Fundamentals of heat transfer and thermal-mechanical control for improved atomic force microscopy

This dissertation presents novel atomic force microscope (AFM) cantilevers and cantilever technology that improve the measurement rate and precision of AFM. AFM cantilevers with integrated heater-thermometers can generate and sense heat flows to measure and manipulate matter at the nanometer scale. These heated cantilevers have been used for local measurements of material properties, tip-based nanomanufacturing, high-density data storage, and thermal topography imaging. This work focuses on thermal topography imaging wherein the cantilever measures the surface topography by tracking changes in the cantilever heat flow. This work shows the experimental and numerical investigation of cantilever heat transfer to substrates. The investigations show that the cantilever measures the topography height regardless of the substrate material properties. The lateral heat flow from the cantilever varies with the topography dimensions and causes the thermal topography to differ from the actual substrate topography. Insights from these investigations reveal a technique that corrects the thermal topography by eliminating most of the lateral heat flow from the cantilever. Arrays of cantilevers can significantly improve the measurement area and speed of AFM but array technology has been mostly inaccessible due to the need for specialized hardware. This dissertation reports the scalable integration of an array of 5 heated cantilevers into a commercial AFM using simple hardware and software. Cantilever temperatures are controlled in closed-loop feedback with 2 ˚C accuracy and 0.1 ˚C precision using analog circuitry rated at 1 MHz bandwidth. Analog cantilever temperature control is autonomous, inexpensive, scalable, and fast compared to conventional software implementations. The cantilever array performs parallel AFM imaging of a 550 µm × 90 µm area at 1.1 mm/sec with 0.6 nm vertical resolution and at 4.0 mm/sec with 44 nm wide pixels. The measurement rate was improved by more than 2 orders of magnitude compared to conventional AFM with a single cantilever. To demonstrate the ability to manufacture and repair nanostructures, the array performs multiple iterations of parallel nanolithography and topography imaging. Heated cantilevers are limited in their ability to precisely measure and control tip-sample forces due to parasitic resonances introduced by conventional piezoelectric actuators. This dissertation presents the development of two heated cantilevers designed for electromagnetic Lorentz force actuation. Electrical current passing through a U-shaped cantilever in the presence of a magnetic field induces a Lorentz force on the cantilever free end, resulting in cantilever actuation. These Lorentz-thermal cantilevers generate up to 7X larger Lorentz force and 2X larger oscillation amplitude compared to the state-of-art heated cantilevers. When used for thermal topography imaging, the Lorentz-thermal cantilevers can measure topography with vertical resolution of 0.2 nm.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Somnath, Suhas

Contributors dc:contributor

• King, William P.
• Ferreira, Placid M.
• Cahill, David G.
• Pop, Eric

• thermomechanical lithography
• scanning thermal microscopy
• nanotopography
• tapping-mode atomic force microscopy (AFM)
• Atomic Force Microscopy (AFM)
• heated cantilever
• heat transfer
• simulation
• array
• temperature control
• magnetic actuation
• Lorentz force
• parallel imaging

Statement dc:rights

• Copyright 2014 Suhas Somnath

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/50358

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/50358