CrystEngComm Blog

ZnO nanostructures have generated much interest recently due to their unique properties, which make them ideal candidates for photo applications such as solar cells, light emitting diodes and field emission displays. While it has been known that Ga doped ZnO shows good field emission properties, there are very few studies on how Ga doping affects the ZnO crystals.

In this paper, the authors investigated Ga doped ZnO nanostructures grown by metal–organic chemical vapor deposition. By varying the growth temperature, Ga concentration and growth time, the authors were able to vary the morphology of the GaZnO nanostructures from wires to a pagoda shape. The formation of the pagodas were also explained via a computational simulation of the growth process.

A study of the field emission properties of the GaZnO nanopagodas demonstrated that the geometry of the nanostructure and the density of the pagodas affects the turn-on voltage of the emitters as well as the field enhancement factor. In general, the nanopagodas demonstrated better field emission properties than pure ZnO nanowires.

This study can guide crystal engineers towards designing and producing better GaZnO nanostructures for practical applications.

Find out more from the article:

Experimental and computational insights in the growth of gallium-doped zinc oxide nanostructures with superior field emission properties
Hsien-Ming Chiu, Hsin-Jung Tsai, Wen-Kuang Hsu and Jenn-Ming Wu
CrystEngComm, 2013, Advance Article
DOI: 10.1039/C3CE40101D, Paper

Following on from a previous blog on CuInS₂ nanocrystals, this post is about a very similar material: AgInS₂ nanocrystals! Similar to CuInS₂, AgInS₂ also shows desirable properties such as a suitable band gap energy, high absorption coefficient and low toxicity, making them good candidates for optoelectronic devices. As the size and morphology of these crystals determine how they perform, it will be useful to produce nanocrystals with uniform shapes and sizes.

In this paper, a method of synthesising AgInS₂ nanocrystals with a uniform size is presented. The authors also demonstrated a way to vary the size of the crystals by changing the composition of the solvents in which the crystals form. An investigation of the photoelectric properties of the AgInS₂ nanocrystals was carried out, in which the crystal were hybridised with poly (3-hexylthiophene) to form nanodevices. These devices operate as switches, and with their high sensitivity to light, fast response times, and stability to reversal, can be utilised in many photoelectric applications.

Read their article and find out more:

Controlled synthesis of AgInS₂ nanocrystals and their application in organic–inorganic hybrid photodetectors
Manjiao Deng, Shuling Shen, Xuewen Wang, Yejun Zhang, Huarui Xu, Ting Zhang and Qiangbin Wang
CrystEngComm, 2013, Advance Article
DOI: 10.1039/C3CE40173A, Communication

CuInS₂ belongs to a class of inorganic semiconductors known as metal chalcogenides, which have desirable optical properties that make them useful in photovoltaics. In solar cell applications, CuInS₂ is usually deposited as nanocrystals, and the size, shape and structure of these crystals determine the properties of the device. Therefore, it will be desirable to have a synthetic method that can produce crystals with a uniform morphology, and to be able to vary this by changing the synthetic conditions.

Jin Chang and Eric R. Waclawik have achieved this by a wet-chemical method in which CuInS₂ forms nanocrystals with a zincblende structure when a weak-coordinating solvent is used, whereas strong-coordinating solvents produce a wurzite structure. The authors were also able to explain the effect by investigating the intermediate species formed during the chemical reaction. This synthetic method was also extended to two other useful materials: Cu₂SnS₃ and Cu₂ZnSnS₄, and they were able to produce pure zincblende or wurzite structures depending on the solvent used.

The synthetic process presented in this paper has the potential to be used in fine tuning the optoelectronic properties of photovoltaic materials, thus yielding better devices for solar energy generation.

Read their article to find out more. 

Controlled synthesis of CuInS₂, Cu₂SnS₃ and Cu₂ZnSnS₄ nano-structures: insight into the universal phase-selectivity mechanism
Jin Chang and Eric R. Waclawik
CrystEngComm, 2013, Advance Article
DOI: 10.1039/C3CE40284C

Metal organic frameworks (MOFs) are porous materials with a high surface area. This makes them useful  for processes such as catalysis and gas storage, including hydrogen storage, which is crucial for environmentally friendly energy applications.

Nevertheless, many MOF structures can only hold onto H₂ molecules at very low temperatures and concentrations. To enable the MOF to hold onto H₂ molecules at higher temperatures and concentrations, Lalonde and colleagues have synthesized MOFs with a zwitterionic structure, where the negatively charged Zn₂(CO₂)₅ groups are separated from the positive imidazole tetra acid groups. The material shows enhanced H₂ adsorption, and is a good candidate for further optimisation. The zwitterionic design can also be applied to synthesizing other MOF structures or porous materials  for use in H₂ storage.

Read their article to find out more:

A zwitterionic metal–organic framework with free carboxylic acid sites that exhibits enhanced hydrogen adsorption energies
Marianne B. Lalonde, Rachel B. Getman, Jeong Yong Lee, John M. Roberts, Amy A. Sarjeant, Karl A. Scheidt, Peter A. Georgiev, Jan P. Embs, Juergen Eckert, Omar K. Farha, Randall Q. Snurr and Joseph T. Hupp
CrystEngComm, 2013, Advance Article
DOI: 10.1039/C3CE40198G

Lotus leaves are superhydrophobic due to their microstructure, and Shuxi Dai and colleagues have pioneered a method of replicating this in a ZnO film by a ‘bottom up’ method. Using real lotus leaves as templates, they replicated the microstructure on ZnO films. The material consists of an array of micropillars, on which further nanostructures form after a second hydrothermal treatment. Depending on the solution used in the second stage, properties of the final structure, such as hydrophobicity, can be tuned.

Many natural materials have microstructures that give them desirable chemical or mechanical properties, and the method presented in this paper enables scientists to mimic them easily on other materials such as functional metal oxides.

Find out more from their article.

Biomimetic fabrication and tunable wetting properties of three-dimensional hierarchical ZnO structures by combining soft lithography templated with lotus leaf and hydrothermal treatments
Shuxi Dai, Dianbo Zhang, Qing Shi, Xiao Han, Shujie Wang and Zuliang Du
CrystEngComm, 2013, Advance Article
DOI: 10.1039/C3CE40238J

Self-assembled Fe₃O₄ superstructures have unique electric and magnetic properties, such as allowing the material to exceed the ‘‘superparamagnetic limit’’ found in Fe₃O₄ with a less well defined structure. Using a novel way of synthesising Fe₃O₄ nanoflakes via an ionic liquid-assisted solvothermal process, Xiaodi Liu and colleagues have made self-assembled Fe₃O₄  structures from nanoparticles. These nanoflakes have a good monodispersity and magnetic properties that are not seen in material made by other synthetic methods, making them good candidates for applications such as high density magnetic recording.

In this study, the authors have also explored how different growth conditions affect the final structure, thus providing a method for optimising the process for making other self-assembled nanomaterials using ionic liquids.

Find out more by downloading their paper:

Ionic liquid-assisted solvothermal synthesis of oriented self-assembled Fe₃O₄ nanoparticles into monodisperse nanoflakes
Xiaodi Liu, Xiaochuan Duan, Qing Qin, Qinglun Wang and Wenjun Zheng

CrystEngComm, 2013, Advance Article
DOI: 10.1039/C3CE00035D, Communication