• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2005.11a
• /
• pp.95-96
• /
• 2005

The general method and mechanism for the polarity control of heteroepitaxial wurtzite films, such as ZnO and GaN, by interface engineering via plasma-assisted molecular beam epitaxy are addressed. We proposed the principle and method controlling the crystal polarity of ZnO on GaN and GaN on ZnO. The crystal polarity of the lower film was maintained by forming a heterointerfce without any interface layer between the upper and the lower layers. However the crystal polarity could be changed by forming the heterointerface with the interface layer having an inversion center. The principle and method suggested here give us a promising tool to fabricate polarity inverted heterostructures, which applicable to invent novel heterostructures and devices.

• Korean Journal of Crystallography
• /
• v.14 no.2
• /
• pp.93-104
• /
• 2003

The crystals of group-Ⅲ nitride semiconductors with wurtzite structure exhibit a strong polarity. Especially, GaN has characteristics of different growth rate, anisotropic electrical and optical properties due to the polarity. In this work, GaN epilayer was grown and the polarities of the crystals were observed by the chemical wet etching and SP-EFM. GaN thin films were deposited on c-plane A1₂O₃ substrate under the variations of growth conditions by HVPE such as the deposition temperature of the buffer layer, the deposition time, the ratio of Group-V and Ⅲ and the deposition temperature of the film. The adquate results were obtained under the conditions of 500℃, 90 seconds, 1333 and 1080℃, respectively. It is observed that the GaN layer grown without the buffer layer has N-polarity and the GaN layer grown on the buffer layer has Ga-polarity. Fine crystal single particles were grown on c-plane A1₂O₃ and SiO₂, layer. The external shape of the crystal shows ｛10-11｝｛10-10｝(000-1) planes as expected in the PBC theory and anisotropic behavior along c-axis is obvious. As a result of etching on each plane, (000-1) and ｛10-11｝planes were etched strongly due to the N-polarity and ｛10-10｝ plane was not affected due to the non-polarity. In the case of the crystal grown on c-plane A1₂O₃, two types of crystals were grown. They were hexagonal pyramidal-shape with ｛10-11｝plane and hexagonal prism with basal plane. The latter might be grown by twin plane reentrant edge (TPRE) growth.

• The Korean Journal of Ceramics
• /
• v.6 no.1
• /
• pp.53-57
• /
• 2000

It was observed that the growth rates are different each other in the opposite direction along c-axis due to the crystal polarity. In according to the calculation based on diffusional equations with consideration of the electrical polarization and the surface charge, the difference of growth rates could be explained. Some experiments were compared with this kinetic explanation.

• Proceedings of the KIEE Conference
• /
• 1999.07d
• /
• pp.1812-1814
• /
• 1999

The effects of polarity of the polymer on transcription-aligned twisted nematic (TN)-liquid crystal display (LCD) on various the polyimide (PI) surfaces were investigated. The monodomain alignment of nematic (N)LC is obtained in cells fabricated by transcription alignment method on PI surface with medium polarity. The LC alignment using transcription alignment method is attributed to polarity of the polymer. The threshold voltage of transcription-aligned TN-LCD decreases with increasing the polarity of the polymer on three kinds of the PI surfaces. The threshold voltage of transcription-aligned TN-LCD on PI surface with high polarity is almost the same compared to rubbing-aligned TN-LCD. The response time of transcription-aligned TN-LCD decreases with the increasing the polarity of the polymer on all PI surfaces. The decay time of transcription-aligned TN-LCD is slow compared with the rubbing-aligned TN-LCD.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1997.04a
• /
• pp.27-30
• /
• 1997

We investigated the electro-optical characteristics of amorphous (a) - twisted nematic (TN) - liquid crystal display (LCD) on polyimide (Pl) films with different polarity. It was found that the threshold voltage of a-TN-LCD is decreased with increasing the polarity of the Pl film. We considered that the threshold voltage in a-TN-LCD is affected to the surface anchoring strength with polarity of the Pl films. Also, we observed the response time of a-TN-LCD on medium polarity of the Pl film is fast compared to high polarity of the Pl film. Finally, we obtained that the viewing angle of a-TN-LCD are almost same on different polarity of the PI films.

• Proceedings of the KIEE Conference
• /
• 1997.07d
• /
• pp.1579-1581
• /
• 1997

We investigated the effect of polarity of polyimide(PI) film in amorphous (a) - twisted nematic (TN) - liquid crystal display(LCD) for response time and viewing angle. We found that the domain size of a-TN-LCD on PI film with high polarity is smaller then medium polarity. It is considered that the electro-optical characteristics are strongly dependent on this domain in a-TN-LCD. We observed the response time of a-TN-LCD on PI film with high polarity is slow as comparing to PI film with medium polarity. We suggest that the response time of a-TN-LCD is attributed surface effect between the LCs and the substrates.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.18 no.3
• /
• pp.97-100
• /
• 2008

Polar and non-polar GaN was grown by the HVPE on various substrates and influence of polarity has been investigated. The $10\;{\mu}m$ thickness GaN were grown by HVPE is along A-plane ($11{\bar{2}}0$), C-plane (0001) and M-Plane ($10{\bar{1}}0$) sapphire substrate respectively. Surface properties were observed by optical microscope and atomic force microscopy. High resolution X-ray diffraction (HR-XRD) confirms the wurtzite structure. The donor band exciton peak located at ${\sim}3.4\;eV$ and also located yellow luminescence peak at 2.2 eV. The polarity of the GaN film has a strong influence on the morphology and the optical properties.

• KIEE International Transactions on Electrophysics and Applications
• /
• v.11C no.4
• /
• pp.142-145
• /
• 2001

The residual DC phenomena in the in-plane switching(IPS)-liquid crystal display(LCD) by the voltage-transmittance (V-T) and capacitance-voltage (C-V) hysteresis method on rubbed polyimide (PI) surfaces were studied. We found that the residual DC voltage in the IPS-LCD was decreasing with the increasing concentration of cyano LCs. The residual DC voltage of the IPS-LCD can be improved by the high polarity of cyano LCs.

• Applied Chemistry for Engineering
• /
• v.18 no.1
• /
• pp.71-76
• /
• 2007

We have demonstrated the resonant resistance pattern changes of the polymer film in the quartz crystal analysis by the function of the molecular polarity phase transition phenomena. PVA and PMMA/PVAc blend films were used as hydrophilic and/or hydrophbic film, respectively. In the comparison between the hydrophilic shows the pattern changes near by the phase transition temperature. For more detailed explanation, the static capacity in the oscillation parameter was measured and the morphology of Au quartz crystal electrode was studied by AFM. It is suggested that the different resonant resistance pattern change is reliable in the condition of different polarity, and the conclusion is important to analysis of the real mechanism a normal quartz crystal experiments.

• Proceeding of EDISON Challenge
• /
• 2016.03a
• /
• pp.373-376
• /
• 2016

Transition metal dichalcogenides (TMDs) such as $MoS_2$ is the thinnest semiconductor, exhibits promising prospects in the applications of optoelectronics, catalysis and hydrogen storage devices. Uniform and high quality $MoS_2$ is highly desirable in large area for its applications on commercial scale and fundamental research. Many experimental techniques i.e CVD have been developed to successfully synthesis $MoS_2$ on large scale, here in this work atomistic detail to understand the growth mechanism is addressed which was greatly overlooked. Here based on first principles calculation we found that polarity of seeding promter (crystal violet considerd in this work) controls the growth mechanism. It is also found that molybdenum destroys the precursor while sulfur adsorption with precursor is favorable.