Name: synthesis of hierarchical zno/cdsse heterostructure nanotrees
Uploaded: 2016-11-29T12:30:00
Description: Watch this Scientific Journal Video about Synthesis of Hierarchical ZnO/CdSSe Heterostructure Nanotrees at JoVE.com

The authors thank Svilen Bobev for his help with the XRD spectra and K. Booksh for assistance with the sputter coater equipment.

1. Synthesis of Tree-like ZnO/CdSSe Nanostructures
<ol>
	<li>Pretreatment and gold coating of sapphire substrates 
	NOTE: The gold film acts as a catalyst in the growth of the ZnO nanowires.
	<ol>
		<li>Clean sapphire slides (a-plane, 10 &#215; 10 &#215; 1 mm) in 99.5% ethanol with 5 min of sonication to prepare the substrate for Au sputtering.</li>
		<li>Deposit a 10-nm (&#177; 2 nm)-thick film of gold onto the sapphire slides with a sputter coater and gold target.</li>
	</ol>
	</li>
	<li>Synthes...

<ol>
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S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photosensitization+of+ZnO+Nanowires+with+CdSe+Quantum+Dots+for+Photovoltaic+Devices.">Photosensitization of ZnO Nanowires with CdSe Quantum Dots for Photovoltaic Devices.</a> Nano Lett. 7 (6), 1793-1798 (2007).</li><li>Gonzalez-Valls, I., Lira-Cantu, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vertically-aligned+nanostructures+of+ZnO+for+excitonic+solar+cells:+a+review.">Vertically-aligned nanostructures of ZnO for excitonic solar cells: a review.</a> Energy Environ Sci. 2 (1), 19-34 (2009).</li><li>Zhu, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+vertically+aligned+ultra-long+ZnO+nanowires+on+heterogeneous+substrates+with+catalyst+at+the+root.">Synthesis of vertically aligned ultra-long ZnO nanowires on heterogeneous substrates with catalyst at the root.</a> Nanotechnology. 23 (5), 055604 (2012).</li><li>Yang, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlled+Growth+of+ZnO+Nanowires+and+Their+Optical+Properties.">Controlled Growth of ZnO Nanowires and Their Optical Properties.</a> Adv. Func. Mater. 12 (5), 323-331 (2002).</li><li>Myung, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Composition-Tuned+ZnO&#8722;CdSSe+Core&#8722;Shell+Nanowire+Arrays.">Composition-Tuned ZnO&#8722;CdSSe Core&#8722;Shell Nanowire Arrays.</a> ACS Nano. 4 (7), 3789-3800 (2010).</li><li>Pan, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Color-Tunable+Photoluminescence+of+Alloyed+CdSxSe1-x+Nanobelts.">Color-Tunable Photoluminescence of Alloyed CdSxSe1-x Nanobelts.</a> J. Am. Chem. Soc. 127 (45), 15692-15693 (2005).</li><li>Rakshit, T., Mondal, S. P., Manna, I., Ray, S. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CdS-decorated+ZnO+nanorod+heterostructures+for+improved+hybrid+photovoltaic+devices.">CdS-decorated ZnO nanorod heterostructures for improved hybrid photovoltaic devices.</a> ACS Appl. Mater. Inter. 4 (11), 6085-6095 (2012).</li><li>Nan, W. N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crystal+Structure+Control+of+Zinc-Blende+CdSe/CdS+Core/Shell+Nanocrystals:+Synthesis+and+Structure-Dependent+Optical+Properties.">Crystal Structure Control of Zinc-Blende CdSe/CdS Core/Shell Nanocrystals: Synthesis and Structure-Dependent Optical Properties.</a> J. Am. Chem. Soc. 134 (48), 19685-19693 (2012).</li><li>Li, Z., Nieto-Pescador, J., Carson, A. J., Blake, J. C., Gundlach, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+Z-scheme+charge+separation+in+novel+vertically+aligned+ZnO/CdSSe+nanotrees.">Efficient Z-scheme charge separation in novel vertically aligned ZnO/CdSSe nanotrees.</a> Nanotechnology. 27 (13), 135401 (2016).</li></ol>

The vertical alignment of ZnO nanowires (stems) is based on epitaxial growth on the substrate. ZnO nanowires grow preferentially along the &#60;0001&#62; direction that matches with the periodicity of the a-plane of sapphire12. Therefore, the type and the quality of the substrate are very important. Different thicknesses of the gold coating on the substrate, from 5 nm to 20 nm, have been tested and showed no significant difference in the growth of ZnO nanowires. The length of the ZnO nanowires can be adjusted ...

