Joongoo Kang

Joongoo Kang
Daegu Gyeongbuk Institute of Science and Technology | DGIST · Department of Emerging Materials Science

PhD

About

74
Publications
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2,798
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Additional affiliations
January 2008 - October 2014
National Renewable Energy Laboratory
Position
  • Researcher

Publications

Publications (74)
Article
Many of important layered semiconductors, such as hexagonal boron nitride (hBN) and transition-metal dichalcogenides (TMDs), are derived from a hexagonal lattice. A single layer of such hexagonal semiconductors generally has a direct bandgap at the high-symmetry point K, whereas it becomes an indirect, optically inactive semiconductor as the number...
Article
Effective control of hydrogenation of graphene is of great scientific and technological importance. However, the reversible control of H density (n_{H}) on graphene is difficult due to the irreversible H_{2} formation of the detached H adatoms. Here we present a novel mechanism for controlling n_{H} by using the unique proton transfer reaction betw...
Article
The development of short-to-medium-range order in atomic arrangements has generally been observed in noncrystalline solid systems such as metallic glasses. Whether such medium-range order (MRO) can exist in materials at well above their melting or glass-transition temperature has been a long-standing important scientific issue. Here, using ab initi...
Article
Understanding gas adsorption confined in nanoscale pores is a fundamental issue with broad applications in catalysis and gas storage. Recently, hysteretic H(2) adsorption was observed in several nanoporous metal-organic frameworks (MOFs). Here, using first-principles calculations and simulated adsorption/desorption isotherms, we present a microscop...
Article
The atomic and electronic structures of the liquid Al/(0001) α-AlâOâ interfaces are investigated by first-principles molecular dynamics simulations. Surprisingly, the formed liquid-solid interface is always atomically abrupt and is characterized by a transitional Al layer that contains a fixed concentration of Al vacancies (â10 at.%). We find that...
Article
The nuclear motions coupled with electronic excitations of reactants play an essential role in electron-induced chemical reactions. Here, we study the vibrational-electronic (vibronic) coupling effects in the anchoring of Ni-phthalocyanine molecules (NiPCs) on Au(111) using scanning tunneling microscopy (STM). The anchoring occurs through the dehyd...
Article
Nonequilibrium growth of Si-III-V or Si-II-VI alloys is a promising approach to obtaining optically more active Si-based materials. We propose a new class of nonisovalent Si2AlP (or Si2ZnS) alloys in which the Al-P (or Zn-S) atomic chains are as densely packed as possible in the host Si matrix. As a hybrid of the lattice-matched parent phases, Si2A...
Article
The local modification of intermolecular interactions in nickel-phthalocyanine molecules (NiPCs) is investigated on an Au(111) substrate using scanning tunneling microscopy. When the molecules are physisorbed on the substrate, they repel each other due to induced charge dipole moments. However, when the NiPC is chemisorbed on the substrate through...
Article
Dislocations are essentially lines of point defects which can act as recombination centers in semiconductor devices. These point defects do not behave as isolated defects. Their spatial proximity enables them to hybridize into a one-dimensional band, and the distribution of resulting defect-band states is determined by both the position of the band...
Article
A nickel(II)–borohydride complex bearing a macrocyclic tridentate N-donor ligand, [Ni(Me3-TACN)(BH4)(CH3CN)]+ (Me3-TACN = 1,4,7-trimethyl-1,4,7-triazacyclononane), was prepared, isolated, and characterized by various physicochemical methods, including UV-vis, ESI-MS, IR and X-ray analyses. The structural and spectroscopic characterization clearly s...
Article
Pinning single molecules at desired positions can provide opportunities to fabricate bottom-up designed molecular machines. Using the combined approach of scanning tunneling microscopy and density functional theory, we report on tip-induced anchoring of Niphthalocyanine molecules on an Au(111) substrate. We demonstrate that the tip-induced current...
Article
Full-text available
Atomic-scale understanding and control of dislocation cores is of great technological importance, because they act as recombination centers for charge carriers in optoelectronic devices. Using hybrid density-functional calculations, we present period-doubling reconstructions of a 90° partial dislocation in GaAs, for which the periodicity of like-at...
