Introduction

Our research uses the principles of nonlinear dynamical systems, fluid-structure interaction, and mechanics to study important and interdisciplinary problems in science and engineering.

As one example, our studies of the nonlinear oscillations of microcantilevers in atomic force microscopy (AFM) are helping scientists worldwide in nanoscience and nanotechnology to interpret images, and improve metrology, speed, and compositional contrast while scanning over a wide range of samples such as living cells, bacteria, viruses, composite materials, and semiconductor devices. Using this knowledge, we are working with biophysicists in developing new AFM based tools for biomechanical assays of living cells and viruses with the ultimate goal of helping cancer specialists and scientists understand the mechanical properties of cancer cells and viruses.

In another example we are studying the nonlinear dynamics of micro-electromechanical systems (MEMS) such as radio-frequency (RF) switches that could be used in weapons stockpiles and high-performance wireless communication systems in order to improve their reliability and to monitor their health.

In yet another example we are working with the department of human kinesiology to understand the nonlinear dynamics of human posture with the goal of identifying from experimental measurements of human sway whether or not a subject may suffer from neuromuscular disorders such as Parkinson’s disease or multiple sclerosis or may be particularly susceptible to stumbling and falling – a particular concern in geriatric health care.

The students and postdocs in the group have a strong foundation in dynamics, vibrations, solid and fluid mechanics, and creative, open minds for learning new research areas beyond the traditional mechanical engineering applications. The research is carried out in the DSSL (Dynamic Systems and Stability Lab) in Rm. 246, ME Bldg, and in two AFM Labs and the DAMN lab (Dynamic analysis of micro- and nanosystems) at the Birck Nanotechnology Center.

We invite you to browse these web pages to meet the group members and learn about their research.

Current Members

Arvind Raman, Ph.D.
Description Needed
raman@purdue.edu
CV Available Upon Request
Alexander Cartagena
Fluid mechanics, micro/nanomechanics, and living cell mechanics studied using AFM in fluid environments
B.S. Mechanical Engineering, University of Puerto Rico at Mayaguez, 2010
alex.xavy@gmail.com
CV Available Upon Request
James Chagdes
Nonlinear dynamics, biomechanics, and vibrations
B.S. Mechanical Engineering, Purdue University, 2007
jchagdes@purdue.edu
CV Available Upon Request
Daniel Kiracofe
Dynamics, Vibrations, and Liquid Environment AFM
B.S. Computer Science and Engineering, Ohio State University, 2002
M.S. Mechanical Engineering, Ohio State University, 2004
drkiraco@purdue.edu
John Melcher
Nonlinear dynamics, grazing oscillators, dynamic atomic force microscopy
B.S. Mechanical Engineering, Purdue University, 2006
jmelcher@purdue.edu
CV Available Upon Request
Gyan Prakash
Nano and micromechanical mass-sensors, Multi-frequency dynamic AFM methods, Electrostatic Force Microscopy (EFM), and Graphene physics
B.S. Physics Indian Institute of Technology, 2002
M.S. Physics Indian Institute of Technology, 2004
gprakash@purdue.edu
CV Available Upon Request
Nurul Shaik
Nonlinear dynamics, vibrations, and MEMS
B.Tech Mechanical Engineering, Acharya Nagarjuna University, 2006
M.Tech, Mechanical Engineering, Indian Institute of Technology, 2008
nurul@purdue.edu
CV Available Upon Request
Hank Thompson
Vibrations, mechanics, nanocomposites, and electrostatic force microscopy
B.S. Mechanical Engineering, University of Nevada, Reno, 2009
hthomps@purdue.edu
CV Available Upon Request
Ryan Tung
Fluid-structure interactions in microsystems, dynamics and vibrations in microsystems, laser Doppler interferometry
B.S. Mechanical Engineering, University of Nevada, Reno, 2006
M.S. Mechanical Engineering, Purdue University, 2008
rtung@purdue.edu
CV Available Upon Request
Ryan Wagner
B.S. Mechanical Engineering, Purdue University, 2008
Atomic Force Microscopy, Nanocomposites, Uncertainty Quantification, Cellulose Nanocrystals, and Mechanical Properties of Nanostructures
rbwagner@purdue.edu
CV Available Upon Request
Xin Xu, Ph.D.
Atomic force microcopy and applications to polymer and biological samples
B.S. Electronic Science and Engineering, Nanjing University, 2000
M.S. Electronic Science and Engineering, Nanjing University, 2003.
Ph.D Mechanical Engineering, Purdue University, 2009
xu55@purdue.edu
CV Available Upon Request
Leyla Yamin
Combined Fluorescence Microscopy with Dynamic Atomic Force Microscopy Methods on live and fixed cells
B.S. Mechanical Engineering, Purdue University, 2010
lyamin@purdue.edu
CV Available Upon Request

Current Research

Nonlinear dynamics of AFM microcantilevers in liquid environments
Funding agency: National Science Foundation (Dynamical systems program, GOALI project).
Collaborators: Agilent AFM division, Profs. Ron Reifenberger (Physics, Purdue) and Joel Chevrier (Institut Neel, Universite Joseph Fourier, Grenoble, France).