ZnO is a II-VI semiconductor featuring a band gap (BG) of 3.3 eV, a high electron mobility, and a large exciton binding energy1,2. It is an abundant semiconducting material with a plethora of present and future applications in optical devices, solar cells, and photocatalysis. However, ZnO is transparent, which limits its application in the visible spectral range. Therefore, materials absorbing visible light, such as narrow-gap semiconductors3, dye molecules4, and photosensitive polymers5, have frequently been employed for sensitizing ZnO to visible light absorption.
CdS (BG 2.43 eV) and CdSe (BG 1.76 eV) are common II-VI narrow-gap semiconductors and have been intensively investigated. The BG and lattice parameters of the ternary alloy CdSSe can be adjusted by varying the mole ratios of the VI components6,7. ZnO/CdSSe nanocomposites have been reported to result in efficient photovoltaic energy conversion8,9.
Combining the efficient electron transport pathway of vertically aligned ZnO nanowires towards a substrate with the improved visible light absorption of the CdSSe branches led to efficient electron transfer between the stem and branches9,10. Thus, we synthesized a new tree-like ZnO/CdSSe nanostructure, where vertically aligned ZnO nanowires are decorated with CdSSe branches. This composite material can act as a building block for novel solar energy conversion devices.
This protocol describes how ZnO nanowire arrays are grown on a sapphire substrate by one-step chemical vapor deposition (CVD) from ZnO and C powders, following a procedure that has previously been published11. Following the growth of ZnO nanowires, a second step of CVD is employed to grow CdSSe branches on the ZnO nanowires. We employ X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) to measure the crystal structures, morphology, and composition of the ZnO/CdSSe nanotrees (NTs). The optical properties and charge carrier transfer mechanism between the branches and stem have been investigated by photoluminescence (PL) spectroscopy and time-resolved PL lifetime measurements.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>ZnO</td>
			<td>Sigma Aldrich</td>
			<td>1314-13-2</td>
			<td></td>
		</tr>
		<tr>
			<td>Activated Carbon</td>
			<td>Alfa</td>
			<td>231-153-3</td>
			<td></td>
		</tr>
		<tr>
			<td>CdSe</td>
			<td>Sigma Aldrich</td>
			<td>1306-24-7</td>
			<td></td>
		</tr>
		<tr>
			<td>CdS</td>
			<td>Sigma Aldrich</td>
			<td>1306-23-6</td>
			<td></td>
		</tr>
		<tr>
			<td>Sapphire</td>
			<td>MTI</td>
			<td>2SP</td>
			<td>a-plane, 10 &#215; 10 &#215; 1 mm</td>
		</tr>
		<tr>
			<td>Furnace</td>
			<td>Lindberg Blue M</td>
			<td>SSP</td>
			<td></td>
		</tr>
		<tr>
			<td>Scanning electron microscope</td>
			<td>Hitachi</td>
			<td>S5700</td>
			<td>assembled with an Oxford Inca X-act detector</td>
		</tr>
		<tr>
			<td>X-ray powder diffractometer&#160;</td>
			<td>Rigaku&#160;</td>
			<td>MiniFlex</td>
			<td>filtered Cu K&#945; radiation (&#955;=1.5418 &#197;)</td>
		</tr>
		<tr>
			<td>Amplified Ti:sapphire oscillator&#160;</td>
			<td>Coherent Mantis</td>
			<td>Coherent Legend-Elite</td>
			<td></td>
		</tr>
		<tr>
			<td>Single photon detection module&#160;</td>
			<td>ID Quantique</td>
			<td>ID-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Sputter coater</td>
			<td>Cressington</td>
			<td>308</td>
			<td>assembled with gold target</td>
		</tr>
		<tr>
			<td>Fiber probe spectrometer</td>
			<td>Photon Control</td>
			<td>SPM-002</td>
			<td></td>
		</tr>
		<tr>
			<td>Colored Glass Filter</td>
			<td>Thorlabs</td>
			<td>FGB37-A - &#216;25 mm BG40</td>
			<td>AR Coated: 350 - 700 nm&#160;</td>
		</tr>
		<tr>
			<td>Compressed argon gas</td>
			<td>Keen</td>
			<td>7440-37-1</td>
			<td></td>
		</tr>
	</tbody>
</table>

