09-723 Proximal Probe Techniques – New Tools For Nanoscience and Nanotechnology

 

Instructor:  Professor Tomasz Kowalewski, MI 525, x 8-5927, tomek@andrew.cmu.edu

TEACHING ASSISTANT: Justin Legleiter, MI 525, x 8-9175, JUSTINL@ANDREW.CMU.EDU

 

Prerequisites:  Familiarity with Differential and Integral Calculus at the undergraduate level, undergraduate Physical Chemistry.  

 

Course meeting times:  Tuesday, Thursday 6:30-7:50  PM, MI 355.

 

Course web site:  http://www.andrew.cmu.edu/course/09-723/ (lecture notes, homework, software handouts, etc.)

 

Office hours: TK: W,F 3-5 PM; JL: M 9-11 AM and by appointment.

 

Course description:  Proximal probe techniques are revolutionizing physical and biological sciences, owing to their ability to explore and manipulate matter at the nanoscale, and to operate in various environments (including liquids).  Proximal probe techniques rely on the use of nanoscale probes, positioned and scanned in the immediate vicinity of the material surface.  Their development is often viewed as a first step towards nanotechnology, since they demonstrate the feasibility of building purposeful structures one atom or one (macro)molecule at a time.  This course is designed for the students of chemistry, biology physics and engineering, who are interested in the fundamentals of proximal probe techniques and in their applications in various areas, converging into a rapidly developing, interdisciplinary field of nanoscience.  It will provide thorough physical background of such basic techniques as Atomic Force Microscopy (AFM), Scanning Tunneling Microscopy (STM), and Near-Field Scanning Optical Microscopy (NSOM) and of their variants.  Learning of proximal probe techniques fundamentals will be aided by the "Virtual Proximal Probe Device" built by students in Simulink throughout the semester.

 

Course Objectives

 

·       Students will become acquainted with state-of-the-art proximal probe techniques and their applications in physical and life sciences, with particular emphasis on nanoscale properties of soft condensed matter.          

·       Students are expected to gain a firm physicochemical background of proximal probe experiments, and of involved interactions.

·       Knowledge acquired through the course should allow students to critically evaluate the literature data and to design new experiments and quantitatively analyze their results.

 

Course Outline

 

Our interest in proximal probe techniques is motivated by the unique opportunities following from their use in the nanoscale studies and manipulation of soft condensed matter.  Thus, instead of following the development of proximal probe techniques chronologically (STM ->  AFM -> …) we will initially focus on the AFM – which is currently most widely used in the studies of physicochemical properties of synthetic and biological macromolecules. 

 

Fundamentals of AFM.  Contact mode AFM maps the nanoscale topography of surfaces by monitoring the deflection of a cantilever ending with an ultra-sharp tip probe and scanned while in contact with the surface.    We will establish the physical background of major phenomena and instrument components critical for the AFM operation, such as: piezoelectric effect and piezoelectric scanners, cantilever probes (mechanical properties, fabrication), detection systems, probe-surface interactions (intermolecular and capillary forces between nanoscale objects, indentation.)  Lateral force AFM and its role in the field of nanotribology, as well as the applications of contact AFM to micro/nano manipulation/testing (nanoindentation, single molecule stretching, etc.) will be discussed.

 

AC techniques.  Lateral forces between the probe tip and the sample present in contact mode AFM pose the major problem in imaging soft matter.  This problem is virtually eliminated in techniques in which the cantilever is oscillated above the surface (ac techniques), and the topography is tracked by monitoring the cantilever oscillation (amplitude, frequency, phase) under the influence of tip-sample interactions.   The set-up in which the non-contact interaction is monitored might appear to be most desirable from the point of view of maintaining the non-invasive character of operation.  However, the intermittent-contact technique, in which the tip taps on the sample surface at the bottom of each oscillation cycle (tapping mode), is currently most widely used.   Despite its widespread popularity, until recently the dynamics of tapping mode AFM and in particular the role of operating frequency and the magnitude of tapping forces were poorly understood.  We will analyze in detail the dynamics of non-contact and tapping-mode AFM, relying extensively on computer simulations with the aid of custom-developed software which will be made available to the students for the duration of the course.  We will replicate the recent work from our laboratory, which resulted in better understanding of tapping mode AFM, opening the way to improved resolution and full control of tapping forces.

 

AFM in liquid environments.  The ability to provide real-time nanoscale images of solid-liquid interfaces is arguably one of the most unique and promising features of AFM, of particular interest to those involved in the studies of colloids, polymers and surface.  The description of major modes of operation under liquids will be followed by the examples of applications of AFM to such problems as: interactions of macromolecules and macromolecular complexes involved in Alzheimer’s disease, wettability of hydrophobic surfaces, measurements of colloidal forces, probing of living cells, imaging and probing of soft extracellular matrix surfaces.

 

Towards chemical sensitivity. Other proximal probe techniques.  In this section we will emphasize the attempts to turn proximal probe techniques into analytical tools with chemical sensitivity.  Following the discussion of chemical force microscopy we will proceed to other major proximal probe techniques such as STM, magnetic force microscopy, Kelvin probe microscopy, near field scanning optical microscopy, scanning thermal probe microscopy, etc. 

 

Geometrical representation and quantitative analysis of AFM images.  This section will begin with the extensive treatment of tip shape contribution to AFM images, and with the discussion of tip shape and image reconstruction techniques. We will then proceed to the determination of size/shape distributions of nanoparticulate objects deposited on surfaces, with the application to the analysis of synthetic nanoparticles and globular proteins.  Subsequently, the application of two-dimensional Fourier transforms to the analysis of periodic patterns as well as its less familiar application to random fractal surfaces will be described.  In this part we will be extensively utilizing image manipulation and analysis capabilities of Matlab. 

 

 

Course organization:  Lecture format, aided by computer simulations using a Simulink model of AFM.  The model will be gradually built by the students based on gained theoretical knowledge.  Increasing levels of complexity will be added progressively, finally yielding a realistic "virtual AFM".   

 

Homework and computer simulation projects: 

 

The participants will be assigned problem sets, most of which will be focused on subsequent steps of model development, and on the use of the model in explorations of various aspects of proximal probe techniques.

 

Course grade: 

 

The course grade will be determined based on homework (40%), midterm examination (30%) and final examination (30%).  

 

Reserve:  There will be no required textbook.  The following recommended books will be placed on Reserve in the Mellon Institute library: