with the aim of reducing further the force interaction in high-speed imaging. Examples of this new version of high-speed AFM imaging will be presented for biological samples.

Atomic Force Microscope (AFM) measurements and analysis on Sagem 05R0025 secondary substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soufli, R; Baker, S L; Robinson, J C

2006-02-22

The summary of Atomic Force Microscope (AFM) on Sagem 05R0025 secondary substrate: (1) 2 x 2 {micro}m{sup 2} and 10 x 10 {micro}m{sup 2} AFM measurements and analysis on Sagem 05R0025 secondary substrate at LLNL indicate rather uniform and extremely isotropic finish across the surface, with high-spatial frequency roughness {sigma} in the range 5.1-5.5 {angstrom} rms; (2) the marked absence of pronounced long-range polishing marks in any direction, combined with increased roughness in the very high spatial frequencies, are consistent with ion-beam polishing treatment on the surface. These observations are consistent with all earlier mirrors they measured from the samemore » vendor; and (3) all data were obtained with a Digital Instruments Dimension 5000{trademark} atomic force microscope.« less

Detection of stiff nanoparticles within cellular structures by contact resonance atomic force microscopy subsurface nanomechanical imaging.

PubMed

Reggente, Melania; Passeri, Daniele; Angeloni, Livia; Scaramuzzo, Francesca Anna; Barteri, Mario; De Angelis, Francesca; Persiconi, Irene; De Stefano, Maria Egle; Rossi, Marco

2017-05-04

Detecting stiff nanoparticles buried in soft biological matrices by atomic force microscopy (AFM) based techniques represents a new frontier in the field of scanning probe microscopies, originally developed as surface characterization methods. Here we report the detection of stiff (magnetic) nanoparticles (NPs) internalized in cells by using contact resonance AFM (CR-AFM) employed as a potentially non-destructive subsurface characterization tool. Magnetite (Fe 3 O 4 ) NPs were internalized in microglial cells from cerebral cortices of mouse embryos of 18 days by phagocytosis. Nanomechanical imaging of cells was performed by detecting the contact resonance frequencies (CRFs) of an AFM cantilever held in contact with the sample. Agglomerates of NPs internalized in cells were visualized on the basis of the local increase in the contact stiffness with respect to the surrounding biological matrix. A second AFM-based technique for nanomechanical imaging, i.e., HarmoniX™, as well as magnetic force microscopy and light microscopy were used to confirm the CR-AFM results. Thus, CR-AFM was demonstrated as a promising technique for subsurface imaging of nanomaterials in biological samples.

Multi-frequency data analysis in AFM by wavelet transform

NASA Astrophysics Data System (ADS)

Pukhova, V.; Ferrini, G.

2017-10-01

Interacting cantilevers in AFM experiments generate non-stationary, multi-frequency signals consisting of numerous excited flexural and torsional modes and their harmonics. The analysis of such signals is challenging, requiring special methodological approaches and a powerful mathematical apparatus. The most common approach to the signal analysis is to apply Fourier transform analysis. However, FT gives accurate spectra for stationary signals, and for signals changing their spectral content over time, FT provides only an averaged spectrum. Hence, for non-stationary and rapidly varying signals, such as those from interacting cantilevers, a method that shows the spectral evolution in time is needed. One of the most powerful techniques, allowing detailed time-frequency representation of signals, is the wavelet transform. It is a method of analysis that allows representation of energy associated to the signal at a particular frequency and time, providing correlation between the spectral and temporal features of the signal, unlike FT. This is particularly important in AFM experiments because signals nonlinearities contains valuable information about tip-sample interactions and consequently surfaces properties. The present work is aimed to show the advantages of wavelet transform in comparison with FT using as an example the force curve analysis in dynamic force spectroscopy.

Vibrational shape tracking of atomic force microscopy cantilevers for improved sensitivity and accuracy of nanomechanical measurements

NASA Astrophysics Data System (ADS)

Wagner, Ryan; Killgore, Jason P.; Tung, Ryan C.; Raman, Arvind; Hurley, Donna C.

2015-01-01

Contact resonance atomic force microscopy (CR-AFM) methods currently utilize the eigenvalues, or resonant frequencies, of an AFM cantilever in contact with a surface to quantify local mechanical properties. However, the cantilever eigenmodes, or vibrational shapes, also depend strongly on tip-sample contact stiffness. In this paper, we evaluate the potential of eigenmode measurements for improved accuracy and sensitivity of CR-AFM. We apply a recently developed, in situ laser scanning method to experimentally measure changes in cantilever eigenmodes as a function of tip-sample stiffness. Regions of maximum sensitivity for eigenvalues and eigenmodes are compared and found to occur at different values of contact stiffness. The results allow the development of practical guidelines for CR-AFM experiments, such as optimum laser spot positioning for different experimental conditions. These experiments provide insight into the complex system dynamics that can affect CR-AFM and lay a foundation for enhanced nanomechanical measurements with CR-AFM.

The distribution of organic material and its contribution to the micro-topography of particles from wettable and water repellent soils

NASA Astrophysics Data System (ADS)

Bryant, Rob; Cheng, Shuying; Doerr, Stefan H.; Wright, Chris J.; Bayer, Julia V.; Williams, Rhodri P.

2010-05-01

Organic coatings on mineral particles will mask the physic-chemical properties of the underlying mineral surface. Surface images and force measurements obtained using atomic force microscopy (AFM) provide information about the nature of and variability in surfaces properties at the micro- to nano-scale. As AFM technology and data processing advance it is anticipated that a significant amount of information will be obtained simultaneously from individual contacts made at high frequency in non-contact or tapping mode operation. For present purposes the surfaces of model materials (smooth glass surfaces and acid-washed sand (AWS)) provide an indication of the dependency of the so-called AFM phase image on the topographic image (which is obtained synoptically). Pixel wise correlation of these images reveals how the modulation of an AFM probe is affected when topographic features are encountered. Adsorption of soil-derived humic acid (HA) or lecithin (LE), used here as an example for natural organic material, on these surfaces provides a soft and compliant, albeit partial, covering on the mineral which modifies the topography and the response of an AFM tip as it partially indents the soft regions (which contributes depth to the phase image). This produces a broadening on the data domain in the topographic/phase scatter diagram. Two dimensional classifications of these data, together with those obtained from sand particles drawn from water repellent and wettable soils, suggest that these large adsorbate molecules appear to have little preference to attach to particular topographic features or elevations. It appears that they may effectively remain on the surface at the point of initial contact. If organic adsorbates present a hydrophobic outer surface, then it seems possible that elevated features will not be immune from this and provide scope for a local, albeit, small contribution to the expression of super-hydrophobicity. It is therefore speculated here that the water repellency of a soil is the result of not only of particle surface chemistry and soil pore space geometry, but also of the micro-topography generated by organic material adsorbed on particle surfaces.

Imaging of viscoelastic soft matter with small indentation using higher eigenmodes in single-eigenmode amplitude-modulation atomic force microscopy.

PubMed

Nikfarjam, Miead; López-Guerra, Enrique A; Solares, Santiago D; Eslami, Babak

2018-01-01

In this short paper we explore the use of higher eigenmodes in single-eigenmode amplitude-modulation atomic force microscopy (AFM) for the small-indentation imaging of soft viscoelastic materials. In viscoelastic materials, whose response depends on the deformation rate, the tip-sample forces generated as a result of sample deformation increase as the tip velocity increases. Since the eigenfrequencies in a cantilever increase with eigenmode order, and since higher oscillation frequencies lead to higher tip velocities for a given amplitude (in viscoelastic materials), the sample indentation can in some cases be reduced by using higher eigenmodes of the cantilever. This effect competes with the lower sensitivity of higher eigenmodes, due to their larger force constant, which for elastic materials leads to greater indentation for similar amplitudes, compared with lower eigenmodes. We offer a short theoretical discussion of the key underlying concepts, along with numerical simulations and experiments to illustrate a simple recipe for imaging soft viscoelastic matter with reduced indentation.

Dynamics-Enabled Nanoelectromechanical Systems (NEMS) Oscillators

DTIC Science & Technology

2014-06-01

it becomes strongly nonlinear, and thus constitutes an archetypal candidate for nonlinear engineering • its fundamental resonant frequency...width of spectral peaks of atomic force microscopy (AFM) resonators as they are brought close to a surface. 39 Approved for public release...alternating current AD Allan Deviation AFM atomic force microscopy AFRL Air Force Research Laboratory AlN aluminum nitride APN Anomalous Phase

Label-free glucose detection using cantilever sensor technology based on gravimetric detection principles.

PubMed

Hsieh, Shuchen; Hsieh, Shu-Ling; Hsieh, Chiung-Wen; Lin, Po-Chiao; Wu, Chun-Hsin

2013-01-01

Efficient maintenance of glucose homeostasis is a major challenge in diabetes therapy, where accurate and reliable glucose level detection is required. Though several methods are currently used, these suffer from impaired response and often unpredictable drift, making them unsuitable for long-term therapeutic practice. In this study, we demonstrate a method that uses a functionalized atomic force microscope (AFM) cantilever as the sensor for reliable glucose detection with sufficient sensitivity and selectivity for clinical use. We first modified the AFM tip with aminopropylsilatrane (APS) and then adsorbed glucose-specific lectin concanavalin A (Con A) onto the surface. The Con A/APS-modified probes were then used to detect glucose by monitoring shifts in the cantilever resonance frequency. To confirm the molecule-specific interaction, AFM topographical images were acquired of identically treated silicon substrates which indicated a specific attachment for glucose-Con A and not for galactose-Con A. These results demonstrate that by monitoring the frequency shift of the AFM cantilever, this sensing system can detect the interaction between Con A and glucose, one of the biomolecule recognition processes, and may assist in the detection and mass quantification of glucose for clinical applications with very high sensitivity.

A simulation of atomic force microscope microcantilever in the tapping mode utilizing couple stress theory.

PubMed

Abbasi, Mohammad

2018-04-01

The nonlinear vibration behavior of a Tapping mode atomic force microscopy (TM-AFM) microcantilever under acoustic excitation force has been modeled and investigated. In dynamic AFM, the tip-surface interactions are strongly nonlinear, rapidly changing and hysteretic. First, the governing differential equation of motion and boundary conditions for dynamic analysis are obtained using the modified couple stress theory. Afterwards, closed-form expressions for nonlinear frequency and effective nonlinear damping ratio are derived utilizing perturbation method. The effect of tip connection position on the vibration behavior of the microcantilever are also analyzed. The results show that nonlinear frequency is size dependent. According to the results, an increase in the equilibrium separation between the tip and the sample surface reduces the overall effect of van der Waals forces on the nonlinear frequency, but its effect on the effective nonlinear damping ratio is negligible. The results also indicate that both the change in the distance between tip and cantilever free end and the reduction of tip radius have significant effects on the accuracy and sensitivity of the TM-AFM in the measurement of surface forces. The hysteretic behavior has been observed in the near resonance frequency response due to softening and hardening of the forced vibration response. Copyright © 2018 Elsevier Ltd. All rights reserved.

AFM feature definition for neural cells on nanofibrillar tissue scaffolds.

PubMed

Tiryaki, Volkan M; Khan, Adeel A; Ayres, Virginia M

2012-01-01

A diagnostic approach is developed and implemented that provides clear feature definition in atomic force microscopy (AFM) images of neural cells on nanofibrillar tissue scaffolds. Because the cellular edges and processes are on the same order as the background nanofibers, this imaging situation presents a feature definition problem. The diagnostic approach is based on analysis of discrete Fourier transforms of standard AFM section measurements. The diagnostic conclusion that the combination of dynamic range enhancement with low-frequency component suppression enhances feature definition is shown to be correct and to lead to clear-featured images that could change previously held assumptions about the cell-cell interactions present. Clear feature definition of cells on scaffolds extends the usefulness of AFM imaging for use in regenerative medicine. © Wiley Periodicals, Inc.

Tendon exhibits complex poroelastic behavior at the nanoscale as revealed by high-frequency AFM-based rheology.

PubMed

Connizzo, Brianne K; Grodzinsky, Alan J

2017-03-21

Tendons transmit load from muscle to bone by utilizing their unique static and viscoelastic tensile properties. These properties are highly dependent on the composition and structure of the tissue matrix, including the collagen I hierarchy, proteoglycans, and water. While the role of matrix constituents in the tensile response has been studied, their role in compression, particularly in matrix pressurization via regulation of fluid flow, is not well understood. Injured or diseased tendons and tendon regions that naturally experience compression are known to have alterations in glycosaminoglycan content, which could modulate fluid flow and ultimately mechanical function. While recent theoretical studies have predicted tendon mechanics using poroelastic theory, no experimental data have directly demonstrated such behavior. In this study, we use high-bandwidth AFM-based rheology to determine the dynamic response of tendons to compressive loading at the nanoscale and to determine the presence of poroelastic behavior. Tendons are found to have significant characteristic dynamic relaxation behavior occurring at both low and high frequencies. Classic poroelastic behavior is observed, although we hypothesize that the full dynamic response is caused by a combination of flow-dependent poroelasticity as well as flow-independent viscoelasticity. Tendons also demonstrate regional dependence in their dynamic response, particularly near the junction of tendon and bone, suggesting that the structural and compositional heterogeneity in tendon may be responsible for regional poroelastic behavior. Overall, these experiments provide the foundation for understanding fluid-flow-dependent poroelastic mechanics of tendon, and the methodology is valuable for assessing changes in tendon matrix compressive behavior at the nanoscale. Copyright © 2017 Elsevier Ltd. All rights reserved.

Structure and Nanomechanics of Model Membranes by Atomic Force Microscopy and Spectroscopy: Insights into the Role of Cholesterol and Sphingolipids.

PubMed

Gumí-Audenis, Berta; Costa, Luca; Carlá, Francesco; Comin, Fabio; Sanz, Fausto; Giannotti, Marina I

2016-12-19

Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the modulation of membrane physical properties. It directly influences the order and mechanical stability of the lipid bilayers, and it is known to laterally segregate in rafts in the outer leaflet of the membrane together with sphingolipids (SLs). Atomic force microscope (AFM) is a powerful tool as it is capable to sense and apply forces with high accuracy, with distance and force resolution at the nanoscale, and in a controlled environment. AFM-based force spectroscopy (AFM-FS) has become a crucial technique to study the nanomechanical stability of SLBs by controlling the liquid media and the temperature variations. In this contribution, we review recent AFM and AFM-FS studies on the effect of Chol on the morphology and mechanical properties of model SLBs, including complex bilayers containing SLs. We also introduce a promising combination of AFM and X-ray (XR) techniques that allows for in situ characterization of dynamic processes, providing structural, morphological, and nanomechanical information.

Structure and Nanomechanics of Model Membranes by Atomic Force Microscopy and Spectroscopy: Insights into the Role of Cholesterol and Sphingolipids

PubMed Central

Gumí-Audenis, Berta; Costa, Luca; Carlá, Francesco; Comin, Fabio; Sanz, Fausto; Giannotti, Marina I.

2016-01-01

Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the modulation of membrane physical properties. It directly influences the order and mechanical stability of the lipid bilayers, and it is known to laterally segregate in rafts in the outer leaflet of the membrane together with sphingolipids (SLs). Atomic force microscope (AFM) is a powerful tool as it is capable to sense and apply forces with high accuracy, with distance and force resolution at the nanoscale, and in a controlled environment. AFM-based force spectroscopy (AFM-FS) has become a crucial technique to study the nanomechanical stability of SLBs by controlling the liquid media and the temperature variations. In this contribution, we review recent AFM and AFM-FS studies on the effect of Chol on the morphology and mechanical properties of model SLBs, including complex bilayers containing SLs. We also introduce a promising combination of AFM and X-ray (XR) techniques that allows for in situ characterization of dynamic processes, providing structural, morphological, and nanomechanical information. PMID:27999368

Occurrence of aflatoxin M₁ in commercial pasteurized milk samples in Sari, Mazandaran province, Iran.

PubMed

Mohammadi, Hamidreza; Shokrzadeh, Mohammad; Aliabadi, Zahra; Riahi-Zanjani, Bamdad

2016-05-01

The frequency and levels of aflatoxin M1 (AFM1) in pasteurized milk samples in Sari, located in Mazandaran province, Iran, were determined by enzyme immunoassay. Seventy-six samples of pasteurized milk from different retail stores were randomly collected over four seasons during the year 2015. AFM1 contamination was detected in all milk samples. The mean concentration of aflatoxin M1 was 65.8 ng/l, with a range of 11.7-106.6 ng/l. The highest AFM1 level was detected in milk samples collected during spring. Forty-six (60.53 %) samples had AFM1 levels that exceeded the maximum acceptable levels (50 ng/l) recommended by the European Union (EU). Comparison of these results with previously published data for AFM1 in milk in Iran shows that the percentage of samples exceeding the EU maximum level is consistently high over the years, indicating a general problem related to AFB1 contamination in dairy feedingstuff.

Aflatoxin M1 in human breast milk in southeastern Turkey.

PubMed

Kılıç Altun, Serap; Gürbüz, Semra; Ayağ, Emin

2017-05-01

This study was performed to determine aflatoxin M 1 (AFM 1 ) in human breast milk samples collected in Şanlıurfa, located in Southeastern region of Turkey, and to investigate a possible correlation between AFM 1 occurrence (frequency and levels) and sampling seasons. Human breast milk samples collected in December 2014 and in June 2015 from a total of 74 nursing women, both outpatient and inpatient volunteers in hospitals located in Şanlıurfa, Turkey, were analyzed using competitive enzyme-linked immunosorbent assay (ELISA) for the presence of AFM 1 . AFM 1 was detected in 66 (89.2%) out of 74 samples at an average concentration of 19.0 ± 13.0 ng/l (min.-max., 9.6-80 ng/l). There was a statistically significant difference between December and June concerning AFM 1 levels (p < 0.05). Further detailed studies will be needed to determine the main sources of aflatoxins in food, to establish protection strategies against maternal and infant exposure to these mycotoxins.

Imaging contrast and tip-sample interaction of non-contact amplitude modulation atomic force microscopy with Q-control

NASA Astrophysics Data System (ADS)

Shi, Shuai; Guo, Dan; Luo, Jianbin

2017-10-01

Active quality factor (Q) exhibits many promising properties in dynamic atomic force microscopy. Energy dissipation and image contrasts are investigated in the non-contact amplitude modulation atomic force microscopy (AM-AFM) with an active Q-control circuit in the ambient air environment. Dissipated power and virial were calculated to compare the highly nonlinear interaction of tip-sample and image contrasts with different Q gain values. Greater free amplitudes and lower effective Q values show better contrasts for the same setpoint ratio. Active quality factor also can be employed to change tip-sample interaction force in non-contact regime. It is meaningful that non-destructive and better contrast images can be realized in non-contact AM-AFM by applying an active Q-control to the dynamic system.

Structural properties of GaAsN grown on (001) GaAs by metalorganic molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Ok, Young-Woo; Choi, Chel-Jong; Seong, Tae-Yeon; Uesugi, K.; Suemune, I.

2001-07-01

Detailed transmission electron microscopy (TEM) and transmission electron diffraction (TED) examination has been made of metalorganic molecular beam epitaxial GaAsN layers grown on (001) GaAs substrates. TEM results show that lateral composition modulation occurs in the GaAs1-xNx layer (x 6.75%). It is shown that increasing N composition and Se (dopant) concentration leads to poor crystallinity. It is also shown that the addition of Se increases N composition. Atomic force microscopy (AFM) results show that the surfaces of the samples experience a morphological change from faceting to islanding, as the N composition and Se concentration increase. Based on the TEM and AFM results, a simple model is given to explain the formation of the lateral composition modulation.

Corrosion process monitoring by AFM higher harmonic imaging

NASA Astrophysics Data System (ADS)

Babicz, S.; Zieliński, A.; Smulko, J.; Darowicki, K.

2017-11-01

The atomic force microscope (AFM) was invented in 1986 as an alternative to the scanning tunnelling microscope, which cannot be used in studies of non-conductive materials. Today the AFM is a powerful, versatile and fundamental tool for visualizing and studying the morphology of material surfaces. Moreover, additional information for some materials can be recovered by analysing the AFM’s higher cantilever modes when the cantilever motion is inharmonic and generates frequency components above the excitation frequency, usually close to the resonance frequency of the lowest oscillation mode. This method has been applied and developed to monitor corrosion processes. The higher-harmonic imaging is especially helpful for sharpening boundaries between objects in heterogeneous samples, which can be used to identify variations in steel structures (e.g. corrosion products, steel heterogeneity). The corrosion products have different chemical structures because they are composed of chemicals other than the original metal base (mainly iron oxides). Thus, their physicochemical properties are different from the primary basis. These structures have edges at which higher harmonics should be more intense because of stronger interference between the tip and the specimen structure there. This means that the AFM’s higher-harmonic imaging is an excellent tool for monitoring surficial effects of the corrosion process.

Design and development of the Waukesha Custom Engine Control Air/Fuel Module

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moss, D.W.

1996-12-31

The Waukesha Custom Engine Control Air/Fuel Module (AFM) is designed to control the air-fuel ratio for all Waukesha carbureted, gaseous fueled, industrial engine. The AFM is programmed with a personal computer to run in one of four control modes: catalyst, best power, best economy, or lean-burn. One system can control naturally aspirated, turbocharged, in-line or vee engines. The basic system consists of an oxygen sensing system, intake manifold pressure transducer, electronic control module, actuator and exhaust thermocouple. The system permits correct operation of Waukesha engines in spite of changes in fuel pressure or temperature, engine load or speed, and fuelmore » composition. The system utilizes closed loop control and is centered about oxygen sensing technology. An innovative approach to applying oxygen sensors to industrial engines provides very good performance, greatly prolongs sensor life, and maintains sensor accuracy. Design considerations and operating results are given for application of the system to stationary, industrial engines operating on fuel gases of greatly varying composition.« less

Increased imaging speed and force sensitivity for bio-applications with small cantilevers using a conventional AFM setup

PubMed Central

Leitner, Michael; Fantner, Georg E.; Fantner, Ernest J.; Ivanova, Katerina; Ivanov, Tzvetan; Rangelow, Ivo; Ebner, Andreas; Rangl, Martina; Tang, Jilin; Hinterdorfer, Peter

2012-01-01

In this study, we demonstrate the increased performance in speed and sensitivity achieved by the use of small AFM cantilevers on a standard AFM system. For this, small rectangular silicon oxynitride cantilevers were utilized to arrive at faster atomic force microscopy (AFM) imaging times and more sensitive molecular recognition force spectroscopy (MRFS) experiments. The cantilevers we used had lengths between 13 and 46 μm, a width of about 11 μm, and a thickness between 150 and 600 nm. They were coated with chromium and gold on the backside for a better laser reflection. We characterized these small cantilevers through their frequency spectrum and with electron microscopy. Due to their small size and high resonance frequency we were able to increase the imaging speed by a factor of 10 without any loss in resolution for images from several μm scansize down to the nanometer scale. This was shown on bacterial surface layers (s-layer) with tapping mode under aqueous, near physiological conditions and on nuclear membranes in contact mode in ambient environment. In addition, we showed that single molecular forces can be measured with an up to 5 times higher force sensitivity in comparison to conventional cantilevers with similar spring constants. PMID:22721963

Traceable quantum sensing and metrology relied up a quantum electrical triangle principle

NASA Astrophysics Data System (ADS)

Fang, Yan; Wang, Hengliang; Yang, Xinju; Wei, Jingsong

2016-11-01

Hybrid quantum state engineering in quantum communication and imaging1-2 needs traceable quantum sensing and metrology, which are especially critical to quantum internet3 and precision measurements4 that are important across all fields of science and technology-. We aim to set up a mode of traceable quantum sensing and metrology. We developed a method by specially transforming an atomic force microscopy (AFM) and a scanning tunneling microscopy (STM) into a conducting atomic force microscopy (C-AFM) with a feedback control loop, wherein quantum entanglement enabling higher precision was relied upon a set-point, a visible light laser beam-controlled an interferometer with a surface standard at z axis, diffractometers with lateral standards at x-y axes, four-quadrant photodiode detectors, a scanner and its image software, a phase-locked pre-amplifier, a cantilever with a kHz Pt/Au conducting tip, a double barrier tunneling junction model, a STM circuit by frequency modulation and a quantum electrical triangle principle involving single electron tunneling effect, quantum Hall effect and Josephson effect5. The average and standard deviation result of repeated measurements on a 1 nm height local micro-region of nanomedicine crystal hybrid quantum state engineering surface and its differential pA level current and voltage (dI/dV) in time domains by using C-AFM was converted into an international system of units: Siemens (S), an indicated value 0.86×10-12 S (n=6) of a relative standard uncertainty was superior over a relative standard uncertainty reference value 2.3×10-10 S of 2012 CODADA quantized conductance6. It is concluded that traceable quantum sensing and metrology is emerging.

A Survey on Aflatoxin M1 Content in Sheep and Goat Milk Produced in Sardinia Region, Italy (2005-2013).

PubMed

Virdis, Salvatore; Scarano, Christian; Spanu, Vincenzo; Murittu, Gavino; Spanu, Carlo; Ibba, Ignazio; De Santis, Enrico Pietro Luigi

2014-12-09

In the present work the results of a survey conducted in Sardinia Region on Aflatoxin M 1 (AFM 1 ) contamination in milk of small ruminants from 2005 to 2013 are reported. A total of 517 sheep and 88 goat milk samples from bulk tank, tank trucks and silo tank milk were collected. Analyses were performed by the Regional Farmers Association laboratory using high-performance liquid chromatography following the ISO 14501:1998 standard. None of the sheep milk samples analysed during 2005-2012 showed AFM 1 contamination. In sheep milk samples collected in 2013, 8 out of 172 (4.6%) were contaminated by AFM 1 with a concentration (mean±SD) of 12.59±14.05 ng/L. In one bulk tank milk sample 58.82 ng/L AFM 1 was detected, exceeding the EU limit. In none of goat milk samples analysed from 2010 to 2012 AFM 1 was detected. In 2013, 9 out of 66 goat milk samples (13.6%) showed an AFM 1 concentration of 47.21±19.58 ng/L. Two of these samples exceeded the EU limit, with concentrations of 62.09 and 138.6 ng/L. Higher contamination frequency and concentration rates were detected in bulk tank milk samples collected at farm than in bulk milk truck or silo samples, showing a dilution effect on AFM 1 milk content along small ruminants supply chain. The rate and levels of AFM 1 contamination in sheep and goat milk samples were lower than other countries. However, the small number of milk samples analysed for AFM 1 in Sardinia Region in 2005-2013 give evidence that food business operators check programmes should be improved to ensure an adequate monitoring of AFM 1 contamination in small ruminant dairy chain.

Analysis of dynamic cantilever behavior in tapping mode atomic force microscopy.

PubMed

Deng, Wenqi; Zhang, Guang-Ming; Murphy, Mark F; Lilley, Francis; Harvey, David M; Burton, David R

2015-10-01

Tapping mode atomic force microscopy (AFM) provides phase images in addition to height and amplitude images. Although the behavior of tapping mode AFM has been investigated using mathematical modeling, comprehensive understanding of the behavior of tapping mode AFM still poses a significant challenge to the AFM community, involving issues such as the correct interpretation of the phase images. In this paper, the cantilever's dynamic behavior in tapping mode AFM is studied through a three dimensional finite element method. The cantilever's dynamic displacement responses are firstly obtained via simulation under different tip-sample separations, and for different tip-sample interaction forces, such as elastic force, adhesion force, viscosity force, and the van der Waals force, which correspond to the cantilever's action upon various different representative computer-generated test samples. Simulated results show that the dynamic cantilever displacement response can be divided into three zones: a free vibration zone, a transition zone, and a contact vibration zone. Phase trajectory, phase shift, transition time, pseudo stable amplitude, and frequency changes are then analyzed from the dynamic displacement responses that are obtained. Finally, experiments are carried out on a real AFM system to support the findings of the simulations. © 2015 Wiley Periodicals, Inc.

Atomic force microscopy imaging of macromolecular complexes.

PubMed

Santos, Sergio; Billingsley, Daniel; Thomson, Neil

2013-01-01

This chapter reviews amplitude modulation (AM) AFM in air and its applications to high-resolution imaging and interpretation of macromolecular complexes. We discuss single DNA molecular imaging and DNA-protein interactions, such as those with topoisomerases and RNA polymerase. We show how relative humidity can have a major influence on resolution and contrast and how it can also affect conformational switching of supercoiled DNA. Four regimes of AFM tip-sample interaction in air are defined and described, and relate to water perturbation and/or intermittent mechanical contact of the tip with either the molecular sample or the surface. Precise control and understanding of the AFM operational parameters is shown to allow the user to switch between these different regimes: an interpretation of the origins of topographical contrast is given for each regime. Perpetual water contact is shown to lead to a high-resolution mode of operation, which we term SASS (small amplitude small set-point) imaging, and which maximizes resolution while greatly decreasing tip and sample wear and any noise due to perturbation of the surface water. Thus, this chapter provides sufficient information to reliably control the AFM in the AM AFM mode of operation in order to image both heterogeneous samples and single macromolecules including complexes, with high resolution and with reproducibility. A brief introduction to AFM, its versatility and applications to biology is also given while providing references to key work and general reviews in the field.

Sub-50 nm metrology on extreme ultra violet chemically amplified resist—A systematic assessment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maas, D. J., E-mail: diederik.maas@tno.nl; Herfst, R.; Veldhoven, E. van

2015-10-15

With lithographic patterning dimensions decreasing well below 50 nm, it is of high importance to understand metrology at such small scales. This paper presents results obtained from dense arrays of contact holes (CHs) with various Critical Dimension (CD) between 15 and 50 nm, as patterned in a chemically amplified resist using an ASML EUV scanner and measured at ASML and TNO. To determine the differences between various (local) CD metrology techniques, we conducted an experiment using optical scatterometry, CD-Scanning Electron Microscopy (CD-SEM), Helium ion Microscopy (HIM), and Atomic Force Microscopy (AFM). CD-SEM requires advanced beam scan strategies to mitigate samplemore » charging; the other tools did not need that. We discuss the observed main similarities and differences between the various techniques. To this end, we assessed the spatial frequency content in the raw images for SEM, HIM, and AFM. HIM and AFM resolve the highest spatial frequencies, which are attributed to the more localized probe-sample interaction for these techniques. Furthermore, the SEM, HIM, and AFM waveforms are analyzed in detail. All techniques show good mutual correlation, albeit the reported CD values systematically differ significantly. HIM systematically reports a 25% higher CD uniformity number than CD-SEM for the same arrays of CHs, probably because HIM has a higher resolution than the CD-SEM used in this assessment. A significant speed boost for HIM and AFM is required before these techniques are to serve the demanding industrial metrology applications like optical critical dimension and CD-SEM do nowadays.« less

Sub-50 nm metrology on extreme ultra violet chemically amplified resist—A systematic assessment

NASA Astrophysics Data System (ADS)

Maas, D. J.; Fliervoet, T.; Herfst, R.; van Veldhoven, E.; Meessen, J.; Vaenkatesan, V.; Sadeghian, H.

2015-10-01

With lithographic patterning dimensions decreasing well below 50 nm, it is of high importance to understand metrology at such small scales. This paper presents results obtained from dense arrays of contact holes (CHs) with various Critical Dimension (CD) between 15 and 50 nm, as patterned in a chemically amplified resist using an ASML EUV scanner and measured at ASML and TNO. To determine the differences between various (local) CD metrology techniques, we conducted an experiment using optical scatterometry, CD-Scanning Electron Microscopy (CD-SEM), Helium ion Microscopy (HIM), and Atomic Force Microscopy (AFM). CD-SEM requires advanced beam scan strategies to mitigate sample charging; the other tools did not need that. We discuss the observed main similarities and differences between the various techniques. To this end, we assessed the spatial frequency content in the raw images for SEM, HIM, and AFM. HIM and AFM resolve the highest spatial frequencies, which are attributed to the more localized probe-sample interaction for these techniques. Furthermore, the SEM, HIM, and AFM waveforms are analyzed in detail. All techniques show good mutual correlation, albeit the reported CD values systematically differ significantly. HIM systematically reports a 25% higher CD uniformity number than CD-SEM for the same arrays of CHs, probably because HIM has a higher resolution than the CD-SEM used in this assessment. A significant speed boost for HIM and AFM is required before these techniques are to serve the demanding industrial metrology applications like optical critical dimension and CD-SEM do nowadays.

On the origin of amplitude reduction mechanism in tapping mode atomic force microscopy

NASA Astrophysics Data System (ADS)

Keyvani, Aliasghar; Sadeghian, Hamed; Goosen, Hans; van Keulen, Fred

2018-04-01

The origin of amplitude reduction in Tapping Mode Atomic Force Microscopy (TM-AFM) is typically attributed to the shift in resonance frequency of the cantilever due to the nonlinear tip-sample interactions. In this paper, we present a different insight into the same problem which, besides explaining the amplitude reduction mechanism, provides a simple reasoning for the relationship between tip-sample interactions and operation parameters (amplitude and frequency). The proposed formulation, which attributes the amplitude reduction to an interference between the tip-sample and dither force, only deals with the linear part of the system; however, it fully agrees with experimental results and numerical solutions of the full nonlinear model of TM-AFM.

Coupled molecular and cantilever dynamics model for frequency-modulated atomic force microscopy.

PubMed

Klocke, Michael; Wolf, Dietrich E

2016-01-01

A molecular dynamics model is presented, which adds harmonic potentials to the atomic interactions to mimic the elastic properties of an AFM cantilever. It gives new insight into the correlation between the experimentally monitored frequency shift and cantilever damping due to the interaction between tip atoms and scanned surface. Applying the model to ionic crystals with rock salt structure two damping mechanisms are investigated, which occur separately or simultaneously depending on the tip position. These mechanisms are adhesion hysteresis on the one hand and lateral excitations of the cantilever on the other. We find that the short range Lennard-Jones part of the atomic interaction alone is sufficient for changing the predominant mechanism. When the long range ionic interaction is switched off, the two damping mechanisms occur with a completely different pattern, which is explained by the energy landscape for the apex atom of the tip. In this case the adhesion hysteresis is always associated with a distinct lateral displacement of the tip. It is shown how this may lead to a systematic shift between the periodic patterns obtained from the frequency and from the damping signal, respectively.

Potential preventive role of lactic acid bacteria against aflatoxin M₁ immunotoxicity and genotoxicity in mice.

PubMed

Ben Salah-Abbès, Jalila; Abbès, Samir; Jebali, Rania; Haous, Zohra; Oueslati, Ridha

2015-01-01

Aflatoxin M1 (AFM1) is a mycotoxin produced by numerous Aspergillus species in pre- or post-harvest cereals and milk. Exposure to AFM1 imparts potent economic losses in the livestock industry. Toxicologically, it also causes severe immune system problems. The aims of this study were to evaluate a new AFM1-binding/degrading microorganism for biologic detoxification, to examine its ability to degrade AFM1 in liquid medium, and to evaluate its potential for in vivo preventative effects against AFM1-induced immunotoxicity and genotoxicity in mice. Lactobacillus plantarum MON03 (LP) isolated from Tunisian artisanal butter was found to display significant binding ability to AFM1 in PBS (93%) within 24 h of incubation. Further, the LP was able to tolerate gastric acidity, bile salts, and adhere efficiently to Caco-3 cells in vitro. The in vivo study used Balb/c mice that received either vehicle (control), LP only (at 1 × 10(9)CFU/L, ∼1 mg/kg bw), AFM1 (100 mg/kg bw), or AFM1 + LP daily for 15 days (by gavage); two other groups received a single dose of colchicine (4 mg/kg) or mitomycin C (1 mg/kg) as positive controls for induction of micronuclei and chromosomal aberrations, respectively. The results showed that, compared to in control mice, AFM1 treatment led to significantly decreased body weight gains, and caused cytotoxic/genotoxic effects as indicated by increases in frequencies of polychromatic erythrocytes, as well as those with micronucleation (PCEMN) and chromosomal aberrations, among bone marrow cells. The concurrent administration of LP with AFM1 strongly reduced the adverse effects of AFM1 on each parameter. Mice receiving AFM1 + LP co-treatment displayed no significant differences in the assayed parameters as compared to the control mice. By itself, the bacteria caused no adverse effects. Based on the data, it is concluded that the test bacteria could potentially be beneficial in the detoxification of AFM1-contaminated foods and feeds for humans and animals.

Dynamic characterization of AFM probes by laser Doppler vibrometry and stroboscopic holographic methodologies

NASA Astrophysics Data System (ADS)

Kuppers, J. D.; Gouverneur, I. M.; Rodgers, M. T.; Wenger, J.; Furlong, C.

2006-08-01

In atomic probe microscopy, micro-probes of various sizes, geometries, and materials are used to define the interface between the samples under investigation and the measuring detectors and instrumentation. Therefore, measuring resolution in atomic probe microscopy is highly dependent on the transfer function characterizing the micro-probes used. In this paper, characterization of the dynamic transfer function of specific micro-cantilever probes used in an Atomic Force Microscope (AFM) operating in the tapping mode is presented. Characterization is based on the combined application of laser Doppler vibrometry (LDV) and real-time stroboscopic optoelectronic holographic microscopy (OEHM) methodologies. LDV is used for the rapid measurement of the frequency response of the probes due to an excitation function containing multiple frequency components. Data obtained from the measured frequency response is used to identify the principal harmonics. In order to identify mode shapes corresponding to the harmonics, full-field of view OEHM is applied. This is accomplished by measurements of motion at various points on the excitation curve surrounding the identified harmonics. It is shown that the combined application of LDV and OEHM enables the high-resolution characterization of mode shapes of vibration, damping characteristics, as well as transient response of the micro-cantilever probes. Such characterization is necessary in high-resolution AFM measurements.

Fast, High Resolution, and Wide Modulus Range Nanomechanical Mapping with Bimodal Tapping Mode.

PubMed

Kocun, Marta; Labuda, Aleksander; Meinhold, Waiman; Revenko, Irène; Proksch, Roger

2017-10-24

Tapping mode atomic force microscopy (AFM), also known as amplitude modulated (AM) or AC mode, is a proven, reliable, and gentle imaging mode with widespread applications. Over the several decades that tapping mode has been in use, quantification of tip-sample mechanical properties such as stiffness has remained elusive. Bimodal tapping mode keeps the advantages of single-frequency tapping mode while extending the technique by driving and measuring an additional resonant mode of the cantilever. The simultaneously measured observables of this additional resonance provide the additional information necessary to extract quantitative nanomechanical information about the tip-sample mechanics. Specifically, driving the higher cantilever resonance in a frequency modulated (FM) mode allows direct measurement of the tip-sample interaction stiffness and, with appropriate modeling, the set point-independent local elastic modulus. Here we discuss the advantages of bimodal tapping, coined AM-FM imaging, for modulus mapping. Results are presented for samples over a wide modulus range, from a compliant gel (∼100 MPa) to stiff materials (∼100 GPa), with the same type of cantilever. We also show high-resolution (subnanometer) stiffness mapping of individual molecules in semicrystalline polymers and of DNA in fluid. Combined with the ability to remain quantitative even at line scan rates of nearly 40 Hz, the results demonstrate the versatility of AM-FM imaging for nanomechanical characterization in a wide range of applications.

The Modeling of the Effects of Soiling, Its Mechanisms, and the Corresponding Abrasion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simpson, Lin; Muller, Matthew; Deceglie, Michael

2016-02-24

Decreasing LCOE with predictive soiling loss models (using site data to predict annualized energy loss), quantification of different soiling mechanisms (using AFM-based characterization), and developing standards for PV module coatings.

Mapping the amide I absorption in single bacteria and mammalian cells with resonant infrared nanospectroscopy

NASA Astrophysics Data System (ADS)

Baldassarre, L.; Giliberti, V.; Rosa, A.; Ortolani, M.; Bonamore, A.; Baiocco, P.; Kjoller, K.; Calvani, P.; Nucara, A.

2016-02-01

Infrared (IR) nanospectroscopy performed in conjunction with atomic force microscopy (AFM) is a novel, label-free spectroscopic technique that meets the increasing request for nano-imaging tools with chemical specificity in the field of life sciences. In the novel resonant version of AFM-IR, a mid-IR wavelength-tunable quantum cascade laser illuminates the sample below an AFM tip working in contact mode, and the repetition rate of the mid-IR pulses matches the cantilever mechanical resonance frequency. The AFM-IR signal is the amplitude of the cantilever oscillations driven by the thermal expansion of the sample after absorption of mid-IR radiation. Using purposely nanofabricated polymer samples, here we demonstrate that the AFM-IR signal increases linearly with the sample thickness t for t \\gt 50 nm, as expected from the thermal expansion model of the sample volume below the AFM tip. We then show the capability of the apparatus to derive information on the protein distribution in single cells through mapping of the AFM-IR signal related to the amide-I mid-IR absorption band at 1660 cm-1. In Escherichia Coli bacteria we see how the topography changes, observed when the cell hosts a protein over-expression plasmid, are correlated with the amide I signal intensity. In human HeLa cells we obtain evidence that the protein distribution in the cytoplasm and in the nucleus is uneven, with a lateral resolution better than 100 nm.

Atomic Force Microscopy | Materials Science | NREL

Science.gov Websites

, the cantilever is oscillated close to its resonant frequency, while the amplitude of the oscillation resonant frequency, which in turns changes the oscillation amplitude. The change in the amplitude is the of photodiodes. Because it uses the force as interaction, AFM can generate high magnifications (up to

Nanoscale surface characterization using laser interference microscopy

NASA Astrophysics Data System (ADS)

Ignatyev, Pavel S.; Skrynnik, Andrey A.; Melnik, Yury A.

2018-03-01

Nanoscale surface characterization is one of the most significant parts of modern materials development and application. The modern microscopes are expensive and complicated tools, and its use for industrial tasks is limited due to laborious sample preparation, measurement procedures, and low operation speed. The laser modulation interference microscopy method (MIM) for real-time quantitative and qualitative analysis of glass, metals, ceramics, and various coatings has a spatial resolution of 0.1 nm for vertical and up to 100 nm for lateral. It is proposed as an alternative to traditional scanning electron microscopy (SEM) and atomic force microscopy (AFM) methods. It is demonstrated that in the cases of roughness metrology for super smooth (Ra >1 nm) surfaces the application of a laser interference microscopy techniques is more optimal than conventional SEM and AFM. The comparison of semiconductor test structure for lateral dimensions measurements obtained with SEM and AFM and white light interferometer also demonstrates the advantages of MIM technique.

AFM and SFG studies of pHEMA-based hydrogel contact lens surfaces in saline solution: adhesion, friction, and the presence of non-crosslinked polymer chains at the surface.

PubMed

Kim, Seong Han; Opdahl, Aric; Marmo, Chris; Somorjai, Gabor A

2002-04-01

The surfaces of two types of soft contact lenses neutral and ionic hydrogels--were characterized by atomic force microscopy (AFM) and sum-frequency-generation (SFG) vibrational spectroscopy. AFM measurements in saline solution showed that the presence of ionic functional groups at the surface lowered the friction and adhesion to a hydrophobic polystyrene tip. This was attributed to the specific interactions of water and the molecular orientation of hydrogel chains at the surface. Friction and adhesion behavior also revealed the presence of domains of non-crosslinked polymer chains at the lens surface. SFG showed that the lens surface became partially dehydrated upon exposure to air. On this partially dehydrated lens surface, the non-crosslinked domains exhibited low friction and adhesion in AFM. Fully hydrated in saline solution, the non-crosslinked domains extended more than tens of nanometers into solution and were mobile.

Modeling viscoelasticity through spring–dashpot models in intermittent-contact atomic force microscopy

PubMed Central

López-Guerra, Enrique A

2014-01-01

Summary We examine different approaches to model viscoelasticity within atomic force microscopy (AFM) simulation. Our study ranges from very simple linear spring–dashpot models to more sophisticated nonlinear systems that are able to reproduce fundamental properties of viscoelastic surfaces, including creep, stress relaxation and the presence of multiple relaxation times. Some of the models examined have been previously used in AFM simulation, but their applicability to different situations has not yet been examined in detail. The behavior of each model is analyzed here in terms of force–distance curves, dissipated energy and any inherent unphysical artifacts. We focus in this paper on single-eigenmode tip–sample impacts, but the models and results can also be useful in the context of multifrequency AFM, in which the tip trajectories are very complex and there is a wider range of sample deformation frequencies (descriptions of tip–sample model behaviors in the context of multifrequency AFM require detailed studies and are beyond the scope of this work). PMID:25551043

Discrimination of bladder cancer cells from normal urothelial cells with high specificity and sensitivity: combined application of atomic force microscopy and modulated Raman spectroscopy.

PubMed

Canetta, Elisabetta; Riches, Andrew; Borger, Eva; Herrington, Simon; Dholakia, Kishan; Adya, Ashok K

2014-05-01

Atomic force microscopy (AFM) and modulated Raman spectroscopy (MRS) were used to discriminate between living normal human urothelial cells (SV-HUC-1) and bladder tumour cells (MGH-U1) with high specificity and sensitivity. MGH-U1 cells were 1.5-fold smaller, 1.7-fold thicker and 1.4-fold rougher than normal SV-HUC-1 cells. The adhesion energy was 2.6-fold higher in the MGH-U1 cells compared to normal SV-HUC-1 cells, which possibly indicates that bladder tumour cells are more deformable than normal cells. The elastic modulus of MGH-U1 cells was 12-fold lower than SV-HUC-1 cells, suggesting a higher elasticity of the bladder cancer cell membranes. The biochemical fingerprints of cancer cells displayed a higher DNA and lipid content, probably due to an increase in the nuclear to cytoplasm ratio. Normal cells were characterized by higher protein contents. AFM studies revealed a decrease in the lateral dimensions and an increase in thickness of cancer cells compared to normal cells; these studies authenticate the observations from MRS. Nanostructural, nanomechanical and biochemical profiles of bladder cells provide qualitative and quantitative markers to differentiate between normal and cancerous cells at the single cellular level. AFM and MRS allow discrimination between adhesion energy, elasticity and Raman spectra of SV-HUC-1 and MGH-U1 cells with high specificity (83, 98 and 95%) and sensitivity (97, 93 and 98%). Such single-cell-level studies could have a pivotal impact on the development of AFM-Raman combined methodologies for cancer profiling and screening with translational significance. Copyright © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Evaluating the potential energy landscape over single molecules at room temperature with lateral force microscopy

NASA Astrophysics Data System (ADS)

Weymouth, Alfred J.; Riegel, Elisabeth; Matencio, Sonia; Giessibl, Franz J.

2018-04-01

One of the challenges of AFM, in contrast to STM, is that the measured signal includes both long-range and short-range components. The most accurate method for removing long-range components is to measure both on and off an adsorbate and to subtract the difference. This on-off method is challenging at room temperature due to thermal drift. By moving to a non-contact scheme in which the lateral component of the force interaction is probed, the measurement is dominated by short-range interactions. We use frequency-modulation lateral force microscopy to measure individual PTCDA molecules adsorbed on Ag/Si(111)-( √{3 }×√{3 } ). By fitting the data to a model potential, we can extract the depth and width of the potential. When the tip is closer to the sample, a repulsive feature can be observed in the data.

Pattering of nanostructures with high aspect ratio in polymer materials

NASA Astrophysics Data System (ADS)

Lyuksyutov, Sergei; Paramonov, Pavel; Sancaktar, Erol; Vaia, Richard; Juhl, Shane

2004-04-01

The generation of features larger than the initial atomic force microscope (AFM) tip-surface distance (presumably less that 1nm for unbiased tip) had previously been reported for silicon and metal oxidation. Such nanostructure (1-50 nm high) formation exceeding AFM tip-sample separation has been observed by us during AFM-assisted nanolithography in polymers [1,2]. The technique produces nanostructures up to 100 nm high in thin (10-30 nm) polymer films through the one-step process. The specific spatial details of the tip-surface contact profile, as well as cantilever motion, with applied bias during writing is not well understood and we are not aware of any comprehensive explanation provided in literature for this effect. In this work we analyze tip-polymer interaction using real-time tip deflection. An abrupt lift-up of biased AFM tip has been recorded experimentally and found to be proportional to the height of polymer nanostructures. This fact was used to pattern robust nanostructures of 20-100 nm high using amplitude modulated AFM-assisted electrostatic nanolithography [2] as the arrays of dots in polystyrene and polybenzoxasole polymer films. References [1] S.F. Lyuksyutov, R.A. Vaia, P.B. Paramonov, S. Juhl, L. Waterhouse, R.M. Ralich, G. Sigalov, and E. Sancaktar, Nature Materials 2(7) 468-472 (2003) [2] S.F. Lyuksyutov, R.A. Vaia, P.B. Paramonov, and S. Juhl, Appl. Phys. Lett. 83 (21), 4405-4407 (2003)

Reconstruction of Laser-Induced Surface Topography from Electron Backscatter Diffraction Patterns.

PubMed

Callahan, Patrick G; Echlin, McLean P; Pollock, Tresa M; De Graef, Marc

2017-08-01

We demonstrate that the surface topography of a sample can be reconstructed from electron backscatter diffraction (EBSD) patterns collected with a commercial EBSD system. This technique combines the location of the maximum background intensity with a correction from Monte Carlo simulations to determine the local surface normals at each point in an EBSD scan. A surface height map is then reconstructed from the local surface normals. In this study, a Ni sample was machined with a femtosecond laser, which causes the formation of a laser-induced periodic surface structure (LIPSS). The topography of the LIPSS was analyzed using atomic force microscopy (AFM) and reconstructions from EBSD patterns collected at 5 and 20 kV. The LIPSS consisted of a combination of low frequency waviness due to curtaining and high frequency ridges. The morphology of the reconstructed low frequency waviness and high frequency ridges matched the AFM data. The reconstruction technique does not require any modification to existing EBSD systems and so can be particularly useful for measuring topography and its evolution during in situ experiments.

Multiple heteroatom substitution to graphene nanoribbon

PubMed Central

Meyer, Ernst

2018-01-01

Substituting heteroatoms into nanostructured graphene elements, such as graphene nanoribbons, offers the possibility for atomic engineering of electronic properties. To characterize these substitutions, functionalized atomic force microscopy (AFM)—a tool to directly resolve chemical structures—is one of the most promising tools, yet the chemical analysis of heteroatoms has been rarely performed. We synthesized multiple heteroatom-substituted graphene nanoribbons and showed that AFM can directly resolve elemental differences and can be correlated to the van der Waals radii, as well as the modulated local electron density caused by the substitution. This elemental-sensitive measurement takes an important step in the analysis of functionalized two-dimensional carbon materials. PMID:29662955

Direct Force Measurements of Receptor-Ligand Interactions on Living Cells

NASA Astrophysics Data System (ADS)

Eibl, Robert H.

The characterization of cell adhesion between two living cells at the level of single receptor-ligand bonds is an experimental challenge. This chapter describes how the extremely sensitive method of atomic force microscopy (AFM) based force spectroscopy can be applied to living cells in order to probe for cell-to-cell or cell-to-substrate interactions mediated by single pairs of adhesion receptors. In addition, it is outlined how single-molecule AFM force spectroscopy can be used to detect physiologic changes of an adhesion receptor in a living cell. This force spectroscopy allows us to detect in living cells rapidly changing, chemokine SDF-1 triggered activation states of single VLA-4 receptors. This recently developed AFM application will allow for the detailed investigation of the integrin-chemokine crosstalk of integrin activation mechanisms and on how other adhesion receptors are modulated in health and disease. As adhesion molecules, living cells and even bacteria can be studied by single-molecule AFM force spectroscopy, this method is set to become a powerful tool that can not only be used in biophysics, but in cell biology as well as in immunology and cancer research.

Sub-nanometer Resolution Imaging with Amplitude-modulation Atomic Force Microscopy in Liquid

PubMed Central

Farokh Payam, Amir; Piantanida, Luca; Cafolla, Clodomiro; Voïtchovsky, Kislon

2016-01-01

Atomic force microscopy (AFM) has become a well-established technique for nanoscale imaging of samples in air and in liquid. Recent studies have shown that when operated in amplitude-modulation (tapping) mode, atomic or molecular-level resolution images can be achieved over a wide range of soft and hard samples in liquid. In these situations, small oscillation amplitudes (SAM-AFM) enhance the resolution by exploiting the solvated liquid at the surface of the sample. Although the technique has been successfully applied across fields as diverse as materials science, biology and biophysics and surface chemistry, obtaining high-resolution images in liquid can still remain challenging for novice users. This is partly due to the large number of variables to control and optimize such as the choice of cantilever, the sample preparation, and the correct manipulation of the imaging parameters. Here, we present a protocol for achieving high-resolution images of hard and soft samples in fluid using SAM-AFM on a commercial instrument. Our goal is to provide a step-by-step practical guide to achieving high-resolution images, including the cleaning and preparation of the apparatus and the sample, the choice of cantilever and optimization of the imaging parameters. For each step, we explain the scientific rationale behind our choices to facilitate the adaptation of the methodology to every user's specific system. PMID:28060262

Thermal characterization of TiCxOy thin films

NASA Astrophysics Data System (ADS)

Fernandes, A. C.; Vaz, F.; Gören, A.; Junge, K. H.; Gibkes, J.; Bein, B. K.; Macedo, F.

2008-01-01

Thermal wave characterization of thin films used in industrial applications can be a useful tool, not just to get information on the films' thermal properties, but to get information on structural-physical parameters, e.g. crystalline structure and surface roughness, and on the film deposition conditions, since the thermal film properties are directly related to the structural-physical parameters and to the deposition conditions. Different sets of TiCXOY thin films, deposited by reactive magnetron sputtering on steel, have been prepared, changing only one deposition parameter at a time. Here, the effect of the oxygen flow on the thermal film properties is studied. The thermal waves have been measured by modulated IR radiometry, and the phase lag data have been interpreted using an Extremum method by which the thermal coating parameters are directly related to the values and modulation frequencies of the relative extrema of the inverse calibrated thermal wave phases. Structural/morphological characterization has been done using X-ray diffraction (XRD) and atomic force microscopy (AFM). The characterization of the films also includes thickness, hardness, and electric resistivity measurements. The results obtained so far indicate strong correlations between the thermal diffusivity and conductivity, on the one hand, and the oxygen flow on the other hand.

Ionic Gel Modulation of RKKY Interactions in Synthetic Anti-Ferromagnetic Nanostructures for Low Power Wearable Spintronic Devices.

PubMed

Yang, Qu; Zhou, Ziyao; Wang, Liqian; Zhang, Hongjia; Cheng, Yuxin; Hu, Zhongqiang; Peng, Bin; Liu, Ming

2018-05-01

To meet the demand of developing compatible and energy-efficient flexible spintronics, voltage manipulation of magnetism on soft substrates is in demand. Here, a voltage tunable flexible field-effect transistor structure by ionic gel (IG) gating in perpendicular synthetic anti-ferromagnetic nanostructure is demonstrated. As a result, the interlayer Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction can be tuned electrically at room temperature. With a circuit gating voltage, anti-ferromagnetic (AFM) ordering is enhanced or converted into an AFM-ferromagnetic (FM) intermediate state, accompanying with the dynamic domain switching. This IG gating process can be repeated stably at different curvatures, confirming an excellent mechanical property. The IG-induced modification of interlayer exchange coupling is related to the change of Fermi level aroused by the disturbance of itinerant electrons. The voltage modulation of RKKY interaction with excellent flexibility proposes an application potential for wearable spintronic devices with energy efficiency and ultralow operation voltage. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Elastic modulus of nanomaterials: resonant contact-AFM measurement and reduced-size effects (Invited Paper)

NASA Astrophysics Data System (ADS)

Nysten, Bernard; Fretigny, Christian; Cuenot, Stephane

2005-05-01

Resonant contact atomic force microscopy (resonant C-AFM) is used to quantitatively measure the elastic modulus of polymer nanotubes and metallic nanowires. To achieve this, an oscillating electric field is applied between the sample holder and the microscope head to excite the oscillation of the cantilever in contact with the nanostructures suspended over the pores of a membrane. The resonance frequency of the cantilever with the tip in contact with a nanostructure is shifted to higher values with respect to the resonance frequency of the free cantilever. It is demonstrated that the system can simply be modeled by a cantilever with the tip in contact with two springs. The measurement of the frequency shift enables the direct determination of the spring stiffness, i.e. the nanowires or nanotube stiffness. The method also enables the determination of the boundary conditions of the nanobeam on the membrane. The tensile elastic modulus is then simply determined using the classical theory of beam deflection. The obtained results for the larger nanostructures fairly agree to the values reported in the literature for the macroscopic elastic modulus of the corresponding materials. The measured modulus of the nanomaterials with smaller diameters is significantly higher than that of the larger ones. The increase of the apparent elastic modulus for the smaller diameters is attributed to the surface tension effects. It is thus demonstrated that resonant C-AFM enables the measurement of the elastic modulus and of the surface tension of nanomaterials.

Thermal noise limit for ultra-high vacuum noncontact atomic force microscopy

PubMed Central

Lübbe, Jannis; Temmen, Matthias; Rode, Sebastian; Rahe, Philipp; Kühnle, Angelika

2013-01-01

Summary The noise of the frequency-shift signal Δf in noncontact atomic force microscopy (NC-AFM) consists of cantilever thermal noise, tip–surface-interaction noise and instrumental noise from the detection and signal processing systems. We investigate how the displacement-noise spectral density d z at the input of the frequency demodulator propagates to the frequency-shift-noise spectral density d Δ f at the demodulator output in dependence of cantilever properties and settings of the signal processing electronics in the limit of a negligible tip–surface interaction and a measurement under ultrahigh-vacuum conditions. For a quantification of the noise figures, we calibrate the cantilever displacement signal and determine the transfer function of the signal-processing electronics. From the transfer function and the measured d z, we predict d Δ f for specific filter settings, a given level of detection-system noise spectral density d z ds and the cantilever-thermal-noise spectral density d z th. We find an excellent agreement between the calculated and measured values for d Δ f. Furthermore, we demonstrate that thermal noise in d Δ f, defining the ultimate limit in NC-AFM signal detection, can be kept low by a proper choice of the cantilever whereby its Q-factor should be given most attention. A system with a low-noise signal detection and a suitable cantilever, operated with appropriate filter and feedback-loop settings allows room temperature NC-AFM measurements at a low thermal-noise limit with a significant bandwidth. PMID:23400758

Thermal noise limit for ultra-high vacuum noncontact atomic force microscopy.

