This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Application of Quantum Dots”.
1. What is the purpose of using self-assembled monolayers in solar cells?
a) Improve the band alignment at electrodes
b) Reduce the cost of fabrication
c) Exhibits fluorescence with lesser photobleaching
d) Slows down mass and electron transfer processes
View Answer
Explanation: Aromatic self-assembled monomers such as 4-nitrobenzoic acid can be employed to improve the band alignment at electrodes inorder to enhance the efficiency. The positioning of the monolayers between ZnO-PbS colloidal quantum dot film junctions modifies the alignment via the dipole moment of the molecules of the monolayer. It has been recorded to increase the power conversion efficiency by 10.7%.
2. Which of the following components is not used in the fabrication of QD – sensitized solar cell?
a) Single crystal ZnO nanowires
b) Mercaptopropionic acid
c) Cadmium selenide QDs
d) Aspartic acid
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Explanation: A QD-sensitized solar cell has capped single-crystal ZnO nanowires with CdSe quantum dots immersed in mercaptopropionic acid that acts as hole transport medium. The electrons have a direct pathway to the photoanode owing to the nanowire morphology. This leads to 50-60% internal quantum efficiency of the solar cells.
3. What is the main application of QDs generated using the method of lithography?
a) Research and development
b) Quantum cryptography
c) Bio-imaging
d) Quantum computation
View Answer
Explanation: QDs produced using electron beam lithography are mainly of interest for experiments and applications involving electron or hole transport that is an electrical current. Individual QDs are created from 2-dimensional electron or hole gases present in remotely doped quantum wells.
4. How are QDs useful in tumour targeting?
a) QDs undergo photolysis releasing metallic ions into the medium
b) QDs are functionalized with tumour specific binding sites
c) QDs generate more permeable membrane
d) QDs allow selective excitation of a dye acceptor
View Answer
Explanation: QDs can be used for tumour targeting under in vivo conditions employing two different types of schemes. These are active and passive targeting. In active targeting, QDs are functionalized with tumour specific binding sites to selectively bind to tumour cells. While in passive targeting enhanced permeation and retention of tumour cells are used for the delivery of QD probes.
5. What is the process involved in the fabrication of quantum dot photodetectors?
a) Hummers process
b) VLS method
c) Exfoliation
d) Solution processing
View Answer
Explanation: Quantum dot photodetectors (QDPs) can be fabricated by the method of solution processing. QDPs formed using this technique can be easily integrated with an almost infinite variety of substrates, and also post processed atop other integrated circuits. They have their applications in industrial inspection, spectroscopy and fluorescent biomedical imaging.
6. Which property makes QDs desirable for photovoltaic devices?
a) Low photostability
b) Water dispersibility
c) Low quantum yield
d) High extinction coefficient
View Answer
Explanation: Quantum dots have tunable absorption spectrum and high extinction coefficient that makes them attractive for light harvesting technologies such as photovoltaics. They can enhance the efficiency of silicon photovoltaic cells. QDs photovoltaic devices would theoretically be cost-effective and economical since they are made using simple chemical reactions.
7. Identify a technique that has a potential application in single molecule tracking.
a) Endosomal sequestration
b) Aggregation
c) Electroporation
d) Cell squeezing
View Answer
Explanation: QDs can be delivered to cell cytoplasm via cell squeezing without inducing aggregation, significant loss of cell viability or trapping material in the endosomes. Individual QDs can be delivered using this approach which is detectable in the cell cytosol making way for the application of this technique in single molecule tracking studies.
8. What is the major drawback of QDs used as photocatalysts?
a) Bandgap excitation in QDs drive redox reactions in the liquid
b) Enhance mass transfer and electron transfer process of QDs
c) Presence of surfactants on the surface of QDs
d) Electron hole pairs are formed in the QDs
View Answer
Explanation: There have been issues in the use of QDs as photocatalysts due to the presence of surfactants on their surfaces. The surfactants or ligands interfere with the chemical reactivity of the dots by slowing down mass and electron transfer processes. QDs made of metal chalcogenides are chemically unstable under oxidizing environment and undergo photo corrosion reactions.
