• Bulletin of the Korean Chemical Society
• /
• 제30권1호
• /
• pp.183-187
• /
• 2009

The structure of nano-crystalline $MnFe_2O_4$ was determined and refined with electron powder diffraction data employing the Rietveld refinement technique. A nano-crystalline sample (with average crystal size of about 10.9 nm) was characterized by selected area electron diffraction in an energy-filtering transmission electron microscope operated at 120 kV. All reflection intensities were extracted from a digitized image plate using the program ELD and then used in the course of structure refinements employing the program FULLPROF for the Rietveld analysis. The final structure was refined in space group Fd-3m (# 227) with lattice parameters a=8.3413(7) $\AA$. The reliability factors of the refinement are $R_F$=7.98% and $R_B$=3.55%. Comparison of crystallographic data between electron powder diffraction data and reference data resulted in better agreement with ICSD-56121 rather than with ICSD-28517 which assumes an initial structure model.

• Applied Microscopy
• /
• 제41권1호
• /
• pp.75-79
• /
• 2011

For quantitative analysis of nano-crystal structure, we reported the accuracy improvement method of lattice parameters measured from electron diffraction. For calculation of Au lattice parameters used as a standard crystal structure, it was considered two different acquisition methods (detector and enegy-filter) and three different calculation methods (conventional, least-square and regression fit). As a result, the measurement reliability could be enhanced by using CCD camera which gives higher performance, while energy-filtering did not affect the improvement the camera constant accuracy. Also, the accuracy of lattice parameters could be improved up to $10^{-4}$ order by regression fitting with correction formula. Finally, it is expected that the combination of regression fitting and intensity extraction from energy-filtered precession electron diffraction gives a solution of quantitative structure analysis for unknown nano-crystals.

• Applied Microscopy
• /
• 제47권4호
• /
• pp.223-225
• /
• 2017

Cryo-electron microscopy (cryo-EM) is arguably the most powerful tool used in structural biology. It is an important analytical technique that is used for gaining insight into the functional and molecular mechanisms of biomolecules involved in several physiological processes. Cryo-EM can be separated into the following three groups according to the analytical purposes and the features of the biological samples: cryo-electron tomography (cryo-ET), cryo-single-particle reconstruction, and cryo-electron crystallography. Cryo-tomography is a unique EM technique that is used to study intact biomolecular complexes within their original environments; it can provide mechanistic insights that are challenging for other EM-methods. However, the resolution of reconstructed three-dimensional (3D) models generated by cryo-ET is relatively low, while single-particle reconstruction can reproduce biomolecular structures having near-atomic resolution without the need for crystallization unless the samples are large (>200 kDa) and highly symmetrical. Cryo-electron crystallography is subdivided into the following two categories according to the types of samples: one category that deals with two-dimensional (2D) crystalline arrays and the other category that uses 3D crystals. These two categories of electron-crystallographic techniques use different diffraction data obtained from still diffraction and continuous-rotation diffraction. In this paper, we review crystal-based cryo-EM techniques and focus on the recently developed 3D electron-crystallographic technique called microcrystal-electron diffraction.

• Applied Microscopy
• /
• 제45권3호
• /
• pp.131-134
• /
• 2015

Here we show how by processing energy dispersive X-ray spectrometry (EDS) data obtained using highly sensitive, new generation EDS detectors in the AZtec LayerProbe software we can obtain data of sufficiently high quality to non-destructively measure the number of layers in two-dimensional (2D) $MoS_2$ and $MoS_2/WSe_2$ and thereby enable the characterization of working devices based on 2D materials. We compare the thickness measurements with EDS to results from atomic force microscopy measurements. We also show how we can use electron backscatter diffraction (EBSD) to address fabrication challenges of 2D materials. Results from EBSD analysis of individual flakes of exfoliated $MoS_2$ obtained using the Nordlys Nano detector are shown to aid a better understanding of the exfoliation process which is still widely used to produce 2D materials for research purposes.

• Applied Microscopy
• /
• 제33권3호
• /
• pp.195-204
• /
• 2003

Imaging plate에 기록된 전자회절 자료의 면간 거리 분석과 상동정시 나타나는 오차 요인들을 고찰하고 실험적인 보정방법을 도출하였다. 각각의 회절방향에 대한 radial intensity distribution plot과 실험적으로 도출된 면간 거리 보정식에 의해 전자회절 자료의 디지털 이미지에서 면간 거리 측정오차는 약 0.5%로 낮아짐을 알 수 있었다. Al 표준시료를 이용하여 imaging plate에 기록된 전자회절 자료의 면간 거리 편차 경향을 분석한 후 [001] gibbsite 시편에 동일한 실험적 보정을 수행하여 120분간의 전자빔 조사로부터 형성된 여러 전이 상들에 대한 면간 거리 측정 및 상 동정을 보다 정밀히 수행할 수 있었다. 그 결과, gibbsite로부터 형성된 주요 전이상들은 ${\chi}$-알루미나, ${\gamma}$-알루미나, ${\sigma}$-알루미나로 구성됨을 명확하게 동정할 수 있었다.

