• Journal of the Korean Vacuum Society
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• v.17 no.4
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• pp.353-358
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• 2008

In order to increase extraction efficiency of AlGaInP-based vertical RED LEDs, chemical wet etching technique was produced by using a roughened surface with triangle-like morphology. A commonly used $H_3PO_4$-based solution was applied for chemical wet etching. The light extraction of AlGaInP LED was related to the n-side roughed surface morphology. The morphology of roughed surface is analyzed by the atomic force microscope (AFM). As a result, the roughed surface AlGaInP LED has a root-mean-square (RMS) roughness of 44 nm. The brightness shows 41% increase after roughening n-side surface, as compared to the ordinary flat surface LED.

• Korean Journal of Materials Research
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• v.8 no.10
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• pp.890-897
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• 1998

The direct wafer bonding between n-InP(001) wafer and the ${Si}_3N_4$(200 nm) film grown on the InP wafer by PECVD method was investigated. The surface states of InP wafer and ${Si}_3N_4$/InP which strongly depend upon the direct wafer bonding strength between them when they are brought into contact, were characterized by the contact angle measurement technique and atomic force microscopy. When InP wafer was etched by $50{\%}$ HF, contact angle was $5^{\circ}$ and RMS roughness was $1.54{\AA}$. When ${Si}_3N_4$ was etched by ammonia solution, RMS roughness was $3.11{\AA}$. The considerable amount of initial bonding strength between InP wafer and ${Si}_3N_4$/InP was observed when the two wafer was contacted after the etching process by $50{\%}$ HF and ammonia solution respectively. The bonded specimen was heat treated in $H^2$ or $N^2$, ambient at the temperature of $580^{\circ}C$-$680^{\circ}C$ for lhr. The bonding state was confirmed by SAT(Scannig Acoustic Tomography). The bonding strength was measured by shear force measurement of ${Si}_3N_4$/InP to InP wafer increased up to the same level of PECVD interface. The direct wafer bonding interface and ${Si}_3N_4$/InP PECVD interface were chracterized by TEM and AES.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.1
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• pp.51-56
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• 2018

To evaluate surface characteristics of AlN single crystal grown by physical vapor transport (PVT) method, chemical mechanical polishing (CMP) were performed with diamond slurry and $SiO_2$ slurry after mechanical polishing (MP), then the surface morphology and analysis of polishing characteristics of the slurry types were analyzed. To estimate how pH of slurry effects polishing process, pH of $SiO_2$ slurry was controlled, the results from estimating the effect of zeta potential and MRR (material removal rate) were compared in accordance with each pH via zeta potential analyzer. Eventually, surface roughness RMS (0.2 nm) could be derived with atomic force microscope (AFM).

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.10 no.4
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• pp.204-210
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• 1998

This paper presents the development of the probability density function applicable for wave heights (peak-to-trough excursions) in finite water depth including shallow water depth. The probability distribution applicable to wave heights of a non-Gaussian random process is derived based on the concept of the maximum entropy method. When wave heights are limited by breaking wave heights (or water depth) and only first and second moments of wave heights are given, the probability density function developed is closed form and expressed in terms of wave parameters such as $H_m$(mean wave height), $H_{rms}$(root-mean-square wave height), $H_b$(breaking wave height). When higher than third moment of wave heights are given, it is necessary to solve the system of nonlinear integral equations numerically using Newton-Raphson method to obtain the parameters of probability density function which is maximizing the entropy function. The probability density function thusly derived agrees very well with the histogram of wave heights in finite water depth obtained during storm. The probability density function of wave heights developed using maximum entropy method appears to be useful in estimating extreme values and statistical properties of wave heights for the design of coastal structures.

