湿化学法调控ZnO纳米/微晶的面向生长
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本研究论文探讨了通过湿化学方法精细调控ZnO纳米/微晶的表面定向生长。研究人员成功地通过一种简单的湿化学方法制备出四种不同形态的ZnO纳米/微晶，包括哑铃形微棒、纳米片、纳米板以及微棒。他们发现生长时间对于这些ZnO晶体的形状具有关键影响：不同的生长时间会导致不同的微观结构形成。
研究者系统地研究了生长条件对晶体形态的影响，主要集中在前体浓度和温度这两个因素上。他们通过调整这两个参数，观察到如何精确控制ZnO的生长方向和尺寸。这种技术对于实现定向生长以及优化材料性能具有重要意义，特别是在光电子学应用中，如太阳能电池、光催化和光电探测器中对晶体的定向选择至关重要。
实验过程中，采用X射线衍射(XRD)技术来分析样品的结构特性，确保了晶体的纯度和结晶质量。扫描电子显微镜(SEM)则提供了对晶体微观形貌的高分辨率图像，揭示了纳米/微晶的表面特征和细节。此外，作者还利用光致发光光谱(PL)研究了样品的光学性质，包括可能存在的缺陷态、带隙能量以及荧光发射强度，这些都是衡量ZnO材料性能的重要指标。
这项工作不仅为ZnO纳米/微晶的可控生长提供了一种实用且经济的方法，而且为未来的纳米材料合成研究开辟了新的可能性，特别是对于那些依赖于晶体定向和形貌调控的特定应用领域。通过优化生长条件和理解其与晶体结构和性能的关系，研究人员有望开发出具有更高效能和定制化特性的ZnO纳米材料。
COL 11(10), 101801(2013) CHINESE OPTICS LETTERS October 10, 2013
Tuning the face orientation of ZnO nano/microcrystals
by a wet chemical method
Aparna Thankappan
1,2∗
, Sheenu Thomas
1
, and V. P. N. Nampoori
1
1
International School of Photonics (ISP), Cochin University of Science and Technology, Kochi, India
2
Inter University Centre for Nanomaterials and Devices (IUCND), Cochin University of
Science and Technology, Kochi, India
∗
Corresponding author: aparna.subhash@gmail.com
Received April 5, 2013; accepted August 2, 2013; posted online September 25, 2013
We successfully synthesize four kinds of ZnO nano/microcrystals including dumbbell microrods, nanoflakes,
nanoplates, and microrods by a simple wet chemical method. Growth duration is found to play a cru cial
role in the morphologies of these ZnO nano/microcrystallites. In addition, growth conditions are system-
atically studied as a function of precursor concentration and temperature. The structural and optical
characteristics of the ZnO samples are further investigated by X-ray diffraction, scanning electron mi-
croscopy, and photoluminescence spectroscopy.
OCIS codes: 180.5810, 300.6470.
doi: 10.3788/COL 201311.101801.
Control over the morphology and structure of nanomate-
rials is essential for the development of future devices
[1]
.
Over the pas t few years, considerable effort has been
exerted in controlling the morphology of nanocrystals
to fine tune their properties for potential applications
because the size, orientation, morphology, aspect ratio
(width-to-length ratio), and even crystal density can sig-
nificantly influence various properties. Therefore, the
morphology -controlled synthesis of nanostructures must
be developed
[2]
to address the demand for exploring the
potentials of ZnO.
Among promising opto e le c tronic semiconductors, ZnO
is a key functional material exhibiting ultraviolet (UV)
photoluminescence emission, transparent conductivity
along with semiconductivity, magnetic properties, and
piezoelectric prop e rties. ZnO also has a wide band gap
with an energy of 3.37 eV, notable biocompatibility,
as well as excellent chemical, mechanical, and thermal
stabilities
[3]
. Thus, ZnO is attracting attention from fun-
damental and practical researchers. ZnO is a polar crys-
tal with hexagonal phase and high anisotropy that leads
to oriented growth along the c-axis
[4]
. Crystal growth
morphology results from the interplay betwe e n crystal-
lographic anisotropy and growth kinetics
[5]
. Anisotropy
is a basic property of crystals. Anisotropic tendency
during crystal growth in association with the relation-
ship between crystal planes of solid materials and their
physicochemical properties has bee n studied by several
researchers
[6]
. Given the poor morpho logy-controlled
syntheses of nanoscale metal oxides, sy stematic studies
on the connection between crystal planes and properties
are limited. Morphology-controlled syntheses can clearly
demonstrate the strong excitation wavelength depen-
dence of the fluoresc e nce emission of ZnO crystals. The
excitation wavelength-dependent features of fluo rescence
emission allows for tunable laser sources.
In this letter, we report on the controlled synthesis of
the ZnO nano/microcrystals with different morphologies
using a simple wet chemical metho d. Dumbbell (DB)
microrods, nanoflakes, nanoplates, and microrods with
good crystalline properties were synthesized at different
growth durations (6–22 h) with excellent reproducibility.
The influences of precursor concentration, reaction time,
and temperatur e on the size and morphology of ZnO
were investigated. Scanning electron microscopy (SEM)
reveals that the mor phology of ZnO can b e effectively
controlled as DB microrods, nanoflakes, nanoplates, and
microrods. X-ray diffraction (XRD) measurements show
that all samples have a hexagonal phase structure. The
room temperature photoluminescence of the as-prepared
ZnO is found to significantly depend on crysta l size, ori-
entation, morphology, aspect ratio, and crystal density.
All chemicals were purchased from Merck Ltd. And
used as received without further purification. A nutri-
ent solution was prepared from an a queous solution of
zinc nitrate hexahydrate (Zn(NO
3
)
2
6H
2
O) and hexam-
ethylenetetramine (HMTA) ((CH
2
)
6
N
4
). A hexamine
solution was added dropwise to the zinc nitrate solution
while stirring.
The following r e actions are involved in the crystal
growth of ZnO
[7]
(CH
2
)6N
4
+6H
2
O→6CHOH+4NH
3
, (1)
NH
3
+H
2
O↔NH
+
4
+OH
−
, (2)
Zn(NO
3
)
2
+H
2
O →Zn
2+
+2HNO
3
, (3)
2OH
−
+Zn
2+
→ZnO(s) +H
2
O. (4)
The reaction decomposes HMTA to formaldehyde
(HCHO) and ammonia (NH
3
), which acts as a pH buffer
by slowly decomposing to provide a gradual and con-
trolled supply of NH
3
. Then, NH
3
forms ammonium
hydroxide and suppo rt OH
−[8]
. Finally, OH
−
anions
react with Zn
2+
cations to form ZnO. Precursor concen-
tration, time, and temperature dependence experiments
were carried out to investigate the growth processes of
ZnO.
The size and morphology of ZnO samples were charac-
terized by SEM (JSM6390, JEOL/EO, USA). XRD data
1671-7694/2013/101801(4) 101801-1
c
2013 Chinese Optics Letters
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