Graphene is a one-atom thick two-dimensional sp2 carbon arrangement. Its ultrahigh surface area, excellent electric conductivity, chemical and physical stability made it a promising material in different research fields. Chemical approaches to the large-scale production of graphene have been realized, and the production of RGO (Reduced Graphene Oxide) in quantity has considerably advanced the development of applications for RGO in photocatalysis, capacitive deionization, and solar cells. In the present study, the improvement of synthesis process of RGO was made in terms of temperature, time and safety, as well as introduction of RGO based nanocomposite material. RGO was synthesized by the two step process which is very simple and easy; the conversion of graphite to GO by oxidation and then reduction of the GO to RGO by hydrothermal treatment. The synthesized RGO was combined with nano-size CdS and CuS compounds. The photocatalytic performance of the composite were investigated with the reduction of Cr(VI) by using RGO-CdS nanocomposite. This results may give an insight for the possibility of RGO-CdS in application for the remover of Cr(VI) ion. The hydrothermally synthesized RGO-CuS contains hexagonal structured CuS. The adsorption kinetics of methylene blue on RGO-CuS nanoparticles were compared with bare CuS. It suggests that RGO-CuS nanocomposite can be used for the adsorbent of methylene blue.
High density arrays of nanostructures over large area can be formed by self-assembly of block copolymers on a
variety of substrates such as silica deposited silicon wafer, glass, GaN, PET etc. This block copolymer thin film,
such that the domains are oriented perpendicularly to the substrate, is particularly useful for the formation of
templates for patterns. The degradation and elimination of the minor component transforms the material into an
array of nanopores to form some patterned template that offer potential benefits in a number of applications. The
morphology of the polymer surface is strongly dependent on the thickness of the polymer layer. Moreover it is
necessary to control the size and shape in order to get the desired properties. Spin coating fallowed by baking the
polymer solution onto the substrate self assembles the components of the polymer. PS and PMMA have significantly
different photodegradation properties. Exposure to ultraviolet radiation degrades the PMMA (polymethyl
methacrylate) chain that can be removed by rinsing in acetic acid giving patterned holes. Sonicating the samples in
different solutions in different steps gives fingerprint pattern or sometimes patterns with PS cylindrical domains with
large interstitial spaces. Moreover the interstitial space depends on the composition of the polymer solution. All
these controlled patterns made on GaN, Glass can be applied to make photonic crystal
Self-assembled InGaN quantum dots are fabricated in a two-flow horizontal MOCVD reactor maintained at the
pressure of 200 torr. The precursors were trimethyl-gallium (TMG) and trimethyl-indium (TMI) and ammonia (NH3),
and the carrier gas was N2 and H2. The optimum condition for periodically interrupted growth (PIG) mode was deduced
to fabricate the InGaN quantum dots. NH3 was supplied in PIG mode with the interval of 3 seconds and 5 seconds while
TMG and TMI were supplied continuously. The carrier gas was N2 in QDs growth, while H2 in nucleation and buffer
layer growth. The influence of number of periodic interrupted NH3 on the structural and optical properties of InGaN
quantum dots was investigated by AFM, FE-SEM and low temperature photoluminescence (LT-PL). The AFM images
give the size of InGaN QDs with diameter of 20 ~ 50 nm, height of 3 ~ 10 nm and density of 1010 #/cm2 ~ 1011 #/cm2. A
strong peak at 362.2 nm (3.41eV) and broad emission peak in 435 nm (2.86 eV) were evolved in the photoluminescence
measurement using Nd-YAG laser. The composition of QDs was estimated to be In0.14Ga0.86N from the relation between
peak energy and indium content. Hence. The periodic interruption growth enables the fabrication of self- assembled
InGaN QDs with high density and uniform size.
The thin films of transparent conductive aluminum doped ZnO have been deposited by the sol-gel process. In this study,
important deposition parameters were thoroughly investigated in order to find appropriate procedures to grow large area
thin films of low resistivity and high transparency at low cost for device applications. Experimental results indicated
that the annealing temperature affected the crystal structure of the aluminum doped ZnO films considerably, but the
controlling of effective doping concentration was the key point to achieve low film resistance by sol-gel process. It was
adjusted by controlling the precursor concentration. Although the structure of our aluminum doped ZnO films did not
have the preferred orientation along (002) plane, they had a high transmittance of over 87 % in visible region. In our
experiments, the most suitable Al doped concentration was 1~4 mol%. The annealing temperature for the pre-heat
treatment was 250 °C and post-heat treatment was 400-600 °C. The Al doped and undoped ZnO films are very uniform
and compact. It is confirmed that the doping concentration and thermal treatment are important factor with electrical
conductivity of ZnO films.
