Atomic-scale characterization of plasma-induced damage in plasma-enhanced atomic layer deposition

Kim, Kangsik,Oh, Il-Kwon,Kim, Hyungjun,Lee, Zonghoon Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.425 No.-

<P><B>Abstract</B></P> <P>Plasma-enhanced atomic layer deposition (PE-ALD) has many advantages for the deposition of thin films. However, an appropriate control of the plasma frequency in the PE-ALD process is required to reduce the plasma-induced damage of the thin films during deposition. In this study, we comparatively studied the effects of conventional 13.56MHz, radio frequency (RF) and 60MHz, very high frequency (VHF) plasma reactants in the PE-ALD during the deposition of Al<SUB>2</SUB>O<SUB>3</SUB>. The plasma damage and the degree of strain of the substrate are investigated by transmission electron microscopy at the atomic scale. In addition, a correlation between the atomic structure and plasma damage at RF and VHF is suggested. Compared to the RF PE-ALD, Al<SUB>2</SUB>O<SUB>3</SUB> thin films deposited with VHF PE-ALD show a clearly effective reduction of the plasma-induced damage. Moreover, the Al<SUB>2</SUB>O<SUB>3</SUB> thin films are grown into a tetrahedral structure near the surface and are then further grown into an octahedral structure, indicating the presence of an increased number of ions and radicals during the plasma-enhanced process. It is evident that the VHF PE-ALD is a more important deposition process for reducing plasma-induced damage to thin films than its RF counterpart.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Deposition process of VHF PE-ALD shows a reduction of the plasma-induced damage. </LI> <LI> VHF plasma technology can control atomic configuration on the surface. </LI> <LI> Increasing number of reactive ions and radicals has an influence on film formation. </LI> <LI> Dielectric constant of amorphous Al<SUB>2</SUB>O<SUB>3</SUB> is related to lattice dielectric constant. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Atomic and Electronic Structures of the Ni-induced Phases on Si(111): Scanning Tunneling Microscopy and Spectroscopy Study

심형준,이근섭,김도환,홍석륜,김세훈 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.6

The atomic and electronic structures of Ni-induced phases formed on a Si(111) surface were investigated using scanning tunneling microscopy (STM) and spectroscopy (STS). STM images show the presence of two kinds of the ring clusters ('1x1'-RCs and √19-RCs) which are related to the known '1x1' and √19×√19 phases, respectively. In addition, a new ordered structure having a √7×√7 periodicity with a considerable domain size was also observed to form on the surface. Islands of the √7×√7 structure embedded in the surface of the √19×√19 structure are found to be made by regular packing of the '1x1'-RCs. High-resolution, dual-bias STM images reveal unprecedented atomistic details of both the ring clusters forming the ordered √19×√19 and √7×√7 structures. STS data indicate that the local √7×√7 phase is semiconducting with a gap of about 1 eV. The √19×√19 structure is either metallic or semiconducting with a gap smaller than 0.2 eV. The peaks in the (dI/dV)/(I/V) curves were attributed to the density of the states expected from the existing atomic models of the two ordered structures.

