• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.17 no.5
• /
• pp.192-195
• /
• 2007

Structural and electronic properties of bulk GaN with nitrogen vacancy($V_N$), oxygen substitution on nitrogen site($O_N$), and complex of nitrogen vacancy and oxygen substitution on nitrogen site($V_N-O_N$) were investigated using the first principle calculations. It was found that stability of defect formation is dependent on the epilayer growth conditions. The complex of $V_N-O_N$ is energetically the most favorable state in a condition of Ga-rich, however, oxygen substitution in nitrogen site is the most favorable state in N-rich condition. The electronic property of complex with negative charge states at $\Gamma$ point was changed from semiconductor to metal. On the contrary, the properties of nitrogen vacancy except for neutral charge state have shown the semiconductor characteristics at $\Gamma$ point. In the oxygen substitution on nitrogen site, the energy differences between conduction band minimum and Fermi level were smaller than that of defect-free GaN.

• Korean Journal of Metals and Materials
• /
• v.50 no.4
• /
• pp.331-337
• /
• 2012

Electrical properties as a function of composition in silicon nitride ($SiN_x$) films grown at low temperatures ($<200^{\circ}C$) were studied for applications to photonic devices and thin film transistors. Both silicon-rich and nitrogen-rich compositions were successfully produced in final films by controlling the source gas mixing ratio, $R=[(N_2\;or\;NH_3)/SiH_4]$, and the RF plasma power. Depending on the film composition, the dielectric and optical properties of $SiN_x$ films varied substantially. Both the resistivity and breakdown field strength showed the maximum value at the stoichiometric composition (N/Si = 1.33), and degraded as the composition deviated to either side. The electrical properties degraded more rapidly when the composition shifted toward the silicon-rich side than toward the nitrogen-rich side. The composition shift from the silicon-rich side to the nitrogen-rich side accompanied the shift in the photoluminescence characteristic peak to a shorter wavelength, indicating an increase in the band gap. As long as the film composition is close to the stoichiometry, the breakdown field strength and the bulk resistivity showed adequate values for use as a gate dielectric layer down to $150^{\circ}C$ of the process temperature.

• Bulletin of the Korean Chemical Society
• /
• v.34 no.8
• /
• pp.2503-2506
• /
• 2013

• Asian-Australasian Journal of Animal Sciences
• /
• v.12 no.4
• /
• pp.573-578
• /
• 1999

An experiment was conducted to investigate the effect of diet for growing-finishing pigs with high level of non-starch polysaccharides (NSP) from by-products on nitrogen excretion and nitrogen losses from slurry during storage. Sixteen commercial crossbred barrows of about 68 kg BW were randomly allotted to one of four diets. The control diet was formulated using tapioca and rice as basal energy sources. In the other diets, tapioca was replaced by either coconut expellar, rice bran or beer by-product. The diets differed mainly in the amount and compostition of NSP. After a 12-day adaptation period, urine and faeces were collected separately in metabolism cages for 9 days. Urine and faeces from the first four days were used to analyse the nitrogen partitioning. Urine and faeces from the last 5 days were mixed as slurry. The slurry was sampled at the end of the collection period and again after 30 days storage, to analyse for nitrogen to calculate the losses. Increasing dietary NSP reduced urinary nitrogen and nitrogen losses from the slurry during storage. The pigs fed the diet based on beer by-product excreted the most nitrogen via faeces and the least nitrogen via urine. Nitrogen losses from slurry of pigs fed the beer by-product were from 34 to 65% lower than from the other three diets. It is concluded that including NSP-rich by-products in the diet of growing-finishing pigs reduces urinary nitrogen excretion and nitrogen losses from slurry during storage.

• Korean Chemical Engineering Research
• /
• v.61 no.3
• /
• pp.463-471
• /
• 2023

Nitrogen-rich carbon dots (NDots) were synthesized by using uric acid as carbon and nitrogen sources. The as-synthesized NDots showed strong dual emissions at 420 nm and 510 nm with excitation at 350 nm and 460 nm, respectively. The physicochemical analyses such as X-ray photoelectron spectroscopy, Transmission electron microscopy and Fourier transform infrared spectroscopy were used to analyze the chemical, physical and morphological structures of NDots. The as-synthesized NDots exhibited wide linear range (0-100 µM) and very low detection limit (124 nM) in Ag⁺ ion sensing. In addition, Ag⁺ saturated NDots could be used as an EDTA sensor by the EDTA induced PL recovery.

