자료유형  

 학위논문

Control Number  

0017164117

International Standard Book Number  

9798346856740

Dewey Decimal Classification Number  

530

Main Entry-Personal Name  

Olson, Karl P.

Publication, Distribution, etc. (Imprint  

[S.l.] : Northwestern University., 2024

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2024

Physical Description  

127 p.

General Note  

Source: Dissertations Abstracts International, Volume: 86-06, Section: B.

General Note  

Advisor: Marks, Laurence D.

Dissertation Note  

Thesis (Ph.D.)--Northwestern University, 2024.

Summary, Etc.  

요약Triboelectricity, the charge transfer that occurs when materials contact or rub, has been studied for centuries. Despite this, the fundamental physics of this charge transfer remain a mystery when at least one of the materials is non-metallic. Flexoelectricity, the coupling of strain gradients with electrical polarization present in all non-metals, was recently proposed as a major driving force behind triboelectricity when combined with the contact of asperities, or the small protrusions at the surface of nominally flat surfaces that truly contact the opposite surface. This dissertation introduces a model of triboelectricity based on flexoelectricity and other well-established physics and validates the model through a combination of experiments directly part of this work and analysis using a wide range of previously published triboelectric experiments.A triboelectric contact model involving a Pt0.8Ir0.2 sphere contacting a Nb-doped SrTiO3 half-space uses Hertzian contact mechanics to determine the stress in the SrTiO3. The resulting strain and strain gradient produce electromechanical changes in the half-space, including a flexoelectric polarization and a potential specific to the relevant electronic band due to the deformation potential and the shift in the mean inner potential with strain. Additionally, the purely electronic effect of depletion region formation at the Schottky contact formed between the two materials is included. These electromechanical effects are calculated numerically and validated by atomic force microscope experiments.Experimental validation is achieved by contacting Nb-doped SrTiO3 samples with a Pt0.8Ir0.2 probe at various forces. This forms a Schottky diode, and at each force, the current is measured as a function of the bias voltage across the probe and sample. From this data, the Schottky barrier height and other parameters are calculated for thermionic emission and thermally assisted tunneling. Because of the electromechanical response of the SrTiO3, the parameters are dependent on the contact force. Across the range of forces, the experimental values of the barrier height and current are compared to those calculated from the theoretical model are shown to have excellent agreement.With a sound model of electromechanical effects in triboelectric contacts, the focus is turned to determining the charge transfer. Bound charges are shown to result from the flexoelectric polarization, and these, along with the space charge of the depletion region, must be compensated by free charges. These free charges are the triboelectric charges transferred during contact. Cases that depend on specific material system parameters, such as the barrier height, surface and bulk conductivities, and amount of electronic trap states at the surface, determine which of the compensating charges are involved in charge transfer. Again, this model is implemented numerically and predictions of charge transfer are possible for given material systems.The theory and computational model are also extended to include contacts with non-spherical shapes that encompass bounding cases of real asperity shapes. The scaling of charge transfer with the contact force and asperity size is shown to strongly depend on the geometry of the asperity. Also considered is sliding triboelectricity, which involves tangential forces that break the symmetry of the contact and lead to a constant tribocurrent during sliding.Finally, the charge transfer theory, including the asperity shape and sliding extensions, is analyzed in the context of numerous published triboelectric experiments. The model is shown to explain qualitative trends in these results, such as increased charging with larger contact forces or increased tribocurrent with faster sliding speeds. It also quantitatively predicts the triboelectric charging for particle impacts and surfaces with artificially-shaped asperities, as well as tribocurrents when atomic force microscope probes slide against surfaces.

Subject Added Entry-Topical Term  

Condensed matter physics.

Subject Added Entry-Topical Term  

Nanoscience.

Subject Added Entry-Topical Term  

Materials science.

Index Term-Uncontrolled  

Asperity

Index Term-Uncontrolled  

Atomic force microscopy

Index Term-Uncontrolled  

Bound charge

Index Term-Uncontrolled  

Electromechanics

Index Term-Uncontrolled  

Flexoelectricity

Index Term-Uncontrolled  

Triboelectricity

Added Entry-Corporate Name  

Northwestern University Materials Science and Engineering

Host Item Entry  

Dissertations Abstracts International. 86-06B.

Electronic Location and Access  

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Control Number  

joongbu:658616