3.052 Nanomechanics of Materials and Biomaterials Prof. Christine Ortiz DMSE, RM Phone : (617) WWW : LECTURE # 4 : EXPERIMENTAL ASPECTS OF HIGH- RESOLUTION FORCE SPECTROSCOPY : THE FORCE TRANDUCER

Review : What is Nanomechanics ? interaction force (electromagnetic in origin) (nN) interaction / indentation distance (nm) a subset of the field of nanotechnology, also sometimes called “Molecular Mechanics” nano= the study of forces, motions, energies, and deformations : 1. statics (force act on bodies at rest) 2. dynamics (force act on bodies at motion) 3. strength of materials (continuum mechanics) TWO OBJECTS : (size~nm) individual atoms individual molecules assemblies of molecules cells interaction energy (kJ/mol)

Nanoindentation versus High Resolution Force Spectroscopy HOW CAN WE MEASURE SUCH TINY FORCES ? i.e. nN (= N), even pN (= N) ! separation distance (nm)

A Typical High-Resolution Force Spectroscopy Technique : Three Main Components  sample I. high-resolution force transducer III. displacement detection system II. high-resolution displacement control z

Example of a Force Transducer : Microfabricated Cantilever Beams and Probe Tips for Atomic Force Microscopy (AFM)

Characteristics of Materials for Cantilever Beams and Probe Tips SILICON(Si) SILICON NITRIDE (Si 3 N 4 )

Attachments to AFM Probe Tips (* (* (*

Biomembrane Surface Probe (*R. MERKEL*†, P. NASSOY*‡, A. LEUNG*, K. RITCHIE* & E. EVANS*§ Nature 397, (1999)) microsphere probe is a nm size colloid force transducer Red Blood Cell pressurized glass pipet suction pressure controls stiffness of transducer

Laser Tweezers (* objective lens cover slip trapped particle ~  m 3D trapping potential trapping laser beam Optical Tweezer, Photonic Tweezers, Optical Trap highly focused laser beam, microns in size which can trap objects in the center region of maximum intensity, light acts as a force transducer and mechanical tool to manipulate  m size objects very low forces : pN

Typical Cantilever Dimensions top view L1L1 b d d 22 L t  b cantilever probe tip side view Typical Values : b= 150  m  =35 o L=200  m L 1 =150  m t =0.6  m d = 18  m

Cantilever Beam Theory F 0 L x   (max)

 <0  =0  >0 surface force sample surface repulsive attractive rest position (*NRL : Example of a Force Transducer : The Cantilever Beam

Fundamental Limit of Force Detection cantilever 