Chapter 10. Nanometrology. Oxford University Press All rights reserved.

Transcription

1 Chapter 10 Nanometrology Oxford University Press All rights reserved. 1

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. 2

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 clothes 4

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 Three dimensional surface topology: size, shape, roughness, defects, electronic structures Scanning Electron Microscopy (SEM) Scanning Tunneling Microscopy (STM) 5

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) 6

7 Transmission Electron Microscope Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through. An image is formed from the interaction of the electrons transmitted through the specimen; the image is magnified and focused onto an imaging device, such as a fluorescent screen, on a layer of photographic film, or to be detected by a sensor such as a CCD camera. 7

8 Transmission Electron Microscope 8

9 Transmission Electron Microscope HRTEM: A faulted particle in a NiTiPt high temperature shape memory alloy 9

10 Transmission Electron Microscope TiNi shape memory alloy Source: 10

11 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, compliant 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

12 Scanning Electron Microscope A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning it with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that can be detected and that contain information about the sample's surface topography and composition. SEM can achieve resolution better than 1 nanometer. Specimens can be observed in high vacuum, in low vacuum, in wet conditions (in environmental SEM), and at a wide range of cryogenic or elevated temperatures. 12

13 Scanning Electron Microscope 13

14 Scanning Electron Microscope Sample preparation All samples must be of an appropriate size to fit in the specimen chamber and are generally mounted rigidly on a specimen holder called a specimen stub. Several models of SEM can examine any part of a 6 inch (15 cm) semiconductor wafer, and some can tilt an object of that size to 45. For conventional imaging in the SEM, specimens must be electrically conductive, at least at the surface, and electrically grounded to prevent the accumulation of electrostatic charge at the surface. Metal objects require little special preparation for SEM except for cleaning and mounting on a specimen stub. Nonconductive specimens: They are usually coated with an ultrathin coating of electrically conducting material, deposited on the sample either by low vacuum sputter coating or by high vacuum evaporation. Conductive materials in current use for specimen coating include gold, gold/palladium alloy, and graphite. 14

15 Scanning Electron Microscope SEM images Scanning electron microscope photograph of a textured silicon surface. University of New South Wales. SEM of polymer fibers. 15

16 Scanning Electron Microscope JEOL JSM 7001F Scanning Electron Microscope 16

17 Student Presentations 17

18 Scanning Tunneling Microscope A scanning tunneling microscope (STM) is an instrument for imaging surfaces at the atomic level. Its development in 1981 earned its inventors, Gerd Binnig and Heinrich Rohrer (at IBM Zürich), the Nobel Prize in Physics in 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 18

19 Scanning Tunneling Microscope Components of STM 19

20 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. 20

21 Atomic Force Microscope Laser Deflection contact AFM 21

22 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. 22

23 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. 23

24 Bragg Law X Ray Diffraction System (XRD) 24

25 2D X Ray Diffraction System (XRD) 25