A simple method has been developed for the controlled patterned growth of the ZnO nanorod arrays with different size and shape on substrate. In order to control the position of the ZnO nanorods, exposed ZnO seed is defined, as orderly aligned arrays, with the assistance of photolithography. This technique hinges on the patterning of the seed layer comprised by ZnO sol-gel precursor. The simple way to create patterned ZnO seed array is to use negative photoresist for ZnO seed coating. The UV exposures were performed though mask patterned various shape. The ZnO arrays are synthesized using solution chemical method at normal atmospheric pressure without any metal catalyst. A simple two-step process is developed for ZnO nanorod on substrate at 90°C. The ZnO seed precutsor is prepared by sol-gel process. The ZnO nanorod is grown by solution chemical method. The ZnO nanorod growth was dependent on the ZnO seed layer. The ZnO nanorods have length of 400~500nm and diameter of 25~50nm. The ZnO nanorod is single crystals with wurtzite and grows along the c axis of the crystal plane. The room temperature photoluminescence measurements have shown ultraviolet peaks 378.3nm (3.27eV) with high intensity.
One dimensional (1-D) ZnO nanorod structure of hexagonal shape was fabricated on epitaxial GaN layer by hydrothermal
method. The growth of GaN epitaxial layer was carried out in a two-flow horizontal MOCVD reactor
maintained at a pressure of 200 torr. Firstly, a 25 nm thick GaN buffer layer was grown at 520 °C. Then 2~3&mgr;m thick
GaN epilayer was deposited at 1070 °C. Trimethylgallium (TMG) and NH3 were used as Ga and N source, and H2 gas
was used as carrier gas. After the deposition of GaN epilayer thin-film, single crystalline ZnO nanorod was fabricated in
aqueous solution. XRD and FE-SEM results showed ZnO nanorod arrays were oriented highly along the (002) plane.
The ZnO nanorod was analyzed to have good quality crystallization by FE-TEM. The SAED pattern has shown that
ZnO nanorod was grown in the direction along (002)-plane. Photoluminescence (PL) has shown that the GaN-ZnO
hetero-structure has shown ultra-violet lasing action at room temperature. Narrow and strong ultra-violet peak was
observed in comparison with PL result from epitaxial GaN layer. The analysis results have proved that aqueous solution
growth method developed in the present work can be a good application for optical electronic device.
Self-assembled InGaN quantum dots are fabricated in a two-flow horizontal MOCVD reactor maintained at the
pressure of 200torr. The precursors were trimethyl-gallium (TMG) and trimethyl-indium (TMI) and ammonia (NH3),
and the carrier gas was N2 and H2. The optimum condition was deduced to fabricate the InGaN quantum dots. GaN
nucleation layer was grown at 500°C with thickness of 25nm, and then 2~3 μm thick GaN buffer-layer was deposited at
1050 °C. InGaN quantum dots were grown on GaN buffer layer. Carrier gas was changed with N2 instead of H2 in QD
growth. In the growth of InGaN quantum dots, NH3 was supplied in cyclic periodic interrupted mode with the interval
of 5 seconds. The influence of number of periodic interrupted NH3 on the structural and optical properties of InGaN
quantum dots was investigated by AFM, FE-SEM and photoluminescence (PL). The InGaN quantum dots are grown by
2 periods growth and have 0.4nm in height and 31nm lateral size. The height of quantum dots was increased with
increase of growth periods, and the lateral size was decreased after 3 periods and then increased in 4 periods. The
density of InGaN quantum dots with 3 periods and 4 periods was measured to be 1.51×1011/cm2 and 8.91×1010/cm2.
Density of InGaN quantum dots was decreased after 3 periods, and this is attributed to the coalescence.
A strong peak at 362.2 nm (3.41eV) and broad emission peak in 532.9~663.9nm (2.33~1.86eV) were evolved in the
photoluminescence measurement using Nd-YAG laser with wavelength of 266nm. Addition emission peak was found in
the range 433.7nm~462.2nm (2.85eV~2.68eV) in the samples with 3 periods and 4 periods interruption, and this peak
was identified as the InGaN quantum dots with low indium concentration.
GaN nanotubular material is fabricated with aluminum oxide membrane in MOCVD. SEM, XRD, TEM and PL are
employed to characterize the fabricated GaN nanotubular material. An aluminum oxide membrane with ordered nano
holes is used as template. Gallium nitride is deposited at the inner wall of the nano holes in aluminum oxide template,
and the nanotubular material with high aspect ratio is synthesized using the precursors of TMG and ammonia gas.
Optimal synthesis condition in MOCVD is obtained successfully for the gallium nitride nanotubular material in this
research. The diameter of GaN nanotube fabricated is approximately 200 ~ 250 nm and the wall thickness is about 40 ~
50 nm. GaN nanotubular material consists of numerous fine GaN particulates with sizes ranging 15 to 30 nm. The
composition of gallium nitride is confirmed to be stoichiometrically 1:1 for Ga and N by EDS. XRD and TEM analyses
indicate that grains in GaN nanotubular material have nano-crystalline structure. No blue shift is found in the PL
spectrum on the GaN nanotubular material fabricated in aluminum oxide template.