This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Carbon Nanotube Metrology – Set 2”.
1. Identify the metrology standard used to determine the purity of SWCNTs.
a) ISO/TS 10798
b) ISO/TS 10868
c) ISO/TR 10929
d) ISO/TS 11888
View Answer
Explanation: Incase of SWCNTs, ISO/TS 10868 is used to describe a method that is needed for the measurement of diameter, purity and fraction of metallic nanotubes. It is done using the optical absorption spectroscopy.
2. There is a limitation on the use of RBM feature for the analysis of large – diameter MWCNTs.
a) True
b) False
View Answer
Explanation: For large diameter tubes especially MWCNTs the RBM feature becomes broad and cannot be resolved experimentally. The dependence of the RBM frequency on the inverse tube diameter also limits the use of RBM feature to study the large-diameter MWCNTs. In case of these CNTs, RBM is observed only when they have small inner tube (below 3nm).
3. Identify the incorrect statement related to Raman Spectroscopy for SWCNT characterization.
a) Raman intensity depends on light polarization
b) Weak point of Raman spectroscopy is the low intensity compared to PL
c) Radical breathing mode is a dominant Raman feature at higher frequency
d) Raman spectra exhibits disorder – induced D band
View Answer
Explanation: Raman spectroscopy is a dominant optical characterization technique for CNTs. The two dominant Raman features are radical breathing mode (RBM) at low frequencies and tangential (G band) mode at higher frequencies. It also shows weak features such as disorder – induced (D band). Incase of Raman spectroscopy, the intensity of the spectra depends on light polarization. The weak point is that it is the low signal intensity procedure compared to photoluminescence (PL).
4. Which of the following is not related to the observation of a D band in the Raman spectra?
a) Defects in tube wall
b) Presence of amorphous – carbon material
c) Symmetry breaking on the hexagonal sp2 bonding lattices
d) Proportionality with Inverse tube diameter
View Answer
Explanation: The D-band in Raman spectroscopy is observed when there is symmetry breaking on the hexagonal sp2 – bonding lattices for CNTs. This observation is related to either the presence of amorphous carbon materials in the sample or the presence of defects in CNT walls. For e.g.:- vacancies dopants etc.
5. What is the major drawback in photoluminescence technique for CNT analysis?
a) Strongest signal intensity
b) Sample preparation
c) Measurement of temperature effect on isolated tubes
d) (n, m) population is rapidly extracted
View Answer
Explanation: Photoluminescence is the strongest signal producing optical technique for CNT characterization so far. However, there is a major downside to this method that is sample preparation. The nanotubes that are obtained in bundles do not luminescence nor can the metallic tubes within a sample be measured.
6. Which was the first technique for structural analysis of SWCNTs?
a) Spectroscopy
b) Bessel – Function Analysis
c) Electron diffraction
d) Scanning probe microscopy
View Answer
Explanation: Electron diffraction was the earliest technique used for the structural analysis of SWCNTs. The recent advancements have allowed nanobeam electron techniques to flourish that uniquely allow direct probing of individual nanotubes and analysis of their atomic structure.
7. Which pair of metrological standards establish methods for elemental composition of SWCNTs?
a) ISO/TS 10979 and ISO/TS 10980
b) ISO/TR 10929 and ISO/TR 11888
c) ISO/TR 11929 and ISO/TR 11865
d) ISO/TS 10797 and ISO/TS 10798
View Answer
Explanation: There are two main metrological standards ISO/TS 10797 and ISO/TS 10798 that are applicable to SWCNTs. These standards establish methods used for characterizing the elemental composition and morphology of the nanotubes. They are determined using scanning electron microscopy and transmission electron microscopy respectively, along with energy dispersive X-ray spectrometry analysis.
8. How can the spherical aberration of the objective lens in TEM be dealt with?
a) Ms Corrector
b) Higher voltage
c) Polaroid lenses
d) Electromagnetic hexapoles
View Answer
Explanation: The spherical aberration of the objective lens in TEM can be corrected by using an additional set of electromagnetic hexapoles, called the Cs corrector. This electron-optical compensation of the aberration enhances the spatial resolution and allows the direct observation of the carbon atom arrangements and in turn determines the chiral indices (n, m).
9. Why is Raman spectroscopy for SWCNT characterization strongly dependent on excitation laser energy?
a) Sensitive characterization tool for nanostructures
b) Exhibits strongly enhanced Raman signal
c) Less work on sample preparation
d) Low signal intensity in comparison to photoluminescence
View Answer
Explanation: Raman spectroscopy is one of the most common optical techniques used for SWCNT characterization. This method of spectroscopy depends strongly on the excitation laser energy (Elaser) because only nanotubes in resonance with Elaser exhibit a strongly enhanced Raman signal. The Raman intensity is dependent on the light polarization. This polarization effect is used to characterize different aspects related to SWCNT orientation.
10. Which of the following standards is applicable to both SWCNTs and MWCNTs?
a) ISO/TS 10798
b) ISO/TR 10929
c) ISO/TS 11888
d) ISO/TS 10868
View Answer
Explanation: ISO/TS 10798 established procedures to characterize the morphology and deduce the elemental composition of SWCNTs. The methods applied for SWCNTs can also be used for the analysis of MWCNTs. The SEM/EDX analysis is applicable to both SWCNTs and MWCNTs.
Sanfoundry Global Education & Learning Series – Nanotechnology.
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