• Applied Microscopy
• /
• 제35권4호
• /
• pp.1-9
• /
• 2005

이 논문에서 Al-Cu-Mg 합금의 미세 석출 입자의 S-상 ($Al_2CuMg$) 결정구조에 대해 전자회절실험에 의한 포괄적인 연구 결과가 보고 되어 있다. 이 실험에는 한 S-상 입자를 포함하는 최소 영역의 일정 zone축의 회절패턴(SAED) 관찰과 이에 대응되는 운동학적 이론을 기초로 한 패턴의 시물레이션과의 비교 분석, 그리고 관측된 회절 패턴 필름으로부터 각 Bragg회절 점의 강도의 정량적 데이터 추출과 운동학적 및 동역학적 회절 강도 계산과의 비교 검토의 과정을 포함하고 있다. 이러한 연구의 한 결과 S-상의 결정구조는 일찍이 X-ray 방법으로부터 얻은 PW 모델결정(Perlitz and Westgren, 1943)과 일치함을 보여주고 있고, HREM 방법에 의해 새로이 구한 RaVel (Radmilovic et al., 1999) 모델과는 전혀 맞지않음이 판명되었다.

• Applied Microscopy
• /
• 제45권4호
• /
• pp.218-224
• /
• 2015

A technical overview on the various sample preparation methods for electron backscattered diffraction (EBSD) analysis is carried out. The mechanical polishing with colloidal silica finish, electro-chemical polishing, dual layer coating and ion beam milling are introduced for the common sample preparation methods for EBSD observation and some issues that are frequently neglected by the common EBSD users but should be considered to get a reliable EBSD data are discussed. This overview would be especially helpful to the people who know what EBSD technique is but do not get a reliable EBSD data because of difficulties in sample preparation.

• 대한화학회지
• /
• 제48권4호
• /
• pp.339-350
• /
• 2004

피코초 시간분해능 전자 회절 분광법(TRED)을 이용하여 $CClF_3$ 분자의평형 구조를 연구하였다. 이 분광법의 분해능은 전자파의 선폭에 의하여 결정된다. 본 연구 방법에 의하여 결정된 $CClF_3$ 분자의 결합 길이들을 고전적인 실시간 전자회절 분광법(GED/RT)에 의하여 보고된 결과들과 비교하였다. GED/RT 방법에 의하여 결정된 C-F 결합 길이와 C-Cl 결합 길이는 각각 132.00(2) pm, 175.20(3) pm이고, TRED 방법에 의하여 결정된 C-F, C-Cl 결합 길이는 각각 132.23(13) pm, 177.23(19) pm 로써 이 두 실험 방법에 의하여 결정된 분자 결합 길이는 좋은 일치성을 보여준다.

• Bulletin of the Korean Chemical Society
• /
• 제34권3호
• /
• pp.788-792
• /
• 2013

A shortcoming of using transmission electron microscopy (TEM) for structural analysis via electron diffraction is the relatively large error of the measurements as compared to X-ray diffraction. To reduce these errors, various internal standard methods from earlier studies have been widely used. We developed a new device to facilitate the application of internal standard methods in preparation of TEM grids used for nanopowder analysis. Through the application of a partial mask on the TEM grid, both the internal standards and the research materials can be loaded on the same grid. Through this process, we conducted a TEM analysis that compared synthetic hydroxyapatite (HAp) nanopowder to bone apatite from a bovine femur. We determined that the accuracy of the d-spacing measurements of the HAp and bone powders could be improved to better than 1% after statistical treatments of the experimental data. By applying a quarter mask, we loaded four different nanoparticles on a single TEM grid, with one section designated for the internal standard.

• Bulletin of the Korean Chemical Society
• /
• 제33권2호
• /
• pp.505-510
• /
• 2012

Cobalt oxide nanostructure materials have been prepared by adding several concentrations of spectator Ni ions in solution, and analyzed by electron microscopy, X-day diffraction, calorimetry/thermogravimetric analysis, UV-vis absorption, Raman, and X-ray photoelectron spectroscopy. The electron microscopy results show that the morphology of the nanostructures is dramatically altered by changing the concentration of spectator ions. The bulk XRD patterns of $350^{\circ}C$-annealed samples indicate that the structure of the cobalt oxide is all of cubic Fd-3m $Co_3O_4$, and show that the major XRD peaks shift slightly with the concentration of Ni ions. In Raman spectroscopy, we can confirm the XRD data through a more obvious change in peak position, broadness, and intensity. For the un-sputtered samples in the XPS measurement process, the XPS peaks of Co 2p and O 1s for the samples prepared without Ni ions exhibit higher binding energies than those for the sample prepared with Ni ions. Upon $Ar^+$ ion sputtering, we found $Co_3O_4$ reduces to CoO, on the basis of XPS data. Our study could be further applied to controlling morphology and surface oxidation state.