PubMed

Lübbe, Jannis; Temmen, Matthias; Rode, Sebastian; Rahe, Philipp; Kühnle, Angelika; Reichling, Michael

2013-01-01

The noise of the frequency-shift signal Δf in noncontact atomic force microscopy (NC-AFM) consists of cantilever thermal noise, tip-surface-interaction noise and instrumental noise from the detection and signal processing systems. We investigate how the displacement-noise spectral density d(z) at the input of the frequency demodulator propagates to the frequency-shift-noise spectral density d(Δ) (f) at the demodulator output in dependence of cantilever properties and settings of the signal processing electronics in the limit of a negligible tip-surface interaction and a measurement under ultrahigh-vacuum conditions. For a quantification of the noise figures, we calibrate the cantilever displacement signal and determine the transfer function of the signal-processing electronics. From the transfer function and the measured d(z), we predict d(Δ) (f) for specific filter settings, a given level of detection-system noise spectral density d(z) (ds) and the cantilever-thermal-noise spectral density d(z) (th). We find an excellent agreement between the calculated and measured values for d(Δ) (f). Furthermore, we demonstrate that thermal noise in d(Δ) (f), defining the ultimate limit in NC-AFM signal detection, can be kept low by a proper choice of the cantilever whereby its Q-factor should be given most attention. A system with a low-noise signal detection and a suitable cantilever, operated with appropriate filter and feedback-loop settings allows room temperature NC-AFM measurements at a low thermal-noise limit with a significant bandwidth.

Cellular-level surgery using nano robots.

PubMed

Song, Bo; Yang, Ruiguo; Xi, Ning; Patterson, Kevin Charles; Qu, Chengeng; Lai, King Wai Chiu

2012-12-01

The atomic force microscope (AFM) is a popular instrument for studying the nano world. AFM is naturally suitable for imaging living samples and measuring mechanical properties. In this article, we propose a new concept of an AFM-based nano robot that can be applied for cellular-level surgery on living samples. The nano robot has multiple functions of imaging, manipulation, characterizing mechanical properties, and tracking. In addition, the technique of tip functionalization allows the nano robot the ability for precisely delivering a drug locally. Therefore, the nano robot can be used for conducting complicated nano surgery on living samples, such as cells and bacteria. Moreover, to provide a user-friendly interface, the software in this nano robot provides a "videolized" visual feedback for monitoring the dynamic changes on the sample surface. Both the operation of nano surgery and observation of the surgery results can be simultaneously achieved. This nano robot can be easily integrated with extra modules that have the potential applications of characterizing other properties of samples such as local conductance and capacitance.

Electrostatic nanolithography in polymer materials: an alternative technique for nanostructures formation

NASA Astrophysics Data System (ADS)

Lyuksyutov, Sergei F.; Paramonov, Pavel B.; Sigalov, Grigori; Vaia, Richard A.; Juhl, Shane; Sancaktar, Erol

2003-10-01

The combination of localized softening attolitres (10^2 -10^4) of polymer film by Jule heating, extremely non-uniform electric field gradients to polarize and manipulate the soften polymer, and single step technique using conventional atomic force microscopy (AFM), establishes a new paradigm for nanolithography in a broad class of polymer materials allowing rapid (order of milliseconds) creation of raised and depressed nanostructures without external heating of a polymer film of AFM tip-film contact [1]. In this work we present recent studies of AFM-assisted electrostatic nanolithography (AFMEN) such as amplitude-modulated AFMEN, and the humidity influence on nanostructures formation during contact mode AFMEN. It has been shown that the aspect ratio of nanostructures grows on the order of magnitude (0.2), while the lateral dimensions of nanodots decreases down to 10-15 nm. [1] S.F. Lyuksyutov, R.A. Vaia, P.B. Paramonov, S. Juhl, L. Waterhouse, R.M. Ralich, G. Sigalov, and E. Sancaktar, "Electrostatic nanolithography in polymers using atomic force microscopy," Nature Materials 2, 468-472 (2003)

PREFACE: NC-AFM 2004: Proceedings of the 7th International Conference on Non-contact Atomic Force Microscopy

NASA Astrophysics Data System (ADS)

Schwarz, Udo

2005-03-01

With the ongoing miniaturization of devices and controlled nanostructuring of materials, the importance of atomic-scale information on surfaces and surface properties is growing continuously. The astonishing progress in nanoscience and nanotechnology that took place during the last two decades was in many ways related to recent progress in high-resolution imaging techniques such as scanning tunnelling microscopy and transmission electron microscopy. Since the mid-1990s, non-contact atomic force microscopy (NC-AFM) performed in ultrahigh vacuum has evolved as an alternative technique that achieves atomic resolution, but without the restriction to conducting surfaces of the previously established techniques. Advances of the rapidly developing field of NC-AFM are discussed at annual conferences as part of a series that started in 1998 in Osaka, Japan. This special issue of Nanotechnology is a compilation of original work presented at the 7th International Conference on Non-contact Atomic Force Microscopy that took place in Seattle, USA, 12-15 September 2004. Over the years, the conference grew in size and scope. Atomic resolution imaging of oxides and semiconductors remains an issue. Noticeable new developments have been presented in this regard such as, e.g., the demonstrated ability to manipulate individual atoms. Additionally, the investigation of individual molecules, clusters, and organic materials gains more and more attention. In this context, considerable effort is undertaken to transfer the NC-AFM principle based on frequency modulation to applications in air and liquids with the goal of enabling high-resolution surface studies of biological material in native environments, as well as to reduce the experimental complexity, which so far involves the availability of (costly) vacuum systems. Force spectroscopy methods continue to be improved and are applied to topics such as the imaging of the three-dimensional force field as a function of the distance with atomic resolution, the investigation of near-surface electronic states, the quantification of adhesion forces, and the lateral mapping of surface potentials. The origin of energy dissipation, which is closely related to an in-depth understanding of tip-surface interactions and imaging mechanisms, was the subject of an ongoing discussion and addressed by various theoretical, computational, and experimental contributions. A characteristic of the NC-AFM conference series is the lively and friendly atmosphere, which year after year stimulates scientific discussions between the participants. This time, the programme included 5 invited talks, 84 contributed presentations, and 113 participants; furthermore, three educational lectures were given as part of a pre-conference workshop targeted at NC-AFM newcomers, which was attended by 30 participants. I would like to thank the members of the international steering committee and the programme committee for their continued effort in organizing the meeting. Special thanks go to the chair of the programme and local organizing committees S Fain and the conference manager J Kvamme for making the meeting a success. Financial support is acknowledged from the corporate sponsors MikroMasch USA, Nanonis GmbH, Nanosurf AG, Omicron Nanotechnology, PSIA, Inc., and RHK Technology, as well as from the institutional sponsors National Science Foundation and PNNL/UW Joint Institute for Nanoscience. Finally, I would like to express my gratitude to everyone who participated in assembling this special issue including the authors, the reviewers, and, in particular, the excellent and experienced journal team from the Institute of Physics Publishing headed by Nina Couzin, for devoting their time and efforts so that we could make this issue a useful representation of the progress in NC-AFM while maintaining our tight publication schedule. In conclusion, I would like to mention that the Seattle conference was the first one of the NC-AFM series that took place in the USA. As such, it was part of a series of recent activities within the USA, which will help in establishing a strong domestic NC-AFM community.

Analysis of Aflatoxin M1 in Breast Milk and Its Association with Nutritional and Socioeconomic Status of Lactating Mothers in Lebanon.

PubMed

Elaridi, Jomana; Bassil, Maya; Kharma, Joelle Abi; Daou, Farah; Hassan, Hussein F

2017-10-01

Aflatoxin B 1 (AFB 1 ) is the most potent of the dietary aflatoxins, and its major metabolite, aflatoxin M 1 (AFM 1 ), is frequently found in the breast milk of lactating mothers. The aim of this study was to assess the occurrence and factors associated with AFM 1 contamination of breast milk collected from lactating mothers in Lebanon. A total of 111 breast milk samples were collected according to the guidelines set by the World Health Organization. Samples were analyzed with a competitive enzyme-linked immunosorbent assay between December 2015 and November 2016. A survey was used to determine the demographic and anthropometric characteristics of participating lactating mothers. Dietary habits were assessed using a semiquantitative food frequency questionnaire. Mean (±standard deviation) concentration of AFM 1 in the breast milk samples was 4.31 ± 1.8 ng/L, and 93.8% of samples contained AFM 1 at 0.2 to 7.9 ng/L. The mean concentration of AFM 1 was significantly lower (P < 0.05) in fall and winter (4.1 ± 1.9 ng/L) than in spring and summer (5.0 ± 1.7 ng/L). None of the samples exceeded the European Commission regulation limit (25 ng/L) for infant milk replacement formula. AFM 1 contamination was significantly associated (P < 0.05) with the daily consumption of white cheeses but not with the consumption of meat or cereal products. No significant association (P > 0.05) was observed between AFM 1 concentrations in breast milk and anthropometric sociodemographic factors (age and level of education) or the governorate of residence of the nursing mothers. The mean AFM 1 estimated daily intake was found to be 0.69 ng/day/kg of body weight. Although the incidence of AFM 1 contamination was low, our first-of-its-kind study highlights the importance of conducting investigations on mycotoxin contamination in breast milk and of developing protection strategies to tackle the exposure of infants to this potent chemical hazard.

Phase transition behaviors of the supported DPPC bilayer investigated by sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM).

PubMed

Wu, Heng-Liang; Tong, Yujin; Peng, Qiling; Li, Na; Ye, Shen

2016-01-21

The phase transition behaviors of a supported bilayer of dipalmitoylphosphatidyl-choline (DPPC) have been systematically evaluated by in situ sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM). By using an asymmetric bilayer composed of per-deuterated and per-protonated monolayers, i.e., DPPC-d75/DPPC and a symmetric bilayer of DPPC/DPPC, we were able to probe the molecular structural changes during the phase transition process of the lipid bilayer by SFG spectroscopy. It was found that the DPPC bilayer is sequentially melted from the top (adjacent to the solution) to bottom leaflet (adjacent to the substrate) over a wide temperature range. The conformational ordering of the supported bilayer does not decrease (even slightly increases) during the phase transition process. The conformational defects in the bilayer can be removed after the complete melting process. The phase transition enthalpy for the bottom leaflet was found to be approximately three times greater than that for the top leaflet, indicating a strong interaction of the lipids with the substrate. The present SFG and AFM observations revealed similar temperature dependent profiles. Based on these results, the temperature-induced structural changes in the supported lipid bilayer during its phase transition process are discussed in comparison with previous studies.

SNOM and AFM microscopy techniques to study the effect of non-ionizing radiation on the morphological and biochemical properties of human keratinocytes cell line (HaCaT).

PubMed

Rieti, S; Manni, V; Lisi, A; Giuliani, L; Sacco, D; D'Emilia, E; Cricenti, A; Generosi, R; Luce, M; Grimaldi, S

2004-01-01

In this study we have employed atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) techniques to study the effect of the interaction between human keratinocytes (HaCaT) and electromagnetic fields at low frequency. HaCaT cells were exposed to a sinusoidal magnetic field at a density of 50 Hz, 1 mT. AFM analysis revealed modification in shape and morphology in exposed cells with an increase in the areas of adhesion between cells. This latter finding was confirmed by SNOM indirect immunofluorescence analysis performed with a fluorescent antibody against the adhesion marker beta4 integrin, which revealed an increase of beta4 integrin segregation in the cell membrane of 50-Hz exposed cells, suggesting that a higher percentage of these cells shows a modified pattern of this adhesion marker.

Association between Urinary Aflatoxin (AFM1) and Dietary Intake among Adults in Hulu Langat District, Selangor, Malaysia

PubMed Central

Sulaiman, Siti Husna

2018-01-01

Aflatoxin is a food contaminant and its exposure through the diet is frequent and ubiquitous. A long-term dietary aflatoxin exposure has been linked to the development of liver cancer in populations with high prevalence of aflatoxin contamination in foods. Therefore, this study was conducted to identify the association between urinary aflatoxin M1 (AFM1), a biomarker of aflatoxin exposure, with the dietary intake among adults in Hulu Langat district, Selangor, Malaysia. Certain food products have higher potential for aflatoxin contamination and these were listed in a Food Frequency Questionnaire, which was given to all study participants. This allowed us to record consumption rates for each food product listed. Concomitantly, urine samples were collected, from adults in selected areas in Hulu Langat district, for the measurement of AFM1 levels using an ELISA kit. Of the 444 urine samples collected and tested, 199 were positive for AFM1, with 37 of them exceeding the limit of detection (LOD) of 0.64 ng/mL. Cereal products showed the highest consumption level among all food groups, with an average intake of 512.54 g per day. Chi-square analysis showed that consumption of eggs (X2 = 4.77, p = 0.03) and dairy products (X2 = 19.36, p < 0.01) had significant associations with urinary AFM1 but both food groups were having a phi and Cramer’s V value that less than 0.3, which indicated that the association between these food groups’ consumption and AFM1 level in urine was weak. PMID:29642443

Atomic Force Microscopy of Isolated Nanostructures: Biomolecular Imaging in Hydrated Environments - Status and Future Prospects

NASA Astrophysics Data System (ADS)

Santos, Sergio; Thomson, Neil H.

The use of the atomic force microscope (AFM) in ambient conditions has some key advantages for characterising isolated nanostructures over other operating environments. The lack of a bulk liquid environment minimises motion of the sample to maximise resolution, while humidity control allows retention of surface water, keeping biomolecules sufficiently hydrated. The use of relatively stiff cantilevers in air (k > 10 N/m) prevents significant energy being transferred to higher modes or frequencies. This enables reliable modelling of the cantilever dynamics with relatively straightforward point mass and spring models. We show herein that combining modelling with experiment leads to robust interpretation of dynamic AFM in air. This understanding has led to new ways of operation, including a true non-contact mode in ambient and small amplitude small set-point (SASS) modes. These modes will be important to gain quantitative information about structure and processes on the nanoscale. We also discuss interpretation of height information obtained from AFM on the nanoscale and summarise a framework for recovery of apparent height loss for nanostructures. A combination of these methods will lead to a new era of quantitative AFM for nanoscience and nanotechnology.

77 FR 49702 - Airworthiness Directives; Embraer S.A. Airplanes

Federal Register 2010, 2011, 2012, 2013, 2014

2012-08-17

... replacing the AMS controller processor module with one containing new software, and a new AFM revision. This... protection system. We are issuing this AD to prevent the possibility of a right-hand (RH) engine compressor... down. Also there is the possibility of right hand (RH) engine compressor to stall after the Auxiliary...

Effect of cholesterol on electrostatics in lipid-protein films of a pulmonary surfactant.

PubMed

Finot, Eric; Leonenko, Yuri; Moores, Brad; Eng, Lukas; Amrein, Matthias; Leonenko, Zoya

2010-02-02

We report the changes in the electrical properties of the lipid-protein film of pulmonary surfactant produced by excess cholesterol. Pulmonary surfactant (PS) is a complex lipid-protein mixture that forms a molecular film at the interface of the lung's epithelia. The defined molecular arrangement of the lipids and proteins of the surfactant film gives rise to the locally highly variable electrical surface potential of the interface, which becomes considerably altered in the presence of cholesterol. With frequency modulation Kelvin probe force microscopy (FM-KPFM) and force measurements, complemented by theoretical analysis, we showed that excess cholesterol significantly changes the electric field around a PS film because of the presence of nanometer-sized electrostatic domains and affects the electrostatic interaction of an AFM probe with a PS film. These changes in the local electrical field would greatly alter the interaction of the surfactant film with charged species and would immediately impact the manner in which inhaled (often charged) airborne nanoparticles and fibers might interact with the lung interface.

Nonlinear tapping dynamics of multi-walled carbon nanotube tipped atomic force microcantilevers

NASA Astrophysics Data System (ADS)

Lee, S. I.; Howell, S. W.; Raman, A.; Reifenberger, R.; Nguyen, C. V.; Meyyappan, M.

2004-05-01

The nonlinear dynamics of an atomic force microcantilever (AFM) with an attached multi-walled carbon nanotube (MWCNT) tip is investigated experimentally and theoretically. We present the experimental nonlinear frequency response of a MWCNT tipped microcantilever in the tapping mode. Several unusual features in the response distinguish it from those traditionally observed for conventional tips. The MWCNT tipped AFM probe is apparently immune to conventional imaging instabilities related to the coexistence of attractive and repulsive tapping regimes. A theoretical interaction model for the system using an Euler elastica MWCNT model is developed and found to predict several unusual features of the measured nonlinear response.

Imaging and quantitative data acquisition of biological cell walls with Atomic Force Microscopy and Scanning Acoustic Microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tittmann, B. R.; Xi, X.

This chapter demonstrates the feasibility of Atomic Force Microscopy (AFM) and High Frequency Scanning Acoustic Microscopy (HF-SAM) as tools to characterize biological tissues. Both the AFM and the SAM have shown to provide imaging (with different resolution) and quantitative elasticity measuring abilities. Plant cell walls with minimal disturbance and under conditions of their native state have been examined with these two kinds of microscopy. After descriptions of both the SAM and AFM, their special features and the typical sample preparation is discussed. The sample preparation is focused here on epidermal peels of onion scales and celery epidermis cells which weremore » sectioned for the AFM to visualize the inner surface (closest to the plasma membrane) of the outer epidermal wall. The nm-wide cellulose microfibrils orientation and multilayer structure were clearly observed. The microfibril orientation and alignment tend to be more organized in older scales compared with younger scales. The onion epidermis cell wall was also used as a test analog to study cell wall elasticity by the AFM nanoindentation and the SAM V(z) feature. The novelty in this work was to demonstrate the capability of these two techniques to analyze isolated, single layered plant cell walls in their natural state. AFM nanoindentation was also used to probe the effects of Ethylenediaminetetraacetic acid (EDTA), and calcium ion treatment to modify pectin networks in cell walls. The results suggest a significant modulus increase in the calcium ion treatment and a slight decrease in EDTA treatment. To complement the AFM measurements, the HF-SAM was used to obtain the V(z) signatures of the onion epidermis. These measurements were focused on documenting the effect of pectinase enzyme treatment. The results indicate a significant change in the V(z) signature curves with time into the enzyme treatment. Thus AFM and HF-SAM open the door to a systematic nondestructive structure and mechanical property study of complex biological cell walls. A unique feature of this approach is that both microscopes allow the biological samples to be examined in their natural fluid (water) environment.« less

Plume Characterization of a Laboratory Model 22 N GPIM Thruster via High-Frequency Raman Spectroscopy

NASA Technical Reports Server (NTRS)

Williams, George J.; Kojima, Jun J.; Arrington, Lynn A.; Deans, Matthew C.; Reed, Brian D.; Kinzbach, McKenzie I.; McLean, Christopher H.

2015-01-01

The Green Propellant Infusion Mission (GPIM) will demonstrate the capability of a green propulsion system, specifically, one using the monopropellant, AF-M315E. One of the risks identified for GPIM is potential contamination of sensitive areas of the spacecraft from the effluents in the plumes of AF-M315E thrusters. Plume characterization of a laboratory-model 22 N thruster via optical diagnostics was conducted at NASA GRC in a space-simulated environment. A high-frequency pulsed laser was coupled with an electron-multiplied ICCD camera to perform Raman spectroscopy in the near-field, low-pressure plume. The Raman data yielded plume constituents and temperatures over a range of thruster chamber pressures and as a function of thruster (catalyst) operating time. Schlieren images of the near-field plume enabled calculation of plume velocities and revealed general plume structure of the otherwise invisible plume. The measured velocities are compared to those predicted by a two-dimensional, kinetic model. Trends in data and numerical results are presented from catalyst mid-life to end-of-life. The results of this investigation were coupled with the Raman and Schlieren data to provide an anchor for plume impingement analysis presented in a companion paper. The results of both analyses will be used to improve understanding of the nature of AF-M315E plumes and their impacts to GPIM and other future missions.

Tapping mode imaging and measurements with an inverted atomic force microscope.

PubMed

Chan, Sandra S F; Green, John-Bruce D

2006-07-18

This report demonstrates the successful use of the inverted atomic force microscope (i-AFM) for tapping mode AFM imaging of cantilever-supported samples. i-AFM is a mode of AFM operation in which a sample supported on a tipless cantilever is imaged by one of many tips in a microfabricated tip array. Tapping mode is an intermittent contact mode whereby the cantilever is oscillated at or near its resonance frequency, and the amplitude and/or phase are used to image the sample. In the process of demonstrating that tapping mode images could be obtained in the i-AFM design, it was observed that the amplitude of the cantilever oscillation decreased markedly as the cantilever and tip array were approached. The source of this damping of the cantilever oscillations was identified to be the well-known "squeeze film damping", and the extent of damping was a direct consequence of the relatively shorter tip heights for the tip arrays, as compared to those of commercially available tapping mode cantilevers with integrated tips. The functional form for the distance dependence of the damping coefficient is in excellent agreement with previously published models for squeeze film damping, and the values for the fitting parameters make physical sense. Although the severe damping reduces the cantilever free amplitude substantially, we found that we were still able to access the low-amplitude regime of oscillation necessary for attractive tapping mode imaging of fragile molecules.

Passive microrheology of soft materials with atomic force microscopy: A wavelet-based spectral analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martinez-Torres, C.; Streppa, L.; Arneodo, A.

2016-01-18

Compared to active microrheology where a known force or modulation is periodically imposed to a soft material, passive microrheology relies on the spectral analysis of the spontaneous motion of tracers inherent or external to the material. Passive microrheology studies of soft or living materials with atomic force microscopy (AFM) cantilever tips are rather rare because, in the spectral densities, the rheological response of the materials is hardly distinguishable from other sources of random or periodic perturbations. To circumvent this difficulty, we propose here a wavelet-based decomposition of AFM cantilever tip fluctuations and we show that when applying this multi-scale methodmore » to soft polymer layers and to living myoblasts, the structural damping exponents of these soft materials can be retrieved.« less

Rotation Matrix Method Based on Ambiguity Function for GNSS Attitude Determination.

PubMed

Yang, Yingdong; Mao, Xuchu; Tian, Weifeng

2016-06-08

Global navigation satellite systems (GNSS) are well suited for attitude determination. In this study, we use the rotation matrix method to resolve the attitude angle. This method achieves better performance in reducing computational complexity and selecting satellites. The condition of the baseline length is combined with the ambiguity function method (AFM) to search for integer ambiguity, and it is validated in reducing the span of candidates. The noise error is always the key factor to the success rate. It is closely related to the satellite geometry model. In contrast to the AFM, the LAMBDA (Least-squares AMBiguity Decorrelation Adjustment) method gets better results in solving the relationship of the geometric model and the noise error. Although the AFM is more flexible, it is lack of analysis on this aspect. In this study, the influence of the satellite geometry model on the success rate is analyzed in detail. The computation error and the noise error are effectively treated. Not only is the flexibility of the AFM inherited, but the success rate is also increased. An experiment is conducted in a selected campus, and the performance is proved to be effective. Our results are based on simulated and real-time GNSS data and are applied on single-frequency processing, which is known as one of the challenging case of GNSS attitude determination.

In situ Electrochemical-AFM Study of LiFePO4 Thin Film in Aqueous Electrolyte.

PubMed

Wu, Jiaxiong; Cai, Wei; Shang, Guangyi

2016-12-01

Lithium-ion (Li-ion) batteries have been widely used in various kinds of electronic devices in our daily life. The use of aqueous electrolyte in Li-ion battery would be an alternative way to develop low cost and environmentally friendly batteries. In this paper, the lithium iron phosphate (LiFePO4) thin film cathode for the aqueous rechargeable Li-ion battery is prepared by radio frequency magnetron sputtering deposition method. The XRD, SEM, and AFM results show that the film is composed of LiFePO4 grains with olivine structure and the average size of 100 nm. Charge-discharge measurements at current density of 10 μAh cm(-2) between 0 and 1 V show that the LiFePO4 thin film electrode is able to deliver an initial discharge capacity of 113 mAh g(-1). Specially, the morphological changes of the LiFePO4 film electrode during charge and discharge processes were investigated in aqueous environment by in situ EC-AFM, which is combined AFM with chronopotentiometry method. The changes in grain area are measured, and the results show that the size of the grains decreases and increases during the charge and discharge, respectively; the relevant mechanism is discussed.

Surface Morphology of Undoped and Doped ZnSe Films

NASA Technical Reports Server (NTRS)

George, T.; Hayes, M.; Chen, H.; Chattopadhyay, K.; Thomas E.; Morgan, S.; Burger, A.

1998-01-01

Rare-earth doped ions in polar II-VI semiconductors have recently played an important role in the optical properties of materials and devices. In this study, undoped ZnSe and erbium doped ZnSe films were grown by radio frequency (RF) magnetron sputtering method. Atomic Force Microscopy (AFM) was used together with optical microscopy and UV-Vis spectroscopy to characterize the films. Doped samples were found to have higher surface roughness and quite different surface morphology compared to that of undoped samples. The grown films generally show a relatively smooth and uniform surface indicating that they are of overall good quality. The impact of plasma etching on ZnSe:Er film examined under AFM is also discussed.

Mechanically modulated dewetting by atomic force microscope for micro- and nano- droplet array fabrication.

PubMed

Wang, Feifei; Li, Pan; Wang, Dong; Li, Longhai; Xie, Shuangxi; Liu, Lianqing; Wang, Yuechao; Li, Wen Jung

2014-10-06

Organizing a material into well-defined patterns during the dewetting process provides an attractive micro-/nano-fabrication method without using a conventional lithographic process, and hence, offers potential applications in organic electronics, optics systems, and memory devices. We report here how the mechanical modification of polymer surface by an Atomic Force Microscope (AFM) can be used to guide thin film dewetting evolution and break the intrinsic spatial correlation of spontaneous instability. An AFM is used to implement the mechanical modification of progressively narrow grids to investigate the influence of pattern size on the modulation of ultrathin polystyrene films dewetting evolution. For films with different initial thicknesses, when grid size is close to or below the characteristic wavelength of instability, the spinodal dewetting is suppressed, and film rupture is restricted to the cutting trench. We will show in this paper it is possible to generate only one droplet per gridded area on a thin film subsequent to nucleation dominated dewetting on a non-patterned substrate. Furthermore, when the grid periodicity exceeds the spinodal length, the number of droplets in predefined areas gradually approaches that associated with unconfined dewetting.

Mechanically Modulated Dewetting by Atomic Force Microscope for Micro- and Nano- Droplet Array Fabrication

PubMed Central

Wang, Feifei; Li, Pan; Wang, Dong; Li, Longhai; Xie, Shuangxi; Liu, Lianqing; Wang, Yuechao; Li, Wen Jung

2014-01-01

Organizing a material into well-defined patterns during the dewetting process provides an attractive micro-/nano-fabrication method without using a conventional lithographic process, and hence, offers potential applications in organic electronics, optics systems, and memory devices. We report here how the mechanical modification of polymer surface by an Atomic Force Microscope (AFM) can be used to guide thin film dewetting evolution and break the intrinsic spatial correlation of spontaneous instability. An AFM is used to implement the mechanical modification of progressively narrow grids to investigate the influence of pattern size on the modulation of ultrathin polystyrene films dewetting evolution. For films with different initial thicknesses, when grid size is close to or below the characteristic wavelength of instability, the spinodal dewetting is suppressed, and film rupture is restricted to the cutting trench. We will show in this paper it is possible to generate only one droplet per gridded area on a thin film subsequent to nucleation dominated dewetting on a non-patterned substrate. Furthermore, when the grid periodicity exceeds the spinodal length, the number of droplets in predefined areas gradually approaches that associated with unconfined dewetting. PMID:25283744

"DNA Origami Traffic Lights" with a Split Aptamer Sensor for a Bicolor Fluorescence Readout.

PubMed

Walter, Heidi-Kristin; Bauer, Jens; Steinmeyer, Jeannine; Kuzuya, Akinori; Niemeyer, Christof M; Wagenknecht, Hans-Achim

2017-04-12

A split aptamer for adenosine triphosphate (ATP) was embedded as a recognition unit into two levers of a nanomechanical DNA origami construct by extension and modification of selected staple strands. An additional optical module in the stem of the split aptamer comprised two different cyanine-styryl dyes that underwent an energy transfer from green (donor) to red (acceptor) emission if two ATP molecules were bound as target molecule to the recognition module and thereby brought the dyes in close proximity. As a result, the ATP as a target triggered the DNA origami shape transition and yielded a fluorescence color change from green to red as readout. Conventional atomic force microscopy (AFM) images confirmed the topology change from the open form of the DNA origami in the absence of ATP into the closed form in the presence of the target molecule. The obtained closed/open ratios in the absence and presence of target molecules tracked well with the fluorescence color ratios and thereby validated the bicolor fluorescence readout. The correct positioning of the split aptamer as the functional unit farthest away from the fulcrum of the DNA origami was crucial for the aptasensing by fluorescence readout. The fluorescence color change allowed additionally to follow the topology change of the DNA origami aptasensor in real time in solution. The concepts of fluorescence energy transfer for bicolor readout in a split aptamer in solution, and AFM on surfaces, were successfully combined in a single DNA origami construct to obtain a bimodal readout. These results are important for future custom DNA devices for chemical-biological and bioanalytical purposes because they are not only working as simple aptamers but are also visible by AFM on the single-molecule level.

Low loss poly-silicon for high performance capacitive silicon modulators.

PubMed

Douix, Maurin; Baudot, Charles; Marris-Morini, Delphine; Valéry, Alexia; Fowler, Daivid; Acosta-Alba, Pablo; Kerdilès, Sébastien; Euvrard, Catherine; Blanc, Romuald; Beneyton, Rémi; Souhaité, Aurélie; Crémer, Sébastien; Vulliet, Nathalie; Vivien, Laurent; Boeuf, Frédéric

2018-03-05

Optical properties of poly-silicon material are investigated to be integrated in new silicon photonics devices, such as capacitive modulators. Test structure fabrication is done on 300 mm wafer using LPCVD deposition: 300 nm thick amorphous silicon layers are deposited on thermal oxide, followed by solid phase crystallization anneal. Rib waveguides are fabricated and optical propagation losses measured at 1.31 µm. Physical analysis (TEM ASTAR, AFM and SIMS) are used to assess the origin of losses. Optimal deposition and annealing conditions have been defined, resulting in 400 nm-wide rib waveguides with only 9.2-10 dB/cm losses.

Investigation of polymer derived ceramics cantilevers for application of high speed atomic force microscopy

NASA Astrophysics Data System (ADS)

Wu, Chia-Yun

High speed Atomic Force Microscopy (AFM) has a wide variety of applications ranging from nanomanufacturing to biophysics. In order to have higher scanning speed of certain AFM modes, high resonant frequency cantilevers are needed; therefore, the goal of this research is to investigate using polymer derived ceramics for possible applications in making high resonant frequency AFM cantilevers using complex cross sections. The polymer derived ceramic that will be studied, is silicon carbide. Polymer derived ceramics offer a potentially more economic fabrication approach for MEMS due to their relatively low processing temperatures and ease of complex shape design. Photolithography was used to make the desired cantilever shapes with micron scale size followed by a wet etching process to release the cantilevers from the substrates. The whole manufacturing process we use borrow well-developed techniques from the semiconducting industry, and as such this project also could offer the opportunity to reduce the fabrication cost of AFM cantilevers and MEMS in general. The characteristics of silicon carbide made from the precursor polymer, SMP-10 (Starfire Systems), were studied. In order to produce high qualities of silicon carbide cantilevers, where the major concern is defects, proper process parameters needed to be determined. Films of polymer derived ceramics often have defects due to shrinkage during the conversion process. Thus control of defects was a central issue in this study. A second, related concern was preventing oxidation; the polymer derived ceramics we chose is easily oxidized during processing. Establishing an environment without oxygen in the whole process was a significant challenge in the project. The optimization of the parameters for using photolithography and wet etching process was the final and central goal of the project; well established techniques used in microfabrication were modified for use in making the cantilever in the project. The techniques developed here open a path to the fabrication of cantilevers with unconventional cross sections.

Stretching of Single Polymer Chains Using the Atomic Force Microscope

NASA Astrophysics Data System (ADS)

Ortiz, C.; van der Vegte, E. W.; van Swieten, E.; Robillard, G. T.; Hadziioannou, G.

1998-03-01

A variety of macroscopic phenomenon involve "nanoscale" polymer deformation including rubber elasticity, shear yielding, strain hardening, stress relaxation, fracture, and flow. With the advent of new and improved experimental techniques, such as the atomic force microscope (AFM), the probing of physical properties of polymers has reached finer and finer scales. The development of mixed self-assembling monolayer techniques and the chemical functionalization of AFM probe tips has allowed for mechanical experiments on single polymer chains of molecular dimensions. In our experiments, mixed monolayers are prepared in which end-functionalized, flexible polymer chains of thiol-terminated poly(methacrylic acid) are covalently bonded, isolated, and randomly distributed on gold substrates. The coils are then imaged, tethered to a gold-coated AFM tip, and stretched between the tip and the substrate in a conventional force / distance experiment. An increase in the attractive force due to entropic, elastic resistance to stretching, as well as fracture of the polymer chain is observed. The effect of chain stiffness, topological constraints, strain rate, mechanical hysteresis, and stress relaxation were investigated. Force modulation techniques were also employed in order to image the viscoelastic character of the polymer chains. Parallel work includes similar studies of biological systems such as wheat gluten proteins and polypeptides.

AFM Study of Charge Transfer Between Metals Due to the Oxygen Redox Couple in Water

NASA Astrophysics Data System (ADS)

Trombley, Jeremy; Panthani, Tessie; Sankaran, Mohan; Angus, John; Kash, Kathleen

2010-03-01

The oxygen redox couple in an adsorbed water film can pin the Fermi level at the surfaces of diamond, GaN and ZnO.footnotetextV. Chakrapani, C. Pendyala, K. Kash, A. B. Anderson, M. K. Sunkara and J. C. Angus, J. Am. Chem. Soc. 130 (2008) 12944-12952, and ref. 6 therein. We report here preliminary observations of the same phenomenon at metal surfaces. A Pt-coated atomic force microscope (AFM) tip was used to take force-distance measurements on Au, Ag, and Pt surfaces placed in pH-controlled water. The work functions of these surfaces vary over ˜2eV and span the electrochemical potential range of the oxygen redox couple, which varies with pH according to the Nernst equation. Adjusting the pH of the water from 4 to 12 allowed us to change the redox potential energy from -5.42eV to -4.95eV, changing the surface charge and the associated screening charge and modulating the pull-off force. This work has relevance to AFM of many materials in air, and to contact electrification, mechanical friction, and nanoscale corona discharges.

Spin-polarized current injection induced magnetic reconstruction at oxide interface

DOE PAGES

Fang, F.; Yin, Y. W.; Li, Qi; ...

2017-01-04

Electrical manipulation of magnetism presents a promising way towards using the spin degree of freedom in very fast, low-power electronic devices. Though there has been tremendous progress in electrical control of magnetic properties using ferromagnetic (FM) nanostructures, an opportunity of manipulating antiferromagnetic (AFM) states should offer another route for creating a broad range of new enabling technologies. Here we selectively probe the interface magnetization of SrTiO 3/La 0.5Ca 0.5MnO 3/La 0.7Sr 0.3MnO 3 heterojunctions and discover a new spin-polarized current injection induced interface magnetoelectric (ME) effect. The accumulation of majority spins at the interface causes a sudden, reversible transition ofmore » the spin alignment of interfacial Mn ions from AFM to FM exchange-coupled, while the injection of minority electron spins alters the interface magnetization from C-type to A-type AFM state. In contrast, the bulk magnetization remains unchanged. We attribute the current-induced interface ME effect to modulations of the strong double-exchange interaction between conducting electron spins and local magnetic moments. As a result, the effect is robust and may serve as a viable route for electronic and spintronic applications.« less

Spin-polarized current injection induced magnetic reconstruction at oxide interface

NASA Astrophysics Data System (ADS)

Fang, F.; Yin, Y. W.; Li, Qi; Lüpke, G.

2017-01-01

Electrical manipulation of magnetism presents a promising way towards using the spin degree of freedom in very fast, low-power electronic devices. Though there has been tremendous progress in electrical control of magnetic properties using ferromagnetic (FM) nanostructures, an opportunity of manipulating antiferromagnetic (AFM) states should offer another route for creating a broad range of new enabling technologies. Here we selectively probe the interface magnetization of SrTiO3/La0.5Ca0.5MnO3/La0.7Sr0.3MnO3 heterojunctions and discover a new spin-polarized current injection induced interface magnetoelectric (ME) effect. The accumulation of majority spins at the interface causes a sudden, reversible transition of the spin alignment of interfacial Mn ions from AFM to FM exchange-coupled, while the injection of minority electron spins alters the interface magnetization from C-type to A-type AFM state. In contrast, the bulk magnetization remains unchanged. We attribute the current-induced interface ME effect to modulations of the strong double-exchange interaction between conducting electron spins and local magnetic moments. The effect is robust and may serve as a viable route for electronic and spintronic applications.

Toward correlating structure and mechanics of platelets.

PubMed

Sorrentino, Simona; Studt, Jan-Dirk; Horev, Melanie Bokstad; Medalia, Ohad; Sapra, K Tanuj

2016-09-02

The primary physiological function of blood platelets is to seal vascular lesions after injury and form hemostatic thrombi in order to prevent blood loss. This task relies on the formation of strong cellular-extracellular matrix interactions in the subendothelial lesions. The cytoskeleton of a platelet is key to all of its functions: its ability to spread, adhere and contract. Despite the medical significance of platelets, there is still no high-resolution structural information of their cytoskeleton. Here, we discuss and present 3-dimensional (3D) structural analysis of intact platelets by using cryo-electron tomography (cryo-ET) and atomic force microscopy (AFM). Cryo-ET provides in situ structural analysis and AFM gives stiffness maps of the platelets. In the future, combining high-resolution structural and mechanical techniques will bring new understanding of how structural changes modulate platelet stiffness during activation and adhesion.

In situ study of Li-ions diffusion and deformation in Li-rich cathode materials by using scanning probe microscopy techniques

NASA Astrophysics Data System (ADS)

Zeng, Kaiyang; Li, Tao; Tian, Tian

2017-08-01

In this paper, the scanning probe microscopy (SPM) based techniques, namely, conductive-AFM, electrochemical strain microscopy (ESM) and AM-FM (amplitude modulation-frequency modulation) techniques, are used to in situ characterize the changes in topography, conductivity and elastic properties of Li-rich layered oxide cathode (Li1.2Mn0.54Ni0.13Co0.13O2) materials, in the form of nanoparticles, when subject to the external electric field. Nanoparticles are the basic building blocks for composite cathode in a Li-ion rechargeable battery. Characterization of the structure and electrochemical properties of the nanoparticles is very important to understand the performance and reliability of the battery materials and devices. In this study, the conductivity, deformation and mechanical properties of the Li-rich oxide nanoparticles under different polarities of biases are studied using the above-mentioned SPM techniques. This information can be correlated with the Li+-ion diffusion and migration in the particles under external electrical field. The results also confirm that the SPM techniques are ideal tools to study the changes in various properties of electrode materials at nano- to micro-scales during or after the ‘simulated’ battery operation conditions. These techniques can also be used to in situ characterize the electrochemical performances of other energy storage materials, especially in the form of the nanoparticles.

A New Method for Single-Epoch Ambiguity Resolution with Indoor Pseudolite Positioning.

PubMed

Li, Xin; Zhang, Peng; Guo, Jiming; Wang, Jinling; Qiu, Weining

2017-04-21

Ambiguity resolution (AR) is crucial for high-precision indoor pseudolite positioning. Due to the existing characteristics of the pseudolite positioning system, such as the geometry structure of the stationary pseudolite which is consistently invariant, the indoor signal is easy to interrupt and the first order linear truncation error cannot be ignored, and a new AR method based on the idea of the ambiguity function method (AFM) is proposed in this paper. The proposed method is a single-epoch and nonlinear method that is especially well-suited for indoor pseudolite positioning. Considering the very low computational efficiency of conventional AFM, we adopt an improved particle swarm optimization (IPSO) algorithm to search for the best solution in the coordinate domain, and variances of a least squares adjustment is conducted to ensure the reliability of the solving ambiguity. Several experiments, including static and kinematic tests, are conducted to verify the validity of the proposed AR method. Numerical results show that the IPSO significantly improved the computational efficiency of AFM and has a more elaborate search ability compared to the conventional grid searching method. For the indoor pseudolite system, which had an initial approximate coordinate precision better than 0.2 m, the AFM exhibited good performances in both static and kinematic tests. With the corrected ambiguity gained from our proposed method, indoor pseudolite positioning can achieve centimeter-level precision using a low-cost single-frequency software receiver.

Elemental Identification by Combining Atomic Force Microscopy and Kelvin Probe Force Microscopy.

PubMed

Schulz, Fabian; Ritala, Juha; Krejčí, Ondrej; Seitsonen, Ari Paavo; Foster, Adam S; Liljeroth, Peter

2018-06-01

There are currently no experimental techniques that combine atomic-resolution imaging with elemental sensitivity and chemical fingerprinting on single molecules. The advent of using molecular-modified tips in noncontact atomic force microscopy (nc-AFM) has made it possible to image (planar) molecules with atomic resolution. However, the mechanisms responsible for elemental contrast with passivated tips are not fully understood. Here, we investigate elemental contrast by carrying out both nc-AFM and Kelvin probe force microscopy (KPFM) experiments on epitaxial monolayer hexagonal boron nitride (hBN) on Ir(111). The hBN overlayer is inert, and the in-plane bonds connecting nearest-neighbor boron and nitrogen atoms possess strong covalent character and a bond length of only ∼1.45 Å. Nevertheless, constant-height maps of both the frequency shift Δ f and the local contact potential difference exhibit striking sublattice asymmetry. We match the different atomic sites with the observed contrast by comparison with nc-AFM image simulations based on the density functional theory optimized hBN/Ir(111) geometry, which yields detailed information on the origin of the atomic-scale contrast.

Direct Measurement of Optical Force Induced by Near-Field Plasmonic Cavity Using Dynamic Mode AFM

PubMed Central

Guan, Dongshi; Hang, Zhi Hong; Marcet, Zsolt; Liu, Hui; Kravchenko, I. I.; Chan, C. T.; Chan, H. B.; Tong, Penger

2015-01-01

Plasmonic nanostructures have attracted much attention in recent years because of their potential applications in optical manipulation through near-field enhancement. Continuing experimental efforts have been made to develop accurate techniques to directly measure the near-field optical force induced by the plasmonic nanostructures in the visible frequency range. In this work, we report a new application of dynamic mode atomic force microscopy (DM-AFM) in the measurement of the enhanced optical force acting on a nano-structured plasmonic resonant cavity. The plasmonic cavity is made of an upper gold-coated glass sphere and a lower quartz substrate patterned with an array of subwavelength gold disks. In the near-field when the sphere is positioned close to the disk array, plasmonic resonance is excited in the cavity and the induced force by a 1550 nm infrared laser is found to be increased by an order of magnitude compared with the photon pressure generated by the same laser light. The experiment demonstrates that DM-AFM is a powerful tool for the study of light induced forces and their enhancement in plasmonic nanostructures. PMID:26586455

Atomic force microscopy as nano-stethoscope to study living organisms, insects

NASA Astrophysics Data System (ADS)

Sokolov, Igor; Dokukin, Maxim; Guz, Nataliia

2012-02-01

Atomic force microscopy (AFM) is a known method to study various surfaces. Here we report on the use of AFM to study surface oscillations (coming from the work of internal organs) of living organisms, like insects. As an example, ladybird beetles (Hippodamia convergens) measured in different parts of the insect at picometer level. This allows us to record a much broader spectral range of possible surface vibrations (up to several kHz) than the previously studied oscillations due to breathing, heartbeat cycles, coelopulses, etc. (up to 5 -10 Hz). The used here AFM method allows collecting signal from the area as small as ˜100nm2 (0.0001μm2) with an example of noise level of (2±0.2)x10-3 nm r.m.s. at the range of frequencies >50Hz (potentially, up to a MHz). Application of this method to humans is discussed. The method, being a relatively non-invasive technique providing a new type of information, may be useful in developing of what could be called ``nanophysiology.''

Intermodulation Atomic Force Microscopy and Spectroscopy

NASA Astrophysics Data System (ADS)

Hutter, Carsten; Platz, Daniel; Tholen, Erik; Haviland, David; Hansson, Hans

2009-03-01

We present a powerful new method of dynamic AFM, which allows to gain far more information about the tip-surface interaction than standard amplitude or phase imaging, while scanning at comparable speed. Our method, called intermodulation atomic force microscopy (ImAFM), employs the manifestly nonlinear phenomenon of intermodulation to extract information about tip-surface forces. ImAFM uses one eigenmode of a mechanical resonator, the latter driven at two frequencies to produce many spectral peaks near its resonace, where sensitivity is highest [1]. We furthermore present a protocol for decoding the combined information encoded in the spectrum of intermodulation peaks. Our theoretical framework suggests methods to enhance the gained information by using a different parameter regime as compared to Ref. [1]. We also discuss strategies for solving the inverse problem, i.e., for extracting the nonlinear tip-surface interaction from the response, also naming limitations of our theoretical analysis. We will further report on latest progress to experimentally employ our new protocol.[3pt] [1] D. Platz, E. A. Tholen, D. Pesen, and D. B. Haviland, Appl. Phys. Lett. 92, 153106 (2008).

Nanoscale observation of organic thin film by atomic force microscopy

NASA Astrophysics Data System (ADS)

Mochizuki, Shota; Uruma, Takeshi; Satoh, Nobuo; Saravanan, Shanmugam; Soga, Tetsuo

2017-08-01

Organic photovoltaics (OPVs) fabricated using organic semiconductors and hybrid solar cells (HSCs) based on organic semiconductors/quantum dots (QDs) have been attracting significant attention owing to their potential use in low-cost solar energy-harvesting applications and flexible, light-weight, colorful, large-area devices. In this study, we observed and evaluated the surface of a photoelectric conversion layer (active layer) of the OPVs and HSCs based on phenyl-C61-butyric acid methyl ester (PCBM), poly(3-hexylthiophene) (P3HT), and zinc oxide (ZnO) nanoparticles. The experiment was performed using atomic force microscopy (AFM) combined with a frequency modulation detector (FM detector) and a contact potential difference (CPD) detection circuit. We experimentally confirmed the changes in film thickness and surface potential, as affected by the ZnO nanoparticle concentration. From the experimental results, we confirmed that ZnO nanoparticles possibly affect the structures of PCBM and P3HT. Also, we prepared an energy band diagram on the basis of the observation results, and analyzed the energy distribution inside the active layer.

Broadband near-field infrared spectromicroscopy using photothermal probes and synchrotron radiation.

PubMed

Donaldson, Paul M; Kelley, Chris S; Frogley, Mark D; Filik, Jacob; Wehbe, Katia; Cinque, Gianfelice

2016-02-08

In this paper, we experimentally demonstrate the use of infrared synchrotron radiation (IR-SR) as a broadband source for photothermal near-field infrared spectroscopy. We assess two methods of signal transduction; cantilever resonant thermal expansion and scanning thermal microscopy. By means of rapid mechanical chopping (50-150 kHz), we modulate the IR-SR at rates matching the contact resonance frequencies of atomic force microscope (AFM) cantilevers, allowing us to record interferograms yielding Fourier transform infrared (FT-IR) photothermal absorption spectra of polystyrene and cyanoacrylate films. Complementary offline measurements using a mechanically chopped CW IR laser confirmed that the resonant thermal expansion IR-SR measurements were below the diffraction limit, with a spatial resolution better than 500 nm achieved at a wavelength of 6 μm, i.e. λ/12 for the samples studied. Despite achieving the highest signal to noise so far for a scanning thermal microscopy measurement under conditions approaching near-field (dictated by thermal diffusion), the IR-SR resonant photothermal expansion FT-IR spectra measured were significantly higher in signal to noise in comparison with the scanning thermal data.

Outstanding resistance and passivation behaviour of new Fe-Co metal-metal glassy alloys in alkaline media

PubMed Central

Al-Harbi, Albandaree K.

2018-01-01

The electrochemical behavior of the oxide layers on two metal-metal glassy alloys, Fe78Co9Cr10Mo2Al1 (VX9)and Fe49Co49V2 (VX50) (at.%), were studied using electrochemical techniques including electrochemical frequency modulation (EFM), electrochemical impedance spectroscopy (EIS) and cyclic polarization (CP) measurements. The morphology and composition of the alloy surfaces were investigated using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion rate and surface roughness of both alloys increased as the concentration of NaOH in aqueous solution was raised. The presence of some protective elements in the composition of the alloys led to the formation of a spontaneous passive layer on the alloy surface. The higher resistance values of both alloys were associated with the magnitude of the dielectric properties of the passive films formed on their surfaces. Both alloys are classified as having outstanding resistance to corrosion, which results from the formation of a passive film that acts as an efficient barrier to corrosion in alkaline solution. PMID:29337992

Outstanding resistance and passivation behaviour of new Fe-Co metal-metal glassy alloys in alkaline media.

PubMed

Emran, Khadijah M; Al-Harbi, Albandaree K

2018-01-01

The electrochemical behavior of the oxide layers on two metal-metal glassy alloys, Fe78Co9Cr10Mo2Al1 (VX9)and Fe49Co49V2 (VX50) (at.%), were studied using electrochemical techniques including electrochemical frequency modulation (EFM), electrochemical impedance spectroscopy (EIS) and cyclic polarization (CP) measurements. The morphology and composition of the alloy surfaces were investigated using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion rate and surface roughness of both alloys increased as the concentration of NaOH in aqueous solution was raised. The presence of some protective elements in the composition of the alloys led to the formation of a spontaneous passive layer on the alloy surface. The higher resistance values of both alloys were associated with the magnitude of the dielectric properties of the passive films formed on their surfaces. Both alloys are classified as having outstanding resistance to corrosion, which results from the formation of a passive film that acts as an efficient barrier to corrosion in alkaline solution.

A combined averaging and frequency mixing approach for force identification in weakly nonlinear high-Q oscillators: Atomic force microscope

NASA Astrophysics Data System (ADS)

Sah, Si Mohamed; Forchheimer, Daniel; Borgani, Riccardo; Haviland, David

2018-02-01

We present a polynomial force reconstruction of the tip-sample interaction force in Atomic Force Microscopy. The method uses analytical expressions for the slow-time amplitude and phase evolution, obtained from time-averaging over the rapidly oscillating part of the cantilever dynamics. The slow-time behavior can be easily obtained in either the numerical simulations or the experiment in which a high-Q resonator is perturbed by a weak nonlinearity and a periodic driving force. A direct fit of the theoretical expressions to the simulated and experimental data gives the best-fit parameters for the force model. The method combines and complements previous works (Platz et al., 2013; Forchheimer et al., 2012 [2]) and it allows for computationally more efficient parameter mapping with AFM. Results for the simulated asymmetric piecewise linear force and VdW-DMT force models are compared with the reconstructed polynomial force and show a good agreement. It is also shown that the analytical amplitude and phase modulation equations fit well with the experimental data.

A mouse model of paralytic myelitis caused by enterovirus D68

PubMed Central

Yu, Guixia; Leser, J. Smith; Yagi, Shigeo; Tyler, Kenneth L.

2017-01-01

In 2014, the United States experienced an epidemic of acute flaccid myelitis (AFM) cases in children coincident with a nationwide outbreak of enterovirus D68 (EV-D68) respiratory disease. Up to half of the 2014 AFM patients had EV-D68 RNA detected by RT-PCR in their respiratory secretions, although EV-D68 was only detected in cerebrospinal fluid (CSF) from one 2014 AFM patient. Given previously described molecular and epidemiologic associations between EV-D68 and AFM, we sought to develop an animal model by screening seven EV-D68 strains for the ability to induce neurological disease in neonatal mice. We found that four EV-D68 strains from the 2014 outbreak (out of five tested) produced a paralytic disease in mice resembling human AFM. The remaining 2014 strain, as well as 1962 prototype EV-D68 strains Fermon and Rhyne, did not produce, or rarely produced, paralysis in mice. In-depth examination of the paralysis caused by a representative 2014 strain, MO/14-18947, revealed infectious virus, virion particles, and viral genome in the spinal cords of paralyzed mice. Paralysis was elicited in mice following intramuscular, intracerebral, intraperitoneal, and intranasal infection, in descending frequency, and was associated with infection and loss of motor neurons in the anterior horns of spinal cord segments corresponding to paralyzed limbs. Virus isolated from spinal cords of infected mice transmitted disease when injected into naïve mice, fulfilling Koch’s postulates in this model. Finally, we found that EV-D68 immune sera, but not normal mouse sera, protected mice from development of paralysis and death when administered prior to viral challenge. These studies establish an experimental model to study EV-D68-induced myelitis and to better understand disease pathogenesis and develop potential therapies. PMID:28231269

Functionalized AFM probes for force spectroscopy: eigenmode shapes and stiffness calibration through thermal noise measurements.

PubMed

Laurent, Justine; Steinberger, Audrey; Bellon, Ludovic

2013-06-07

The functionalization of an atomic force microscope (AFM) cantilever with a colloidal bead is a widely used technique when the geometry between the probe and the sample must be controlled, particularly in force spectroscopy. But some questions remain: how does a bead glued at the end of a cantilever influence its mechanical response? And more importantly for quantitative measurements, can we still determine the stiffness of the AFM probe with traditional techniques?In this paper, the influence of the colloidal mass loading on the eigenmode shape and resonant frequency is investigated by measuring the thermal noise on rectangular AFM microcantilevers with and without beads attached at their extremities. The experiments are performed with a home-made ultra-sensitive AFM, based on differential interferometry. The focused beam from the interferometer probes the cantilever at different positions and the spatial shapes of the modes are determined up to the fifth resonance, without external excitation. The results clearly demonstrate that the first eigenmode is almost unchanged by mass loading. However the oscillation behavior of higher resonances presents a marked difference: with a particle glued at its extremity, the nodes of the modes are displaced towards the free end of the cantilever. These results are compared to an analytical model taking into account the mass and inertial moment of the load in an Euler-Bernoulli framework, where the normalization of the eigenmodes is explicitly worked out in order to allow a quantitative prediction of the thermal noise amplitude of each mode. A good agreement between the experimental results and the analytical model is demonstrated, allowing a clean calibration of the probe stiffness.

Influence of modulation frequency in rubidium cell frequency standards

NASA Technical Reports Server (NTRS)

Audoin, C.; Viennet, J.; Cyr, N.; Vanier, J.

1983-01-01

The error signal which is used to control the frequency of the quartz crystal oscillator of a passive rubidium cell frequency standard is considered. The value of the slope of this signal, for an interrogation frequency close to the atomic transition frequency is calculated and measured for various phase (or frequency) modulation waveforms, and for several values of the modulation frequency. A theoretical analysis is made using a model which applies to a system in which the optical pumping rate, the relaxation rates and the RF field are homogeneous. Results are given for sine-wave phase modulation, square-wave frequency modulation and square-wave phase modulation. The influence of the modulation frequency on the slope of the error signal is specified. It is shown that the modulation frequency can be chosen as large as twice the non-saturated full-width at half-maximum without a drastic loss of the sensitivity to an offset of the interrogation frequency from center line, provided that the power saturation factor and the amplitude of modulation are properly adjusted.

High temperature spin dynamics in linear magnetic chains, molecular rings, and segments by nuclear magnetic resonance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adelnia, Fatemeh; Lascialfari, Alessandro; Dipartimento di Fisica, Università degli Studi di Pavia and INSTM, Pavia

2015-05-07

We present the room temperature proton nuclear magnetic resonance (NMR) nuclear spin-lattice relaxation rate (NSLR) results in two 1D spin chains: the Heisenberg antiferromagnetic (AFM) Eu(hfac){sub 3}NITEt and the magnetically frustrated Gd(hfac){sub 3}NITEt. The NSLR as a function of external magnetic field can be interpreted very well in terms of high temperature spin dynamics dominated by a long time persistence of the decay of the two-spin correlation function due to the conservation of the total spin value for isotropic Heisenberg chains. The high temperature spin dynamics are also investigated in Heisenberg AFM molecular rings. In both Cr{sub 8} closed ringmore » and in Cr{sub 7}Cd and Cr{sub 8}Zn open rings, i.e., model systems for a finite spin segment, an enhancement of the low frequency spectral density is found consistent with spin diffusion but the high cut-off frequency due to intermolecular anisotropic interactions prevents a detailed analysis of the spin diffusion regime.« less

[Observation of the L929 cell membrane after infrasound exposure with atomic force microscope].

PubMed

Wang, Bing-shui; Chen, Jing-zao; Liu, Bin; Li, Ling; Yi, Nan; Liu, Jing; Zhang, Sa

2005-12-01

To observe the changes of L929 cell membrane with atomic force microscope (AFM) after infrasound exposure and to explore the mechanisms of effect of infrasound on cell membrane. After primary culture, the L929 cells were exposed to infrasound with intensity output of 130 dB and frequency of 16 Hz 2 hours each day for 3 days. The subsequent changes in the membrane of the control cells and the cells exposed to the infrasound were determined by nano-scale scanning with AFM. After infrasound exposure, the normal prominence of the membrane became short and the dent became shallow in the 7.5 microm x 7.5 microm and 4.0 microm x 4.0 microm photographs. The prominence appeared as cobblestones. The surface of the membrane became smooth. The membrane structure of the L929 cells can be changed by infrasound exposure with intensity of 130 dB and frequency of 16 Hz. The change might be one of the characteristics of effect of infrasound on cell membrane.

Estimation of the center frequency of the highest modulation filter.

PubMed

Moore, Brian C J; Füllgrabe, Christian; Sek, Aleksander

2009-02-01

For high-frequency sinusoidal carriers, the threshold for detecting sinusoidal amplitude modulation increases when the signal modulation frequency increases above about 120 Hz. Using the concept of a modulation filter bank, this effect might be explained by (1) a decreasing sensitivity or greater internal noise for modulation filters with center frequencies above 120 Hz; and (2) a limited span of center frequencies of the modulation filters, the top filter being tuned to about 120 Hz. The second possibility was tested by measuring modulation masking in forward masking using an 8 kHz sinusoidal carrier. The signal modulation frequency was 80, 120, or 180 Hz and the masker modulation frequencies covered a range above and below each signal frequency. Four highly trained listeners were tested. For the 80-Hz signal, the signal threshold was usually maximal when the masker frequency equaled the signal frequency. For the 180-Hz signal, the signal threshold was maximal when the masker frequency was below the signal frequency. For the 120-Hz signal, two listeners showed the former pattern, and two showed the latter pattern. The results support the idea that the highest modulation filter has a center frequency in the range 100-120 Hz.

