Imaging the Elastic Nanostructure of Ge Islands by Ultrasonic Force Microscopy

Kolosov, Oleg; Castell, Martin R.; Marsh, C.D.; Briggs, G. Andrew D.; Kamins, T. I.; Williams, R. Stanley

doi:10.1103/physrevlett.81.1046

Cited by 140 publications

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References 27 publications

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“…Reported observations of molecular vibrations by Inelastic Scanning Tunnelling Spectroscopy (IESTS) require an electrically conducting substrate [1]. Atomic Force Microscopy (AFM) experiments involving ultrasonic oscillations of elastically indented samples [2,3] can be performed on electrically insulating systems, but yield subsurface images with nanoscale resolution at best. Building on the high spatial resolution and sensitivity of dynamic non-contact AFM [4,5], we introduce Damping Force Spectroscopy (DFS) as a non-invasive tool to study subsurface structure and vibrational modes in complex molecular systems at the atomic scale.…”

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“…We elucidate the physical origin of damping in a microscopic model and provide quantitative interpretation of the observations by calculating the vibrational spectrum and damping of Dy@C82 inside nanotubes with different diameters using ab initio total energy and molecular dynamics calculations. [2,3] can be performed on electrically insulating systems, but yield subsurface images with nanoscale resolution at best. Building on the high spatial resolution and sensitivity of dynamic non-contact AFM [4, 5], we introduce Damping Force Spectroscopy (DFS) as a non-invasive tool to study subsurface structure and vibrational modes in complex molecular systems at the atomic scale.…”

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Revealing Subsurface Vibrational Modes by Atom-Resolved Damping Force Spectroscopy

et al. 2009

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We propose to use the damping signal of an oscillating cantilever in dynamic atomic force microscopy as a noninvasive tool to study the vibrational structure of the substrate. We present atomically resolved maps of damping in carbon nanotube peapods, capable of identifying the location and packing of enclosed Dy@C82 molecules as well as local excitations of vibrational modes inside nanotubes of different diameter. We elucidate the physical origin of damping in a microscopic model and provide quantitative interpretation of the observations by calculating the vibrational spectrum and damping of Dy@C82 inside nanotubes with different diameters using ab initio total energy and molecular dynamics calculations. [2,3] can be performed on electrically insulating systems, but yield subsurface images with nanoscale resolution at best. Building on the high spatial resolution and sensitivity of dynamic non-contact AFM [4, 5], we introduce Damping Force Spectroscopy (DFS) as a non-invasive tool to study subsurface structure and vibrational modes in complex molecular systems at the atomic scale. We have chosen carbon nanotube peapods [6,7,8] consisting of linear chains of fullerenes enclosed in single-wall carbon nanotubes (SWNTs) [9] as a prominent example of supramolecular compounds. Of particular interest are (M@C n )@SWNT peapods containing M@C n metallofullerenes, hollow cages of n carbon atoms surrounding the metal atom M, known for their unusual electronic transport behavior [10].Here, we demonstrate that monitoring the damping of an oscillating AFM tip provides invaluable information not only about topography, but also the subsurface vibrational modes that have not been observed before with atomic-scale spatial resolution. Our DFS studies of (Dy@C 82 )@SWNT indicate that the observed damping of the tip oscillation depends sensitively on its position and host tube diameter of (Dy@C 82 )@SWNT, in agreement with extensive molecular dynamics (MD) studies reported here. Results of our predictive calculations trace back the observed damping to the excitation of local vibrational modes by transferring energy from the oscillating AFM tip. This truly mechanical oscillator couples to the enclosing nanotube first and subsequently to the enclosed molecules, revealing their packing structure.(Dy@C 82 )@SWNT peapods were prepared by encapsulating Dy@C 82 metallofullerenes in open-ended SWNTs at a filling rate of ≈60%, as confirmed by high-resolution transmission electron microscopy and DFS [11]. The peapods were deposited at low coverage onto an insulating flat SiO 2 surface of a Si substrate and observed by a home-built dynamic AFM [11], shown schematically in Fig. 1(a). The AFM, equipped with a commercial Si cantilever (spring constant of 34.3 N/m, eigenfrequency of 159 kHz) and Si tip (nominal tip radius of 20Å), was operated at constant oscillation amplitude of 21 − 23Å under ultra-high vacuum (p < 1×10 −8 Pa) at low temperature (T < 13 K).High-resolution AFM topography observations of SWNTs and peapods, illustrated in Fig. 1(...

