13 research outputs found
Characterization of Fe-N nanocrystals and nitrogen–containing inclusions in (Ga,Fe)N thin films using transmission electron microscopy
Nanometric inclusions filled with nitrogen, located adjacent to FenN (nÂĽ3 or 4) nanocrystals
within (Ga,Fe)N layers, are identified and characterized using scanning transmission electron
microscopy (STEM) and electron energy-loss spectroscopy (EELS). High-resolution STEM images reveal a truncation of the Fe-N nanocrystals at their boundaries with the nitrogen-containing inclusions. A controlled electron beam hole drilling experiment is used to release nitrogen gas from an inclusion in situ in the electron microscope. The density of nitrogen in an individual inclusion is measured to be 1.460.3 g/cm3. These observations provide an explanation for the location of surplus nitrogen in the (Ga,Fe)N layers, which is liberated by the nucleation of FenN (n>1) nanocrystals during growth
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KLaF4 nanocrystallisation in oxyfluoride glass-ceramics
Nanocrystallisation of the cubic and hexagonal polymorphs of KLaF 4 in a 70SiO2-7Al2O3-16K 2O-7LaF3 (mol%) glass has been achieved by heat treatment above the glass transition temperature. For treatment at 580°C, only the cubic structure crystallises, with a maximum crystallite size of ~9 nm. At higher temperatures, crystallisation of the hexagonal structure also takes place. The crystallisation process has been analysed using several thermal and structural techniques and is revealed to occur from a constant number of nuclei. The formation of a viscous barrier which inhibits further crystal growth and limits the crystal size to the nanometric range is observed. The title materials doped with lanthanide ions may be good candidates for optical applications
KLaF4 nanocrystallisation in oxyfluoride glass-ceramics
Nanocrystallisation of the cubic and hexagonal polymorphs of KLaF 4 in a 70SiO2-7Al2O3-16K 2O-7LaF3 (mol%) glass has been achieved by heat treatment above the glass transition temperature. For treatment at 580°C, only the cubic structure crystallises, with a maximum crystallite size of ~9 nm. At higher temperatures, crystallisation of the hexagonal structure also takes place. The crystallisation process has been analysed using several thermal and structural techniques and is revealed to occur from a constant number of nuclei. The formation of a viscous barrier which inhibits further crystal growth and limits the crystal size to the nanometric range is observed. The title materials doped with lanthanide ions may be good candidates for optical applications
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Time, Energy, and Spatially Resolved TEM Investigations of Defects in InGaN
A novel sample preparation technique is reported to fabricate electron transparent samples from devices utilizing a FIB process with a successive wet etching step. The high quality of the obtained samples allows for band gap--and chemical composition measurements of In{sub x}Ga{sub 1-x}N quantum wells where electron beam induced damage can be controlled and shown to be negligible. The results reveal indium enrichment in nanoclusters and defects that cause fluctuations of the band gap energy and can be measured by low loss Electron Energy Spectroscopy with nm resolution. Comparing our time, energy, and spatially resolved measurements of band gap energies, chemical composition, and their related fluctuations with literature data, we find quantitative agreement if the band gap energy of InN is 1.5-2 eV
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On the feasibility to investigate point defects by advanced electron microscopy
Transmission Electron Microscopy evolves rapidly as a primary tool to investigate nano structures on a truly atomic level. Its resolution reaches into the sub Angstrom region by now. Together with a better correction of lens aberrations, sensitivities are drastically enhanced. Utilizing advanced electron microscopes, it is feasible to promote experiments that aim to detect single atoms. This enables local investigations of non-stoichiometry. This paper reviews the current state-of-the-art
Achromatic Elemental Mapping Beyond the Nanoscale in the Transmission Electron Microscope
C1 - Journal Articles RefereedNewly developed achromatic electron optics allows the use of wide energy windows and makes feasible energy-filtered transmission electron microscopy (EFTEM) at atomic resolution. In this Letter we present EFTEM images formed using electrons that have undergone a silicon L(2,3) core-shell energy loss, exhibiting a resolution in EFTEM of 1.35 Ă…. This permits elemental mapping beyond the nanoscale provided that quantum mechanical calculations from first principles are done in tandem with the experiment to understand the physical information encoded in the images