9. Which of the following application is not related to the photostability of QDs?
a) Real time tracking of molecules
b) Organic dyes
c) Tumour targeting
d) Cellular imaging
View Answer
Explanation: High photostability of QDs allow for the acquisition of many consecutive focal plan images that can be reconstructed into a high resolution three dimensional image. This helps in the advancement of cellular imaging. This property also allows for real time tracking of molecules and cells over extended period of time. QDs are also useful as dyes since they are way brighter than traditional dyes and have commendable high photostability.
10. Choose the incorrect statement from the following.
a) QDs can operate as a single electron transistor
b) QDs are extremely useful for quantum information processing
c) QDs have indistinct density of states than higher dimensional structures
d) QDs are well suited for optical encoding and multiplexing applications
View Answer
Explanation: QDs can operate like a single electron transistor. They can be used as qubits for quantum information processing and as active elements for thermo electrics. They have sharper density of states, due to their zero-dimensionality. Owing to the broad excitation profiles, narrow and symmetric emission spectra of QDs, they can be employed in applications involving optical encoding and multiplexing.
11. What was the first commercial use of QDs?
a) Electron microscope
b) Flat panel televisions
c) Hybrid watches
d) Solar cells
View Answer
Explanation: The first commercial application of QDs was the Sony XBR X90OAseries of flat panel televisions launched in the year 2013. Sony incorporated technology from the company QD vision that made prototypes of quantum dot displays that are quite similar to OLED displays.
12. Find out the correct pair of application of QDs with the respective properties responsible for it.
a) Organic dyes – particle size and degree of quantum confinement
b) Donor fluorophores – large extinction coefficient
c) Photovoltaic cells – production of monochromatic light
d) Photocatalysts – improved band alignment
View Answer
Explanation: QDs are used as dyes owing to their higher photostability and quantum yield. In biology they are used as donor fluorophores in Förster resonance energy transfer using their large extinction coefficient and spectral purity. QDs also find their application in photovoltaic cells and devices by virtue of their high extinction coefficients and tunable absorption spectrum. They have also been used as photocatalysts due to their small particle size and degree of confinement which generate incredible photochemical activity.
13. Why are QDs superior to traditional organic dyes?
a) High photostability
b) Low quantum yield
c) Tunable absorption spectrum
d) High molar extinction
View Answer
Explanation: Organic dyes have been used in bioimaging for several years now. However, there are certain issues of low quantum yield and low photostability with these organic dyes. This made research necessary into QDs which have come out as superior to traditional organic dyes in many respects. One of the most obvious reasons for the same is brightness, which is almost 20 times than that of traditional dyes. They also have greater stability allowing lesser photobleaching.
14. Quantum dots can become an effective alternative of traditional antibiotics.
a) True
b) False
View Answer
Explanation: QDs posses antimicrobial properties similar to nanoparticles. They can kill bacteria in a dose dependent manner. The mechanisms involved in killing the bacteria are inducing free radicals, disrupting cell walls, membranes and even arresting gene expression. QDs have been shown to be effective against both gram positive and gram negative bacteria.
15. Why are silicon nanowires preferred to planar silicon for their application in solar cell?
a) Exhibit poor antireflection properties
b) Generate monochromatic light
c) Have better trapping ability
d) Improved band alignment at electrodes
View Answer
Explanation: Silicon nanowires (SiNWs) are preferred to planar silicon since the use of SiNWs increases the antireflection properties of Si. Moreover, these nanowires exhibit extraordinary light trapping effect SiNWs used in association with carbon quantum dots result in 9.10% power conversion efficiency of solar cell.
Sanfoundry Global Education & Learning Series – Nanotechnology.
To practice all areas of Nanotechnology, here is complete set of 1000+ Multiple Choice Questions and Answers.
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