Perhaps the greatest advantage of the atomic force microscope (AFM) lies in its capability to study biomechanics and biophysics at tiny length scales, in the watery realm of individual proteins, DNA, and viruses under natural, in-vitro conditions in aqueous buffer solutions. The nonlinear dynamics of microcantilevers are quite unique and interesting under these highly damped conditions (Q-factors ~1 or damping ratio ζ ~ 0.5) when the tip-sample interaction forces are mostly repulsive in nature. Moreover the cantilevers are also subject to Langevin forces from the Brownian motion of the surrounding molecules. When resonant AFM cantilevers scan over biological samples in liquid environments their nonlinear vibration responses change significantly due to variations in local material properties. For example, shown in the figure above are experimental time series data and Fourier spectra of resonant cantilevers tapping on mica (left) and bacteriorhodpsin (or purple) membrane (right) clearly show nonlinear modal interactions with the second eigenmode in the form of higher harmonics that are enhanced near the second mode natural frequency.

In this work we are studying the fundamentals of nonlinear and stochastic dynamics of microcantilevers tapping on samples in liquid environments, with a focus on those phenomena that are most sensitive to local material properties and can be used to map local material property contrast. Possible applications include the local elasticity mapping of biological samples with nanometer resolution, molecular recognition mapping or for studying the ordering of water molecules of solid-liquid interfaces.

Related publications:

  • Kiracofe, D. and Raman, A., "Microcantilever dynamics in atomic force microscopy when using higher order eigenmodes in liquid environments," Journal of Applied Physics, accepted, 2010.
  • Xu, X., Melcher, J., and Raman, A., "Accurate force spectroscopy in tapping mode atomic force microscopy in liquids", Physical Review B, Vol. 81(3), pp. 7, 2010. PDF
  • Kiracofe, D. and Raman, A., "On eigenmodes, stiffness, and sensitivity of atomic force microscope cantilevers in air versus liquids", Journal of Applied Physics, Vol. 107(3), pp. 9, 2010. PDF
  • Melcher, J., Carrasco, C., Xu, X., Carrascosa, J.L., Gomez-Herrero, J., de Pablo, P.J., and Raman, A., "Origins of phase contrast in the atomic force microscope in liquids", Proceedings of the National Academy of Sciences of the United States of America, Vol. 106(33), pp. 13655-13660, 2009. PDF
  • Xu, X., Melcher, J., Basak, S., Reifenberger, R., and Raman, A., "Compositional contrast of biological materials in liquids using the momentary excitation of higher eigenmodes in dynamic atomic force microscopy", Physical Review Letters, Vol. 102(6), pp. 4, 2009. PDF
  • Melcher, J., Xu, X., and Raman, A., "Multiple impact regimes in liquid environment dynamic atomic force microscopy", Applied Physics Letters, Vol. 93(9), pp. 3, 2008. PDF
  • Tung, R.C., Jana, A., and Raman, A., "Hydrodynamic loading of microcantilevers oscillating near rigid walls", Journal of Applied Physics, Vol. 104(11), pp. 8, 2008. PDF
  • Xu, X., Carrasco, C., de Pablo, P.J., Gomez-Herrero, J., and Raman, A., "Unmasking imaging forces on soft biological samples in liquids when using dynamic atomic force microscopy: A case study on viral capsids", Biophysical Journal, Vol. 95(5), pp. 2520-2528, 2008. PDF
  • Basak, S. and Raman, A., "Dynamics of tapping mode atomic force microscopy in liquids: Theory and experiments", Applied Physical Letters, Vol. 91(6), pp. 3, 2007. PDF
  • Xu, X. and Raman, A., "Comparative dynamics of magnetically, acoustically, and Brownian motion driven microcantilevers in liquids", Journal of Applied Physical, Vol. 102(3), pp. 8, 2007. PDF

Biomechanical assays of viruses/living cells using advanced dynamic AFM techniques
Funding agency: National Science Foundation (Materials World Network program and Dynamical systems program, GOALI).
Collaborators: Sonia Contera and Sonia Trigueros (University of Oxford, UK) and Pedro j. de Pablo (Universidad Autonoma de Madrid, Spain), Eric Nauman (ME, BME, Purdue).

In recent years there has been a growing realization of the importance of mechanical properties in biology. Cell morphogenesis including processes such as cell division, tissue growth, or cancer proliferation has complex mechanisms in which mechanical properties play a central organizational role. To the materials engineer or nanotechnologist, viruses are perfectly defined organic nanoparticles which are commonly used as scaffolds or as nano-containers. Because their structure can be directed by tailored evolution and their production can be commercially viable, viruses are becoming the basis of whole new approaches to the manufacture of nanomaterials far beyond applications in biology and medicine.

In this project we are developing new modes of dynamic AFM using resonant AFM microcantilevers to map the local properties of living cells and viruses under near-physiological conditions, i.e. in saline buffer solutions. The multi-frequency techniques exploit the nonlinear dynamics of cantilevers in liquids that are mediated by the soft surface interactions.

