The design and fabrication of a thermal microprobe integrated on an atomic force microscope probe tip

A thermal microprobe has been designed and built for high resolution temperature sensing. The thermal microprobe consists of a very-thin-film thermocouple junction confined to the very end of a low mass Atomic Force Microscope (AFM) probe tip. Essential to high resolution temperature sensing is the confinement of the thermocouple junction to a short distance at the AFM tip. This confinement is achieved by controlled photoresist coating. Experimental prototypes have been made with the junction confined to within 0.3 µm of the tip. The couple is made of Au/Pd, and the two metals are electrically separated elsewhere by a thin insulating layer. The device is designed for insertion in an AFM instrument so that topographical and thermal images can be made with the same tip. Large contact pads permit mechanical and ohmic contacting with spring clamps. Processing begins with double-polished, n-type, 4-inch-diameter, and 300 µm thick silicon wafers. Probe tips are formed by a combination of RIE, wet chemical etching, and oxidation sharpening, which makes the tips atomically sharp. The hot thermocouple junction is formed by controlled photoresist coating. The metal layers are sputtering deposited and the cantilevers are released by KOH etching and RIE. The thermal microprobe gives a high temperature resolution and a high spatial resolution. The thermal mass is kept low in order to cause minimal disturbance of the component under measurement. The thermal output of the microprobe is 5.6 µV/°C and is linear over the temperature range 25 - 110°C

A STUDY OF FACTORS AFFECTING ENTREPRENEURIAL INTENTION: THE MODERATING ROLE OF INDIVIDUALISM

The main purpose of this study is to identify the factors which affect the entrepreneurial intention (EI) of the university students of Gilgit-Baltistan. This research study mainly focuses on the theory of planned behaviour (TPB) and Hofstede national culture dimension of individualism. The quantitative research method was applied for the data analysis. The data were collected from the public sector universities of Gilgit-Baltistan with the total number of 362 final year students. Moreover, to test the hypothesis of the study structural equation modeling (PLS-SEM) version 4.0 software were used for the data analysis and interpretation. The findings of the research are follows: i) attitude towards behaviour positively influence the entrepreneurial intention of the university students ii) subjective norms also significantly affect the entrepreneurial intention iii) perceived behaviour control has a positive effect on the entrepreneurial intention of the university students. However, the moderating variable of individualism does not moderate the relationship between TPB and EI. Moreover, this research study provides a comprehensive research model which includes the behavioural, and culture factors that were analyzed and validated through empirical evidence. It is also one of the pioneer research conducted in the rural areas i.e. Gilgit-Baltistan of Pakistan

Design of a chemical sampling and analysis system using excimer laser ablation and quartz microcolumns

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1997.Includes bibliographical references (leaves 108-112).by Luis G. Ortiz.M.S

Optically-resonant nanostructure-based systems for spectral selectivity

This thesis presents two different approaches for spectrally-selective nanostructure-based systems with their specific advantages and disadvantages; see Chapter 1 for spectrally-selective Mie-resonant metasurfaces, and Chapter 2 for nanostructure-modulated FP resonators. Furthermore, to bridge the gap between fundamental science and industry, novel fabrication techniques laser-induced tailoring and structuring of metasurfaces are presented; see Chapter 3. All things considered, this work is not intended to revolutionize optics. Still, it is written with a bit of hope to put a small step in the development of nanophotonics and its applicability in real-world applications

Carbon Nanotube Synthesis for Microsystems Applications

Modern day engineering systems research presently lacks techniques to exploit the unique properties of many nanomaterials; coupled with this challenge exists the need to interface these nanomaterials with microscale and macroscale platforms. A nanomaterial of particular interest is the carbon nanotube (CNT), due to its enhanced physical properties. In addition to varied electrical properties, the CNT has demonstrated high thermal conductivity and tensile strength compared to conventional fiber materials. CNTs are beginning to see commercial applications in areas in which sufficient study has been dedicated. While a large part of the worldwide focus of CNT research has been in synthesis, an equally important area of research lies in CNT integration processes. The unique and useful properties of many nanostructured materials will never be realized in mainstream manufacturing processes and commercial applications without the proper exploration of integration methods such as those detailed in this thesis. The primary motivation for the research detailed in this thesis has been to develop CNT synthesis processing techniques that allow for novel interfacing methods between carbon nanotubes and eventual applications. In this study, an investigation was performed to look at several approaches to integrating CNTs into micro-electromechanical systems (MEMS). Synthesis of CNTs was studied in two different settings. Synthesis was first performed, directly on the microsystem, via a global scale chemical vapor deposition (CVD) process. Secondly, synthesis was performed directly onto a microsystem device via localized resistive heating. Following synthesis, the application of atomically layered, protective coatings was then investigated. Integration methods were then investigated to allow for CNT transfer to microsystem applications incapable of withstanding synthesis temperatures. The developed integration methods were evaluated by creating functional microscale electrical circuits in flexible substrates via hot emboss imprint lithography. Lastly, post synthesis processing methods were used to create micropatterned cell guidance substrates as well as neuronal stimulating substrates.M.S.Committee Chair: Dr. Samuel Graham; Committee Co-Chair: Dr. William King; Committee Member: Dr. Satish Kuma

