• Composites Research
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• 제29권4호
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• pp.194-202
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• 2016

이차원 구조의 탄소 결합체인 그래핀은 뛰어난 물리적, 화학적 특성으로 인해 미래 전자 소자의 소재로 크게 각광을 받고 있는 물질이다. 따라서, 소자에서 사용된 기판이 그래핀의 물리적 특성에 끼치는 영향에 대한 이해는 그래핀의 응용에 있어서 필수적이며, 그에 대한 연구를 수행하였다. 니켈 (111)과 (100) 결정면에서 각각 성장한 그래핀과 니켈 기판의 상호작용에 대한 연구를 수행함과 동시에, 산화규소 기판으로 전사한 후, 기판과 그래핀과의 상호작용을 라만 분광법을 이용하여 연구하였다. 니켈 기판에서 성장한 그래핀은 기판의 면 방향과 상관없이 기판으로부터 전하의 이동에 따른 도핑효과는 발견되지 않았으며, 산화규소 기판 또한 도핑효과는 없었다. 니켈 기판과 그래핀 사이의 결합력이 그래핀과 산화규소 기판과의 결합력합보다 더 큰 것으로 분석이 되었으며, 니켈에서 성장한 그래핀은 기판의 영향을 받아 수축되어 있었고, 니켈 (100) 면에서는 그래핀이 엇맞음 성장하였음을 확인하였다. 마지막으로, 니켈 (111), (100) 면에서 성장한 그래핀을 산화 규소 기판으로 전사하면 서로 다른 파수 값에서 2D band의 픽이 관측되었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.134-134
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• 2011

High-k dielectric materials such as $HfO_2$, $ZrO_2$ and $Al_2O_3$ increase gate capacitance and reduce gate leakage current in MOSFET structures. This behavior suggests that high-k materials will be promise candidates to substitute as a tunnel barrier. Furthermore, stack structure of low-k and high-k tunnel barrier named variable oxide thickness (VARIOT) is more efficient.[1] In this study, we fabricated the $WSi_2$ nanocrystals nonvolatile memory device with $SiO_2/HfO_2/Al_2O_3$ tunnel layer. The $WSi_2$ nano-floating gate capacitors were fabricated on p-type Si (100) wafers. After wafer cleaning, the phosphorus in-situ doped poly-Si layer with a thickness of 100 nm was deposited on isolated active region to confine source and drain. Then, on the gate region defined by using reactive ion etching, the barrier engineered multi-stack tunnel layers of $SiO_2/HfO_2/Al_2O_3$ (2 nm/1 nm/3 nm) were deposited the gate region on Si substrate by using atomic layer deposition. To fabricate $WSi_2$ nanocrystals, the ultrathin $WSi_2$ film with a thickness of 3-4 nm was deposited on the multi-stack tunnel layer by using direct current magnetron sputtering system [2]. Subsequently, the first post annealing process was carried out at $900^{\circ}C$ for 1 min by using rapid thermal annealing system in nitrogen gas ambient. The 15-nm-thick $SiO_2$ control layer was deposited by using ultra-high vacuum magnetron sputtering. For $SiO_2$ layer density, the second post annealing process was carried out at $900^{\circ}C$ for 30 seconds by using rapid thermal annealing system in nitrogen gas ambient. The aluminum gate electrodes of 200-nm thickness were formed by thermal evaporation. The electrical properties of devices were measured by using a HP 4156A precision semiconductor parameter analyzer with HP 41501A pulse generator, an Agillent 81104A 80MHz pulse/pattern generator and an Agillent E5250A low leakage switch mainframe. We will discuss the electrical properties for application next generation non-volatile memory device.

• 한국광물학회지
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• 제30권2호
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• pp.59-70
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• 2017