Related publications:

  • Melcher, J., Carrasco, C., Xu, X., Carrascosa, J.L., Gomez-Herrero, J., de Pablo, P.J., and Raman, A., "Origins of phase contrast in the atomic force microscope in liquids", Proceedings of the National Academy of Sciences of the United States of America, Vol. 106(33), pp. 13655-13660, 2009. PDF
  • Xu, X., Melcher, J., Basak, S., Reifenberger, R., and Raman, A., "Compositional contrast of biological materials in liquids using the momentary excitation of higher eigenmodes in dynamic atomic force microscopy", Physical Review Letters, Vol. 102(6), pp. 4, 2009. PDF
Fluid structure interaction and nonlinear dynamics in RF-MEMS devices (part of the PRISM center for the prediction of reliability, integrability, and survivability of microsystems)
Funding Agency: National Nuclear Safety Administration.
Collaborators: Profs. J. Murthy, A. Alexeenko, D. Peroulis (Purdue).

RF MEMS switches are a prototypical contact MEMS device where a metallic, doubly-clamped beam is suspended over a thin dielectric layer which covers an electrode. A thin air film separates the metallic beam from the dielectric creating a capacitance. A sufficiently large voltage applied to the electrode rapidly pulls-in the beam onto the dielectric layer changing the switch capacitance thus toggling between its “on” and “off” states. The reliability of RF-MEMS contact switches is to a large extent limited by electrical charge build-up in the dielectric layer onto which the conducting bridge pulls-in when a sufficiently large voltage step is applied to the electrode. In this project we are studying the mechanisms of gas damping in such devices where the rapidly decreasing gap causes a large increase in Knudsen number as well as a change in fluid boundary condition during a switch event. This in turn significantly affects the impact velocity and thus charge injection and wear of the dielectric. Both continuum and sub-continuum modeling approaches are used, and a dedicated experimental facility using a controlled pressure chamber and a laser Doppler vibrometer is used in the DAMN lab. On the dynamics and vibrations side, we are investigating how the linear and nonlinear vibration response of switches can be used for condition monitoring and charge buildup on the device.

Related publications:

  • Lee, J-W., Mahopatro, A., Peroulis, D., and Raman, A., "Vibration based monitoring and diagnosis of dielectric charging in RF-MEMS switches", IEE-ASME Journal of Micro-electromechanical Systemsin review, in review, 2010. PDF
  • Lee, J-W., Tung, R., Raman, A., Sumali, H., Sullivan, J.P., "Squeeze-film damping of flexible microcantilevers at low ambient pressures: theory and experiment", Journal of Micromechanics and Microengineering, Vol. 19(10), pp. 14, 2009. PDF
  • Bidkar, R.A., Tung, R.C., Alexeenko, A.A., Sumali, H., Raman, A., "Unified theory of gas damping of flexible microcantilevers at low ambient pressures", Applied Physical Letters, Vol. 94(16), pp. 3, 2009. PDF
High gain, high bandwidth force and mass sensing based on silver nanowires
Funding Agency: National Institutes of Health (STTR program).
Collaborators: Prof. R. Reifenberger, NaugaNeedles Inc..

In this project we are trying to develop a new force sensing machine that can be used for measuring the mechanical properties of single molecules or of soft materials with high resolution. The idea is based on our recent discovery that laser doppler vibrometers can be adapted to measure the vibrations of thin nanowires (diameters less than 200 nm) such as those made of Silver Gallium produced by NaugaNeedles Inc.. On the right is shown an SEM image of a particularly long nanowire and its measured vibration spectrum that shows the capability of our system to measure upto several MHz (upto 20 MHz) and several eigenmodes of the cantilever. We have also been able to measure the nanowire vibrations in water using this method. Silver nanowires have stiffnesses in the range of 10 femtoNewton/nm to 10 picoNewton/nm with high resonant frequencies making them ideal for the study of mechanical properties of single biological molecules. In the course of this project we are developing a new instrument that integrates nanowires and laser Doppler Velocimetry for soft matter force sensing and imaging.

Related publications:

  • Biedermann, L.B., Tung, R.C., Raman, A., Reifenberger, R.G., Yazdanpanah, M., and Cohn R., "High sensitivity, high bandwidth force and mass sensing using silver gallium nanocantilevers", Nanotechnology, Vol. in press, 2010. PDF
  • Biedermann, L.B., Tung, R.C., Raman, A., Reifenberger, R.G., "Flexural vibration spectra of carbon nanotubes measured using laser Doppler vibrometry", Nanotechnology, Vol. 20(3), pp. 6, 2009. PDF
Mechanics of carbon nanotube/graphene/polymer nanocomposistes and carbon fiber-polymer microcomposite materials
Funding Agency: Boeing Atoms-to-aircraft program (Phantomworks) and NSF (DMR).
Collaborators: Profs. A. Strachan (MSE), M. Koslowski (ME), R. B. Pipes (MSE/AAE/ChE).

These two projects both relate to the use of dynamic AFM (using vibrating microcantilevers) to study the interactions between carbon nanotubes/graphene sheets and polymers (for nanocomposites applications) and between carbon fibers and polymer matrix in microcomposites (as used in the Boeing dreamliner). The AFM results are being used to assist in computational models of the nano-micro-macro scale properties, especially ultimate properties of such materials. We are currently developing methods using oscillating microcantilevers that allow the imaging of carbon nanotube networks beneath the surface of the polymer and in the quantitative measurement of viscoeleastic properties of the matrix polymer for of carbon-fiber composites.

Computational Atomic Force Microscopy
Funding Agency: Network for Computational Nanotechnology (NSF) and Dow Inc.
Collaborators: Profs. A. Strachan (MSE).