synthesis of hierarchical zno/cdsse heterostructure nanotrees

A two-step chemical vapor deposition procedure is here employed to prepare tree-like hierarchical ZnO/CdSSe hetero-nanostructures. The structures are composed of CdSSe branches grown on ZnO nanowires that are vertically aligned on a transparent sapphire substrate. The morphology was measured via scanning electron microscopy. The crystal structure was determined by X-ray powder diffraction analysis. Both the ZnO stem and CdSSe branches have a predominantly wurtzite crystal structure. The mole ratio of S and Se in the CdSSe branches was measured by energy dispersive X-ray spectroscopy. The CdSSe branches result in strong visible light absorption. Photoluminescence (PL) spectroscopy showed that the stem and branches form a type-II heterojunction. PL lifetime measurements showed a decrease in the lifetime of emission from the trees when compared to emission from individual ZnO stems or CdSSe branches and indicate fast charge transfer between CdSSe and ZnO. The vertically aligned ZnO stems provide a direct electron transport pathway to the substrate and allow for efficient charge separation after photoexcitation by visible light. The combination of the abovementioned properties makes ZnO/CdSSe nanotrees promising candidates for applications in solar cells, photocatalysis, and opto-electronic devices.

Figure 1 shows the growth mechanism of ZnO/CdSSe NTs. The procedure involved a catalytic vapor-liquid-solid (VLS) process followed by a non-catalytic vapor-solid (VS) growth. In the first VLS step, ZnO and C react in the Ar atmosphere, resulting in metallic Zn and carbon oxide. Zn is subsequently dissolved in the gold precursor on the sapphire substrate. ZnO nanowires grow from the dissolved Zn and residual oxygen. In the second step, exposure to air results in the growth...

Watch this Scientific Journal Video about Synthesis of Hierarchical ZnO/CdSSe Heterostructure Nanotrees at JoVE.com

Synthesis of Hierarchical ZnO/CdSSe Heterostructure Nanotrees

Here, we prepare and characterize novel tree-like hierarchical ZnO/CdSSe nanostructures, where CdSSe branches are grown on vertically aligned ZnO nanowires. The resulting nanotrees are a potential material for solar energy conversion and other opto-electronic devices.

A two-step chemical vapor deposition procedure is here employed to prepare tree-like hierarchical ZnO/CdSSe hetero-nanostructures. The structures are ...