$SiO_2$는 지각과 맨틀을 구성하는 풍부한 물질로 고압 상태의 $SiO_2$ 원자구조를 결정짓는 전자구조적 특성에 대한 상세한 이해는 지구 내부의 탄성과 열역학적 성질에 대한 통찰을 제공한다. $SiO_2$처럼 경원소(low-z)로 이루어진 지구 물질의 고압상 전자구조는 in situ 고압 XRS (x-ray Raman scattering) 실험을 통해 연구되어 왔다. 하지만 기존의 고압 실험 방법으로는 물질의 국소 원자구조와 XRS 스펙트럼 간 상관관계를 밝히는데 한계가 있다. 이를 극복하고 더 높은 압력에서 존재하는 $SiO_2$에 대한 XRS 정보를 얻기 위해 밀도 범함수 이론(density functional theory; DFT)에 기반을 둔 제1원리(ab initio) 계산법을 이용한 XRS 스펙트럼 계산 연구들이 진행되고 있다. 비탄성 X-선 산란에 의하여 원자핵 주변 1s 오비탈에 만들어지는 전자-정공(core-hole)은 경원소 물질의 국소 전자구조에 크게 영향을 미치기 때문에 O K-edge XRS 스펙트럼 형태를 계산할 때 중요하게 고려해야 한다. 본 연구에서는 온-퍼텐셜 선형보충파(full-potential linearized augmented plane wave; FP-LAPW) 방법론에 기반하는 WIEN2k 프로그램을 사용하여 ${\alpha}-quartz$, ${\alpha}-cristobalite$ 그리고 $CaCl_2$-구조를 갖는 $SiO_2$에 대한 O 원자 전자 오비탈의 부분 상태밀도(partial density of states; PDOS)와 O K-edge XRS 스펙트럼을 계산하였다. 또한, $CaCl_2$-구조를 갖는 $SiO_2$의 O 원자 PDOS의 전자-정공 효과의 적용 여부에 따른 차이를 비교하여, 원자핵 부근 전자구조 변화에 따른 PDOS의 피크 세기와 위치 변화가 크게 나타났다는 사실을 확인할 수 있었다. 또한 계산된 각 $SiO_2$ 구조의 O K-edge XRS 스펙트럼이 각 $SiO_2$ 구조에서 계산된 O 원자의 $p^*$ 오비탈의 PDOS 결과와 매우 유사한 형태를 갖고 있음을 확인하였다. 이는 O K-edge XRS 스펙트럼이 갖는 대부분의 특징적인 피크들이 O 원자의 점유 1s 오비탈에서 $2p^*$ 오비탈로의 전자전이에 기인하기 때문이다. 본 연구의 결과는 $SiO_2$에 대한 정확한 O K-edge XRS 스펙트럼을 계산하는데 있어 전자-정공 효과를 고려해야 한다는 사실을 보여준다. 또한, 실험적으로는 재현이 어려운 고압 환경에 존재하는 $CaCl_2$-구조를 갖는 $SiO_2$ (~63 GPa)에 대한 O K-edge XRS 스펙트럼 계산을 통해, 제1원리 계산이 고압상 물질의 물성 연구에 이용될 수 있다는 사실을 보여준다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.286-286
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• 2016

Hexagonal boron nitride (hBN) is a dielectric insulator with a two-dimensional (2D) layered structure. It is an appealing substrate dielectric for many applications due to its favorable properties, such as a wide band gap energy, chemical inertness and high thermal conductivity[1]. Furthermore, its remarkable mechanical strength renders few-layered hBN a flexible and transparent substrate, ideal for next-generation electronics and optoelectronics in applications. However, the difficulty of preparing high quality large-area hBN films has hindered their widespread use. Generally, large-area hBN layers prepared by chemical vapor deposition (CVD) usually exhibit polycrystalline structures with a typical average grain size of several microns. It has been reported that grain boundaries or dislocations in hBN can degrade its electronic or mechanical properties. Accordingly, large-area single crystalline hBN layers are desired to fully realize the potential advantages of hBN in device applications. In this presentation, we report the growth and transfer of centimeter-sized, nearly single crystal hexagonal boron nitride (hBN) few-layer films using Ni(111) single crystal substrates. The hBN films were grown on Ni(111) substrates using atmospheric pressure chemical vapor deposition (APCVD). The grown films were transferred to arbitrary substrates via an electrochemical delamination technique, and remaining Ni(111) substrates were repeatedly re-used. The crystallinity of the grown films from the atomic to centimeter scale was confirmed based on transmission electron microscopy (TEM) and reflection high energy electron diffraction (RHEED). Careful study of the growth parameters was also carried out. Moreover, various characterizations confirmed that the grown films exhibited typical characteristics of hexagonal boron nitride layers over the entire area. Our results suggest that hBN can be widely used in various applications where large-area, high quality, and single crystalline 2D insulating layers are required.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2000년도 추계학술발표회 초록집
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• pp.3-4
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• 2000

