Nanotechnology Questions and Answers – Synthesis of Nanorods

This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Synthesis of Nanorods”.

1. What is the most important factor influencing the physical morphology and crystal growth direction of ZnO nanorods?
a) Temperature of reaction
b) pH of the solution
c) Pressure maintained
d) Precursor concentration
View Answer

Answer: d
Explanation: The growth of nanorods can be controlled by choosing the appropriate initial precursor concentration and deposition time. Upon increasing the precursor concentration, the average diameters of ZnO nanorods enlarge. It is thus inferred that precursor concentration influences the physical morphology and crystal growth direction of ZnO nanorods.

2. Which of the following is not a pitfall of the VLS method for ZnO nanorod production?
a) Controlled growth
b) Slow process
c) High temperature requirement
d) Impure product
View Answer

Answer: a
Explanation: The VLS method requires very high temperature > 900°C to dissolve zinc vapour in the gold catalyst simultaneously forming an alloy droplet. Apart from the high temperature it also requires catalysts such as gold and copper, which are expensive, to promote the nanorod formation. This makes it uneconomical for large scale production. The process is generally slow. Also, the tips of ZnO nanorods have impurity particles that might be undesirable for fabrication.

3. Choose the correct statement from the given options.
a) Chromium alumina sulphate is used as a precursor in wet chemical synthesis of iron nanorods
b) Iron arsenide acts as a precursor for template mediated technique for fabrication of iron oxide nanorods.
c) Aluminium iron oxide nanorods can be transformed to biocompatible iron oxide nanocapsules
d) Iron pentacarbonyl in the presence of oleic acid can result in single crystal nanorods in a solvothermal process
View Answer

Answer: d
Explanation: Wet chemical synthesis involves the production of iron oxide nanorods using a surfactant, a template compound polyethylene glycol (PEG) and precursor ferrous ammonia sulphate. The template mediated approach makes use of iron oleate as a precursor for iron oxide nanorod synthesis. Biocompatible iron oxide nanocapsules can be produced from β-FeOOH nanorods. The solvothermal process generates Fe3O4 single crystal nanorods using Fe(CO5) in the presence of oleic acid.

4. Why has the top-down method become unattractive in fundamental research?
a) Extremely fast process
b) Electron scattering at GBs
c) Inexpensive technique
d) Enhanced plasmonic properties
View Answer

Answer: b
Explanation: Top-down method has various snags such as its time consuming and expensive which makes it quite uneconomical for production of gold nanorods at large scale. Further vacuum deposition techniques produce gold nanorods that undergo degradation in plasmonic properties due to the electron scattering at the grain boundaries.

5. What method makes use of organic precursor for ZnO nanorod synthesis?
a) ALD
c) VLS
d) MBE
View Answer

Answer: b
Explanation: Metal organic chemical vapour deposition (MOCVD) makes use of organic precursors such as Zn(C2H5)2 and O2 system. The process conditions are gas flow ratio of Ar to O2 in the range of 1 – 2, the substrate temperature ranging between 250 and 500˚C and the deposition time set to 10 minutes.

6. Which of these is not a benefit of the electrochemical deposition method used in ZnO nanorod fabrication?
a) Lower temperature
b) Inexpensive technique
c) Complex process
d) Uniform size of nanorods
View Answer

Answer: c
Explanation: The electrochemical deposition is quite an advantageous method for the preparation of ZnO nanorods. It requires a low growth temperature, is an inexpensive process and does not need vacuum systems for preparing nanorods. The ZnO formed using this process has high crystallinity, good vertical alignment and relatively uniform size. This process is easily scaled up and provides good electrical contact between the structures and substrate.

7. Which of the following condition does not prevail in the quartz tube during CVD process for ZnO nanorod synthesis?
a) Catalyst- Vanadium pentoxide
b) 700˚C or more temperature
c) Vacuum range – 10-2Torr
d) Pressure – 1 atm
View Answer

Answer: a
Explanation: The CVD process for ZnO nanorod synthesis requires certain conditions to be maintained in the quartz tube. These are – vacuum in the range of 10-2 Torr, purging with Ag gas to maintain a 1 atm pressure. Furnace temperature is rapidly increased to 700˚C under constant Ag flow. Gold is used as a catalyst.

8. Why is tributylphosphine commonly used in synthesizing iron oxide nanorod in co-precipitation method?
a) Behaves as a stabilizer
b) Provides optimum temperature to solution
c) Prevents uncontrolled precipitation
d) Acts as an electrolyte
View Answer

Answer: c
Explanation: Co-precipitation method is a conventional method for synthesizing iron oxide nanorods. It uses certain compounds such as trioctylphosphine (TOP), tributylephosphine (TBP), trioctylphosphine oxide (TOPO) or oleylamine (OA) to prevent the uncontrolled precipitation.

9. What is the main drawback of the seed mediated growth method for gold nanorod synthesis?
a) Formation of gold nanospheres
b) Requirement of silver ions
c) A tedious growth process
d) Drastic changes in aspect ratio
View Answer

Answer: a
Explanation: Seed mediated growth method is a very common technique employed for producing gold nanorods. It generates longer monodisperse nanorods having greater uniformity. Also, the rate of crystal growth is easily controlled. However, the limitation to this method involves formation of gold nanospheres which requires non-trivial separations and cleanings.

10. Which of the following is not a limitation of the bottom-up methods of gold nanorod synthesis?
a) Different shape and size of nanorods in different batches
b) Random nature of the reduction of the nanorods
c) Difficult placement of nanorods into larger, ordered arrays
d) Monodisperse nanorod formation having small diameter
View Answer

Answer: d
Explanation: Bottom up methods produce excellent monodisperse gold nanorods with high uniformity. However, there are certain downsides to this method. It is difficult to selectively place gold nanorods at desired locations on the substrates due to the random nature of the reduction of gold ions and the deposition of gold atoms in reaction solutions. The optical and catalytic properties are also affected due to the varied shape and size of the gold nanorods produced from different synthesis batches. Moreover, it is difficult to place gold nanorods into large-area ordered arrays.

11. Find out the odd one from the following.
a) Tin
b) Caesium
c) Copper
d) Gold
View Answer

Answer: b
Explanation: The vapour-liquid-solid (VLS) process, originated in 1964 is the most common process to synthesize ZnO nanorods. In the typical process certain metal catalysts such as gold (Au), tin (Sn), copper (Cu) or nickel (Ni) is used inorder to promote the formation of ZnO nanorods.

12. Identify the method in which iron oxide nanodots string together in a row forming rod-structure.
a) Hydrothermal method
b) Template mediated method
c) Wet chemical synthesis
d) Solvothermal method
View Answer

Answer: b
Explanation: The template mediated approach gives rise to iron oxide nanodots string together in a row to form rod structure. These nanorods formed are small and thin and exhibit super paramagnetism. They show twisted crystal orientations of single nanocrystals when observed under a TEM.

13. What is the most popular method for production of high quality gold nanorods?
a) Cation exchange method
b) Microwave assisted method
c) Seed mediated method
d) Sonochemical method
View Answer

Answer: c
Explanation: Seed mediated method is employed for the production of high-quality gold nanorods. This process generates pure, monodisperse nanorods that have greater uniformity. The technique proceeds with seed addition to the bulk HAuCl4 with ascorbic acid, in the presence of a surfactant and silver ions. Seeds used can be citrate-capped gold nanoparticles. Preparation of the growth solution includes reduction of HAuCl4 with ascorbic acid in the presence of a surfactant and silver ions.

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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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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