• Speech Sciences
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• v.7 no.1
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• pp.109-141
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• 2000

Acoustic and aerodynamic characteristics of Cheju consonants were examined with the focus on the well-known three-way distinction among stops (i.e., lenis, fortis, aspirated) and the two-way distinction between sand s*. Acoustic parameters examined for the stops included VOT, relative stop burst energy, Fo at the vowel onset, H1-H2, and H1-F2 at the vowel onset. For the fricatives s and s*, acoustic parameters were fricative duration, Fo, centroid of the fricative noise, RMS energy of the frication, H1-H2 and Hl-F2 at the onset of the following vowel. In investigating aerodynamics, intraoral pressure and oral flow were included for the bilabial stops. Results indicate that, although Cheju and Korean are not mutually intelligible, acoustic and aerodynamic properties of Cheju consonants are very similar in every respect to those of the standard Korean. Among other findings there are three crucial points worth recapitulating. First, stops are systematically differentiated by the voice quality of the following vowel. Second, stops are also differentiated by aerodynamic mechanisms. The aspirated and fortis stops are similar in supralaryngeal articulation, but employ a different relation between intraoral pressure and flow. Finally, our study suggests that the fricative s is better categorized as 'lenis' than as 'aspirated' in terms of its phonetic realization.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.9
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• pp.616-621
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• 1999

A planar inductively coupled $CH_4/H_2/Ar$plasma was used to investigate dry etch characteristics of GaN as a function of input power, RF bias power, and etch gas composition. Etch rate of GaN increased with input power up to 600 W and was saturated at the higher power. Also, the etch rates increased with increasing RF bias power, composition of $CH_4$ and Ar gas. We achieved the maximum etch rate of $930{\AA}$/min at the input power 400 W, RF bias power 250 W, and operational pressure 10 mTorr. This paper shows that smooth etched surface having roughness less than 1 nm in rms can be obtained by using planar inductively coupled plasma with $CH_4/H_2/Ar$ gas chemistry.

• Journal of Biosystems Engineering
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• v.16 no.4
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• pp.346-354
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• 1991

Turning behavior of tractor-trailer system was studied to guide the tractor and trailer. Based upon kinematic relationship between the tractor and the trailer, a mathematical model was developed and analyzed by computer simulation. A field test was carried out to verify the mathematical model. Following conclusions were drawn from this study. 1. A mathematical model and a simulation program for turning behavior of tractor-trailer system were developed. 2. The results of the field tests showed that the RMS errors were less than 0.33m and the mathematical model based upon kinematic relationship can be used for mapping guidance system for tractor and trailer. 3. As the steering angle was increased, the turning radius was decreased. When the tractor travelled at the low speed, the travel speed of the tractor did not affect turning radius but did affect running time and stability for steering. 4. When the tractor travelled under the critical velocity, the towed trailer followed smoothly. When the the tractor travelled faster than the critical velocity, the towed trailer oscillated. The critical velocity was determined from the specification of the tractor and the trailer.

• Journal of Sensor Science and Technology
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• v.22 no.3
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• pp.175-180
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• 2013

This paper describes the characteristics of cubic silicon carbide (3C-SiC) films grown on a carbonized Si(100) substrate, using hexamethyldisilane (HMDS, $Si_2(CH_3)_6$) as a safe organosilane single precursor in a nonflammable $H_2$/Ar ($H_2$ in Ar) mixture carrier gas by atmospheric pressure chemical vapor deposition (APCVD) at $1280^{\circ}C$. The growth process was performed under various conditions to determine the optimized growth and carbonization condition. Under the optimized condition, grown film has a single crystalline 3C-SiC with well crystallinity, small voids, low residual stress, low carrier concentration, and low RMS. Therefore, the 3C-SiC film on the carbonized Si (100) substrate is suitable to power device and MEMS fields.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.468-472
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• 2005

This paper is to investigate the influence of the endface quality on the loss characteristics of a plastic optical fiber connector for in-car network service. Using the parameters of the surface roughness and applied load, insertion loss of connector is measured. Due to scattering and change of refractive index, an optimal condition for low-loss coupling exists. We present the optimal condition as surface roughness $R_{rms}$ = 8 nm and contact load up to 50 N.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2408-2410
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• 1999

The ageing process was checked by leakage current monitoring in Inclined-Plane Method. In order to monitor leakage current, DAS with 12-bit, 8-channel A/D converter was prepared. The monitored components of leakage current were averages of the rms and peak, max peak, cumulative charge, and the number of peaks in the ranges of 1-10, 10-20, 20-30, 30-40, 40-50, >50 mA. And, erosion depth was measured to be used as the index of the ageing. So, the results of leakage current components and erosion depth measurement were compared to find one or more components of which trends of changes were similar to that of erosion.