• The Journal of Korean Institute of Communications and Information Sciences
• /
• 제17권1호
• /
• pp.58-67
• /
• 1992

Optical absorption and photoluminescences(PL) of MgGa2Se4 and MgGa2Se4 : Co2+ single crustals were guown by the Bridgman method have been investigated in the visible and near-in frared regions. The optical absorption spectrum showed three absorption peak at 760 nm(13158nm, -1, 1.63eV), 1640nm(6097cm-1, 0.75eV).and 2500nm(4000cm-1,0.49eV) which are assigned the electronic transitions between the ground state and excited states of Co2+ ions with Td sym-metry in MgGa2Se4 host lattice. In PL spectrum the visible emission bands as well as the infrared emission band in these single cuystals are obserned. The visible emission bands are explained due to the radiative transitions of electrons from quasi continusly distributed tarps below the bottom of the conduction band to acceptor levels above the top of the valence band in the proposed energy level scheme. At the same time, it is considered that the infrated emission bands are attributed to electron transitions from the deep levels to the acceptor levels. The mechanism of the optical transition os well explained in terms of the energy diagram of MgGa2Se4.

• Journal of Electrical Engineering and Technology
• /
• 제9권3호
• /
• pp.1009-1015
• /
• 2014

Chalcopyrite $CuInSe_2$ (CIS) thin films were prepared without Se- / S-containing gas by co-sputtering using $CuSe_2$ and $InSe_2$ selenide-targets and rapid thermal annealing. The grain size increased to a maximum of 54.68 nm with a predominant (112) plane. The tetragonal distortion parameter ${\eta}$ decreased and the inter-planar spacing $d_{(112)}$ increased in the RTA-treated CIS thin films annealed at a $400^{\circ}C$, which indicates better crystal quality. The increased carrier concentration of RTA-treated p-type CIS thin films led to a decrease in resistivity due to an increase in Cu composition at annealing temperatures ${\geq}350^{\circ}C$. The optical band gap energy ($E_g$) of CIS thin films decreased to 1.127 eV in RTA-treated CIS thin films annealed at $400^{\circ}C$ due to the improved crystallinity, elevated carrier concentration and decreased In composition.

• Bulletin of the Korean Chemical Society
• /
• 제28권11호
• /
• pp.1996-2002
• /
• 2007

The redox behavior of a [Ni6(μ3-Se)2(μ4-Se)3(Fe(η 5-C5H4P-Ph2)2)3] (= [Ni-Se-dppf], dppf = 1,1-bis(diphenylphosphino) ferrocene) cluster was studied using platinum (Pt) and glassy carbon electrodes (GCE) in nonaqueous media. The cluster showed electrochemical activity at the potential range between +1.6 and ?1.6 V. In the negative region (0 to ?1.6 V), the cluster exhibited two-step reductions. The first step was one-electron reversible, while the second step was a five-electron quasi-reversible process. On the other hand, in the positive region (0 to +1.6 V), the first step involved one-electron quasi-reversible process. The applicability of the cluster was found towards the electrocatalytic reduction of CO2 and was evaluated by experiments using rotating ring disc electrode (RRDE). RRDE experiments demonstrated that two electrons were involved in the electrocatalytic reduction of CO2 to CO at the Se-Ni-dppf-modified electrode.

• Korean Journal of Materials Research
• /
• 제21권10호
• /
• pp.550-555
• /
• 2011

A high-quality CIGS film with a selenization process needs to be developed for low-cost and large-scale production. In this study, we used $Cu_2In_3$, CuGa and $Cu_2Se$ sputter targets for the deposition of a precursor. The precursor deposited by sputtering was selenized in Se vapor. The precursor layer deposited by the co-sputtering of $Cu_2In_3$, CuGa and $Cu_2Se$ showed a uniform distribution of Cu, In, Ga, and Se throughout the layer with Cu, In, CuIn, CuGa and $Cu_2Se$ phases. After selenization at $550^{\circ}C$ for 30 min, the CIGS film showed a double-layer microstructure with a large-grained top layer and a small-grained bottom layer. In the AES depth profile, In was found to have accumulated near the surface while Cu had accumulated in the middle of the CIGS film. By adding a Cu-In-Ga interlayer between the co-sputtered precursor layer and the Mo film and adding a thin $Cu_2Se$ layer onto the co-sputtered precursor layer, large CIGS grains throughout the film were produced. However, the Cu accumulated in the middle of CIGS film in this case as well. By supplying In, Ga and Se to the CIGS film, a uniform distribution of Cu, In, Ga and Se was achieved in the middle of the CIGS film.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 한국전기전자재료학회 2002년도 제4회 영호남학술대회 논문집
• /
• pp.31-36
• /
• 2002

In this work $Cd_{4}GeSe_{6}$ and $Cd_{4}GeSe_{6}:Co^{2+}$ single crystals were grown by the chemical transport reaction method and the structure of $Cd_{4}GeSe_{6}$ and $Cd_{4}GeSe_{6}:Co$ single crystals were monoclinic structure. The temperature dependence of optical energy gap was fitted well to Varshni equation. Also, the entropy, enthalpy and heat capacity were deduced from the temperature dependence of optical energy gap.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
• /
• pp.85-87
• /
• 2009

