Nanotechnology-Enabled Sensors

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186 Chapter 4: Nano Fabrication and Patterning Techniques organometallic film to a metal oxide in addition to enabling and controlling crystallisation and grain growth. It also serves to remove organic compounds, which usually evaporate off the film at elevated temperatures. Furthermore, it promotes adhesion to the substrate. Unlike many other fabrication methods, which require starting materials to have the same composition as the final product, sol-gel offers an economically feasible avenue to explore different ratios and combinations of the compounds. The sol-gel method can be employed to form nanostructured thin films for sensing applications and the grain size of these thin films can be engineered for the right application. As can be seen in Fig. 4.41, nanostructured In2O3 was prepared using ethanolic solutions of an indium isopropoxide (In(OC3H7)3) precursor. The solutions were spin coated on sapphire substrates and annealed at 500°C for 1 h in air. This resulted in a welldeveloped polycrystalline and highly porous microstructure composed of approximately spherical grains with an average size of approximately 20 nm. 73 Fig. 4.41 SEM photomicrograph of an In2O3 film fabricated using the sol-gel method. Reprinted with the permission from the Elsevier publications. 73 4.9 Nanolithography and Nano-Patterning Nanolithography and nano-patterning are processes for making patterns on substrate surfaces with nanometer precision. The basis of lithography is
4.9 Nanolithography and Nano-Patterning 187 very old. Photolithography has been used in microtechnology for more than 50 years. However, when we wish to position atoms or molecules precisely on surfaces many problems can occur. Many of such problems are due to the quantum nature of atoms and physical phenomena occurring at nanoscale dimensions. In this section we introduce some of the most widely utilized nano-patterning techniques. 4.9.1 Photolithography This is a process that is extensively employed throughout the semiconductor industry to transfer a pattern from a photomask onto a substrate’s surface. Photolithography coupled with the etching process (Fig. 4.42) involves the combination of the following steps which are described below: 1. Thin film deposition: The thin film material to be patterned is first deposited onto substrate. Any of the previously mentioned deposition techniques can be used. 2. Application of photoresist: A thin film of photoresist is deposited on the surface by spin-coating. 3. Soft-baking: the substrate is heated in an oven to evaporate the photoresist’s solvent, solidifying and curing it. 4. Exposure: upon exposure to light (generally UV), the photoresist undergoes a chemical reaction. Depending on the photoresist’s chemical composition, it can react in two different ways when the light impinges on it. A positive photoresist, is polymerized where it is exposed to light, however, the opposite is true for negative photoresist. 5. Developing: after exposure, the sample is soaked in a developer solution which removes the un-polymerized portion of the photoresist. This leaves a copy of the photomask’s pattern on the surface. 6. Etching: the uncovered surface is etched. This typically involves immersion in a solution which dissolves the deposited thin film whilst not having any effect on the polymerized photoresist. There is another type of lithography that utilizes the lift-off process (Fig. 4.42). In the lift-off process, a pattern is first defined on a substrate with standard photolithographic technique. Then a film is deposited over the substrate, covering the patterned photoresist and areas in which the photoresist has been cleared. During the actual lifting-off, the photoresist under the film is removed with a photoresist solvent taking the film with it. This
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Nanotechnology-Enabled Sensors
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Kourosh Kalantar-zadeh RMIT Univers
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Acknowledgments We have been fortun
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viii Contents Chapter 3: Transducti
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x Contents 5.7.1 Scanning Electron
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xii Contents 7.5 Nano-sensors based
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2 Chapter 1: Introduction Nobel lau
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4 Chapter 1: Introduction Fig. 1.2
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6 Chapter 1: Introduction ensure th
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8 Chapter 1: Introduction ments, th
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10 Chapter 1: Introduction aim is t
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12 Chapter 1: Introduction Referenc
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14 Chapter 2: Sensor Characteristic
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64 Chapter 3: Transduction Platform
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100 Chapter 3: Transduction Platfor
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236 Chapter 5: Characterization Tec
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Chapter 6: Inorganic Nanotechnology
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6.2 Density and Number of States 28
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2 6.2 Density and Number of States
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6.3 Gas Sensing with Nanostructured
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6.3.7 Surface Modification 6.3 Gas
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This is the dispersion relation for
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6.4 Phonons in Low Dimensional Stru
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335 vibrational degrees of freedom
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337 ing ballistic transport of elec
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339 Fig. 6.36 Nanoresonators made o
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6.5 Nanotechnology Enabled Mechanic
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6.6 Nanotechnology Enabled Optical
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6.7 Magnetically Engineered Spintro
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ferromagnetic haematite (a form of
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References 365 21 E. Comini, G. Fag
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References 367 58 D. E. Williams an
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References 369 96 J. J. Shi, Y. F.
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Chapter 7: Organic Nanotechnology E
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7.2 Surface Interactions 373 can be
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7.2 Surface Interactions 375 Carbox
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7.2 Surface Interactions 377 Fig. 7
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7.2 Surface Interactions 379 There
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Fig. 7.12 The schematic of physical
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Fig. 7.13 Formation of SAMs. 7.2 Su
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7.2 Surface Interactions 385 ple, t
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7.3 Surface Materials and Surface M
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7.4 Proteins in Nanotechnology Enab
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7.4.4 Using Proteins as Nanodevices
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Fig. 7.36 The general structure of
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+ 7.4 Proteins in Nanotechnology En
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7.5 Nano-sensors based on Nucleotid
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Fig. 7.57 The structure of DNA stra
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7.6 Sensors Based on Molecules with
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7.6 Sensors Based on Molecules with
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7.8 Biomagnetic Sensors 7.8 Biomagn
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7.9 Summary 471 metal oxides, carbo
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References 473 19 T. Kunitake, Ange
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63 J. X. Huang, S. Virji, B. H. Wei
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References 477 105 M. Plomer, G. G.
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References 479 145 R. F. Service, S
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7.8 References 481 185 J. Wang, D.
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Remote plasma enhanced CVD (RPECVD)
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Thin film equivalent circuit ... 32
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Optical waveguides ................
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Semiconductor-semiconductor junctio
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About the Authors Dr. Kourosh Kalan
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