Photothermal effects in micro/nano electromechanical systems

• Author / Creator

  Miriyala, Naresh

• Micro and nano electromechanical sensors have been explored for various applications as highly sensitive mass sensors up to a mass resolution of a single proton and even down to a level of yoctogram mass. Such gravimetric sensors lack intrinsic selectivity and typically rely on the chemo-selective interfaces which add complexity and give irreproducible results due to unspecific and weak nature of intermolecular interactions. On the other hand, spectroscopy techniques are simple, highly selective and provide molecular identification even in complex mixtures hence, they are widely explored in basic sciences. Conventional IR spectroscopy in the mid-IR range provides information on molecular vibrations that result in a sample-specific absorption spectrum, a so-called molecular fingerprint but, unfortunately, they suffer from erratic signals in case of small quantity of samples (~ ng mass) and weak IR absorbing analytes. In contrast, photothermal spectroscopy techniques are highly sensitive and offer a direct way of measuring optical absorption keeping it away from scattering and reflection losses that interfere with signals. The basis of the photothermal technique is the photo-induced change in the thermal state of the sample. The aim of this Ph.D. project is to explore the innovative and unexplored design of sensors to obtain spectroscopic information from trace amounts of mass ($\approx$ fg) and weak IR absorbing analytes such as liquids. To achieve this goal, two types of unexplored micro/nanomechanical resonators have been investigated; namely, a novel design of bimaterial microchannel cantilevers (BMC) that can contain picoliter volumes of liquid and nanomechanical string resonators. As temperature or heat is the external stimulus in spectroscopy, these sensors are treated as thermal sensors. Detailed theoretical and experimental investigations were carried out in optimizing the most influential parameters and understanding the basic thermomechanical behavior of these sensors. Photothermal spectroscopy applications are demonstrated with an improved sensitivity to obtain the chemical identity from trace amounts of samples. Efforts are made to observe the photothermal effect on functional material suspended nanowires such as BiFeO$_3$ (BFO) and in the process we have explored many interesting and anomalous photo properties of BFO under visible light. The underlying concept of all these devices presented in this thesis is the extremely low mass of the devices that makes them susceptible to minute changes in added mass and heat flux. Insights were drawn to extend the applications of these devices not just limited to nanomechanical IR photothermal spectrometry but also to use them as thermo-analytical tools.

• Subjects / Keywords

  • Thermomechanics of sensors
  • Photothermal spectroscopy
  • Nanomechanical strings
  • Photocatalysis
  • Microchannel cantilevers

• Graduation date

  Spring 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R37659P72

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.