리튬이차전지용 리튬과잉계 양극 산화물의 충방전 과정 중 원자 구조 열화 과정과 전기화학 특성에 대한 분석

박서현 ( Seohyeon Park ),오필건 ( Pilgun Oh ) 한국공업화학회 2020 공업화학 Vol.31 No.1

최근 리튬이차전지 양극 소재의 다양한 열화 메커니즘들이 밝혀지면서 이것을 제어하여 새로운 전기화학적 특성을 구현하고 기존 소재의 한계점을 극복하고자 하는 연구결과들이 많이 보고되고 있다. 특히, 리튬과잉산화물은 250 mA h g^-1이상의 고 용량 차세대 리튬이차전지 양극 물질로 주목받고 있으나, 충방전 과정 중에 소재 특유의 원자 구조 열화로 인해 활용이 제한되고 있다. 본 연구는 0.4Li₂MnO_{3_}0.6LiNi_1/3Co_1/3Mn_1/3O₂ 리튬과잉소재의 충방전 과정 중에서 겪는 원자구조 변화 과정을 분석하여 소재의 열화 과정을 밝히고 이를 개선하기 위한 연구 방향을 제시하고자 한다. 이를 위해, 원자 단위의 분해능을 갖는 전자투과현미경을 활용하여 충방전 중 원자 구조의 변화 과정을 분석하고 이러한 구조 변화가 소재의 전기화학적 특성에 어떠한 영향을 미치는지 밝히고자 하였다. 충전 과정 중에 발생한 다량의 리튬 빈자리로 인해 구조 불안정성이 일어났고, 이로 인해 전이 금속이 리튬 빈 자리로 이동하면서 구조 열화가 확인되었다. 결과적으로 이러한 구조 변이는 리튬과잉소재의 가장 큰 문제점인 방전 전압 강하 특성을 야기한다는 것을 알아내었다. Recently, various degradation mechanisms of lithium secondary battery cathode materials have been revealed. As a result, many studies on overcoming the limitation of cathode materials and realizing new electrochemical properties by controlling the degradation mechanism have been reported. Li-rich layered oxide is one of the most promising cathode materials due to its high reversible capacity. However, the utilization of Li-rich layered oxide has been restricted, because it undergoes a unique atomic structure change during the cycle, in turn resulting in unwanted electrochemical degradations. To understand an atomic structure deterioration mechanism and suggest a research direction of Li-rich layered oxide, we deeply evaluated the atomic structure of 0.4Li₂MnO_{3_}0.6LiNi_1/3Co_1/3Mn_1/3O₂ Li-rich layered oxide during electrochemical cycles, by using an atomic-resolution analysis tool. During a charge process, Li-rich materials undergo a cation migration of transition metal ions from transition metal slab to lithium slab due to the structural instability from lithium vacancies. As a result, the partial structural degradation leads to discharge voltage drop, which is the biggest drawback of Li-rich materials.

Atomic Structures of a Monolayer of AlAs, GaAs, and InAs on Si(111)

이근정,윤영귀 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.2

We study atomic structures of a monolayer of AlAs, GaAs, and InAs on a Si(111) substrate from first-principles. The surface with the stacking sequence of ...SiSiMAsSiAs is energetically more stable than the surface with the stacking sequence of ...SiSiSiAsMAs, where M is Al, Ga, or In. The atomic structure of the three top layers of the low-energy surfaces are quite robust, irrespective of M, and the atomic structure of the AlAsSiAs terminated surface and that of the GaAsSiAs terminated surface are very similar. For the high-energy AsMAs terminated surfaces, the broken local tetrahedral symmetry plays an important role in the atomic structures. The calculated atomic structures of InAs on the Si(111) substrate depart most from the structure of crystalline Si.

Elastic and electronic properties of partially ordered and disordered Zr(C₁₋ <i> _x </i>N<i> _x </i>) solid solution compounds: A first principles calculation study

Kim, Jiwoong,Kwon, Hanjung,Kim, Jae-Hee,Roh, Ki-Min,Shin, Doyun,Jang, Hee Dong Elsevier 2015 JOURNAL OF ALLOYS AND COMPOUNDS Vol.619 No.-

<P><B>Abstract</B></P> <P>The elastic properties and electronic structures of partially ordered and disordered Zr(C<SUB>1−</SUB> <I> <SUB>x</SUB> </I>N<I> <SUB>x</SUB> </I>) solid solution compounds were investigated using first principles calculations to understand the effects of nitrogen content and atomic distribution. To obtain a proper exchange–correlation energy, we used local density and generalized gradient approximations with Perdew–Burke–Ernzerhof (LDA and GGA-PBE) parametrization. Partially ordered and disordered structures of Zr(C<SUB>1−</SUB> <I> <SUB>x</SUB> </I>N<I> <SUB>x</SUB> </I>) compounds were expressed using unit cell and special quasi-random structure (SQS) models, respectively. We demonstrated that although the disordered models have P1 symmetry with different model sizes and cell shapes compared with ordered models, they reproduce the equilibrium structure and elastic properties of the Zr(C<SUB>1−</SUB> <I> <SUB>x</SUB> </I>N<I> <SUB>x</SUB> </I>) compounds with B1 (Fm-3m) symmetry. However, clear differences exist in the electronic structures. Therefore, the atomic configuration is essential for calculating the electronic structures of the Zr(C<SUB>1−</SUB> <I> <SUB>x</SUB> </I>N<I> <SUB>x</SUB> </I>) compounds.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Elastic and electronic properties of Zr(C<SUB>1−<I>x</I> </SUB>N<SUB> <I>x</I> </SUB>) compounds by first principles. </LI> <LI> We elucidate the effects of atomic configuration on compound properties. </LI> <LI> Ordered and disordered models are depicted by unit cell and special quasi-random structures. </LI> <LI> Disordered structures are suitable models to estimate compound elastic properties. </LI> <LI> The atomic configuration is essential to obtain accurate electronic structures. </LI> </UL> </P>

