1) What is electron spectroscopy? Explain Auger Electron Spectroscopy(AES) and Electron Spectroscopy for Chemical Analysis (ESCA) briefly. (Armağan and Dilek)
Electron spectroscopy is an analytical technique to study the electronic structure and its dynamics in molecules.
Auger Electron Spectroscopy (AES) is a widely used technique to investigate the composition of surfaces. It is based upon the measurement of the kinetic energies of the emitted electrons.
ESCA is a quantitative spectroscopic technique that measures the elemental composition, empirical formula, chemical state and electronic state of the elements that exist within a material.
2) What is the basic task of the fluorescence microscope? Explain how it works briefly. (Didem and Bengi)
The basic function of a fluorescence microscope is to radiate the specimen with a specific band of wavelengths, and then to separate the much weaker emitted fluorescence from the excitation light. First, the microscope has a filter that only lets through radiation with the specific wavelength that matches material. The radiation collides with the atoms in specimen and electrons are excited to a higher energy level. When they relax to a lower level, they emit light. The emission light passes back through the dichromatic mirror and is filtered by a barrier (or emission) filter, which blocks the excitation wavelengths. Thus, only the emission light from the specimen reaches the eye or detector. The fluorescing areas shine against a dark background.
3) On which equation does the XRD spectrum depend? What are the XRD components? What are its advantages? (Ulya and Melodi)
Bragg's Equation λ = 2 d sin(θ)
XRD components are:
- X-ray source
- Device for restricting wavelength range “goniometer”
- Sample holder
- Radiation detector
- Signal processor and readout
Its advantages are:
- Fast identification of materials,
- Ease of sample preparation,
- Computer-aided material identification,
- Large library of known crystalline structures.
4) What are the advantages and disadvantages of AFM? (Sevinç and Tolga)
Advantages:
- Can provide higher resolution to TEM/SEM
- Can provide height, volume, 3D display
- Easy Sample preparation
Disadvantages:
- Limited vertical range
- Incorrect choice of the tip can lead to cause image artifact.
- Tip or sample can be damaged.
5) What are the advantages of TEM? (Duygu and Emine)
- It has better resolution than any other electron microscope,
- It allows to “see” single atoms and image nanomaterials,
- It helps to determine the grain size/particles size, structure, shape and crystallography of materials,
- It helps to identify substances, precipitates,
- It allows the study of internal stresses, lattice strains and various other defects,
- Depth of material can be observed,
- We can study with biological and nonbiological materials.
6) What is hardness? What are the main hardness testing methods and their working principle? (Serkan and Gizem)
Hardness is the resistance of a metal to plastic deformation, usually by indentation. However, the term may also refer to stiffness or temper or it may refer to resistance to scratching, abrasion, or cutting. It is the property of a metal, which gives it the ability to resist being permanently deformed (bent, broken, or have its shape changed), when a load is applied. The greater the hardness of the metal, the greater resistance it has to deformation.
There are three main types of hardness testing methods:
- Brinell hardness test,
- Rockwell hardness test,
- Vickers hardness test.
Principle of any hardness testing method is forcing an indenter into the sample surface followed by measuring dimensions of the indentation (depth or actual surface area of the indentation).
7) What are the advantages of an optical microscope? (Tuğba and Özge)
- Relatively easy to use,
- Samples analyzed in water or air,
- Samples shown in natural color,
- Magnifications are 100x to 1000x.
8) What is EDS? List at least 3 applications. (Şaban and Gökay)
EDS identifies the elemental composition of materials imaged in a Scanning Electron Microscope (SEM) for all elements with an atomic number greater than boron. Applications:
- Foreign material analysis,
- Corrosion evaluation,
- Coating composition analysis,
- Rapid material alloy identification,
- Small component material analysis,
- Phase identification and distribution
9) What are the industrial applications of an inverted microscope? (Merve and Tuba)
Industrial applications of an inverted microscope are:
- Three-dimensional analysis of metals,
- Analysis of semiconductor materials
- Analysis of surface defects
- Analysis of grain size and incursions in QA/QC (quality assurance/quality control)
- Analysis of surface microstructures in a variety of sample types in metallurgy and metallography
10) What are the three main differences between Tensile Test and Charpy Impact Test? (Ayça and Baran)
Tensile Test:
- Measures the resistance of material to a static or slowly applied force,
- The strain rates are very small,
- The test is possible within a temperature range from –40 ºC to +200 ºC.
Charpy Impact Test:
- Measures the resistance to failure of a material to a suddenly applied force,
- The strain rates are very high,
- The test is possible within a temperature range from –60 ºC to +23 ºC. It can be done at the oven temperature 200 ºC, room temperature 25 ºC and liquid nitrogen temperature -196 ºC to test if transition from ductile-to-brittle exists.
11) Write the types of nucleation and explain them briefly. (Gözde and Serhenk)
There are homogeneous nucleation and heterogeneous nucleation.
Nucleation without preferential nucleation sites is homogeneous nucleation. Homogeneous nucleation occurs spontaneously and randomly, but it requires that the supercooling below the melting temperature becomes large enough to cause the formation of a stable nucleus.
Heterogeneous nucleation occurs in the presence of nucleation sites. Therefore, supercooling does not have to be at the exact level required for homogeneous nucleation and causes the formation of impurities on both surfaces and interfaces.