Modulation of high frequency noise by engine tones of small boats.

PubMed

Pollara, Alexander; Sutin, Alexander; Salloum, Hady

2017-07-01

The effect of modulation of high frequency ship noise by propeller rotation frequencies is well known. This modulation is observed with the Detection of Envelope Modulation on Noise (DEMON) algorithm. Analysis of the DEMON spectrum allows the revolutions per minute and number of blades of the propeller to be determined. This work shows that the high frequency noise of a small boat can also be modulated by engine frequencies. Prior studies have not reported high frequency noise amplitude modulated at engine frequencies. This modulation is likely produced by bubbles from the engine exhaust system.

Nanoscale control of oxide interface conduction in graphene-complex-oxide heterostructures

NASA Astrophysics Data System (ADS)

Huang, Mengchen; Ryu, Sangwoo; Ghahari, Fereshte; Jnawali, Giriraj; Ravichandran, Jayakanth; Irvin, Patrick; Kim, Philip; Eom, Chang-Beom; Levy, Jeremy

2014-03-01

Graphene is a promising material for high-speed optoelectronic devices such as THz modulators and detectors. Recently, broadband THz emission and detection can be achieved with nanostructures at the LaAlO3/SrTiO3 interface [2]. We have mechanically exfoliated single layer and multilayer graphene on top of 3.4 unit cell LaAlO3/SrTiO3 and successfully sketched nanowires in the 2DEG underneath graphene using conductive AFM lithgraphy [3]. Raman and AFM investigations confirm that the graphene quality and surface morphology remain unaltered by the writing process. These first experimental demonstrations of integrating graphene and LaAlO3/SrTiO3 are promising for future DC-THz photonic applications. We gratefully acknowledge support for this work from ONR (N00014-13-1-0806), NSF(DMR-1124131, DMR-1104191), and AFOSR (FA9550-12-1-0342).

Characterization and evaluation of 5-fluorouracil-loaded solid lipid nanoparticles prepared via a temperature-modulated solidification technique.

PubMed

Patel, Meghavi N; Lakkadwala, Sushant; Majrad, Mohamed S; Injeti, Elisha R; Gollmer, Steven M; Shah, Zahoor A; Boddu, Sai Hanuman Sagar; Nesamony, Jerry

2014-12-01

The aim of this research was to advance solid lipid nanoparticle (SLN) preparation methodology by preparing glyceryl monostearate (GMS) nanoparticles using a temperature-modulated solidification process. The technique was reproducible and prepared nanoparticles without the need of organic solvents. An anticancer agent, 5-fluorouracil (5-FU), was incorporated in the SLNs. The SLNs were characterized by particle size analysis, zeta potential analysis, differential scanning calorimetry (DSC), infrared spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), drug encapsulation efficiency, in vitro drug release, and in vitro cell viability studies. Particle size of the SLN dispersion was below 100 nm, and that of redispersed lyophilizates was ~500 nm. DSC and infrared spectroscopy suggested that the degree of crystallinity did not decrease appreciably when compared to GMS. TEM and AFM images showed well-defined spherical to oval particles. The drug encapsulation efficiency was found to be approximately 46%. In vitro drug release studies showed that 80% of the encapsulated drug was released within 1 h. In vitro cell cultures were biocompatible with blank SLNs but demonstrated concentration-dependent changes in cell viability to 5-FU-loaded SLNs. The 5-FU-loaded SLNs can potentially be utilized in an anticancer drug delivery system.

System and method for tuning adjusting the central frequency of a laser while maintaining frequency stabilization to an external reference

NASA Technical Reports Server (NTRS)

Livas, Jeffrey (Inventor); Thorpe, James I. (Inventor); Numata, Kenji (Inventor)

2011-01-01

A method and system for stabilizing a laser to a frequency reference with an adjustable offset. The method locks a sideband signal generated by passing an incoming laser beam through the phase modulator to a frequency reference, and adjusts a carrier frequency relative to the locked sideband signal by changing a phase modulation frequency input to the phase modulator. The sideband signal can be a single sideband (SSB), dual sideband (DSB), or an electronic sideband (ESB) signal. Two separate electro-optic modulators can produce the DSB signal. The two electro-optic modulators can be a broadband modulator and a resonant modulator. With a DSB signal, the method can introduce two sinusoidal phase modulations at the phase modulator. With ESB signals, the method can further drive the optical phase modulator with an electrical signal with nominal frequency OMEGA(sub 1) that is phase modulated at a frequency OMEGA(sub 2)

Encoding of frequency-modulation (FM) rates in human auditory cortex.

PubMed

Okamoto, Hidehiko; Kakigi, Ryusuke

2015-12-14

Frequency-modulated sounds play an important role in our daily social life. However, it currently remains unclear whether frequency modulation rates affect neural activity in the human auditory cortex. In the present study, using magnetoencephalography, we investigated the auditory evoked N1m and sustained field responses elicited by temporally repeated and superimposed frequency-modulated sweeps that were matched in the spectral domain, but differed in frequency modulation rates (1, 4, 16, and 64 octaves per sec). The results obtained demonstrated that the higher rate frequency-modulated sweeps elicited the smaller N1m and the larger sustained field responses. Frequency modulation rate had a significant impact on the human brain responses, thereby providing a key for disentangling a series of natural frequency-modulated sounds such as speech and music.

Dynamic response of a cracked atomic force microscope cantilever used for nanomachining

PubMed Central

2012-01-01

The vibration behavior of an atomic force microscope [AFM] cantilever with a crack during the nanomachining process is studied. The cantilever is divided into two segments by the crack, and a rotational spring is used to simulate the crack. The two individual governing equations of transverse vibration for the cracked cantilever can be expressed. However, the corresponding boundary conditions are coupled because of the crack interaction. Analytical expressions for the vibration displacement and natural frequency of the cracked cantilever are obtained. In addition, the effects of crack flexibility, crack location, and tip length on the vibration displacement of the cantilever are analyzed. Results show that the crack occurs in the AFM cantilever that can significantly affect its vibration response. PACS: 07.79.Lh; 62.20.mt; 62.25.Jk PMID:22335820

Uncertainty in least-squares fits to the thermal noise spectra of nanomechanical resonators with applications to the atomic force microscope.

PubMed

Sader, John E; Yousefi, Morteza; Friend, James R

2014-02-01

Thermal noise spectra of nanomechanical resonators are used widely to characterize their physical properties. These spectra typically exhibit a Lorentzian response, with additional white noise due to extraneous processes. Least-squares fits of these measurements enable extraction of key parameters of the resonator, including its resonant frequency, quality factor, and stiffness. Here, we present general formulas for the uncertainties in these fit parameters due to sampling noise inherent in all thermal noise spectra. Good agreement with Monte Carlo simulation of synthetic data and measurements of an Atomic Force Microscope (AFM) cantilever is demonstrated. These formulas enable robust interpretation of thermal noise spectra measurements commonly performed in the AFM and adaptive control of fitting procedures with specified tolerances.

Uncertainty in least-squares fits to the thermal noise spectra of nanomechanical resonators with applications to the atomic force microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sader, John E., E-mail: jsader@unimelb.edu.au; Yousefi, Morteza; Friend, James R.

2014-02-15

Thermal noise spectra of nanomechanical resonators are used widely to characterize their physical properties. These spectra typically exhibit a Lorentzian response, with additional white noise due to extraneous processes. Least-squares fits of these measurements enable extraction of key parameters of the resonator, including its resonant frequency, quality factor, and stiffness. Here, we present general formulas for the uncertainties in these fit parameters due to sampling noise inherent in all thermal noise spectra. Good agreement with Monte Carlo simulation of synthetic data and measurements of an Atomic Force Microscope (AFM) cantilever is demonstrated. These formulas enable robust interpretation of thermal noisemore » spectra measurements commonly performed in the AFM and adaptive control of fitting procedures with specified tolerances.« less

Refurbishing of carbon contaminated pre-mirror of reflectivity beam line at Indus-1

NASA Astrophysics Data System (ADS)

Yadav, P. K.; Kumar, M.; Gupta, R. K.; Sinha, M.; Patel, H. S.; Modi, M. H.

2018-04-01

In recent days optics contamination and its refurbishing is a serious issue for synchrotron radiation beam line community. Here we refurbished a carbon contaminated mirror by Ar and O2 gas mixed (1:1) radio frequency plasma. For structural analysis pre and post characterization of the mirror was done by Soft X-ray reflectivity (SXRR), Raman Spectroscopy (RS) and Atomic force microscopy (AFM). Before refurbishing mirror, a low density graphitic carbon layer of thickness 400 Å with surface roughness about 55 Å and Au surface roughness 14Å was estimated by SXRR. After one hour RF plasma exposure it is observed by SXRR and Raman spectroscopy that carbon layer is completely removed. The AFM and SXRR results show that roughness of Au surface not increase after plasma exposure.

DNA G-segment bending is not the sole determinant of topology simplification by type II DNA topoisomerases.

PubMed

Thomson, Neil H; Santos, Sergio; Mitchenall, Lesley A; Stuchinskaya, Tanya; Taylor, James A; Maxwell, Anthony

2014-08-21

DNA topoisomerases control the topology of DNA. Type II topoisomerases exhibit topology simplification, whereby products of their reactions are simplified beyond that expected based on thermodynamic equilibrium. The molecular basis for this process is unknown, although DNA bending has been implicated. To investigate the role of bending in topology simplification, the DNA bend angles of four enzymes of different types (IIA and IIB) were measured using atomic force microscopy (AFM). The enzymes tested were Escherichia coli topo IV and yeast topo II (type IIA enzymes that exhibit topology simplification), and Methanosarcina mazei topo VI and Sulfolobus shibatae topo VI (type IIB enzymes, which do not). Bend angles were measured using the manual tangent method from topographical AFM images taken with a novel amplitude-modulated imaging mode: small amplitude small set-point (SASS), which optimises resolution for a given AFM tip size and minimises tip convolution with the sample. This gave improved accuracy and reliability and revealed that all 4 topoisomerases bend DNA by a similar amount: ~120° between the DNA entering and exiting the enzyme complex. These data indicate that DNA bending alone is insufficient to explain topology simplification and that the 'exit gate' may be an important determinant of this process.

Surface initiated atom transfer radical polymerization grafting of sodium styrene sulfonate from titanium and silicon substrates.

PubMed

Foster, Rami N; Keefe, Andrew J; Jiang, Shaoyi; Castner, David G

2013-11-01

This study investigates the grafting of poly-sodium styrene sulfonate (pNaSS) from trichlorosilane/10-undecen-1-yl 2-bromo-2-methylpropionate functionalized Si and Ti substrates by atom transfer radical polymerization (ATRP). The composition, molecular structure, thickness, and topography of the grafted pNaSS films were characterized with x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), variable angle spectroscopic ellipsometry (VASE), and atomic force microscopy (AFM), respectively. XPS and ToF-SIMS results were consistent with the successful grafting of a thick and uniform pNaSS film on both substrates. VASE and AFM scratch tests showed the films were between 25 and 49 nm thick on Si, and between 13 and 35 nm thick on Ti. AFM determined root-mean-square roughness values were ∼2 nm on both Si and Ti substrates. Therefore, ATRP grafting is capable of producing relatively smooth, thick, and chemically homogeneous pNaSS films on Si and Ti substrates. These films will be used in subsequent studies to test the hypothesis that pNaSS-grafted Ti implants preferentially adsorb certain plasma proteins in an orientation and conformation that modulates the foreign body response and promotes formation of new bone.

DNA G-segment bending is not the sole determinant of topology simplification by type II DNA topoisomerases

NASA Astrophysics Data System (ADS)

Thomson, Neil H.; Santos, Sergio; Mitchenall, Lesley A.; Stuchinskaya, Tanya; Taylor, James A.; Maxwell, Anthony

2014-08-01

DNA topoisomerases control the topology of DNA. Type II topoisomerases exhibit topology simplification, whereby products of their reactions are simplified beyond that expected based on thermodynamic equilibrium. The molecular basis for this process is unknown, although DNA bending has been implicated. To investigate the role of bending in topology simplification, the DNA bend angles of four enzymes of different types (IIA and IIB) were measured using atomic force microscopy (AFM). The enzymes tested were Escherichia coli topo IV and yeast topo II (type IIA enzymes that exhibit topology simplification), and Methanosarcina mazei topo VI and Sulfolobus shibatae topo VI (type IIB enzymes, which do not). Bend angles were measured using the manual tangent method from topographical AFM images taken with a novel amplitude-modulated imaging mode: small amplitude small set-point (SASS), which optimises resolution for a given AFM tip size and minimises tip convolution with the sample. This gave improved accuracy and reliability and revealed that all 4 topoisomerases bend DNA by a similar amount: ~120° between the DNA entering and exiting the enzyme complex. These data indicate that DNA bending alone is insufficient to explain topology simplification and that the `exit gate' may be an important determinant of this process.

Surface initiated atom transfer radical polymerization grafting of sodium styrene sulfonate from titanium and silicon substrates

PubMed Central

Foster, Rami N.; Keefe, Andrew J.; Jiang, Shaoyi; Castner, David G.

2013-01-01

This study investigates the grafting of poly-sodium styrene sulfonate (pNaSS) from trichlorosilane/10-undecen-1-yl 2-bromo-2-methylpropionate functionalized Si and Ti substrates by atom transfer radical polymerization (ATRP). The composition, molecular structure, thickness, and topography of the grafted pNaSS films were characterized with x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), variable angle spectroscopic ellipsometry (VASE), and atomic force microscopy (AFM), respectively. XPS and ToF-SIMS results were consistent with the successful grafting of a thick and uniform pNaSS film on both substrates. VASE and AFM scratch tests showed the films were between 25 and 49 nm thick on Si, and between 13 and 35 nm thick on Ti. AFM determined root-mean-square roughness values were ∼2 nm on both Si and Ti substrates. Therefore, ATRP grafting is capable of producing relatively smooth, thick, and chemically homogeneous pNaSS films on Si and Ti substrates. These films will be used in subsequent studies to test the hypothesis that pNaSS-grafted Ti implants preferentially adsorb certain plasma proteins in an orientation and conformation that modulates the foreign body response and promotes formation of new bone. PMID:24482558

Wide-band analog frequency modulation of optic signals using indirect techniques

NASA Technical Reports Server (NTRS)

Fitzmartin, D. J.; Balboni, E. J.; Gels, R. G.

1991-01-01

The wideband frequency modulation (FM) of an optical carrier by a radio frequency (RF) or microwave signal can be accomplished independent of laser type when indirect modulation is employed. Indirect modulators exploit the integral relation of phase to frequency so that phase modulators can be used to impress frequency modulation on an optical carrier. The use of integrated optics phase modulators, which are highly linear, enables the generation of optical wideband FM signals with very low intermodulation distortion. This modulator can be used as part of an optical wideband FM link for RF and microwave signals. Experimental results from the test of an indirect frequency modulator for an optical carrier are discussed.

Optical Characterization of Pulse Laser Deposition of Thin Film of Hard Materials Using RHEED and AFM Techniques (DURIP)

DTIC Science & Technology

2011-09-26

determine g-factor of the atomic system, it is convenient experimentally to fix 0 and to find the resonance magnetic field Hres corresponding to the...given frequency ( Hres = res/). In ferromagnetic materials, there exist strong internal anisotropic magnetic fields, which are caused by the magnetic

3-Dimensional atomic scale structure of the ionic liquid-graphite interface elucidated by AM-AFM and quantum chemical simulations

NASA Astrophysics Data System (ADS)

Page, Alister J.; Elbourne, Aaron; Stefanovic, Ryan; Addicoat, Matthew A.; Warr, Gregory G.; Voïtchovsky, Kislon; Atkin, Rob

2014-06-01

In situ amplitude modulated atomic force microscopy (AM-AFM) and quantum chemical simulations are used to resolve the structure of the highly ordered pyrolytic graphite (HOPG)-bulk propylammonium nitrate (PAN) interface with resolution comparable with that achieved for frozen ionic liquid (IL) monolayers using STM. This is the first time that (a) molecular resolution images of bulk IL-solid interfaces have been achieved, (b) the lateral structure of the IL graphite interface has been imaged for any IL, (c) AM-AFM has elucidated molecular level structure immersed in a viscous liquid and (d) it has been demonstrated that the IL structure at solid surfaces is a consequence of both thermodynamic and kinetic effects. The lateral structure of the PAN-graphite interface is highly ordered and consists of remarkably well-defined domains of a rhomboidal superstructure composed of propylammonium cations preferentially aligned along two of the three directions in the underlying graphite lattice. The nanostructure is primarily determined by the cation. Van der Waals interactions between the propylammonium chains and the surface mean that the cation is enriched in the surface layer, and is much less mobile than the anion. The presence of a heterogeneous lateral structure at an ionic liquid-solid interface has wide ranging ramifications for ionic liquid applications, including lubrication, capacitive charge storage and electrodeposition.In situ amplitude modulated atomic force microscopy (AM-AFM) and quantum chemical simulations are used to resolve the structure of the highly ordered pyrolytic graphite (HOPG)-bulk propylammonium nitrate (PAN) interface with resolution comparable with that achieved for frozen ionic liquid (IL) monolayers using STM. This is the first time that (a) molecular resolution images of bulk IL-solid interfaces have been achieved, (b) the lateral structure of the IL graphite interface has been imaged for any IL, (c) AM-AFM has elucidated molecular level structure immersed in a viscous liquid and (d) it has been demonstrated that the IL structure at solid surfaces is a consequence of both thermodynamic and kinetic effects. The lateral structure of the PAN-graphite interface is highly ordered and consists of remarkably well-defined domains of a rhomboidal superstructure composed of propylammonium cations preferentially aligned along two of the three directions in the underlying graphite lattice. The nanostructure is primarily determined by the cation. Van der Waals interactions between the propylammonium chains and the surface mean that the cation is enriched in the surface layer, and is much less mobile than the anion. The presence of a heterogeneous lateral structure at an ionic liquid-solid interface has wide ranging ramifications for ionic liquid applications, including lubrication, capacitive charge storage and electrodeposition. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr01219d

Laser frequency-offset locking based on the frequency modulation spectroscopy with higher harmonic detection

NASA Astrophysics Data System (ADS)

Wang, Anqi; Meng, Zhixin; Feng, Yanying

2017-10-01

We design a fiber electro-optic modulator (FEOM)-based laser frequency-offset locking system using frequency modulation spectroscopy (FMS) with the 3F modulation. The modulation signal and the frequency-offset control signal are simultaneously loaded on the FEOM by a mixer in order to suppress the frequency and power jitter caused by internal modulation on the current or piezoelectric ceramic transducer (PZT). It is expected to accomplish a fast locking, a widely tunable frequency-offset, a sensitive and rapid detection of narrow spectral features with the 3F modulation. The laser frequency fluctuation is limited to +/-1MHz and its overlapping Allan deviation is around 10-12 in twenty minutes, which successfully meets the requirements of the cold atom interferometer.

From molecular to macroscopic engineering: shaping hydrogen-bonded organic nanomaterials.

PubMed

Yoosaf, K; Llanes-Pallas, Anna; Marangoni, Tomas; Belbakra, Abdelhalim; Marega, Riccardo; Botek, Edith; Champagne, Benoît; Bonifazi, Davide; Armaroli, Nicola

2011-03-07

The self-assembly and self-organization behavior of chromophoric acetylenic scaffolds bearing 2,6-bis(acetylamino)pyridine (1, 2) or uracyl-type (3-9) terminal groups has been investigated by photophysical and microscopic methods. Systematic absorption and luminescence studies show that 1 and 2, thanks to a combination of solvophilic/solvophobic forces and π-π stacking interactions, undergo self-organization in apolar solvents (i.e., cyclohexane) and form spherical nanoparticles, as evidenced by wide-field optical microscopy, TEM, and AFM analysis. For the longer molecular module, 2, a more uniform size distribution is found (80-200 nm) compared to 1 (20-1000 nm). Temperature scans in the range 283-353 K show that the self-organized nanoparticles are reversibly formed and destroyed, being stable at lower temperatures. Molecular modules 1 and 2 were then thoroughly mixed with the complementary triply hydrogen-bonding units 3-9. Depending on the specific geometrical structure of 3-9, different nanostructures are evidenced by microscopic investigations. Combination of modules 1 or 2 with 3, which bears only one terminal uracyl unit, leads to the formation of vesicular structures; instead, when 1 is combined with bis-uracyl derivative 4 or 5, a structural evolution from nanoparticles to nanowires is observed. The length of the wires obtained by mixing 1 and 4 or 1 and 5 can be controlled by addition of 3, which prompts transformation of the wires into shorter rods. The replacement of linear system 5 with the related angular modules 6 and 7 enables formation of helical nanostructures, unambiguously evidenced by AFM. Finally, thermally induced self-assembly was studied in parallel with modules 8 and 9, in which the uracyl recognition sites are protected with tert-butyloxycarbonyl (BOC) groups. This strategy allows further control of the self-assembly/self-organization process by temperature, since the BOC group is completely removed on heating. Microscopy studies show that the BOC-protected ditopic modules 8 self-assemble and self-organize with 1 into ordered linear nanostructures, whereas BOC-protected tritopic system 9 gives rise to extended domains of circular nano-objects in combination with 1. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

47 CFR 80.213 - Modulation requirements.

Code of Federal Regulations, 2010 CFR

2010-10-01

... must be maintained between 75 and 100 percent; (2) When phase or frequency modulation is used in the 156-162 MHz band the peak modulation must be maintained between 75 and 100 percent. A frequency... installed between the modulation limiter and the modulated radio frequency stage. At frequencies between 3 k...

Analyzing the vibrational response of an AFM cantilever in liquid with the consideration of tip mass by comparing the hydrodynamic and contact repulsive force models in higher modes

NASA Astrophysics Data System (ADS)

Korayem, Moharam Habibnejad; Nahavandi, Amir

2017-04-01

This paper investigates the vibration of a tapping-mode Atomic Force Microscope (AFM) cantilever covered with two whole piezoelectric layers in a liquid medium. The authors of this article have already modeled the vibration of a cantilever immersed in liquid over rough surfaces. Five new ideas have been considered for improving the results of the previous work. Mass and damping of a cantilever probe tip have been considered. Since the probe tip of an AFM cantilever has a mass, which can itself affect the natural frequency of vibration, the significance of this mass has been explored. Also, two hydrodynamic force models for analyzing the mass and damping added to a cantilever in liquid medium have been evaluated. In modeling the vibration of a cantilever in liquid, simplifications are made to the theoretical equations used in the modeling, which may make the obtained results different from those in the real case. So, two hydrodynamic force models are introduced and compared with each other. In addition to the already introduced DMT model, the JKR model has been proposed. The forces acting on a probe tip have attractive and repulsive effects. The attractive Van der Waals force can vary depending on the surface smoothness or roughness, and the repulsive contact force, which is independent of the type of surface roughness and usually varies with the hardness or softness of a surface. When the first mode is used in the vibration of an AFM cantilever, the changes of the existing physical parameters in the simulation do not usually produce a significant difference in the response. Thus, three cantilever vibration modes have been investigated. Finally, an analytical approach for obtaining the response of equations is presented which solves the resulting motion equation by the Laplace method and, thus, a time function is obtained for cantilever deflection is determined. Also, using the COMSOL software to model a cantilever in a liquid medium, the computed natural frequencies have been compared.

Optical nanoscopy of high T c cuprate nanoconstriction devices patterned by helium ion beams

DOE PAGES

Gozar, Adrian; Litombe, N. E.; Hoffman, Jennifer E.; ...

2017-02-06

Helium ion beams (HIB) focused to subnanometer scales have emerged as powerful tools for high-resolution imaging as well as nanoscale lithography, ion milling, or deposition. Quantifying irradiation effects is an essential step toward reliable device fabrication, but most of the depth profiling information is provided by computer simulations rather than the experiment. Here, we demonstrate the use of atomic force microscopy (AFM) combined with scanning near-field optical microscopy (SNOM) to provide three-dimensional (3D) dielectric characterization of high-temperature superconductor devices fabricated by HIB. By imaging the infrared dielectric response obtained from light demodulation at multiple harmonics of the AFM tapping frequency,more » we find that amorphization caused by the nominally 0.5 nm HIB extends throughout the entire 26.5 nm thickness of the cuprate film and by ~500 nm laterally. This unexpectedly widespread damage in morphology and electronic structure can be attributed to a helium depth distribution substantially modified by the internal device interfaces. Lastly, our study introduces AFM-SNOM as a quantitative tomographic technique for noninvasive 3D characterization of irradiation damage in a wide variety of nanoscale devices.« less

Helical waves in easy-plane antiferromagnets

NASA Astrophysics Data System (ADS)

Semenov, Yuriy G.; Li, Xi-Lai; Xu, Xinyi; Kim, Ki Wook

2017-12-01

Effective spin torques can generate the Néel vector oscillations in antiferromagnets (AFMs). Here, it is theoretically shown that these torques applied at one end of a normal AFM strip can excite a helical type of spin wave in the strip whose properties are drastically different from characteristic spin waves. An analysis based on both a Néel vector dynamical equation and the micromagnetic simulation identifies the direction of magnetic anisotropy and the damping factor as the two key parameters determining the dynamics. Helical wave propagation requires the hard axis of the easy-plane AFM to be aligned with the traveling direction, while the damping limits its spatial extent. If the damping is neglected, the calculation leads to a uniform periodic domain wall structure. On the other hand, finite damping decelerates the helical wave rotation around the hard axis, ultimately causing stoppage of its propagation along the strip. With the group velocity staying close to spin-wave velocity at the wave front, the wavelength becomes correspondingly longer away from the excitation point. In a sufficiently short strip, a steady-state oscillation can be established whose frequency is controlled by the waveguide length as well as the excitation energy or torque.

Controlling the electric charge of gold nanoplatelets on an insulator by field emission nc-AFM

NASA Astrophysics Data System (ADS)

Baris, Bulent; Alchaar, Mohanad; Prasad, Janak; Gauthier, Sébastien; Dujardin, Erik; Martrou, David

2018-03-01

Charging of 2D Au nanoplatelets deposited on an insulating SiO2 substrate to or from the tip of a non-contact atomic force microscope (nc-AFM) is demonstrated. Charge transfer is controlled by monitoring the resonance frequency shift Δf(V) during the bias voltage ramp V applied to the tip-back electrode junction. The onset of charge transfer is revealed by a transition from a capacitive parabolic behavior to a constant Δf(V) region for both polarities. An analytical model, based on charging by electron field emission, shows that the field-emitted current saturates shortly after the onset of the charging, due to the limiting effect of the charge-induced rise of the Au platelet potential. The value of this current plateau depends only on the rate of the bias voltage ramp and on the value of the platelet/SiO2/back electrode capacitance. This analysis is confirmed by numerical simulations based on a virtual nc-AFM model that faithfully matches the experimental data. Our charging protocol could be used to tune the potential of the platelets at the single charge level.

Direct measurement of optical force induced by near-field plasmonic cavity using dynamic mode AFM

DOE PAGES

Guan, Dongshi; Hang, Zhi Hong; Marset, Zsolt; ...

2015-11-20

Plasmonic nanostructures have attracted much attention in recent years because of their potential applications in optical manipulation through near-field enhancement. Continuing experimental efforts have been made to develop accurate techniques to directly measure the near-field optical force induced by the plasmonic nanostructures in the visible frequency range. In this work, we report a new application of dynamic mode atomic force microscopy (DM-AFM) in the measurement of the enhanced optical force acting on a nano-structured plasmonic resonant cavity. The plasmonic cavity is made of an upper gold-coated glass sphere and a lower quartz substrate patterned with an array of subwavelength goldmore » disks. In the near-field when the sphere is positioned close to the disk array, plasmonic resonance is excited in the cavity and the induced force by a 1550 nm infrared laser is found to be increased by an order of magnitude compared with the photon pressure generated by the same laser light. Lastly, the experiment demonstrates that DM-AFM is a powerful tool for the study of light induced forces and their enhancement in plasmonic nanostructures.« less

Local Viscoelastic Properties of Live Cells Investigated Using Dynamic and Quasi-Static Atomic Force Microscopy Methods

PubMed Central

Cartagena, Alexander; Raman, Arvind

2014-01-01

The measurement of viscoelasticity of cells in physiological environments with high spatio-temporal resolution is a key goal in cell mechanobiology. Traditionally only the elastic properties have been measured from quasi-static force-distance curves using the atomic force microscope (AFM). Recently, dynamic AFM-based methods have been proposed to map the local in vitro viscoelastic properties of living cells with nanoscale resolution. However, the differences in viscoelastic properties estimated from such dynamic and traditional quasi-static techniques are poorly understood. In this work we quantitatively reconstruct the local force and dissipation gradients (viscoelasticity) on live fibroblast cells in buffer solutions using Lorentz force excited cantilevers and present a careful comparison between mechanical properties (local stiffness and damping) extracted using dynamic and quasi-static force spectroscopy methods. The results highlight the dependence of measured viscoelastic properties on both the frequency at which the chosen technique operates as well as the interactions with subcellular components beyond certain indentation depth, both of which are responsible for differences between the viscoelasticity property maps acquired using the dynamic AFM method against the quasi-static measurements. PMID:24606928

Understanding the stability of surface nanobubbles.

PubMed

Wang, Shuo; Liu, Minghuan; Dong, Yaming

2013-05-08

Surface nanobubbles emerging at solid-liquid interfaces show extreme stability. In this paper, the stability of surface nanobubbles in degassed water is discussed and investigated by AFM. The result demonstrates that surface nanobubbles are kinetically stable and the liquid/gas interface is gas impermeable. The force modulation experiment further proves that there is a layer coating on nanobubbles. These critical properties suggest that surface nanobubbles may be stabilized by a layer which has a great diffusive resistance.

High-resolution high-speed dynamic mechanical spectroscopy of cells and other soft materials with the help of atomic force microscopy.

PubMed

Dokukin, M; Sokolov, I

2015-07-28

Dynamic mechanical spectroscopy (DMS), which allows measuring frequency-dependent viscoelastic properties, is important to study soft materials, tissues, biomaterials, polymers. However, the existing DMS techniques (nanoindentation) have limited resolution when used on soft materials, preventing them from being used to study mechanics at the nanoscale. The nanoindenters are not capable of measuring cells, nanointerfaces of composite materials. Here we present a highly accurate DMS modality, which is a combination of three different methods: quantitative nanoindentation (nanoDMA), gentle force and fast response of atomic force microscopy (AFM), and Fourier transform (FT) spectroscopy. This new spectroscopy (which we suggest to call FT-nanoDMA) is fast and sensitive enough to allow DMS imaging of nanointerfaces, single cells, while attaining about 100x improvements on polymers in both spatial (to 10-70 nm) and temporal resolution (to 0.7 s/pixel) compared to the current art. Multiple frequencies are measured simultaneously. The use of 10 frequencies are demonstrated here (up to 300 Hz which is a rather relevant range for biological materials and polymers, in both ambient conditions and liquid). The method is quantitatively verified on known polymers and demonstrated on cells and polymers blends. Analysis shows that FT-nanoDMA is highly quantitative. The FT-nanoDMA spectroscopy can easily be implemented in the existing AFMs.

Laser Speckle Rheology for evaluating the viscoelastic properties of hydrogel scaffolds

PubMed Central

Hajjarian, Zeinab; Nia, Hadi Tavakoli; Ahn, Shawn; Grodzinsky, Alan J.; Jain, Rakesh K.; Nadkarni, Seemantini K.

2016-01-01

Natural and synthetic hydrogel scaffolds exhibit distinct viscoelastic properties at various length scales and deformation rates. Laser Speckle Rheology (LSR) offers a novel, non-contact optical approach for evaluating the frequency-dependent viscoelastic properties of hydrogels. In LSR, a coherent laser beam illuminates the specimen and a high-speed camera acquires the time-varying speckle images. Cross-correlation analysis of frames returns the speckle intensity autocorrelation function, g2(t), from which the frequency-dependent viscoelastic modulus, G*(ω), is deduced. Here, we establish the capability of LSR for evaluating the viscoelastic properties of hydrogels over a large range of moduli, using conventional mechanical rheometry and atomic force microscopy (AFM)-based indentation as reference-standards. Results demonstrate a strong correlation between |G*(ω)| values measured by LSR and mechanical rheometry (r = 0.95, p < 10−9), and z-test analysis reports that moduli values measured by the two methods are identical (p > 0.08) over a large range (47 Pa – 36 kPa). In addition, |G*(ω)| values measured by LSR correlate well with indentation moduli, E, reported by AFM (r = 0.92, p < 10−7). Further, spatially-resolved moduli measurements in micro-patterned substrates demonstrate that LSR combines the strengths of conventional rheology and micro-indentation in assessing hydrogel viscoelastic properties at multiple frequencies and small length-scales. PMID:27905494

Laser Speckle Rheology for evaluating the viscoelastic properties of hydrogel scaffolds.

PubMed

Hajjarian, Zeinab; Nia, Hadi Tavakoli; Ahn, Shawn; Grodzinsky, Alan J; Jain, Rakesh K; Nadkarni, Seemantini K

2016-12-01

Natural and synthetic hydrogel scaffolds exhibit distinct viscoelastic properties at various length scales and deformation rates. Laser Speckle Rheology (LSR) offers a novel, non-contact optical approach for evaluating the frequency-dependent viscoelastic properties of hydrogels. In LSR, a coherent laser beam illuminates the specimen and a high-speed camera acquires the time-varying speckle images. Cross-correlation analysis of frames returns the speckle intensity autocorrelation function, g 2 (t), from which the frequency-dependent viscoelastic modulus, G*(ω), is deduced. Here, we establish the capability of LSR for evaluating the viscoelastic properties of hydrogels over a large range of moduli, using conventional mechanical rheometry and atomic force microscopy (AFM)-based indentation as reference-standards. Results demonstrate a strong correlation between |G*(ω)| values measured by LSR and mechanical rheometry (r = 0.95, p < 10 -9 ), and z-test analysis reports that moduli values measured by the two methods are identical (p > 0.08) over a large range (47 Pa - 36 kPa). In addition, |G*(ω)| values measured by LSR correlate well with indentation moduli, E, reported by AFM (r = 0.92, p < 10 -7 ). Further, spatially-resolved moduli measurements in micro-patterned substrates demonstrate that LSR combines the strengths of conventional rheology and micro-indentation in assessing hydrogel viscoelastic properties at multiple frequencies and small length-scales.

High-resolution high-speed dynamic mechanical spectroscopy of cells and other soft materials with the help of atomic force microscopy

PubMed Central

Dokukin, M.; Sokolov, I.

2015-01-01

Dynamic mechanical spectroscopy (DMS), which allows measuring frequency-dependent viscoelastic properties, is important to study soft materials, tissues, biomaterials, polymers. However, the existing DMS techniques (nanoindentation) have limited resolution when used on soft materials, preventing them from being used to study mechanics at the nanoscale. The nanoindenters are not capable of measuring cells, nanointerfaces of composite materials. Here we present a highly accurate DMS modality, which is a combination of three different methods: quantitative nanoindentation (nanoDMA), gentle force and fast response of atomic force microscopy (AFM), and Fourier transform (FT) spectroscopy. This new spectroscopy (which we suggest to call FT-nanoDMA) is fast and sensitive enough to allow DMS imaging of nanointerfaces, single cells, while attaining about 100x improvements on polymers in both spatial (to 10–70 nm) and temporal resolution (to 0.7s/pixel) compared to the current art. Multiple frequencies are measured simultaneously. The use of 10 frequencies are demonstrated here (up to 300 Hz which is a rather relevant range for biological materials and polymers, in both ambient conditions and liquid). The method is quantitatively verified on known polymers and demonstrated on cells and polymers blends. Analysis shows that FT-nanoDMA is highly quantitative. The FT-nanoDMA spectroscopy can easily be implemented in the existing AFMs. PMID:26218346

An investigation into the effects of frequency-modulated transcutaneous electrical nerve stimulation (TENS) on experimentally-induced pressure pain in healthy human participants.

PubMed

Chen, Chih-Chung; Johnson, Mark I

2009-10-01

Frequency-modulated transcutaneous electrical nerve stimulation (TENS) delivers currents that fluctuate between preset boundaries over a fixed period of time. This study compared the effects of constant-frequency TENS and frequency-modulated TENS on blunt pressure pain in healthy human volunteers. Thirty-six participants received constant-frequency TENS (80 pps), frequency-modulated TENS (20 to 100 pps), and placebo (no current) TENS at a strong nonpainful intensity in a randomized cross-over manner. Pain threshold was taken from the forearm using pressure algometry. There were no statistical differences between constant-frequency TENS and frequency-modulated TENS after 20 minutes (OR = 1.54; CI, 0.29, 8.23, P = 1.0). Both constant-frequency TENS and frequency-modulated TENS were superior to placebo TENS (OR = 59.5, P < .001 and OR = 38.5, P < .001, respectively). Frequency-modulated TENS does not influence hypoalgesia to any greater extent than constant-frequency TENS when currents generate a strong nonpainful paraesthesia at the site of pain. The finding that frequency-modulated TENS and constant-frequency TENS were superior to placebo TENS provides further evidence that a strong yet nonpainful TENS intensity is a prerequisite for hypoalgesia. This study provides evidence that TENS, delivered at a strong nonpainful intensity, increases pain threshold to pressure algometry in healthy participants over and above that seen with placebo (no current) TENS. Frequency-modulated TENS does not increase hypoalgesia to any appreciable extent to that seen with constant-frequency TENS.

Spectro-temporal modulation masking patterns reveal frequency selectivity.

PubMed

Oetjen, Arne; Verhey, Jesko L

2015-02-01

The present study investigated the possibility that the human auditory system demonstrates frequency selectivity to spectro-temporal amplitude modulations. Threshold modulation depth for detecting sinusoidal spectro-temporal modulations was measured using a generalized masked threshold pattern paradigm with narrowband masker modulations. Four target spectro-temporal modulations were examined, differing in their temporal and spectral modulation frequencies: a temporal modulation of -8, 8, or 16 Hz combined with a spectral modulation of 1 cycle/octave and a temporal modulation of 4 Hz combined with a spectral modulation of 0.5 cycles/octave. The temporal center frequencies of the masker modulation ranged from 0.25 to 4 times the target temporal modulation. The spectral masker-modulation center-frequencies were 0, 0.5, 1, 1.5, and 2 times the target spectral modulation. For all target modulations, the pattern of average thresholds for the eight normal-hearing listeners was consistent with the hypothesis of a spectro-temporal modulation filter. Such a pattern of modulation-frequency sensitivity was predicted on the basis of psychoacoustical data for purely temporal amplitude modulations and purely spectral amplitude modulations. An analysis of separability indicates that, for the present data set, selectivity in the spectro-temporal modulation domain can be described by a combination of a purely spectral and a purely temporal modulation filter function.

System and Method for Generating a Frequency Modulated Linear Laser Waveform

NASA Technical Reports Server (NTRS)

Pierrottet, Diego F. (Inventor); Petway, Larry B. (Inventor); Amzajerdian, Farzin (Inventor); Barnes, Bruce W. (Inventor); Lockard, George E. (Inventor); Hines, Glenn D. (Inventor)

2017-01-01

A system for generating a frequency modulated linear laser waveform includes a single frequency laser generator to produce a laser output signal. An electro-optical modulator modulates the frequency of the laser output signal to define a linear triangular waveform. An optical circulator passes the linear triangular waveform to a band-pass optical filter to filter out harmonic frequencies created in the waveform during modulation of the laser output signal, to define a pure filtered modulated waveform having a very narrow bandwidth. The optical circulator receives the pure filtered modulated laser waveform and transmits the modulated laser waveform to a target.

System and Method for Generating a Frequency Modulated Linear Laser Waveform

NASA Technical Reports Server (NTRS)

Pierrottet, Diego F. (Inventor); Petway, Larry B. (Inventor); Amzajerdian, Farzin (Inventor); Barnes, Bruce W. (Inventor); Lockard, George E. (Inventor); Hines, Glenn D. (Inventor)

2014-01-01

A system for generating a frequency modulated linear laser waveform includes a single frequency laser generator to produce a laser output signal. An electro-optical modulator modulates the frequency of the laser output signal to define a linear triangular waveform. An optical circulator passes the linear triangular waveform to a band-pass optical filter to filter out harmonic frequencies created in the waveform during modulation of the laser output signal, to define a pure filtered modulated waveform having a very narrow bandwidth. The optical circulator receives the pure filtered modulated laser waveform and transmits the modulated laser waveform to a target.

Sensitivity to Envelope Interaural Time Differences at High Modulation Rates

PubMed Central

Bleeck, Stefan; McAlpine, David

2015-01-01

Sensitivity to interaural time differences (ITDs) conveyed in the temporal fine structure of low-frequency tones and the modulated envelopes of high-frequency sounds are considered comparable, particularly for envelopes shaped to transmit similar fidelity of temporal information normally present for low-frequency sounds. Nevertheless, discrimination performance for envelope modulation rates above a few hundred Hertz is reported to be poor—to the point of discrimination thresholds being unattainable—compared with the much higher (>1,000 Hz) limit for low-frequency ITD sensitivity, suggesting the presence of a low-pass filter in the envelope domain. Further, performance for identical modulation rates appears to decline with increasing carrier frequency, supporting the view that the low-pass characteristics observed for envelope ITD processing is carrier-frequency dependent. Here, we assessed listeners’ sensitivity to ITDs conveyed in pure tones and in the modulated envelopes of high-frequency tones. ITD discrimination for the modulated high-frequency tones was measured as a function of both modulation rate and carrier frequency. Some well-trained listeners appear able to discriminate ITDs extremely well, even at modulation rates well beyond 500 Hz, for 4-kHz carriers. For one listener, thresholds were even obtained for a modulation rate of 800 Hz. The highest modulation rate for which thresholds could be obtained declined with increasing carrier frequency for all listeners. At 10 kHz, the highest modulation rate at which thresholds could be obtained was 600 Hz. The upper limit of sensitivity to ITDs conveyed in the envelope of high-frequency modulated sounds appears to be higher than previously considered. PMID:26721926

FIBER AND INTEGRATED OPTICS. OTHER TOPICS IN QUANTUM ELECTRONICS: Increase of the bandwidth and of the efficiency of integrated optical traveling-wave modulators

NASA Astrophysics Data System (ADS)

Zolotov, Evgenii M.; Pelekhatyĭ, V. M.; Tavlykaev, R. F.

1990-05-01

A simultaneous increase in the frequency bandwidth and a reduction in the control (drive) power of integrated optical traveling-wave modulators can be achieved as a result of the electrooptic interaction in accordance with a linear frequency-modulated oscillatory law derived by inverse Fourier transformation of a rectangular amplitude-frequency characteristic and a quadratic phase-frequency characteristic of a modulator. This oscillatory law is realized using planar electrode structures with triangular or trapezoidal toothed edges. The tooth repetition frequency is governed by the linearly frequency-modulated oscillations and it rises on increase in the light modulation frequency.

140 GHz pulsed Fourier transform microwave spectrometer

DOEpatents

Kolbe, W.F.; Leskovar, B.

1985-07-29

A high frequency energy pulsing system suitable for use in a pulsed microwave spectrometer, including means for generating a high frequency carrier signal, and means for generating a low frequency modulating signal. The carrier signal is continuously fed to a modulator and the modulating signal is fed through a pulse switch to the modulator. When the pulse switch is on, the modulator will produce sideband signals above and below the carrier signal frequency. A frequency-responsive device is tuned to one of the sideband signals and sway from the carrier frequency so that the high frequency energization of the frequency-responsive device is controlled by the pulse switch.

140 GHz pulsed Fourier transform microwave spectrometer

DOEpatents

Kolbe, W.F.; Leskovar, B.

1987-10-27

A high frequency energy pulsing system suitable for use in a pulsed microwave spectrometer, including means for generating a high frequency carrier signal, and means for generating a low frequency modulating signal is disclosed. The carrier signal is continuously fed to a modulator and the modulating signal is fed through a pulse switch to the modulator. When the pulse switch is on, the modulator will produce sideband signals above and below the carrier signal frequency. A frequency-responsive device is tuned to one of the sideband signals and away from the carrier frequency so that the high frequency energization of the frequency-responsive device is controlled by the pulse switch. 5 figs.

In situ sensing and modeling of molecular events at the cellular level

NASA Astrophysics Data System (ADS)

Yang, Ruiguo

We developed the Atomic Force Microscopy (AFM) based nanorobot in combination with other nanomechanical sensors for the investigation of cell signaling pathways. The AFM nanorobotics hinge on the superior spatial resolution of AFM in imaging and extends it into the measurement of biological processes and manipulation of biological matters. A multiple input single output control system was designed and implemented to solve the issues of nanomanipulation of biological materials, feedback, response frequency and nonlinearity. The AFM nanorobotic system therefore provide the human-directed position, velocity and force control with high frequency feedback, and more importantly it can feed the operator with the real-time imaging of manipulation result from the fast-imaging based local scanning. The use of the system has taken the study of cellular process at the molecular scale into a new level. The cellular response to the physiological conditions can be significantly manifested in cellular mechanics. Dynamic mechanical property has been regarded as biomarkers, sometimes even regulators of the signaling and physiological processes, thus the name mechanobiology. We sought to characterize the relationship between the structural dynamics and the molecular dynamics and the role of them in the regulation of cell behavior. We used the AFM nanorobotics to investigate the mechanical properties in real-time of cells that are stimulated by different chemical species. These reagents could result in similar ion channel responses but distinctive mechanical behaviors. We applied these measurement results to establish a model that describes the cellular stimulation and the mechanical property change, a "two-hit" model that comprises the loss of cell adhesion and the initiation of cell apoptosis. The first hit was verified by functional experiments: depletion of Calcium and nanosurgery to disrupt the cellular adhesion. The second hit was tested by a labeling of apoptotic markers that were revealed by flow cytometry. The model would then be able to decipher qualitatively the molecular dynamics infolded in the regulation of cell behavior. To decipher the signaling pathway quantitatively, we employed a nanomechanical sensor at the bottom of the cell, quartz crystal microbalance with energy dissipation monitoring (QCM-D) to monitor the change at the basal area of the cell. This would provide the real time focal adhesion information and would be used in accordance with the AFM measurement data on the top of the cell to build a more complete mechanical profile during the antibody induced signaling process. We developed a model from a systematic control perspective that considers the signaling cascade at certain stimulation as the controller and the mechanical and structural interaction of the cell as the plant. We firstly derived the plant model based on QCM-D and AFM measurement processes. A signaling pathway model was built on a grey box approach where part of the pathway map was delineated in detail while others were condensed into a single reaction. The model parameters were obtained by extracting the mechanical response from the experiment. The model refinements were conducted by testing a series of inhibition mechanisms and comparing the simulation data with the experimental data. The model was then used to predict the existences of certain reactions that are qualitatively reported in the literature.

Fruit softening and pectin disassembly: an overview of nanostructural pectin modifications assessed by atomic force microscopy

PubMed Central

Paniagua, Candelas; Posé, Sara; Morris, Victor J.; Kirby, Andrew R.; Quesada, Miguel A.; Mercado, José A.

2014-01-01

Background One of the main factors that reduce fruit quality and lead to economically important losses is oversoftening. Textural changes during fruit ripening are mainly due to the dissolution of the middle lamella, the reduction of cell-to-cell adhesion and the weakening of parenchyma cell walls as a result of the action of cell wall modifying enzymes. Pectins, major components of fruit cell walls, are extensively modified during ripening. These changes include solubilization, depolymerization and the loss of neutral side chains. Recent evidence in strawberry and apple, fruits with a soft or crisp texture at ripening, suggests that pectin disassembly is a key factor in textural changes. In both these fruits, softening was reduced as result of antisense downregulation of polygalacturonase genes. Changes in pectic polymer size, composition and structure have traditionally been studied by conventional techniques, most of them relying on bulk analysis of a population of polysaccharides, and studies focusing on modifications at the nanostructural level are scarce. Atomic force microscopy (AFM) allows the study of individual polymers at high magnification and with minimal sample preparation; however, AFM has rarely been employed to analyse pectin disassembly during fruit ripening. Scope In this review, the main features of the pectin disassembly process during fruit ripening are first discussed, and then the nanostructural characterization of fruit pectins by AFM and its relationship with texture and postharvest fruit shelf life is reviewed. In general, fruit pectins are visualized under AFM as linear chains, a few of which show long branches, and aggregates. Number- and weight-average values obtained from these images are in good agreement with chromatographic analyses. Most AFM studies indicate reductions in the length of individual pectin chains and the frequency of aggregates as the fruits ripen. Pectins extracted with sodium carbonate, supposedly located within the primary cell wall, are the most affected. PMID:25063934

A versatile variable field module for Asylum Cypher scanning probe system

NASA Astrophysics Data System (ADS)

Liu, Hongxue; Comes, Ryan; Lu, Jiwei; Wolf, Stuart; Hodgson, Jim; Rutgers, Maarten

2013-03-01

Atomic force microscopy (AFM) has become one of the most widely used techniques for measuring and manipulating various characteristics of materials at the nanoscale. However, there are very limited option for the characterization of field dependence properties. In this work, we demonstrate a versatile variable field module (VFM) with magnetic field up to 1800 Oe for the Asylum Research Cypher system. The magnetic field is changed by adjusting the distance between a rare earth magnet and the AFM probe. A built-in Hall sensor makes it possible to perform in-situ measurements of the field. Rotating the magnet makes it possible to do angular field dependent measurements. The capability of the VFM system is demonstrated by degaussing a floppy disk media with increasing magnetic field. The written bits are erased at about 800 Oe. Angular dependence measurements clearly show the evolution of magnetic domain structures. A completely reversible magnetic force microscopy (MFM) phase contrast is observed when the magnetic field is rotated by 180°. Further demonstration of successful magnetic switching of CoFe2O4 pillars in CoFe2O4-BiFeO3 nanocomposites will be presented and field dependent MFM and piezoresponse force microscopy (PFM) will be discussed. The work at University of Virginia was supported by DARPA under contract no. HR-0011-10-1-0072.

Direct Imaging of Protein Organization in an Intact Bacterial Organelle Using High-Resolution Atomic Force Microscopy

PubMed Central

2016-01-01

The function of bioenergetic membranes is strongly influenced by the spatial arrangement of their constituent membrane proteins. Atomic force microscopy (AFM) can be used to probe protein organization at high resolution, allowing individual proteins to be identified. However, previous AFM studies of biological membranes have typically required that curved membranes are ruptured and flattened during sample preparation, with the possibility of disruption of the native protein arrangement or loss of proteins. Imaging native, curved membranes requires minimal tip–sample interaction in both lateral and vertical directions. Here, long-range tip–sample interactions are reduced by optimizing the imaging buffer. Tapping mode AFM with high-resonance-frequency small and soft cantilevers, in combination with a high-speed AFM, reduces the forces due to feedback error and enables application of an average imaging force of tens of piconewtons. Using this approach, we have imaged the membrane organization of intact vesicular bacterial photosynthetic “organelles”, chromatophores. Despite the highly curved nature of the chromatophore membrane and lack of direct support, the resolution was sufficient to identify the photosystem complexes and quantify their arrangement in the native state. Successive imaging showed the proteins remain surprisingly static, with minimal rotation or translation over several-minute time scales. High-order assemblies of RC-LH1-PufX complexes are observed, and intact ATPases are successfully imaged. The methods developed here are likely to be applicable to a broad range of protein-rich vesicles or curved membrane systems, which are an almost ubiquitous feature of native organelles. PMID:28114766

Systems and methods for pressure and temperature measurement

DOEpatents

Challener, William Albert; Airey, Li

2016-12-06

A measurement system in one embodiment includes an acquisition module and a determination module. The acquisition module is configured to acquire resonant frequency information corresponding to a sensor disposed in a remote location from the acquisition module. The resonant frequency information includes first resonant frequency information for a first resonant frequency of the sensor corresponding to environmental conditions of the remote location, and also includes second resonant frequency information for a different, second resonant frequency of the sensor corresponding to the environmental conditions of the remote location. The determination module is configured to use the first resonant frequency information and the second resonant frequency information to determine the temperature and the pressure at the remote location.

140 GHz pulsed fourier transform microwave spectrometer

DOEpatents

Kolbe, William F.; Leskovar, Branko

1987-01-01

A high frequency energy pulsing system suitable for use in a pulsed microwave spectrometer (10), including means (11, 19) for generating a high frequency carrier signal, and means (12) for generating a low frequency modulating signal. The carrier signal is continuously fed to a modulator (20) and the modulating signal is fed through a pulse switch (23) to the modulator. When the pulse switch (23) is on, the modulator (20) will produce sideband signals above and below the carrier signal frequency. A frequency-responsive device (31) is tuned to one of the sideband signals and away from the carrier frequency so that the high frequency energization of the frequency-responsive device (31) is controlled by the pulse switch (23).

Electrogenerated chemiluminescence reactions between the [Ru(bpy)3](2+) complex and PAMAM GX.0 dendrimers in an aqueous medium.

PubMed

Jimenez-Ruiz, A; Grueso, E; Perez-Tejeda, P

2015-10-01

Electrogenerated chemiluminescence, ECL, reactions between tris(2,2'-bipyridine)ruthenium(II), [Ru(bpy)3](2+), and PAMAM GX.0 (X=1 and 2) dendrimers in an aqueous medium were carried out at pH10 (fully deprotonated dendrimer surface). ECL was detected in the presence of GX.0 dendrimers without addition of any known coreactant. Atomic force microscopy, AFM, measurements for GX.0 dendrimers in the presence of the [Ru(bpy)3](2+) complex were also done. AFM images showed the existence of aggregates (pillars) of globular shape, as well as interdendrimer networks forming fibers in the x-y direction for dendrimer aqueous solutions. ECL and AFM results in cooperation suggest that the coreactant effect of the end amine groups is improved by both the dendritic branched shells and the globular z-type aggregates. The ECL efficiency trends as a function of [GX.0] (whole range) can be interpreted taking into account the coreactant effect modulated by the presence of the z and x-y type aggregates. Importantly, ECL efficiency values can be taken as a measure of the change induced on the dendrimer aggregation in aqueous solutions when their concentrations rise. Redox potentials of the [Ru(bpy)3](3+/2+) couple in the presence of the G1.0 and G2.0 dendrimers were also determined. Copyright © 2015 Elsevier Inc. All rights reserved.

Modified atomic force microscope applied to the measurement of elastic modulus for a single peptide molecule

NASA Astrophysics Data System (ADS)

Ptak, Arkadiusz; Takeda, Seiji; Nakamura, Chikashi; Miyake, Jun; Kageshima, Masami; Jarvis, Suzanne P.; Tokumoto, Hiroshi

2001-09-01

A modified atomic force microscopy (AFM) system, based on a force modulation technique, has been used to find an approximate value for the elastic modulus of a single peptide molecule directly from a mechanical test. For this purpose a self-assembled monolayer built from two kinds of peptides, reactive (able to anchor to the AFM tip) and nonreactive, was synthesized. In a typical experiment a single C3K30C (C=cysteine, K=lysine) peptide molecule was stretched between a Au(111) substrate and the gold-coated tip of an AFM cantilever to which it was attached via gold-sulfur bonds. The amplitude of the cantilever oscillations, due to an external force applied via a magnetic particle to the cantilever, was recorded by a lock-in amplifier and recalculated into stiffness of the stretched molecule. A longitudinal Young's modulus for the α-helix of a single peptide molecule and for the elongated state of this molecule has been estimated. The obtained values; 1.2±0.3 and 50±15 GPa, for the peptide α-helix and elongated peptide backbone, respectively, seem to be reasonable comparing them to the Young's modulus of protein crystals and linear organic polymers. We believe this research opens up a means by which scientists can perform quantitative studies of the elastic properties of single molecule, especially of biologically important polymers like peptides or DNA.

Synchronous Oscillations in Van Der Pol Generator with Modulated Natural Frequency

NASA Astrophysics Data System (ADS)

Nimets, A. Yu.; Vavriv, D. M.

2015-12-01

The synchronous operation of Van Der Pole generator with the low-frequency modulated natural frequency has been investigated. The presence of low-frequency modulation is shown to lead to formation of additional synchronization regions. The appearance of such regions is found to be caused by threefrequency resonances resulted from the interaction between oscillations of the generator natural frequency, modulation frequency and synchronized signal frequency. Characteristics of synchronous oscillations due to the below mentioned three-frequency interaction are obtained and comparison with the case of synchronization of oscillator on the main mode made.

A High-Q AFM Sensor Using a Balanced Trolling Quartz Tuning Fork in the Liquid

PubMed Central

Li, Yingzi; Song, Zihang; Lin, Rui; Chen, Yifu; Qian, Jianqiang

2018-01-01

A quartz tuning fork (QTF) has been widely used as a force sensor of the frequency modulation atomic force microscope due to its ultrahigh stiffness, high quality factor and self-sensing nature. However, due to the bulky structure and exposed surface electrode arrangement, its application is limited, especially in liquid imaging of in situ biological samples, ionic liquids, electrochemical reaction, etc. Although the complication can be resolved by coating insulating materials on the QTF surface and then immersing the whole QTF into the liquid, it would result in a sharp drop of the quality factor, which will reduce the sensitivity of the QTF. To solve the problem, a novel method, called the balanced trolling quartz tuning fork (BT-QTF), is introduced here. In this method, two same probes are glued on both prongs of the QTF separately while only one probe immersed in the liquid. With the method, the hydrodynamic interaction can be reduced, thus the BT-QTF can retain a high quality factor and constant resonance frequency. The stable small vibration of the BT-QTF can be achieved in the liquid. Initially, a theoretical model is presented to analyze the sensing performance of the BT-QTF in the liquid. Then, the sensing performance analysis experiments of the BT-QTF have been performed. At last, the proposed method is applied to atomic force microscope imaging different samples in the liquid, which proves its feasibility. PMID:29783740

Modulating action of low frequency oscillations on high frequency instabilities in Hall thrusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liqiu, Wei, E-mail: weiliqiu@gmail.com, E-mail: weiliqiu@hit.edu.cn; Liang, Han; Ziyi, Yang

2015-02-07

It is found that the low frequency oscillations have modulating action on high frequency instabilities in Hall thrusters. The physical mechanism of this modulation is discussed and verified by numerical simulations. Theoretical analyses indicate that the wide-range fluctuations of plasma density and electric field associated with the low frequency oscillations affect the electron drift velocity and anomalous electron transport across the magnetic field. The amplitude and frequency of high frequency oscillations are modulated by low frequency oscillations, which show the periodic variation in the time scale of low frequency oscillations.

