Tesis doctoral de Aitor Fernandez Lopeandia
The general tendency of science and industry to explore new materials in the nanoscale and in thin film form requires improvements in sensitivity of established characterization techniques. This interest is driven by the fact that in size reduced materials the physical property can vary from those present in bulk, both by quantum or surface effects. A suitable technique to characterize kinetic and thermodynamic properties of materials is calorimetry which is based in the study of the changes of heat, released or absorbed by a material, during any process. However, measurement very small quantities of sample with conventional calorimeters available in the market results troublesome if not impossible. The fundamental problem relies in the reduction of the heat capacity addenda of the calorimetric cell to the same order of the sample. The advance in microfabrication techniques has paved the possibility to develop a new family of microdevices, based on a very thin free-standing membrane, to be used as a high sensitive calorimeter with very low addenda. However, this field it is still under development and further improvements are needed essentially at high temperatures and low heating rates. in this thesis it is presented the development of a membrane-based calorimeter that is capable of measuring the heat released or absorbed during a phase transformation in ultra-thin films from temperatures of 77 up to 1200 k. The standard semiconductor processing techniques are used to fabricate the microdevices. The 180 nm silicon nitride membrane serves as mechanical support to deposit thin film actuators and the nanoscopic sample, preserving a low heat capacity addenda (below mu j) to enhance sensitivity. The design of the membrane has been optimized to preserve the mechanically stability for temperatures below 1250 k. Heating and sensing is typically performed using pt(100nm)/ti(10nm) thin films covered by 150 nm of al_{2}o_{3} to ensure high-temperature electrical stability,
Datos académicos de la tesis doctoral «Development of membrane-based calorimeters to measure phase transitions at the nanoscale«
- Título de la tesis: Development of membrane-based calorimeters to measure phase transitions at the nanoscale
- Autor: Aitor Fernandez Lopeandia
- Universidad: Autónoma de barcelona
- Fecha de lectura de la tesis: 22/06/2007
Dirección y tribunal
- Director de la tesis
- Javier Rodriguez Viejo
- Tribunal
- Presidente del tribunal: María teresa Mora aznar
- christoph Schick (vocal)
- ramón Burriel lahoz (vocal)
- eduardo Hernandez bocanegra (vocal)