Article
A set of nickel(III) peroxo complexes bearing tetraazamacrocyclic ligands, [Ni(III)(TBDAP)(O2)](+) (TBDAP = N,N'-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane) and [Ni(III)(CHDAP)(O2)](+) (CHDAP = N,N'-dicyclohexyl-2,11-diaza[3.3](2,6)pyridinophane), were prepared by reacting [Ni(II)(TBDAP)(NO3)(H2O)](+) and [Ni(II)(CHDAP)(NO3)](+), respectively,...
Article
Full-text available
Unique optoelectronic properties and interlayer coupling are observed in the artificial two-dimensional (2D) heterostructures based on Graphene, MoS2 and WS2 monolayers. In the graphene/WS2 heterostructures, substantial photoluminescence (PL) quenching and significant stiffening phonon modes emerge due to the strong interlayer coupling. Such hybrid...
Article
The diffusion of particles in solid-state materials generally involves several sequential thermal-activation processes. However, presently, diffusion coefficient theory only deals with a single barrier, i.e., it lacks an accurate description to deal with multiple-barrier diffusion. Here, we develop a general diffusion coefficient theory for multipl...
Article
Full-text available
We present the optical function spectra of Cu 2SnSe3 determined from 0.30 to 6.45 eV by spectroscopic ellipsometry (SE) at room temperature. We analyze the SE data using the Tauc-Lorentz model and obtain the direct-bandgap energy of 0.49 ± 0.02 eV, which is much smaller than the previously known value of 0.84 eV for the monoclinic-phase Cu 2SnSe3....
Article
Full-text available
Using first-principles density functional calculations, we investigate the relative stability and electronic structure of the grain boundaries (GBs) in zinc-blende CdTe. Among the low-Σ-value symmetric tilt Σ3 (111), Σ3 (112), Σ5 (120), and Σ5 (130) GBs, we show that the Σ3 (111) GB is always the most stable due to the absence of dangling bonds and...
Article
The Fermi level of a material is a fundamental quantity that determines its electronic properties. Thus, the ability to tune Fermi levels is important for developing electronic device materials. However, for most materials, the Fermi level is limited to a certain range in the band gap due to the existence of certain intrinsic compensating defects....
Article
We propose an effective co-alloying approach to creating an intermediate band (IB) in bulk ZnTe. First-principles calculations show that a donor–acceptor co-alloying scheme can produce an IB within the band gap of ZnTe and that the position of the IB can be tuned by choosing appropriate donor–acceptor pairs. We find that the position of the IB is g...
Article
Nanofluids are often proposed as advanced heat transfer fluids. In this work, using a one-step nanoemulsification method, we synthesize gallium, indium, and indium-bismuth nanofluids in poly-alpha-olefin (PAO). The size distributions of the resulting nanoparticles are analyzed using transmission electron microscopy (TEM). X-ray diffraction (XRD) an...
Article
Halide perovskites have recently emerged as promising materials for low-cost, high-efficiency solar cells. The efficiency of perovskite-based solar cells has increased rapidly, from 3.8% in 2009 to 19.3% in 2014, by using the all-solid-state thin-film architecture and engineering cell structures with mixed-halide perovskites. The emergence of perov...
Article
Lattice-matched and pseudomorphic tunnel junctions have been developed in the past for application in a variety of semiconductor devices, including heterojunction bipolar transistors, vertical cavity surface-emitting lasers, and multijunction solar cells. However, metamorphic tunnel junctions have received little attention. In 4-junction Ga0.51In0....
Article
The optical and electrical properties of many III-V alloys change with the degree of CuPt atomic ordering, which is very sensitive to growth conditions. The bulk ordered alloy is elongated along the normal to the ordered planes, and is asymmetrically strained when coherent to a cubic substrate. Here, we demonstrate in situ measurement of the anisot...
