Atomic force acoustic microscopy methods to determine thin-film elastic properties

Abstract

We discuss atomic force acoustic microscopy ͑AFAM͒ methods to determine quantitative values for the elastic properties of thin films. The AFAM approach measures the frequencies of an AFM cantilever's first two flexural resonances while in contact with a material. The indentation modulus M of an unknown or test material can be obtained by comparing the resonant spectrum of the test material to that of a reference material. We examined a niobium film (dϭ280Ϯ30 nm) with AFAM using two separate reference materials and two different cantilever geometries. Data were analyzed by two methods: an analytical model based on conventional beam dynamics, and a finite element method that accommodated variable cantilever cross section and viscous damping. AFAM values of M varied significantly depending on the specific experimental configuration and analysis technique.By averaging values obtained with both reference materials, very good agreement ͑5-10 % difference͒ with values determined by other methods was achieved. These results provide insight into using AFAM methods to attain reliable, accurate measurements of elastic properties on the nanoscale.

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

“…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.…”

Contact resonances of U-shaped atomic force microscope probes

“…In order for new material designs to be fully understood, measurements that can quantify behavior at appropriate scales, often down to the nanoscale, are required. The contact resonance atomic force microscope (CR-AFM) technique is a promising materials characterization approach, which can quantify the elastic [1][2][3][4][5][6][7][8][9] as well as viscoelastic [10][11][12][13][14][15][16] properties of materials with spatial resolution on the order of tens of nanometers. CR-AFM uses the vibration spectra of an AFM probe during vibrations for both the noncontact case, and when the tip is in contact with a sample.…”

“…CR-AFM is becoming well accepted for analyzing the properties of a wide variety of materials such as polymers, [11][12][13][14]16,18,23 biological materials, 16,25,26 composite materials, 27 dielectric materials, 28 metallic glass, 29 and metals. 6,8,9 It has shown great promise for many interesting problems especially those involving the interfaces of a multi-phase material. These are some examples that illustrate the demand for nanoscale property measurements.…”

Image contrast reversals in contact resonance atomic force microscopy

“…[13][14][15][16] Moreover, by modulating the tip-sample interaction at a frequency close to one of the contact resonance frequencies while scanning the sample surface, or by recording contact resonances point-by-point across the scan area and calculating subsequently, semi-quantitative or even quantitative mapping of the mechanical properties of the sample surface can be realized. [17][18][19][20][21][22] However, the material properties, contact conditions, loading forces, excitation amplitudes and the operating frequency can affect the final results. Therefore, an in-depth analysis of the effects of these factors is urgently needed for better image interpretation.…”