Formation of surface relief grating in polymers with pendant azobenzene chromophores as studied by AFM/UFM

NASA Astrophysics Data System (ADS)

Kulikovska, Olga; Gharagozloo-Hubmann, Kati; Stumpe, Joachim; Huey, Bryan D.; Bliznyuk, Valery N.

2012-12-01

We studied peculiarities of the structural reconstruction within holographically recorded gratings on the surface of several different amorphous azobenzene-containing polymers. Under illumination with a light interference pattern, two processes take place in this type of polymer. The first process is the light-induced orientation of azobenzene units perpendicular to the polarization plane of the incident light. The second one is a transfer of macromolecules along the grating vector (i.e. perpendicular to the grating lines). These two processes result in the creation of a volume orientation grating (alternating regions of different direction or degree of molecular orientation) and a surface relief grating (SRG)—i.e. modulation of film thickness. One can assume that both orientation of molecules and their movement might change the local mechanical properties of the material. Therefore, formation of the SRG is expected to result also in modulation of the local stiffness of the polymer film. To reveal and investigate these stiffness changes within the grating, spin-coated polymer films were prepared and the gratings were recorded on them in two different ways: with an orthogonal circular or orthogonal linear polarization of two recording light beams. A combination of atomic force microscopy (AFM) and ultrasonic force microscopy (UFM) techniques was applied for SRG development monitoring. We demonstrate that formation of the phase gratings depends on the chemical structure of polymers being used, polymer film thickness, and recording parameters, with the height of grating structures (depth of modulation) increasing with both the exposure time and the film thickness. UFM images suggest that the slopes of the topographic peaks in the phase gratings exhibit an increased stiffness with respect to the grating depressions.

Annexin-A6 presents two modes of association with phospholipid membranes. A combined QCM-D, AFM and cryo-TEM study.

PubMed

Buzhynskyy, Nikolay; Golczak, Marcin; Lai-Kee-Him, Joséphine; Lambert, Olivier; Tessier, Béatrice; Gounou, Céline; Bérat, Rémi; Simon, Anne; Granier, Thierry; Chevalier, Jean-Marc; Mazères, Serge; Bandorowicz-Pikula, Joanna; Pikula, Slawomir; Brisson, Alain R

2009-10-01

Annexins are soluble proteins that bind to biological membranes in a Ca(2+)-dependent manner. Annexin-A6 (AnxA6) is unique in the annexin family as it consists of the repeat of two annexin core modules, while all other annexins consist of a single module. AnxA6 has been proposed to participate in various membrane-related processes, including endocytosis and exocytosis, yet the molecular mechanism of association of AnxA6 with biological membranes, especially its ability to aggregate membranes, is still unclear. To address this question, we studied the association of AnxA6 with model phospholipid membranes by combining the techniques of quartz crystal microbalance with dissipation monitoring (QCM-D), (cryo-) transmission electron microscopy (TEM) and atomic force microscopy (AFM). The properties of membrane binding and membrane aggregation of AnxA6 were compared to two reference systems, annexin A5 (AnxA5), which is the annexin prototype, and a chimerical AnxA5-dimer molecule, which is able to aggregate two membranes in a symmetrical manner. We show that AnxA6 presents two modes of association with lipid membranes depending on Ca(2+)-concentration. At low Ca(2+)-concentration ( approximately 60-150microM), AnxA6 binds to membranes via its two coplanar annexin modules and is not able to associate two separate membranes. At high Ca(2+)-concentration ( approximately 2mM), AnxA6 molecules are able to bind two adjacent phospholipid membranes and present a conformation similar to the AnxA6 3D crystallographic structure. Possible biological implications of these novel membrane-binding properties of AnxA6 are discussed.

Atomic-Scale Variations of the Mechanical Response of 2D Materials Detected by Noncontact Atomic Force Microscopy.

PubMed

de la Torre, B; Ellner, M; Pou, P; Nicoara, N; Pérez, Rubén; Gómez-Rodríguez, J M

2016-06-17

We show that noncontact atomic force microscopy (AFM) is sensitive to the local stiffness in the atomic-scale limit on weakly coupled 2D materials, as graphene on metals. Our large amplitude AFM topography and dissipation images under ultrahigh vacuum and low temperature resolve the atomic and moiré patterns in graphene on Pt(111), despite its extremely low geometric corrugation. The imaging mechanisms are identified with a multiscale model based on density-functional theory calculations, where the energy cost of global and local deformations of graphene competes with short-range chemical and long-range van der Waals interactions. Atomic contrast is related with short-range tip-sample interactions, while the dissipation can be understood in terms of global deformations in the weakly coupled graphene layer. Remarkably, the observed moiré modulation is linked with the subtle variations of the local interplanar graphene-substrate interaction, opening a new route to explore the local mechanical properties of 2D materials at the atomic scale.

Development of in-situ high-voltage and high-temperature stressing capability on atomic force microscopy platform

DOE PAGES

Xiao, Chuanxiao; Jiang, Chun-Sheng; Johnston, Steve; ...

2017-10-18

Reliability has become an increasingly important issue as photovoltaic technologies mature. However, researching reliability at the nanometer scale is in its infancy; in particular, in-situ studies have not been reported to date. Here, to investigate potential-induced degradation (PID) of solar cell modules, we have developed an in-situ stressing capability with applied high voltage (HV) and high temperature (HT) on an atomic force microscopy (AFM) platform. We designed a sample holder to simultaneously accommodate 1000-V HV and 200 degrees C HT stressing. Three technical challenges have been overcome along with the development: thermal drift at HT, HV interference with measurement, andmore » arc discharge caused by HV. We demonstrated no observable measurement artifact under the stress conditions. Based on our in-situ stressing AFM, Kelvin probe force microscopy potential imaging revealed the evolution of electrical potential across the junction along with the PID stressing time, which provides vital information to further study the PID mechanism.« less

Development of in-situ high-voltage and high-temperature stressing capability on atomic force microscopy platform

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiao, Chuanxiao; Jiang, Chun-Sheng; Johnston, Steve

Reliability has become an increasingly important issue as photovoltaic technologies mature. However, researching reliability at the nanometer scale is in its infancy; in particular, in-situ studies have not been reported to date. Here, to investigate potential-induced degradation (PID) of solar cell modules, we have developed an in-situ stressing capability with applied high voltage (HV) and high temperature (HT) on an atomic force microscopy (AFM) platform. We designed a sample holder to simultaneously accommodate 1000-V HV and 200 degrees C HT stressing. Three technical challenges have been overcome along with the development: thermal drift at HT, HV interference with measurement, andmore » arc discharge caused by HV. We demonstrated no observable measurement artifact under the stress conditions. Based on our in-situ stressing AFM, Kelvin probe force microscopy potential imaging revealed the evolution of electrical potential across the junction along with the PID stressing time, which provides vital information to further study the PID mechanism.« less

Amplitude modulation detection with concurrent frequency modulation.

PubMed

Nagaraj, Naveen K

2016-09-01

Human speech consists of concomitant temporal modulations in amplitude and frequency that are crucial for speech perception. In this study, amplitude modulation (AM) detection thresholds were measured for 550 and 5000 Hz carriers with and without concurrent frequency modulation (FM), at AM rates crucial for speech perception. Results indicate that adding 40 Hz FM interferes with AM detection, more so for 5000 Hz carrier and for frequency deviations exceeding the critical bandwidth of the carrier frequency. These findings suggest that future cochlear implant processors, encoding speech fine-structures may consider limiting the FM to narrow bandwidth and to low frequencies.

Frequency modulation detection in cochlear implant subjects

NASA Astrophysics Data System (ADS)

Chen, Hongbin; Zeng, Fan-Gang

2004-10-01

Frequency modulation (FM) detection was investigated in acoustic and electric hearing to characterize cochlear-implant subjects' ability to detect dynamic frequency changes and to assess the relative contributions of temporal and spectral cues to frequency processing. Difference limens were measured for frequency upward sweeps, downward sweeps, and sinusoidal FM as a function of standard frequency and modulation rate. In electric hearing, factors including electrode position and stimulation level were also studied. Electric hearing data showed that the difference limen increased monotonically as a function of standard frequency regardless of the modulation type, the modulation rate, the electrode position, and the stimulation level. In contrast, acoustic hearing data showed that the difference limen was nearly a constant as a function of standard frequency. This difference was interpreted to mean that temporal cues are used only at low standard frequencies and at low modulation rates. At higher standard frequencies and modulation rates, the reliance on the place cue is increased, accounting for the better performance in acoustic hearing than for electric hearing with single-electrode stimulation. The present data suggest a speech processing strategy that encodes slow frequency changes using lower stimulation rates than those typically employed by contemporary cochlear-implant speech processors. .

Parametric Amplification Protocol for Frequency-Modulated Magnetic Resonance Force Microscopy Signals

NASA Astrophysics Data System (ADS)

Harrell, Lee; Moore, Eric; Lee, Sanggap; Hickman, Steven; Marohn, John

2011-03-01

We present data and theoretical signal and noise calculations for a protocol using parametric amplification to evade the inherent tradeoff between signal and detector frequency noise in force-gradient magnetic resonance force microscopy signals, which are manifested as a modulated frequency shift of a high- Q microcantilever. Substrate-induced frequency noise has a 1 / f frequency dependence, while detector noise exhibits an f2 dependence on modulation frequency f . Modulation of sample spins at a frequency that minimizes these two contributions typically results in a surface frequency noise power an order of magnitude or more above the thermal limit and may prove incompatible with sample spin relaxation times as well. We show that the frequency modulated force-gradient signal can be used to excite the fundamental resonant mode of the cantilever, resulting in an audio frequency amplitude signal that is readily detected with a low-noise fiber optic interferometer. This technique allows us to modulate the force-gradient signal at a sufficiently high frequency so that substrate-induced frequency noise is evaded without subjecting the signal to the normal f2 detector noise of conventional demodulation.

Electrical power inverter having a phase modulated, twin-inverter, high frequency link and an energy storage module

DOEpatents

Pitel, Ira J.

1987-02-03

The present invention provides an electrical power inverter method and apparatus, which includes a high frequency link, for converting DC power into AC power. Generally stated, the apparatus includes a first high frequency module which produces an AC voltage at a first output frequency, and a second high frequency inverter module which produces an AC voltage at a second output frequency that is substantially the same as the first output frequency. The second AC voltage is out of phase with the first AC voltage by a selected angular phase displacement. A mixer mixes the first and second output voltages to produce a high frequency carrier which has a selected base frequency impressed on the sidebands thereof. A rectifier rectifies the carrier, and a filter filters the rectified carrier. An output inverter inverts the filtered carrier to produce an AC line voltage at the selected base frequency. A phase modulator adjusts the relative angular phase displacement between the outputs of the first and second high frequency modules to control the base frequency and magnitude of the AC line voltage.

Electrical power inverter having a phase modulated, twin-inverter, high frequency link and an energy storage module

DOEpatents

Pitel, I.J.

1987-02-03

The present invention provides an electrical power inverter method and apparatus, which includes a high frequency link, for converting DC power into AC power. Generally stated, the apparatus includes a first high frequency module which produces an AC voltage at a first output frequency, and a second high frequency inverter module which produces an AC voltage at a second output frequency that is substantially the same as the first output frequency. The second AC voltage is out of phase with the first AC voltage by a selected angular phase displacement. A mixer mixes the first and second output voltages to produce a high frequency carrier which has a selected base frequency impressed on the sidebands thereof. A rectifier rectifies the carrier, and a filter filters the rectified carrier. An output inverter inverts the filtered carrier to produce an AC line voltage at the selected base frequency. A phase modulator adjusts the relative angular phase displacement between the outputs of the first and second high frequency modules to control the base frequency and magnitude of the AC line voltage. 19 figs.

Cellular level robotic surgery: Nanodissection of intermediate filaments in live keratinocytes.

PubMed

Yang, Ruiguo; Song, Bo; Sun, Zhiyong; Lai, King Wai Chiu; Fung, Carmen Kar Man; Patterson, Kevin C; Seiffert-Sinha, Kristina; Sinha, Animesh A; Xi, Ning

2015-01-01

We present the nanosurgery on the cytoskeleton of live cells using AFM based nanorobotics to achieve adhesiolysis and mimic the effect of pathophysiological modulation of intercellular adhesion. Nanosurgery successfully severs the intermediate filament bundles and disrupts cell-cell adhesion similar to the desmosomal protein disassembly in autoimmune disease, or the cationic modulation of desmosome formation. Our nanomechanical analysis revealed that adhesion loss results in a decrease in cellular stiffness in both cases of biochemical modulation of the desmosome junctions and mechanical disruption of intercellular adhesion, supporting the notion that intercellular adhesion through intermediate filaments anchors the cell structure as focal adhesion does and that intermediate filaments are integral components in cell mechanical integrity. The surgical process could potentially help reveal the mechanism of autoimmune pathology-induced cell-cell adhesion loss as well as its related pathways that lead to cell apoptosis. Copyright © 2015 Elsevier Inc. All rights reserved.

Calibration-free absolute frequency response measurement of directly modulated lasers based on additional modulation.

PubMed

Zhang, Shangjian; Zou, Xinhai; Wang, Heng; Zhang, Yali; Lu, Rongguo; Liu, Yong

2015-10-15

A calibration-free electrical method is proposed for measuring the absolute frequency response of directly modulated semiconductor lasers based on additional modulation. The method achieves the electrical domain measurement of the modulation index of directly modulated lasers without the need for correcting the responsivity fluctuation in the photodetection. Moreover, it doubles measuring frequency range by setting a specific frequency relationship between the direct and additional modulation. Both the absolute and relative frequency response of semiconductor lasers are experimentally measured from the electrical spectrum of the twice-modulated optical signal, and the measured results are compared to those obtained with conventional methods to check the consistency. The proposed method provides calibration-free and accurate measurement for high-speed semiconductor lasers with high-resolution electrical spectrum analysis.

AFM-IR: Technology and Applications in Nanoscale Infrared Spectroscopy and Chemical Imaging.

PubMed

Dazzi, Alexandre; Prater, Craig B

2016-12-13

Atomic force microscopy-based infrared spectroscopy (AFM-IR) is a rapidly emerging technique that provides chemical analysis and compositional mapping with spatial resolution far below conventional optical diffraction limits. AFM-IR works by using the tip of an AFM probe to locally detect thermal expansion in a sample resulting from absorption of infrared radiation. AFM-IR thus can provide the spatial resolution of AFM in combination with the chemical analysis and compositional imaging capabilities of infrared spectroscopy. This article briefly reviews the development and underlying technology of AFM-IR, including recent advances, and then surveys a wide range of applications and investigations using AFM-IR. AFM-IR applications that will be discussed include those in polymers, life sciences, photonics, solar cells, semiconductors, pharmaceuticals, and cultural heritage. In the Supporting Information , the authors provide a theoretical section that reviews the physics underlying the AFM-IR measurement and detection mechanisms.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eslami, Babak; López-Guerra, Enrique A.; Raftari, Maryam

Addition of a strong base to Nafion{sup ®} proton exchange membranes is a common practice in industry to increase their overall performance in fuel cells. Here, we investigate the evolution of the nano-rheological properties of Nafion thin films as a function of the casting pH, via characterization with static and dynamic, contact and intermittent-contact atomic force microscopy (AFM) techniques. The addition of KOH causes non-monotonic changes in the viscoelastic properties of the films, which behave as highly dissipative, softer materials near neutral pH values, and as harder, more elastic materials at extreme pH values. We quantify this behavior through calculationmore » of the temporal evolution of the compliance and the glassy compliance under static AFM measurements. We complement these observations with dynamic AFM metrics, including dissipated power and virial (for intermittent-contact-mode measurements), and contact resonance frequency and quality factor (for dynamic contact-mode measurements). We explain the non-monotonic material property behavior in terms of the degree of ionic crosslinking and moisture content of the films, which vary with the addition of KOH. This work focuses on the special case study of the addition of strong bases, but the observed mechanical property changes are broadly related to water plasticizing effects and ionic crosslinking, which are also important in other types of films.« less

Development and calibration of a compact self-sensing atomic force microscope head for micro-nano characterization

NASA Astrophysics Data System (ADS)

Guo, Tong; Wang, Siming; Zhao, Jian; Chen, Jinping; Fu, Xing; Hu, Xiaotang

2011-12-01

A compact self-sensing atomic force microscope (AFM) head is developed for the micro-nano dimensional measurement. This AFM head works in tapping mode equipped with a commercial self-sensing probe. This kind of probe can benefit not only from the tuning fork's stable resonant frequency and high quality factor but also from the silicon cantilever's reasonable spring constant. The head is convenient to operate by its simplicity of structure, since it does not need any optical detector to measure the bending of the cantilever. The compact structure makes the head ease to combine with other measuring methods. According to the probe"s characteristics, a method is proposed to quickly calculate the cantilever"s resonance amplitude through measuring its electro-mechanical coupling factor. An experiment system is established based on the nano-measuring machine (NMM) as a high precision positioning stage. Using this system, the approach/retract test is carried out for calibrating the head. The tests can be traced to the meter definition by interferometers in NMM. Experimental results show that the non-linearity error of this AFM head is smaller than 1%, the sensitivity reaches 0.47nm/mV and the measurement stroke is several hundreds of nanometers.

Active Damping of a Piezoelectric Tube Scanner using Self-Sensing Piezo Actuation

PubMed Central

Kuiper, S.; Schitter, G.

2010-01-01

In most Atomic Force Microscopes (AFM), a piezoelectric tube scanner is used to position the sample underneath the measurement probe. Oscillations stemming from the weakly damped resonances of the tube scanner are a major source of image distortion, putting a limitation on the achievable imaging speed. This paper demonstrates active damping of these oscillations in multiple scanning axes without the need for additional position sensors. By connecting the tube scanner in a capacitive bridge circuit the scanner oscillations can be measured in both scanning axes, using the same piezo material as an actuator and sensor simultaneously. In order to compensate for circuit imbalance caused by hysteresis in the piezo element, an adaptive balancing circuit is used. The obtained measurement signal is used for feedback control, reducing the resonance peaks in both scanning axes by 18 dB and the cross-coupling at those frequencies by 30 dB. Experimental results demonstrate a significant reduction in scanner oscillations when applying the typical triangular scanning signals, as well as a strong reduction in coupling induced oscillations. Recorded AFM images show a considerable reduction in image distortion due to the proposed control method, enabling artifact free AFM imaging at a speed of 122 lines per second with a standard piezoelectric tube scanner. PMID:26412944

Adaptive AFM scan speed control for high aspect ratio fast structure tracking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmad, Ahmad; Schuh, Andreas; Rangelow, Ivo W.

2014-10-15

Improved imaging rates in Atomic Force Microscopes (AFM) are of high interest for disciplines such as life sciences and failure analysis of semiconductor wafers, where the sample topology shows high aspect ratios. Also, fast imaging is necessary to cover a large surface under investigation in reasonable times. Since AFMs are composed of mechanical components, they are associated with comparably low resonance frequencies that undermine the effort to increase the acquisition rates. In particular, high and steep structures are difficult to follow, which causes the cantilever to temporarily loose contact to or crash into the sample. Here, we report on amore » novel approach that does not affect the scanner dynamics, but adapts the lateral scanning speed of the scanner. The controller monitors the control error signal and, only when necessary, decreases the scan speed to allow the z-piezo more time to react to changes in the sample's topography. In this case, the overall imaging rate can be significantly increased, because a general scan speed trade-off decision is not needed and smooth areas are scanned fast. In contrast to methods trying to increase the z-piezo bandwidth, our method is a comparably simple approach that can be easily adapted to standard systems.« less

Observation of giant exchange bias in bulk Mn50Ni42Sn8 Heusler alloy

NASA Astrophysics Data System (ADS)

Sharma, Jyoti; Suresh, K. G.

2015-02-01

We report a giant exchange bias (EB) field of 3520 Oe in bulk Mn50Ni42Sn8 Heusler alloy. The low temperature magnetic state of the martensite phase has been studied by DC magnetization and AC susceptibility measurements. Frequency dependence of spin freezing temperature (Tf) on critical slowing down relation and observation of memory effect in zero field cooling mode confirms the super spin glass (SSG) phase at low temperatures. Large EB is attributed to the strong exchange coupling between the SSG clusters formed by small regions of ferromagnetic order embedded in an antiferromagnetic (AFM) matrix. The temperature and cooling field dependence of EB have been studied and related to the change in unidirectional anisotropy at SSG/AFM interface. The training effect also corroborates with the presence of frozen (SSG) moments at the interface and their role in EB.

Advanced capability RFID system

DOEpatents

Gilbert, Ronald W.; Steele, Kerry D.; Anderson, Gordon A.

2007-09-25

A radio-frequency transponder device having an antenna circuit configured to receive radio-frequency signals and to return modulated radio-frequency signals via continuous wave backscatter, a modulation circuit coupled to the antenna circuit for generating the modulated radio-frequency signals, and a microprocessor coupled to the antenna circuit and the modulation circuit and configured to receive and extract operating power from the received radio-frequency signals and to monitor inputs on at least one input pin and to generate responsive signals to the modulation circuit for modulating the radio-frequency signals. The microprocessor can be configured to generate output signals on output pins to associated devices for controlling the operation thereof. Electrical energy can be extracted and stored in an optional electrical power storage device.

Features of anti-inflammatory effects of modulated extremely high-frequency electromagnetic radiation.

PubMed

Gapeyev, Andrew B; Mikhailik, Elena N; Chemeris, Nikolay K

2009-09-01

Using a model of acute zymosan-induced paw edema in NMRI mice, we test the hypothesis that anti-inflammatory effects of extremely high-frequency electromagnetic radiation (EHF EMR) can be essentially modified by application of pulse modulation with certain frequencies. It has been revealed that a single exposure of animals to continuous EHF EMR for 20 min reduced the exudative edema of inflamed paw on average by 19% at intensities of 0.1-0.7 mW/cm(2) and frequencies from the range of 42.2-42.6 GHz. At fixed effective carrier frequency of 42.2 GHz, the anti-inflammatory effect of EHF EMR did not depend on modulation frequencies, that is, application of different modulation frequencies from the range of 0.03-100 Hz did not lead to considerable changes in the effect level. On the contrary, at "ineffective" carrier frequencies of 43.0 and 61.22 GHz, the use of modulation frequencies of 0.07-0.1 and 20-30 Hz has allowed us to restore the effect up to a maximal level. The results obtained show the critical dependence of anti-inflammatory action of low-intensity EHF EMR on carrier and modulation frequencies. Within the framework of this study, the possibility of changing the level of expected biological effect of modulated EMR by a special selection of combination of carrier and modulation frequencies is confirmed.

Tuning of Human Modulation Filters Is Carrier-Frequency Dependent

PubMed Central

Simpson, Andrew J. R.; Reiss, Joshua D.; McAlpine, David

2013-01-01

Recent studies employing speech stimuli to investigate ‘cocktail-party’ listening have focused on entrainment of cortical activity to modulations at syllabic (5 Hz) and phonemic (20 Hz) rates. The data suggest that cortical modulation filters (CMFs) are dependent on the sound-frequency channel in which modulations are conveyed, potentially underpinning a strategy for separating speech from background noise. Here, we characterize modulation filters in human listeners using a novel behavioral method. Within an ‘inverted’ adaptive forced-choice increment detection task, listening level was varied whilst contrast was held constant for ramped increments with effective modulation rates between 0.5 and 33 Hz. Our data suggest that modulation filters are tonotopically organized (i.e., vary along the primary, frequency-organized, dimension). This suggests that the human auditory system is optimized to track rapid (phonemic) modulations at high sound-frequencies and slow (prosodic/syllabic) modulations at low frequencies. PMID:24009759

Optimal sensitivity for molecular recognition MAC-mode AFM

PubMed

Schindler; Badt; Hinterdorfer; Kienberger; Raab; Wielert-Badt; Pastushenko

2000-02-01

Molecular recognition force microscopy (MRFM) using the magnetic AC mode (MAC mode) atomic force microscope (AFM) was recently investigated to locate and probe recognition sites. A flexible crosslinker carrying a ligand is bound to the tip for the molecular recognition of receptors on the surface of a sample. In this report, the driving frequency is calculated which optimizes the sensitivity (S). The sensitivity of MRFM is defined as the relative change of the magnetically excited cantilever deflection amplitude arising from a crosslinker/antibody/antigen connection that is characterized by a very small force constant. The sensitivity is calculated in a damped oscillator model with a certain value of quality factor Q, which, together with load, defines the frequency response (unloaded oscillator shows resonance at Q > 0.707). If Q < 1, the greatest value of S corresponds to zero driving frequency omega (measured in units of eigenfrequency). Therefore, for Q < 1, MAC-mode has no advantage in comparison with DC-mode. Two additional extremes are found at omegaL = (1 - 1/Q)(1/2) and omegaR = (1 + 1/Q)(1/2), with corresponding sensitivities S(L) = Q2/(2Q - 1), S(R) = Q2/(2Q + 1). The L-extreme exists only for Q > 1, and then S(L) > S(R), i.e. the L-extreme is the main one. For Q > 1, S(L) > 1, and for Q > 2.41, S(R) > 1. These are the critical Q-values, above which selecting driving frequency equal to sigmaL or sigmaR brings advantage to MAC mode vs. DC mode. Satisfactory quality of the oscillator model is demonstrated by comparison of some results with those calculated within the classical description of cantilevers.

Microscopy imaging system and method employing stimulated raman spectroscopy as a contrast mechanism

DOEpatents

Xie, Xiaoliang Sunney [Lexington, MA; Freudiger, Christian [Boston, MA; Min, Wei [Cambridge, MA

2011-09-27

A microscopy imaging system includes a first light source for providing a first train of pulses at a first center optical frequency .omega..sub.1, a second light source for providing a second train of pulses at a second center optical frequency .omega..sub.2, a modulator system, an optical detector, and a processor. The modulator system is for modulating a beam property of the second train of pulses at a modulation frequency f of at least 100 kHz. The optical detector is for detecting an integrated intensity of substantially all optical frequency components of the first train of pulses from the common focal volume by blocking the second train of pulses being modulated. The processor is for detecting, a modulation at the modulation frequency f, of the integrated intensity of the optical frequency components of the first train of pulses to provide a pixel of an image for the microscopy imaging system.

Frequency modulation spectroscopy with a THz quantum-cascade laser.

PubMed

Eichholz, R; Richter, H; Wienold, M; Schrottke, L; Hey, R; Grahn, H T; Hübers, H-W

2013-12-30

We report on a terahertz spectrometer for high-resolution molecular spectroscopy based on a quantum-cascade laser. High-frequency modulation (up to 50 MHz) of the laser driving current produces a simultaneous modulation of the frequency and amplitude of the laser output. The modulation generates sidebands, which are symmetrically positioned with respect to the laser carrier frequency. The molecular transition is probed by scanning the sidebands across it. In this way, the absorption and the dispersion caused by the molecular transition are measured. The signals are modeled by taking into account the simultaneous modulation of the frequency and amplitude of the laser emission. This allows for the determination of the strength of the frequency as well as amplitude modulation of the laser and of molecular parameters such as pressure broadening.

47 CFR 101.811 - Modulation requirements.

Code of Federal Regulations, 2010 CFR

2010-10-01

... signaling on frequencies below 500 MHz is not authorized. (b) When amplitude modulation is used, the... frequency modulation is used for single channel radiotelephony on frequencies below 500 MHz, the deviation... 47 Telecommunication 5 2010-10-01 2010-10-01 false Modulation requirements. 101.811 Section 101...

Extinction-ratio-independent electrical method for measuring chirp parameters of Mach-Zehnder modulators using frequency-shifted heterodyne.

PubMed

Zhang, Shangjian; Wang, Heng; Zou, Xinhai; Zhang, Yali; Lu, Rongguo; Liu, Yong

2015-06-15

An extinction-ratio-independent electrical method is proposed for measuring chirp parameters of Mach-Zehnder electric-optic intensity modulators based on frequency-shifted optical heterodyne. The method utilizes the electrical spectrum analysis of the heterodyne products between the intensity modulated optical signal and the frequency-shifted optical carrier, and achieves the intrinsic chirp parameters measurement at microwave region with high-frequency resolution and wide-frequency range for the Mach-Zehnder modulator with a finite extinction ratio. Moreover, the proposed method avoids calibrating the responsivity fluctuation of the photodiode in spite of the involved photodetection. Chirp parameters as a function of modulation frequency are experimentally measured and compared to those with the conventional optical spectrum analysis method. Our method enables an extinction-ratio-independent and calibration-free electrical measurement of Mach-Zehnder intensity modulators by using the high-resolution frequency-shifted heterodyne technique.

[Research of dual-photoelastic-modulator-based beat frequency modulation and Fourier-Bessel transform imaging spectrometer].

PubMed

Wang, Zhi-Bin; Zhang, Rui; Wang, Yao-Li; Huang, Yan-Fei; Chen, You-Hua; Wang, Li-Fu; Yang, Qiang

2014-02-01

As the existing photoelastic-modulator(PEM) modulating frequency in the tens of kHz to hundreds of kHz between, leading to frequency of modulated interference signal is higher, so ordinary array detector cannot effectively caprure interference signal..A new beat frequency modulation method based on dual-photoelastic-modulator (Dual-PEM) and Fourier-Bessel transform is proposed as an key component of dual-photoelastic-modulator-based imaging spectrometer (Dual-PEM-IS) combined with charge coupled device (CCD). The dual-PEM are operated as an electro-optic circular retardance modulator, Operating the PEMs at slightly different resonant frequencies w1 and w2 respectively, generates a differential signal at a much lower heterodyne frequency that modulates the incident light. This method not only retains the advantages of the existing PEM, but also the frequency of modulated photocurrent decreased by 2-3 orders of magnitude (10-500 Hz) and can be detected by common array detector, and the incident light spectra can be obtained by Fourier-Bessel transform of low frequency component in the modulated signal. The method makes the PEM has the dual capability of imaging and spectral measurement. The basic principle is introduced, the basic equations is derived, and the feasibility is verified through the corresponding numerical simulation and experiment. This method has' potential applications in imaging spectrometer technology, and analysis of the effect of deviation of the optical path difference. This work provides the necessary theoretical basis for remote sensing of new Dual-PEM-IS and for engineering implementation of spectra inversion.

Characteristics of spectro-temporal modulation frequency selectivity in humans.

PubMed

Oetjen, Arne; Verhey, Jesko L

2017-03-01

There is increasing evidence that the auditory system shows frequency selectivity for spectro-temporal modulations. A recent study of the authors has shown spectro-temporal modulation masking patterns that were in agreement with the hypothesis of spectro-temporal modulation filters in the human auditory system [Oetjen and Verhey (2015). J. Acoust. Soc. Am. 137(2), 714-723]. In the present study, that experimental data and additional data were used to model this spectro-temporal frequency selectivity. The additional data were collected to investigate to what extent the spectro-temporal modulation-frequency selectivity results from a combination of a purely temporal amplitude-modulation filter and a purely spectral amplitude-modulation filter. In contrast to the previous study, thresholds were measured for masker and target modulations with opposite directions, i.e., an upward pointing target modulation and a downward pointing masker modulation. The comparison of this data set with previous corresponding data with the same direction from target and masker modulations indicate that a specific spectro-temporal modulation filter is required to simulate all aspects of spectro-temporal modulation frequency selectivity. A model using a modified Gabor filter with a purely temporal and a purely spectral filter predicts the spectro-temporal modulation masking data.

AFM Investigation of Liquid-Filled Polymer Microcapsules Elasticity.

PubMed

Sarrazin, Baptiste; Tsapis, Nicolas; Mousnier, Ludivine; Taulier, Nicolas; Urbach, Wladimir; Guenoun, Patrick

2016-05-10

Elasticity of polymer microcapsules (MCs) filled with a liquid fluorinated core is studied by atomic force microscopy (AFM). Accurately characterized spherical tips are employed to obtain the Young's moduli of MCs having four different shell thicknesses. We show that those moduli are effective ones because the samples are composites. The strong decrease of the effective MC elasticity (from 3.0 to 0.1 GPa) as the shell thickness decreases (from 200 to 10 nm) is analyzed using a novel numerical approach. This model describes the evolution of the elasticity of a coated half-space according to the contact radius, the thickness of the film, and the elastic moduli of bulk materials. This numerical model is consistent with the experimental data and allows simulating the elastic behavior of MCs at high frequencies (5 MHz). While the quasi-static elasticity of the MCs is found to be very dependent on the shell thickness, the high frequency (5 MHz) elastic behavior of the core leads to a stable behavior of the MCs (from 2.5 to 3 GPa according to the shell thickness). Finally, the effect of thermal annealing on the MCs elasticity is investigated. The Young's modulus is found to decrease because of the reduction of the shell thickness due to the loss of the polymer.

A near-field scanning microwave microscope based on a superconducting resonator for low power measurements.

PubMed

de Graaf, S E; Danilov, A V; Adamyan, A; Kubatkin, S E

2013-02-01

We report on the design and performance of a cryogenic (300 mK) near-field scanning microwave microscope. It uses a microwave resonator as the near-field sensor, operating at a frequency of 6 GHz and microwave probing amplitudes down to 100 μV, approaching low enough photon population (N ∼ 1000) of the resonator such that coherent quantum manipulation becomes feasible. The resonator is made out of a miniaturized distributed fractal superconducting circuit that is integrated with the probing tip, micromachined to be compact enough such that it can be mounted directly on a quartz tuning-fork, and used for parallel operation as an atomic force microscope (AFM). The resonator is magnetically coupled to a transmission line for readout, and to achieve enhanced sensitivity we employ a Pound-Drever-Hall measurement scheme to lock to the resonance frequency. We achieve a well localized near-field around the tip such that the microwave resolution is comparable to the AFM resolution, and a capacitive sensitivity down to 6.4 × 10(-20) F/Hz, limited by mechanical noise. We believe that the results presented here are a significant step towards probing quantum systems at the nanoscale using near-field scanning microwave microscopy.

Coordinated control strategy for improving the two drops of the wind storage combined system

NASA Astrophysics Data System (ADS)

Qian, Zhou; Chenggen, Wang; Jing, Bu

2018-05-01

In the power system with high permeability wind power, due to wind power fluctuation, the operation of large-scale wind power grid connected to the system brings challenges to the frequency stability of the system. When the doubly fed wind power generation unit does not reserve spare capacity to participate in the system frequency regulation, the system frequency will produce two drops in different degrees when the wind power exits frequency modulation and enters the speed recovery stage. To solve this problem, based on the complementary advantages of wind turbines and energy storage systems in power transmission and frequency modulation, a wind storage combined frequency modulation strategy based on sectional control is proposed in this paper. Based on the TOP wind power frequency modulation strategy, the wind power output reference value is determined according to the linear relationship between the output and the speed of the wind turbine, and the auxiliary wind power load reduction is controlled when the wind power exits frequency modulation into the speed recovery stage, so that the wind turbine is recovered to run at the optimal speed. Then, according to the system frequency and the wind turbine operation state, set the energy storage system frequency modulation output. Energy storage output active support is triggered during wind speed recovery. And then when the system frequency to return to the normal operating frequency range, reduce energy storage output or to exit frequency modulation. The simulation results verify the effectiveness of the proposed method.

Visualization of frequency-modulated electric field based on photonic frequency tracking in asynchronous electro-optic measurement system

NASA Astrophysics Data System (ADS)

Hisatake, Shintaro; Yamaguchi, Koki; Uchida, Hirohisa; Tojyo, Makoto; Oikawa, Yoichi; Miyaji, Kunio; Nagatsuma, Tadao

2018-04-01

We propose a new asynchronous measurement system to visualize the amplitude and phase distribution of a frequency-modulated electromagnetic wave. The system consists of three parts: a nonpolarimetric electro-optic frequency down-conversion part, a phase-noise-canceling part, and a frequency-tracking part. The photonic local oscillator signal generated by electro-optic phase modulation is controlled to track the frequency of the radio frequency (RF) signal to significantly enhance the measurable RF bandwidth. We demonstrate amplitude and phase measurement of a quasi-millimeter-wave frequency-modulated continuous-wave signal (24 GHz ± 80 MHz with a 2.5 ms period) as a proof-of-concept experiment.

Modulation linearization of a frequency-modulated voltage controlled oscillator, part 3

NASA Technical Reports Server (NTRS)

Honnell, M. A.

1975-01-01

An analysis is presented for the voltage versus frequency characteristics of a varactor modulated VHF voltage controlled oscillator in which the frequency deviation is linearized by using the nonlinear characteristics of a field effect transistor as a signal amplifier. The equations developed are used to calculate the oscillator output frequency in terms of pertinent circuit parameters. It is shown that the nonlinearity exponent of the FET has a pronounced influence on frequency deviation linearity, whereas the junction exponent of the varactor controls total frequency deviation for a given input signal. A design example for a 250 MHz frequency modulated oscillator is presented.

System for transmitting low frequency analog signals over AC power lines

DOEpatents

Baker, Steven P.; Durall, Robert L.; Haynes, Howard D.

1989-01-01

A system for transmitting low frequency analog signals over AC power lines using FM modulation. A low frequency analog signal to be transmitted is first applied to a voltage-to-frequency converter where it is converted to a signal whose frequency varies in proportion to the analog signal amplitude. This signal is then used to modulate the carrier frequency of an FM transmitter coupled to an AC power line. The modulation signal frequency range in selected to be within the response band of the FM transmitter. The FM modulated carrier signal is received by an FM receiver coupled to the AC power line, demodulated and the demodulated signal frequency is converted by a frequency-to-voltage converter back to the form of the original low frequency analog input signal.

System for transmitting low frequency analog signals over AC power lines

DOEpatents

Baker, Steven P.; Durall, Robert L.; Haynes, Howard D.

1989-09-05

A system for transmitting low frequency analog signals over AC power lines using FM modulation. A low frequency analog signal to be transmitted is first applied to a voltage-to-frequency converter where it is converted to a signal whose frequency varies in proportion to the analog signal amplitude. This signal is then used to modulate the carrier frequency of an FM transmitter coupled to an AC power line. The modulation signal frequency range in selected to be within the response band of the FM transmitter. The FM modulated carrier signal is received by an FM receiver coupled to the AC power line, demodulated and the demodulated signal frequency is converted by a frequency-to-voltage converter back to the form of the original low frequency analog input signal.

A system for tranmitting low frequency analog signals over ac power lines

DOEpatents

Baker, S.P.; Durall, R.L.; Haynes, H.D.

1987-07-30

A system for transmitting low frequency analog signals over ac power lines using FM modulation. A low frequency analog signal to be transmitted is first applied to a voltage-to-frequency converter where it is converted to a signal whose frequency varies in proportion to the analog signal amplitude. This signal is then used to modulate the carrier frequency of an FM transmitter coupled to an ac power line. The modulation signal frequency range is selected to be within the response band of the FM transmitter. The FM modulated carrier signal is received by an FM receiver coupled to the ac power line, demodulated and the demodulated signal frequency is converted by a frequency-to-voltage converter back to the form of the original low frequency analog input signal. 4 figs.

Note: Demodulation of spectral signal modulated by optical chopper with unstable modulation frequency.

PubMed

Zhang, Shengzhao; Li, Gang; Wang, Jiexi; Wang, Donggen; Han, Ying; Cao, Hui; Lin, Ling; Diao, Chunhong

2017-10-01

When an optical chopper is used to modulate the light source, the rotating speed of the wheel may vary with time and subsequently cause jitter of the modulation frequency. The amplitude calculated from the modulated signal would be distorted when the frequency fluctuations occur. To precisely calculate the amplitude of the modulated light flux, we proposed a method to estimate the range of the frequency fluctuation in the measurement of the spectrum and then extract the amplitude based on the sum of power of the signal in the selected frequency range. Experiments were designed to test the feasibility of the proposed method and the results showed lower root means square error than the conventional way.

Miniature Surface Plasmon Polariton Amplitude Modulator by Beat Frequency and Polarization Control

PubMed Central

Chang, Cheng-Wei; Lin, Chu-En; Yu, Chih-Jen; Yeh, Ting-Tso; Yen, Ta-Jen

2016-01-01

The miniaturization of modulators keeps pace for the compact devices in optical applications. Here, we present a miniature surface plasmon polariton amplitude modulator (SPPAM) by directing and interfering surface plasmon polaritons on a nanofabricated chip. Our results show that this SPPAM enables two kinds of modulations. The first kind of modulation is controlled by encoding angular-frequency difference from a Zeeman laser, with a beat frequency of 1.66 MHz; the second of modulation is validated by periodically varying the polarization states from a polarization generator, with rotation frequencies of 0.5–10 k Hz. In addition, the normalized extinction ratio of our plasmonic structure reaches 100. Such miniaturized beat-frequency and polarization-controlled amplitude modulators open an avenue for the exploration of ultrasensitive nanosensors, nanocircuits, and other integrated nanophotonic devices. PMID:27558516

MEMS based Low Cost Piezoresistive Microcantilever Force Sensor and Sensor Module

PubMed Central

Pandya, H. J.; Kim, Hyun Tae; Roy, Rajarshi; Desai, Jaydev P.

2014-01-01

In the present work, we report fabrication and characterization of a low-cost MEMS based piezoresistive micro-force sensor with SU-8 tip using laboratory made silicon-on-insulator (SOI) substrate. To prepare SOI wafer, silicon film (0.8 µm thick) was deposited on an oxidized silicon wafer using RF magnetron sputtering technique. The films were deposited in Argon (Ar) ambient without external substrate heating. The material characteristics of the sputtered deposited silicon film and silicon film annealed at different temperatures (400–1050°C) were studied using atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. The residual stress of the films was measured as a function of annealing temperature. The stress of the as-deposited films was observed to be compressive and annealing the film above 1050°C resulted in a tensile stress. The stress of the film decreased gradually with increase in annealing temperature. The fabricated cantilevers were 130 µm in length, 40 µm wide and 1.0 µm thick. A series of force-displacement curves were obtained using fabricated microcantilever with commercial AFM setup and the data were analyzed to get the spring constant and the sensitivity of the fabricated microcantilever. The measured spring constant and sensitivity of the sensor was 0.1488N/m and 2.7mV/N. The microcantilever force sensor was integrated with an electronic module that detects the change in resistance of the sensor with respect to the applied force and displays it on the computer screen. PMID:24855449

MEMS based Low Cost Piezoresistive Microcantilever Force Sensor and Sensor Module.

PubMed

Pandya, H J; Kim, Hyun Tae; Roy, Rajarshi; Desai, Jaydev P

2014-03-01

In the present work, we report fabrication and characterization of a low-cost MEMS based piezoresistive micro-force sensor with SU-8 tip using laboratory made silicon-on-insulator (SOI) substrate. To prepare SOI wafer, silicon film (0.8 µm thick) was deposited on an oxidized silicon wafer using RF magnetron sputtering technique. The films were deposited in Argon (Ar) ambient without external substrate heating. The material characteristics of the sputtered deposited silicon film and silicon film annealed at different temperatures (400-1050°C) were studied using atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. The residual stress of the films was measured as a function of annealing temperature. The stress of the as-deposited films was observed to be compressive and annealing the film above 1050°C resulted in a tensile stress. The stress of the film decreased gradually with increase in annealing temperature. The fabricated cantilevers were 130 µm in length, 40 µm wide and 1.0 µm thick. A series of force-displacement curves were obtained using fabricated microcantilever with commercial AFM setup and the data were analyzed to get the spring constant and the sensitivity of the fabricated microcantilever. The measured spring constant and sensitivity of the sensor was 0.1488N/m and 2.7mV/N. The microcantilever force sensor was integrated with an electronic module that detects the change in resistance of the sensor with respect to the applied force and displays it on the computer screen.

Phase diagram of (Li(1-x)Fe(x))OHFeSe: a bridge between iron selenide and arsenide superconductors.

PubMed

Dong, Xiaoli; Zhou, Huaxue; Yang, Huaixin; Yuan, Jie; Jin, Kui; Zhou, Fang; Yuan, Dongna; Wei, Linlin; Li, Jianqi; Wang, Xinqiang; Zhang, Guangming; Zhao, Zhongxian

2015-01-14

Previous experimental results have shown important differences between iron selenide and arsenide superconductors which seem to suggest that the high-temperature superconductivity in these two subgroups of iron-based families may arise from different electronic ground states. Here we report the complete phase diagram of a newly synthesized superconducting (SC) system, (Li1-xFex)OHFeSe, with a structure similar to that of FeAs-based superconductors. In the non-SC samples, an antiferromagnetic (AFM) spin-density-wave (SDW) transition occurs at ∼127 K. This is the first example to demonstrate such an SDW phase in an FeSe-based superconductor system. Transmission electron microscopy shows that a well-known √5×√5 iron vacancy ordered state, resulting in an AFM order at ∼500 K in AyFe2-xSe2 (A = metal ions) superconductor systems, is absent in both non-SC and SC samples, but a unique superstructure with a modulation wave vector q = (1)/2(1,1,0), identical to that seen in the SC phase of KyFe2-xSe2, is dominant in the optimal SC sample (with an SC transition temperature Tc = 40 K). Hence, we conclude that the high-Tc superconductivity in (Li1-xFex)OHFeSe stems from the similarly weak AFM fluctuations as FeAs-based superconductors, suggesting a universal physical picture for both iron selenide and arsenide superconductors.

Development of frequency modulation reflectometer for KSTAR tokamak: Data analysis based on Gaussian derivative waveleta)

NASA Astrophysics Data System (ADS)

Seo, Seong-Heon; Lee, K. D.

2012-10-01

A frequency modulation reflectometer has been developed to measure the density profile of the KSTAR tokamak. It has two channels operating in X-mode in the frequency range of Q band (33-50 GHz) and V band (50-75 GHz). The full band is swept in 20 μs. The mixer output is directly digitized at the sampling rate of 100 MSamples/s. A new phase detection algorithm is developed to analyze both amplitude and frequency modulated signal. The algorithm is benchmarked for a synthesized amplitude modulation-frequency modulation signal. This new algorithm is applied to the data analysis of KSTAR reflectometer.

Synchronous radio-frequency FM signal generator using direct digital synthesizers

NASA Astrophysics Data System (ADS)

Arablu, Masoud; Kafashi, Sajad; Smith, Stuart T.

2018-04-01

A novel Radio-Frequency Frequency-Modulated (RF-FM) signal generation method is introduced and a prototype circuit developed to evaluate its functionality and performance. The RF-FM signal generator uses a modulated, voltage-controlled time delay to correspondingly modulate the phase of a 10 MHz sinusoidal reference signal. This modulated reference signal is, in turn, used to clock a Direct Digital Synthesizer (DDS) circuit resulting in an FM signal at its output. The modulating signal that is input to the voltage-controlled time delay circuit is generated by another DDS that is synchronously clocked by the same 10 MHz sine wave signal before modulation. As a consequence, all of the digital components are timed from a single sine wave oscillator that forms the basis of all timing. The resultant output signal comprises a center, or carrier, frequency plus a series of phase-synchronized sidebands having exact integer harmonic frequency separation. In this study, carrier frequencies ranging from 10 MHz to 70 MHz are generated with modulation frequencies ranging from 10 kHz to 300 kHz. The captured spectra show that the FM signal characteristics, amplitude and phase, of the sidebands and the modulation depth are consistent with the Jacobi-Anger expansion for modulated harmonic signals.

Frequency characteristics of standing-wave acoustooptic modulators

NASA Astrophysics Data System (ADS)

Apolonskii, A. A.; Shchebetov, S. D.

1991-10-01

Experimental data are presented on the performance of wide-aperture standing-wave acoustooptic modulators used as laser mode lockers. In particular, attention is given to the acoustooptic and electrical frequency characteristics of the modulators. The existence of a large effective diffraction frequency region below the fundamental frequency is demonstrated. Individual frequency regions of effective diffraction do not correspond to the even and odd harmonics.

Variable Bandwidth Filtering for Improved Sensitivity of Cross-Frequency Coupling Metrics

PubMed Central

McDaniel, Jonathan; Liu, Song; Cornew, Lauren; Gaetz, William; Roberts, Timothy P.L.; Edgar, J. Christopher

2012-01-01

Abstract There is an increasing interest in examining cross-frequency coupling (CFC) between groups of oscillating neurons. Most CFC studies examine how the phase of lower-frequency brain activity modulates the amplitude of higher-frequency brain activity. This study focuses on the signal filtering that is required to isolate the higher-frequency neuronal activity which is hypothesized to be amplitude modulated. In particular, previous publications have used a filter bandwidth fixed to a constant for all assessed modulation frequencies. The present article demonstrates that fixed bandwidth filtering can destroy amplitude modulation and create false-negative CFC measures. To overcome this limitation, this study presents a variable bandwidth filter that ensures preservation of the amplitude modulation. Simulated time series data were created with theta-gamma, alpha-gamma, and beta-gamma phase-amplitude coupling. Comparisons between filtering methods indicate that the variable bandwidth approach presented in this article is preferred when examining amplitude modulations above the theta band. The variable bandwidth method of filtering an amplitude modulated signal is proposed to preserve amplitude modulation and enable accurate CFC measurements. PMID:22577870

Iodine-frequency-stabilized laser diode and displacement-measuring interferometer based on sinusoidal phase modulation

NASA Astrophysics Data System (ADS)

Duong, Quang Anh; Vu, Thanh Tung; Higuchi, Masato; Wei, Dong; Aketagawa, Masato

2018-06-01

We propose a sinusoidal phase modulation method to achieve both the frequency stabilization of an external-cavity laser diode (ECLD) to an 127I2 saturated absorption transition near 633 nm and displacement measurement using a Mach–Zehnder interferometer. First, the frequency of the ECLD is stabilized to the b 21 hyperfine component of the P(33) 6-3 transition of 127I2 by combining sinusoidal phase modulation by an electro-optic modulator and frequency modulation spectroscopy by chopping the pump beam using an acousto-optic modulator. Even though a small modulation index of m  =  3.768 rad is utilized, a relative frequency stability of 10‑11 order is obtained over a sampling time of 400 s. Secondly, the frequency-stabilized ECLD is applied as a light source to a Mach–Zehnder interferometer. From the two consecutive modulation harmonics (second and third orders) involved in the interferometer signal, the displacement of the moving mirror is determined for four optical path differences (L 0  =  100, 200, 500, and 1000 mm). The measured modulation indexes for the four optical path differences coincide with the designated value (3.768 rad) within 0.5%. Compared with the sinusoidal frequency modulation Michelson interferometer (Vu et al 2016 Meas. Sci. Technol. 27 105201) which was demonstrated by some of the same authors of this paper, the phase modulation Mach–Zhender interferometer could fix the modulation index to a constant value for the four optical path differences. In this report, we discuss the measurement principle, experimental system, and results.

Relationship Between Peripheral and Psychophysical Measures of Amplitude Modulation Detection in Cochlear Implant Users.

PubMed

Tejani, Viral D; Abbas, Paul J; Brown, Carolyn J

This study investigates the relationship between electrophysiological and psychophysical measures of amplitude modulation (AM) detection. Prior studies have reported both measures of AM detection recorded separately from cochlear implant (CI) users and acutely deafened animals, but no study has made both measures in the same CI users. Animal studies suggest a progressive loss of high-frequency encoding as one ascends the auditory pathway from the auditory nerve to the cortex. Because the CI speech processor uses the envelope of an ongoing acoustic signal to modulate pulse trains that are subsequently delivered to the intracochlear electrodes, it is of interest to explore auditory nerve responses to modulated stimuli. In addition, psychophysical AM detection abilities have been correlated with speech perception outcomes. Thus, the goal was to explore how the auditory nerve responds to AM stimuli and to relate those physiologic measures to perception. Eight patients using Cochlear Ltd. Implants participated in this study. Electrically evoked compound action potentials (ECAPs) were recorded using a 4000 pps pulse train that was sinusoidally amplitude modulated at 125, 250, 500, and 1000 Hz rates. Responses were measured for each pulse over at least one modulation cycle for an apical, medial, and basal electrode. Psychophysical modulation detection thresholds (MDTs) were also measured via a three-alternative forced choice, two-down, one-up adaptive procedure using the same modulation frequencies and electrodes. ECAPs were recorded from individual pulses in the AM pulse train. ECAP amplitudes varied sinusoidally, reflecting the sinusoidal variation in the stimulus. A modulated response amplitude (MRA) metric was calculated as the difference in the maximal and minimum ECAP amplitudes over the modulation cycles. MRA increased as modulation frequency increased, with no apparent cutoff (up to 1000 Hz). In contrast, MDTs increased as the modulation frequency increased. This trend is inconsistent with the physiologic measures. For a fixed modulation frequency, correlations were observed between MDTs and MRAs; this trend was evident at all frequencies except 1000 Hz (although only statistically significant for 250 and 500 Hz AM rates), possibly an indication of central limitations in processing of high modulation frequencies. Finally, peripheral responses were larger and psychophysical thresholds were lower in the apical electrodes relative to basal and medial electrodes, which may reflect better cochlear health and neural survival evidenced by lower preoperative low-frequency audiometric thresholds and steeper growth of neural responses in ECAP amplitude growth functions for apical electrodes. Robust ECAPs were recorded for all modulation frequencies tested. ECAP amplitudes varied sinusoidally, reflecting the periodicity of the modulated stimuli. MRAs increased as the modulation frequency increased, a trend we attribute to neural adaptation. For low modulation frequencies, there are multiple current steps between the peak and valley of the modulation cycle, which means successive stimuli are more similar to one another and neural responses are more likely to adapt. Higher MRAs were correlated with lower psychophysical thresholds at low modulation frequencies but not at 1000 Hz, implying a central limitation to processing of modulated stimuli.

Single mode CO2 laser frequency modulation up to 350 MHz

NASA Technical Reports Server (NTRS)

Leeb, W. R.; Peruso, C. J.

1977-01-01

Experiments on internal frequency modulation (FM) of a CO2 laser showed no limitation of FM by the linewidth. However, distortions in the form of strong enhancement of sideband amplitude arise for frequencies equal to the cavity resonant frequencies, most pronounced if the modulator is positioned near a cavity mirror.

Fruit softening and pectin disassembly: an overview of nanostructural pectin modifications assessed by atomic force microscopy.

PubMed

Paniagua, Candelas; Posé, Sara; Morris, Victor J; Kirby, Andrew R; Quesada, Miguel A; Mercado, José A

2014-10-01

One of the main factors that reduce fruit quality and lead to economically important losses is oversoftening. Textural changes during fruit ripening are mainly due to the dissolution of the middle lamella, the reduction of cell-to-cell adhesion and the weakening of parenchyma cell walls as a result of the action of cell wall modifying enzymes. Pectins, major components of fruit cell walls, are extensively modified during ripening. These changes include solubilization, depolymerization and the loss of neutral side chains. Recent evidence in strawberry and apple, fruits with a soft or crisp texture at ripening, suggests that pectin disassembly is a key factor in textural changes. In both these fruits, softening was reduced as result of antisense downregulation of polygalacturonase genes. Changes in pectic polymer size, composition and structure have traditionally been studied by conventional techniques, most of them relying on bulk analysis of a population of polysaccharides, and studies focusing on modifications at the nanostructural level are scarce. Atomic force microscopy (AFM) allows the study of individual polymers at high magnification and with minimal sample preparation; however, AFM has rarely been employed to analyse pectin disassembly during fruit ripening. In this review, the main features of the pectin disassembly process during fruit ripening are first discussed, and then the nanostructural characterization of fruit pectins by AFM and its relationship with texture and postharvest fruit shelf life is reviewed. In general, fruit pectins are visualized under AFM as linear chains, a few of which show long branches, and aggregates. Number- and weight-average values obtained from these images are in good agreement with chromatographic analyses. Most AFM studies indicate reductions in the length of individual pectin chains and the frequency of aggregates as the fruits ripen. Pectins extracted with sodium carbonate, supposedly located within the primary cell wall, are the most affected. © The Author 2014. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Automatic Modulation Classification of Common Communication and Pulse Compression Radar Waveforms using Cyclic Features

DTIC Science & Technology

2013-03-01

intermediate frequency LFM linear frequency modulation MAP maximum a posteriori MATLAB® matrix laboratory ML maximun likelihood OFDM orthogonal frequency...spectrum, frequency hopping, and orthogonal frequency division multiplexing ( OFDM ) modulations. Feature analysis would be a good research thrust to...determine feature relevance and decide if removing any features improves performance. Also, extending the system for simulations using a MIMO receiver or

Absolute Frequency Measurements with a Set of Transportable HE-NE/CH4 Optical Frequency Standards and Prospects for Future Design and Applications

NASA Astrophysics Data System (ADS)

Gubin, M.; Kovalchuk, E.; Petrukhin, E.; Shelkovnikov, A.; Tyurikov, D.; Gamidov, R.; Erdogan, C.; Sahin, E.; Felder, R.; Gill, P.; Lea, S. N.; Kramer, G.; Lipphardt, B.

2002-04-01

The accumulated results of absolute frequency measurements (AFM) carried out in 1997-2000 with transportable double-mode He-Ne/CH4 optical frequency standards (λ = 3 .39μm) in a collaboration of several laboratories are presented. The performance of this secondary optical frequency standard is estimated on the level of 10-13 (in repeatability), and 1 × 10-14/s (in stability). The next steps towards He-Ne/CH4 standards with one order of magnitude better performance, including devices based on monolithic zerodur resonators, are discussed. Important applications of transportable He-Ne/CH4 optical frequency standards have appeared now due to dramatic progress in the field of optical frequency measurements. Used to stabilize the repetition rate of a Ti:Sa fs laser, these compact secondary standards can transfer their performance into the whole optical range covered by a fs comb. Thus they can play the role of a narrow spectrum interrogative oscillator for super-accurate optical or microwave frequency standards substituting in some tasks a H-maser or oscillators based on cryogenic sapphire resonators.

Modeling of Millimeter-Wave Modulation Characteristics of Semiconductor Lasers under Strong Optical Feedback

PubMed Central

Bakry, Ahmed

2014-01-01

This paper presents modeling and simulation on the characteristics of semiconductor laser modulated within a strong optical feedback (OFB-)induced photon-photon resonance over a passband of millimeter (mm) frequencies. Continuous wave (CW) operation of the laser under strong OFB is required to achieve the photon-photon resonance in the mm-wave band. The simulated time-domain characteristics of modulation include the waveforms of the intensity and frequency chirp as well as the associated distortions of the modulated mm-wave signal. The frequency domain characteristics include the intensity modulation (IM) and frequency modulation (FM) responses in addition to the associated relative intensity noise (RIN). The signal characteristics under modulations with both single and two mm-frequencies are considered. The harmonic distortion and the third order intermodulation distortion (IMD3) are examined and the spurious free dynamic range (SFDR) is calculated. PMID:25383381

Mid-infrared wavelength- and frequency-modulation spectroscopy with a pump-modulated singly-resonant optical parametric oscillator

NASA Astrophysics Data System (ADS)

Lindsay, I. D.; Groß, P.; Lee, C. J.; Adhimoolam, B.; Boller, K.-J.

