24 research outputs found
Observing Growth of Nanostructured ZnO in Liquid
Hydrothermal
synthesis is commonly used to produce a large area
of ZnO nanowires because of its simple and inexpensive process. However,
the mechanism of hydrothermal synthesis remains unknown. In this work,
zinc acetate and HMTA dissolved in deionized water as a precursor
solution were sealed in a liquid cell for observation by <i>in
situ</i> transmission electron microscopy. The growth of ZnO
nanowires was classified into two steps. The first step was the nucleation
and growth of ZnO nanoparticles. The ZnO nanoparticles grew as a result
of either isotropic monomer attachment on the {21Ì…1Ì…0}
and {01Ì…10} surfaces or coalescence of nanoparticles in the
same crystal arrangement. The second step was the anisotropic growth
of ZnO nanoparticles into nanowires on the (0001) surface. Because
the (0001) surface is Zn-terminated with positive charges that can
attract the negatively charged monomers, i.e., [ZnÂ(OH)<sub>4</sub>]<sup>2–</sup>,the monomers tended to deposit on the (0001)
surface, resulting in ZnO nanowires growing along the [0001] direction.
Moreover, the growth of ZnO nanowires was identified to be a reaction-controlled
system. The direct observation of the dynamic process sheds light
on the hydrothermal synthesis method
Revealing Controllable Nanowire Transformation through Cationic Exchange for RRAM Application
One dimensional metal oxide nanostructures
have attracted much
attention owing to their fascinating functional properties. Among
them, piezoelectricity and photocatalysts along with their related
materials have stirred significant interests and widespread studies
in recent years. In this work, we successfully transformed piezoelectric
ZnO into photocatalytic TiO<sub>2</sub> and formed TiO<sub>2</sub>/ZnO axial heterostructure nanowires with flat interfaces by solid
to solid cationic exchange reactions in high vacuum (approximately
10<sup>–8</sup> Torr) transmission electron microscope (TEM).
Kinetic behavior of the single crystalline TiO<sub>2</sub> was systematically
analyzed. The nanoscale growth rate of TiO<sub>2</sub> has been measured
using in situ TEM videos. On the basis of the rate, we can control
the dimensions of the axial-nanoheterostructure. In addition, the
unique Pt/ ZnO / TiO<sub>2</sub>/ ZnO /Pt heterostructures with complementary
resistive switching (CRS) characteristics were designed to solve the
important issue of sneak-peak current. The resistive switching behavior
was attributed to the migration of oxygen and TiO<sub>2</sub> layer
served as reservoir, which was confirmed by energy dispersive spectrometry
(EDS) analysis. This study not only supplied a distinct method to
explore the transformation mechanisms but also exhibited the potential
application of ZnO/TiO<sub>2</sub> heterostructure in nanoscale crossbar
array resistive random-access memory (RRAM)
In Situ TEM Investigation of the Electrochemical Behavior in CNTs/MnO<sub>2</sub>‑Based Energy Storage Devices
Transition metal
oxides have attracted much interest owing to their ability to provide
high power density in lithium batteries; therefore, it is important
to understand the electrochemical behavior and mechanism of lithiation–delithiation
processes. In this study, we successfully and directly observed the
structural evolution of CNTs/MnO<sub>2</sub> during the lithiation
process using transmission electron microscopy (TEM). CNTs/MnO<sub>2</sub> were selected due to their high surface area and capacitance
effect, and the lithiation mechanism of the CNT wall expansion was
systematically analyzed. Interestingly, the wall spacings of CNTs/MnO<sub>2</sub> and CNTs were obviously expanded by 10.92% and 2.59%, respectively.
The MnO<sub>2</sub> layer caused structural defects on the CNTs surface
that could allow penetration of Li<sup>+</sup> and Mn<sup>4+</sup> through the tube wall and hence improve the ionic transportation
speed. This study provided direct evidence for understanding the role
of CNTs/MnO<sub>2</sub> in the lithiation process used in lithium
ion batteries and also offers potential benefits for applications
and development of supercapacitors
Phosphorus-Doped p–n Homojunction ZnO Nanowires: Growth Kinetics in Liquid and Their Optoelectronic Properties
For wide-ranging applications in
nanoscale electronic devices,
durable and reproducible p-type nanostructures are essential. In this
work, simple ZnO nanowire (NW) p–n homojunctions were grown
using a two-step hydrothermal synthesis method. P<sub>2</sub>O<sub>5</sub> served as a doping source to obtain p-type ZnO NWs. The morphology
of the ZnO NW arrays was examined using field emission scanning electron
microscopy. The high-resolution transmission electron microscopy (HRTEM)
image indicated that the ZnO NW p–n homojunction is single-crystalline
with a ⟨0001⟩ growth direction. The distribution of
P element was analyzed using energy-dispersive spectroscopy. The dynamic
growth observation was conducted using liquid in situ TEM to investigate
the ZnO nucleation and growth mechanism. We divided the ZnO nanocrystal
precipitation into three processes. Whether two adjacent particles
grow stably or not was found to be related to the distance. Moreover,
the temperature-dependent photoluminescence spectra revealed that
two extra emission peaks located at 416 and 435 nm were emitted from
the ZnO NW p–n homojunction, which resulted from donor–acceptor
recombination. In addition, the electron transport properties confirmed
the rectification behavior of the multi ZnO NW p–n homojunctions.