Despite the success of $Cu(In,Ga)Se_2$ (CIGS) based PV technology now emerging in several industrial initiatives, concerns about the cost of In and Ga are often expressed. It is believed that the cost of those elements will eventually limit the cost reduction of this technology. one candidate to replace CIGS is $Cu_2ZnSnSe_4$ (CZTSe), fabricated by co-evaporation technique. Effects of substrate temperature of $Cu_2ZnSnSe_4$ absorber layer on the performance of thin films solar cells were investigated. As substrate temperature increased, the grain size of $Cu_2ZnSnSe_4$ films increased presumably. At a optimal condition of substrate temperature is $320^{\circ}C$, the solar cell shows a conversion efficiency of 1.79% with $V_{OC}$ of 0.213V, JSC of $16.91mA/cm^2$ and FF of 49.7%.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• 제17권2호
• /
• pp.52-56
• /
• 2007

We have installed an ultra high vacuum (UHV) molecular beam epitaxy (MBE) system and investigated into the characteristics of MBE-grown ZnSe/GaAs [001] using scanning electron microscopy (SEM), atomic force microscopy (AFM), we confirmed that layer's surface was dense and uniform of molecular layer. We used x-ray diffractometer (XRD) and confirmed two peaks correspond to GaAs [001] substrate and ZnSe epilayer, respectively. We observed photoluminescence (PL) peak approximately at 437 nm and measured PL mapping of 2 inch ZnSe epilayer.

• Journal of Nuclear Fuel Cycle and Waste Technology
• /
• 제1권1호
• /
• pp.57-63
• /
• 2013

Natural green rust (GR) can retard the migration of anions through geological media because it has a Layer Double Hydroxyl (LDH) structure with a positive charge. In this study, the sorption behaviors of anions such as selenite ($Se(IV)O{_3}^{2-}$), selenate ($Se(VI)O{_4}^{2-}$), and iodide ($I^-$) onto green rusts with different structures, i.e., GR($Cl^-$) and GR($CO{_3}^{2-}$), were investigated by conducting batch sorption experiments in an anoxic condition. Experimental results showed that selenite was mostly sorbed onto GR($CO{_3}^{2-}$) and then partly reduced to metal selenium, Se(0). However, little selenate and iodide was sorbed onto GR($CO{_3}^{2-}$) while some iodide was sorbed onto GR($Cl^-$). It is presumed from the experimental results that the major sorption mechanism of $SeO{_3}^{2-}$ and $I^-$ onto green rusts is the anion exchange reaction with the anions existing in the interlayer of the rusts. Green rust, therefore, can play an important role in the retardation of anions migrating through deep geological environments owing to its LDH structure with a high anion exchange capacity.

• Clean Technology
• /
• 제29권3호
• /
• pp.178-184
• /
• 2023

Transition metal chalcogenides have garnered significant attention as anode materials for sodium-ion batteries due to their high theoretical capacity. Nevertheless, their practical application is impeded by their limited lifespan resulting from substantial volume expansion during cycling and their low electrical conductivity. To tackle these issues, this study devised a solution by synthesizing a nanostructured anode material composed of porous CNT (carbon nanotube) spheres and (Ni,Co)Se₂ nanocrystals. By employing spray pyrolysis and subsequent heat treatments, a porous-structured (Ni,Co)Se₂-CNT composite microsphere was successfully synthesized, and its electrochemical properties as an anode for sodium-ion batteries were evaluated. The synthesized (Ni,Co)Se₂-CNT microsphere possesses a porous structure due to the nanovoids that formed as a result of the decomposition of the polystyrene (PS) nanobeads during spray pyrolysis. This porous structure can effectively accommodate the volume expansion that occurs during repeated cycling, while the CNT scaffold enhances electronic conductivity. Consequently, the (Ni,Co)Se₂-CNT anode exhibited an initial discharge capacity of 698 mA h g^-1 and maintained a high discharge capacity of 400 mA h g^-1 after 100 cycles at a current density of 0.2 A g^-1.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• 제52권7호
• /
• pp.275-281
• /
• 2003

$Zn_{0.5}Cd_{0.5}Al_{2}Se_{4}$ and $Zn_{0.5}Cd_{0.5}Al_{2}Se_{4}$:$Co^{2+}$ single crystals were grown by CTR method. The grown single crystals have defect chalcopyrite structure with lattice constant a=5.5966$\AA$, c=10.8042$\AA$ for the pure, a=5.6543$\AA$, c=10.8205$\AA$ for the Co-doped single crystal, respectively. The optical energy band gap was given as indirect band gap. The optical energy band gap was decreased according to add of Co-impurity Temperature dependence of optical energy band gap was fitted well to the Varshni equation. From this relation, we can deduced the entropy, enthalpy and heat capacity. Also, we can observed the Co-impurity optical absorption peaks assigned to the $Co^{2+}$ ion sited at the $T_{d}$ symmetry lattice and we consider that they were attributed to the electron transitions between energy levels of ions.