This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Carbon Nanotube Metrology”.
1. Why are the optical techniques used for CNT analysis considered non-destructive?
a) One – dimensional confinement of electronic structure of CNT
b) Performed at ambient temperature and pressure
c) Faster operation and results relative to SPM
d) Use of charge less probe for detection
View Answer
Explanation: Optical techniques are very advantageous. They are non-invasive and non-destructive because they use photons as probes. These are massless as well as charge less particles. These techniques are widely available, simple to operate and quite fast in the analysis.
2. What is the main advantage of TEM over SEM?
a) Higher resolution
b) Less time taken to create images
c) Examine larger samples
d) Create 3-D images
View Answer
Explanation: SEM and TEM are both quite effective in observing the morphology of CNTs. Though SEM has greater availability and simpler way of application, yet TEM is used for more precise results. This is because TEM has higher resolution than SEM which helps in distinguishing the types of CNTs i.e., single, double or multi-walled and to check if the CNTs are in bundles or not.
3. Choose the correct statement with regards to intrinsic layerline distance analysis.
a) ξi corresponding to each nonequatorial layerline is given by ξi = Do2/di
b) The method requires calibration of the EDP but the effect of tilt remains uncompensated
c) Simultaneous solutions of ξ1 = (n-m)/√3π and ξ4 = √3m/π give the chiral indices (n, m)
d) The method has certain limitation for (n, m) determination with EDP
View Answer
Explanation: Electron – diffraction analysis of SWCNTs via intrinsic layerline distance analysis helps to determine (n, m) more accurately. The intrinsic layerline spacing (ξi) corresponding to each non-equatorial layerline is given by ξi = Dodi. Simultaneous solutions of any two layerlines give the chiral indices (n, m). This method of analysis does not require any calibration of the EDP and the effect of the tilt stands compensated for the (n, m) determination. Moreover, there is no significant limitations for the (n, m) determination with EDP.
4. Which of the following is not an advantage of the optical techniques used to characterize CNTs?
a) Operated at room temperature
b) Non – invasive method
c) Readily available
d) Lower optical resolution
View Answer
Explanation: Optical techniques are widely used for CNT characterization owing to its advantages in both experimental and fundamental aspects. Experimentally, the techniques are readily available, relatively simple, fast and operative at room temperature and ambient pressure. Fundamentally, the techniques are non-destructive and non-invasive. Moreover, these experiments can be carried out on the single-nanotubes because of the unusually high optical response of nanotubes.
5. Why is SEM more frequently used than STM or TEM for CNT observation?
a) Prolonged time to form image
b) Wider availability
c) Use of electrons
d) Higher resolution
View Answer
Explanation: Scanning electron microscope (SEM) is more frequently used to observe CNTs rather than transmission electron microscope (TEM) and scanning tunneling microscope (STM). This is because of their wider availability, lesser complexity, simpler sample preparation methods and relative ease of use.
6. What does the vertical resolution of STM depend on?
a) Quality of the probing tip used
b) Size of the sample under observation
c) Exponential variation of (I) with the (d)
d) Interactions of the tip and sample
View Answer
Explanation: STM has very high vertical resolution due to the exponential dependence of tunneling current (I) on the distance of the gap (d) between the tip and the substrate surface. For every increase of 0.1nm in (d) there is a decrease in the (I) by one order of magnitude.
7. The RBM frequency is not dependent on which of the following factor?
a) Laser heating
b) Tube length
c) Doping
d) Tube diameter
View Answer
Explanation: The radial breathing mode of Raman spectroscopy is unique to CNTs. The frequency of the RBM is proportional to inverse tube diameter. Simple force-constant calculations predict the two quantities to be linearly dependent. It is also weakly dependent on doping (charge transfer) and laser heating or temperature-dependent effects. For smaller-diameter tubes, frequency is expected to depend on the chiral angle θ. In case of DWCNTs inner tube frequency depends on the outer tubes.
8. Find out the incorrect statement regarding STM.
a) The sample can be conducting or non- conducting
b) It uses both constant height and constant current imaging modes
c) The tip has a raster movement over the sample during scanning
d) STM uses a feedback system to keep the tunneling current constant
View Answer
Explanation: Incase of STM both the probing tip and the surface of analysis should be conducting. When the tip is brought near the surface it exhibits a raster movement for scanning. The instrument uses both constant height and constant current imaging modes. A feedback system is used for keeping the tunneling current constant.
9. Tube – environmental interaction has no effect on RBMs.
a) True
b) False
View Answer
Explanation: Several tube environmental effects have been observed in RBM. There has been effect in the intensities of the resonance Raman profiles that are associated with the relative population of the different (n, m) nanotubes within the sample. Effects have been observed when the nanotubes are dispersed in different surfactants due to the different dielectric constants of the surroundings of the nanotubes.
10. STM has the capability of probing local vibrational modes of SWCNTs.
a) True
b) False
View Answer
Explanation: STM can make use of their high lateral resolution to probe the local vibrational modes of SWCNTs by detecting the inelastic tunneling processes, especially near defects. Unlike conventional optical spectroscopy that requires averaging over the surface of substrate, (IETS-STM) probes vibrational spectroscopy by lateral resolution approaching atomic dimensions.
Sanfoundry Global Education & Learning Series – Nanotechnology.
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