Article
Full-text available
Ordering-induced effects on dislocations in metallic alloys have been extensively studied due to their importance in technology applications. We demonstrate that dislocation behavior in ordered III-V semiconductor alloys can be drastically different. This is because ordering in bulk metallic alloys is generally stable, whereas the surface-stabilize...
Article
Ductile metals such as Ni and Cu can become brittle when certain impurities (e.g., Bi) diffuse and segregate into their grain boundaries (GBs). Using first-principles calculations, we investigate the microscopic origin of the Bi-induced loss of cohesion of Ni and Cu GBs. We find that the Bi bilayer interfacial phase is the most stable impurity phas...
Article
When compressive strain is applied to a single-layered material, the layer generally ripples along the third dimension to release the strain energy. In contrast, such a rippling effect is not favored when it is under tensile strain. Here, using first-principles density-functional calculations, we show that molecular adsorption on boron-doped graphe...
Article
Graphene magnetism has been proposed but based on thermodynamically unstable zigzag edges and dangling electrons with broken sublattice symmetry. From results of first-principles calculations, we propose a way to realize thermodynamically stable graphene ferromagnetism by seamlessly incorporating transition metals into the graphene honeycomb networ...
Article
The interaction of lithium peroxide (Li2O2) with carbon electrodes in Li-air batteries is studied with model systems of graphene-intercalated Li2O2, using density functional theory (DFT) methods. Although both the Li2O2 bulk and its stoichiometric surface structures (without single O atoms) are insulating, the incorporation of graphene sheets into...
Article
Open-site paddle wheels, comprised of two transition metals bridged with four carboxylate ions, have been widely used for constructing metal–organic frameworks with large surface area and high binding energy sites. Using first-principles density functional theory calculations, we have investigated atomic and electronic structures of various 3d tran...
Article
One interesting oxidation phenomenon is the difference of the oxidation of Cu and Al. Cu forms disordered domains, large surface reconstructions and oxide islands on the surface with some O atoms diffuse into inner layers to further oxidize inner Cu atoms. Al forms a dense oxide layer which protects the inner Al atoms from oxidation. In this talk,...
Article
Cu2O thin films were grown on Si and SiO2/Si substrates via RF sputtering deposition at various temperatures. The Cu2O thin films had a smooth surface when grown at RT, but developed grain boundaries when grown at 300 ^oC. We observed the high-energy photoluminescence (PL) peaks at 3.18 eV (Ep) and 3.27 eV (Eq). The dielectric functions of the Cu2O...
Article
Lithium-air batteries (LABs) have recently been revitalized as a promising electrical energy storage system due to their exceptionally high theoretical energy density. However, its usage is limited by poor rate capability and large polarization in the cell voltage due primarily to the formation of Li2O2 in the air cathode. Here, using hybrid densit...
Article
Lithium–air batteries (LABs) are an intriguing next-generation technology due to their high theoretical energy density of ∼11 kWh/kg. However, LABs are hindered by both poor rate capability and significant polarization in cell voltage, primarily due to the formation of Li2O2 in the air cathode. Here, by employing hybrid density functional theory, w...
Article
Cuprous oxide (Cu2O) thin films were grown via radio frequency sputtering deposition at various temperatures. The dielectric functions and luminescence properties of the Cu2O thin films were measured using spectroscopic ellipsometry and photoluminescence, respectively. High-energy peaks were observed in the photoluminescence spectra. Several critic...
Article
Full-text available
The ternary semiconductors Cu2SnX3 (X=S, Se) are found frequently as secondary phases in synthesized Cu2ZnSnS4 and Cu2ZnSnSe4 samples, but previous reports on their crystal structures and electronic band gaps are conflicting. Here we report their structural and electronic properties as calculated using a first-principles approach. We find that (i)...
Article
As the size of the material decreases to the nanoscale, the distinction between batteries and electrochemical capacitors becomes obscured. Here, a first-principles approach is developed to calculate electrochemical capacitance of nanomaterials. Using TiO2 anatase nanosheets interfaced with lithium ion-containing electrolytes as an example, we revea...