2006-12-01

We describe the implementation of the wavelength- and frequency-modulation spectroscopy techniques using a singly-resonant optical parametric oscillator (OPO) pumped by a fiber-amplified diode laser. Frequency modulation of the diode laser was transferred to the OPO’s mid-infrared idler output, avoiding the need for external modulation devices. This approach thus provides a means of implementing these important techniques with powerful, widely tunable, mid-infrared sources while retaining the simple, flexible modulation properties of diode lasers.

Laser frequency modulation with electron plasma

NASA Technical Reports Server (NTRS)

Burgess, T. J.; Latorre, V. R.

1972-01-01

When laser beam passes through electron plasma its frequency shifts by amount proportional to plasma density. This density varies with modulating signal resulting in corresponding modulation of laser beam frequency. Necessary apparatus is relatively inexpensive since crystals are not required.

Laser frequency modulator for modulating a laser cavity

DOEpatents

Erbert, Gaylen V.

1992-01-01

The present invention relates to a laser frequency modulator for modulating a laser cavity. It is known in the prior art to utilize a PZT (piezoelectric transducer) element in combination with a mirror to change the cavity length of a laser cavity (which changes the laser frequency). Using a PZT element to drive the mirror directly is adequate at frequencies below 10 kHz. However, in high frequency applications (100 kHz and higher) PZT elements alone do not provide a sufficient change in the cavity length. The present invention utilizes an ultrasonic concentrator with a PZT element and mirror to provide modulation of the laser cavity. With an ultrasonic concentrator, the mirror element at the end of a laser cavity can move at larger amplitudes and higher frequencies.

Evaluation and optimization of quartz resonant-frequency retuned fork force sensors with high Q factors, and the associated electric circuits, for non-contact atomic force microscopy.

PubMed

Ooe, Hiroaki; Fujii, Mikihiro; Tomitori, Masahiko; Arai, Toyoko

2016-02-01

High-Q factor retuned fork (RTF) force sensors made from quartz tuning forks, and the electric circuits for the sensors, were evaluated and optimized to improve the performance of non-contact atomic force microscopy (nc-AFM) performed under ultrahigh vacuum (UHV) conditions. To exploit the high Q factor of the RTF sensor, the oscillation of the RTF sensor was excited at its resonant frequency, using a stray capacitance compensation circuit to cancel the excitation signal leaked through the stray capacitor of the sensor. To improve the signal-to-noise (S/N) ratio in the detected signal, a small capacitor was inserted before the input of an operational (OP) amplifier placed in an UHV chamber, which reduced the output noise from the amplifier. A low-noise, wideband OP amplifier produced a superior S/N ratio, compared with a precision OP amplifier. The thermal vibrational density spectra of the RTF sensors were evaluated using the circuit. The RTF sensor with an effective spring constant value as low as 1000 N/m provided a lower minimum detection limit for force differentiation. A nc-AFM image of a Si(111)-7 × 7 surface was produced with atomic resolution using the RTF sensor in a constant frequency shift mode; tunneling current and energy dissipation images with atomic resolution were also simultaneously produced. The high-Q factor RTF sensor showed potential for the high sensitivity of energy dissipation as small as 1 meV/cycle and the high-resolution analysis of non-conservative force interactions.

Basic characteristics of high-frequency Stark-effect modulation of CO2 lasers.

NASA Technical Reports Server (NTRS)

Claspy, P. C.; Pao, Y. H.

1971-01-01

The molecular Stark effect and its application to the modulation of infrared laser radiation have been investigated both theoretically and experimentally. Using a density matrix approach, a quantum mechanical description of the effect of a time-varying electric field on the absorption coefficient and refractive index of a molecular gas near an absorption line has been formulated. For modulation applications a quantity known as the ?modulation depth' is of prime importance. Theoretical expressions for the frequency dependence of the modulation depth show that the response to the frequency of a time-varying Stark field is separated into a nondispersive and a dispersive region, depending on whether the modulating frequency is less than or greater than the homogeneous absorption linewidth. Experimental results showing nondispersive modulation at frequencies to 30 MHz are presented. In addition it is shown that the response of modulation depth to Stark field amplitude is separated into linear and nonlinear regions, the field at which nonlinearities begin being determined by the absorption spectrum of the molecule being used.

Electrically-driven pure amplitude and frequency modulation in a quantum cascade laser.

PubMed

Shehzad, Atif; Brochard, Pierre; Matthey, Renaud; Blaser, Stéphane; Gresch, Tobias; Maulini, Richard; Muller, Antoine; Südmeyer, Thomas; Schilt, Stéphane

2018-04-30

We present pure amplitude modulation (AM) and frequency modulation (FM) achieved electrically in a quantum cascade laser (QCL) equipped with an integrated resistive heater (IH). The QCL output power scales linearly with the current applied to the active region (AR), but decreases with the IH current, while the emission frequency decreases with both currents. Hence, a simultaneous modulation applied to the current of the AR and IH sections with a proper relative amplitude and phase can suppress the AM, resulting in a pure FM, or vice-versa. The adequate modulation parameters depend on the applied modulation frequency. Therefore, they were first determined from the individual measurements of the AM and FM transfer functions obtained for a modulation applied to the current of the AR or IH section, respectively. By optimizing the parameters of the two modulations, we demonstrate a reduction of the spurious AM or FM by almost two orders of magnitude at characteristic frequencies of 1 and 10 kHz compared to the use of the AR current only.

Specificity of the Human Frequency Following Response for Carrier and Modulation Frequency Assessed Using Adaptation.

PubMed

Gockel, Hedwig E; Krugliak, Alexandra; Plack, Christopher J; Carlyon, Robert P

2015-12-01

The frequency following response (FFR) is a scalp-recorded measure of phase-locked brainstem activity to stimulus-related periodicities. Three experiments investigated the specificity of the FFR for carrier and modulation frequency using adaptation. FFR waveforms evoked by alternating-polarity stimuli were averaged for each polarity and added, to enhance envelope, or subtracted, to enhance temporal fine structure information. The first experiment investigated peristimulus adaptation of the FFR for pure and complex tones as a function of stimulus frequency and fundamental frequency (F0). It showed more adaptation of the FFR in response to sounds with higher frequencies or F0s than to sounds with lower frequency or F0s. The second experiment investigated tuning to modulation rate in the FFR. The FFR to a complex tone with a modulation rate of 213 Hz was not reduced more by an adaptor that had the same modulation rate than by an adaptor with a different modulation rate (90 or 504 Hz), thus providing no evidence that the FFR originates mainly from neurons that respond selectively to the modulation rate of the stimulus. The third experiment investigated tuning to audio frequency in the FFR using pure tones. An adaptor that had the same frequency as the target (213 or 504 Hz) did not generally reduce the FFR to the target more than an adaptor that differed in frequency (by 1.24 octaves). Thus, there was no evidence that the FFR originated mainly from neurons tuned to the frequency of the target. Instead, the results are consistent with the suggestion that the FFR for low-frequency pure tones at medium to high levels mainly originates from neurons tuned to higher frequencies. Implications for the use and interpretation of the FFR are discussed.

Evolution of nano-rheological properties of Nafion¯ thin films during pH modification by strong base treatment: A static and dynamic force spectroscopy study

NASA Astrophysics Data System (ADS)

Eslami, Babak; López-Guerra, Enrique A.; Raftari, Maryam; Solares, Santiago D.

2016-04-01

Addition of a strong base to Nafion® proton exchange membranes is a common practice in industry to increase their overall performance in fuel cells. Here, we investigate the evolution of the nano-rheological properties of Nafion thin films as a function of the casting pH, via characterization with static and dynamic, contact and intermittent-contact atomic force microscopy (AFM) techniques. The addition of KOH causes non-monotonic changes in the viscoelastic properties of the films, which behave as highly dissipative, softer materials near neutral pH values, and as harder, more elastic materials at extreme pH values. We quantify this behavior through calculation of the temporal evolution of the compliance and the glassy compliance under static AFM measurements. We complement these observations with dynamic AFM metrics, including dissipated power and virial (for intermittent-contact-mode measurements), and contact resonance frequency and quality factor (for dynamic contact-mode measurements). We explain the non-monotonic material property behavior in terms of the degree of ionic crosslinking and moisture content of the films, which vary with the addition of KOH. This work focuses on the special case study of the addition of strong bases, but the observed mechanical property changes are broadly related to water plasticizing effects and ionic crosslinking, which are also important in other types of films.

Comparative study of sub-micrometer polymeric structures: Dot-arrays, linear and crossed gratings generated by UV laser based two-beam interference, as surfaces for SPR and AFM based bio-sensing

NASA Astrophysics Data System (ADS)

Csete, M.; Sipos, Á.; Kőházi-Kis, A.; Szalai, A.; Szekeres, G.; Mathesz, A.; Csákó, T.; Osvay, K.; Bor, Zs.; Penke, B.; Deli, M. A.; Veszelka, Sz.; Schmatulla, A.; Marti, O.

2007-12-01

Two-dimensional gratings are generated on poly-carbonate films spin-coated onto thin gold-silver bimetallic layers by two-beam interference method. Sub-micrometer periodic polymer dots and stripes are produced illuminating the poly-carbonate surface by p- and s-polarized beams of a frequency quadrupled Nd:YAG laser, and crossed gratings are generated by rotating the substrates between two sequential treatments. It is shown by pulsed force mode atomic force microscopy that the mean value of the adhesion is enhanced on the dot-arrays and on the crossed gratings. The grating-coupling on the two-dimensional structures results in double peaks on the angle dependent resonance curves of the surface plasmons excited by frequency doubled Nd:YAG laser. The comparison of the resonance curves proves that a surface profile ensuring minimal undirected scattering is required to optimize the grating-coupling, in addition to the minimal modulation amplitude, and to the optimal azimuthal orientation. The secondary minima are the narrowest in presence of linear gratings on multi-layers having optimized composition, and on crossed structures consisting of appropriately oriented polymer stripes. The large coupling efficiency and adhesion result in high detection sensitivity on the crossed gratings. Bio-sensing is realized by monitoring the rotated-crossed grating-coupled surface plasmon resonance curves, and detecting the chemical heterogeneity by tapping-mode atomic force microscopy. The interaction of Amyloid-β peptide, a pathogenetic factor in Alzheimer disease, with therapeutical molecules is demonstrated.

Nonlinear optical modulation in a plasmonic Bi:YIG Mach-Zehnder interferometer

NASA Astrophysics Data System (ADS)

Firby, C. J.; Elezzabi, A. Y.

2017-02-01

In this work, we propose a magnetoplasmonic modulator for nonlinear radio-frequency (RF) modulation of an integrated optical signal. The modulator consists of a plasmonic Mach-Zehnder interferometer (MZI), constructed of the ferrimagnetic garnet, bismuth-substituted yttrium iron garnet (Bi:YIG). The transverse component of the Bi:YIG magnetization induces a nonreciprocal phase shift (NRPS) onto the guided optical mode, which can be actively modulated through external magnetic fields. In an MZI, the modulated phase shift in turn modulates the output optical intensity. Due to the highly nonlinear evolution of the Bi:YIG magnetization, we show that the spectrum of the output modulated intensity signal can contain harmonics of the driving RF field, frequency splitting around the driving frequency, down-conversion, or mixing of multiple RF signals. This device provides a unique mechanism of simultaneously generating a number of modulation frequencies within a single device.

Realization of pure frequency modulation of DFB laser via combined optical and electrical tuning.

PubMed

Tian, Chao; Chen, I-Chun Anderson; Park, Seong-Wook; Martini, Rainer

2013-04-08

In this paper we present a novel approach to convert AM signal into FM signal in semiconductor lasers via off resonance optical pumping and report on experimental results obtained with a commercial DFB laser. Aside of demonstrating discrete and fast frequency modulation, we achieve pure frequency modulation through combination with electrical modulation suppressing the associated amplitude modulation, which is detrimental to application such as spectroscopy and communication.

The transmission of low frequency medical data using delta modulation techniques.

NASA Technical Reports Server (NTRS)

Arndt, G. D.; Dawson, C. T.

1972-01-01

The transmission of low-frequency medical data using delta modulation techniques is described. The delta modulators are used to distribute the low-frequency data into the passband of the telephone lines. Both adaptive and linear delta modulators are considered. Optimum bit rates to minimize distortion and intersymbol interference are discussed. Vibrocardiographic waves are analyzed as a function of bit rate and delta modulator configuration to determine their reproducibility for medical evaluation.

Application of atomic force microscopy as a nanotechnology tool in food science.

PubMed

Yang, Hongshun; Wang, Yifen; Lai, Shaojuan; An, Hongjie; Li, Yunfei; Chen, Fusheng

2007-05-01

Atomic force microscopy (AFM) provides a method for detecting nanoscale structural information. First, this review explains the fundamentals of AFM, including principle, manipulation, and analysis. Applications of AFM are then reported in food science and technology research, including qualitative macromolecule and polymer imaging, complicated or quantitative structure analysis, molecular interaction, molecular manipulation, surface topography, and nanofood characterization. The results suggested that AFM could bring insightful knowledge on food properties, and the AFM analysis could be used to illustrate some mechanisms of property changes during processing and storage. However, the current difficulty in applying AFM to food research is lacking appropriate methodology for different food systems. Better understanding of AFM technology and developing corresponding methodology for complicated food systems would lead to a more in-depth understanding of food properties at macromolecular levels and enlarge their applications. The AFM results could greatly improve the food processing and storage technologies.

Electroacoustic verification of frequency modulation systems in cochlear implant users.

PubMed

Fidêncio, Vanessa Luisa Destro; Jacob, Regina Tangerino de Souza; Tanamati, Liége Franzini; Bucuvic, Érika Cristina; Moret, Adriane Lima Mortari

2017-12-26

The frequency modulation system is a device that helps to improve speech perception in noise and is considered the most beneficial approach to improve speech recognition in noise in cochlear implant users. According to guidelines, there is a need to perform a check before fitting the frequency modulation system. Although there are recommendations regarding the behavioral tests that should be performed at the fitting of the frequency modulation system to cochlear implant users, there are no published recommendations regarding the electroacoustic test that should be performed. Perform and determine the validity of an electroacoustic verification test for frequency modulation systems coupled to different cochlear implant speech processors. The sample included 40 participants between 5 and 18 year's users of four different models of speech processors. For the electroacoustic evaluation, we used the Audioscan Verifit device with the HA-1 coupler and the listening check devices corresponding to each speech processor model. In cases where the transparency was not achieved, a modification was made in the frequency modulation gain adjustment and we used the Brazilian version of the "Phrases in Noise Test" to evaluate the speech perception in competitive noise. It was observed that there was transparency between the frequency modulation system and the cochlear implant in 85% of the participants evaluated. After adjusting the gain of the frequency modulation receiver in the other participants, the devices showed transparency when the electroacoustic verification test was repeated. It was also observed that patients demonstrated better performance in speech perception in noise after a new adjustment, that is, in these cases; the electroacoustic transparency caused behavioral transparency. The electroacoustic evaluation protocol suggested was effective in evaluation of transparency between the frequency modulation system and the cochlear implant. Performing the adjustment of the speech processor and the frequency modulation system gain are essential when fitting this device. Copyright © 2017 Associação Brasileira de Otorrinolaringologia e Cirurgia Cérvico-Facial. Published by Elsevier Editora Ltda. All rights reserved.

Nothing more than a pair of curvatures: A common mechanism for the detection of both radial and non-radial frequency patterns.

PubMed

Schmidtmann, Gunnar; Kingdom, Frederick A A

2017-05-01

Radial frequency (RF) patterns, which are sinusoidal modulations of a radius in polar coordinates, are commonly used to study shape perception. Previous studies have argued that the detection of RF patterns is either achieved globally by a specialized global shape mechanism, or locally using as cue the maximum tangent orientation difference between the RF pattern and the circle. Here we challenge both ideas and suggest instead a model that accounts not only for the detection of RF patterns but also for line frequency patterns (LF), i.e. contours sinusoidally modulated around a straight line. The model has two features. The first is that the detection of both RF and LF patterns is based on curvature differences along the contour. The second is that this curvature metric is subject to what we term the Curve Frequency Sensitivity Function, or CFSF, which is characterized by a flat followed by declining response to curvature as a function of modulation frequency, analogous to the modulation transfer function of the eye. The evidence that curvature forms the basis for detection is that at very low modulation frequencies (1-3 cycles for the RF pattern) there is a dramatic difference in thresholds between the RF and LF patterns, a difference however that disappears at medium and high modulation frequencies. The CFSF feature on the other hand explains why thresholds, rather than continuously declining with modulation frequency, asymptote at medium and high modulation frequencies. In summary, our analysis suggests that the detection of shape modulations is processed by a common curvature-sensitive mechanism that is subject to a shape-frequency-dependent transfer function. This mechanism is independent of whether the modulation is applied to a circle or a straight line. Copyright © 2017 Elsevier Ltd. All rights reserved.

Dynamic nuclear polarization using frequency modulation at 3.34 T.

PubMed

Hovav, Y; Feintuch, A; Vega, S; Goldfarb, D

2014-01-01

During dynamic nuclear polarization (DNP) experiments polarization is transferred from unpaired electrons to their neighboring nuclear spins, resulting in dramatic enhancement of the NMR signals. While in most cases this is achieved by continuous wave (cw) irradiation applied to samples in fixed external magnetic fields, here we show that DNP enhancement of static samples can improve by modulating the microwave (MW) frequency at a constant field of 3.34 T. The efficiency of triangular shaped modulation is explored by monitoring the (1)H signal enhancement in frozen solutions containing different TEMPOL radical concentrations at different temperatures. The optimal modulation parameters are examined experimentally and under the most favorable conditions a threefold enhancement is obtained with respect to constant frequency DNP in samples with low radical concentrations. The results are interpreted using numerical simulations on small spin systems. In particular, it is shown experimentally and explained theoretically that: (i) The optimal modulation frequency is higher than the electron spin-lattice relaxation rate. (ii) The optimal modulation amplitude must be smaller than the nuclear Larmor frequency and the EPR line-width, as expected. (iii) The MW frequencies corresponding to the enhancement maxima and minima are shifted away from one another when using frequency modulation, relative to the constant frequency experiments. Copyright © 2013 Elsevier Inc. All rights reserved.

Altered self-assembly and apatite binding of amelogenin induced by N-terminal proline mutation

PubMed Central

Zhu, Li; Uskoković, Vuk; Le, Thuan; DenBesten, Pamela; Huang, Yulei; Habelitz, Stefan; Li, Wu

2012-01-01

Objective A single Pro-70 to Thr (p.P70T) mutation of amelogenin is known to result in hypomineralized amelogenesis imperfecta (AI). This study aims to test the hypothesis that the given mutation affects the self-assembly of amelogenin molecules and impairs their ability to conduct the growth of apatite crystals. Design Recombinant human full-length wild-type (rh174) and p.P70T mutated amelogenins were analyzed using dynamic light scattering (DLS), protein quantification assay and atomic force microscopy (AFM) before and after the binding of amelogenins to hydroxyapatite crystals. The crystal growth modulated by both amelogenins in a dynamic titration system was observed using AFM. Results As compared to rh174 amelogenin, p.P70T mutant displayed significantly increased sizes of the assemblies, higher binding affinity to apatite, and decreased crystal height. Conclusions Pro-70 plays an important structural role in the biologically relevant amelogenin self-assembly. The disturbed regularity of amelogenin nanospheres by this single mutation resulted in an increased binding to apatite and inhibited crystal growth. PMID:21081224

Wideband laser locking to an atomic reference with modulation transfer spectroscopy.

PubMed

Negnevitsky, V; Turner, L D

2013-02-11

We demonstrate that conventional modulated spectroscopy apparatus, used for laser frequency stabilization in many atomic physics laboratories, can be enhanced to provide a wideband lock delivering deep suppression of frequency noise across the acoustic range. Using an acousto-optic modulator driven with an agile oscillator, we show that wideband frequency modulation of the pump laser in modulation transfer spectroscopy produces the unique single lock-point spectrum previously demonstrated with electro-optic phase modulation. We achieve a laser lock with 100 kHz feedback bandwidth, limited by our laser control electronics. This bandwidth is sufficient to reduce frequency noise by 30 dB across the acoustic range and narrows the imputed linewidth by a factor of five.

How sensitivity to ongoing interaural temporal disparities is affected by manipulations of temporal features of the envelopes of high-frequency stimuli

PubMed Central

Bernstein, Leslie R.; Trahiotis, Constantine

2009-01-01

This study addressed how manipulating certain aspects of the envelopes of high-frequency stimuli affects sensitivity to envelope-based interaural temporal disparities (ITDs). Listener’s threshold ITDs were measured using an adaptive two-alternative paradigm employing “raised-sine” stimuli [John, M. S., et al. (2002). Ear Hear. 23, 106–117] which permit independent variation in their modulation frequency, modulation depth, and modulation exponent. Threshold ITDs were measured while manipulating modulation exponent for stimuli having modulation frequencies between 32 and 256 Hz. The results indicated that graded increases in the exponent led to graded decreases in envelope-based threshold ITDs. Threshold ITDs were also measured while parametrically varying modulation exponent and modulation depth. Overall, threshold ITDs decreased with increases in the modulation depth. Unexpectedly, increases in the exponent of the raised-sine led to especially large decreases in threshold ITD when the modulation depth was low. An interaural correlation-based model was generally able to capture changes in threshold ITD stemming from changes in the exponent, depth of modulation, and frequency of modulation of the raised-sine stimuli. The model (and several variations of it), however, could not account for the unexpected interaction between the value of raised-sine exponent and its modulation depth. PMID:19425666

Frequency chirped light at large detuning with an injection-locked diode laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teng, K.; Disla, M.; Dellatto, J.

2015-04-15

We have developed a laser system to generate frequency-chirped light at rapid modulation speeds (∼100 MHz) with a large frequency offset. Light from an external cavity diode laser with its frequency locked to an atomic resonance is passed through a lithium niobate electro-optical phase modulator. The phase modulator is driven by a ∼6 GHz signal whose frequency is itself modulated with a RF MHz signal (<200 MHz). A second injection locked diode laser is used to filter out all of the light except the frequency-chirped ±1 order by more than 30 dB. Using this system, it is possible to generatemore » a 1 GHz frequency chirp in 5 ns.« less

Testing the concept of a modulation filter bank: the audibility of component modulation and detection of phase change in three-component modulators.

PubMed

Sek, Aleksander; Moore, Brian C J

2003-05-01

Two experiments were performed to test the concept that the auditory system contains a "modulation filter bank" (MFB). Experiment 1 examined the ability to "hear out" the modulation frequency of the central component of a three-component modulator applied to a 4-kHz sinusoidal carrier. On each trial, three modulated stimuli were presented. The modulator of the first stimulus contained three components. Within a run the frequencies of the outer two components were fixed and the frequency of the central ("target") component was drawn randomly from one of five values. The modulators of second and third stimuli contained one component. One had a frequency equal to that of the target and the other had a frequency randomly selected from one of the other possible values. Subjects indicated whether the target corresponded to the second or third stimulus. Scores were around 80% correct when the components in the three-component modulator were widely spaced and when the frequencies of the target and comparison differed sufficiently. Experiment 2 examined the ability to hear a change in the relative phase of the components in a three-component modulator with harmonically spaced components, using a 31FC task. The frequency of the central component, f(c), was either 50 or 100 Hz. Scores were 80%-90% correct when the component spacing was < or = 0.5 f(c), but decreased markedly for greater spacings. Performance was only slightly impaired by randomizing the overall modulation depth from one stimulus to the next. The results of both experiments are broadly consistent with what would be expected from a MFB with a Q value of 1 or slightly less.

Photomask applications of traceable atomic force microscope dimensional metrology at NIST

NASA Astrophysics Data System (ADS)

Dixson, Ronald; Orji, Ndubuisi G.; Potzick, James; Fu, Joseph; Allen, Richard A.; Cresswell, Michael; Smith, Stewart; Walton, Anthony J.; Tsiamis, Andreas

2007-10-01

The National Institute of Standards and Technology (NIST) has a multifaceted program in atomic force microscope (AFM) dimensional metrology. Three major instruments are being used for traceable measurements. The first is a custom in-house metrology AFM, called the calibrated AFM (C-AFM), the second is the first generation of commercially available critical dimension AFM (CD-AFM), and the third is a current generation CD-AFM at SEMATECH - for which NIST has established the calibration and uncertainties. All of these instruments have useful applications in photomask metrology. Linewidth reference metrology is an important application of CD-AFM. We have performed a preliminary comparison of linewidths measured by CD-AFM and by electrical resistance metrology on a binary mask. For the ten selected test structures with on-mask linewidths between 350 nm and 600 nm, most of the observed differences were less than 5 nm, and all of them were less than 10 nm. The offsets were often within the estimated uncertainties of the AFM measurements, without accounting for the effect of linewidth roughness or the uncertainties of electrical measurements. The most recent release of the NIST photomask standard - which is Standard Reference Material (SRM) 2059 - was also supported by CD-AFM reference measurements. We review the recent advances in AFM linewidth metrology that will reduce the uncertainty of AFM measurements on this and future generations of the NIST photomask standard. The NIST C-AFM has displacement metrology for all three axes traceable to the 633 nm wavelength of the iodine-stabilized He-Ne laser. One of the important applications of the C-AFM is step height metrology, which has some relevance to phase shift calibration. In the current generation of the system, the approximate level of relative standard uncertainty for step height measurements at the 100 nm scale is 0.1 %. We discuss the monitor history of a 290 nm step height, originally measured on the C-AFM with a 1.9 nm (k = 2) expanded uncertainty, and describe advances that bring the step height uncertainty of recent measurements to an estimated 0.6 nm (k = 2). Based on this work, we expect to be able to reduce the topographic component of phase uncertainty in alternating aperture phase shift masks (AAPSM) by a factor of three compared to current calibrations based on earlier generation step height references.

Visual sensitivity to spatially sampled modulation in human observers

NASA Technical Reports Server (NTRS)

Mulligan, Jeffrey B.; Macleod, Donald I. A.

1991-01-01

Thresholds were measured for detecting spatial luminance modulation in regular lattices of visually discrete dots. Thresholds for modulation of a lattice are generally higher than the corresponding threshold for modulation of a continuous field, and the size of the threshold elevation, which depends on the spacing of the lattice elements, can be as large as a one log unit. The largest threshold elevations are seen when the sample spacing is 12 min arc or greater. Theories based on response compression cannot explain the further observation that the threshold elevations due to spatial sampling are also dependent on modulation frequency: the greatest elevations occur with higher modulation frequencies. The idea that this is due to masking of the modulation frequency by the spatial frequencies in the sampling lattice is considered.

Multi-level RF identification system

DOEpatents

Steele, Kerry D.; Anderson, Gordon A.; Gilbert, Ronald W.

2004-07-20

A radio frequency identification system having a radio frequency transceiver for generating a continuous wave RF interrogation signal that impinges upon an RF identification tag. An oscillation circuit in the RF identification tag modulates the interrogation signal with a subcarrier of a predetermined frequency and modulates the frequency-modulated signal back to the transmitting interrogator. The interrogator recovers and analyzes the subcarrier signal and determines its frequency. The interrogator generates an output indicative of the frequency of the subcarrier frequency, thereby identifying the responding RFID tag as one of a "class" of RFID tags configured to respond with a subcarrier signal of a predetermined frequency.

High-frequency modulation of the four states of polarization of light with a single phase modulator

NASA Astrophysics Data System (ADS)

Compain, Eric; Drevillon, Bernard

1998-04-01

A method for light polarization modulation is described. It allows us to independently modulate, at a high frequency, the four components of the Stokes vector of light using a single phase modulator. It works in a double-pass configuration: the polarization of light is modulated a first time by the phase modulator, and is then modified by a coupling object before being modulated a second time by the same modulator. The coupling object consists of multiple glass plates, oriented at the Brewster angle, acting as a partial polarizer and in a right angle prism acting as a phase shifter and back reflector. Its polarimetric properties are obtained from refractive index contrast effects, which provides optimized and constant properties over a wide spectral range. The phase modulator can be either an electro-optic modulator providing a very high-frequency capability (up to 100 MHz) or a photoelastic modulator providing a wide spectral range capability. It is robust because there is no moving part and simple to implement because of the presence of one modulation. It displays a high level of sensitivity because all the components are high-frequency modulated. Two applications using this modulator in a polarimeter or in a polarization states generator are described. The four modulations, having the same fundamental frequency, are easily demodulated by numerical data processing. Optimized demodulation processing, adapted to the different kind of phase modulator is described. Its adaptation taking into account the bandwidth limitation and the variation of the sampling phase, are finally presented in the case of a photoelastic modulator.

Frequency response control of semiconductor laser by using hybrid modulation scheme.

PubMed

Mieda, Shigeru; Yokota, Nobuhide; Isshiki, Ryuto; Kobayashi, Wataru; Yasaka, Hiroshi

2016-10-31

A hybrid modulation scheme that simultaneously applies the direct current modulation and intra-cavity loss modulation to a semiconductor laser is proposed. Both numerical calculations using rate equations and experiments using a fabricated laser show that the hybrid modulation scheme can control the frequency response of the laser by changing a modulation ratio and time delay between the two modulations. The modulation ratio and time delay provide the degree of signal mixing of the two modulations and an optimum condition is found when a non-flat frequency response for the intra-cavity loss modulation is compensated by that for the direct current modulation. We experimentally confirm a 8.64-dB improvement of the modulation sensitivity at 20 GHz compared with the pure direct current modulation with a 0.7-dB relaxation oscillation peak.

High-Bandwidth Dynamic Full-Field Profilometry for Nano-Scale Characterization of MEMS

NASA Astrophysics Data System (ADS)

Chen, Liang-Chia; Huang, Yao-Ting; Chang, Pi-Bai

2006-10-01

The article describes an innovative optical interferometric methodology to delivery dynamic surface profilometry with a measurement bandwidth up to 10MHz or higher and a vertical resolution up to 1 nm. Previous work using stroboscopic microscopic interferometry for dynamic characterization of micro (opto)electromechanical systems (M(O)EMS) has been limited in measurement bandwidth mainly within a couple of MHz. For high resonant mode analysis, the stroboscopic light pulse is insufficiently short to capture the moving fringes from dynamic motion of the detected structure. In view of this need, a microscopic prototype based on white-light stroboscopic interferometry with an innovative light superposition strategy was developed to achieve dynamic full-field profilometry with a high measurement bandwidth up to 10MHz or higher. The system primarily consists of an optical microscope, on which a Mirau interferometric objective embedded with a piezoelectric vertical translator, a high-power LED light module with dual operation modes and light synchronizing electronics unit are integrated. A micro cantilever beam used in AFM was measured to verify the system capability in accurate characterisation of dynamic behaviours of the device. The full-field seventh-mode vibration at a vibratory frequency of 3.7MHz can be fully characterized and nano-scale vertical measurement resolution as well as tens micrometers of vertical measurement range can be performed.

Application of the Maxwell-Wagner-Hanai effective medium theory to the analysis of the interfacial polarization relaxations in conducting composite films

NASA Astrophysics Data System (ADS)

J-P Adohi, B.; Vanga Bouanga, C.; Fatyeyeva, K.; Tabellout, M.

2009-01-01

A new approach to explain the interfacial polarization phenomenon in conducting composite films is proposed. HCl-doped poly(ethylene terephthalate) (PET) and polyamide-6 (PA-6) matrices with embedded polyaniline (PANI) particles as filler were investigated and analysed, combining dielectric spectroscopy and AFM electrical images with the effective medium theory analysis. Up to three relaxation peaks attributed to the interfacial polarization phenomena were detected in the studied frequency range (0.1 Hz-1 MHz). The AFM electrical images revealed that the doped PA-6/PANI composite can be modelled as a single-type particle medium and the PET/PANI one as a two-type particle medium. A simple dielectric loss expression was derived from the Maxwell-Wagner-Hanai mixture equation and was applied to the experimental data to identify the interfaces involved in each of the relaxation peaks. The parameter values (permittivity, conductivity, volume fraction of the PANI particles) were found to agree well with the measured one, hence validating the models.

Observation of giant exchange bias in bulk Mn{sub 50}Ni{sub 42}Sn{sub 8} Heusler alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Jyoti; Suresh, K. G., E-mail: suresh@iitb.ac.in

2015-02-16

We report a giant exchange bias (EB) field of 3520 Oe in bulk Mn{sub 50}Ni{sub 42}Sn{sub 8} Heusler alloy. The low temperature magnetic state of the martensite phase has been studied by DC magnetization and AC susceptibility measurements. Frequency dependence of spin freezing temperature (T{sub f}) on critical slowing down relation and observation of memory effect in zero field cooling mode confirms the super spin glass (SSG) phase at low temperatures. Large EB is attributed to the strong exchange coupling between the SSG clusters formed by small regions of ferromagnetic order embedded in an antiferromagnetic (AFM) matrix. The temperature and coolingmore » field dependence of EB have been studied and related to the change in unidirectional anisotropy at SSG/AFM interface. The training effect also corroborates with the presence of frozen (SSG) moments at the interface and their role in EB.« less

Enhanced quality factors and force sensitivity by attaching magnetic beads to cantilevers for atomic force microscopy in liquid

NASA Astrophysics Data System (ADS)

Hoof, Sebastian; Nand Gosvami, Nitya; Hoogenboom, Bart W.

2012-12-01

Dynamic-mode atomic force microscopy (AFM) in liquid remains complicated due to the strong viscous damping of the cantilever resonance. Here, we show that a high-quality resonance (Q >20) can be achieved in aqueous solution by attaching a microgram-bead at the end of the nanogram-cantilever. The resulting increase in cantilever mass causes the resonance frequency to drop significantly. However, the force sensitivity—as expressed via the minimum detectable force gradient—is hardly affected, because of the enhanced quality factor. Through the enhancement of the quality factor, the attached bead also reduces the relative importance of noise in the deflection detector. It can thus yield an improved signal-to-noise ratio when this detector noise is significant. We describe and analyze these effects for a set-up that includes magnetic actuation of the cantilevers and that can be easily implemented in any AFM system that is compatible with an inverted optical microscope.

A diamond-based scanning probe spin sensor operating at low temperature in ultra-high vacuum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schaefer-Nolte, E.; Wrachtrup, J.; 3rd Institute of Physics and Research Center SCoPE, University Stuttgart, 70569 Stuttgart

2014-01-15

We present the design and performance of an ultra-high vacuum (UHV) low temperature scanning probe microscope employing the nitrogen-vacancy color center in diamond as an ultrasensitive magnetic field sensor. Using this center as an atomic-size scanning probe has enabled imaging of nanoscale magnetic fields and single spins under ambient conditions. In this article we describe an experimental setup to operate this sensor in a cryogenic UHV environment. This will extend the applicability to a variety of molecular systems due to the enhanced target spin lifetimes at low temperature and the controlled sample preparation under UHV conditions. The instrument combines amore » tuning-fork based atomic force microscope (AFM) with a high numeric aperture confocal microscope and the facilities for application of radio-frequency (RF) fields for spin manipulation. We verify a sample temperature of <50 K even for strong laser and RF excitation and demonstrate magnetic resonance imaging with a magnetic AFM tip.« less

Temperature-Dependent Magnetic Response of Antiferromagnetic Doping in Cobalt Ferrite Nanostructures.

PubMed

Nairan, Adeela; Khan, Maaz; Khan, Usman; Iqbal, Munawar; Riaz, Saira; Naseem, Shahzad

2016-04-18

In this work Mn x Co 1- x Fe₂O₄ nanoparticles (NPs) were synthesized using a chemical co-precipitation method. Phase purity and structural analyses of synthesized NPs were performed by X-ray diffractometer (XRD). Transmission electron microscopy (TEM) reveals the presence of highly crystalline and narrowly-dispersed NPs with average diameter of 14 nm. The Fourier transform infrared (FTIR) spectrum was measured in the range of 400-4000 cm -1 which confirmed the formation of vibrational frequency bands associated with the entire spinel structure. Temperature-dependent magnetic properties in anti-ferromagnet (AFM) and ferromagnet (FM) structure were investigated with the aid of a physical property measurement system (PPMS). It was observed that magnetic interactions between the AFM (Mn) and FM (CoFe₂O₄) material arise below the Neel temperature of the dopant. Furthermore, hysteresis response was clearly pronounced for the enhancement in magnetic parameters by varying temperature towards absolute zero. It is shown that magnetic properties have been tuned as a function of temperature and an externally-applied field.

Structural changes of a-CNx thin films induced by thermal annealing

NASA Astrophysics Data System (ADS)

Aziz, Siti Aisyah Abd; Awang, Rozidawati

2018-04-01

In this work, amorphous carbon nitride (a-CNx) thin films were deposited by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) technique at different RF powers of 60, 70, 80, 90 and 100 W for 30 min. These films were prepared using a mixture of acetylene (C2H2) at 20 sccm and nitrogen (N2) gases at 50 sccm. The films were then annealed at 400 °C in a quartz tube furnace in argon (Ar) gas. The chemical bondings of the film were analyzed by Fourier Transform Infra-red Spectroscopy (FTIR) while surface morphology and film roughness were determined by Atomic Force Microscopy (AFM). The FTIR analysis reveals that annealing resulted in the loss of C-H and C-N bonds and formation of graphitic sp2C cluster with the dissociation of N and C in the films. AFM indicates that the film surface becomes less rough which effectually enhances structural modifications and the rearrangement of the microstructure of the films after annealing.

The dynamics of integrate-and-fire: mean versus variance modulations and dependence on baseline parameters.

PubMed

Pressley, Joanna; Troyer, Todd W

2011-05-01

The leaky integrate-and-fire (LIF) is the simplest neuron model that captures the essential properties of neuronal signaling. Yet common intuitions are inadequate to explain basic properties of LIF responses to sinusoidal modulations of the input. Here we examine responses to low and moderate frequency modulations of both the mean and variance of the input current and quantify how these responses depend on baseline parameters. Across parameters, responses to modulations in the mean current are low pass, approaching zero in the limit of high frequencies. For very low baseline firing rates, the response cutoff frequency matches that expected from membrane integration. However, the cutoff shows a rapid, supralinear increase with firing rate, with a steeper increase in the case of lower noise. For modulations of the input variance, the gain at high frequency remains finite. Here, we show that the low-frequency responses depend strongly on baseline parameters and derive an analytic condition specifying the parameters at which responses switch from being dominated by low versus high frequencies. Additionally, we show that the resonant responses for variance modulations have properties not expected for common oscillatory resonances: they peak at frequencies higher than the baseline firing rate and persist when oscillatory spiking is disrupted by high noise. Finally, the responses to mean and variance modulations are shown to have a complementary dependence on baseline parameters at higher frequencies, resulting in responses to modulations of Poisson input rates that are independent of baseline input statistics.

Timbral Sharpness and Modulations in Frequency and Amplitude: Implications for the Fusion of Musical Sounds.

NASA Astrophysics Data System (ADS)

Goad, Pamela Joy

The fusion of musical voices is an important aspect of musical blend, or the mixing of individual sounds. Yet, little research has been done to explicitly determine the factors involved in fusion. In this study, the similarity of timbre and modulation were examined for their contribution to the fusion of sounds. It is hypothesized that similar timbres will fuse better than dissimilar timbres, and, voices with the same kind of modulation will fuse better than voices of different modulations. A perceptually-based measure, known as sharpness was investigated as a measure of timbre. The advantages of using sharpness are that it is based on hearing sensitivities and masking phenomena of inner ear processing. Five musical instrument families were digitally recorded in performances across a typical playing range at two extreme dynamic levels. Analyses reveal that sharpness is capable of uncovering subtle changes in timbre including those found in musical dynamics, instrument design, and performer-specific variations. While these analyses alone are insufficient to address fusion, preliminary calculations of timbral combinations indicate that sharpness has the potential to predict the fusion of sounds used in musical composition. Three experiments investigated the effects of modulation on the fusion of a harmonic major sixth interval. In the first experiment using frequency modulation, stimuli varied in deviation about a mean fundamental frequency and relative modulation phase between the two tones. Results showed smaller frequency deviations promoted fusion and relative phase differences had a minimal effect. In a second experiment using amplitude modulation, stimuli varied in deviation about a mean amplitude level and relative phase of modulation. Results showed smaller amplitude deviations promoted better fusion, but unlike frequency modulation, relative phase differences were also important. In a third experiment, frequency modulation, amplitude modulation and mixed modulation were arranged in all possible voicings. Results showed frequency modulation in the lower voice and less variance in amplitude envelopes contributed to an increase in fusion. The theory that similar modulations would promote better fusion was only marginally supported. For these experiments, results revealed differences depending on modulation type and that a lesser amount of modulation fosters greater fusion.

Frequency-specific attentional modulation in human primary auditory cortex and midbrain.

PubMed

Riecke, Lars; Peters, Judith C; Valente, Giancarlo; Poser, Benedikt A; Kemper, Valentin G; Formisano, Elia; Sorger, Bettina

2018-07-01

Paying selective attention to an audio frequency selectively enhances activity within primary auditory cortex (PAC) at the tonotopic site (frequency channel) representing that frequency. Animal PAC neurons achieve this 'frequency-specific attentional spotlight' by adapting their frequency tuning, yet comparable evidence in humans is scarce. Moreover, whether the spotlight operates in human midbrain is unknown. To address these issues, we studied the spectral tuning of frequency channels in human PAC and inferior colliculus (IC), using 7-T functional magnetic resonance imaging (FMRI) and frequency mapping, while participants focused on different frequency-specific sounds. We found that shifts in frequency-specific attention alter the response gain, but not tuning profile, of PAC frequency channels. The gain modulation was strongest in low-frequency channels and varied near-monotonically across the tonotopic axis, giving rise to the attentional spotlight. We observed less prominent, non-tonotopic spatial patterns of attentional modulation in IC. These results indicate that the frequency-specific attentional spotlight in human PAC as measured with FMRI arises primarily from tonotopic gain modulation, rather than adapted frequency tuning. Moreover, frequency-specific attentional modulation of afferent sound processing in human IC seems to be considerably weaker, suggesting that the spotlight diminishes toward this lower-order processing stage. Our study sheds light on how the human auditory pathway adapts to the different demands of selective hearing. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

Power-Amplifier Module for 145 to 165 GHz

NASA Technical Reports Server (NTRS)

Samoska, Lorene; Peralta, Alejandro

2007-01-01

A power-amplifier module that operates in the frequency range of 145 to 165 GHz has been designed and constructed as a combination of (1) a previously developed monolithic microwave integrated circuit (MMIC) power amplifier and (2) a waveguide module. The amplifier chip was needed for driving a high-electron-mobility-transistor (HEMT) frequency doubler. While it was feasible to connect the amplifier and frequency-doubler chips by use of wire bonds, it was found to be much more convenient to test the amplifier and doubler chips separately. To facilitate separate testing, it was decided to package the amplifier and doubler chips in separate waveguide modules. Figure 1 shows the resulting amplifier module. The amplifier chip was described in "MMIC HEMT Power Amplifier for 140 to 170 GHz" (NPO-30127), NASA Tech Briefs, Vol. 27, No. 11, (November 2003), page 49. To recapitulate: This is a three-stage MMIC power amplifier that utilizes HEMTs as gain elements. The amplifier was originally designed to operate in the frequency range of 140 to 170 GHz. The waveguide module is based on a previously developed lower frequency module, redesigned to support operation in the frequency range of 140 to 220 GHz. Figure 2 presents results of one of several tests of the amplifier module - measurements of output power and gain as functions of input power at an output frequency of 150 GHz. Such an amplifier module has many applications to test equipment for power sources above 100 GHz.

47 CFR 97.307 - Emission standards.

Code of Federal Regulations, 2013 CFR

2013-10-01

...-modulated emission may have a modulation index greater than 1 at the highest modulation frequency. (2) No..., or for frequency-shift keying, the frequency shift between mark and space must not exceed 1 kHz. (5... Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO...

47 CFR 97.307 - Emission standards.

Code of Federal Regulations, 2011 CFR

2011-10-01

...-modulated emission may have a modulation index greater than 1 at the highest modulation frequency. (2) No..., or for frequency-shift keying, the frequency shift between mark and space must not exceed 1 kHz. (5... Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO...

47 CFR 97.307 - Emission standards.

Code of Federal Regulations, 2012 CFR

2012-10-01

...-modulated emission may have a modulation index greater than 1 at the highest modulation frequency. (2) No..., or for frequency-shift keying, the frequency shift between mark and space must not exceed 1 kHz. (5... Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO...

47 CFR 97.307 - Emission standards.

Code of Federal Regulations, 2014 CFR

2014-10-01

...-modulated emission may have a modulation index greater than 1 at the highest modulation frequency. (2) No..., or for frequency-shift keying, the frequency shift between mark and space must not exceed 1 kHz. (5... Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO...

47 CFR 97.307 - Emission standards.

Code of Federal Regulations, 2010 CFR

2010-10-01

...-modulated emission may have a modulation index greater than 1 at the highest modulation frequency. (2) No..., or for frequency-shift keying, the frequency shift between mark and space must not exceed 1 kHz. (5... Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO...

47 CFR 74.535 - Emission and bandwidth.

Code of Federal Regulations, 2010 CFR

2010-10-01

... transmitter power (PMEAN) in accordance with the following schedule: (1) When using frequency modulation: (i... employed when digital modulation occupies 50 percent or more of the total peak frequency deviation of a... deviation produced by the digital modulation signal and the deviation produced by any frequency division...

Isolating spectral cues in amplitude and quasi-frequency modulation discrimination by reducing stimulus duration.

PubMed

Borucki, Ewa; Berg, Bruce G

2017-05-01

This study investigated the psychophysical effects of distortion products in a listening task traditionally used to estimate the bandwidth of phase sensitivity. For a 2000 Hz carrier, estimates of modulation depth necessary to discriminate amplitude modulated (AM) tones and quasi-frequency modulated (QFM) were measured in a two interval forced choice task as a function modulation frequency. Temporal modulation transfer functions were often non-monotonic at modulation frequencies above 300 Hz. This was likely to be due to a spectral cue arising from the interaction of auditory distortion products and the lower sideband of the stimulus complex. When the stimulus duration was decreased from 200 ms to 20 ms, thresholds for low-frequency modulators rose to near-chance levels, whereas thresholds in the region of non-monotonicities were less affected. The decrease in stimulus duration appears to hinder the listener's ability to use temporal cues in order to discriminate between AM and QFM, whereas spectral information derived from distortion product cues appears more resilient. Copyright © 2017. Published by Elsevier B.V.

Multidimensional signal modulation and/or demodulation for data communications

DOEpatents

Smith, Stephen F [London, TN; Dress, William B [Camas, WA

2008-03-04

Systems and methods are described for multidimensional signal modulation and/or demodulation for data communications. A method includes modulating a carrier signal in a first domain selected from the group consisting of phase, frequency, amplitude, polarization and spread; modulating the carrier signal in a second domain selected from the group consisting of phase, frequency, amplitude, polarization and spread; and modulating the carrier signal in a third domain selected from the group consisting of phase, frequency, amplitude, polarization and spread.

Subharmonic Oscillations and Chaos in Dynamic Atomic Force Microscopy

NASA Technical Reports Server (NTRS)

Cantrell, John H.; Cantrell, Sean A.

2015-01-01

The increasing use of dynamic atomic force microscopy (d-AFM) for nanoscale materials characterization calls for a deeper understanding of the cantilever dynamics influencing scan stability, predictability, and image quality. Model development is critical to such understanding. Renormalization of the equations governing d- AFM provides a simple interpretation of cantilever dynamics as a single spring and mass system with frequency dependent cantilever stiffness and damping parameters. The renormalized model is sufficiently robust to predict the experimentally observed splitting of the free-space cantilever resonance into multiple resonances upon cantilever-sample contact. Central to the model is the representation of the cantilever sample interaction force as a polynomial expansion with coefficients F(sub ij) (i,j = 0, 1, 2) that account for the effective interaction stiffness parameter, the cantilever-to-sample energy transfer, and the amplitude of cantilever oscillation. Application of the Melnikov method to the model equation is shown to predict a homoclinic bifurcation of the Smale horseshoe type leading to a cascade of period doublings with increasing drive displacement amplitude culminating in chaos and loss of image quality. The threshold value of the drive displacement amplitude necessary to initiate subharmonic generation depends on the acoustic drive frequency, the effective damping coefficient, and the nonlinearity of the cantilever-sample interaction force. For parameter values leading to displacement amplitudes below threshold for homoclinic bifurcation other bifurcation scenarios can occur, some of which lead to chaos.

Demonstration of correlative atomic force and transmission electron microscopy using actin cytoskeleton

PubMed Central

Yamada, Yutaro; Konno, Hiroki; Shimabukuro, Katsuya

2017-01-01

In this study, we present a new technique called correlative atomic force and transmission electron microscopy (correlative AFM/TEM) in which a targeted region of a sample can be observed under AFM and TEM. The ultimate goal of developing this new technique is to provide a technical platform to expand the fields of AFM application to complex biological systems such as cell extracts. Recent advances in the time resolution of AFM have enabled detailed observation of the dynamic nature of biomolecules. However, specifying molecular species, by AFM alone, remains a challenge. Here, we demonstrate correlative AFM/TEM, using actin filaments as a test sample, and further show that immuno-electron microscopy (immuno-EM), to specify molecules, can be integrated into this technique. Therefore, it is now possible to specify molecules, captured under AFM, by subsequent observation using immuno-EM. In conclusion, correlative AFM/TEM can be a versatile method to investigate complex biological systems at the molecular level. PMID:28828286

Relative sideband amplitudes versus modulation index for common functions using frequency and phase modulation. [for design and testing of communication system

NASA Technical Reports Server (NTRS)

Stocklin, F.

1973-01-01

The equations defining the amplitude of sidebands resulting from either frequency modulation or phase modulation by either square wave, sine wave, sawtooth or triangular modulating functions are presented. Spectral photographs and computer generated tables of modulation index vs. relative sideband amplitudes are also included.

Local Nanomechanical Motion of the Cell Wall of Saccharomyces cerevisiae

NASA Astrophysics Data System (ADS)

Pelling, Andrew E.; Sehati, Sadaf; Gralla, Edith B.; Valentine, Joan S.; Gimzewski, James K.

2004-08-01

We demonstrate that the cell wall of living Saccharomyces cerevisiae (baker's yeast) exhibits local temperature-dependent nanomechanical motion at characteristic frequencies. The periodic motions in the range of 0.8 to 1.6 kHz with amplitudes of ~3 nm were measured using the cantilever of an atomic force microscope (AFM). Exposure of the cells to a metabolic inhibitor causes the periodic motion to cease. From the strong frequency dependence on temperature, we derive an activation energy of 58 kJ/mol, which is consistent with the cell's metabolism involving molecular motors such as kinesin, dynein, and myosin. The magnitude of the forces observed (~10 nN) suggests concerted nanomechanical activity is operative in the cell.

Single-sideband modulator for frequency domain multiplexing of superconducting qubit readout

NASA Astrophysics Data System (ADS)

Chapman, Benjamin J.; Rosenthal, Eric I.; Kerckhoff, Joseph; Vale, Leila R.; Hilton, Gene C.; Lehnert, K. W.

2017-04-01

We introduce and experimentally characterize a superconducting single-sideband modulator compatible with cryogenic microwave circuits and propose its use for frequency domain multiplexing of superconducting qubit readout. The monolithic double-balanced modulators that comprise the device are formed with purely reactive elements (capacitors and Josephson junction inductors) and require no microwave-frequency control tones. Microwave signals in the 4 to 8 GHz band, with power up to -85 dBm, are converted up or down in frequency by as much as 120 MHz. Spurious harmonics in the device can be suppressed by up to 25 dB for select probe and modulation frequencies.

Effect of synthetic jet modulation schemes on the reduction of a laminar separation bubble

NASA Astrophysics Data System (ADS)

Seo, J. H.; Cadieux, F.; Mittal, R.; Deem, E.; Cattafesta, L.

2018-03-01

The response of a laminar separation bubble to synthetic jet forcing with various modulation schemes is investigated via direct numerical simulations. A simple sinusoidal waveform is considered as a reference case, and various amplitude modulation schemes, including the square-wave "burst" modulation, are employed in the simulations. The results indicate that burst modulation is less effective at reducing the length of the flow separation than the sinusoidal forcing primarily because burst modulation is associated with a broad spectrum of input frequencies that are higher than the target frequency for the flow control. It is found that such high-frequency forcing delays vortex roll-up and promotes vortex pairing and merging, which have an adverse effect on reducing the separation bubble length. A commonly used amplitude modulation scheme is also found to have reduced effectiveness due to its spectral content. A new amplitude modulation scheme which is tailored to impart more energy at the target frequency is proposed and shown to be more effective than the other modulation schemes. Experimental measurements confirm that modulation schemes can be preserved through the actuator and used to enhance the energy content at the target modulation frequency. The present study therefore suggests that the effectiveness of synthetic jet-based flow control could be improved by carefully designing the spectral content of the modulation scheme.

Encoding frequency contrast in primate auditory cortex

PubMed Central

Scott, Brian H.; Semple, Malcolm N.

2014-01-01

Changes in amplitude and frequency jointly determine much of the communicative significance of complex acoustic signals, including human speech. We have previously described responses of neurons in the core auditory cortex of awake rhesus macaques to sinusoidal amplitude modulation (SAM) signals. Here we report a complementary study of sinusoidal frequency modulation (SFM) in the same neurons. Responses to SFM were analogous to SAM responses in that changes in multiple parameters defining SFM stimuli (e.g., modulation frequency, modulation depth, carrier frequency) were robustly encoded in the temporal dynamics of the spike trains. For example, changes in the carrier frequency produced highly reproducible changes in shapes of the modulation period histogram, consistent with the notion that the instantaneous probability of discharge mirrors the moment-by-moment spectrum at low modulation rates. The upper limit for phase locking was similar across SAM and SFM within neurons, suggesting shared biophysical constraints on temporal processing. Using spike train classification methods, we found that neural thresholds for modulation depth discrimination are typically far lower than would be predicted from frequency tuning to static tones. This “dynamic hyperacuity” suggests a substantial central enhancement of the neural representation of frequency changes relative to the auditory periphery. Spike timing information was superior to average rate information when discriminating among SFM signals, and even when discriminating among static tones varying in frequency. This finding held even when differences in total spike count across stimuli were normalized, indicating both the primacy and generality of temporal response dynamics in cortical auditory processing. PMID:24598525

Effects Of Local Oscillator Errors On Digital Beamforming

DTIC Science & Technology

2016-03-01

processor EF element factor EW electronic warfare FFM flicker frequency modulation FOV field-of-view FPGA field-programmable gate array FPM flicker...frequencies and also more difficult to measure [15]. 2. Flicker frequency modulation The source for flicker frequency modulation ( FFM ) is attributed to...a physical resonance mechanism of an oscillator or issues controlling electronic components. Some oscillators might not show FFM noise, which might

47 CFR 73.758 - System specifications for digitally modulated emissions in the HF broadcasting service.

Code of Federal Regulations, 2010 CFR

2010-10-01

... this paragraph. (4) Modulation. Quadrature amplitude modulation (QAM) with orthogonal frequency... frequency broadcasting (HFBC) band, provided the protection afforded to the analog emissions is at least as... used for either DSB or SSB emissions. (c) Emission characteristics—(1) Bandwidth and center frequency...

Spin polarization of {sup 87}Rb atoms with ultranarrow linewidth diode laser: Numerical simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Z. G.; Interdisciplinary Center of Quantum Information, National University of Defense Technology, Changsha, 410073; College of Science, National University of Defense Technology, Changsha, 410073

2016-08-15

In order to polarize {sup 87}Rb vapor effectively with ultranarrow linewidth diode laser, we studied the polarization as a function of some parameters including buffer gas pressure and laser power. Moreover, we also discussed the methods which split or modulate the diode laser frequency so as to pump the two ground hyperfine levels efficiently. We obtained some useful results through numerical simulation. If the buffer gas pressure is so high that the hyperfine structure is unresolved, the polarization is insensitive to laser frequency at peak absorption point so frequency splitting and frequency modulation methods do not show improvement. At lowmore » pressure and laser power large enough, where the hyperfine structure is clearly resolved, frequency splitting and frequency modulation methods can increase polarization effectively. For laser diodes, frequency modulation is easily realized with current modulation, so this method is attractive since it does not add any other components in the pumping laser system.« less

Nano-Wilhelmy investigation of dynamic wetting properties of AFM tips through tip-nanobubble interaction

PubMed Central

Wang, Yuliang; Wang, Huimin; Bi, Shusheng; Guo, Bin

2016-01-01

The dynamic wetting properties of atomic force microscopy (AFM) tips are of much concern in many AFM-related measurement, fabrication, and manipulation applications. In this study, the wetting properties of silicon and silicon nitride AFM tips are investigated through dynamic contact angle measurement using a nano-Wilhelmy balance based method. This is done by capillary force measurement during extension and retraction motion of AFM tips relative to interfacial nanobubbles. The working principle of the proposed method and mathematic models for dynamic contact angle measurement are presented. Geometric models of AFM tips were constructed using scanning electronic microscopy (SEM) images taken from different view directions. The detailed process of tip-nanobubble interaction was investigated using force-distance curves of AFM on nanobubbles. Several parameters including nanobubble height, adhesion and capillary force between tip and nanobubbles are extracted. The variation of these parameters was studied over nanobubble surfaces. The dynamic contact angles of the AFM tips were calculated from the capillary force measurements. The proposed method provides direct measurement of dynamic contact angles for AFM tips and can also be taken as a general approach for nanoscale dynamic wetting property investigation. PMID:27452115

Nano-Wilhelmy investigation of dynamic wetting properties of AFM tips through tip-nanobubble interaction

NASA Astrophysics Data System (ADS)

Wang, Yuliang; Wang, Huimin; Bi, Shusheng; Guo, Bin

2016-07-01

The dynamic wetting properties of atomic force microscopy (AFM) tips are of much concern in many AFM-related measurement, fabrication, and manipulation applications. In this study, the wetting properties of silicon and silicon nitride AFM tips are investigated through dynamic contact angle measurement using a nano-Wilhelmy balance based method. This is done by capillary force measurement during extension and retraction motion of AFM tips relative to interfacial nanobubbles. The working principle of the proposed method and mathematic models for dynamic contact angle measurement are presented. Geometric models of AFM tips were constructed using scanning electronic microscopy (SEM) images taken from different view directions. The detailed process of tip-nanobubble interaction was investigated using force-distance curves of AFM on nanobubbles. Several parameters including nanobubble height, adhesion and capillary force between tip and nanobubbles are extracted. The variation of these parameters was studied over nanobubble surfaces. The dynamic contact angles of the AFM tips were calculated from the capillary force measurements. The proposed method provides direct measurement of dynamic contact angles for AFM tips and can also be taken as a general approach for nanoscale dynamic wetting property investigation.

