This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Characterization of Nanoparticles”.
1. Match the following statements.
i) Bremsstrahlung X-ray emission due to deceleration of electrons I) Plasmon scattering ii) Incident electrons excite collective, resonant oscillations II) Direct radiation excitation iii) Atomic vibrations are excited by incident electrons in the sample III) Direct radiation losses iv) Lightly bound valence electrons are removed from atoms IV) Phonon scattering
a) i – III; ii – IV; iii –I; iv – II
b) ii – II; i – IV; iv – I; iii – III
c) iii – I; iv – III; i – II; ii – IV
d) iv – IV; iii – II; ii – III; i – I
View Answer
Explanation: Bremsstrahung X-ray emission caused by the deceleration of electrons, are the principal direct radiation losses. Plasmon scattering involves the excitation of plasmons of the valence electrons of the sample by the incident electrons. Phonon scattering includes the excitation of phonons or atomic vibrations in the sample. In single electron excitation, lightly bound valence electrons are ejected from atoms.
2. Single – particle measurements form the basis of microscopy.
a) True
b) False
View Answer
Explanation: One of the basic principles of microscopy is that it’s based on single – particle measurements. This indicates that large numbers of individual particles are characterized inorder to estimate, on a whole, the bulk properties.
3. Define interaction volume.
a) Production of various signals due to the interaction of the electrons and specimen
b) Depth of the electron penetration in the sample is roughly dependent on V3/2
c) Electrons have sufficient energy for their interaction with the specimen
d) Electrons leaving the specimen with kinetic energy higher than 50 eV
View Answer
Explanation: The interaction volume can be defined as the space in which electrons have sufficient energy to interact with the specimen. As the electrons travel through the volume, 95% of them are brought to rest by scattering because of the loss of energy and change in direction with each atomic interaction.
4. What is the method applied to reduce spherical aberration for electromagnetic lenses?
a) Using combination of concave and convex lens
b) Decreasing the aperture angle
c) Applying externally imposed fields
d) Using low – dispersion glasses
View Answer
Explanation: In case of optical microscopy, chromatic and spherical aberrations are reduced by using combinations of concave and convex lens elements. But, for electromagnetic lens this method is not preferable. Instead the reduction in aperture angle, α, can decrease the aberration.
5. Which of the following is an advantage of FIM?
a) Exclusion of contaminated or adsorbed surface species
b) Sample preparation requires considerable precision
c) No lenses involved in the set-up
d) Geometrical constraints on specimen
View Answer
Explanation: Field ion microscopy (FIM) was one of the first devices to provide images of atoms and their arrangement at the tip. They can provide images of local imperfections and give us the location of vacancies. One of the major advantages of FIM is that it does not involve lenses and thus limitations associated with depth – of – field or diffraction are not shown by it.
6. Which of the following is used for secondary electron detection in SEM?
a) Geiger Mueller Counter
b) Everhart – Thornley detector
c) Refractive Index detector
d) Neutrino detector
View Answer
Explanation: A scintillator – photo – multiplier system known as Everhart – Thornley (ET) detector is used for the secondary electron detection in SEM. The ET detector collects nearly all the secondary electrons emitted from the specimen surface. Thus, images appear to look down holes and over hills.
7. How can the emitted X-rays be made monochromatic?
a) Using storage ring
b) Using cyclotron
c) Using filters
d) Using synchrotron
View Answer
Explanation: Emitted X-rays are generally collimated and made monochromatic by the use of filters or crystal monochromators which are either flat or curved inorder to provide a focusing action. However, extremely high intensity X-rays of varying wavelengths can be produced by accelerating electrons around the storage ring of a synchrotron and wiggling their trajectories.
8. What is the Bragg’s equation?
a) Z1 = (Z)/1-K
b) λ = h/mv
c) mλ = 2dsinθ
d) ΔxΔp ≥ h/4π
View Answer
Explanation: Bragg’s equation is given by,
mλ = 2dsinθ where m = integers = 1,2,3,….