Article
Microscopic understanding of thermal behaviors of metal nanoparticles is important for nanoscale catalysis and thermal energy storage applications. Using first-principles molecular dynamics simulations, we reveal the microscopic origin of the diverse melting behaviors of AlN clusters with N around 55 [1,2]. The conceptual link between the degree of...
Presentation
The experimentally observed enhancement of hydrogen adsorption in Cu2-tetracarboxylate paddle-wheel frameworks is investigated by first-principles density-functional theory calculations [1]. We reveal that the puzzling enhancement is due to the effective orbital coupling between the occupied H2 sigma and the unoccupied Cu 4s-derived states. The non...
Article
Microscopic understanding of thermal behaviors of metal nanoparticles is important for nanoscale catalysis and thermal energy storage applications. However, it is a challenge to obtain a structural interpretation at the atomic level from measured thermodynamic quantities such as heat capacity. Using first-principles molecular dynamics simulations,...
Article
The experimentally observed enhancement of hydrogen adsorption in Cu2-tetracarboxylate paddle-wheel frameworks is investigated by ab initio density-functional theory calculations. We reveal that the puzzling enhancement is due to the effective orbital coupling between the occupied H2 σ and the unoccupied Cu 4s-derived states. The nontrivial dihydro...
Article
A new dynamic melting state, which has both solid and liquid characteristics, is revealed from first-principles molecular dynamics simulations of Al(55) clusters. In thermal fluctuations near the melting point, the low-energy tetrahedral-like Al(55) survives through rapid, collective surface transformations-such as parity conversions and correlated...
Article
Porphyrin is a very important component of natural and artificial catalysis and oxygen delivery in blood. Here, we report that, based on first-principles density-functional calculations, a hydrogen molecule can be adsorbed non-dissociatively onto Ti-, V-, and Fe-porphyrins, similar to oxygen adsorption in heme-containing proteins, with a significan...
Article
It is a challenge to synthesize clusters having a certain shape associated with a desirable property. In this study, we perform density functional calculations on ligand-protected Al(7) and Al(77) clusters. It is found that small ligands such as NH(2) still prefer the compact structure of bare Al clusters. However, large ligands such as N(SiMe(3))(...
Article
Recently there has been much interest in development of new electrochemical capacitors to meet high-power and high-energy applications. Pseudo-capacitors using fast surface redox reactions can store electrical energy of 10 to 100 times larger than supercapacitors and still exhibit fast and reversible charge-discharge responses in contrast to batter...
Article
First-principles calculations show that the electronic structure of graphene on SiO2 strongly depends on the surface polarity and interface geometry. Surface dangling bonds mediate the coupling to graphene and can induce hole or electron doping via charge transfer even in the absence of extrinsic impurities in substrate. In an interface geometry wh...
Article
Using first-principles theoretical calculations, we find that Ga-vacancies (VGa) strongly interact with the Mn ions in GaN and thereby significantly affect the electronic and magnetic properties. When Ga-vacancies are present in the neighbourhood of the Mn ions, a charge transfer occurs from the Mn d band to the acceptor level of VGa. Due to the de...
Article
Doping control is an important issue in wideband gap semiconductors such as nitrides and oxides that can be characterized by doping asymmetry, indicating that it is difficult to achieve both low-resistivity p- and n-type semiconductors. Despite theoretical predictions that group-V acceptors have high activation energies, p-type ZnO doped with N, P,...
Article
We perform first-principles matrix Green’s function calculations to study the coherent charge tunneling through ultrathin SiO2 layers in metal-oxide-semiconductor devices. The tunneling behavior is analyzed within the atomistic picture based on the overlap of Si-induced gap states in the oxide region. We find that, while interface roughness defects...
Article
Based on perturbation theory and local-density-functional calculations, we study the effect of atomic-scale defects, whose potentials vary on the scale of interatomic distance, on the electronic structure of graphene in the region of low energies. If defects are identical, for example, vacancies at the same sublattice sites or the Stone-Wales defec...
