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Nanoscale Mechanics by Contact Resonance Atomic Force Microscopy

Summary:

Atomic force microscopy (AFM) provides unique accessibility at the nanoscale. Capabilities in terms of nanoscale mechanical property measurements are added to AFM by contact-resonance AFM (AFM) for a large range of elastic modulus from few GPa to hundred GPa. The nanoscale spatial resolution and robust elastic modulus calibration of CR-AFM are used in quantitative measurements of elastic properties of one-dimensional structures (nanowires, nanotubes, fibers), two-dimensional structures (thin film coatings), nanocomposites etc. Integrative CR-AFM measurements and computation provide a unique mechanical characterization for the next generation of materials and structures used in nanoscale applications and devices.

Contact Resonance Atomic Force Microscopy
Measurements of the normal and tangential elastic moduli of nanowires.

Description:

Contact-resonance AFM (CR-AFM) has been demonstrated to provide accurate, noninvasive, and reliable measurements at the nanoscale. In CR-AFM the local elasticity of a material is probed by measuring the resonance frequency of an AFM probe brought into contact with the material. The resonance frequency of the AFM cantilever changes accordingly with the stiffness of the probe-sample contact and it is this contact stiffness that is converted into elastic modulus.

Contact resonance atomic force microscopy mapping on granular Au films.
Contact resonance atomic force microscopy mapping on granular Au films.

CR-AFM has the spatial resolution of order of few nanometers (limited by the probing contact radius) and a measurement resolution of about 5% for elastic moduli in the range from few GPa to hundreds of GPa. With the AFM versatility of probing substrate-supported nanostructures, CR-AFM can be used for elastic modulus measurements of various one-dimensional nanostructures (nanowires, nanotubes, etc) or two-dimensional nanostructures (atomic sheets, thin coatings, films with complex stack structure etc). Unlike most of currently developed nansocale mechanical tests (e.g. tensile tests observed inside a scanning electron microscope), CR-AFM requires no additional testing device or specimen manipulation.

CR-AFM views of a Cu line embedded into a low-k dielectric material (http://nanotechweb.org/cws/article/lab/49833).
CR-AFM views of a Cu line embedded into a low-k dielectric material (http://nanotechweb.org/cws/article/lab/49833).

For mechanical property measurements, like the ones accessible by CR-AFM, the benefit of such combination is a self-consistent validation of experiments and theory by combining measurements with simulations. As a property mapping AFM technique, CR-AFM has the spatial resolution to provide elastic and viscoelastic property measurements that can be used in atomistic simulations. Few advantages are noted in the case of CR-AFM: i) A better probe-sample interaction could be captured by simulations rather than analytical models; ii) An improved material property characterization of complex structures; iii) Address the characterization of materials with reduced dimensionality (coatings in the form of atomic sheets, nanostructures).

Bending states prior fracture of a Si NW.
Bending states prior fracture of a Si NW.

Major Accomplishments:

Elastic modulus measurements on various one-dimensional structures: ZnO NWs (Nano Letters 7, 3691, 2007), Te NWs (Applied Physics Letters 92, 241908, 2008; Ultramicroscopy 109, 929, 2009), AlN NTs (Nanotechnology 20, 035706, 2009), Si NWs (Nano Letters 10, 2031, 2010); fracture strength of Si NWs (Nano Letters 12, 2599, 2012; Journal of Materials Research 27, 562, 2012); elastic modulus mapping at the nanoscale (Nanotechnology 19, 235701, 2008); nanoscale mechanical properties of low-k dielectric materials and Cu integrated circuits (Journal of Materials Research 24, 2960, 2009; Nanotechnology 23, 215703, 2012); CR-AFM developments and new scanning capabilities (Review of Scientific Instruments 77, 103707, 2006).

Nanotechnology-Cover

Lead Organizational Unit:

mml

Customers/Contributors/Collaborators:

Intel Corp., Bruker Nano Surfaces Division, Materials Measurement Science Division (NIST, MML), Materials Science and Engineering Division (NIST, MML), Department of Mechanical Engineering and Materials Science at Colorado School of Mines, Advanced Materials Sciences Department at Sandia National Laboratories