The turn-on voltage and the current were approximately 2.8 V and 10<sup>–4</sup> to 10<sup>–5</sup> A, respectively, under
forward bias. The results indicate the potential application of ZnO
NW p–n homojunctions as nanoscale light-emitting diodes
Phosphorus-Doped p–n Homojunction ZnO Nanowires: Growth Kinetics in Liquid and Their Optoelectronic Properties
For wide-ranging applications in
nanoscale electronic devices,
durable and reproducible p-type nanostructures are essential. In this
work, simple ZnO nanowire (NW) p–n homojunctions were grown
using a two-step hydrothermal synthesis method. P<sub>2</sub>O<sub>5</sub> served as a doping source to obtain p-type ZnO NWs. The morphology
of the ZnO NW arrays was examined using field emission scanning electron
microscopy. The high-resolution transmission electron microscopy (HRTEM)
image indicated that the ZnO NW p–n homojunction is single-crystalline
with a ⟨0001⟩ growth direction. The distribution of
P element was analyzed using energy-dispersive spectroscopy. The dynamic
growth observation was conducted using liquid in situ TEM to investigate
the ZnO nucleation and growth mechanism. We divided the ZnO nanocrystal
precipitation into three processes. Whether two adjacent particles
grow stably or not was found to be related to the distance. Moreover,
the temperature-dependent photoluminescence spectra revealed that
two extra emission peaks located at 416 and 435 nm were emitted from
the ZnO NW p–n homojunction, which resulted from donor–acceptor
recombination. In addition, the electron transport properties confirmed
the rectification behavior of the multi ZnO NW p–n homojunctions.
The turn-on voltage and the current were approximately 2.8 V and 10<sup>–4</sup> to 10<sup>–5</sup> A, respectively, under
forward bias. The results indicate the potential application of ZnO
NW p–n homojunctions as nanoscale light-emitting diodes
Real Time Observation of the Formation of Hollow Nanostructures through Solid State Reactions
We
demonstrate the formation of hollow nickel germanide nanostructures
of Ni–Ge core–shell nanoparticles by solid state reactions.
The structural evolutions of nickel germanide hollow nanostructures
have been investigated in real-time ultrahigh vacuum transmission
electron microscopy (UHV-TEM). Annealed above 450 °C, the nonequilibrium
interdiffusion of core and shell species occurred at the interface;
thus, Ni germanide hollow nanostructures were formed by solid state
reactions involving the Kirkendall effect. In addition, the different
hollow nanostructures formed from different core diameters of Ni–Ge
core–shell nanoparticles have been studied. Also, we propose
the mechanism with effects of the size and annealing duration on the
solid state reactions based on the Kirkendall effect
Purification of chitosanase from jelly fig latex<sup>1</sup>.
<p>Purification of chitosanase from jelly fig latex<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0150490#t002fn001" target="_blank"><sup>1</sup></a>.</p
Ion-exchange chromatography of chitosanase on a DEAE-Sephacel column.
<p>The column (1.0 × 20 cm) was equilibrated with 0.025 M imidazole-HCl buffer (pH 7.4), after which the chitosanase obtained from the <i>p</i>APMA-Sepharose 4B column was applied. The bound proteins were eluted with a linear gradient of NaCl (0–0.5 M) in equilibrium buffer at a flow rate of 30 mL/h; 3 mL fractions were collected.</p
Effect of the degree of chitosan deacetylation on the activity of the purified chitosanse<sup>1</sup>.
<p>Effect of the degree of chitosan deacetylation on the activity of the purified chitosanse<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0150490#t003fn001" target="_blank"><sup>1</sup></a>.</p
SDS-PAGE of the purified chitosanase.
<p>Electrophoresis was performed in 12.5% acrylamide gel containing glycol chitosan (B) or glycol chitin (C). Chitosanase or chitinase activity was detected by Calcofluor White M2R staining after the lysis of glycol chitosan or glycol chitin in the gel. Lane M contains the protein molecular weight marker; lane 1 contains purified chitosanase.</p