Virtual Environment for Dynamic AFM (VEDA) is a state-of-the-art simulation tool that predicts the AFM cantilever dynamics in vacuum, air and in liquids on a variety of substrates. The simulations are run off the US teragrid and are supported via the nanoHUB (www.nanohub.org). Our group maintains and develops all new simulation tools in VEDA, which is now used by ~1000 users worldwide including many AFM companies. The tools include multiple cantilever eigenmodes, many nonlinear tip sample models, several excitation and detection schemes, tunable lock-in parameters, and scanning simulations where the user constructs a landscape and specifies scanning parameters. We are currently investigating how molecular dynamics based models can be integrated into VEDA.

Related publications:

  • Melcher, J., Hu, S.Q., and Raman, A., "VEDA: A web-based virtual environment for dynamic atomic force microscopy", Review of Scientific Instruments, featured cover article, Vol. 79(6), pp. 11, 2008. PDF
Nonlinear dynamics and control of human posture
Funding Agency: Purdue Research Foundation.
Collaborators: Profs. S. Rietdyk (HK), J.M. Haddad (HK), H.N. Zelaznik (HK).

Standing upright and balancing is a deceptively simple activity that belies the underlying complexity of neuromuscular feedback loops that continually stabilize what is an unstable, nonlinear mechanical system. Described mechanically, the goal of stability is to actively control the center of mass so it remains within the base of support. (see Fig for a depiction of these variables). Measurements made by researchers on subjects standing still on force platforms reveal that the center of mass and center of pressure actually evolve in time tracing out characteristic trajectories (see Fig.).

Any impairment of neuromuscular response due to disease, old age, or accident will lead to changes in the posture control movements that in principle can be detected in the posture time series. The goal of the project is to develop nonlinear dynamical system models and highly sensitive signal analysis methods to diagnose human posture time series data for early and reliable detection of neuromuscular diseases or conditions that lead to problems with movement such as Parkinson’s disease, multiple sclerosis, cerebrovascular accidents (strokes) and aging. We are actively collaborating with colleagues in the Department of Human Kinesiology (Profs. Rietdyk, Zelaznik, and Haddad on this project).

Related publications:

  • Chagdes, J.R., Rietdyk, S., Haddad, J.M., Zelaznik, H.N., Raman, A., Rhea, C.K., and Silver, T.A., "Multiple timescales in postural dynamics associated with vision and a secondary task are revealed by wavelet analysis", Experimental Brain Research, Vol. 197(3), pp. 297-310, 2009. PDF
Quantitative nanomechanics and uncertainty quantification in nanomechanical measurements using the AFM – case study on Cellulose Nanocrystals
Funding Agency: Forest Products Laboratory.
Collaborators: Profs. Robert Moon (MSE), Ashlie Martini (ME), Jon Pratt (NIST).

Cellulose is the most common organic compound on earth and is widely present in trees, plants, algae and bacteria. Cellulose self-assembles into microfibrils that are composed of crystalline and amorphous regions from which the nanosized crystalline regions can be released with acid hydrolysis. These stiff cellulose crystalline nanorods are called cellulose nanocrystals (CNCs) and consist of cellulose chains systematically bundled together by intermolecular bonds (See Fig.). CNCs as a nanomaterial alternative have several unique advantages: (a) their elastic modulus exceeds that of Kevlar and is comparable to that of other nanoparticle reinforcements, (b) CNC’s have high aspect ratio, low density, and a reactive surface that enables easy surface functionalization, (c) they can be processed at industrial scale quantities and at low costs (e.g. wood CNCs are a byproduct of the paper industry, and CNCs are a potential byproduct of any cellulose to biofuels program), neither of which are true for many other nanomaterials, (d) cellulose is a polysaccharide that has minimal environmental, health and safety risks, and (e) the microcrystalline sources that CNC are extracted from are themselves sustainable, biodegradable, carbon neutral, and have low environmental, health and safety risks.

In this research program we are using the AFM for measuring the quantitative nanomechanical properties of CNC’s using AFM methods shown in Fig.2 above. One major effort is in quantifying uncertainties in elastic moduli or adhesive energy as measured from AFM. The ongoing work will also use the AFM for measuring CNC interactions with polymers in nanocomposites.

Related publications:

  • Lahiji, R., Xu, X., Reifenberger, R., Raman, A., Rudie, A., and Moon, R.B., “Atomic Force Microscopy characterization of cellulose nanocrystals”, Langmuir, 26(6), pp. 4480, 2009. PDF

Journal Publications

2010:

  • Biedermann, L.B., Tung, R.C., Raman, A., Reifenberger, R.G., Yazdanpanah, M., and Cohn R., "High sensitivity, high bandwidth force and mass sensing using silver gallium nanocantilevers", Nanotechnology, Vol. in press, 2010. PDF
  • Kiracofe, D. and Raman, A., "Microcantilever dynamics in atomic force microscopy when using higher order eigenmodes in liquid environments," Journal of Applied Physics, accepted, 2010.
  • Lee, J-W., Mahopatro, A., Peroulis, D., and Raman, A., "Vibration based monitoring and diagnosis of dielectric charging in RF-MEMS switches", IEE-ASME Journal of Micro-electromechanical Systemsin review, in review, 2010. PDF
  • Kiracofe, D. and Raman, A., "On eigenmodes, stiffness, and sensitivity of atomic force microscope cantilevers in air versus liquids", Journal of Applied Physics, Vol. 107(3), pp. 9, 2010. PDF
  • Xu, X., Melcher, J., and Raman, A., "Accurate force spectroscopy in tapping mode atomic force microscopy in liquids", Physical Review B, Vol. 81(3), pp. 7, 2010. PDF

