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Title:Electro-thermal nanoprobes for nanometrology and nanofabrication
Author(s):Fletcher, Patrick C.
Director of Research:King, William P.
Doctoral Committee Member(s):Yu, Min-Feng; Kim, Seok; Pop, Eric
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):atomic force microscope
ferroelectric, diamond
heat transfer
Abstract:The atomic force microscope (AFM) is a versatile instrument for studying and manipulating material at nanometer length scales. Localized control of temperature and electric potential with an AFM microcantilever facilitates metrology and fabrication with nanometer precision and relatively low cost. Current self-heating AFM microcantilevers have technological limitations that inhibit their application towards nanofabrication, including difficulty in maintaining tip shape under harsh conditions, an inability to simultaneously control thermal and electric potentials, and inadequate methods for determining tip-substrate interface temperature. This dissertation seeks to address these issues by developing multifunctional AFM microcantilevers for control of thermal and electric fields during tip-based sample interrogation. Microcantilevers are designed, fabricated, characterized, and experimentally tested for applications in nanometrology and nanofabrication. The first microcantilever introduced in this work is a silicon cantilever whose tip is coated in a thin film of polycrystalline diamond to protect the tip from wear and reduce debris buildup. The tip of a conventional scanning probe changes unpredictably over time due to wear, damage, and the accumulation of debris; this is a significant hurdle preventing the widespread use of AFMs in industry. AFM scans are a convolution of the substrate topography and the scanning tip, so a stable tip shape is critical to establishing the validity of measurements. The device developed in this section of the dissertation has a tip radius as small as 15 nm and an integrated solid-state heater for raising the temperature of the tip. The diamond-coated microcantilever tip was tested for resistance to wear under harsh conditions necessary for tip-based nanofabrication. The second microcantilever platform described in this dissertation is a silicon cantilever with simultaneous and independent control of temperature and electric potential at the tip. Previous AFM devices have been able to apply localized electric potentials or temperature gradients, but have not been able to do both simultaneously. The present electro-thermal microcantilever combines the functions of heated and electrically-conductive AFM cantilevers. In one device design, electrical separation of the solid-state heater and tip electrode in single-crystal silicon was achieved using selective doping to form semiconductor diodes at the free end of the microcantilever. In an alternate device design, this electrical separation was accomplished using a metal electrode insulated from the heater with thermally grown oxide. Both designs were extensively characterized and demonstrate good electrical isolation between active elements until the voltage potential difference reaches ~ 10 V. The metalized electro-thermal microcantilever was used to measure thermoelectric voltage of a thermocouple point contact for determining tip-substrate interface temperature. The interface temperature between a nanometer-scale tip and substrate has been historically difficult to establish. In this work, the interface temperature is directly measured as a function of cantilever heater temperature during tip-side heating, which circumvents the need for calibration on temperature-sensitive materials requiring constant tip-substrate thermal conductance. When the non-dimensional cantilever heater temperature is 1, the tip-substrate interface temperature is 0.593 on glass and 0.125 on quartz. The measurements match well with a resistor network model that assumes the interfacial contact resistance is 108 K/W. This interface temperature calibration technique is appropriate for substrates with thermal conductivity < 20 W/mK. Finally, a heated nanoprobe was fabricated whose sharp tip has a conformal coating of a thin, crystalline ferroelectric material. The ferroelectric-coated nanoprobes demonstrate tip polarization switching with the intention of being used for enhanced pyroelectric electron emission.
Issue Date:2013-05-24
Rights Information:Copyright 2011 Patrick C. Fletcher
Date Available in IDEALS:2013-05-24
Date Deposited:2011-12

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