Many researchers are interested in the synthesis and characterization of carbon nitride and diamond-like carbon (DLq because they show excellent mechanical properties such as low friction and high wear resistance and excellent electrical properties such as controllable electical resistivity and good field electron emission. We have deposited amorphous carbon nitride (a-C:N) thin films and DLC thin films by shielded arc ion plating (SAIP) and evaluated the structural and tribological properties. The application of appropriate negative bias on substrates is effective to increase the film hardness and wear resistance. This paper reports on the deposition and tribological OLC films in relation to the substrate bias voltage (Vs). films are compared with those of the OLC films. A high purity sintered graphite target was mounted on a cathode as a carbon source. Nitrogen or argon was introduced into a deposition chamber through each mass flow controller. After the initiation of an arc plasma at 60 A and 1 Pa, the target surface was heated and evaporated by the plasma. Carbon atoms and clusters evaporated from the target were ionized partially and reacted with activated nitrogen species, and a carbon nitride film was deposited onto a Si (100) substrate when we used nitrogen as a reactant gas. The surface of the growing film also reacted with activated nitrogen species. Carbon macropartic1es (0.1 -100 maicro-m) evaporated from the target at the same time were not ionized and did not react fully with nitrogen species. These macroparticles interfered with the formation of the carbon nitride film. Therefore we set a shielding plate made of stainless steel between the target and the substrate to trap the macropartic1es. This shielding method is very effective to prepare smooth a-CN films. We, therefore, call this method "shielded arc ion plating (SAIP)". For the deposition of DLC films we used argon instead of nitrogen. Films of about 150 nm in thickness were deposited onto Si substrates. Their structures, chemical compositions and chemical bonding states were analyzed by using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and infrared spectroscopy. Hardness of the films was measured with a nanointender interfaced with an atomic force microscope (AFM). A Berkovich-type diamond tip whose radius was less than 100 nm was used for the measurement. A force-displacement curve of each film was measured at a peak load force of 250 maicro-N. Load, hold and unload times for each indentation were 2.5, 0 and 2.5 s, respectively. Hardness of each film was determined from five force-displacement curves. Wear resistance of the films was analyzed as follows. First, each film surface was scanned with the diamond tip at a constant load force of 20 maicro-N. The tip scanning was repeated 30 times in a 1 urn-square region with 512 lines at a scanning rate of 2 um/ s. After this tip-scanning, the film surface was observed in the AFM mode at a constant force of 5 maicro-N with the same Berkovich-type tip. The hardness of a-CN films was less dependent on Vs. The hardness of the film deposited at Vs=O V in a nitrogen plasma was about 10 GPa and almost similar to that of Si. It slightly increased to 12 - 15 GPa when a bias voltage of -100 - -500 V was applied to the substrate with showing its maximum at Vs=-300 V. The film deposited at Vs=O V was least wear resistant which was consistent with its lowest hardness. The biased films became more wear resistant. Particularly the film deposited at Vs=-300 V showed remarkable wear resistance. Its wear depth was too shallow to be measured with AFM. On the other hand, the DLC film, deposited at Vs=-l00 V in an argon plasma, whose hardness was 35 GPa was obviously worn under the same wear test conditions. The a-C:N films show higher wear resistance than DLC films and are useful for wear resistant coatings on various mechanical and electronic parts.nic parts.

• 한국자기학회지
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• 제18권6호
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• pp.211-216
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• 2008

Si이 체심입방구조(body centered cubic; bcc) Fe에 불순물로 포함된 경우에 Fe의 전자구조와 자성에 미치는 영향을 스핀-궤도 상호작용(spin-orbit coupling, SOC)을 고려한 제일원리방법을 통하여 연구하였다. Si 불순물의 효과를 기술하기 위하여 27개의 원자가 포함된 bcc Fe 초격자 구조를 고려하였다. 제일원리방법은 전전자 총퍼텐셜선형보강평면파(all-electron full-potential linearized augmented plane wave, FLAPW) 방법을 일반기울기 근사(generalized gradient approximation, GGA) 하에서 계산하였다. 스핀-궤도 상호작용은 스핀대각항 만을 고려한 이차변분방법을 이용하여 자체충족적으로 계산하였다. SOC를 고려하지 않은 강자성(ferromagnetic, FM) 상태의 경우 Si 불순물의 경우에는 $-0.143{\mu}B$의 스핀 자기모멘트가 계산되었으며, Fe 원자가 Si 불순물에서 멀어지면서 각각 $2.214{\mu}B$, $2.327{\mu}B$, 및 $2.354{\mu}B$의 값을 얻었다. 그러나, SOC를 고려한 경우 Si 불순물의 스핀 자기모멘트는 $-0.144{\mu}B$로 계산되어 SOC의 효과가 크지 않았으나, Fe 원자의 경우 각각 $2.189{\mu}B$, $2.310{\mu}B$, 및 $2.325{\mu}B$로 계산되어 SOC를 고려한 경우 스핀 자기모멘트 값이 줄어드는 것을 알 수 있었다. 총전하 및 스핀밀도의 비교와 상태밀도의 비교를 통하여 이러한 현상은 Si 불순물에 의한 영향을 가리는데 참여하는 Fe 원자의 $t_{2g}$ 전자 궤도의 변형의 효과로서 SOC를 고려할 때만 얻을 수 있다.