Article
Graphene is a single layer of carbon atoms packed in a honeycomb lattice, and its quasiparticles behave like massless Dirac fermions. Since graphene is usually supported and deposited on dielectric materials such as SiO2 and SiC, interactions between graphene and substrate atoms can modify the electronic structure of graphene. In this work we study...
Article
We investigate the effect of Ge on the retardation of B diffusion in SiGe alloys through first-principle calculations, and find that the Ge bonding effect is most significant in the nearest-neighborhood of B. The B dopant diffuses from a self-interstitial–B pair via an interstitialcy mechanism for neutral charge state, while a kick-out mechanism is...
Article
We perform first-principles theoretical calculations to investigate the effect of the presence of Ga vacancy on the defect and magnetic properties of Mn-doped GaN. When a Ga vacancy (VGa) is introduced to the Mn ions occupying the Ga lattice sites, a charge transfer occurs from the Mn d band to the acceptor levels of VGa, and strong Mn-N bonds are...
Article
We perform first-principles density-functional calculations to study the chemical bonding effect of Ge atoms on the diffusion pathway and migration barrier of a B dopant in Si. The binding energy of a B-Ge pair is extremely small, thus, it is ruled out that the pairing of the B and Ge atoms immobilizes the B atom. When a Ge atom is located in the f...
Article
We use a first-principles computational scheme to study the transport properties of devices based on telescoping carbon nanotubes. The transmission function is calculated through the matrix Green's function method using a Gaussian basis set. Varying the overlap region of the two nanotubes, we compare the effect of interwall interactions on the tran...
Article
We perform first‐principles pseudopotential calculations to investigate the effect of Mn delta‐doping on the stability of the zinc‐blende and wurtzite structures in GaN. In bulk GaN, it is possible for the zinc‐blende structure to become a stable phase againt the wurtzite one with increasing the concentration of the delta‐doped Mn ions. On GaN sur...
Article
Based on first‐principles theoretical calculations, we investigate the hydrogenation effect on the defect properties of oxygen vacancies (VO) in HfO2. A defect complex of VO and H behaves as a shallow donor, being in a positive charge state for a wide range of the Fermi levels, and this complex is very stable against its dissociation into VO and H....
Article
Based on first-principles theoretical calculations, we investigate the electronic structure of various defects in P-doped ZnO. We find that a P O impurity occupying an O site is a deep acceptor while a P Zn atom at a Zn site is the dominant donor, causing a compensation of acceptors. Under O-rich growth conditions, Zn vacancies (VZn) are the main s...
Article
The ability to shrink Si-based transistors is reaching the spatial scale of sub-0.1 μm, close to fundamental limits. For an oxide thickness as low as 2 nm, quantum effects start to become important, and an acceptable reliability is not achievable. High-k dielectrics provide high capacitance, which is compatible with SiO2-based devices with larger p...
Article
As the size of metal-oxide-semiconductor devices is scaled down to the sub-10-nm regime, the thickness of SiO2 insulating layers reaches the range of 1-2 nm. Then, gate leakage current is unavoidable due to direct tunneling of electrons. In this work, we study the electron tunneling current through thin gate oxide layers for various Si(100)/SiO2 in...
Article
We perform first-principles pseudopotential calculations to study the influence of Mn doping on the stability of two polytypes, wurtzite and zinc-blende, in GaN. In Mn δ-doped GaN and GaMnN alloys, we find similar critical concentrations of the Mn ions for stabilizing the zinc-blende phase against the wurtzite phase. Using a slab geometry of hexago...
Conference Paper
The magnetization curve as a function of the magnetic field as 5 K indicated that the magnetization in the (Ga<sub>0.995</sub>Mn<sub>0.005</sub>)N thin film is significantly enhanced due to Mn delta-doping. The magnetization curve as a function of the temperature showed that the Curie temperature of the Mn delta-doped (Ga<sub>0.995</sub>Mn<sub>0.00...