λ = wavelength of the radiation incident on a crystal
d = distance between the lattice planes of the crystal
θ = allowed angles for diffraction
9. Identify a compound that has higher brightness than tungsten in an electron gun set up for electron beam generation.
a) LiF
b) CaCO3
c) LaB6
d) N2O
View Answer
Explanation: In a thermionic electron gun one of the important parameters is the brightness of the source ꞵ, which is the current density per unit solid angle. This brightness can be increased by the use of lanthanum hexaboride (LaB6) filament that has lower threshold energy than tungsten. It provides an increase in ꞵ by an order of magnitude.
10. What is the disadvantage of an environmental scanning electron microscopy?
a) Liquid phase electron microscopy
b) Degradation of image resolution
c) Imaging electrically non-conductive specimens
d) Presence of gas is useful in detection
View Answer
Explanation: Environmental scanning electron microscopy (ESEM) has many pros and cons to its operation. The cons include degradation in image resolution due to interaction of the incident and scattered electron beams with the gaseous atmosphere.
11. Identify a method used for characterization of nanoparticles.
a) Centrifugation
b) Electrophoresis
c) Filtration
d) Chromatography
View Answer
Explanation: Electrophoresis is a method used for determining the surface area of the nanoparticles. Chromatography, filtration and centrifugation are however used only for the separation of nanoparticles on the basis of size or other physical properties before their characterization.
12. Why should the field strength at the specimen tip of a FIM be high?
a) Emit atoms from the specimen tip
b) Limit the resolution of an individual atom
c) Ionize the gas atoms in the chamber
d) Evaporate the field
View Answer
Explanation: In case of field ion microscopy (FIM), the specimen comprises of a conducting fine tip or probe. The field strength at this tip must be high enough to ionize the gaseous atoms that are introduced in the chamber. However, too high field strength can result in field evaporation or atom emissions from the tip.
13. What is the purpose of a Wehnelt cylinder in a thermionic electron gun?
a) Electron generation
b) Focusing electrons
c) Electron acceleration
d) Providing potential to electrodes
View Answer
Explanation: A thermionic electron gun employs a hot cathode which is usually made up of a tungsten filament. This is heated to create a stream of electrons by thermionic emission. These emitted electrons are collimated and focused using a Wehnelt cylinder to a beam of typically 50μm in diameter.
14. Which of the following is not a limitation of SNOM?
a) Low working distance
b) Shallow depth of field
c) Experimentally challenging
d) Provide chemical information
View Answer
Explanation: Scanning near field optical microscopy (SNOM) is an optical microscope for surface scanning that provides a limit of resolution beyond the diffraction limit. It provides chemical information of sample using near – field spectroscopy. However, it has several disadvantages like very low working distance, extremely shallow depth of field, long scan times for larger samples and experimentally challenging.
15. Choose the correctly matched pair from the given options.
a) Chromatic aberration – lens with different focal lengths; Astigmatism – difference in focal lengths in two axial planes
b) Spherical Aberration – difference in focal lengths of lens; Chromatic Aberration – variation with the aperture of the image distance
c) Astigmatism – variation in length of path for rays; Spherical Aberration – difference in foci of the rays travelling in perpendicular planes
d) Chromatic Aberration – refraction of light rays striking off-centre of lens; Astigmatism – Axial ray travelling along the optical axis is focused further away from the lens
View Answer
Explanation: Chromatic aberration in electromagnetic lens occurs due to the different focal lengths for different wavelengths of incident radiation. Astigmatism, on the other hand, arises owing to the different focal lengths of lens in two axial planes perpendicular to each other.
Sanfoundry Global Education & Learning Series – Nanotechnology.
To practice all areas of Nanotechnology, here is complete set of 1000+ Multiple Choice Questions and Answers.
If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]
