Chapter 12. Nanometrology. Oxford University Press All rights reserved.

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1 Chapter 12 Nanometrology

2 Introduction Nanometrology is the science of measurement at the nanoscale level. Figure illustrates where nanoscale stands in relation to a meter and sub divisions of meter. Nanometrology addresses two main issues; the precise measurement of sizes in the nanometre range, and adapting existing or developing new methods to characterize properties as a function of size.

3 Types of Nanomaterials Type of nanomaterial Nanocrystals Material Diameter / thickness in nm Metals, Inorganic materials (oxides, 1 50 nitrides, sulphides, etc) Nanofilms Nanowires Nanotubes Nanosurfaces Layers of quantum dots made of lead selenide, indium arsenide, etc Metals, oxides, nitrides, sulphides, etc Carbon, metals, inorganic materials Various materials

4 Applications of Nanotechnology Nanosensors Water Purification Lighting Nanocomputers Nano technology based Garments

5 Nanometrology Techniques Sl. No. Parameter / Property Measurement Technique 1 Morphology: size and shape of Transmission Electron particles, Crystallographic information: Microscopy (TEM) detection of atomic scale defects 2 3 Topography: the surface features, Morphology: shape and size of the particles, Composition: the elements and compounds the sample is composed of, Crystallographic Information: the arrangement of atoms Three dimensional surface topology: size, shape, roughness, defects, electronic structures Scanning Electron Microscopy (SEM) Scanning Tunneling Microscopy (STM)

6 Nanometrology Techniques Sl. No. Parameter / Property Measurement Technique 4 Topology, roughness and elasticity of surface, grain size, frictional characteristics, specific molecular interactions and magnetic features on surface. Atomic Force Microscopy (AFM) or Scanning Force Microscopy (SFM) 5 Crystallographic information: type of crystal structure, film thickness, interface roughness and surface topology. X Ray Diffraction (XRD)

7 Transmission Electron Microscope It is possible to form a transmission electron diffraction pattern from electrons that have passed through a thin specimen. If these transmitted electrons are focused, their very short wavelength would allow the specimen to be imaged with a spatial resolution much better than the light optical microscope. In a transmission electron microscope (TEM), electrons penetrate a thin specimen and are then imaged by appropriate lenses, quite similar to optical microscope. One limitation of the TEM is that, unless the specimen is made very thin, electrons are strongly scattered within the specimen, or even absorbed rather than transmitted.

8 Transmission Electron Microscope

9 Transmission Electron Microscope

10 Scanning Electron Microscope The scanning electron microscope is arguably the most versatile microscope with magnification ranging from 5X to as high as 10 6 X. It provides excellent resolution, amenable to automation and user friendly. These features have made it the most widely used of all electron beam instruments. The sample preparation and examination is also relatively simple compared other techniques. A wide range of nanomaterials, starting from powders to films, pellets, wafers, carbon nanotubes, and even wet samples can be examined. It is also possible to correlate the observations made at nan scale to macro scale and draw reliable conclusions.

11 Scanning Electron Microscope Signals generated in an SEM

12 Scanning Electron Microscope Components of Scanning Electron Microscope

13 Scanning Electron Microscope Scan Pattern in SEM

14 Scanning Tunneling Microscope The STM works on the principle of quantum tunneling. When an atomically sharpened tip under a small voltage is brought close to the surface of a sample, so that the separation is of the order of a nanometer, there is a small change in current in the circuit. This effect is called the quantum tunneling effect. The induced current is referred to as the tunneling current. The tunneling current increases as the gap between the tip and the sample decreases. The change in tunneling current can be calibrated with respect to the change in gap. In other words, if we scan the tip over the sample surface while keeping the tunneling current constant, the tip movement depicts the surface topography, because the separation between the tip apex and the sample surface is always constant

15 Scanning Tunneling Microscope Components of STM

16 Atomic Force Microscope An AFM is rather different from other microscopes, because it does not form an image by focusing light or electrons onto a surface, like an optical or electron microscope. An AFM physically feels the sample s surface with a sharp probe, building up a map of the height of the sample s surface. By scanning a probe over the sample surface it builds up a map of the height or topography of the surface as it goes along.

17 Atomic Force Microscope Laser Deflection contact AFM

18 X Ray Diffraction System (XRD) X-ra Diffraction System (XRD) X ray diffraction is an ideal method for examining samples of metals, polymers, ceramics, semiconductors, thin films and coatings. It can also be employed for forensic and archeological analysis. A two dimensional diffraction pattern provides abundant information about the atomic arrangement, microstructure, and defects of a solid or liquid material.

19 X Ray Diffraction System (XRD) Bragg s Law Bragg law describes the relationship between the diffraction pattern and the material structure. If the incident X rays hit the crystal planes with an incident angle θ and reflection angle θ as shown in figure in the next slide, the diffraction peak is observed when the Bragg condition is satisfied That is, nλ = 2d.sin θ where λ is the wavelength, d is the distance between each adjacent crystal planes, θ is the Bragg angle at which one observes a diffraction peak, and n is an integer number, called the order of reflection.

20 Bragg Law X Ray Diffraction System (XRD)

21 2D X Ray Diffraction System (XRD)