Article
We perform first-principles theoretical calculations to study the atomic and the electronic structures of Si impurities in HfO 2. We also examine the impact of Si impurities on the threshold voltage problems in ploy-Si/HfO 2 gates and the growth morphology of HfO 2 films on Si substrates. In the ploy-Si/HfO 2 interface region, Si atoms easily migra...
Article
Based on theoretical calculations, we find that at p+ polycrystalline silicon (poly-Si)/HfO2 gates, Si interstitials are easily migrated from the electrode, forming Hf–Si bonds with a charge transfer to the electrode, and the resulting interface dipole raises the Fermi level of poly-Si toward the pinning level, causing high flat band voltage shifts...
Article
Based on first-principles spin-density functional calculations, we investigate the magnetic properties of Mn-doped GaN. We find that the magnetic interaction between two Mn ions has a short-range nature, effective for Mn–Mn distances up to about 7Å, and it favors the ferromagnetic coupling via the double exchange mechanism. As the Mn atom interacts...
Article
We study the defect properties of P dopants in ZnO through first-principles pseudopotential calculations. Because of the large size-mismatch between the P and O atoms, the acceptor level of a substitutional P (PO) at an O lattice site is deeper than for N acceptors. A substitutional P (PZn) at a Zn antisite is found to be the dominant donor. Under...
Article
Among many types of DMS materials, (Ga1-xMnx)As DMS have been mostly studied. However, since the highest Tc obtained from the (Ga1-xMnx)As has been 172 K, which is too low for practical applications. As alternative DMS materials with the high Tc, (Ga1-xMnx)N DMSs are of current interest because their Tc values can be as high as room temperature. Th...
Article
Based on first-principles pseudopotential calculations, we investigated the electronic structure of various P-related defects in ZnO and the p-type doping efficiency for two forms of P dopant sources such as P2O5 and Zn3P2. As compared to N dopants, a substitutional P at an O site has a higher ionization energy of about 0.62 eV, which makes it diff...
Article
We study the trend of structural stability and magnetic moment for MnX (X=N, P, As, and Sb) binary compounds in the NiAs and zinc-blende structures through first-principles spin-density-functional calculations. The exchange splitting and magnetic moment are generally lower in the stable structure, which corresponds to the NiAs structure for MnP, Mn...
Article
The effects of Mn delta-doping on the magnetic properties of (Ga1−xMnx)N thin films grown on GaN buffer layers by molecular-beam epitaxy were studied. The magnetization curve as a function of the magnetic field as 5 K indicated that ferromagnetisms existed in the Mn delta-doped (Ga1−xMnx)N and (Ga1−xMnx)N thin films and that the magnetization in th...
Article
We investigate the magnetic properties of Mn-doped GaN through first-principles pseudopotential calculations within the spin-density-functional approximation. We examine the nature of magnetic interactions between Mn ions, and find that the ferromagnetic coupling has a short-range nature, effective for Mn–Mn distances up to about 7~{}. For Mn conce...
Article
Based on the first-principles spin-density functional calculations, we investigate the magnetic interactions between Mn ions in Mn-doped GaN. We find that the ferromagnetic coupling has a short-range nature, effective for Mn-Mn distances up to about 7 Å. For Mn concentrations of about 6%, the ferromagnetic solution is more stable than the antiferro...
Article
Recently, Mn-doped GaN has attracted much attention because of the ferromagnetism observed in this material. However, experimental data so far are quite controversial, reporting the Curie temperatures ranging from 10 to 940 K. Very recent experiments showed that Mn delta-doped GaN films have high hole carrier concentrations, which lead to the high...
Article
Based on first-principles theoretical calculations, we investigate the hydrogenation effect on the defect properties of oxygen vacancies (VO) in HfO2. A defect complex of VO and H behaves as a shallow donor for a wide range of Fermi levels, with a positive charge state, and this complex is energetically stable against its dissociation into VO and H...
Article
We investigate the phase transformation of HfO2 under hydrostatic pressure through first-principles pseudopotential calculations within the local-density-functional approximation (LDA) and the generalized gradient approximation (GGA). We find that with increasing of pressure, HfO2 undergoes a series of structural transformations from monoclinic to...

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