Thermal-AFM under aqueous environment

The aim of this thesis is to describe the work developing and demonstrating the use of Scanning Thermal Microscopy (SThM) in an aqueous electrically conductive environment for the first time. This has been achieved by using new instrumentation to allow conventional SThM probes to measure and manipulate the temperature of non-biological and biological samples. For the latter, the aqueous environment is crucial to allow in-vitro experimentation, which is important for the future use of SThM in the life sciences. SThM is known to be a powerful technique able to acquire simultaneous topographic and thermal images of samples. It is able to measure the microscopic thermal properties of a surface with nanoscale spatial resolution. However, SThM has traditionally been limited to use in vacuum, air and electrically inert liquids. The aqueous Scanning Thermal Microscopy (a-SThM) described in this thesis is an entirely novel technique that opens up a new field for thermal-AFM. The first challenge addressed in this work was the adaptation of a commercial Multimode Nanoscope IIIa AFM to permit electrical access to a SThM probe completely immersed in aqueous solutions. By employing a newly designed probe holder and electronic instrumentation, the probe could then be electrically biased without inducing electrochemical reactions. This approach permitted conventional microfabricated thermal probes to be operated whilst fully immersed in water. This innovation allowed SThM measurements under deionized (DI) water to be performed on a simple solid sample (Pt on Si3N4) and the results compared with in-air scans and accurate 3D Finite Element (FE) simulations. Once the validity of the technique was proven, its performance was investigated, including crucially the limit of its thermal-spatial resolution; this was investigated using nanofabricated solid samples (Au on Si3N4) with well-defined features. These results were compared to the FE model, allowing an understanding of the mechanisms limiting resolution to be developed. In order to demonstrate the advantages granted by the water’s superior thermal conductivity compared to air or other liquids, non-contact thermal images were also acquired using the same samples. The final part of this thesis was focused on extending SThM into the biological area; a completely new field for this technique. New results are presented for soft 4 samples: I-collagen gel and collagen fibrils, which were thermally manipulated using a self-heated SThM probe. This successfully demonstrated the possibility of using heat to alter a biological sample within a very well localised area while being operated for long time in an aqueous environment. The difference in force response originated from the AFM scans with different levels of self-heating further proved the robustness of the technique. Finally, the technique was employed to study MG-63 living cells: The SThM probe was left in contact with each cell for a pre-determined period of time, with and without self heating. The results demonstrated that only the heated cells, directly beneath the probe tip died, tallying with the highly localised temperature gradient predicted by FE analysis

Laser writing of electronic circuitry in thin film molybdenum disulfide: A transformative manufacturing approach

Electronic circuits, the backbone of modern electronic devices, require precise integration of conducting, insulating, and semiconducting materials in two- and three-dimensional space to control the flow of electric current. Alternative strategies to pattern these materials outside of a cleanroom environment, such as additive manufacturing, have enabled rapid prototyping and eliminated design constraints imposed by traditional fabrication. In this work, a transformative manufacturing approach using laser processing is implemented to directly realize conducting, insulating, and semiconducting phases within an amorphous molybdenum disulfide thin film precursor. This is achieved by varying the incident visible (514 nm) laser intensity and raster-scanning the thin film a-MoS2 sample (900 nm thick) at different speeds for micro-scale control of the crystallization and reaction kinetics. The overall result is the transformation of select regions of the a-MoS2 film into MoO2, MoO3, and 2H-MoS2 phases, exhibiting conducting, insulating, and semiconducting properties, respectively. A mechanism for this precursor transformation based on crystallization and oxidation is developed using a thermal model paired with a description of the reaction kinetics. Finally, by engineering the architecture of the three crystalline phases, electrical devices such as a resistor, capacitor, and chemical sensor were laser-written directly within the precursor film, representing an entirely transformative manufacturing approach for the fabrication of electronic circuitry

Study Of Low Dimensional Tungsten Oxide By Anodization And Sol-Gel Methods

Low dimensional tungsten oxides (WO≤3) have attracted considerable research attention due to potential applications such as electrochromic devices, gas sensors, photocatalysts for water splitting, dye-sensitized solar cells and humidity sensors. The use of tungsten oxide for surface-sensitive device applications requires cost-effective fabrication of tungsten oxide with controllable morphological property. Both anodization and sol-gel methods offer facile ways to synthesize nanostructured tungsten trioxide (WO3)