2009:

  • Bidkar, R.A., Kimber, M., Raman, A., Bajaj, A.K., and Garimella, S.V., "Nonlinear aerodynamic damping of sharp-edged flexible beams oscillating at low Keulegan-Carpenter numbers," Journal of Fluid Mechanics, Vol. 63(4), pp. 269-289, 2009. PDF
  • Bidkar, R.A., Tung, R.C., Alexeenko, A.A., Sumali, H. and Raman, A., "Unified theory of gas damping of flexible microcantilevers at low ambient pressures", Applied Physics Letters, Vol. 94(16), pp. 3, 2009. PDF
  • Biedermann, L.B., Tung, R.C., Raman, A. and Reifenberger, R.G., "Flexural vibration spectra of carbon nanotubes measured using laser Doppler vibrometry", Nanotechnology, Vol. 20(3), pp. 6, 2009. PDF
  • Chagdes, J.R., Rietdyk, S., Haddad, J.M., Zelaznik, H.N., Raman, A., Rhea, C.K., and Silver, T.A., "Multiple timescales in postural dynamics associated with vision and a secondary task are revealed by wavelet analysis", Experimental Brain Research, Vol. 197(3), pp. 297-310, 2009. PDF
  • Gil-Santos, E., Ramos, D., Jana, A., Calleja, M., Raman, A., and Tamayo, J., "Mass sensing based on deterministic and stochastic responses of elastically coupled nanocantilevers", Nano Letters, Vol. 9(12), pp. 4122-4127, 2009. PDF
  • Jalili, N., Saggere, L., and Raman, A., "Special issue on dynamic modeling, control and manipulation at the nanoscale", Journal of Dynamic Systems Measurement and Control-Transactions of the Asme, Vol. 131(6), pp. 2, 2009. PDF
  • Lee, J-W., Tung, R., Raman, A., Sumali, H., Sullivan, J.P., "Squeeze-film damping of flexible microcantilevers at low ambient pressures: theory and experiment", Journal of Micromechanics and Microengineering, Vol. 19(10), pp. 14, 2009. PDF
  • Lahiji, R., Xu, X., Reifenberger, R., Raman, A., Rudie, A., and Moon, R.B., “Atomic Force Microscopy characterization of cellulose nanocrystals”, Langmuir, 26(6), pp. 4480, 2009. PDF
  • Melcher, J., Carrasco, C., Xu, X., Carrascosa, J.L., Gomez-Herrero, J., de Pablo, P.J., and Raman, A., "Origins of phase contrast in the atomic force microscope in liquids", Proceedings of the National Academy of Sciences of the United States of America, Vol. 106(33), pp. 13655-13660, 2009. PDF
  • Prakash, G., Hu, S., Raman, A. and Reifenberger, R., "Theoretical basis of parametric-resonance-based atomic force microscopy", Physical Review B, Vol. 79(9), pp. 10, 2009. PDF
  • Strus, M.C., Cano, C., Nguyen, C.V., Raman, A. and Pipes, R.B., “Adhesion between carbon nanotubes and select polymers through the use of peeling force spectroscopy,” Composite Science and Technology, Vol. 69 pp. 1580-1586, 2009. PDF
  • Xu, X., Melcher, J., Basak, S., Reifenberger, R. and Raman, A., "Compositional contrast of biological materials in liquids using the momentary excitation of higher eigenmodes in dynamic atomic force microscopy", Physical Review Letters, Vol. 102(6), pp. 4, 2009. PDF
  • Zhang, X.R., Fisher, T.S., Raman, A., and Sands, T.D., "Linear coefficient of thermal expansion of porous anodic alumina thin films from atomic force microscopy," Vol. 13(4), pp. 243-252, 2009. PDF

2008:

  • Bidkar, R.A., Raman, A. and Bajaj, A.K., "Aeroelastic stability of wide webs and narrow ribbons in cross flow", Journal of Applied Mechanics-Transactions of the Asme, Vol. 75(4), pp. 9, 2008. PDF
  • Conley, W.G., Krousgrill, C.M. and Raman, A., "Stick-slip motions in the friction force microscope: Effects of tip compliance", Tribology Letters, Tribology Letters, c. PDF
  • Conley, W.G., Raman, A., Krousgrill, C.M. and Mohammadi, S., "Nonlinear and nonplanar dynamics of suspended nanotube and nanowire resonators", Nano Letters, Vol. 8(6), pp. 1590-1595, 2008. PDF
  • Hu, S.Q. and Raman, A., "Inverting amplitude and phase to reconstruct tip-sample interaction forces in tapping mode atomic force microscopy", Nanotechnology, Vol. 19(37), pp. 11, 2008. PDF
  • Melcher, J., Hu, S.Q. and Raman, A., "Invited Article: VEDA: A web-based virtual environment for dynamic atomic force microscopy", Review of Scientific Instruments, Vol. 79(6), pp. 11, 2008. PDF
  • Melcher, J., Xu, X. and Raman, A., "Multiple impact regimes in liquid environment dynamic atomic force microscopy", Applied Physics Letters, Vol. 93(9), pp. 3, 2008. PDF
  • Raman, A., Melcher, J. and Tung, R., "Cantilever dynamics in atomic force microscopy", Nano Today, Vol. 3(1-2), pp. 20-27, 2008. PDF
  • Spletzer, M., Raman, A., Sumali, H. and Sullivan, J.P., "Highly sensitive mass detection and identification using vibration localization in coupled microcantilever arrays", Applied Physics Letters, Vol. 92(11), pp. 3, 2008. PDF
  • Strus, M.C., Zalamea, L., Raman, A., Pipes, R.B., Nguyen, C.V. and Stach, E.A., "Peeling force spectroscopy: Exposing the adhesive nanomechanics of one-dimensional nanostructures", Nano Letters, Vol. 8(2), pp. 544-550, 2008. PDF
  • Tung, R.C., Jana, A. and Raman, A., "Hydrodynamic loading of microcantilevers oscillating near rigid walls", Journal of Applied Physics, Vol. 104(11), pp. 8, 2008. PDF
  • Xu, X., Carrasco, C., de Pablo, P.J., Gomez-Herrero, J. and Raman, A., "Unmasking imaging forces on soft biological samples in liquids when using dynamic atomic force microscopy: A case study on viral capsids", Biophysical Journal, Vol. 95(5), pp. 2520-2528, 2008. PDF

2007:

  • Basak, S., Beyder, A., Spagnoli, C., Raman, A. and Sachs, F., "Hydrodynamics of torsional probes for atomic force microscopy in liquids", Journal of Applied Physics, Vol. 102(2), pp. 7, 2007. PDF
  • Basak, S. and Raman, A., "Dynamics of tapping mode atomic force microscopy in liquids: Theory and experiments", Applied Physics Letters, Vol. 91(6), pp. 3, 2007. PDF
  • Basak, S. and Raman, A., "Hydrodynamic coupling between micromechanical beams oscillating in viscous fluids", Physics of Fluids, Vol. 19(1), pp. 13, 2007. PDF
  • Dorrestijn, M., Bietsch, A., Acikalin, T., Raman, A., Hegner, M., Meyer, E. and Gerber, C., "Chladni figures revisited based on nanomechanics", Physical Review Letters, Vol. 98(2), pp. 4, 2007. PDF
  • Hu, S.Q. and Raman, A., "Analytical formulas and scaling laws for peak interaction forces in dynamic atomic force microscopy", Applied Physics Letters, Vol. 91(12), pp. 3, 2007. PDF
  • Jana, A., Raman, A., Dhayal, B., Tripp, S.L. and Reifenberger, R.G., "Microcantilever mechanics in flowing viscous fluids", Applied Physics Letters, Vol. 90(11), pp. 3, 2007. PDF
  • Kimber, M., Garimella, S.V. and Raman, A., "Local heat transfer coefficients induced by piezoelectrically actuated vibrating cantilevers", Journal of Heat Transfer-Transactions of the Asme, Vol. 129(9), pp. 1168-1176, 2007. PDF
  • Melcher, J., Hu, S.Q. and Raman, A., "Equivalent point-mass models of continuous atomic force microscope probes", Applied Physics Letters, Vol. 91(5), pp. 3, 2007. PDF
  • Spletzer, M., Raman, A. and Reifenberger, R., "Elastometric sensing using higher flexural eigenmodes of microcantilevers", Applied Physics Letters, Vol. 91(18), pp. 3, 2007. PDF
  • Wait, S.M., Basak, S., Garimella, S.V. and Raman, A., "Piezoelectric fans using higher flexural modes for electronics cooling applications", Ieee Transactions on Components and Packaging Technologies, Vol. 30(1), pp. 119-128, 2007. PDF
  • Xu, X. and Raman, A., "Comparative dynamics of magnetically, acoustically, and Brownian motion driven microcantilevers in liquids", Journal of Applied Physicss, Vol. 102(3), pp. 8, 2007. PDF

2006:

  • Basak, S., Raman, A. and Garimella, S.V., "Hydrodynamic loading of microcantilevers vibrating in viscous fluids", Journal of Applied Physics, Vol. 99(11), pp. 10, 2006. PDF
  • Hu, S.Q. and Raman, A., "Chaos in atomic force microscopy", Physical Review Letters, Vol. 96(3), pp. 4, 2006. PDF
  • Jana, A. and Raman, A., "Aeroelastic flutter of a disk rotating in an unbounded acoustic medium", Journal of Sound and Vibrationn, Vol. 289(3), pp. 612-631, 2006. PDF
  • Kang, N. and Raman, A., "Vibrations and stability of a flexible disk rotating in a gas-filled enclosure - Part 2: Experimental study", Journal of Sound and Vibration, Vol. 296(4-5), pp. 676-689, 2006. PDF
  • Kang, N. and Raman, A., "Vibrations and stability of a flexible disk rotating in a gas-filled enclosure - Part 1: Theoretical study", Journal of Sound and Vibration, Vol. 296(4-5), pp. 651-675, 2006. PDF
  • Moreno-Moreno, M., Raman, A., Gomez-Herrero, J. and Reifenberger, R., "Parametric resonance based scanning probe microscopy", Applied Physics Letters, Vol. 88(19), pp. 3, 2006. PDF
  • Spletzer, M., Raman, A., Wu, A.Q., Xu, X.F. and Reifenberger, R., "Ultrasensitive mass sensing using mode localization in coupled microcantilevers", Applied Physics Letters, Vol. 88(25), pp. 3, 2006. PDF

2005:

  • Basak, S., Raman, A. and Garimella, S.V., "Dynamic response optimization of piezoelectrically excited thin resonant beams", Journal of Vibration and Acoustics-Transactions of the Asme, Vol. 127(1), pp. 18-27, 2005. PDF
  • Conley, W.G., Raman, A. and Krousgrill, C.M., "Nonlinear dynamics in Tomlinson's model for atomic-scale friction and friction force microscopy", Journal of Applied Physics, Vol. 98(5), pp. 10, 2005. PDF
  • Crittenden, S., Raman, A. and Reifenberger, R., "Probing attractive forces at the nanoscale using higher-harmonic dynamic force microscopy", Physical Review B, Vol. 72(23), pp. 13, 2005. PDF
  • Jana, A. and Raman, A., "Nonlinear dynamics of a flexible spinning disc coupled to a precompressed spring", Nonlinear Dynamics, Vol. 40(1), pp. 1-20, 2005. PDF
  • Lee, S.I., Howell, S.W., Raman, A., Reifenberger, R., Nguyen, C.V. and Meyyappan, M., "Complex dynamics of carbon nanotube probe tips", Ultramicroscopy, Vol. 103(2), pp. 95-102, 2005. PDF
  • Strus, M.C., Raman, A., Han, C.S. and Nguyen, C.V., "Imaging artefacts in atomic force microscopy with carbon nanotube tips", Nanotechnology, Vol. 16(11), pp. 2482-2492, 2005. PDF

2004:

  • Acikalin, T., Wait, S.M., Garimella, S.V. and Raman, A., "Experimental investigation of the thermal performance of piezoelectric fans", Heat Transfer Engineering, Vol. 25(1), pp. 4-14, 2004. PDF
  • Hu, S.Q., Howell, S., Raman, A., Reifenberger, R. and Franchek, M., "Frequency domain identification of tip-sample van der Waals interactions in resonant atomic force microcantilevers", Journal of Vibration and Acoustics-Transactions of the Asme, Vol. 126(3), pp. 343-351, 2004. PDF
  • Kang, N.C. and Raman, A., "Aeroelastic flutter mechanisms of a flexible disk rotating in an enclosed compressible fluid", Journal of Applied Mechanics-Transactions of the Asme, Vol. 71(1), pp. 120-130, 2004. PDF
  • Lee, S.I., Howell, S.W., Raman, A., Reifenberger, R., Nguyen, C.V. and Meyyappan, M., "Nonlinear tapping dynamics of multi-walled carbon nanotube tipped atomic force microcantilevers", Nanotechnology, Vol. 15(5), pp. 416-421, 2004. PDF
  • Sharos, L.B., Raman, A., Crittenden, S. and Reifenberger, R., "Enhanced mass sensing using torsional and lateral resonances in microcantilevers", Applied Physics Letterss, Vol. 84(23), pp. 4638-4640, 2004. PDF
  • Vyas, A., Bajaj, A.K. and Raman, A., "Dynamics of structures with wideband autoparametric vibration absorbers: experiment", Proceedings of the Royal Society of London Series a-Mathematical Physical and Engineering Sciences, Vol. 460(2047), pp. 1857-1880, 2004. PDF
  • Vyas, A., Bajaj, A.K. and Raman, A., "Dynamics of structures with wideband autoparametric vibration absorbers: theory", Proceedings of the Royal Society of London Series a-Mathematical Physical and Engineering Sciences, Vol. 460(2046), pp. 1547-1581, 2004. PDF

2003 & Earlier:

  • Acikalin, T., Raman, A. and Garimella, S.V., "Two-dimensional streaming flows induced by resonating, thin beams", Journal of the Acoustical Society of Americaa, Vol. 114(4), pp. 1785-1795, 2003. PDF
  • Rutzel, S., Lee, S.I. and Raman, A., "Nonlinear dynamics of atomic-force-microscope probes driven in Lennard-Jones potentials", Proceedings of the Royal Society a-Mathematical Physical and Engineering Sciences, Vol. 459(2036), pp. 1925-1948, 2003. PDF
  • Lee, S.I., Howell, S.W., Raman, A. and Reifenberger, R., "Nonlinear dynamics of microcantilevers in tapping mode atomic force microscopy: A comparison between theory and experiment", Physical Review B, Vol. 66(11), pp. 10, 2002. PDF
  • Raman, A., Hansen, M.H. and Mote, C.D., "A note on the post-flutter dynamics of a rotating disk", Journal of Applied Mechanics-Transactions of the Asme, Vol. 69(6), pp. 864-866, 2002. PDF
  • Raman, A. and Mote, C.D., "Remarks on the non-linear vibration of an axisymmetric circular disk near critical speed", International Journal of Non-Linear Mechanics, Vol. 37(1), pp. 35-41, 2002. PDF
  • Hansen, M.H., Raman, A. and Mote, C.D., "Estimation of nonconservative aerodynamic pressure leading to flutter of spinning disks", Journal of Fluids and Structuress, Vol. 15(1), pp. 39-57, 2001. PDF
  • Raman, A. and Mote, C.D., "Experimental studies on the non-linear oscillations of imperfect circular disks spinning near critical speed", International Journal of Non-Linear Mechanics, Vol. 36(2), pp. 291-305, 2001. PDF
  • Raman, A. and Mote, C.D., "Effects of imperfection on the non-linear oscillations of circular plates spinning near critical speed", International Journal of Non-Linear Mechanics, Vol. 36(2), pp. 261-289, 2001. PDF
  • Kim, B.C., Raman, A. and Mote, C.D., "Prediction of aeroelastic flutter in a hard disk drive", Journal of Sound and Vibration, Vol. 238(2), pp. 309-325, 2000. PDF
  • Raman, A. and Bajaj, A.K., "On the non-stationary passage through bifurcations in resonantly forced Hamiltonian oscillators", International Journal of Non-Linear Mechanics, Vol. 33(5), pp. 907-933, 1998. PDF
  • Raman, A., Bajaj, A.K. and Davies, P., "On the slow transition across instabilities in non-linear dissipative systems", Journal of Sound and Vibration, Vol. 192(4), pp. 835-865, 1996. PDF

