Scanning Probe Microscopy

Measurements and Standards N

Our goal is to develop standard reference materials and quantitative, 

ANOMATERIALS

reproducible, measurement methods and protocols for scanning probe 

microscopes, to enable accurate dimensional, force, and material 

property measurements at the nanoscale. For example, our approach 

will allow force measurements in atomic force microscopes to be both 

precise and accurate.

Objective

Impact and Customers

• A broad spectrum of industries, government agencies, and academic institutions use scanning probe instruments to 

develop, characterize, and manufacture products from ceramics, metals, polymers, and semiconductors.

• Atomic Force Microscopes (AFMs) are the most common scanning probe instrument, with an estimated 10,000 AFMs in 

use in virtually every materials research and development laboratory worldwide.

• Calibrating delicate measurement tools such as AFMs is difficult: at small 

length scales, the forces that affect probe-material interactions, and their 

relative magnitudes, are often unknown, but are certainly dominated by 

surface effects.

• Currently, the lack of SI-traceable stiffness calibration standards hampers 

progress towards making AFM force measurements quantitative; such 

measurements can be precise, but there is an incomplete understanding 

of accuracy.

Approach

Materials Science and Engineering Laboratory

A NIST Standard Reference Material (SRM 3461) will be produced that will enable 

accurate calibration of the flexural stiffness of AFM test cantilevers. An array of extremely 

precise rectangular cantilevers will be microfabricated from silicon-on-insulator wafers. 

The uniformity of the cantilever population on each wafer will be verified with resonance 

frequency measurements using Laser Doppler Velocimetry and Euler-Bernoulli modeling. 

Calibrations traceable to the International System of Units (SI) will be performed on a 

statistical subset of the population using the electrostatic force balance developed by the 

Manufacturing Engineering Laboratory at NIST. 

Further, AFM methods will be developed to enable mechanical property measurements at 

the nanoscale. Contact resonance methods will be used to determine elastic properties. AFM experiments using conducting 

probes have demonstrated the ability to measure thin interfacial oxide and organic films.

852-09-91b
Materials Science and Engineering Laboratory

A series of extremely uniform prototype 

reference cantilever arrays were created that 

can be used to calibrate the spring constants 

of atomic force microscopy cantilevers and 

other micromechanical structures. Nominal 

spring constants were estimated to be in the 

range of 0.02 Nm-1 to 0.2 Nm-1. Resonance 

frequency measurements were used to assess 

the uniformity of devices from different 

portions of a silicon-on-insulator wafer, and 

from different processing batches. Variations 

of less than 1% (relative standard deviation) 

in resonance frequency attested to the high 

degree of uniformity achieved. Independent 

calibration of cantilevers in an array using 

an electrostatic force balance indicated that 

the actual spring constants ranged from 

0.0260 ± 0.0005 Nm-1 (±1.9%) to 0.2099 

± 0.0009 Nm-1 (±0.43%). The results 

confirmed the feasibility of creating uniform 

reference cantilevers and calibrating them 

using an SI-traceable technique, making 

these devices excellent candidates for small 

force calibration standards for AFM. An SRM 

production batch is currently in process.

A method for calibrating the stiffness of 

AFM cantilevers was developed using the 

prototype reference cantilever array. A series 

of force-displacement curves was obtained 

using a commercial AFM test cantilever on 

the reference cantilever array, and the data 

were analyzed using an Euler-Bernoulli model 

to extract the test cantilever spring constant 

from linear regression fitting. The method 

offers improvements in precision over the 

reference cantilever method (factor of five) 

and the added mass calibration method 

(factor of three) that are currently used for 

AFM calibration.

A new “Hammerhead” AFM cantilever 

has been developed that is capable of 

providing precise lateral force (e.g. friction) 

measurements on surfaces using a commercial 

instrument. The “wings” projecting from 

the sides of the cantilever are used along 

with a specially designed calibration chip 

that allows for precise determination 

of the optical torsional sensitivity of the 

photodetector, which is usually very difficult 

to measure. A production batch of reference 

material “Hammerhead” cantilevers is being 

developed and fabricated to make these 

devices available to the research community.

A new, higher-precision contact-resonance 

AFM (CR-AFM) method was developed to 

quantitatively determine material indentation 

moduli by measuring local mechanical 

responses. A dual reference method has 

been shown to be capable of extracting 

the modulus of a material within 3% of 

the calculated expected value, without any 

assumptions of the probe’s mechanical 

properties.

Using this CR-AFM technique, select 

nanostructures have been studied to elucidate 

their nanomechanical properties. The 

most recent work included analysis of ZnO 

nanowires as small as 26 nm in diameter, 

and AlN nanotubes 200 nm in diameter but 

with wall thicknesses of only 19 nm.

Accomplishments

Mark Reitsma

Gheorghe Stan

Frank DelRio

Jon Pratt (MEL)

Robert Cook

Richard Gates

(Ceramics Division)

(301) 975-3677

richard.gates@nist.gov

www.nist.gov/ceramics

Learn More Publications

Gates RS and Pratt JR, Prototype Cantilevers for SI-Traceable Nanonewton Force 

Calibration Meas. Sci. Technol., 17: 2852 (2006)

Gates RS and Reitsma MG Precise Atomic Force Microscope Cantilever Spring Constant 

Calibration Using a Reference Cantilever Array Rev. Sci. Instrum., 78: 086101 (2007)

Kim DI, Namboodiri P, DelRio FW and Cook RF Mechanical and Electrical Coupling at 

Metal-Insulator-Metal Nanoscale Contacts Applied Physics Letters, 93: 203102 (2008)

Stan G, Ciobanu CV, Thayer TP, Wang GT, Creighton JR, Purushotham KP, Bendersky 

LA and Cook RF Elastic Moduli of Faceted Aluminum Nitride Nanotubes by Contact 

Resonance Atomic Force Microscopy Nanotechnology, 20: 035706 (2009)

Agreement between stiffness measurements and 

models

Comparison of calibration methods

Prototype “Hammerhead” cantilever for precise 

lateral force measurment in an AFM

A split AlN nanotube used for morphology and 

contact resonance AFM analysis