The overall goal of this experiment is to synthesize a tree-like nanostructure with zinc oxide stems and cadmium sulphoselenide branches. And characterize its morphology, crystal structure, and optical properties. This method can help answer key questions in the application of nanocomposite materials in optical and electro-optical applications.The main advantage of this technique is that chemical vapor deposition is a simple and cost-effective way to produce tree-like nanostructures with well-defined interfaces. The cadmium sulphoselenide branches absorb visible light and form of type-II heterojunction with a zinc-oxide stem. The heterojunction facilitates efficient electric transfer from the branches to the stem.The optical properties indicate that the nano trees are promising materials for applications that benefit from a z-scheme charge transfer mechanism, like solar cells and other optoelectronic devices. Though this matter can provide insight into zinc-oxide cadmium sulphoselenide nanotrees, it can also be applied to other systems, such as nanowires, nanotubes, nanobots and so on. Generally, individuals new to this method will struggle because each parameter, such as emulsification, temperature and fluoride will affect the morphology of the nanotrees.First, clean a sapphire slide by sonication in 99.5%ethanol for five minutes. Then using a sputter coater, deposit a 10-nanometer thick gold film onto the slide. Next, stir one gram of a one-to-one mixture by mass of zinc oxide nanopowder and activated carbon into 10 milliliters of 99.5%ethanol.Sonicate the mixture in a water bath at 20 degrees Celsius for 30 minutes. This step insures that no air is present in the mixture. And zinc oxide and carbon are in close contact.Dry the sonicated mixture at 80 degrees Celsius for five hours. Then place the dry mixture in an alumina combustion boat and compact it with a spatula to exclude air from the mixture. Place a gold-coated slide on top of the combustion boat, gold-side down.Place the boat in the center of the quartz tube of a horizontal tube furnace. Then set the heating and cooling parameters on the furnace. Purge the tube with argon gas at a flow rate of 40 standard cubic centimeters per minute at room temperature for one hour.Then increase the temperature from room temperature to 900 degrees Celsius at 80 degrees Celsius per minute and remain at that temperature for two hours. Then, open the tube to air at both ends to provide oxygen for the reaction. Continue heating the sample at 900 degrees Celsius with the tube open to air for three hours.Cool the furnace down to room temperature at 10 degrees Celsius per minute and remove the boat and slide. The white film on the slide consists of the zinc oxide nanowires. Next, thoroughly mix 0.25 grams each of cadmium sulfide and cadmium selenide powder and place the mixture in another alumina combustion boat.Compact the mixture well. Place the zinc oxide nanowire-coated slide about 10 centimeters downstream from the boat. Place the boat in the center of the quartz furnace tube.On the slide, ensure that the zinc oxide nanowires face up. Again, set the parameters on the furnace. Purge the quartz tube of the furnace with argon gas at 40 standard cubic centimeters per minute at room temperature for one hour.Then heat the furnace to 820 degrees Celsius at 80 degrees Celsius per minute and hold the temperature at 820 degrees for 30 minutes. A different temperature will give rise to a different composition and morphology. Then cool the furnace down to room temperature at 10 degrees Celsius per minute and remove the boat and slide from the furnace.The zinc oxide cadmium sulphoselenide nanotrees are obtained as an orange-yellow film on the slide. Prepare control samples of zinc oxide and cadmium sulphoselenide nanowires on clean, gold-coated sapphire slides using the same procedures. Characterize the nanostructures with scanning electron microscopy, X-ray powder diffraction, and energy-dispersive X-ray spectroscopy.Obtain photoluminescence emission spectra and measure the time result photoluminescence and fluorescence decay lifetimes. cadmium sulphoselenide nanowires were grown by chemical vapor deposition on zinc oxide nanowires to form tree-like nanostructures. The stems were capped with cadmium sulphoselenide.The nanotrees showed X-ray diffraction peaks characteristic of both the pure zinc oxide nanowires and the pure cadmium sulphoselenide nanowires. An additional peak observed in the XRD spectrum is assigned to a different phase of cadmium sulphoselenide forming on point defects on the zinc oxide stem initiating branch growth. The mole percentage ratio of sulfur to selenium in the branches was determined from EDS and XRD to be about 54 to 46.The mole ratio affects the band gap of the branches and can be tuned by altering the branch growth temperature. The photoluminescence lifetime of the nanotrees was shorter than the lifetimes of the zinc oxide and cadmium sulphoselenide nanowires. This suggests that fast electronic transfer occurs across the interface of the nanostructure providing an alternate relaxation pathway.Once mastered, this technique can be done in eight hours if it is performed properly. Six hours for zinc oxide preparation and two hours for cadmium sulphoselenide growth. And don't forget that working with cadmium sulfur and cadmium selenide can be extremely hazardous.And precautions such as wearing gloves, lab coat, and closed shoes should always be taken while performing this procedure.

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