Alumni

Postdocs
Prof. Jin Woo Lee, postdoc from 2007-2009
Currently Assistant Professor, Mechanical Engineering, Ajou University, S. Korea
jinwoolee@ajou.ac.kr
Prof. Nam-Cheol Kang, postdoc from 2005-2006
Currently Assistant Professor, Mechanical Engineering, National Kyungpook University, S. Korea
nckang@knu.ac.kr
Prof. Soo-Il Lee, postdoc from 2002-2004
Currently Associate Professor, Mechanical and Information Engineering, University of Seoul, S. Korea
leesooil@uos.ac.kr
Doctoral Students
Mark Strus, Ph.D., 2009
Currently NRC postdoctoral fellow, Materials Reliability Division, NIST, Boulder
mstrus@purdue.edu
Rahul Bidkar, Ph.D., 2008
Currently at GE Global Research, NY
bidkar@ge.com
William G. Conley, Ph.D., 2008
Currently at Naval Surface Warfare Center, Crane, Indiana
william.g.conley@navy.mil
Anirban Jana, Ph.D., 2008
Currently Senior Scientific Specialist at Carnegie Mellon University
anirban@psc.edu
Matthew Spletzer, Ph.D., 2008
Currently member of staff, Sandia National Labs
masplet@sandia.gov
Ashwin Vyas, Ph.D., 2008
Currently at Cummins Inc., IN (co-supervised with Prfs Bajaj, Peroulis)
ashwinv@purdue.edu
Xin Xu, Ph.D., 2008
Currently Staff Scientists at Birck Nanotechnology Center, Purdue University
xu55@purdue.edu
Sudipta Basak, Ph.D., 2007
Currently at Silverbrook Research, Sydney, Australia
Memjet, San Diego, California
basaks@gmail.com
Shuiqing Hu, Ph.D., 2007
Currently at Veeco AFM Division
shu@veeco.com
Prof. Nam-Cheol Kang, Ph.D., 2005
Currently Assistant Professor, Mechanical Engineering, National Kyungpook University, S. Korea
nckang@knu.ac.kr
Other Students
  • Ryan Tung, M.S.M.E. 2008
  • Trevor Slack, M.S.M.E. 2005
  • Mauritz DeRidder, M.S.M.E. 2005 (non-thesis)
  • Lawrence Bradley Sharos, M.S.M.E. 2004
  • Sydney Wait, M.S.M.E. 2004 (co-advisor, Prof. Garimella)
  • Sudipta Basak, M.S.M.E. 2003
  • Dr. Philipp Buermann, M.S.M.E. 2003, later Ph.D. from TU-Dresden, Germany, currently at DLR, Hamburg, Germany
  • Merrill Vaughan, M.S.M.E. 2003
  • Tolga Acikalin, M.S.M.E. 2002 (with Prof. Garimella)
  • Mike Tiller, M.S.M.E 2002 (non-thesis), currently at Seagate Technologies, CA
  • Dr. Sebastian Reutzel, Diplomarbeit student, 2001, later Ph.D. from TU-Darmstadt, Germany
  • Ashwin Vyas, M.S.M.E. 2001 (with Prof. Bajaj)
B.S. Honors Students
  • William Conley
  • Kedar Hippalgaonkar (currently PhD student with Prof Majumdar's group, UC Berkeley)
  • Ruben Lai
  • John Melcher
Research Visitors
  • Dr. Changsoo Han, Korean Institute of Machinery and Materials, “Carbon nanotube probe fabrication and mechanics”, 2003-2004
  • Mr. Hyungwoo Lee, KAIST, Korea, “Carbon nanotube probe fabrication and mechanics”, 2003-2004
  • Dr. Jong-Gil Lee, Andong University, Korea, “Vibrations of carbon nanotube resonators and filters”, 2003-2004
  • Jin-Woo Lee, Seoul National University, Korea, “Acoustic structure interaction in hard disk drives”, 2001
  • Sebastian Rützel, Darmstadt University of Technology, Germany, “Dynamic response of atomic force microscopes in high-speed scanning applications”, 2000/2001