Digital quadrature phase detection

DOEpatents

Smith, James A.; Johnson, John A.

1992-01-01

A system for detecting the phase of a frequency of phase modulated signal that includes digital quadrature sampling of the frequency or phase modulated signal at two times that are one quarter of a cycle of a reference signal apart, determination of the arctangent of the ratio of a first sampling of the frequency or phase modulated signal to the second sampling of the frequency or phase modulated signal, and a determination of quadrant in which the phase determination is increased by 2.pi. when the quadrant changes from the first quadrant to the fourth quadrant and decreased by 2.pi. when the quadrant changes from the fourth quadrant to the first quadrant whereby the absolute phase of the frequency or phase modulated signal can be determined using an arbitrary reference convention.

Digital quadrature phase detection

DOEpatents

Smith, J.A.; Johnson, J.A.

1992-05-26

A system for detecting the phase of a frequency or phase modulated signal that includes digital quadrature sampling of the frequency or phase modulated signal at two times that are one quarter of a cycle of a reference signal apart, determination of the arctangent of the ratio of a first sampling of the frequency or phase modulated signal to the second sampling of the frequency or phase modulated signal, and a determination of quadrant in which the phase determination is increased by 2[pi] when the quadrant changes from the first quadrant to the fourth quadrant and decreased by 2[pi] when the quadrant changes from the fourth quadrant to the first quadrant whereby the absolute phase of the frequency or phase modulated signal can be determined using an arbitrary reference convention. 6 figs.

Atomic Force Microscopy Techniques for Nanomechanical Characterization: A Polymeric Case Study

NASA Astrophysics Data System (ADS)

Reggente, Melania; Rossi, Marco; Angeloni, Livia; Tamburri, Emanuela; Lucci, Massimiliano; Davoli, Ivan; Terranova, Maria Letizia; Passeri, Daniele

2015-04-01

Atomic force microscopy (AFM) is a versatile tool to perform mechanical characterization of surface samples at the nanoscale. In this work, we review two of such methods, namely contact resonance AFM (CR-AFM) and torsional harmonics AFM (TH-AFM). First, such techniques are illustrated and their applicability on materials with elastic moduli in different ranges are discussed, together with their main advantages and limitations. Then, a case study is presented in which we report the mechanical characterization using both CR-AFM and TH-AFM of polyaniline and polyaniniline doped with nanodiamond particles tablets prepared by a pressing process. We determined the indentation modulus values of their surfaces, which were found in fairly good agreement, thus demonstrating the accuracy of the techniques. Finally, the determined surface elastic moduli have been compared with the bulk ones measured through standard indentation testing.

Stimulus-dependent modulation of spontaneous low-frequency oscillations in the rat visual cortex.

PubMed

Huang, Liangming; Liu, Yadong; Gui, Jianjun; Li, Ming; Hu, Dewen

2014-08-06

Research on spontaneous low-frequency oscillations is important to reveal underlying regulatory mechanisms in the brain. The mechanism for the stimulus modulation of low-frequency oscillations is not known. Here, we used the intrinsic optical imaging technique to examine stimulus-modulated low-frequency oscillation signals in the rat visual cortex. The stimulation was presented monocularly as a flashing light with different frequencies and intensities. The phases of low-frequency oscillations in different regions tended to be synchronized and the rhythms typically accelerated within a 30-s period after stimulation. These phenomena were confined to visual stimuli with specific flashing frequencies (12.5-17.5 Hz) and intensities (5-10 mA). The acceleration and synchronization induced by the flashing frequency were more marked than those induced by the intensity. These results show that spontaneous low-frequency oscillations can be modulated by parameter-dependent flashing lights and indicate the potential utility of the visual stimulus paradigm in exploring the origin and function of low-frequency oscillations.

FREQUENCY MODULATION OF DIRECTLY IMAGED EXOPLANETS: GEOMETRIC EFFECT AS A PROBE OF PLANETARY OBLIQUITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kawahara, Hajime, E-mail: kawahara@eps.s.u-tokyo.ac.jp; Research Center for the Early Universe, School of Science, The University of Tokyo, Tokyo 113-0033

2016-05-10

We consider the time–frequency analysis of a scattered light curve of a directly imaged exoplanet. We show that the geometric effect due to planetary obliquity and orbital inclination induce the frequency modulation of the apparent diurnal periodicity. We construct a model of the frequency modulation and compare it with the instantaneous frequency extracted from the pseudo-Wigner distribution of simulated light curves of a cloudless Earth. The model provides good agreement with the simulated modulation factor, even for the light curve with Gaussian noise comparable to the signal. Notably, the shape of the instantaneous frequency is sensitive to the difference betweenmore » the prograde, retrograde, and pole-on spin rotations. While our technique requires the albedo map to be static, it does not need to solve the albedo map of the planet. The time–frequency analysis is complementary to other methods which utilize the amplitude modulation. This paper demonstrates the importance of the frequency domain of the photometric variability for the characterization of directly imaged exoplanets in future research.« less

Polarimetric Imaging using Two Photoelastic Modulators

NASA Technical Reports Server (NTRS)

Wang, Yu; Cunningham, Thomas; Diner, David; Davis, Edgar; Sun, Chao; Hancock, Bruce; Gutt, Gary; Zan, Jason; Raouf, Nasrat

2009-01-01

A method of polarimetric imaging, now undergoing development, involves the use of two photoelastic modulators in series, driven at equal amplitude but at different frequencies. The net effect on a beam of light is to cause (1) the direction of its polarization to rotate at the average of two excitation frequencies and (2) the amplitude of its polarization to be modulated at the beat frequency (the difference between the two excitation frequencies). The resulting modulated optical light beam is made to pass through a polarizing filter and is detected at the beat frequency, which can be chosen to equal the frame rate of an electronic camera or the rate of sampling the outputs of photodetectors in an array. The method was conceived to satisfy a need to perform highly accurate polarimetric imaging, without cross-talk between polarization channels, at frame rates of the order of tens of hertz. The use of electro-optical modulators is necessitated by a need to obtain accuracy greater than that attainable by use of static polarizing filters over separate fixed detectors. For imaging, photoelastic modulators are preferable to such other electrio-optical modulators as Kerr cells and Pockels cells in that photoelastic modulators operate at lower voltages, have greater angular acceptances, and are easier to use. Prior to the conception of the present method, polarimetric imaging at frame rates of tens of hertz using photoelastic modulators was not possible because the resonance frequencies of photoelastic modulators usually lie in the range from about 20 to about 100 kHz.

Large scale modulation of high frequency acoustic waves in periodic porous media.

PubMed

Boutin, Claude; Rallu, Antoine; Hans, Stephane

2012-12-01

This paper deals with the description of the modulation at large scale of high frequency acoustic waves in gas saturated periodic porous media. High frequencies mean local dynamics at the pore scale and therefore absence of scale separation in the usual sense of homogenization. However, although the pressure is spatially varying in the pores (according to periodic eigenmodes), the mode amplitude can present a large scale modulation, thereby introducing another type of scale separation to which the asymptotic multi-scale procedure applies. The approach is first presented on a periodic network of inter-connected Helmholtz resonators. The equations governing the modulations carried by periodic eigenmodes, at frequencies close to their eigenfrequency, are derived. The number of cells on which the carrying periodic mode is defined is therefore a parameter of the modeling. In a second part, the asymptotic approach is developed for periodic porous media saturated by a perfect gas. Using the "multicells" periodic condition, one obtains the family of equations governing the amplitude modulation at large scale of high frequency waves. The significant difference between modulations of simple and multiple mode are evidenced and discussed. The features of the modulation (anisotropy, width of frequency band) are also analyzed.

Bio-sensing based on plasmon-coupling caused by rotated sub-micrometer gratings in metal-dielectric interfacial layers

NASA Astrophysics Data System (ADS)

Csete, M.; Sipos, Á.; Szalai, A.; Mathesz, A.; Deli, M. A.; Veszelka, Sz.; Schmatulla, A.; Kőházi-Kis, A.; Osvay, K.; Marti, O.; Bor, Zs.

2007-09-01

Novel plasmonic sensor chips are prepared by generating sub-micrometer periodic patterns in the interfacial layers of bimetal-polymer films via master-grating based interference method. Poly-carbonate films spin-coated onto vacuum evaporated silver-gold bimetallic layers are irradiated by the two interfering UV beams of a Nd:YAG laser. It is proven by pulsed force mode AFM that periodic adhesion pattern corresponds to the surface relief gratings, consisting of sub-micrometer droplet arrays and continuous polymer stripes, induced by p- and s-polarized beams, respectively. The characteristic periods are the same, but more complex and larger amplitude adhesion modulation is detectable on the droplet arrays. The polar and azimuthal angle dependence of the resonance characteristic of plasmons is studied by combining the prism- and grating-coupling methods in a modified Kretschmann arrangement, illuminating the structured metal-polymer interface by a frequency doubled Nd:YAG laser through a semi-cylinder. It is proven that the grating-coupling results in double-peaked plasmon resonance curves on both of the droplet arrays and line gratings, when the grooves are rotated to an appropriate azimuthal angle, and the modulation amplitude of the structure is sufficiently large. Streptavidin seeding is performed to demonstrate that small amount of protein can be detected monitoring the shift of the secondary resonance minima. The available high concentration sensitivity is explained by the promotion of protein adherence in the structure's valleys due to the enhanced adhesion. The line-shaped polymer gratings resulting in narrow resonance peaks are utilized to demonstrate the effect of therapeutic molecules on Amyloid-Β peptide, a pathogenic factor in Alzheimer disease.

Frequency-doubled microwave waveforms generation using a dual-polarization quadrature phase shift keying modulator driven by a single frequency radio frequency signal

NASA Astrophysics Data System (ADS)

Zhu, Zihang; Zhao, Shanghong; Li, Xuan; Qu, Kun; Lin, Tao

2018-01-01

A photonic approach to generate frequency-doubled microwave waveforms using an integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator driven by a sinusoidal radio frequency (RF) signal is proposed. By adjusting the dc bias points of the DP-QPSK modulator, the obtained second-order and six-order harmonics are in phase while the fourth-order harmonics are complementary when the orthogonal polarized outputs of the modulator are photodetected. After properly setting the modulation indices of the modulator, the amplitude of the second-order harmonic is 9 times of that of the six-order harmonic, indicating a frequency-doubled triangular waveform is generated. If a broadband 90° microwave phase shifter is attached after the photodetector (PD) to introduce a 90° phase shift, a frequency-doubled square waveform can be obtained after adjusting the amplitude of the second-order harmonic 3 times of that of the six-order harmonic. The proposal is first theoretically analyzed and then validated by simulation. Simulation results show that a 10 GHz triangular and square waveform sequences are successfully generated from a 5 GHz sinusoidal RF drive signal.

Ultimate linewidth reduction of a semiconductor laser frequency-stabilized to a Fabry-Pérot interferometer.

PubMed

Bahoura, Messaoud; Clairon, André

2003-11-01

We report a theoretical dynamical analysis on effect of semiconductor laser phase noise on the achievable linewidth when locked to a Fabry-Pérot cavity fringe using a modulation-demodulation frequency stabilization technique such as the commonly used Pound-Drever-Hall frequency locking scheme. We show that, in the optical domain, the modulation-demodulation operation produces, in the presence of semiconductor laser phase noise, two kinds of excess noise, which could be much above the shot noise limit, namely, conversion noise (PM-to-AM) and intermodulation noise. We show that, in typical stabilization conditions, the ultimate semiconductor laser linewidth reduction can be severely limited by the intermodulation excess noise. The modulation-demodulation operation produces the undesirable nonlinear intermodulation effect through which the phase noise spectral components of the semiconductor laser, in the vicinity of even multiples of the modulation frequency, are downconverted into the bandpass of the frequency control loop. This adds a spurious signal, at the modulation frequency, to the error signal and limits the performance of the locked semiconductor laser. This effect, reported initially in the microwave domain using the quasistatic approximation, can be considerably reduced by a convenient choice of the modulation frequency.

Light beam frequency comb generator

DOEpatents

Priatko, G.J.; Kaskey, J.A.

1992-11-24

A light beam frequency comb generator uses an acousto-optic modulator to generate a plurality of light beams with frequencies which are uniformly separated and possess common noise and drift characteristics. A well collimated monochromatic input light beam is passed through this modulator to produce a set of both frequency shifted and unshifted optical beams. An optical system directs one or more frequency shifted beams along a path which is parallel to the path of the input light beam such that the frequency shifted beams are made incident on the modulator proximate to but separated from the point of incidence of the input light beam. After the beam is thus returned to and passed through the modulator repeatedly, a plurality of mutually parallel beams are generated which are frequency-shifted different numbers of times and possess common noise and drift characteristics. 2 figs.

Light beam frequency comb generator

DOEpatents

Priatko, Gordon J.; Kaskey, Jeffrey A.

1992-01-01

A light beam frequency comb generator uses an acousto-optic modulator to generate a plurality of light beams with frequencies which are uniformly separated and possess common noise and drift characteristics. A well collimated monochromatic input light beam is passed through this modulator to produce a set of both frequency shifted and unshifted optical beams. An optical system directs one or more frequency shifted beams along a path which is parallel to the path of the input light beam such that the frequency shifted beams are made incident on the modulator proximate to but separated from the point of incidence of the input light beam. After the beam is thus returned to and passed through the modulator repeatedly, a plurality of mutually parallel beams are generated which are frequency-shifted different numbers of times and possess common noise and drift characteristics.

Harmonic generation with a dual frequency pulse.

PubMed

Keravnou, Christina P; Averkiou, Michalakis A

2014-05-01

Nonlinear imaging was implemented in commercial ultrasound systems over the last 15 years offering major advantages in many clinical applications. In this work, pulsing schemes coupled with a dual frequency pulse are presented. The pulsing schemes considered were pulse inversion, power modulation, and power modulated pulse inversion. The pulse contains a fundamental frequency f and a specified amount of its second harmonic 2f. The advantages and limitations of this method were evaluated with both acoustic measurements of harmonic generation and theoretical simulations based on the KZK equation. The use of two frequencies in a pulse results in the generation of the sum and difference frequency components in addition to the other harmonic components. While with single frequency pulses, only power modulation and power modulated pulse inversion contained odd harmonic components, with the dual frequency pulse, pulse inversion now also contains odd harmonic components.

3D Nanofabrication Using AFM-Based Ultrasonic Vibration Assisted Nanomachining

NASA Astrophysics Data System (ADS)

Deng, Jia

Nanolithography and nanofabrication processes have significant impact on the recent development of fundamental research areas such as physics, chemistry and biology, as well as the modern electronic devices that have reached nanoscale domain such as optoelectronic devices. Many advanced nanofabrication techniques have been developed and reported to satisfy different requirements in both research areas and applications such as electron-beam lithography. However, it is expensive to use and maintain the equipment. Atomic Force Microscope (AFM) based nanolithography processes provide an alternative approach to nanopatterning with significantly lower cost. Recently, three dimensional nanostructures have attracted a lot of attention, motivated by many applications in various fields including optics, plasmonics and nanoelectromechanical systems. AFM nanolithography processes are able to create not only two dimensional nanopatterns but also have the great potential to fabricate three dimensional nanostructures. The objectives of this research proposal are to investigate the capability of AFM-based three dimensional nanofabrication processes, to transfer the three dimensional nanostructures from resists to silicon surfaces and to use the three dimensional nanostructures on silicon in applications. Based on the understanding of literature, a novel AFM-based ultrasonic vibration assisted nanomachining system is utilized to develop three dimensional nanofabrication processes. In the system, high-frequency in plane circular xy-vibration was introduced to create a virtual tool, whose diameter is controlled by the amplitude of xy-vibration and is larger than that of a regular AFM tip. Therefore, the feature width of a single trench is tunable. Ultrasonic vibration of sample in z-direction was introduced to control the depth of single trenches, creating a high-rate 3D nanomachining process. Complicated 3D nanostructures on PMMA are fabricated under both the setpoint force and z-height control modes. Complex contours and both discrete and continuous height changes are able to be fabricated by the novel 3D nanofabrication processes. Results are imaged clearly after cleaning the debris covering on the 3D nanostructures after nanomachining process. The process is validated by fabricating various 3D nanostructures. The advantages and disadvantages are compared between these two control modes. Furthermore, the 3D nanostructures were further transferred from PMMA surfaces onto silicon surfaces using reactive ion etching (RIE) process. Recipes are developed based on the functionality of the etching gas in the transfer process. Tunable selectivity and controllable surface finishes are achieved by varying the flow rate of oxygen. The developed 3D nanofabrication process is used as a novel technique in two applications, master fabrication for soft lithography and SERS substrates fabrication. 3D nanostructures were reversely molded on PDMS and then duplicated on new PMMA substrates. 3D nanostructures are fabricated, which can be either directly used or transferred on silicon as SERS substrates after coating 80 nm gold layers. They greatly enhanced the intensity of Raman scattering with the enhancement factor of 3.11x103. These applications demonstrate the capability of the novel process of AFM-based 3D nanomachining.

Method and apparatus for coherent burst ranging

DOEpatents

Wachter, Eric A.; Fisher, Walter G.

1998-01-01

A high resolution ranging method is described utilizing a novel modulated waveform, hereafter referred to as coherent burst modulation. In the coherent burst method, high frequency modulation of an acoustic or electromagnetic transmitter, such as a laser, is performed at a modulation frequency. This modulation frequency is transmitted quasi-continuously in the form of interrupted bursts of radiation. Energy from the transmitter is directed onto a target, interacts with the target, and the returning energy is collected. The encoded burst pattern contained in the collected return signal is detected coherently by a receiver that is tuned so as to be principally sensitive to the modulation frequency. The receiver signal is processed to determine target range using both time-of-flight of the burst envelope and phase shift of the high frequency modulation. This approach effectively decouples the maximum unambiguous range and range resolution relationship of earlier methods, thereby allowing high precision ranging to be conducted at arbitrarily long distances using at least one burst of encoded energy. The use of a receiver tuned to the high frequency modulation contained within the coherent burst vastly improves both sensitivity in the detection of the target return signal and rejection of background interferences, such as ambient acoustic or electromagnetic noise. Simultaneous transmission at several energies (or wavelengths) is possible by encoding each energy with a separate modulation frequency or pattern; electronic demodulation at the receiver allows the return pattern for each energy to be monitored independently. Radial velocity of a target can also be determined by monitoring change in phase shift of the return signal as a function of time.

Method and apparatus for coherent burst ranging

DOEpatents

Wachter, E.A.; Fisher, W.G.

1998-04-28

A high resolution ranging method is described utilizing a novel modulated waveform, hereafter referred to as coherent burst modulation. In the coherent burst method, high frequency modulation of an acoustic or electromagnetic transmitter, such as a laser, is performed at a modulation frequency. This modulation frequency is transmitted quasi-continuously in the form of interrupted bursts of radiation. Energy from the transmitter is directed onto a target, interacts with the target, and the returning energy is collected. The encoded burst pattern contained in the collected return signal is detected coherently by a receiver that is tuned so as to be principally sensitive to the modulation frequency. The receiver signal is processed to determine target range using both time-of-flight of the burst envelope and phase shift of the high frequency modulation. This approach effectively decouples the maximum unambiguous range and range resolution relationship of earlier methods, thereby allowing high precision ranging to be conducted at arbitrarily long distances using at least one burst of encoded energy. The use of a receiver tuned to the high frequency modulation contained within the coherent burst vastly improves both sensitivity in the detection of the target return signal and rejection of background interferences, such as ambient acoustic or electromagnetic noise. Simultaneous transmission at several energies (or wavelengths) is possible by encoding each energy with a separate modulation frequency or pattern; electronic demodulation at the receiver allows the return pattern for each energy to be monitored independently. Radial velocity of a target can also be determined by monitoring change in phase shift of the return signal as a function of time. 12 figs.

Magnetic skin layer of NiO(100) probed by polarization-dependent spectromicroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mandal, Suman, E-mail: suman.mandal@sscu.iisc.ernet.in; Menon, Krishnakumar S. R., E-mail: krishna.menon@saha.ac.in; Belkhou, Rachid

2014-06-16

Using polarization-dependent x-ray photoemission electron microscopy, we have investigated the surface effects on antiferromagnetic (AFM) domain formation. Depth-resolved information obtained from our study indicates the presence of strain-induced surface AFM domains on some of the cleaved NiO(100) crystals, which are unusually thinner than bulk AFM domain wall widths (∼150 nm). Existence of such magnetic skin layer is substantiated by exchange-coupled ferromagnetic Fe domains in Fe/NiO(100), thereby evidencing the influence of this surface AFM domains on interfacial magnetic coupling. Our observations demonstrate a depth evolution of AFM structure in presence of induced surface strain, while the surface symmetry-breaking in absence of inducedmore » strain does not modify the bulk AFM domain structure. Realization of such thin surface AFM layer will provide better microscopic understanding of the exchange bias phenomena.« less

Antiferromagnetic Skyrmion: Stability, Creation and Manipulation

NASA Astrophysics Data System (ADS)

Zhang, Xichao; Zhou, Yan; Ezawa, Motohiko

2016-04-01

Magnetic skyrmions are particle-like topological excitations in ferromagnets, which have the topo-logical number Q = ± 1, and hence show the skyrmion Hall effect (SkHE) due to the Magnus force effect originating from the topology. Here, we propose the counterpart of the magnetic skyrmion in the antiferromagnetic (AFM) system, that is, the AFM skyrmion, which is topologically protected but without showing the SkHE. Two approaches for creating the AFM skyrmion have been described based on micromagnetic lattice simulations: (i) by injecting a vertical spin-polarized current to a nanodisk with the AFM ground state; (ii) by converting an AFM domain-wall pair in a nanowire junction. It is demonstrated that the AFM skyrmion, driven by the spin-polarized current, can move straightly over long distance, benefiting from the absence of the SkHE. Our results will open a new strategy on designing the novel spintronic devices based on AFM materials.

Elastic modulus measurements at variable temperature: Validation of atomic force microscopy techniques

NASA Astrophysics Data System (ADS)

Natali, Marco; Reggente, Melania; Passeri, Daniele; Rossi, Marco

2016-06-01

The development of polymer-based nanocomposites to be used in critical thermal environments requires the characterization of their mechanical properties, which are related to their chemical composition, size, morphology and operating temperature. Atomic force microscopy (AFM) has been proven to be a useful tool to develop techniques for the mechanical characterization of these materials, thanks to its nanometer lateral resolution and to the capability of exerting ultra-low loads, down to the piconewton range. In this work, we demonstrate two techniques, one quasi-static, i.e., AFM-based indentation (I-AFM), and one dynamic, i.e., contact resonance AFM (CR-AFM), for the mechanical characterization of compliant materials at variable temperature. A cross-validation of I-AFM and CR-AFM has been performed by comparing the results obtained on two reference materials, i.e., low-density polyethylene (LDPE) and polycarbonate (PC), which demonstrated the accuracy of the techniques.

Application of focused ion beam for the fabrication of AFM probes

NASA Astrophysics Data System (ADS)

Kolomiytsev, A. S.; Lisitsyn, S. A.; Smirnov, V. A.; Fedotov, A. A.; Varzarev, Yu N.

2017-10-01

The results of an experimental study of the probe tips fabrication for critical-dimension atomic force microscopy (CD-AFM) using the focused ion beam (FIB) induced deposition are presented. Methods of the FIB-induced deposition of tungsten and carbon onto the tip of an AFM probe are studied. Based on the results obtained in the study, probes for the CD-AFM technique with a tip height about 1 μm and radius of 20 nm were created. The formation of CD-AFM probes by FIB-induced deposition allows creating a high efficiency tool for nanotechnology and nanodiagnostics. The use of modified cantilevers allows minimizing the artefacts of AFM images and increasing the accuracy of the relief measurement. The obtained results can be used for fabrication of AFM probes for express monitoring of the technological process in the manufacturing of the elements for micro- and nanoelectronics.

Multiple frequency optical mixer and demultiplexer and apparatus for remote sensing

NASA Technical Reports Server (NTRS)

Chen, Jeffrey R. (Inventor)

2010-01-01

A pulsed laser system includes a modulator module configured to provide pulsed electrical signals and a plurality of solid-state seed sources coupled to the modulator module and configured to operate, responsive to the pulsed electrical signals, in a pulse mode. Each of the plurality of solid-state seed sources is tuned to a different frequency channel separated from any adjacent frequency channel by a frequency offset. The pulsed laser system also includes a combiner that combines outputs from each of the solid state seed sources into a single optical path and an optical doubler and demultiplexer coupled to the single optical path and providing each doubled seed frequency on a separate output path.

Interaural time sensitivity of high-frequency neurons in the inferior colliculus.

PubMed

Yin, T C; Kuwada, S; Sujaku, Y

1984-11-01

Recent psychoacoustic experiments have shown that interaural time differences provide adequate cues for lateralizing high-frequency sounds, provided the stimuli are complex and not pure tones. We present here physiological evidence in support of these findings. Neurons of high best frequency in the cat inferior colliculus respond to interaural phase differences of amplitude modulated waveforms, and this response depends upon preservation of phase information of the modulating signal. Interaural phase differences were introduced in two ways: by interaural delays of the entire waveform and by binaural beats in which there was an interaural frequency difference in the modulating waveform. Results obtained with these two methods are similar. Our results show that high-frequency cells can respond to interaural time differences of amplitude modulated signals and that they do so by a sensitivity to interaural phase differences of the modulating waveform.

Switching circuit to improve the frequency modulation difference-intensity THz quantum cascade laser imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saat, N. K.; Dean, P.; Khanna, S. P.

2015-04-24

We demonstrate new switching circuit for difference-intensity THz quantum cascade laser (QCL) imaging by amplitude modulation and lock in detection. The switching circuit is designed to improve the frequency modulation so that it can stably lock the amplitude modulation of the QCL and the detector output. The combination of a voltage divider and a buffer in switching circuit to quickly switch the amplitude of the QCL biases of 15.8 V and 17.2 V is successfully to increase the frequency modulation up to ∼100 Hz.

System for adjusting frequency of electrical output pulses derived from an oscillator

DOEpatents

Bartholomew, David B.

2006-11-14

A system for setting and adjusting a frequency of electrical output pulses derived from an oscillator in a network is disclosed. The system comprises an accumulator module configured to receive pulses from an oscillator and to output an accumulated value. An adjustor module is configured to store an adjustor value used to correct local oscillator drift. A digital adder adds values from the accumulator module to values stored in the adjustor module and outputs their sums to the accumulator module, where they are stored. The digital adder also outputs an electrical pulse to a logic module. The logic module is in electrical communication with the adjustor module and the network. The logic module may change the value stored in the adjustor module to compensate for local oscillator drift or change the frequency of output pulses. The logic module may also keep time and calculate drift.

High-speed atomic force microscopy imaging of live mammalian cells

PubMed Central

Shibata, Mikihiro; Watanabe, Hiroki; Uchihashi, Takayuki; Ando, Toshio; Yasuda, Ryohei

2017-01-01

Direct imaging of morphological dynamics of live mammalian cells with nanometer resolution under physiological conditions is highly expected, but yet challenging. High-speed atomic force microscopy (HS-AFM) is a unique technique for capturing biomolecules at work under near physiological conditions. However, application of HS-AFM for imaging of live mammalian cells was hard to be accomplished because of collision between a huge mammalian cell and a cantilever during AFM scanning. Here, we review our recent improvements of HS-AFM for imaging of activities of live mammalian cells without significant damage to the cell. The improvement of an extremely long (~3 μm) AFM tip attached to a cantilever enables us to reduce severe damage to soft mammalian cells. In addition, a combination of HS-AFM with simple fluorescence microscopy allows us to quickly locate the cell in the AFM scanning area. After these improvements, we demonstrate that developed HS-AFM for live mammalian cells is possible to image morphogenesis of filopodia, membrane ruffles, pits open-close formations, and endocytosis in COS-7, HeLa cells as well as hippocampal neurons. PMID:28900590

Probing ternary solvent effect in high V oc polymer solar cells using advanced AFM techniques

DOE PAGES

Li, Chao; Soleman, Mikhael; Lorenzo, Josie; ...

2016-01-25

This work describes a simple method to develop a high V oc low band gap PSCs. In addition, two new atomic force microscopy (AFM)-based nanoscale characterization techniques to study the surface morphology and physical properties of the structured active layer are introduced. With the help of ternary solvent processing of the active layer and C 60 buffer layer, a bulk heterojunction PSC with V oc more than 0.9 V and conversion efficiency 7.5% is developed. In order to understand the fundamental properties of the materials ruling the performance of the PSCs tested, AFM-based nanoscale characterization techniques including Pulsed-Force-Mode AFM (PFM-AFM)more » and Mode-Synthesizing AFM (MSAFM) are introduced. Interestingly, MSAFM exhibits high sensitivity for direct visualization of the donor–acceptor phases in the active layer of the PSCs. Lastly, conductive-AFM (cAFM) studies reveal local variations in conductivity in the donor and acceptor phases as well as a significant increase in photocurrent in the PTB7:ICBA sample obtained with the ternary solvent processing.« less

Fiber-based polarization-sensitive Mueller matrix optical coherence tomography with continuous source polarization modulation.

PubMed

Jiao, Shuliang; Todorović, Milos; Stoica, George; Wang, Lihong V

2005-09-10

We report on a new configuration of fiber-based polarization-sensitive Mueller matrix optical coherence tomography that permits the acquisition of the round-trip Jones matrix of a biological sample using only one light source and a single depth scan. In this new configuration, a polarization modulator is used in the source arm to continuously modulate the incident polarization state for both the reference and the sample arms. The Jones matrix of the sample can be calculated from the two frequency terms in the two detection channels. The first term is modulated by the carrier frequency, which is determined by the longitudinal scanning mechanism, whereas the other term is modulated by the beat frequency between the carrier frequency and the second harmonic of the modulation frequency of the polarization modulator. One important feature of this system is that, for the first time to our knowledge, the Jones matrix of the sample can be calculated with a single detection channel and a single measurement when diattenuation is negligible. The system was successfully tested by imaging both standard polarization elements and biological samples.

Sensitivity of human auditory cortex to rapid frequency modulation revealed by multivariate representational similarity analysis.

PubMed

Joanisse, Marc F; DeSouza, Diedre D

2014-01-01

Functional Magnetic Resonance Imaging (fMRI) was used to investigate the extent, magnitude, and pattern of brain activity in response to rapid frequency-modulated sounds. We examined this by manipulating the direction (rise vs. fall) and the rate (fast vs. slow) of the apparent pitch of iterated rippled noise (IRN) bursts. Acoustic parameters were selected to capture features used in phoneme contrasts, however the stimuli themselves were not perceived as speech per se. Participants were scanned as they passively listened to sounds in an event-related paradigm. Univariate analyses revealed a greater level and extent of activation in bilateral auditory cortex in response to frequency-modulated sweeps compared to steady-state sounds. This effect was stronger in the left hemisphere. However, no regions showed selectivity for either rate or direction of frequency modulation. In contrast, multivoxel pattern analysis (MVPA) revealed feature-specific encoding for direction of modulation in auditory cortex bilaterally. Moreover, this effect was strongest when analyses were restricted to anatomical regions lying outside Heschl's gyrus. We found no support for feature-specific encoding of frequency modulation rate. Differential findings of modulation rate and direction of modulation are discussed with respect to their relevance to phonetic discrimination.

Generation of Optical Millimeter Wave Using Two Cascaded Polarization Modulators Based on Frequency Octupling Without Filtering

NASA Astrophysics Data System (ADS)

Yang, Yang; Ma, Jianxin; Zhang, Ruijiao; Xin, Xiangjun; Zhang, Junyi

2015-11-01

An approach to generate an optical millimeter wave is introduced with frequency octupling using two cascaded polarization modulators followed by polarizers, respectively. By adjusting the modulation indexes of polarization modulators, only the ±4th-order sidebands are generated with a pure spectrum. Since no filter is needed, the proposed technique can be used to generate a frequency-tunable millimeter wave with a large frequency-tunable range. To prove the feasibility of the proposed approach, a simulation is conducted to generate an 80-GHz millimeter wave, and then its transmission performance is checked.

Atomic force microscopy of RNA: State of the art and recent advancements.

PubMed

Schön, Peter

2018-01-01

The atomic force microscope (AFM) has become a powerful tool for the visualization, probing and manipulation of RNA at the single molecule level. AFM measurements can be carried out in buffer solution in a physiological medium, which is crucial to study the structure and function of biomolecules, also allowing studying them at work. Imaging the specimen in its native state is a great advantage compared to other high resolution methods such as electron microscopy and X-ray diffraction. There is no need to stain, freeze or crystallize biological samples. Moreover, compared to NMR spectroscopy for instance, for AFM studies the size of the biomolecules is not limiting. Consequently the AFM allows one also to investigate larger RNA molecules. In particular, structural studies of nucleic acids and assemblies thereof, have been carried out by AFM routinely including ssRNA, dsRNA and nucleoprotein complexes thereof, as well as RNA aggregates and 2D RNA assemblies. These are becoming increasingly important as novel unique building blocks in the emerging field of RNA nanotechnology. In particular by AFM unique information can be obtained on these RNA based assemblies. Moreover, the AFM is of fundamental relevance to study biological relevant RNA interactions and dynamics. In this short review a brief overview will be given on structural studies that have been done related to AFM topographic imaging of RNA, RNA assemblies and aggregates. Finally, an overview on AFM beyond imaging will be provided. This includes force spectroscopy of RNA under physiological conditions in aqueous buffer to probe RNA interaction with proteins and ligands as well as other AFM tip based RNA probing. Important applications include the detection and quantification of RNA in biological samples. A selection of recent highlights and breakthroughs will be provided related to structural and functional studies by AFM. The main intention of this short review to provide the reader with a flavor of what AFM is able to contribute to RNA research and engineering. Copyright © 2017 Elsevier Ltd. All rights reserved.

Temporal modulation transfer functions in cochlear implantees using a method that limits overall loudness cues

PubMed Central

Fraser, Matthew; McKay, Colette M.

2012-01-01

Temporal modulation transfer functions (TMTFs) were measured for six users of cochlear implants, using different carrier rates and levels. Unlike most previous studies investigating modulation detection, the experimental design limited potential effects of overall loudness cues. Psychometric functions (percent correct discrimination of modulated from unmodulated stimuli versus modulation depth) were obtained. For each modulation depth, each modulated stimulus was loudness balanced to the unmodulated reference stimulus, and level jitter was applied in the discrimination task. The loudness-balance data showed that the modulated stimuli were louder than the unmodulated reference stimuli with the same average current, thus confirming the need to limit loudness cues when measuring modulation detection. TMTFs measured in this way had a low-pass characteristic, with a cut-off frequency (at comfortably loud levels) similar to that for normal-hearing listeners. A reduction in level caused degradation in modulation detection efficiency and a lower-cut-off frequency (i.e. poorer temporal resolution). An increase in carrier rate also led to a degradation in modulation detection efficiency, but only at lower levels or higher modulation frequencies. When detection thresholds were expressed as a proportion of dynamic range, there was no effect of carrier rate for the lowest modulation frequency (50 Hz) at either level. PMID:22146425

Comparing the information conveyed by envelope modulation for speech intelligibility, speech quality, and music quality.

PubMed

Kates, James M; Arehart, Kathryn H

2015-10-01

This paper uses mutual information to quantify the relationship between envelope modulation fidelity and perceptual responses. Data from several previous experiments that measured speech intelligibility, speech quality, and music quality are evaluated for normal-hearing and hearing-impaired listeners. A model of the auditory periphery is used to generate envelope signals, and envelope modulation fidelity is calculated using the normalized cross-covariance of the degraded signal envelope with that of a reference signal. Two procedures are used to describe the envelope modulation: (1) modulation within each auditory frequency band and (2) spectro-temporal processing that analyzes the modulation of spectral ripple components fit to successive short-time spectra. The results indicate that low modulation rates provide the highest information for intelligibility, while high modulation rates provide the highest information for speech and music quality. The low-to-mid auditory frequencies are most important for intelligibility, while mid frequencies are most important for speech quality and high frequencies are most important for music quality. Differences between the spectral ripple components used for the spectro-temporal analysis were not significant in five of the six experimental conditions evaluated. The results indicate that different modulation-rate and auditory-frequency weights may be appropriate for indices designed to predict different types of perceptual relationships.

Amplitude modulation reduces loudness adaptation to high-frequency tones.

PubMed

Wynne, Dwight P; George, Sahara E; Zeng, Fan-Gang

2015-07-01

Long-term loudness perception of a sound has been presumed to depend on the spatial distribution of activated auditory nerve fibers as well as their temporal firing pattern. The relative contributions of those two factors were investigated by measuring loudness adaptation to sinusoidally amplitude-modulated 12-kHz tones. The tones had a total duration of 180 s and were either unmodulated or 100%-modulated at one of three frequencies (4, 20, or 100 Hz), and additionally varied in modulation depth from 0% to 100% at the 4-Hz frequency only. Every 30 s, normal-hearing subjects estimated the loudness of one of the stimuli played at 15 dB above threshold in random order. Without any amplitude modulation, the loudness of the unmodulated tone after 180 s was only 20% of the loudness at the onset of the stimulus. Amplitude modulation systematically reduced the amount of loudness adaptation, with the 100%-modulated stimuli, regardless of modulation frequency, maintaining on average 55%-80% of the loudness at onset after 180 s. Because the present low-frequency amplitude modulation produced minimal changes in long-term spectral cues affecting the spatial distribution of excitation produced by a 12-kHz pure tone, the present result indicates that neural synchronization is critical to maintaining loudness perception over time.

Comparing the information conveyed by envelope modulation for speech intelligibility, speech quality, and music quality

PubMed Central

Kates, James M.; Arehart, Kathryn H.

2015-01-01

This paper uses mutual information to quantify the relationship between envelope modulation fidelity and perceptual responses. Data from several previous experiments that measured speech intelligibility, speech quality, and music quality are evaluated for normal-hearing and hearing-impaired listeners. A model of the auditory periphery is used to generate envelope signals, and envelope modulation fidelity is calculated using the normalized cross-covariance of the degraded signal envelope with that of a reference signal. Two procedures are used to describe the envelope modulation: (1) modulation within each auditory frequency band and (2) spectro-temporal processing that analyzes the modulation of spectral ripple components fit to successive short-time spectra. The results indicate that low modulation rates provide the highest information for intelligibility, while high modulation rates provide the highest information for speech and music quality. The low-to-mid auditory frequencies are most important for intelligibility, while mid frequencies are most important for speech quality and high frequencies are most important for music quality. Differences between the spectral ripple components used for the spectro-temporal analysis were not significant in five of the six experimental conditions evaluated. The results indicate that different modulation-rate and auditory-frequency weights may be appropriate for indices designed to predict different types of perceptual relationships. PMID:26520329

Precision and broadband frequency swept laser source based on high-order modulation-sideband injection-locking.

PubMed

Wei, Fang; Lu, Bin; Wang, Jian; Xu, Dan; Pan, Zhengqing; Chen, Dijun; Cai, Haiwen; Qu, Ronghui

2015-02-23

A precision and broadband laser frequency swept technique is experimentally demonstrated. Using synchronous current compensation, a slave diode laser is dynamically injection-locked to a specific high-order modulation-sideband of a narrow-linewidth master laser modulated by an electro-optic modulator (EOM), whose driven radio frequency (RF) signal can be agilely, precisely controlled by a frequency synthesizer, and the high-order modulation-sideband enables multiplied sweep range and tuning rate. By using 5th order sideband injection-locking, the original tuning range of 3 GHz and tuning rate of 0.5 THz/s is multiplied by 5 times to 15 GHz and 2.5 THz/s respectively. The slave laser has a 3 dB-linewidth of 2.5 kHz which is the same to the master laser. The settling time response of a 10 MHz frequency switching is 2.5 µs. By using higher-order modulation-sideband and optimized experiment parameters, an extended sweep range and rate could be expected.

Super-contrast photoacoustic resonance imaging

NASA Astrophysics Data System (ADS)

Gao, Fei; Zhang, Ruochong; Feng, Xiaohua; Liu, Siyu; Zheng, Yuanjin

2018-02-01

In this paper, a new imaging modality, named photoacoustic resonance imaging (PARI), is proposed and experimentally demonstrated. Being distinct from conventional single nanosecond laser pulse induced wideband PA signal, the proposed PARI method utilizes multi-burst modulated laser source to induce PA resonant signal with enhanced signal strength and narrower bandwidth. Moreover, imaging contrast could be clearly improved than conventional single-pulse laser based PA imaging by selecting optimum modulation frequency of the laser source, which originates from physical properties of different materials beyond the optical absorption coefficient. Specifically, the imaging steps is as follows: 1: Perform conventional PA imaging by modulating the laser source as a short pulse to identify the location of the target and the background. 2: Shine modulated laser beam on the background and target respectively to characterize their individual resonance frequency by sweeping the modulation frequency of the CW laser source. 3: Select the resonance frequency of the target as the modulation frequency of the laser source, perform imaging and get the first PARI image. Then choose the resonance frequency of the background as the modulation frequency of the laser source, perform imaging and get the second PARI image. 4: subtract the first PARI image from the second PARI image, then we get the contrast-enhanced PARI results over the conventional PA imaging in step 1. Experimental validation on phantoms have been performed to show the merits of the proposed PARI method with much improved image contrast.

47 CFR 95.607 - CB transmitter modification.

Code of Federal Regulations, 2010 CFR

2010-10-01

... transmitting frequencies, increased modulation level, a different form of modulation, or increased TP (RF... modulating frequency, typically 0.1 seconds at maximum power) or peak envelope power (TP averaged during 1 RF cycle at the highest crest of the modulation envelope), as measured at the transmitter output antenna...

Rydberg-atom based radio-frequency electrometry using frequency modulation spectroscopy in room temperature vapor cells.

PubMed

Kumar, Santosh; Fan, Haoquan; Kübler, Harald; Jahangiri, Akbar J; Shaffer, James P

2017-04-17

Rydberg atom-based electrometry enables traceable electric field measurements with high sensitivity over a large frequency range, from gigahertz to terahertz. Such measurements are particularly useful for the calibration of radio frequency and terahertz devices, as well as other applications like near field imaging of electric fields. We utilize frequency modulated spectroscopy with active control of residual amplitude modulation to improve the signal to noise ratio of the optical readout of Rydberg atom-based radio frequency electrometry. Matched filtering of the signal is also implemented. Although we have reached similarly, high sensitivity with other read-out methods, frequency modulated spectroscopy is advantageous because it is well-suited for building a compact, portable sensor. In the current experiment, ∼3 µV cm^-1 Hz^-1/2 sensitivity is achieved and is found to be photon shot noise limited.

Laser frequency stabilization by combining modulation transfer and frequency modulation spectroscopy.

PubMed

Zi, Fei; Wu, Xuejian; Zhong, Weicheng; Parker, Richard H; Yu, Chenghui; Budker, Simon; Lu, Xuanhui; Müller, Holger

2017-04-01

We present a hybrid laser frequency stabilization method combining modulation transfer spectroscopy (MTS) and frequency modulation spectroscopy (FMS) for the cesium D₂ transition. In a typical pump-probe setup, the error signal is a combination of the DC-coupled MTS error signal and the AC-coupled FMS error signal. This combines the long-term stability of the former with the high signal-to-noise ratio of the latter. In addition, we enhance the long-term frequency stability with laser intensity stabilization. By measuring the frequency difference between two independent hybrid spectroscopies, we investigate the short-and long-term stability. We find a long-term stability of 7.8 kHz characterized by a standard deviation of the beating frequency drift over the course of 10 h and a short-term stability of 1.9 kHz characterized by an Allan deviation of that at 2 s of integration time.

A low-cost, tunable laser lock without laser frequency modulation

NASA Astrophysics Data System (ADS)

Shea, Margaret E.; Baker, Paul M.; Gauthier, Daniel J.

2015-05-01

Many experiments in optical physics require laser frequency stabilization. This can be achieved by locking to an atomic reference using saturated absorption spectroscopy. Often, the laser frequency is modulated and phase sensitive detection used. This method, while well-proven and robust, relies on expensive components, can introduce an undesirable frequency modulation into the laser, and is not easily frequency tuned. Here, we report a simple locking scheme similar to those implemented previously. We modulate the atomic resonances in a saturated absorption setup with an AC magnetic field created by a single solenoid. The same coil applies a DC field that allows tuning of the lock point. We use an auto-balanced detector to make our scheme more robust against laser power fluctuations and stray magnetic fields. The coil, its driver, and the detector are home-built with simple, cheap components. Our technique is low-cost, simple to setup, tunable, introduces no laser frequency modulation, and only requires one laser. We gratefully acknowledge the financial support of the NSF through Grant # PHY-1206040.

High-speed atomic force microscopy coming of age

NASA Astrophysics Data System (ADS)

Ando, Toshio

2012-02-01

High-speed atomic force microscopy (HS-AFM) is now materialized. It allows direct visualization of dynamic structural changes and dynamic processes of functioning biological molecules in physiological solutions, at high spatiotemporal resolution. Dynamic molecular events unselectively appear in detail in an AFM movie, facilitating our understanding of how biological molecules operate to function. This review describes a historical overview of technical development towards HS-AFM, summarizes elementary devices and techniques used in the current HS-AFM, and then highlights recent imaging studies. Finally, future challenges of HS-AFM studies are briefly discussed.

Low frequency steady-state brain responses modulate large scale functional networks in a frequency-specific means.

PubMed

Wang, Yi-Feng; Long, Zhiliang; Cui, Qian; Liu, Feng; Jing, Xiu-Juan; Chen, Heng; Guo, Xiao-Nan; Yan, Jin H; Chen, Hua-Fu

2016-01-01

Neural oscillations are essential for brain functions. Research has suggested that the frequency of neural oscillations is lower for more integrative and remote communications. In this vein, some resting-state studies have suggested that large scale networks function in the very low frequency range (<1 Hz). However, it is difficult to determine the frequency characteristics of brain networks because both resting-state studies and conventional frequency tagging approaches cannot simultaneously capture multiple large scale networks in controllable cognitive activities. In this preliminary study, we aimed to examine whether large scale networks can be modulated by task-induced low frequency steady-state brain responses (lfSSBRs) in a frequency-specific pattern. In a revised attention network test, the lfSSBRs were evoked in the triple network system and sensory-motor system, indicating that large scale networks can be modulated in a frequency tagging way. Furthermore, the inter- and intranetwork synchronizations as well as coherence were increased at the fundamental frequency and the first harmonic rather than at other frequency bands, indicating a frequency-specific modulation of information communication. However, there was no difference among attention conditions, indicating that lfSSBRs modulate the general attention state much stronger than distinguishing attention conditions. This study provides insights into the advantage and mechanism of lfSSBRs. More importantly, it paves a new way to investigate frequency-specific large scale brain activities. © 2015 Wiley Periodicals, Inc.

Enhanced modulation rates via field modulation in spin torque nano-oscillators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Purbawati, A.; Garcia-Sanchez, F.; Buda-Prejbeanu, L. D.

Spin Transfer Nano-Oscillators (STNOs) are promising candidates for telecommunications applications due to their frequency tuning capabilities via either a dc current or an applied field. This frequency tuning is of interest for Frequency Shift Keying concepts to be used in wireless communication schemes or in read head applications. For these technological applications, one important parameter is the characterization of the maximum achievable rate at which an STNO can respond to a modulating signal, such as current or field. Previous studies of in-plane magnetized STNOs on frequency modulation via an rf current revealed that the maximum achievable rate is limited bymore » the amplitude relaxation rate Γ{sub p}, which gives the time scale over which amplitude fluctuations are damped out. This might be a limitation for applications. Here, we demonstrate via numerical simulation that application of an additional rf field is an alternative way for modulation of the in-plane magnetized STNO configuration, which has the advantage that frequency modulation is not limited by the amplitude relaxation rate, so that higher modulation rates above GHz are achievable. This occurs when the modulating rf field is oriented along the easy axis (longitudinal rf field). Tilting the direction of the modulating rf field in-plane and perpendicularly with respect to the easy axis (transverse rf field), the modulation is again limited by the amplitude relaxation rate similar to the response observed in current modulation.« less

Apparatus and method for qualitative and quantitative measurements of optical properties of turbid media using frequency-domain photon migration

DOEpatents

Tromberg, B.J.; Tsay, T.T.; Berns, M.W.; Svaasand, L.O.; Haskell, R.C.

1995-06-13

Optical measurements of turbid media, that is media characterized by multiple light scattering, is provided through an apparatus and method for exposing a sample to a modulated laser beam. The light beam is modulated at a fundamental frequency and at a plurality of integer harmonics thereof. Modulated light is returned from the sample and preferentially detected at cross frequencies at frequencies slightly higher than the fundamental frequency and at integer harmonics of the same. The received radiance at the beat or cross frequencies is compared against a reference signal to provide a measure of the phase lag of the radiance and modulation ratio relative to a reference beam. The phase and modulation amplitude are then provided as a frequency spectrum by an array processor to which a computer applies a complete curve fit in the case of highly scattering samples or a linear curve fit below a predetermined frequency in the case of highly absorptive samples. The curve fit in any case is determined by the absorption and scattering coefficients together with a concentration of the active substance in the sample. Therefore, the curve fitting to the frequency spectrum can be used both for qualitative and quantitative analysis of substances in the sample even though the sample is highly turbid. 14 figs.

Apparatus and method for qualitative and quantitative measurements of optical properties of turbid media using frequency-domain photon migration

DOEpatents

Tromberg, Bruce J.; Tsay, Tsong T.; Berns, Michael W.; Svaasand, Lara O.; Haskell, Richard C.

1995-01-01

Optical measurements of turbid media, that is media characterized by multiple light scattering, is provided through an apparatus and method for exposing a sample to a modulated laser beam. The light beam is modulated at a fundamental frequency and at a plurality of integer harmonics thereof. Modulated light is returned from the sample and preferentially detected at cross frequencies at frequencies slightly higher than the fundamental frequency and at integer harmonics of the same. The received radiance at the beat or cross frequencies is compared against a reference signal to provide a measure of the phase lag of the radiance and modulation ratio relative to a reference beam. The phase and modulation amplitude are then provided as a frequency spectrum by an array processor to which a computer applies a complete curve fit in the case of highly scattering samples or a linear curve fit below a predetermined frequency in the case of highly absorptive samples. The curve fit in any case is determined by the absorption and scattering coefficients together with a concentration of the active substance in the sample. Therefore, the curve fitting to the frequency spectrum can be used both for qualitative and quantitative analysis of substances in the sample even though the sample is highly turbid.

Task-induced frequency modulation features for brain-computer interfacing.

PubMed

Jayaram, Vinay; Hohmann, Matthias; Just, Jennifer; Schölkopf, Bernhard; Grosse-Wentrup, Moritz

2017-10-01

Task-induced amplitude modulation of neural oscillations is routinely used in brain-computer interfaces (BCIs) for decoding subjects' intents, and underlies some of the most robust and common methods in the field, such as common spatial patterns and Riemannian geometry. While there has been some interest in phase-related features for classification, both techniques usually presuppose that the frequencies of neural oscillations remain stable across various tasks. We investigate here whether features based on task-induced modulation of the frequency of neural oscillations enable decoding of subjects' intents with an accuracy comparable to task-induced amplitude modulation. We compare cross-validated classification accuracies using the amplitude and frequency modulated features, as well as a joint feature space, across subjects in various paradigms and pre-processing conditions. We show results with a motor imagery task, a cognitive task, and also preliminary results in patients with amyotrophic lateral sclerosis (ALS), as well as using common spatial patterns and Laplacian filtering. The frequency features alone do not significantly out-perform traditional amplitude modulation features, and in some cases perform significantly worse. However, across both tasks and pre-processing in healthy subjects the joint space significantly out-performs either the frequency or amplitude features alone. This result only does not hold for ALS patients, for whom the dataset is of insufficient size to draw any statistically significant conclusions. Task-induced frequency modulation is robust and straight forward to compute, and increases performance when added to standard amplitude modulation features across paradigms. This allows more information to be extracted from the EEG signal cheaply and can be used throughout the field of BCIs.

A diode laser-based velocimeter providing point measurements in unseeded flows using modulated filtered Rayleigh scattering (MFRS)

NASA Astrophysics Data System (ADS)

Jagodzinski, Jeremy James

2007-12-01

The development to date of a diode-laser based velocimeter providing point-velocity-measurements in unseeded flows using molecular Rayleigh scattering is discussed. The velocimeter is based on modulated filtered Rayleigh scattering (MFRS), a novel variation of filtered Rayleigh scattering (FRS), utilizing modulated absorption spectroscopy techniques to detect a strong absorption of a relatively weak Rayleigh scattered signal. A rubidium (Rb) vapor filter is used to provide the relatively strong absorption; alkali metal vapors have a high optical depth at modest vapor pressures, and their narrow linewidth is ideally suited for high-resolution velocimetry. Semiconductor diode lasers are used to generate the relatively weak Rayleigh scattered signal; due to their compact, rugged construction diode lasers are ideally suited for the environmental extremes encountered in many experiments. The MFRS technique utilizes the frequency-tuning capability of diode lasers to implement a homodyne detection scheme using lock-in amplifiers. The optical frequency of the diode-based laser system used to interrogate the flow is rapidly modulated about a reference frequency in the D2-line of Rb. The frequency modulation is imposed on the Rayleigh scattered light that is collected from the probe volume in the flow under investigation. The collected frequency modulating Rayleigh scattered light is transmitted through a Rb vapor filter before being detected. The detected modulated absorption signal is fed to two lock-in amplifers synchronized with the modulation frequency of the source laser. High levels of background rejection are attained since the lock-ins are both frequency and phase selective. The two lock-in amplifiers extract different Fourier components of the detected modulated absorption signal, which are ratioed to provide an intensity normalized frequency dependent signal from a single detector. A Doppler frequency shift in the collected Rayleigh scattered light due to a change in the velocity of the flow under investigation results in a change in the detected modulated absorption signal. This change in the detected signal provides a quantifiable measure of the Doppler frequency shift, and hence the velocity in the probe volume, provided that the laser source exhibits acceptable levels of frequency stability (determined by the magnitude of the velocities being measured). An extended cavity diode laser (ECDL) in the Littrow configuration provides frequency tunable, relatively narrow-linewidth lasing for the MFRS velocimeter. Frequency stabilization of the ECDL is provided by a proportional-integral-differential (PID) controller based on an error signal in the reference arm of the experiment. The optical power of the Littrow laser source is amplified by an antireflection coated (AR coated) broad stripe diode laser. The single-mode, frequency-modulatable, frequency-stable O(50 mW) of optical power provided by this extended cavity diode laser master oscillator power amplifier (ECDL-MOPA) system provided sufficient scattering signal from a condensing jet of CO2 to implement the MFRS technique in the frequency-locked mode of operation.

Acute Flaccid Myelitis

MedlinePlus

... the symptoms of AFM, possible causes, diagnosis, and general prevention and treatment information. AFM Investigation Information about investigations of AFM in the United States. For Clinicians and Health Departments Information about the ...

Atomic Force Microscopy for Soil Analysis

NASA Astrophysics Data System (ADS)

gazze, andrea; doerr, stefan; dudley, ed; hallin, ingrid; matthews, peter; quinn, gerry; van keulen, geertje; francis, lewis

2016-04-01

Atomic Force Microscopy (AFM) is a high-resolution surface-sensitive technique, which provides 3-dimensional topographical information and material properties of both stiff and soft samples in their natural environments. Traditionally AFM has been applied to samples with low roughness: hence its use for soil analysis has been very limited so far. Here we report the optimization settings required for a standardization of high-resolution and artefact-free analysis of natural soil with AFM: soil immobilization, AFM probe selection, artefact recognition and minimization. Beyond topography, AFM can be used in a spectroscopic mode to evaluate nanomechanical properties, such as soil viscosity, stiffness, and deformation. In this regards, Bruker PeakForce-Quantitative NanoMechanical (QNM) AFM provides a fast and convenient way to extract physical properties from AFM force curves in real-time to obtain soil nanomechanical properties. Here we show for the first time the ability of AFM to describe the topography of natural soil at nanometre resolution, with observation of micro-components, such as clays, and of nano-structures, possibly of biotic origin, the visualization of which would prove difficult with other instrumentations. Finally, nanomechanical profiling has been applied to different wettability states in soil and the respective physical patterns are discussed.

Characterization of fiber-forming peptides and proteins by means of atomic force microscopy.

PubMed

Creasey, Rhiannon G; Gibson, Christopher T; Voelcker, Nicolas H

2012-05-01

The atomic force microscope (AFM) is widely used in biological sciences due to its ability to perform imaging experiments at high resolution in a physiological environment, without special sample preparation such as fixation or staining. AFM is unique, in that it allows single molecule information of mechanical properties and molecular recognition to be gathered. This review sets out to identify methodological applications of AFM for characterization of fiber-forming proteins and peptides. The basics of AFM operation are detailed, with in-depth information for any life scientist to get a grasp on AFM capabilities. It also briefly describes antibody recognition imaging and mapping of nanomechanical properties on biological samples. Subsequently, examples of AFM application to fiber-forming natural proteins, and fiber-forming synthetic peptides are given. Here, AFM is used primarily for structural characterization of fibers in combination with other techniques, such as circular dichroism and fluorescence spectroscopy. More recent developments in antibody recognition imaging to identify constituents of protein fibers formed in human disease are explored. This review, as a whole, seeks to encourage the life scientists dealing with protein aggregation phenomena to consider AFM as a part of their research toolkit, by highlighting the manifold capabilities of this technique.

A Computer-Controlled Classroom Model of an Atomic Force Microscope

NASA Astrophysics Data System (ADS)

Engstrom, Tyler A.; Johnson, Matthew M.; Eklund, Peter C.; Russin, Timothy J.