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Revealing Subsurface Vibrational Modes by Atom-Resolved Damping Force Spectroscopy

et al. 2009

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“…Although a number of techniques are available for surface characterization, methods to assess subsurface structures at the nanoscale remain largely in development. Several successful efforts at nanoscale subsurface imaging have involved combining the lateral resolution of the atomic force microscope 1 (AFM) with the nondestructive capability of acoustical methodologies for assessing subsurface features of materials [2][3][4][5][6][7][8][9][10][11] . The utilization of the AFM in principle provides the necessary lateral resolution for obtaining subsurface images at the nanoscale.…”

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Nanoscale subsurface imaging via resonant difference-frequency atomic force ultrasonic microscopy

Cantrell

Lillehei

2007

Journal of Applied Physics

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A novel scanning probe microscope methodology has been developed that employs an ultrasonic wave launched from the bottom of a sample while the cantilever of an atomic force microscope, driven at a frequency differing from the ultrasonic frequency by the fundamental resonance frequency of the cantilever, engages the sample top surface. The nonlinear mixing of the oscillating cantilever and the ultrasonic wave in the region defined by the cantilever tip-sample surface interaction force generates differencefrequency oscillations at the cantilever fundamental resonance. The resonance-enhanced difference-frequency signals are used to create images of embedded nanoscale features.PACS numbers: 68.37. Tj, 82.35.Np, https://ntrs.nasa.gov/search.jsp?R=20080007508 2018-05-12T16:13:39+00:00Z

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“…Set-point P An additional assumption made in UFM measurements is related to the dynamic behavior of the AFM cantilever. The cantilever is usually regarded as a point mass with no dynamic response at high frequencies [KOL98]. For a cantilevered beam, the linear response w(x,t) to a high frequency excitation is a superposition of all modes given by…”

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Ultrasonic Studies of the Fundamental Mechanisms of Recrystallization and Sintering of Metals

Turner¹

2005

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ObjectivesThe purpose of this project was to develop a fundamental understanding of the interaction of an ultrasonic wave with complex media, with specific emphases on recrystallization and sintering of metals. A combined analytical, numerical, and experimental research program was implemented. Theoretical models of elastic wave propagation through these complex materials were developed using stochastic wave field techniques. The numerical simulations focused on finite element wave propagation solutions through complex media. The experimental efforts were focused on corroboration of the models developed and on the development of new experimental techniques. The analytical and numerical research allows the experimental results to be interpreted quantitatively. Alteration in Collaborative ArrangementIn fall 2002, the Ames Lab partner, Dr. James C. Foley, announced that he was leaving for another position at Los Alamos National Laboratory. Dr. R. Bruce Thompson has served as the primary contact for this collaboration since Dr. Foley departed. Accomplishments (Recrystallization)Analytical Modeling. Expressions for the ultrasonic attenuation in media with arbitrary texture have been developed using stochastic wave propagation theory. Initial attempts at deriving simple expressions for the attenuation were unsuccessful. Therefore, a modified technique was developed that relies slightly more on numerical calculations. The method is based on a generalized function of a single scalar variable σ that characterizes the state of texture. In this case the weighting function for the individual grains is given by ( ) with θ as the grain orientation angle. Thus, when σ → 0 all grains are aligned and the material is transversely isotropic at the macroscale. As σ → ∞, all grains are randomly oriented and the material is isotropic at the macroscale.In terms of attenuation, the covariance of the microstructure is the primary quantity needed for the calculation of attenuation. It is defined by in which both Eqs. (2) and (3) include the grain orientation distribution function F such that and are dependent on σ. Example results using Eq. (2) are shown in Fig. 1 for both the average elastic properties as well as quasilongitudinal slowness surfaces in terms of σ. The transition from transversely isotropy to complete isotropy is captured well using the grain orientation distribution function. Example results for attenuation are shown in Fig. 2. Again, the transition from transverse isotropy to complete isotropy is shown. Of particular note is the peak observed in the SH attenuation when σ is about 0.5. Such information may be useful for process monitoring. (a) (b)Progress was also made in the study of multiple scattering in slab geometries. These results have applications associated with heterogeneous bonding and interface layers. Two example results are shown in Fig. 3. The layer is insonified by a plane longitudinal wave. One question in the multiple scattering regime is associated with the applicability of the diffusion li...

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Imaging the Elastic Nanostructure of Ge Islands by Ultrasonic Force Microscopy

Cited by 140 publications

References 27 publications

Revealing Subsurface Vibrational Modes by Atom-Resolved Damping Force Spectroscopy

Revealing Subsurface Vibrational Modes by Atom-Resolved Damping Force Spectroscopy

Nanoscale subsurface imaging via resonant difference-frequency atomic force ultrasonic microscopy

Ultrasonic Studies of the Fundamental Mechanisms of Recrystallization and Sintering of Metals

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