기계적 합금화에 의한 Cr-N계 합금의 비정질화 과정

이충효,이성희,이상진,권영순 한국분말야금학회 2003 한국분말재료학회지 (KPMI) Vol.10 No.4

Mechanical alloying (MA) by high energy ball mill of Pure chromium Powders was carried out under the nitrogen gas atmosphere. Cr-N amorphous alloy powders have been produced through the solid-gas reaction subjected to MA. The atomic structure during amorphization process was observed by X-ray and neutron diffractions. An advantage of the neutron diffraction technique allows us to observe the local atomic structure surrounding a nitrogen atom. The coordination number of metal atoms around a N atom turns out to be 5.5 atoms. This implies that a nitrogen atom is located at both of centers of the tetrahedron and octahedron formed by metal atoms to stabilize an amorphous Cr-N structure. Also, we have revealed that a Cr-N amorphous alloy may produced from a mixture of pure Cr and Cr nitrides powders by solid-solid reaction during mechanical alloying.

Influence of p-Type Double-Doping on the Crystals and Electronic Structures of Two Polar Intermetallics: La4.57(1)Li0.43Ge3.80(3)In0.20 and Nd4.32(1)Li0.68Ge3.87(3)In0.13

전지은,이준수,유태수 대한화학회 2018 Bulletin of the Korean Chemical Society Vol.39 No.9

Two quaternary polar intermetallic compounds La4.57(1)Li0.43Ge3.80(3)In0.20 and Nd4.32(1)Li0.68Ge3.87(3)In0.13 were synthesized using a conventional high temperature synthetic method as we attempted to introduce the p-type double-doping of Li and In for RE and Ge in the RE5-xLixGe4-y (RE = rare-earth metals) system, and their crystal structures were characterized by single crystal X-ray diffraction experiments. The two title compounds crystallize in the orthorhombic space group Pnma (Pearson code oP16, Z = 4) with six crystallographically independent asymmetric atomic sites and adopt the Gd5Si4-type structure. Overall crystal structures of two isotypic title compounds can be described as a 1:1 assembly of the hypothetical 2-dimensional (2D) RE2(RE/Li)(In/Ge)2 layered structure adopting the Mo2FeB2-type structure and the dumbbell-shaped inter-slab (In/Ge)2 dimers bridging two such neighboring 2D layers along the crystallographic b-axis direction. The observed ?direction selective? structural transformation from the Sm5Ge4-type to the Gd5Si4-type structure can be understood as a result of the simultaneous double-doping by the relatively smaller amount of Li substitution for La at the RE3 site than that in the La4LiGe4 and the partial In substitution for Ge at both of the M1 and M3 sites. The site-preference of In for two particular anionic sites were thoroughly studied using four hypothetical La4LiGe3In models having different atomic arrangements by the tight-binding linear muffin-tin orbital (TB-LMTO) method. The overall electronic structure and individual chemical bonding influenced by the given double-doping were also discussed on the basis of the density of states (DOS) and crystal orbital Hamilton population (COHP) curves analyses.

Deposition temperature dependence of titanium oxide thin films grown by remote‐plasma atomic layer deposition

Lee, Jaesang,Lee, Seung Jae,Han, Won Bae,Jeon, Heeyoung,Park, Jingyu,Jang, Woochool,Yoon, Chong Seung,Jeon, Hyeongtag WILEY‐VCH Verlag 2013 Physica status solidi. PSS. A, Applications and ma Vol.210 No.2