2015-12-01

The concept of "seeing by feeling" as a way to circumvent limitations on sight is universal on the macroscopic scale—reading Braille, feeling one's way around a dark room, etc. The development of the atomic force microscope (AFM) in 1986 extended this concept to imaging in the nanoscale. While there are classroom demonstrations that use a tactile probe to map the topography or some other property of a sample, the rastering of the probe over the sample is manually controlled, which is both tedious and potentially inaccurate. Other groups have used simulation or tele-operation of an AFM probe. In this paper we describe a teaching AFM with complete computer control to map out topographic and magnetic properties of a "crystal" consisting of two-dimensional arrays of spherical marble "atoms." Our AFM is well suited for lessons on the "Big Ideas of Nanoscale" such as tools and instrumentation, as well as a pre-teaching activity for groups with remote access AFM or mobile AFM. The principle of operation of our classroom AFM is the same as that of a real AFM, excepting the nature of the force between sample and probe.

Phase coded, micro-power impulse radar motion sensor

DOEpatents

McEwan, Thomas E.

1996-01-01

A motion sensing, micro-power impulse radar MIR impresses on the transmitted signal, or the received pulse timing signal, one or more frequencies lower than the pulse repetition frequency, that become intermediate frequencies in a "IF homodyne" receiver. Thus, many advantages of classical RF receivers can be thereby be realized with ultra-wide band radar. The sensor includes a transmitter which transmits a sequence of electromagnetic pulses in response to a transmit timing signal at a nominal pulse repetition frequency. A receiver samples echoes of the sequence of electromagnetic pulses from objects within the field with controlled timing, in response to a receive timing signal, and generates a sample signal in response to the samples. A timing circuit supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver. The relative timing of the transmit timing signal and the receive timing signal is modulated between a first relative delay and a second relative delay at an intermediate frequency, causing the receiver to sample the echoes such that the time between transmissions of pulses in the sequence and samples by the receiver is modulated at the intermediate frequency. Modulation may be executed by modulating the pulse repetition frequency which drives the transmitter, by modulating the delay circuitry which controls the relative timing of the sample strobe, or by modulating amplitude of the transmitted pulses. The electromagnetic pulses will have a nominal center frequency related to pulse width, and the first relative delay and the second relative delay between which the timing signals are modulated, differ by less than the nominal pulse width, and preferably by about one-quarter wavelength at the nominal center frequency of the transmitted pulses.

Phase coded, micro-power impulse radar motion sensor

DOEpatents

McEwan, T.E.

1996-05-21

A motion sensing, micro-power impulse radar MIR impresses on the transmitted signal, or the received pulse timing signal, one or more frequencies lower than the pulse repetition frequency, that become intermediate frequencies in a ``IF homodyne`` receiver. Thus, many advantages of classical RF receivers can be thereby be realized with ultra-wide band radar. The sensor includes a transmitter which transmits a sequence of electromagnetic pulses in response to a transmit timing signal at a nominal pulse repetition frequency. A receiver samples echoes of the sequence of electromagnetic pulses from objects within the field with controlled timing, in response to a receive timing signal, and generates a sample signal in response to the samples. A timing circuit supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver. The relative timing of the transmit timing signal and the receive timing signal is modulated between a first relative delay and a second relative delay at an intermediate frequency, causing the receiver to sample the echoes such that the time between transmissions of pulses in the sequence and samples by the receiver is modulated at the intermediate frequency. Modulation may be executed by modulating the pulse repetition frequency which drives the transmitter, by modulating the delay circuitry which controls the relative timing of the sample strobe, or by modulating amplitude of the transmitted pulses. The electromagnetic pulses will have a nominal center frequency related to pulse width, and the first relative delay and the second relative delay between which the timing signals are modulated, differ by less than the nominal pulse width, and preferably by about one-quarter wavelength at the nominal center frequency of the transmitted pulses. 5 figs.

Frequency of gamma oscillations in humans is modulated by velocity of visual motion

PubMed Central

Butorina, Anna V.; Sysoeva, Olga V.; Prokofyev, Andrey O.; Nikolaeva, Anastasia Yu.; Stroganova, Tatiana A.

2015-01-01

Gamma oscillations are generated in networks of inhibitory fast-spiking (FS) parvalbumin-positive (PV) interneurons and pyramidal cells. In animals, gamma frequency is modulated by the velocity of visual motion; the effect of velocity has not been evaluated in humans. In this work, we have studied velocity-related modulations of gamma frequency in children using MEG/EEG. We also investigated whether such modulations predict the prominence of the “spatial suppression” effect (Tadin D, Lappin JS, Gilroy LA, Blake R. Nature 424: 312-315, 2003) that is thought to depend on cortical center-surround inhibitory mechanisms. MEG/EEG was recorded in 27 normal boys aged 8–15 yr while they watched high-contrast black-and-white annular gratings drifting with velocities of 1.2, 3.6, and 6.0°/s and performed a simple detection task. The spatial suppression effect was assessed in a separate psychophysical experiment. MEG gamma oscillation frequency increased while power decreased with increasing velocity of visual motion. In EEG, the effects were less reliable. The frequencies of the velocity-specific gamma peaks were 64.9, 74.8, and 87.1 Hz for the slow, medium, and fast motions, respectively. The frequency of the gamma response elicited during slow and medium velocity of visual motion decreased with subject age, whereas the range of gamma frequency modulation by velocity increased with age. The frequency modulation range predicted spatial suppression even after controlling for the effect of age. We suggest that the modulation of the MEG gamma frequency by velocity of visual motion reflects excitability of cortical inhibitory circuits and can be used to investigate their normal and pathological development in the human brain. PMID:25925324

Solidification of a liquid crystal: Morphologies and transitions. Ph.D. thesis, Simon Fraser University (Canada)

NASA Astrophysics Data System (ADS)

Hutter, Jeffrey Lee

When a material freezes, the form it takes depends on the solidification conditions. For instance, as the undercooling is increased, one typically sees solidification into less-ordered forms. The resulting growth modes appear to be generic, with qualitative similarities between systems whose microscopic details are quite dissimilar. I have used both optical and atomic-force microscopy to study the transitions between different growth morphologies during the solidification of a particular liquid crystal, 10 OCB. We have observed six different solidification modes, each with a distinct micro and meso structure. The front-velocity-vs.-undercooling curve has a discontinuity in its slope and, in some cases, in the curve itself at mode transitions, suggesting that these transitions are analogous to phase transitions. Such transitions have been seen in other systems, but no general rule has been found that can predict which morphology will be selected. We show that, contrary to intuition and widespread speculation, the fastest-growing mode is not always the one selected. One of the growth modes exhibited by 10 OCB is known as banded spherulitic growth. Spherulites have been seen in a wide variety of materials including minerals, pure elements, polymers, biomolecules, and metal alloys. However, despite a century of study, there is no generally accepted theory of spherulitic growth. In particular, the cause of the concentric banding seen in many spherulites remains a mystery. Our studies of banded spherulites in 10 OCB using both optical and atomic-force microscopy show that the bands are associated with a density modulation and thus are not merely the result of a birefringent effect, as is commonly believed. As the atomic-force microscope (AFM) is a relatively new tool, some time was spent studying its capabilities. We found that because the AFM resolution is largely determined by attractive forces between the tip of the probe and the sample, resolution can be improved by imaging in a suitable liquid medium. We also developed a simple method for calibrating AFM cantilevers--a crucial step in using the AFM to obtain quantitative force data. This work is presented in an appendix.

Seasonal patterns of aflatoxin M1 contamination in commercial pasteurised milk from different areas in Thailand.

PubMed

Suriyasathaporn, Witaya; Nakprasert, Watinee

2012-01-01

Aflatoxin M1 (AFM1) levels were determined in pasteurised milk from five commercial trademarks produced in different areas in Thailand. One hundred and twenty milk samples were collected from local markets in Chiang Mai province, Thailand, to evaluate AFM1 concentrations using immunoaffinity columns and high-performance liquid chromatography with fluorescence detection. The overall median AFM1 level was 0.023 µg L(-1) ranging from 0.004 to 0.293 µg L(-1). All trademarks had average AFM1 concentrations lower than 0.05 µg L(-1), with those in Trademarks 3 to 5 being higher than Trademarks 1 and 2 (P < 0.01). All trademarks had different seasonal patterns of AFM1, even though operating in the same area. However, only Trademark 3 showed significant differences of AFM1 levels between seasons. The results suggested that farm management factors, rather than environment factors, were likely to be the main cause of AFM1 contamination in dairy products.

Real-Time Optical Image Processing Techniques

DTIC Science & Technology

1988-10-31

pursued through the analysis, design, and fabrication of pulse frequency modulated halftone screens and the modification of micro-chan- nel spatial...required for non-linear operation. Real-time nonlinear processing was performed using the halftone screen and MSLM. The experiments showed the effectiveness...pulse frequency modulation has been pursued through the analysis, design, and fabrication of pulse frequency modulated halftone screens and the

Cross-Modulated Amplitudes and Frequencies Characterize Interacting Components in Complex Systems

NASA Astrophysics Data System (ADS)

Gans, Fabian; Schumann, Aicko Y.; Kantelhardt, Jan W.; Penzel, Thomas; Fietze, Ingo

2009-03-01

The dynamics of complex systems is characterized by oscillatory components on many time scales. To study the interactions between these components we analyze the cross modulation of their instantaneous amplitudes and frequencies, separating synchronous and antisynchronous modulation. We apply our novel technique to brain-wave oscillations in the human electroencephalogram and show that interactions between the α wave and the δ or β wave oscillators as well as spatial interactions can be quantified and related with physiological conditions (e.g., sleep stages). Our approach overcomes the limitation to oscillations with similar frequencies and enables us to quantify directly nonlinear effects such as positive or negative frequency modulation.

FIBER AND INTEGRATED OPTICS: Radio-frequency electrooptic modulation in optical fibers

NASA Astrophysics Data System (ADS)

Bulyuk, A. N.

1992-10-01

The electrooptic interaction in single-mode optical fibers with both linear and circular birefringe is analyzed. In most cases, a large interaction length imposes a limit on the modulation frequency. A circular birefringence in an optical fiber may lead to an effective coupling of polarization normal modes if a phase-matching condition is satisfied. Through an appropriate choice of polarization states of the light at the entrance and exit of the device, one can achieve a polarization modulation or a frequency shift of the light. There are possible applications in rf polarization modulators, devices for shifting the frequency of light, and detectors of electromagnetic fields.

Measurement of a free spectral range of a Fabry-Perot cavity using frequency modulation and null method under off-resonance conditions

NASA Astrophysics Data System (ADS)

Aketagawa, Masato; Kimura, Shohei; Yashiki, Takuya; Iwata, Hiroshi; Banh, Tuan Quoc; Hirata, Kenji

2011-02-01

In this paper, we discuss a method to measure the free spectral range (FSR) of a Fabry-Perot cavity (FP-cavity) using frequency modulation with one electric optical modulator (EOM) and the null method. A laser beam modulated by the EOM, to which a sine wave signal is supplied from a radio frequency (RF) oscillator, is incident on the FP-cavity. The transmitted or reflected light from the FP-cavity is observed and converted to an RF signal by a high-speed photodetector, and the RF signal is synchronously demodulated with a lock-in amplifier by referring to a cosine wave signal from the oscillator. We theoretically and experimentally demonstrate that the lock-in amplifier signal for the transmitted or reflected light becomes null with a steep slope when the modulation frequency is equal to the FSR under the condition that the carrier frequency of the laser is slightly detuned from the resonance of the FP-cavity. To reduce the measurement uncertainty for the FSR, we also discuss a selection method for laser power, a modulation index and the detuning shift of the carrier frequency, respectively.

Growth of a New Ternary BON Crystal on Si(100) by Plasma-Assisted MOCVD and Study on the Effects of Fed Gas and Growth Temperature

NASA Astrophysics Data System (ADS)

Chen, G. C.; Lee, S.-B.; Boo, J.-H.

A new ternary BOxNy crystal was grown on Si(100) substrate at 500°C by low-frequency (100 kHz) radio-frequency (rf) derived plasma-assisted MOCVD with an organoborate precursor. The as-grown deposits were characterized by SEM, TED, XPS, XRD, AFM and FT-IR. The experimental results showed that BOxNy crystal was apt to be formed at N-rich atmosphere and high temperature. The decrease of hydrogen flux in fed gases was of benefit to form BON crystal structure. The crystal structure of BOxNy was as similar to that of H3BO3 in this study.

An assessment of envelope-based demodulation in case of proximity of carrier and modulation frequencies

NASA Astrophysics Data System (ADS)

Shahriar, Md Rifat; Borghesani, Pietro; Randall, R. B.; Tan, Andy C. C.

2017-11-01

Demodulation is a necessary step in the field of diagnostics to reveal faults whose signatures appear as an amplitude and/or frequency modulation. The Hilbert transform has conventionally been used for the calculation of the analytic signal required in the demodulation process. However, the carrier and modulation frequencies must meet the conditions set by the Bedrosian identity for the Hilbert transform to be applicable for demodulation. This condition, basically requiring the carrier frequency to be sufficiently higher than the frequency of the modulation harmonics, is usually satisfied in many traditional diagnostic applications (e.g. vibration analysis of gear and bearing faults) due to the order-of-magnitude ratio between the carrier and modulation frequency. However, the diversification of the diagnostic approaches and applications shows cases (e.g. electrical signature analysis-based diagnostics) where the carrier frequency is in close proximity to the modulation frequency, thus challenging the applicability of the Bedrosian theorem. This work presents an analytic study to quantify the error introduced by the Hilbert transform-based demodulation when the Bedrosian identity is not satisfied and proposes a mitigation strategy to combat the error. An experimental study is also carried out to verify the analytical results. The outcome of the error analysis sets a confidence limit on the estimated modulation (both shape and magnitude) achieved through the Hilbert transform-based demodulation in case of violated Bedrosian theorem. However, the proposed mitigation strategy is found effective in combating the demodulation error aroused in this scenario, thus extending applicability of the Hilbert transform-based demodulation.

Cerenkov emissions of ion acoustic-like waves generated by electron beams emitted during TSS 1R

NASA Astrophysics Data System (ADS)

Huang, C. Y.; Burke, W. J.; Hardy, D. A.; Gough, M. P.; Olson, D. G.; Gentile, L. C.; Gilchrist, B. E.; Bonifazi, C.; Raitt, W. J.; Thompson, D. C.

During the Tethered Satellite System reflight the Spacecraft Particle Correlation Experiment detected fluxes of energetic electrons and ions that were simultaneously modulated at low frequencies during firings of both the fast pulsed electron gun (FPEG) and the electron generator assembly (EGA). The modulations have been interpreted as signatures of large-amplitude, ion acoustic-like waves excited in Cerenkov interactions between electron beams and ambient plasmas as the shuttle moved at supersonic speeds across the ionospheric magnetic field. We present examples of particle modulations observed during steady beam emissions. Measurements show that (1) most electron modulations were at frequencies of several hundred Hertz and (2) ions modulated at similar frequencies appeared at spectral energy peaks during shuttle negative charging events. Detection of modulated ion fluxes confirms the Cerenkov emission hypothesis. Observed frequency variations indicate that the EGA beam underwent more spatial spreading than the FPEG beam.

High frequency modulation and injection locking of terahertz quantum cascade lasers

NASA Astrophysics Data System (ADS)

Gu, L.; Wan, W. J.; Zhu, Y. H.; Fu, Z. L.; Li, H.; Cao, J. C.

2017-06-01

Due to intersubband transitions, the quantum cascade laser (QCL) is free of relaxations and able to work under fast modulations. In this work, the authors investigate the fast modulation properties of a continuous wave (cw) terahertz QCL emitting around 3 THz (˜100 μm). Both simulation and experimental results show that the 3 dB modulation bandwidth for the device can reach 11.5 GHz and the modulation response curve is relatively flat upto ˜16 GHz. The radio frequency (RF) injection measurements verify that around the laser threshold the inter-mode beat note interacts strongly with the RF signal and the laser can be modulated at the round trip frequency of 15.5 GHz.

Multi-frequency tapping-mode atomic force microscopy beyond three eigenmodes in ambient air

PubMed Central

An, Sangmin; Long, Christian J

2014-01-01

Summary We present an exploratory study of multimodal tapping-mode atomic force microscopy driving more than three cantilever eigenmodes. We present tetramodal (4-eigenmode) imaging experiments conducted on a thin polytetrafluoroethylene (PTFE) film and computational simulations of pentamodal (5-eigenmode) cantilever dynamics and spectroscopy, focusing on the case of large amplitude ratios between the fundamental eigenmode and the higher eigenmodes. We discuss the dynamic complexities of the tip response in time and frequency space, as well as the average amplitude and phase response. We also illustrate typical images and spectroscopy curves and provide a very brief description of the observed contrast. Overall, our findings are promising in that they help to open the door to increasing sophistication and greater versatility in multi-frequency AFM through the incorporation of a larger number of driven eigenmodes, and in highlighting specific future research opportunities. PMID:25383276

Strain Manipulated Magnetic Properties in ZnO and GaN Induced by Cation Vacancy

NASA Astrophysics Data System (ADS)

Gai, Yanqin; Jiang, Jiaping; Wu, Yuxi; Tang, Gang

2016-07-01

The effects of isotropic strains on the magnetic properties in ZnO and GaN induced by cation vacancies are comparatively investigated by density functional theory calculations. The magnetic moments and the couplings between vacancies in different charged states are calculated as a function of strains. The modulation of strain on the magnetic properties relies on the materials and the charge states of cation vacancies in them. As the occurrence of charge transfer in ZnO: V Zn under compression, the coupling between V_{{Zn}}0 is antiferromagnetic (AFM) and it could be stabilized by strains. Tensions can strengthen the ferromagnetic (FM) coupling between V_{{Zn}}0 but weaken that of V_{{Ga}}^{ - } . The neutral V Ga are always AFM coupling under strains from -6 to +6% and could be stabilized by compressions. The interactions between V_{{Ga}}^{ - } are always FM with ignorable variations under strains; however, the FM couplings between V_{{Ga}}^{2 - } could be strengthened by compressions. These varying trends of magnetic coupling under strains are interpreted by the band coupling models. Therefore, strain-engineering provides a route to manipulate and design high Curie temperature ferromagnetism derived and mediated by intrinsic defect for spintronic applications.

Visualizing molecular polar order in tissues via electromechanical coupling

PubMed Central

Denning, Denise; Alilat, Sofiane; Habelitz, Stefan; Fertala, Andrzej; Rodriguez, Brian J.

2015-01-01

Electron microscopy (EM) and atomic force microscopy (AFM) techniques have long been used to characterize collagen fibril ordering and alignment in connective tissues. These techniques, however, are unable to map collagen fibril polarity, i.e., the polar orientation that is directed from the amine to the carboxyl termini. Using a voltage modulated AFM-based technique called piezoresponse force microscopy (PFM), we show it is possible to visualize both the alignment of collagen fibrils within a tissue and the polar orientation of the fibrils with minimal sample preparation. We demonstrate the technique on rat tail tendon and porcine eye tissues in ambient conditions. In each sample, fibrils are arranged into domains whereby neighboring domains exhibit opposite polarizations, which in some cases extend to the individual fibrillar level. Uniform polarity has not been observed in any of the tissues studied. Evidence of anti-parallel ordering of the amine to carboxyl polarity in bundles of fibrils or in individual fibrils is found in all tissues, which has relevance for understanding mechanical and biofunctional properties and the formation of connective tissues. The technique can be applied to any biological material containing piezoelectric biopolymers or polysaccharides. PMID:22985991

Preparation and mechanical properties of layers made of recombinant spider silk proteins and silk from silk worm

NASA Astrophysics Data System (ADS)

Junghans, F.; Morawietz, M.; Conrad, U.; Scheibel, T.; Heilmann, A.; Spohn, U.

2006-02-01

Layers of recombinant spider silks and native silks from silk worms were prepared by spin-coating and casting of various solutions. FT-IR spectra were recorded to investigate the influence of the different mechanical stress occurring during the preparation of the silk layers. The solubility of the recombinant spider silk proteins SO1-ELP, C16, AQ24NR3, and of the silk fibroin from Bombyx mori were investigated in hexafluorisopropanol, ionic liquids and concentrated salt solutions. The morphology and thickness of the layers were determined by Atomic Force Microscopy (AFM) or with a profilometer. The mechanical behaviour was investigated by acoustic impedance analysis by using a quartz crystal microbalance (QCMB) as well as by microindentation. The density of silk layers (d<300 nm) was determined based on AFM and QCMB measurements. At silk layers thicker than 300 nm significant changes of the half-band-half width can be correlated with increasing energy dissipation. Microhardness measurements demonstrate that recombinant spider silk and sericine-free Bombyx mori silk layers achieve higher elastic penetration modules EEP and Martens hardness values HM than those of polyethylenterephthalate (PET) and polyetherimide (PEI) foils.

Transcranial alternating current stimulation modulates auditory temporal resolution in elderly people.

PubMed

Baltus, Alina; Vosskuhl, Johannes; Boetzel, Cindy; Herrmann, Christoph Siegfried

2018-05-13

Recent research provides evidence for a functional role of brain oscillations for perception. For example, auditory temporal resolution seems to be linked to individual gamma frequency of auditory cortex. Individual gamma frequency not only correlates with performance in between-channel gap detection tasks but can be modulated via auditory transcranial alternating current stimulation. Modulation of individual gamma frequency is accompanied by an improvement in gap detection performance. Aging changes electrophysiological frequency components and sensory processing mechanisms. Therefore, we conducted a study to investigate the link between individual gamma frequency and gap detection performance in elderly people using auditory transcranial alternating current stimulation. In a within-subject design, twelve participants were electrically stimulated with two individualized transcranial alternating current stimulation frequencies: 3 Hz above their individual gamma frequency (experimental condition) and 4 Hz below their individual gamma frequency (control condition) while they were performing a between-channel gap detection task. As expected, individual gamma frequencies correlated significantly with gap detection performance at baseline and in the experimental condition, transcranial alternating current stimulation modulated gap detection performance. In the control condition, stimulation did not modulate gap detection performance. In addition, in elderly, the effect of transcranial alternating current stimulation on auditory temporal resolution seems to be dependent on endogenous frequencies in auditory cortex: elderlies with slower individual gamma frequencies and lower auditory temporal resolution profit from auditory transcranial alternating current stimulation and show increased gap detection performance during stimulation. Our results strongly suggest individualized transcranial alternating current stimulation protocols for successful modulation of performance. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

AFM 4.0: a toolbox for DNA microarray analysis

PubMed Central

Breitkreutz, Bobby-Joe; Jorgensen, Paul; Breitkreutz, Ashton; Tyers, Mike

2001-01-01

We have developed a series of programs, collectively packaged as Array File Maker 4.0 (AFM), that manipulate and manage DNA microarray data. AFM 4.0 is simple to use, applicable to any organism or microarray, and operates within the familiar confines of Microsoft Excel. Given a database of expression ratios, AFM 4.0 generates input files for clustering, helps prepare colored figures and Venn diagrams, and can uncover aneuploidy in yeast microarray data. AFM 4.0 should be especially useful to laboratories that do not have access to specialized commercial or in-house software. PMID:11532221

Interactions between amplitude modulation and frequency modulation processing: Effects of age and hearing loss.

PubMed

Paraouty, Nihaad; Ewert, Stephan D; Wallaert, Nicolas; Lorenzi, Christian

2016-07-01

Frequency modulation (FM) and amplitude modulation (AM) detection thresholds were measured for a 500-Hz carrier frequency and a 5-Hz modulation rate. For AM detection, FM at the same rate as the AM was superimposed with varying FM depth. For FM detection, AM at the same rate was superimposed with varying AM depth. The target stimuli always contained both amplitude and frequency modulations, while the standard stimuli only contained the interfering modulation. Young and older normal-hearing listeners, as well as older listeners with mild-to-moderate sensorineural hearing loss were tested. For all groups, AM and FM detection thresholds were degraded in the presence of the interfering modulation. AM detection with and without interfering FM was hardly affected by either age or hearing loss. While aging had an overall detrimental effect on FM detection with and without interfering AM, there was a trend that hearing loss further impaired FM detection in the presence of AM. Several models using optimal combination of temporal-envelope cues at the outputs of off-frequency filters were tested. The interfering effects could only be predicted for hearing-impaired listeners. This indirectly supports the idea that, in addition to envelope cues resulting from FM-to-AM conversion, normal-hearing listeners use temporal fine-structure cues for FM detection.

Systems and methods for selective detection and imaging in coherent Raman microscopy by spectral excitation shaping

DOEpatents

Xie, Xiaoliang Sunney; Freudiger, Christian; Min, Wei

2016-03-15

A microscopy imaging system is disclosed that includes a light source system, a spectral shaper, a modulator system, an optics system, an optical detector and a processor. The light source system is for providing a first train of pulses and a second train of pulses. The spectral shaper is for spectrally modifying an optical property of at least some frequency components of the broadband range of frequency components such that the broadband range of frequency components is shaped producing a shaped first train of pulses to specifically probe a spectral feature of interest from a sample, and to reduce information from features that are not of interest from the sample. The modulator system is for modulating a property of at least one of the shaped first train of pulses and the second train of pulses at a modulation frequency. The optical detector is for detecting an integrated intensity of substantially all optical frequency components of a train of pulses of interest transmitted or reflected through the common focal volume. The processor is for detecting a modulation at the modulation frequency of the integrated intensity of substantially all of the optical frequency components of the train of pulses of interest due to the non-linear interaction of the shaped first train of pulses with the second train of pulses as modulated in the common focal volume, and for providing an output signal for a pixel of an image for the microscopy imaging system.

47 CFR 90.242 - Travelers' information stations.

Code of Federal Regulations, 2010 CFR

2010-10-01

... the modulation limiter and the modulated stage. At audio frequencies between 3 kHz and 20 kHz this...' information stations. (a) The frequencies 530 through 1700 kHz in 10 kHz increments may be assigned to the... consideration of possible cross-modulation and inter-modulation interference effects which may result from the...

Beam-induced electron modulations observed during TSS 1R

NASA Astrophysics Data System (ADS)

Rubin, A. G.; Burke, W. J.; Gough, M. P.; Machuzak, J. S.; Gentile, L. C.; Huang, C. Y.; Hardy, D. A.; Thompson, D. C.; Raitt, W. J.

1999-08-01

We report on modulations of electron fluxes at megahertz frequencies measured by the Shuttle Potential and Return Electron Experiment (SPREE) during fast pulsed electron gun (FPEG) beam experiments conducted after the tether break event of the Tethered Satellite System Reflight. Six intervals of sustained modulations were identified while FPEG emitted a 100 mA beam of 1 kev electrons. During five events the beam pitch angle αB was near 90° and the modulations were near even or odd half harmonics of the electron gyrofrequency fce. In the sixth event with 60°>=αB>=45°, electron modulations were near estimated values of the electron plasma frequency fpe and 2fpe. Whenever SPREE detected beam electrons modulated at a given frequency, secondary electrons were also modulated at the same frequency over a broad range of energies. Occasionally, some secondary electrons were modulated simultaneously at a second frequency. Multiple frequencies were related as ratios of low integers. In one case the beam electrons were simultaneously modulated at 0.8 MHz and 1.25 kHz. SPREE measurements suggest that the beam electrons propagate in cylindrical shells whose inner edge is marked by steep spatial gradients in fluxes at 1 keV [Hardy et al., 1995]. Inside the shell, electron distribution functions have positive slopes ∂f/∂v⊥>0 at velocities near that of the beam. Velocity space gradients act as free-energy sources to drive cavity modes that alter the instantaneous guiding centers of electrons causing SPREE to sample alternating parts of the beam cylinder's inner edge. Associated time-varying electric fields also modulated the fluxes of secondary electrons reaching SPREE. Other cavity modes may be excited through nonlinear processes [Calvert, 1982]. With αB far from 90°, electrons in the beam cylinder evolved toward bump-on-tail distributions to excite large-amplitude Langmuir modulations at fpe and its harmonics [Klimas, 1983]. Low-frequency modulations are attributed to electron interactions with ion acoustic-like waves generated as the beam moved across magnetic field lines in the ionosphere at supersonic speeds.

Optimum Detection Of Slow-Frequency-Hopping Signals

NASA Technical Reports Server (NTRS)

Levitt, Barry K.; Cheng, Unjeng

1994-01-01

Two papers present theoretical analyses of various schemes for coherent and noncoherent detection of M-ary-frequency-shift-keyed (MFSK) signals with slow frequency hopping. Special attention focused on continuous-phase-modulation (CPM) subset of SFH/MFSK signals, for which frequency modulation such carrier phase remains continuous (albeit unknown) during each hop.

Single cell active force generation under dynamic loading - Part I: AFM experiments.

PubMed

Weafer, P P; Reynolds, N H; Jarvis, S P; McGarry, J P

2015-11-01

A novel series of experiments are performed on single cells using a bespoke AFM system where the response of cells to dynamic loading at physiologically relevant frequencies is uncovered. Measured forces for the untreated cells are dramatically different to cytochalasin-D (cyto-D) treated cells, indicating that the contractile actin cytoskeleton plays a critical role in the response of cells to dynamic loading. Following a change in applied strain magnitude, while maintaining a constant applied strain rate, the compression force for contractile cells recovers to 88.9±7.8% of the steady state force. In contrast, cyto-D cell compression forces recover to only 38.0±6.7% of the steady state force. Additionally, untreated cells exhibit strongly negative (pulling) forces during unloading half-cycles when the probe is retracted. In comparison, negligible pulling forces are measured for cyto-D cells during probe retraction. The current study demonstrates that active contractile forces, generated by actin-myosin cross-bridge cycling, dominate the response of single cells to dynamic loading. Such active force generation is shown to be independent of applied strain magnitude. Passive forces generated by the applied deformation are shown to be of secondary importance, exhibiting a high dependence on applied strain magnitude, in contrast to the active forces in untreated cells. A novel series of experiments are performed on single cells using a bespoke AFM system where the response of cells to dynamic loading at physiologically relevant frequencies is uncovered. Contractile cells, which contain the active force generation machinery of the actin cytoskeleton, are shown to be insensitive to applied strain magnitude, exhibiting high resistance to dynamic compression and stretching. Such trends are not observed for cells in which the actin cytoskeleton has been chemically disrupted. These biomechanical insights have not been previously reported. This detailed characterisation of single cell active and passive stress during dynamic loading has important implications for tissue engineering strategies, where applied deformation has been reported to significantly affect cell mechanotransduction and matrix synthesis. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Ac electronic tunneling at optical frequencies

NASA Technical Reports Server (NTRS)

Faris, S. M.; Fan, B.; Gustafson, T. K.

1974-01-01

Rectification characteristics of non-superconducting metal-barrier-metal junctions deduced from electronic tunneling have been observed experimentally for optical frequency irradiation of the junction. The results provide verification of optical frequency Fermi level modulation and electronic tunneling current modulation.

High current nonlinear transmission line based electron beam driver

NASA Astrophysics Data System (ADS)

Hoff, B. W.; French, D. M.; Simon, D. S.; Lepell, P. D.; Montoya, T.; Heidger, S. L.

2017-10-01

A gigawatt-class nonlinear transmission line based electron beam driver is experimentally demonstrated. Four experimental series, each with a different Marx bank charge voltage (15, 20, 25, and 30 kV), were completed. Within each experimental series, shots at peak frequencies ranging from 950 MHz to 1.45 GHz were performed. Peak amplitude modulations of the NLTL output voltage signal were found to range between 18% and 35% for the lowest frequency shots and between 5% and 20% for the highest frequency shots (higher modulation at higher Marx charge voltage). Peak amplitude modulations of the electron beam current were found to range between 10% and 20% for the lowest frequency shots and between 2% and 7% for the highest frequency shots (higher modulation at higher Marx charge voltage).

Frequency range selection method of trans-impedance amplifier for high sensitivity lock-in amplifier used in the optical sensors

NASA Astrophysics Data System (ADS)

Park, Chang-In; Jeon, Su-Jin; Hong, Nam-Pyo; Choi, Young-Wan

2016-03-01

Lock-in amplifier (LIA) has been proposed as a detection technique for optical sensors because it can measure low signal in high noise level. LIA uses synchronous method, so the input signal frequency is locked to a reference frequency that is used to carry out the measurements. Generally, input signal frequency of LIA used in optical sensors is determined by modulation frequency of optical signal. It is important to understand the noise characteristics of the trans-impedance amplifier (TIA) to determine the modulation frequency. The TIA has a frequency range in which noise is minimized by the capacitance of photo diode (PD) and the passive component of TIA feedback network. When the modulation frequency is determined in this range, it is possible to design a robust system to noise. In this paper, we propose a method for the determination of optical signal modulation frequency selection by using the noise characteristics of TIA. Frequency response of noise in TIA is measured by spectrum analyzer and minimum noise region is confirmed. The LIA and TIA circuit have been designed as a hybrid circuit. The optical sensor is modeled by the laser diode (LD) and photo diode (PD) and the modulation frequency was used as the input to the signal generator. The experiments were performed to compare the signal to noise ratio (SNR) of the minimum noise region and the others. The results clearly show that the SNR is enhanced in the minimum noise region of TIA.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sivasakthi, P.; Sekar, R.; Bapu, G.N.K.Ramesh, E-mail: bapu2657@yahoo.com

Highlights: • Nickel deposits from sulphamate solutions using pulse method are prepared. • Effect of duty cycle and frequency are studied. • XRD, SEM and AFM of the nickel deposits are characterized. • Corrosion characteristics of the nickel deposit are reported. - Abstract: Nickel deposits have been obtained on mild steel substrate by pulse current (PC) electrodeposition method using nickel sulphamate electrolyte. Micro hardness values increased with decreasing duty cycle and pulse frequency. X-ray diffraction studies revealed that (2 0 0) plane was predominant and the nickel deposit obtained at low duty cycle and low frequency has the smallest grainmore » size. The surface morphology of the coatings was explored by scanning electron microscopy (SEM) and atomic force microscopy. These studies showed that the microstructure of the nickel coatings changed from pyramidal structure to homogeneous structure with increasing duty cycle and pulse frequencies. The corrosion resistance of coatings was evaluated by potentiodynamic polarization and electrochemical impedance studies in 3.5 wt% sodium chloride (NaCl) solutions. An enhancement of the corrosion resistance, charge-transfer resistance and wear resistance has been obtained at low duty cycle and low frequencies.« less

Intrinsic and extrinsic dielectric responses of CaCu3Ti4O12 thin films

NASA Astrophysics Data System (ADS)

Rubinger, C. P. L.; Moreira, R. L.; Ribeiro, G. M.; Matinaga, F. M.; Autier Laurent, S.; Mercey, B.; Lobo, R. P. S. M.

2011-10-01

CaCu3Ti4O12 thin films were epitaxially grown on (001) LaAlO3 substrates by pulsed laser deposition under optimized growth conditions. The crystal structure and sample morphology were characterized by x-ray diffraction, AFM, TEM, ellipsometry, and Raman spectroscopy. The dielectric responses of the films were investigated in a large temperature range (5 to 375 K) by infrared reflectivity and impedance spectroscopies. The films exhibited a colossal dielectric response, with the dielectric permittivity reaching 104 at 100 Hz. The results obtained in a broad frequency range allowed us to investigate the behavior of intrinsic and extrinsic dielectric responses of this material. The room temperature centrosymmetrical cubic structure remains stable down to 5 K, though softening of the lower frequency infrared phonon modes indicates an incipient ferroelectric character. The radio frequency dielectric response reveals two relaxations of extrinsic origin, a primary higher frequency relaxation responsible for the colossal dielectric behavior and a secondary one of lower frequency. The activation energies of these processes are compatible with the presence of shallow defect levels created by oxygen vacancies.

Advanced Digital Signal Processing for Hybrid Lidar

DTIC Science & Technology

2014-10-30

obtain range measurements . A MATLAB- based system developed at Clarkson University in FY14 has been used to perform real-time FDR ranging... measurement accuracy. There have been various methods that attempt to reduce the backscatter. One method is to increase the modulation frequency beyond...an unambiguous range measurement . In general, it is desired to determine which combination of Radio Frequency (RF) modulation frequencies, modulation

Multicarrier orthogonal spread-spectrum (MOSS) data communications

DOEpatents

Smith, Stephen F [London, TN; Dress, William B [Camas, WA

2008-01-01

Systems and methods are described for multicarrier orthogonal spread-spectrum (MOSS) data communication. A method includes individually spread-spectrum modulating at least two of a set of orthogonal frequency division multiplexed carriers, wherein the resulting individually spread-spectrum modulated at least two of a set of orthogonal frequency division multiplexed carriers are substantially mutually orthogonal with respect to both frequency division multiplexing and spread-spectrum modulation.

Spectrum Control through Discrete Frequency Diffraction in the Presence of Photonic Gauge Potentials

NASA Astrophysics Data System (ADS)

Qin, Chengzhi; Zhou, Feng; Peng, Yugui; Sounas, Dimitrios; Zhu, Xuefeng; Wang, Bing; Dong, Jianji; Zhang, Xinliang; Alù; , Andrea; Lu, Peixiang

2018-03-01

By using optical phase modulators in a fiber-optical circuit, we theoretically and experimentally demonstrate large control over the spectrum of an impinging signal, which may evolve analogously to discrete diffraction in spatial waveguide arrays. The modulation phase acts as a photonic gauge potential in the frequency dimension, realizing efficient control of the central frequency and bandwidth of frequency combs. We experimentally achieve a 50 GHz frequency shift and threefold bandwidth expansion of an impinging comb, as well as the frequency analogue of various refraction phenomena, including negative refraction and perfect focusing in the frequency domain, both for discrete and continuous incident spectra. Our study paves a promising way towards versatile frequency management for optical communications and signal processing using time modulation schemes.

Effects of single cycle binaural beat duration on auditory evoked potentials.

PubMed

Mihajloski, Todor; Bohorquez, Jorge; Özdamar, Özcan

2014-01-01

Binaural beat (BB) illusions are experienced as continuous central pulsations when two sounds with slightly different frequencies are delivered to each ear. It has been shown that steady-state auditory evoked potentials (AEPs) to BBs can be captured and investigated. The authors recently developed a new method of evoking transient AEPs to binaural beats using frequency modulated stimuli. This methodology was able to create single BBs in predetermined intervals with varying carrier frequencies. This study examines the effects of the BB duration and the frequency modulating component of the stimulus on the binaural beats and their evoked potentials. Normal hearing subjects were tested with a set of four durations (25, 50, 100, and 200 ms) with two stimulation configurations, binaural dichotic (binaural beats) and diotic (frequency modulation). The results obtained from the study showed that out of the given durations, the 100 ms beat, was capable of evoking the largest amplitude responses. The frequency modulation effect showed a decrease in peak amplitudes with increasing beat duration until their complete disappearance at 200 ms. Even though, at 200 ms, the frequency modulation effects were not present, the binaural beats were still perceived and captured as evoked potentials.

Adhesion between peptides/antibodies and breast cancer cells

NASA Astrophysics Data System (ADS)

Meng, J.; Paetzell, E.; Bogorad, A.; Soboyejo, W. O.

2010-06-01

Atomic force microscopy (AFM) techniques were used to measure the adhesion forces between the receptors on breast cancer cells specific to human luteinizing hormone-releasing hormone (LHRH) peptides and antibodies specific to the EphA2 receptor. The adhesion forces between LHRH-coated AFM tips and human MDA-MB-231 cells (breast cancer cells) were shown to be about five times greater than those between LHRH-coated AFM tips and normal Hs578Bst breast cells. Similarly, those between EphA2 antibody-coated AFM tips and breast cancer cells were over five times greater than those between EphA2 antibody-coated AFM tips and normal breast cells. The results suggest that AFM can be used for the detection of breast cancer cells in biopsies. The implications of the results are also discussed for the early detection and localized treatment of cancer.

Measuring bacterial cells size with AFM

PubMed Central

Osiro, Denise; Filho, Rubens Bernardes; Assis, Odilio Benedito Garrido; Jorge, Lúcio André de Castro; Colnago, Luiz Alberto

2012-01-01

Atomic Force Microscopy (AFM) can be used to obtain high-resolution topographical images of bacteria revealing surface details and cell integrity. During scanning however, the interactions between the AFM probe and the membrane results in distortion of the images. Such distortions or artifacts are the result of geometrical effects related to bacterial cell height, specimen curvature and the AFM probe geometry. The most common artifact in imaging is surface broadening, what can lead to errors in bacterial sizing. Several methods of correction have been proposed to compensate for these artifacts and in this study we describe a simple geometric model for the interaction between the tip (a pyramidal shaped AFM probe) and the bacterium (Escherichia coli JM-109 strain) to minimize the enlarging effect. Approaches to bacteria immobilization and examples of AFM images analysis are also described. PMID:24031837

Modulation characteristics of a high-power semiconductor Master Oscillator Power Amplifier (MOPA)

NASA Technical Reports Server (NTRS)

Cornwell, Donald Mitchell, Jr.

1992-01-01

A semiconductor master oscillator-power amplifier was demonstrated using an anti-reflection (AR) coated broad area laser as the amplifier. Under CW operation, diffraction-limited single-longitudinal-mode powers up to 340 mW were demonstrated. The characteristics of the far-field pattern were measured and compared to a two-dimensional reflective Fabry-Perot amplifier model of the device. The MOPA configuration was modulated by the master oscillator. Prior to injection into the amplifier, the amplitude and frequency modulation properties of the master oscillator were characterized. The frequency response of the MOPA configuration was characterized for an AM/FM modulated injection beam, and was found to be a function of the frequency detuning between the master oscillator and the resonant amplifier. A shift in the phase was also observed as a function of frequency detuning; this phase shift is attributed to the optical phase shift imparted to a wave reflected from a Fabry-Perot cavity. Square-wave optical pulses were generated at 10 MHz and 250 MHz with diffraction-limited peak powers of 200 mW and 250 mW. The peak power for a given modulation frequency is found to be limited by the injected power and the FM modulation at that frequency. The modulation results make the MOPA attractive for use as a transmitter source in applications such as free-space communications and ranging/altimetry.

Programmable formation of catalytic RNA triangles and squares by assembling modular RNA enzymes.

PubMed

Oi, Hiroki; Fujita, Daisuke; Suzuki, Yuki; Sugiyama, Hiroshi; Endo, Masayuki; Matsumura, Shigeyoshi; Ikawa, Yoshiya

2017-05-01

RNA is a biopolymer that is attractive for constructing nano-scale objects with complex structures. Three-dimensional (3D) structures of naturally occurring RNAs often have modular architectures. The 3D structure of a group I (GI) ribozyme from Tetrahymena has a typical modular architecture, which can be separated into two structural modules (ΔP5 and P5abc). The fully active ribozyme can be reconstructed by assembling the two separately prepared modules through highly specific and strong assembly between ΔP5 ribozyme and P5abc RNA. Such non-covalent assembly of the two modules allows the design of polygonal RNA nano-structures. Through rational redesign of the parent GI ribozyme, we constructed variant GI ribozymes as unit RNAs for polygonal-shaped (closed) oligomers with catalytic activity. Programmed trimerization and tetramerization of the unit RNAs afforded catalytically active nano-sized RNA triangles and squares, the structures of which were directly observed by atomic force microscopy (AFM). © The Authors 2017. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.

Bi-Frequency Modulated Quasi-Resonant Converters: Theory and Applications

NASA Astrophysics Data System (ADS)

Zhang, Yuefeng

1995-01-01

To avoid the variable frequency operation of quasi -resonant converters, many soft-switching PWM converters have been proposed, all of them require an auxiliary switch, which will increase the cost and complexity of the power supply system. In this thesis, a new kind of technique for quasi -resonant converters has been proposed, which is called the bi-frequency modulation technique. By operating the quasi-resonant converters at two switching frequencies, this technique enables quasi-resonant converters to achieve the soft-switching, at fixed switching frequencies, without an auxiliary switch. The steady-state analysis of four commonly used quasi-resonant converters, namely, ZVS buck, ZCS buck, ZVS boost, and ZCS boost converter has been presented. Using the concepts of equivalent sources, equivalent sinks, and resonant tank, the large signal models of these four quasi -resonant converters were developed. Based on these models, the steady-state control characteristics of BFM ZVS buck, BFM ZCS buck, BFM ZVS boost, and BFM ZCS boost converter have been derived. The functional block and design consideration of the bi-frequency controller were presented, and one of the implementations of the bi-frequency controller was given. A complete design example has been presented. Both computer simulations and experimental results have verified that the bi-frequency modulated quasi-resonant converters can achieve soft-switching, at fixed switching frequencies, without an auxiliary switch. One of the application of bi-frequency modulation technique is for EMI reduction. The basic principle of using BFM technique for EMI reduction was introduced. Based on the spectral analysis, the EMI performances of the PWM, variable-frequency, and bi-frequency modulated control signals was evaluated, and the BFM control signals show the lowest EMI emission. The bi-frequency modulated technique has also been applied to the power factor correction. A BFM zero -current switching boost converter has been designed for the power factor correction, and the simulation results show that the power factor has been improved.

A practical implementation of multi-frequency widefield frequency-domain FLIM

PubMed Central

Chen, Hongtao

2013-01-01

Widefield frequency-domain fluorescence lifetime imaging microscopy (FD-FLIM) is a fast and accurate method to measure the fluorescence lifetime, especially in kinetic studies in biomedical researches. However, the small range of modulation frequencies available in commercial instruments makes this technique limited in its applications. Here we describe a practical implementation of multi-frequency widefield FD-FLIM using a pulsed supercontinuum laser and a direct digital synthesizer. In this instrument we use a pulse to modulate the image intensifier rather than the more conventional sine wave modulation. This allows parallel multi-frequency FLIM measurement using the Fast Fourier Transform and the cross-correlation technique, which permits precise and simultaneous isolation of individual frequencies. In addition, the pulse modulation at the cathode of image intensifier restored the loss of optical resolution caused by the defocusing effect when the voltage at the cathode is sinusoidally modulated. Furthermore, in our implementation of this technique, data can be graphically analyzed by the phasor method while data are acquired, which allows easy fit-free lifetime analysis of FLIM images. Here our measurements of standard fluorescent samples and a Föster resonance energy transfer pair demonstrate that the widefield multi-frequency FLIM system is a valuable and simple tool in fluorescence imaging studies. PMID:23296945

Modulated Source Interferometry with Combined Amplitude and Frequency Modulation

NASA Technical Reports Server (NTRS)

Gutierrez, Roman C. (Inventor)

1998-01-01

An improved interferometer is produced by modifying a conventional interferometer to include amplitude and/or frequency modulation of a coherent light source at radio or higher frequencies. The phase of the modulation signal can be detected in an interfering beam from an interferometer and can be used to determine the actual optical phase of the beam. As such, this improvement can be adapted to virtually any two-beam interferometer, including: Michelson, Mach-Zehnder, and Sagnac interferometers. The use of an amplitude modulated coherent tight source results in an interferometer that combines the wide range advantages of coherent interferometry with the precise distance measurement advantages of white light interferometry.

Vibrotactile sensory substitution for object manipulation: amplitude versus pulse train frequency modulation.

PubMed

Stepp, Cara E; Matsuoka, Yoky

2012-01-01

Incorporating sensory feedback with prosthetic devices is now possible, but the optimal methods of providing such feedback are still unknown. The relative utility of amplitude and pulse train frequency modulated stimulation paradigms for providing vibrotactile feedback for object manipulation was assessed in 10 participants. The two approaches were studied during virtual object manipulation using a robotic interface as a function of presentation order and a simultaneous cognitive load. Despite the potential pragmatic benefits associated with pulse train frequency modulated vibrotactile stimulation, comparison of the approach with amplitude modulation indicates that amplitude modulation vibrotactile stimulation provides superior feedback for object manipulation.

Studies of chain substitution caused sub-fibril level differences in stiffness and ultrastructure of wildtype and oim/oim collagen fibers using multifrequency-AFM and molecular modeling.

PubMed

Li, Tao; Chang, Shu-Wei; Rodriguez-Florez, Naiara; Buehler, Markus J; Shefelbine, Sandra; Dao, Ming; Zeng, Kaiyang

2016-11-01

Molecular alteration in type I collagen, i.e., substituting the α2 chain with α1 chain in tropocollagen molecule, can cause osteogenesis imperfecta (OI), a brittle bone disease, which can be represented by a mouse model (oim/oim). In this work, we use dual-frequency Atomic Force Microscopy (AFM) and incorporated with molecular modeling to quantify the ultrastructure and stiffness of the individual native collagen fibers from wildtype (+/+) and oim/oim diseased mice humeri. Our work presents direct experimental evidences that the +/+ fibers have highly organized and compact ultrastructure and corresponding ordered stiffness distribution. In contrast, oim/oim fibers have ordered but loosely packed ultrastructure with uncorrelated stiffness distribution, as well as local defects. The molecular model also demonstrates the structural and molecular packing differences between +/+ and oim/oim collagens. The molecular mutation significantly altered sub-fibril structure and mechanical property of collagen fibers. This study can give the new insight for the mechanisms and treatment of the brittle bone disease. Copyright © 2016 Elsevier Ltd. All rights reserved.

Universal aspects of sonolubrication in amorphous and crystalline materials

NASA Astrophysics Data System (ADS)

Pfahl, V.; Ma, C.; Arnold, W.; Samwer, K.

2018-01-01

We studied sonolubricity, a phenomenon reducing the friction between two sliding surfaces by ultrasound. Friction force measurements were performed using an atomic force microscope (AFM) when the tip-surface contact was excited to out-of-plane oscillations by a transducer attached to the rear of the sample or by oscillating the AFM cantilever by the built-in piezoelectric element in the cantilever holder. Experiments were carried out near or at the first cantilever contact-resonance. We studied friction on crystalline and amorphous Pd77.5Cu6Si16.5 ribbons, on a silicon wafer at room temperature, and on a La0.6Sr0.4MnO3 (LSMO) thin film at different temperatures. Measurements were carried out varying the cantilever amplitude, the ultrasonic frequency, and the normal static load. The effect of sonolubrication is explained by the non-linear force-distance curve between the sample and the tip due to the local interaction potential. The reduction of friction in LSMO as a function temperature is due to the direct coupling of the tip's stress-field to the electrons.

Morphology and inhibition performance of Ag thin film as antimicrobial coating deposited by RF-PVD on 316 L stainless steel

NASA Astrophysics Data System (ADS)

Purniawan, A.; Khrisna, Y. S. A.; Rasyida, A.; Atmono, T. M.

2018-04-01

Foreign body related infection (FBRIs) is caused by forming biofilm of bacterial colony of medical equipment surfaces. In many cases, the FBRIs is still happened on the surface after medical sterilization process has been performed. In order to avoid the case, surface modification by antimicrobial coating was used. In this work, we present silver (Ag) thin film on 316 L stainless steel substrate surface was deposited using Radio Frequency Sputtering PVD (RF-PVD). The morphology of Ag thin film were characterized using SEM-EDX. Surface roughness of the thin film was measured by AFM. In addition, Kirby Bauer Test in Escherichia coli (E. coli) was conducted in order to evaluate the inhibition performance of the Ag thin film antimicrobial coating. Based on SEM and AFM results show that the particle size is increased from 523 nm to 708 nm and surface roughness from 9 to 20 nm for deposition time 10 minutes to 20 minutes, respectively. In addition, the inhibition layer of the coating is about 29 mm.

Tailoring the charge carrier in few layers MoS2 field-effect transistors by Au metal adsorbate

NASA Astrophysics Data System (ADS)

Singh, Arun Kumar; Pandey, Rajiv K.; Prakash, Rajiv; Eom, Jonghwa

2018-04-01

It is an essential to tune the charge carrier concentrations in semiconductor in order to approach high-performance of the electronic and optoelectronic devices. Here, we report the effect of thin layer of gold (Au) metal on few layer (FL) molybdenum disulfide (MoS2) by atomic force microscopy (AFM), Raman spectroscopy and electrical charge transport measurements. The Raman spectra and charge transport measurements show that Au thin layer affect the electronic properties of the FL MoS2. After deposition of Au thin layer, the threshold voltages of FL MoS2 field-effect transistors (FETs) shift towards positive gate voltages, this reveal the p-doping in FL MoS2 nanosheets. The shift of peak frequencies of the Raman bands are also analyzed after the deposition of Au metal films of different thickness on FL MoS2 nanosheets. The surface morphology of Au metal on FL MoS2 is characterized by AFM and shows the smoother and denser film in comparison to Au metal on SiO2.

Microbial Cell Imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doktycz, Mitchel John; Sullivan, Claretta; Mortensen, Ninell P

Atomic force microscopy (AFM) is finding increasing application in a variety of fields including microbiology. Until the emergence of AFM, techniques for ivnestigating processes in single microbes were limited. From a biologist's perspective, the fact that AFM can be used to generate high-resolution images in buffers or media is its most appealing feature as live-cell imaging can be pursued. Imaging living cells by AFM allows dynamic biological events to be studied, at the nanoscale, in real time. Few areas of biological research have as much to gain as microbiology from the application of AFM. Whereas the scale of microbes placesmore » them near the limit of resolution for light microscopy. AFM is well suited for the study of structures on the order of a micron or less. Although electron microscopy techniques have been the standard for high-resolution imaging of microbes, AFM is quickly gaining favor for several reasons. First, fixatives that impair biological activity are not required. Second, AFM is capable of detecting forces in the pN range, and precise control of the force applied to the cantilever can be maintained. This combination facilitates the evaluation of physical characteristics of microbes. Third, rather than yielding the composite, statistical average of cell populations, as is the case with many biochemical assays, the behavior of single cells can be monitored. Despite the potential of AFM in microbiology, there are several limitations that must be considered. For example, the time required to record an image allows for the study of gross events such as cell division or membrane degradation from an antibiotic but precludes the evaluation of biological reactions and events that happen in just fractions of a second. Additionally, the AFM is a topographical tool and is restricted to imaging surfaces. Therefore, it cannot be used to look inside cells as with opticla and transmission electron microscopes. other practical considerations are the limitation on the maximum scan size (roughly 100 x 100 {mu}m) and the restricted movement of the cantilever in the Z (or height) direction. In most commercial AFMs, the Z range is restricted to roughly 10 {mu}m such that the height of cells to be imaged must be seriously considered. Nevertheless, AFM can provide structural-functional information at nanometer resolution and do so in physiologically relevant environments. Further, instrumentation for scanning probe microscopy continues to advance. Systems for high-speed imaging are becoming available, and techniques for looking inside the cells are being demonstrated. The ability to combine AFM with other imaging modalities is likely to have an even greater impact on microbiological studies. AFM studies of intact microbial cells started to appear in the literature in the 1990s. For example, AFM studies of Saccharomyces cerevisiae examined buddings cars after cell division and detailed changes related to cell growth processes. Also, the first AFM studies of bacterial biofilms appeared. In the late 1990s, AFM studies of intact fungal spores described clear changes in spore surfaces upon germination, and studies of individual bacterial cells were also described. These early bacterial imaging studies examined changes in bacterial morphology due to antimicrobial peptides exposure and bacterial adhesion properties. The majority of these early studies were carried out on dried samples and took advantage of the resolving power of AFM. The lack of cell mounting procedures presented an impediment for cell imaging studies. Subsequently, several approaches to mounting microbial cells have been developed, and these techniques are described later. Also highlighted are general considerations for microbial imaging and a description of some of the various applications of AFM to microbiology.« less

Task-induced frequency modulation features for brain-computer interfacing

NASA Astrophysics Data System (ADS)

Jayaram, Vinay; Hohmann, Matthias; Just, Jennifer; Schölkopf, Bernhard; Grosse-Wentrup, Moritz

2017-10-01

Objective. Task-induced amplitude modulation of neural oscillations is routinely used in brain-computer interfaces (BCIs) for decoding subjects’ intents, and underlies some of the most robust and common methods in the field, such as common spatial patterns and Riemannian geometry. While there has been some interest in phase-related features for classification, both techniques usually presuppose that the frequencies of neural oscillations remain stable across various tasks. We investigate here whether features based on task-induced modulation of the frequency of neural oscillations enable decoding of subjects’ intents with an accuracy comparable to task-induced amplitude modulation. Approach. We compare cross-validated classification accuracies using the amplitude and frequency modulated features, as well as a joint feature space, across subjects in various paradigms and pre-processing conditions. We show results with a motor imagery task, a cognitive task, and also preliminary results in patients with amyotrophic lateral sclerosis (ALS), as well as using common spatial patterns and Laplacian filtering. Main results. The frequency features alone do not significantly out-perform traditional amplitude modulation features, and in some cases perform significantly worse. However, across both tasks and pre-processing in healthy subjects the joint space significantly out-performs either the frequency or amplitude features alone. This result only does not hold for ALS patients, for whom the dataset is of insufficient size to draw any statistically significant conclusions. Significance. Task-induced frequency modulation is robust and straight forward to compute, and increases performance when added to standard amplitude modulation features across paradigms. This allows more information to be extracted from the EEG signal cheaply and can be used throughout the field of BCIs.

Biomechanics and Biotensegrity: Study Method and Frequency Response of the Simplex and 3-bar-SVD Tensegrity Configurations

NASA Astrophysics Data System (ADS)

Castro Arenas, C.; Ghersi, I.; Miralles, M. T.

2016-04-01

The purpose of this work is to study the frequency response of 3D tensegrity structures. These are structures that have been used, since the 80’s, to model biological systems of different scales. This fact led to the origin of the field of biotensegrity, which includes biomechanics as a natural field of application. In this work: a) A simple method for the analysis of frequency response of different nodes in 3D tensegrity structures was set up and tuned. This method is based on a video-analysis algorithm, which was applied to the structures, as they were vibrated along their axis of symmetry, at frequencies from 1 Hz to 60 Hz. b) Frequency-response analyses were performed, for the simplest 3D structure, the Simplex module, as well as for two towers, formed by stacking two and three Simplex modules, respectively. Resonant frequencies were detected for the Simplex module at (19.2±0.1) Hz and (50.2±0.1) Hz (the latter being an average of frequencies between homologous nodes). For the towers with two and three modules, each selected node presented a characteristic frequency response, modulated by their spatial placement in each model. Resonances for the two-stage tower were found at: (12±0.1) Hz; (16.2±0.1) Hz; (29.4±0.1) Hz and (37.2±0.1) Hz. For the tower with three Simplex modules, the main resonant frequencies were found at (12.0±0.1) Hz and (21.0±0.1) Hz. Results show that the proposed method is adequate for the study (2D) of any 3D tensegrity structure, with the potential of being generalized to the study of oscillations in three dimensions. A growing complexity and variability in the frequency response of the nodes was observed, as modules were added to the structures. These findings were compared to those found in the available literature.

AFM nanoscale indentation in air of polymeric and hybrid materials with highly different stiffness

NASA Astrophysics Data System (ADS)

Suriano, Raffaella; Credi, Caterina; Levi, Marinella; Turri, Stefano

2014-08-01

In this study, nanomechanical properties of a variety of polymeric materials was investigated by means of AFM. In particular, selecting different AFM probes, poly(methyl methacrylate) (PMMA), polydimethylsiloxane (PDMS) bulk samples, sol-gel hybrid thin films and hydrated hyaluronic acid hydrogels were indented in air to determine the elastic modulus. The force-distance curves and the indentation data were found to be greatly affected by the cantilever stiffness and by tip geometry. AFM indentation tests show that the choice of the cantilever spring constant and of tip shape is crucially influenced by elastic properties of samples. When adhesion-dominated interactions occur between the tip and the surface of samples, force-displacement curves reveal that a suitable functionalization of AFM probes allows the control of such interactions and the extraction of Young' modulus from AFM curves that would be otherwise unfeasible. By applying different mathematical models depending on AFM probes and materials under investigation, the values of Young's modulus were obtained and compared to those measured by rheological and dynamic mechanical analysis or to literature data. Our results show that a wide range of elastic moduli (10 kPa-10 GPa) can be determined by AFM in good agreement with those measured by conventional macroscopic measurements.

DDB2 (damaged-DNA binding 2) protein: a new modulator of nanomechanical properties and cell adhesion of breast cancer cells

NASA Astrophysics Data System (ADS)

Barbieux, Claire; Bacharouche, Jalal; Soussen, Charles; Hupont, Sébastien; Razafitianamaharavo, Angélina; Klotz, Rémi; Pannequin, Rémi; Brie, David; Bécuwe, Philippe; Francius, Grégory; Grandemange, Stéphanie

2016-02-01

DDB2, known for its role in DNA repair, was recently shown to reduce mammary tumor invasiveness by inducing the transcription of IκBα, an inhibitor of NF-κB activity. Since cellular adhesion is a key event during the epithelial to mesenchymal transition (EMT) leading to the invasive capacities of breast tumor cells, the aim of this study was to investigate the role of DDB2 in this process. Thus, using low and high DDB2-expressing MDA-MB231 and MCF7 cells, respectively, in which DDB2 expression was modulated experimentally, we showed that DDB2 overexpression was associated with a decrease of adhesion abilities on glass and plastic areas of breast cancer cells. Then, we investigated cell nanomechanical properties by atomic force microscopy (AFM). Our results revealed significant changes in the Young's Modulus value and the adhesion force in MDA-MB231 and MCF7 cells, whether DDB2 was expressed or not. The cell stiffness decrease observed in MDA-MB231 and MCF7 expressing DDB2 was correlated with a loss of the cortical actin-cytoskeleton staining. To understand how DDB2 regulates these processes, an adhesion-related gene PCR-Array was performed. Several adhesion-related genes were differentially expressed according to DDB2 expression, indicating that important changes are occurring at the molecular level. Thus, this work demonstrates that AFM technology is an important tool to follow cellular changes during tumorigenesis. Moreover, our data revealed that DDB2 is involved in early events occurring during metastatic progression of breast cancer cells and will contribute to define this protein as a new marker of metastatic progression in this type of cancer.

Accurate formulas for interaction force and energy in frequency modulation force spectroscopy

NASA Astrophysics Data System (ADS)

Sader, John E.; Jarvis, Suzanne P.

2004-03-01

Frequency modulation atomic force microscopy utilizes the change in resonant frequency of a cantilever to detect variations in the interaction force between cantilever tip and sample. While a simple relation exists enabling the frequency shift to be determined for a given force law, the required complementary inverse relation does not exist for arbitrary oscillation amplitudes of the cantilever. In this letter we address this problem and present simple yet accurate formulas that enable the interaction force and energy to be determined directly from the measured frequency shift. These formulas are valid for any oscillation amplitude and interaction force, and are therefore of widespread applicability in frequency modulation dynamic force spectroscopy.

Photonic measurement of microwave frequency based on phase modulation.

PubMed

Zhou, Junqiang; Fu, Songnian; Shum, Perry Ping; Aditya, Sheel; Xia, Li; Li, Jianqiang; Sun, Xiaoqiang; Xu, Kun

2009-04-27

A photonic approach for microwave frequency measurement is proposed. In this approach, an optical carrier is modulated by an unknown microwave signal through a phase modulator. The modulated optical signal is then split into two parts; one part passes through a spool of polarization maintaining fiber (PMF) and the other one, through a dispersion compensation fiber (DCF), to introduce different microwave power penalties. After the microwave powers of the two parts are measured by two photodetectors, a fixed frequency-to-power mapping is established by obtaining an amplitude comparison function (ACF). A proof-of-concept experiment demonstrates frequency measurement over a range of 10.5 GHz, with measurement error less than +/-0.07 GHz.

Athermalization in atomic force microscope based force spectroscopy using matched microstructure coupling.

PubMed

Torun, H; Finkler, O; Degertekin, F L

2009-07-01

The authors describe a method for athermalization in atomic force microscope (AFM) based force spectroscopy applications using microstructures that thermomechanically match the AFM probes. The method uses a setup where the AFM probe is coupled with the matched structure and the displacements of both structures are read out simultaneously. The matched structure displaces with the AFM probe as temperature changes, thus the force applied to the sample can be kept constant without the need for a separate feedback loop for thermal drift compensation, and the differential signal can be used to cancel the shift in zero-force level of the AFM.

An Evaluation of the Impacts of AF-M315E Propulsion Systems for Varied Mission Applications

NASA Technical Reports Server (NTRS)

Deans, Matthew C.; Oleson, Steven R.; Fittje, James; Colozza, Anthony; Packard, Tom; Gyekenyesi, John; McLean, Christopher H.; Spores, Ronald A.

2015-01-01

The purpose of the AF-M315E COMPASS study is to identify near-term (3-5 years) and long term (5 years +) opportunities for infusion, specifically the thruster and associated component technologies being developed as part of the GPIM project. Develop design reference missions which show the advantages of the AF-M315E green propulsion system. Utilize a combination of past COMPASS designs and selected new designs to demonstrate AF-M315E advantages. Use the COMPASS process to show the puts and takes of using AF-M315E at the integrated system level.

Atomic force microscopy of starch systems.

PubMed

Zhu, Fan

2017-09-22

Atomic force microscopy (AFM) generates information on topography, adhesion, and elasticity of sample surface by touching with a tip. Under suitable experimental settings, AFM can image biopolymers of few nanometers. Starch is a major food and industrial component. AFM has been used to probe the morphology, properties, modifications, and interactions of starches from diverse botanical origins at both micro- and nano-structural levels. The structural information obtained by AFM supports the blocklet structure of the granules, and provides qualitative and quantitative basis for some physicochemical properties of diverse starch systems. It becomes evident that AFM can complement other microscopic techniques to provide novel structural insights for starch systems.

Modulation limit of semiconductor lasers by some parametric modulation schemes

NASA Astrophysics Data System (ADS)

Iga, K.

1985-07-01

Using the simple rate equations and small signal analysis, the modulation speed limit of semiconductor lasers with modulation schemes such as gain switching, modulation of nonradiative recombination lifetime of minority carriers, and cavity Q modulation, is calculated and compared with the injection modulation scheme of Ikegami and Suematsu (1968). It is found that the maximum modulation frequency for the gain and Q modulation can exceed the resonance-like frequency by a factor equal to the coefficient of the time derivative of the modulation parameter, though the nonradiative lifetime modulation is not shown to be different from the injection modulation. A solution for the carrier lifetime modulation of LED is obtained, and the possibility of wideband modulation in this scheme is demonstrated.

Feasibility study of microwave modulation DIAL system for global CO II monitoring

NASA Astrophysics Data System (ADS)

Hirano, Yoshihito; Kameyama, Shumpei; Ueno, Shinichi; Sugimoto, Nobuo; Kimura, Toshiyoshi

2006-12-01

A new concept of DIAL (DIfferential Absorption Lidar) system for global CO II monitoring using microwave modulation is introduced. This system uses quasi-CW lights which are intensity modulated in microwave region and receives a backscattered light from the ground. In this system, ON/OFF wavelength laser lights are modulated with microwave frequencies, and received lights of two wavelengths are able to be discriminated by modulation frequencies in electrical signal domain. Higher sensitivity optical detection can be realized compared with the conventional microwave modulation lidar by using direct down conversion of modulation frequency. The system also has the function of ranging by using pseudo-random coding in modulation. Fiber-based optical circuit using wavelength region of 1.6 micron is a candidate for the system configuration. After the explanation of this configuration, feasibility study of this system on the application to global CO II monitoring is introduced.

Membrane-based actuation for high-speed single molecule force spectroscopy studies using AFM.

PubMed

Sarangapani, Krishna; Torun, Hamdi; Finkler, Ofer; Zhu, Cheng; Degertekin, Levent

2010-07-01

Atomic force microscopy (AFM)-based dynamic force spectroscopy of single molecular interactions involves characterizing unbinding/unfolding force distributions over a range of pulling speeds. Owing to their size and stiffness, AFM cantilevers are adversely affected by hydrodynamic forces, especially at pulling speeds >10 microm/s, when the viscous drag becomes comparable to the unbinding/unfolding forces. To circumvent these adverse effects, we have fabricated polymer-based membranes capable of actuating commercial AFM cantilevers at speeds >or=100 microm/s with minimal viscous drag effects. We have used FLUENT, a computational fluid dynamics (CFD) software, to simulate high-speed pulling and fast actuation of AFM cantilevers and membranes in different experimental configurations. The simulation results support the experimental findings on a variety of commercial AFM cantilevers and predict significant reduction in drag forces when membrane actuators are used. Unbinding force experiments involving human antibodies using these membranes demonstrate that it is possible to achieve bond loading rates >or=10(6) pN/s, an order of magnitude greater than that reported with commercial AFM cantilevers and systems.

Thermal noise model of antiferromagnetic dynamics: A macroscopic approach

NASA Astrophysics Data System (ADS)

Li, Xilai; Semenov, Yuriy; Kim, Ki Wook

In the search for post-silicon technologies, antiferromagnetic (AFM) spintronics is receiving widespread attention. Due to faster dynamics when compared with its ferromagnetic counterpart, AFM enables ultra-fast magnetization switching and THz oscillations. A crucial factor that affects the stability of antiferromagnetic dynamics is the thermal fluctuation, rarely considered in AFM research. Here, we derive from theory both stochastic dynamic equations for the macroscopic AFM Neel vector (L-vector) and the corresponding Fokker-Plank equation for the L-vector distribution function. For the dynamic equation approach, thermal noise is modeled by a stochastic fluctuating magnetic field that affects the AFM dynamics. The field is correlated within the correlation time and the amplitude is derived from the energy dissipation theory. For the distribution function approach, the inertial behavior of AFM dynamics forces consideration of the generalized space, including both coordinates and velocities. Finally, applying the proposed thermal noise model, we analyze a particular case of L-vector reversal of AFM nanoparticles by voltage controlled perpendicular magnetic anisotropy (PMA) with a tailored pulse width. This work was supported, in part, by SRC/NRI SWAN.

Radio Frequency Identification (RFID) in medical environment: Gaussian Derivative Frequency Modulation (GDFM) as a novel modulation technique with minimal interference properties.

PubMed

Rieche, Marie; Komenský, Tomás; Husar, Peter

2011-01-01

Radio Frequency Identification (RFID) systems in healthcare facilitate the possibility of contact-free identification and tracking of patients, medical equipment and medication. Thereby, patient safety will be improved and costs as well as medication errors will be reduced considerably. However, the application of RFID and other wireless communication systems has the potential to cause harmful electromagnetic disturbances on sensitive medical devices. This risk mainly depends on the transmission power and the method of data communication. In this contribution we point out the reasons for such incidents and give proposals to overcome these problems. Therefore a novel modulation and transmission technique called Gaussian Derivative Frequency Modulation (GDFM) is developed. Moreover, we carry out measurements to show the inteference properties of different modulation schemes in comparison to our GDFM.

Intelligent Data Transfer for Multiple Sensor Networks over a Broad Temperature Range

NASA Technical Reports Server (NTRS)

Krasowski, Michael (Inventor)

2018-01-01

A sensor network may be configured to operate in extreme temperature environments. A sensor may be configured to generate a frequency carrier, and transmit the frequency carrier to a node. The node may be configured to amplitude modulate the frequency carrier, and transmit the amplitude modulated frequency carrier to a receiver.

Method and apparatus for resonant frequency waveform modulation

DOEpatents

Taubman, Matthew S [Richland, WA

2011-06-07

A resonant modulator device and process are described that provide enhanced resonant frequency waveforms to electrical devices including, e.g., laser devices. Faster, larger, and more complex modulation waveforms are obtained than can be obtained by use of conventional current controllers alone.

Effect of Spatial Locality Prefetching on Structural Locality

DTIC Science & Technology

1991-12-01

Pollution module calculates the SLC and CAM cache pollution percentages. And finally, the Generate Reference Frequency List module produces the output...3.2.5 Generate Reference Frequency List 3.2.6 Each program module in the structure chart is mapped into an Ada package. By performing this encapsulation...call routine to generate reference -- frequency list -- end if -- end loop -- close input, output, and reference files end Cache Simulator Figure 3.5

Parametric resonance in acoustically levitated water drops

NASA Astrophysics Data System (ADS)

Shen, C. L.; Xie, W. J.; Wei, B.

2010-05-01

Liquid drops can be suspended in air with acoustic levitation method. When the sound pressure is periodically modulated, the levitated drop is usually forced into an axisymmetric oscillation. However, a transition from axisymmetric oscillation into sectorial oscillation occurs when the modulation frequency approaches some specific values. The frequency of the sectorial oscillation is almost exactly half of the modulation frequency. It is demonstrated that this transition is induced by the parametric resonance of levitated drop. The natural frequency of sectorial oscillation is found to decrease with the increase of drop distortion extent.

Electro-optic modulator with ultra-low residual amplitude modulation for frequency modulation and laser stabilization.

PubMed

Tai, Zhaoyang; Yan, Lulu; Zhang, Yanyan; Zhang, Xiaofei; Guo, Wenge; Zhang, Shougang; Jiang, Haifeng

2016-12-01

The reduction of the residual amplitude modulation (RAM) induced by electro-optic modulation is essential for many applications of frequency modulation spectroscopy requiring a lower system noise floor. Here, we demonstrate a simple passive approach employing an electro-optic modulator (EOM) cut at Brewster's angle. The proposed EOM exhibits a RAM of a few parts per million, which is comparable with that achieved by a common EOM under critical active temperature and bias voltage controls. The frequency instability of a 10 cm cavity-stabilized laser induced by the RAM effect of the proposed EOM is below 3×10^-17 for integration times from 1 to 1000 s, and below 4×10^-16 for comprehensive noise contributions for integration times from 1 to 100 s.

A versatile atomic force microscope integrated with a scanning electron microscope.

PubMed

Kreith, J; Strunz, T; Fantner, E J; Fantner, G E; Cordill, M J

2017-05-01

A versatile atomic force microscope (AFM), which can be installed in a scanning electron microscope (SEM), is introduced. The flexible design of the instrument enables correlated analysis for different experimental configurations, such as AFM imaging directly after nanoindentation in vacuum. In order to demonstrate the capabilities of the specially designed AFM installed inside a SEM, slip steps emanating around nanoindents in single crystalline brass were examined. This example showcases how the combination of AFM and SEM imaging can be utilized for quantitative dislocation analysis through the measurement of the slip step heights without the hindrance of oxide formation. Finally, an in situ nanoindentation technique is introduced, illustrating the use of AFM imaging during indentation experiments to examine plastic deformation occurring under the indenter tip. The mechanical indentation data are correlated to the SEM and AFM images to estimate the number of dislocations emitted to the surface.

Stripe Antiferromagnetic Spin Fluctuations in SrCo 2As 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jayasekara, Wageesha; Lee, Young-Jin; Pandey, Abhishek

Inelastic neutron scattering measurements of paramagnetic SrCo 2As 2 at T = 5 K reveal antiferromagnetic (AFM) spin fluctuations that are peaked at a wave vector of Q AFM = (1/2, 1/2, 1) and possess a large energy scale. These stripe spin fluctuations are similar to those found in AFe 2As 2 compounds, where spin-density wave AFM is driven by Fermi surface nesting between electron and hole pockets separated by Q AFM. SrCo 2As 2 has a more complex Fermi surface and band-structure calculations indicate a potential instability toward either a ferromagnetic or stripe AFM ground state. The results suggestmore » that stripe AFM magnetism is a general feature of both iron and cobalt-based arsenides and the search for spin fluctuation-induced unconventional superconductivity should be expanded to include cobalt-based compounds.« less

Mitigating Oscillator Pulling Due To Magnetic Coupling in Monolithic Mixed-Signal Radio-Frequency Integrated Circuits

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sobering, Ian David

2014-01-01

An analysis of frequency pulling in a varactor-tuned LC VCO under coupling from an on-chip PA is presented. The large-signal behavior of the VCO's inversion-mode MOS varactors is outlined, and the susceptibility of the VCO to frequency pulling from PA aggressor signals with various modulation schemes is discussed. We show that if the aggressor signal is aperiodic, band-limited, or amplitude-modulated, the varactor-tuned LC VCO will experience frequency pulling due to time-modulation of the varactor capacitance. However, if the aggressor signal has constant-envelope phase modulation, VCO pulling can be eliminated, even in the presence of coupling, through careful choice of VCOmore » frequency and divider ratio. Additional mitigation strategies, including new inductor topologies and system-level architectural choices, are also examined.« less

Temporal and spectral properties of the songs of the southern green stink bug Nezara viridula (L.) from Slovenia.

PubMed

Cokl, A; Virant-Doberlet, M; Stritih, N

2000-01-01

Substrate born songs of the southern green stinkbug Nezara viridula (L.) from Slovenia were recorded and analysed. The male calling song is composed of narrow-band regularly repeated single pulses and of broad-band frequency modulated pulses grouped into pulse trains. The female calling song is characterised by broad-band pulsed and narrow-band non-pulsed pulse trains. A frequency modulated pre-pulse precedes the narrow-band pulse train. A frequency-modulated post-pulse usually follows the pulse train of the male courtship song. The male calling song triggers broad-band pulse trains of the female courtship song. The female also produces a repelling low-frequency vibration that inhibits male calling and courtship. The male rival song is characterised by prolonged pulses with a typical frequency modulation.

Potentials evoked by chirp-modulated tones: a new technique to evaluate oscillatory activity in the auditory pathway.

PubMed

Artieda, J; Valencia, M; Alegre, M; Olaziregi, O; Urrestarazu, E; Iriarte, J

2004-03-01

Steady-state potentials are oscillatory responses generated by a rhythmic stimulation of a sensory pathway. The frequency of the response, which follows the frequency of stimulation, is maximal at a stimulus rate of 40 Hz for auditory stimuli. The exact cause of these maximal responses is not known, although some authors have suggested that they might be related to the 'working frequency' of the auditory cortex. Testing of the responses to different frequencies of stimulation may be lengthy if a single frequency is studied at a time. Our aim was to develop a fast technique to explore the oscillatory response to auditory stimuli, using a tone modulated in amplitude by a sinusoid whose frequency increases linearly in frequency ('chirp') from 1 to 120 Hz. Time-frequency transforms were used for the analysis of the evoked responses in 10 subjects. Also, we analyzed whether the peaks in these responses were due to increases of amplitude or to phase-locking phenomena, using single-sweep time-frequency transforms and inter-trial phase analysis. The pattern observed in the time-frequency transform of the chirp-evoked potential was very similar in all subjects: a diagonal band of energy was observed, corresponding to the frequency of modulation at each time instant. Two components were present in the band, one around 45 Hz (30-60 Hz) and a smaller one between 80 and 120 Hz. Inter-trial phase analysis showed that these components were mainly due to phase locking phenomena. A simultaneous testing of the amplitude-modulation-following oscillatory responses to auditory stimulation is feasible using a tone modulated in amplitude at increasing frequencies. The maximal energies found at stimulation frequencies around 40 Hz are probably due to increased phase-locking of the individual responses.

Development of Tuning Fork Based Probes for Atomic Force Microscopy

NASA Astrophysics Data System (ADS)

Jalilian, Romaneh; Yazdanpanah, Mehdi M.; Torrez, Neil; Alizadeh, Amirali; Askari, Davood

2014-03-01

This article reports on the development of tuning fork-based AFM/STM probes in NaugaNeedles LLC for use in atomic force microscopy. These probes can be mounted on different carriers per customers' request. (e.g., RHK carrier, Omicron carrier, and tuning fork on a Sapphire disk). We are able to design and engineer tuning forks on any type of carrier used in the market. We can attach three types of tips on the edge of a tuning fork prong (i.e., growing Ag2Ga nanoneedles at any arbitrary angle, cantilever of AFM tip, and tungsten wire) with lengths from 100-500 μm. The nanoneedle is located vertical to the fork. Using a suitable insulation and metallic coating, we can make QPlus sensors that can detect tunneling current during the AFM scan. To make Qplus sensors, the entire quartz fork will be coated with an insulating material, before attaching the nanoneedle. Then, the top edge of one prong is coated with a thin layer of conductive metal and the nanoneedle is attached to the fork end of the metal coated prong. The metal coating provides electrical connection to the tip for tunneling current readout and to the electrodes and used to read the QPlus current. Since the amount of mass added to the fork is minimal, the resonance frequency spectrum does not change and still remains around 32.6 KHz and the Q factor is around 1,200 in ambient condition. These probes can enhance the performance of tuning fork based atomic microscopy.

Modulated scattering technique in the terahertz domain enabled by current actuated vanadium dioxide switches

PubMed Central

Vitale, W. A.; Tamagnone, M.; Émond, N.; Le Drogoff, B.; Capdevila, S.; Skrivervik, A.; Chaker, M.; Mosig, J. R.; Ionescu, A. M.

2017-01-01

The modulated scattering technique is based on the use of reconfigurable electromagnetic scatterers, structures able to scatter and modulate an impinging electromagnetic field in function of a control signal. The modulated scattering technique is used in a wide range of frequencies up to millimeter waves for various applications, such as field mapping of circuits or antennas, radio-frequency identification devices and imaging applications. However, its implementation in the terahertz domain remains challenging. Here, we describe the design and experimental demonstration of the modulated scattering technique at terahertz frequencies. We characterize a modulated scatterer consisting in a bowtie antenna loaded with a vanadium dioxide switch, actuated using a continuous current. The modulated scatterer behavior is demonstrated using a time domain terahertz spectroscopy setup and shows significant signal strength well above 0.5 THz, which makes this device a promising candidate for the development of fast and energy-efficient THz communication devices and imaging systems. Moreover, our experiments allowed us to verify the operation of a single micro-meter sized VO2 switch at terahertz frequencies, thanks to the coupling provided by the antenna. PMID:28145523

Volitional exaggeration of body size through fundamental and formant frequency modulation in humans

PubMed Central

Pisanski, Katarzyna; Mora, Emanuel C.; Pisanski, Annette; Reby, David; Sorokowski, Piotr; Frackowiak, Tomasz; Feinberg, David R.

2016-01-01

Several mammalian species scale their voice fundamental frequency (F0) and formant frequencies in competitive and mating contexts, reducing vocal tract and laryngeal allometry thereby exaggerating apparent body size. Although humans’ rare capacity to volitionally modulate these same frequencies is thought to subserve articulated speech, the potential function of voice frequency modulation in human nonverbal communication remains largely unexplored. Here, the voices of 167 men and women from Canada, Cuba, and Poland were recorded in a baseline condition and while volitionally imitating a physically small and large body size. Modulation of F0, formant spacing (∆F), and apparent vocal tract length (VTL) were measured using Praat. Our results indicate that men and women spontaneously and systemically increased VTL and decreased F0 to imitate a large body size, and reduced VTL and increased F0 to imitate small size. These voice modulations did not differ substantially across cultures, indicating potentially universal sound-size correspondences or anatomical and biomechanical constraints on voice modulation. In each culture, men generally modulated their voices (particularly formants) more than did women. This latter finding could help to explain sexual dimorphism in F0 and formants that is currently unaccounted for by sexual dimorphism in human vocal anatomy and body size. PMID:27687571

Precision saturated absorption spectroscopy of H3+

NASA Astrophysics Data System (ADS)

Guan, Yu-Chan; Chang, Yung-Hsiang; Liao, Yi-Chieh; Peng, Jin-Long; Wang, Li-Bang; Shy, Jow-Tsong

2018-03-01

In our previous work on the Lamb-dips of the ν2 fundamental band transitions of H3+, the saturated absorption spectrum was obtained by third-derivative spectroscopy using frequency modulation with an optical parametric oscillator (OPO). However, frequency modulation also caused errors in the absolute frequency determination. To solve this problem, we built a tunable offset locking system to lock the pump frequency of the OPO to an iodine-stabilized Nd:YAG laser. With this improvement, we were able to scan the OPO idler frequency precisely and obtain the saturated absorption profile using intensity modulation. Furthermore, ion concentration modulation was employed to subtract the background noise and increase the signal-to-noise ratio. To determine the absolute frequency of the idler wave, the OPO signal frequency was locked to an optical frequency comb. The absolute frequency accuracy of our spectrometer was better than 7 kHz, demonstrated by measuring the wavelength standard transition of methane at 3.39 μm. Finally, we measured 16 transitions of H3+ and our results agree very well with other precision measurements. This work successfully resolved the discrepancies between our previous measurements and other precision measurements.

Design and Processing of a Novel Chaos-Based Stepped Frequency Synthesized Wideband Radar Signal.

PubMed

Zeng, Tao; Chang, Shaoqiang; Fan, Huayu; Liu, Quanhua

2018-03-26

The linear stepped frequency and linear frequency shift keying (FSK) signal has been widely used in radar systems. However, such linear modulation signals suffer from the range-Doppler coupling that degrades radar multi-target resolution. Moreover, the fixed frequency-hopping or frequency-coded sequence can be easily predicted by the interception receiver in the electronic countermeasures (ECM) environments, which limits radar anti-jamming performance. In addition, the single FSK modulation reduces the radar low probability of intercept (LPI) performance, for it cannot achieve a large time-bandwidth product. To solve such problems, we propose a novel chaos-based stepped frequency (CSF) synthesized wideband signal in this paper. The signal introduces chaotic frequency hopping between the coherent stepped frequency pulses, and adopts a chaotic frequency shift keying (CFSK) and phase shift keying (PSK) composited coded modulation in a subpulse, called CSF-CFSK/PSK. Correspondingly, the processing method for the signal has been proposed. According to our theoretical analyses and the simulations, the proposed signal and processing method achieve better multi-target resolution and LPI performance. Furthermore, flexible modulation is able to increase the robustness against identification of the interception receiver and improve the anti-jamming performance of the radar.

Digitally synthesized beat frequency-multiplexed fluorescence lifetime spectroscopy

PubMed Central

Chan, Jacky C. K.; Diebold, Eric D.; Buckley, Brandon W.; Mao, Sien; Akbari, Najva; Jalali, Bahram

2014-01-01

Frequency domain fluorescence lifetime imaging is a powerful technique that enables the observation of subtle changes in the molecular environment of a fluorescent probe. This technique works by measuring the phase delay between the optical emission and excitation of fluorophores as a function of modulation frequency. However, high-resolution measurements are time consuming, as the excitation modulation frequency must be swept, and faster low-resolution measurements at a single frequency are prone to large errors. Here, we present a low cost optical system for applications in real-time confocal lifetime imaging, which measures the phase vs. frequency spectrum without sweeping. Deemed Lifetime Imaging using Frequency-multiplexed Excitation (LIFE), this technique uses a digitally-synthesized radio frequency comb to drive an acousto-optic deflector, operated in a cat’s-eye configuration, to produce a single laser excitation beam modulated at multiple beat frequencies. We demonstrate simultaneous fluorescence lifetime measurements at 10 frequencies over a bandwidth of 48 MHz, enabling high speed frequency domain lifetime analysis of single- and multi-component sample mixtures. PMID:25574449

Development of a frequency-modulated ultrasonic sensor inspired by bat echolocation

NASA Astrophysics Data System (ADS)

Kepa, Krzysztof; Abaid, Nicole

2015-03-01

Bats have evolved to sense using ultrasonic signals with a variety of different frequency signatures which interact with their environment. Among these signals, those with time-varying frequencies may enable the animals to gather more complex information for obstacle avoidance and target tracking. Taking inspiration from this system, we present the development of a sonar sensor capable of generating frequency-modulated ultrasonic signals. The device is based on a miniature mobile computer, with on board data capture and processing capabilities, which is designed for eventual autonomous operation in a robotic swarm. The hardware and software components of the sensor are detailed, as well their integration. Preliminary results for target detection using both frequency-modulated and constant frequency signals are discussed.

Frequency-Diversity Reception for Phase Modulation

NASA Technical Reports Server (NTRS)

Brockman, M. H.

1984-01-01

Signal-to-noise ratio improved. System receives phase modulation transmitted simultaneously on different carrier frequencies. Used for carriers received through different antennas or through same antenna.

Influence of time dependent longitudinal magnetic fields on the cooling process, exchange bias and magnetization reversal mechanism in FM core/AFM shell nanoparticles: a Monte Carlo study.

PubMed

Yüksel, Yusuf; Akıncı, Ümit

2016-12-07

Using Monte Carlo simulations, we have investigated the dynamic phase transition properties of magnetic nanoparticles with ferromagnetic core coated by an antiferromagnetic shell structure. Effects of field amplitude and frequency on the thermal dependence of magnetizations, magnetization reversal mechanisms during hysteresis cycles, as well as on the exchange bias and coercive fields have been examined, and the feasibility of applying dynamic magnetic fields on the particle have been discussed for technological and biomedical purposes.

Non-linear transfer characteristics of stimulation and recording hardware account for spurious low-frequency artifacts during amplitude modulated transcranial alternating current stimulation (AM-tACS).

PubMed

Kasten, Florian H; Negahbani, Ehsan; Fröhlich, Flavio; Herrmann, Christoph S

2018-05-31

Amplitude modulated transcranial alternating current stimulation (AM-tACS) has been recently proposed as a possible solution to overcome the pronounced stimulation artifact encountered when recording brain activity during tACS. In theory, AM-tACS does not entail power at its modulating frequency, thus avoiding the problem of spectral overlap between brain signal of interest and stimulation artifact. However, the current study demonstrates how weak non-linear transfer characteristics inherent to stimulation and recording hardware can reintroduce spurious artifacts at the modulation frequency. The input-output transfer functions (TFs) of different stimulation setups were measured. Setups included recordings of signal-generator and stimulator outputs and M/EEG phantom measurements. 6 th -degree polynomial regression models were fitted to model the input-output TFs of each setup. The resulting TF models were applied to digitally generated AM-tACS signals to predict the frequency of spurious artifacts in the spectrum. All four setups measured for the study exhibited low-frequency artifacts at the modulation frequency and its harmonics when recording AM-tACS. Fitted TF models showed non-linear contributions significantly different from zero (all p < .05) and successfully predicted the frequency of artifacts observed in AM-signal recordings. Results suggest that even weak non-linearities of stimulation and recording hardware can lead to spurious artifacts at the modulation frequency and its harmonics. These artifacts were substantially larger than alpha-oscillations of a human subject in the MEG. Findings emphasize the need for more linear stimulation devices for AM-tACS and careful analysis procedures, taking into account low-frequency artifacts to avoid confusion with effects of AM-tACS on the brain. Copyright © 2018 Elsevier Inc. All rights reserved.

Aflatoxin M1 in Pasteurized Milk in Babol city, Mazandaran Province, Iran.

PubMed

Sefidgar, Saa; Mirzae, M; Assmar, M; Naddaf, Sr

2011-01-01

Aflatoxin M(1) (AFM(1)) is the metabolite of aflatoxin B1 (AFB(1)) and is found in milk when lactating animals are fed with contaminated feedstuff. The presence of AFM(1) in milk, pose a major risk for humans especially kids as it can have immunosuppressive, mutagenic, teratogenic and carcinogenic effects. The present study is aimed to investigate the occurrence of AFM(1) in subsidized pasteurized milk in Babol, Mazandaran Province, Iran. Some 72 pasteurized milk packages were collected from supermarkets in various districts of city during January to March 2006. Milk samples were centrifuged and amounts of 100 μl of skimmed milk were tested for AFM(1) contamination by competitive ELISA. All the samples (100%) exhibited contamination with AFM(1). The contamination levels means in January, February, and March were 227.85, 229.64, and 233.1ng/l, respectively. The amount of AFM(1) in all the samples were above 50ng/l, the threshold set by the European community regulations. Monitoring of AFM(1) level should be part of quality control procedures in dairy factories, particularly the ones providing infant's milk. Production of safer and healthier milk and other dairy products with minimum AFM(1) level can be achieved by adopting prophylactic measures including control of humidity and water content of feedstuff, which favors mould production.

Force Spectroscopy with 9-μs Resolution and Sub-pN Stability by Tailoring AFM Cantilever Geometry.

PubMed

Edwards, Devin T; Faulk, Jaevyn K; LeBlanc, Marc-André; Perkins, Thomas T

2017-12-19

Atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS) is a powerful yet accessible means to characterize the unfolding/refolding dynamics of individual molecules and resolve closely spaced, transiently occupied folding intermediates. On a modern commercial AFM, these applications and others are now limited by the mechanical properties of the cantilever. Specifically, AFM-based SMFS data quality is degraded by a commercial cantilever's limited combination of temporal resolution, force precision, and force stability. Recently, we modified commercial cantilevers with a focused ion beam to optimize their properties for SMFS. Here, we extend this capability by modifying a 40 × 18 μm 2 cantilever into one terminated with a gold-coated, 4 × 4 μm 2 reflective region connected to an uncoated 2-μm-wide central shaft. This "Warhammer" geometry achieved 8.5-μs resolution coupled with improved force precision and sub-pN stability over 100 s when measured on a commercial AFM. We highlighted this cantilever's biological utility by first resolving a calmodulin unfolding intermediate previously undetected by AFM and then measuring the stabilization of calmodulin by myosin light chain kinase at dramatically higher unfolding velocities than in previous AFM studies. More generally, enhancing data quality via an improved combination of time resolution, force precision, and force stability will broadly benefit biological applications of AFM. Published by Elsevier Inc.

Tip Characterization Method using Multi-feature Characterizer for CD-AFM

PubMed Central

Orji, Ndubuisi G.; Itoh, Hiroshi; Wang, Chumei; Dixson, Ronald G.; Walecki, Peter S.; Schmidt, Sebastian W.; Irmer, Bernd

2016-01-01

In atomic force microscopy (AFM) metrology, the tip is a key source of uncertainty. Images taken with an AFM show a change in feature width and shape that depends on tip geometry. This geometric dilation is more pronounced when measuring features with high aspect ratios, and makes it difficult to obtain absolute dimensions. In order to accurately measure nanoscale features using an AFM, the tip dimensions should be known with a high degree of precision. We evaluate a new AFM tip characterizer, and apply it to critical dimension AFM (CD-AFM) tips used for high aspect ratio features. The characterizer is made up of comb-shaped lines and spaces, and includes a series of gratings that could be used as an integrated nanoscale length reference. We also demonstrate a simulation method that could be used to specify what range of tip sizes and shapes the characterizer can measure. Our experiments show that for non re-entrant features, the results obtained with this characterizer are consistent to 1 nm with the results obtained by using widely accepted but slower methods that are common practice in CD-AFM metrology. A validation of the integrated length standard using displacement interferometry indicates a uniformity of better than 0.75%, suggesting that the sample could be used as highly accurate and SI traceable lateral scale for the whole evaluation process. PMID:26720439

Aflatoxin M1 in Pasteurized Milk in Babol city, Mazandaran Province, Iran

PubMed Central

Sefidgar, SAA; Mirzae, M; Assmar, M; Naddaf, SR

2011-01-01

Background: Aflatoxin M1 (AFM1) is the metabolite of aflatoxin B1 (AFB1) and is found in milk when lactating animals are fed with contaminated feedstuff. The presence of AFM1 in milk, pose a major risk for humans especially kids as it can have immunosuppressive, mutagenic, teratogenic and carcinogenic effects. The present study is aimed to investigate the occurrence of AFM1 in subsidized pasteurized milk in Babol, Mazandaran Province, Iran. Methods: Some 72 pasteurized milk packages were collected from supermarkets in various districts of city during January to March 2006. Milk samples were centrifuged and amounts of 100 μl of skimmed milk were tested for AFM1 contamination by competitive ELISA. Results: All the samples (100%) exhibited contamination with AFM1. The contamination levels means in January, February, and March were 227.85, 229.64, and 233.1ng/l, respectively. The amount of AFM1 in all the samples were above 50ng/l, the threshold set by the European community regulations. Conclusion: Monitoring of AFM1 level should be part of quality control procedures in dairy factories, particularly the ones providing infant’s milk. Production of safer and healthier milk and other dairy products with minimum AFM1 level can be achieved by adopting prophylactic measures including control of humidity and water content of feedstuff, which favors mould production. PMID:23113064

Infants’ Exposure to Aflatoxin M1 from Mother’s Breast Milk in Iran

PubMed Central

Ghiasian, SA; Maghsood, AH

2012-01-01

Background The occurrence of aflatoxin M1 (AFM1) in milk, especially breast milk, is a valuable biomarker for exposure determination to aflatoxin B1 (AFB1). In the present study, the risk of exposure to AFM1 in infants fed breast milk was investigated. Methods: An enzyme-linked immunosorbent assay (ELISA) was used for the analysis of AFM1 in breast milk samples from 132 lactating mothers referred to four urban Mothers and Babies Care Unit of Hamadan, western Iran. Results: AFM1 was detected in eight samples (6.06%) at mean concentration of 9.45 ng/L. The minimum and maximum of concentration was 7.1 to 10.8 ng/L, respectively. Although the concentration of AFM1 in none of the samples was higher than the maximum tolerance limit accepted by USA and European Union (25 ng/kg) however, 25% had a level of AFM1 above the allowable level of Australia and Switzerland legal limit (10 ng/L). Conclusions: Lactating mothers and infants in western parts of Iran could be at risk for AFB1 and AFM1 exposure, respectively. Considering all this information, the investigation of AFM1 in lactating mothers as a biomarker for post-natal exposure of infants to this carcinogen deserves further studies in various seasons and different parts of Iran. PMID:23113156

Aflatoxin M1 Concentration in Various Dairy Products: Evidence for Biologically Reduced Amount of AFM1 in Yoghurt

PubMed Central

RAHIMIRAD, Amir; MAALEKINEJAD, Hassan; OSTADI, Araz; YEGANEH, Samal; FAHIMI, Samira

2014-01-01

Abstract Background Aflatoxin M1 (AFM1), a carcinogenic substance is found in milk and dairy products. The effect of season and type of dairy products on AFMi level in northern Iran was investigated in this study. Methods Three hundred samples (each season 75 samples) including raw and pasteurized milk, yoghurt, cheese, and cream samples were collected from three distinct milk producing farms. The samples were subjected to chemical and solid phase extractions and were analyzed by using HPLC technique. Recovery percentages, limit of detection and limit of quantification values were determined. Results Seventy percent and 98% were the minimum and maximum recoveries for cheese and raw milk, respectively and 0.021 and 0.063 ppb were the limit of detection and limit of quantification values for AFM1. We found that in autumn and winter the highest level (0.121 ppb) of AFM1 in cheese and cream samples and failed to detect any AFM1 in spring samples. Interestingly, our data showed that the yoghurt samples had the lowest level of AFM1 in all seasons. Conclusion There are significant differences between the AFM1 levels in dairy products in various seasons and also various types of products, suggesting spring and summer yoghurt samples as the safest products from AFM1 level point of view. PMID:25927044

Mechanical stress-controlled tunable active frequency-selective surface

NASA Astrophysics Data System (ADS)

Huang, Bo-Cin; Hong, Jian-Wei; Lo, Cheng-Yao

2017-01-01

This study proposes a tunable active frequency-selective surface (AFSS) realized by mechanically expanding or contracting a split-ring resonator (SRR) array. The proposed AFSS transfers mechanical stress from its elastic substrate to the top of the SRR, thereby achieving electromagnetic (EM) modulation without the need for an additional external power supply, meeting the requirements for the target application: the invisibility cloak. The operating mechanism of the proposed AFSS differs from those of other AFSSs, supporting modulations in arbitrary frequencies in the target range. The proposed stress-controlled or strain-induced EM modulation proves the existence of an identical and linear relationship between the strain gradient and the frequency shift, implying its suitability for other EM modulation ranges and applications.

Extracting a shape function for a signal with intra-wave frequency modulation.

PubMed

Hou, Thomas Y; Shi, Zuoqiang

2016-04-13

In this paper, we develop an effective and robust adaptive time-frequency analysis method for signals with intra-wave frequency modulation. To handle this kind of signals effectively, we generalize our data-driven time-frequency analysis by using a shape function to describe the intra-wave frequency modulation. The idea of using a shape function in time-frequency analysis was first proposed by Wu (Wu 2013 Appl. Comput. Harmon. Anal. 35, 181-199. (doi:10.1016/j.acha.2012.08.008)). A shape function could be any smooth 2π-periodic function. Based on this model, we propose to solve an optimization problem to extract the shape function. By exploring the fact that the shape function is a periodic function with respect to its phase function, we can identify certain low-rank structure of the signal. This low-rank structure enables us to extract the shape function from the signal. Once the shape function is obtained, the instantaneous frequency with intra-wave modulation can be recovered from the shape function. We demonstrate the robustness and efficiency of our method by applying it to several synthetic and real signals. One important observation is that this approach is very stable to noise perturbation. By using the shape function approach, we can capture the intra-wave frequency modulation very well even for noise-polluted signals. In comparison, existing methods such as empirical mode decomposition/ensemble empirical mode decomposition seem to have difficulty in capturing the intra-wave modulation when the signal is polluted by noise. © 2016 The Author(s).

Intra-pulse modulation recognition using short-time ramanujan Fourier transform spectrogram

NASA Astrophysics Data System (ADS)

Ma, Xiurong; Liu, Dan; Shan, Yunlong

2017-12-01

Intra-pulse modulation recognition under negative signal-to-noise ratio (SNR) environment is a research challenge. This article presents a robust algorithm for the recognition of 5 types of radar signals with large variation range in the signal parameters in low SNR using the combination of the Short-time Ramanujan Fourier transform (ST-RFT) and pseudo-Zernike moments invariant features. The ST-RFT provides the time-frequency distribution features for 5 modulations. The pseudo-Zernike moments provide invariance properties that are able to recognize different modulation schemes on different parameter variation conditions from the ST-RFT spectrograms. Simulation results demonstrate that the proposed algorithm achieves the probability of successful recognition (PSR) of over 90% when SNR is above -5 dB with large variation range in the signal parameters: carrier frequency (CF) for all considered signals, hop size (HS) for frequency shift keying (FSK) signals, and the time-bandwidth product for Linear Frequency Modulation (LFM) signals.

Dual-tone optical vector millimeter wave signal generated by frequency-nonupling the radio frequency 16-star quadrature-amplitude-modulation signal

NASA Astrophysics Data System (ADS)

Wu, Tonggen; Ma, Jianxin

2017-12-01

This paper proposes an original scheme to generate the photonic dual-tone optical millimeter wave (MMW) carrying the 16-star quadrature-amplitude-modulation (QAM) signal via an optical phase modulator (PM) and an interleaver with adaptive photonic frequency-nonupling without phase precoding. To enable the generated optical vector MMW signal to resist the power fading effect caused by the fiber chromatic dispersion, the modulated -5th- and +4th-order sidebands are selected from the output of the PM, which is driven by the precoding 16-star QAM signal. The modulation index of the PM is optimized to gain the maximum opto-electrical conversion efficiency. A radio over fiber link is built by simulation, and the simulated constellations and the bit error rate graph demonstrate that the frequency-nonupling 16-star QAM MMW signal has good transmission performance. The simulation results agree well with our theoretical results.

47 CFR 73.322 - FM stereophonic sound transmission standards.

Code of Federal Regulations, 2010 CFR

2010-10-01

... frequency in a transmission system meeting the following parameters: (1) The modulating signal for the main... frequency modulate the main carrier between the limits of 8 and 10 percent. (3) One stereophonic subcarrier... stereophomic subcarriers are not precluded. (4) Double sideband, suppressed-carrier, amplitude modulation of...

Precision Saturated Absorption Spectroscopy of H3+

NASA Astrophysics Data System (ADS)

Guan, Yu-chan; Liao, Yi-Chieh; Chang, Yung-Hsiang; Peng, Jin-Long; Shy, Jow-Tsong

2016-06-01

In our previous work on the Lamb dips of the νb{2} fundamental band of H3+, the saturated absorption spectrum was obtained by the third-derivative spectroscopy using frequency modulation [1]. However, the frequency modulation also causes error in absolute frequency determination. To solve this problem, we have built an offset-locking system to lock the OPO pump frequency to an iodine-stabilized Nd:YAG laser. With this modification, we are able to scan the OPO idler frequency precisely and obtain the profile of the Lamb dips. Double modulation (amplitude modulation of the idler power and concentration modulation of the ion) is employed to subtract the interference fringes of the signal and increase the signal-to-noise ratio effectively. To Determine the absolute frequency of the idler wave, the pump wave is offset locked on the R(56) 32-0 a10 hyperfine component of 127I2, and the signal wave is locked on a GPS disciplined fiber optical frequency comb (OFC). All references and lock systems have absolute frequency accuracy better than 10 kHz. Here, we demonstrate its performance by measuring one transition of methane and sixteen transitions of H3+. This instrument could pave the way for the high-resolution spectroscopy of a variety of molecular ions. [1] H.-C. Chen, C.-Y. Hsiao, J.-L. Peng, T. Amano, and J.-T. Shy, Phys. Rev. Lett. 109, 263002 (2012).

Optimisation of frequency-modulated characteristics of output radiation in a lidar with Raman amplification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grigorievsky, V I; Tezadov, Ya A

2016-03-31

The reported study is aimed at increasing the power in the transmission path of a lidar with Raman amplification for longpath sensing of methane by optimising the frequency-modulated characteristics of the output radiation. The pump current of the used distributed-feedback master laser was modulated by a linearfrequency signal with simultaneous application of a non-synchronous high-frequency signal. For such a modulation regime, the Raman amplifier provided the mean output power of 2.5 W at a wavelength of 1650 nm. The spectral broadening did not significantly decrease the lidar sensitivity at long paths. (lidars)

Frequency shift, damping, and tunneling current coupling with quartz tuning forks in noncontact atomic force microscopy

NASA Astrophysics Data System (ADS)

Nony, Laurent; Bocquet, Franck; Para, Franck; Loppacher, Christian

2016-09-01

A combined experimental and theoretical approach to the coupling between frequency-shift (Δ f ) , damping, and tunneling current (It) in combined noncontact atomic force microscopy/scanning tunneling microscopy using quartz tuning forks (QTF)-based probes is reported. When brought into oscillating tunneling conditions, the tip located at the QTF prong's end radiates an electromagnetic field which couples to the QTF prong motion via its piezoelectric tensor and loads its electrodes by induction. Our approach explains how those It-related effects ultimately modify the Δ f and the damping measurements. This paradigm to the origin of the coupling between It and the nc-AFM regular signals relies on both the intrinsic piezoelectric nature of the quartz constituting the QTF and its electrodes design.

Frequency-Modulation Correlation Spectrometer

NASA Technical Reports Server (NTRS)

Margolis, J. S.; Martonchik, J. V.

1985-01-01

New type of correlation spectrometer eliminates need to shift between two cells, one empty and one containing reference gas. Electrooptical phase modulator sinusoidally shift frequencies of sample transmission spectrum.

Study of magnetic resonance with parametric modulation in a potassium vapor cell

NASA Astrophysics Data System (ADS)

Zhang, Rui; Wang, Zhiguo; Peng, Xiang; Li, Wenhao; Li, Songjian; Guo, Hong; Cream Team

2017-04-01

A typical magnetic-resonance scheme employs a static bias magnetic field and an orthogonal driving magnetic field oscillating at the Larmor frequency, at which the atomic polarization precesses around the static magnetic field. We demonstrate in a potassium vapor cell the variations of the resonance condition and the spin precession dynamics resulting from the parametric modulation of the bias field, which are in well agreement with theoretical predictions from the Bloch equation. We show that, the driving magnetic field with the frequency detuned by different harmonics of the parametric modulation frequency can lead to resonance as well. Also, a series of frequency sidebands centered at the driving frequency and spaced by the parametric modulation frequency can be observed in the precession of the atomic polarization. These effects could be used in different atomic magnetometry applications. This work is supported by the National Science Fund for Distinguished Young Scholars of China (Grant No. 61225003) and the National Natural Science Foundation of China (Grant Nos. 61531003 and 61571018).

Ultra-wideband microwave photonic frequency downconverter based on carrier-suppressed single-sideband modulation

NASA Astrophysics Data System (ADS)

Wang, Yunxin; Li, Jingnan; Wang, Dayong; Zhou, Tao; Xu, Jiahao; Zhong, Xin; Yang, Dengcai; Rong, Lu

2018-03-01

An ultra-wideband microwave photonic frequency downconverter is proposed based on carrier-suppressed single-sideband (CS-SSB) modulation. A radio frequency (RF) signal and a local oscillator (LO) signal are combined to drive a dual-parallel Mach-Zehnder modulator (DPMZM) through the electrical 90°hybrid coupler. To break through the bandwidth limit, an optical bandpass filter (OBPF) is applied simultaneously. Then a photodetector (PD) after OBPF is used to obtain intermediate frequency (IF) signal. Experimental results demonstrate that the proposed frequency downconverter can generate the CS-SSB modulation signal from 2 to 40 GHz in optical spectrum. All the mixing spurs are completely suppressed under the noise floor in electrical spectrum, and the output IF signal possesses high purity with a suppression ratio of the undesired signals (≥40 dB). Furthermore, the multi-octave downconversion can also be implemented to satisfy the bandwidth requirement of multi-channel communication. The proposed frequency downconverter supplies an ultra-wideband and high-purity alternative for the signal processing in microwave photonic applications.

Ultrasonic speech translator and communications system

DOEpatents

Akerman, M.A.; Ayers, C.W.; Haynes, H.D.

1996-07-23

A wireless communication system undetectable by radio frequency methods for converting audio signals, including human voice, to electronic signals in the ultrasonic frequency range, transmitting the ultrasonic signal by way of acoustical pressure waves across a carrier medium, including gases, liquids, or solids, and reconverting the ultrasonic acoustical pressure waves back to the original audio signal. The ultrasonic speech translator and communication system includes an ultrasonic transmitting device and an ultrasonic receiving device. The ultrasonic transmitting device accepts as input an audio signal such as human voice input from a microphone or tape deck. The ultrasonic transmitting device frequency modulates an ultrasonic carrier signal with the audio signal producing a frequency modulated ultrasonic carrier signal, which is transmitted via acoustical pressure waves across a carrier medium such as gases, liquids or solids. The ultrasonic receiving device converts the frequency modulated ultrasonic acoustical pressure waves to a frequency modulated electronic signal, demodulates the audio signal from the ultrasonic carrier signal, and conditions the demodulated audio signal to reproduce the original audio signal at its output. 7 figs.

Insight into conformational changes of a single α-helix peptide molecule through stiffness measurements

NASA Astrophysics Data System (ADS)

Kageshima, Masami; Lantz, Mark A.; Jarvis, Suzanne P.; Tokumoto, Hiroshi; Takeda, Seiji; Ptak, Arkadiusz; Nakamura, Chikashi; Miyake, Jun

2001-07-01

Stiffness variations during the conformational change of a single α-helix polylysine peptide molecule were measured in a liquid environment using atomic force microscopy (AFM) with magnetic cantilever modulation. At the initial stage of the stretching process the stiffness decreased due to the breaking of hydrogen bonds and then increased due to the stretching of the helix backbone. These changes were reversible on reversal of the stretching motion. Below p K, the stiffness did not show increase on reversal, indicating that the reforming of hydrogen bonds did not take place. Conformational changes in the molecule were examined via these changes in stiffness.

Computational expressions for signals in frequency-modulation spectroscopy.

PubMed

Di Rosa, Michael D; Reiten, M T

2015-06-01

General expressions for the signals in frequency-modulation spectroscopy (FMS) appear in the literature but are often reduced to simple analytical equations following the assumption of a weak modulation index. This is little help to the experimentalist who wants to predict signals for modulation depths of the order of unity or greater, where strong FMS signals reside. Here, we develop general formulas for FMS signals in the case of an absorber with a Voigt line shape and then link these expressions to an example and existing numerical code for the line shape. The resulting computational recipe is easy to implement and exercised here to show where the larger FMS signals are found over the coordinates of modulation index and modulation frequency. One can also estimate from provided curves the in-phase FMS signal over a wide range of modulation parameters at either the Lorentzian-broadening or Doppler-broadening limit, or anywhere in between by interpolation.

NMR studies of the incommensurate helical antiferromagnet EuCo 2 P 2 : Determination of antiferromagnetic propagation vector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Higa, Nonoka; Ding, Qing -Ping; Yogi, Mamoru

Recently, Q.-P. Ding et al. reported that their nuclear magnetic resonance (NMR) study on EuCo 2As 2 successfully characterized the antiferromagnetic (AFM) propagation vector of the incommensurate helix AFM state, showing that NMR is a unique tool for determination of the spin structures in incommensurate helical AFMs. Motivated by this work, we have carried out 153Eu, 31P, and 59Co NMR measurements on the helical antiferromagnet EuCo 2P 2 with an AFM ordering temperature T N = 66.5 K. An incommensurate helical AFM structure was clearly confirmed by 153Eu and 31P NMR spectra on single-crystalline EuCo 2P 2 in zero magneticmore » field at 1.6 K and its external magnetic field dependence. Furthermore, based on 59Co NMR data in both the paramagnetic and incommensurate AFM states, we have determined the model-independent value of the AFM propagation vector k = (0,0,0.73±0.09)2π/c, where c is the c-axis lattice parameter. As a result, the temperature dependence of k is also discussed.« less

NMR studies of the incommensurate helical antiferromagnet EuCo 2 P 2 : Determination of antiferromagnetic propagation vector

DOE PAGES

Higa, Nonoka; Ding, Qing -Ping; Yogi, Mamoru; ...

2017-07-06

Recently, Q.-P. Ding et al. reported that their nuclear magnetic resonance (NMR) study on EuCo 2As 2 successfully characterized the antiferromagnetic (AFM) propagation vector of the incommensurate helix AFM state, showing that NMR is a unique tool for determination of the spin structures in incommensurate helical AFMs. Motivated by this work, we have carried out 153Eu, 31P, and 59Co NMR measurements on the helical antiferromagnet EuCo 2P 2 with an AFM ordering temperature T N = 66.5 K. An incommensurate helical AFM structure was clearly confirmed by 153Eu and 31P NMR spectra on single-crystalline EuCo 2P 2 in zero magneticmore » field at 1.6 K and its external magnetic field dependence. Furthermore, based on 59Co NMR data in both the paramagnetic and incommensurate AFM states, we have determined the model-independent value of the AFM propagation vector k = (0,0,0.73±0.09)2π/c, where c is the c-axis lattice parameter. As a result, the temperature dependence of k is also discussed.« less

Detection of aflatoxin M1 in milk using spectroscopy and multivariate analyses.

PubMed

Jaiswal, Pranita; Jha, Shyam Narayan; Kaur, Jaspreet; Borah, Anjan; Ramya, H G

2018-01-01

Aflatoxin M1 (AFM1), a potentially carcinogenic compound, is found in milk obtained from animals that consume contaminated feed. Spectra of bovine milk, spiked with AFM1 (0, 0.02, 0.04, 0.06, 0.08 and 0.1μg/l) were acquired using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectrometer. Spectra revealed significant differences among pure and AFM1 spiked samples in spectral regions 1800-650cm -1 and 3689-3499cm -1 , which may be attributed to complex chemical structure of AFM1. Principal component analysis (PCA) showed clear clustering of samples (p⩽0.05). The models could successfully classify (>86%) and detect even 0.02μg/l AFM1 in milk (p⩽0.05) using SIMCA. AFM1 was best predicted in wavenumber range of 1800-650cm -1 with coefficient of determination (R 2 ) of 0.99 and 0.98, for calibration and validation, respectively, using partial least square (PLS) regression. The study indicated feasibility of ATR-FTIR spectroscopy and chemometrics in rapid detection and quantification of AFM1 in milk. Copyright © 2016 Elsevier Ltd. All rights reserved.

Advances in research on structural characterisation of agricultural products using atomic force microscopy.

PubMed

Liu, Dongli; Cheng, Fang

2011-03-30

Atomic force microscopy (AFM) has many unique features compared with other conventional microscopies, such as high magnification with high resolution, minimal sample preparation, acquiring 2D and 3D images at the same time, observing ongoing processes directly, the possibility of manipulating macromolecules, etc. As a nanotechnology tool, AFM has been used to investigate the nanostructure of materials in many fields. This mini-review focuses mainly on its latest application to characterise the macromolecular nanostructure and surface topography of agricultural products. First the fundamentals of AFM are briefly explained. Then the macromolecular nanostructure information on agricultural products from AFM images is introduced by exploring the structure-function relationship in three aspects: agricultural product processing, agricultural product ripening and storage, and genetic and environmental factors. The surface topography characterisation of agricultural products using AFM is also discussed. The results reveal that AFM could be a powerful nanotechnology tool to acquire a deeper understanding of the mechanisms of structure and quality variations of agricultural products, which could be instructive in improving processing and storage technologies, and AFM is also helpful to reveal the essential nature of a product at nanoscale. Copyright © 2011 Society of Chemical Industry.

Broadband unidirectional ultrasound propagation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sinha, Dipen N.; Pantea, Cristian

A passive, linear arrangement of a sonic crystal-based apparatus and method including a 1D sonic crystal, a nonlinear medium, and an acoustic low-pass filter, for permitting unidirectional broadband ultrasound propagation as a collimated beam for underwater, air or other fluid communication, are described. The signal to be transmitted is first used to modulate a high-frequency ultrasonic carrier wave which is directed into the sonic crystal side of the apparatus. The apparatus processes the modulated signal, whereby the original low-frequency signal exits the apparatus as a collimated beam on the side of the apparatus opposite the sonic crystal. The sonic crystalmore » provides a bandpass acoustic filter through which the modulated high-frequency ultrasonic signal passes, and the nonlinear medium demodulates the modulated signal and recovers the low-frequency sound beam. The low-pass filter removes remaining high-frequency components, and contributes to the unidirectional property of the apparatus.« less