• Journal of Information Display
• /
• v.11 no.3
• /
• pp.109-112
• /
• 2010

The solid phase compositions and dielectric properties of silicon nitride ($SiN_x$) films prepared using the plasma enhanced chemical vapor deposition (PECVD) technique at a low temperature ($200^{\circ}C$) were studied. Controlling the source gas mixing ratio, R = $[N_2]/[SiH_4]$, and the plasma power successfully produced both silicon-rich and nitrogen-rich compositions in the final films. The composition parameter, X, varied from 0.83 to 1.62. Depending on the film composition, the dielectric properties of the $SiN_x$ films also varied substantially. Silicon-rich silicon nitride (SRSN) films were obtained at a low plasma power and a low R. The photoluminescence (PL) spectra of these films revealed the existence of nano-sized silicon particles even in the absence of a post-annealing process. Nitrogen-rich silicon nitride (NRSN) films were obtained at a high plasma power and a high R. These films showed a fairly high dielectric constant ($\kappa$ = 7.1) and a suppressed hysteresis window in their capacitance-voltage (C-V) characteristics.

• Korean Journal of Materials Research
• /
• v.21 no.12
• /
• pp.639-643
• /
• 2011

Zinc oxide as an optoelectronic device material was studied to utilize its wide band gap of 3.37 eV and high exciton biding energy of 60 meV. Using anti-site nitrogen to generate p-type zinc oxide has shown a deep acceptor level and low solubility. To increase the nitrogen solubility in zinc oxide, group 13 elements (aluminum, gallium, and indium) was co-added to nitrogen. The effect of aluminum on nitrogen solubility in a $3{\times}3{\times}2$ zinc oxide super cell containing 72 atoms was investigated using density functional theory with hybrid functionals of Heyd, Scuseria, and Ernzerhof (HSE). Aluminum and nitrogen were substituted for zinc and oxygen sites in the super cell, respectively. The band gap of the undoped super cell was calculated to be 3.36 eV from the density of states, and was in good agreement with the experimentally obtained value. Formation energies of a nitrogen molecule and nitric oxide in the zinc oxide super cell in zinc-rich conditions were lower than those in oxygen-rich conditions. When the number of nitrogen molecules near the aluminum increased from one to four in the super cell, their formation energies decreased to approach the valence band maximum to some degree. However, the acceptor level of nitrogen in zinc oxide with the co-incorporation of aluminum was still deep.

• Journal of Microbiology and Biotechnology
• /
• v.30 no.8
• /
• pp.1235-1243
• /
• 2020

The use of microalgal biomass as feedstock for biofuels has been discussed for decades as it provides a sustainable approach to producing fuels for the future. Nonetheless, its feasibility has not been established yet and various aspects of biomass applications such as CO₂ biofixation should also be explored. Therefore, in this study, the CO₂ biofixation and lipid/carbohydrate production potential of Chlorella sp. ABC-001 were examined under various nitrogen concentrations. The highest biomass productivity and CO₂ biofixation rate of 0.422 g/l/d and 0.683 g/l/d, respectively, were achieved under a nitrogen-rich condition (15 mM nitrate). Carbohydrate content was generally proportional to initial nitrate concentration and showed the highest value of 41.5% with 15 mM. However, lipid content showed an inverse relationship with nitrogen supplementation and showed the highest value of 47.4% with 2.5 mM. In consideration as feedstock for biofuels (bioethanol, biodiesel, and biogas), the sum of carbohydrate and lipid contents were examined and the highest value of 79.6% was achieved under low nitrogen condition (2.5 mM). For lipid-based biofuel production, low nitrogen supplementation should be pursued. However, considering the lower feasibility of biodiesel, pursuing CO₂ biofixation and the production of carbohydrate-based fuels under nitrogen-rich condition might be more rational. Thus, nitrogen status as a cultivation strategy must be optimized according to the objective, and this was confirmed with the promising alga Chlorella sp. ABC-001.

• Korean Journal of Soil Science and Fertilizer
• /
• v.16 no.4
• /
• pp.368-371
• /
• 1983

Energy rich rice straw was subjected to biological processes involving the transformation of added nitrogen. A part of soil ammonium nitrogen was steadily exhausted when energy rich rice straw was decomposed. More vigorous transformation of added nitrogen ocurred during the first 5 days of incubation period than after 10 days of incubation period. Furthermore, transformation of added nitrogen occurred more markedly when more rice straw and less nitrogen were added. Remineralization of immobilized nitrogen did not take place in this experiment with 50 days of incubation.

• The Korean Journal of Ceramics
• /
• v.6 no.3
• /
• pp.250-257
• /
• 2000

The feasibility of synthesizing SiC-AlN solid solution by field-activated combustion synthesis was demonstrated. At lower fields of 8-16.5V/cm, composites of AlN-rich and SiC-rich phases were synthesized, but at fields of 25-30 V/cm, the product was a 2H structure solid solution. Combustion synthesis of the solid solution by nitridation of aluminum with silicon carbide under a nitrogen gas pressure of 4-8 MPa was also investigated. The maximum combustion temperature and wave propagation velocity were found to be influenced by the electric field in the field-activated combustion synthesis, and by the green density and nitrogen pressure in the combustion nitridation. In both cases the formation of solid solutions is complete within seconds, considerably faster than in conventional methods which require hours.