<P><B>Abstract</B></P><P>Titanium dioxide (TiO<SUB>2</SUB>) thin films were deposited by remote‐plasma atomic layer deposition (RPALD). The process window was determined in the range from 150 to 300 °C for atomic layer deposition of TiO<SUB>2</SUB> thin film. The crystal structure and grain size of the TiO<SUB>2</SUB> thin films deposited by RPALD was controlled via the variations of the deposition temperature and post‐deposition thermal annealing. The as‐deposited TiO<SUB>2</SUB> thin film grown at 150 °C was amorphous whereas the TiO<SUB>2</SUB> thin films grown above 200 °C were polycrystalline, consisting of anatase phase. As the deposition temperature increased, the grain size of the anatase phase progressively decreased. Meanwhile, when annealed at 900 °C, the amorphous TiO<SUB>2</SUB> thin film deposited at 150 °C crystallized into anatase structure. The film deposited at 200 °C retained the anatase structure up to 900 °C while incurring minimal grain growth. However, the post‐annealed TiO<SUB>2</SUB> thin films deposited at 250 and 300 °C partially transformed to the rutile structure, resulting in a mixture of anatase and rutile phases. It is speculated that the relatively large grain size of the films deposited below 200 °C likely suppressed the anatase → rutile transformation during annealing as the reduction of total fraction of grains boundaries, which acted as primary nucleation sites for the rutile transition, delayed the anatase → rutile transformation.</P>

금속클러스터 M_(13)의 구조

성동철,박노정,홍석륜 한국물리학회 2011 새물리 Vol.61 No.3

We have performed density functional theory (DFT) calculations to find the low-energy structure of various types of small metal clusters. We investigated the electronic structure of M13 clusters consisting of Al, Au, and transition metal atoms, such as Pd, Pt and Ti. Icosahedron and cuboctahedron consisting of 13 atoms are minimal cluster shapes of closed atomic shells. As a result,we found low-energy structures for several metal clusters. For the cases of Al and Ti clusters, the icosahedron structure has the lowest energy. On the other hand, gold clusters are flake-like, and Pd and Pt clusters have a cage shape for their low-energy structures. Finally, we calculated the magnetic moments of the transition metal clusters. 이 논문에서는 다양한 종류의 금속 클러스터에 대한 안정된 구조를 찾기위하여 제일원리 밀도범함수 이론을 이용한 연구를 수행하였다. 먼저우리는 13개의 원자로 이루어진 알루미늄과 금, 그리고 팔라듐, 백금,타이타늄과 같은 전이금속에 대한 전자구조를 조사하였다. 정십이면체(icosahedron)와 육팔면체(cuboctahedron)은 가장 작은 수의닫힌 원자껍질을 가지는 구조이다. 우리는 이 구조를 기본으로 금속원자13개로 이루어진 클러스터의 안정된 구조를 얻기 위해서 클러스터의모양을 여러 형태로 바꿔서 계산을 하였다. 그 결과, 알루미늄과타이타늄은 정십이면체 구조가 가장 안정된 구조이고, 팔라듐과 백금은새장(cage) 구조, 금은 박편(flake) 구조가 가장 안정된 구조임을 알게되었다. 마지막으로 각 금속클러스터의 구조에 따른 자기모멘트(magnetic moment)를 계산하였다.

Stability of the Crystal Structure of -BiFeO3

Fayyaz Ahmad,Ishrat Naz,장재경,이유열 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.4

Density-functional-theory-based calculations have been carried out to investigate the structural stability of bismuth ferrite (-BiFeO3). -BiFeO3 was generally observed to be in a hexagonal phase with the space group R3c. In a new experiment, however, several different crystal structures were suggested, and the triclinic phase (space group: P1) was claimed to be the most stable one. In order to confirm the claim theoretically, we carried out electronic-structure calculations for the various crystal structures suggested experimentally. Unlike the new experimental claim, we found that the hexagonal phase (R3c) had the lowest total energy. Furthermore, the hexagonal phase has a direct band gap of 0.87 eV. Even though this value is much smaller than the experimental value (1.3 eV) because of the notorious deficiency of the generalized-gradient approximation employed in this investigation, it is the closest one to the experimental one among the calculated band gaps of the investigated models. To understand the differences among different models, we investigated the band structure, density of states, and charge density. Along with the bonding process, the charge transfer was analyzed using the atoms-in-molecules theory. Based on this topological analysis of the bonding character, the evolution of the bonding strength with the critical points along the bonding trajectory and the valence charge in the atomic basins are presented quantitatively. The results show that the hexagonal phase has the strongest ionic character. Furthermore, the stability of our claimed model can be further assured by the bond ellipticity, which is a measure of the deviation of the charge distribution of a bond path from axial symmetry.