Browsing by Subject "Atomic force microscopy"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item AFM-based measurement of the mechanical properties of thin polymer films and determination of the optical path length of nearly index-matched cavities(2008-05) Wieland, Christopher F., 1980-; Shih, Chih-KangTwo technologies, immersion and imprint lithography, represent important stepping stones for the development of the next generation of lithography tools. However, although the two approaches offer important advantages, both pose many significant technological challenges that must be overcome before they can be successfully implemented. For imprint lithography, special care must be taken when choosing an etch barrier because studies have indicated that some physical material properties may be size dependent. Additionally, regarding immersion lithography, proper image focus requires that the optical path length between the lens and substrate be maintained during the entire writing process. The work described in this document was undertaken to address the two challenges described above. A new mathematical model was developed and used in conjunction with AFM nano-indentation techniques to measure the elastic modulus of adhesive, thin polymer films as a function of the film thickness. It was found that the elastic modulus of the polymer tested did not change appreciably from the value determined using bulk measurement techniques in the thickness range probed. Additionally, a method for monitoring and controlling the optical path length within the gap of a nearly index-matching cavity based on coherent broadband interference was developed. In this method, the spectrum reflected for a cavity illuminated with a modelocked Ti:Sapphire laser was collected and analyzed using Fourier techniques. It was found that this method could determine the optical path length of the cavity, quickly and accurately enough to control a servo-based feedback system to correct deviations in the optical path length in real time when coupled with special computation techniques that minimized unnecessary operations.Item The fabrication of specialized probes for surface metrology(2007-12) Williams, Ryan Donald, 1981-; Stevenson, Keith J.This dissertation will demonstrate the synergy of nanoscopic materials and surface metrology methods by the fabrication and implementation of CNT atomic force microscopy (AFM) tips, CNT scanning tunneling microscopy (STM) tips, Pt spike AFM tips, and Pt spike near-field scanning optical microscopy (NSOM) tips for the methods of critical dimension metrology, STM, AFM phase imaging, scanning surface potential AFM (SSPM), NSOM, and three-dimensional AFM. Chapter 1 provides a general overview of the information that will be discussed in this dissertation. Chapter 2 describes two methods for the simultaneous fabrication of carbon nanotube atomic force microscopy and scanning tunneling microscopy probes. The fabrication of these high resolution probes, as well as their imaging characteristics, is described in detail. Resolution standards were used to characterize their behavior and resolution limits. In Chapter 3, the effect of high aspect ratio probe length on AFM phase imaging is studied by fabricating highly controllable Pt spike AFM tips. By monitoring phase shifts on homogenous surfaces as a function of Pt spike length, it is shown that attractive forces at the tip are significantly reduced when high aspect ratio structures are added to conventional AFM probes. In Chapter 4, the effect of probe geometry on scanning surface potential microscopy (SSPM) is described. By studying the effect of scan height in SSPM, it was found that large surface area probe geometries, such as conventional Pt coated AFM tips, have lower surface potential resolution because of contributions from the sides of the tip as well as the cantilever. Spatial resolution standards were probed to evaluate the effect of probe geometry on SSPM sensitivity and resolution. Chapter 5 describes the fabrication of specialized probes for three-dimensional atomic force microscopy, scanning near-field optical microscopy, and scanning electrochemical -- atomic force microscopy (SECM-AFM). Using techniques described in Chapters 2-4, high aspect ratio structures were added to conventional probes used in 3D AFM, NSOM and SECM-AFM to solve limitations inherent to current probe designs for each method. Preliminary data indicates that each probe will have a significant beneficial effect on the resolution limit of its technique.Item Nano-mechanical studies of prostate cancer cells using atomic force microscopy(2012-05) Bastatas, Lyndon D; Park, Soyeun; Myles, Charles W.Nano-mechanical properties of prostate cancer cells with different metastatic potentials were investigated, in vitro, to shed light on the issue whether those properties could be utilized as indicators of their aggressiveness. Experimentations involved atomic force microscopy-based indenting and force mapping experiments acquired at LNCaP (lowly metastatic) and CL-1 (highly metastatic) prostate cancer cells that were cultured on plain glass and nano-scaffolds. Various models were applied to extract the mechanical information pertaining to the elasticity, adhesion and topography of the cells. Deviating from the general perspective for metastasis, the elasticity measurements reveal that the elastic modulus of highly metastatic cancer cells, CL-1, is about twice as high (i.e., stiffer) as the elastic modulus of lowly metastatic cancer cells, LNCaP, both at the center of cells’ body and lamellipodia. The two-dimensional maps of adhesion property, in conjunction with the results from the experiments conducted on the nano-scaffolds, reveal that the stiffer cells, CL-1, are more adherent than softer cells, LNCaP. These findings are consistent to the reports observed at in vitro nano-mechanical studies that cultured adherent cells are less deformable than the non-adherent ones. We postulate that the enhanced adhesion generates larger cortical tension that leads to higher elastic modulus observed in CL-1.Item Real-space electronic structure methods for modeling nanowires and atomic force microscopy imaging(2016-12) Lee, Alex Jemyung; Chelikowsky, James R.; Demkov, Alexander A.; Hwang, Gyeong S.; Korgel, Brian A.; Sanchez, Isaac C.Our group develops a pseudopotential-based electronic structure code constructed within first-principles density functional theory to study various problems in chemical engineering and condensed matter physics. One of the code's unique features is that it performs calculations on a real-space grid without using an explicit basis. This makes it particularly well-suited for examining localized systems with confined dimensionalities, such as nanostructures. In the dissertation we apply our code to the study of two main topics: germanium nanowires and atomic force microscopy simulations. First we examine how the electronic properties of germanium nanowires are affected by mechanical strain. We find that applying strain can drastically influence the transport properties of nanowires by inducing band crossings that change the nature of the band gap from direct to indirect, hampering carrier mobilities. In another project we take advantage of the real-space formalism for charged systems to devise a computationally efficient method to calculate accurate doping binding energies for nanowires. We demonstrate the method on phosphorus-doped germanium nanowires. The second focus of the dissertation is atomic force microscopy simulations. Atomic force microscopy is a powerful probe-based imaging technique that can be used to visualize and characterize chemical phenomena. However, the interpretation of experimental images is not well-understood. We develop a theoretical simulation method in order to better understand the fundamental physics behind the imaging mechanism. In one study, we clarify the mechanism for imaging hydrogen bonds. Experimental findings on certain organic oligomers have reported striking images showing what appear to be direct visualizations of intermolecular bonding. We apply our simulation technique to show that tip tilting is responsible for resolving these apparent hydrogen bonds. In another study, we examine the phenomenon of contrast inversion. We find that the key factor responsible for contrast inversion is the chemical reactivity of the tip. Theoretical imaging simulations such as these can be used to guide the experimental acquisition of images and to help characterize results.