Nanomaterial electronic structure investigation by valence electron energy loss spectroscopy—An example of doped ZnO nanowires

Wang, Juan; Li, Quan; Ronning, Carsten; Stichtenoth, D.; Müller, Sven; Tang, Dinghao

doi:10.1016/j.micron.2007.10.015

Cited by 6 publications

(5 citation statements)

References 25 publications

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“…The conduction band onset can be determined from a VEEL spectrum upon careful subtraction of the ZLP and by using different deconvolution routines. ,, Performing a Fourier-log or Fourier-ratio deconvolution of noisy data can introduce artifacts and was thus not applied in the present work. The tails of the ZLP are noisy in our data, and therefore subtracting a spectrum acquired in vacuum as an approximation to the ZLP could be counterproductive.…”

Section: Resultsmentioning

confidence: 99%

Band Gap Extraction from Individual Two-Dimensional Perovskite Nanosheets Using Valence Electron Energy Loss Spectroscopy

et al. 2016

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Rapid progress in the synthesis of nanostructures with tailor-made morphologies necessitates adequate analytical tools to unravel their physical properties. In our study, we investigate, on the nanometer scale, the band gap of individual [TBA x H1–x ]+[Ca2Nb3O10]− nanosheets obtained through intercalation–exfoliation of the layered bulk phase KCa2Nb3O10 with tetra-n-butylammonium hydroxide (TBAOH) using valence electron energy loss spectroscopy (VEELS) in the scanning transmission electron microscope (STEM). The nanosheets consist of an anionically charged perovskite layer with cationic organic ligands surrounding it. Because of the hybrid nature, a careful acquisition and analysis protocol is required since the nanosheets disintegrate easily under electron beam irradiation. The VEELS data reveal a fundamental band gap of an individual freely suspended perovskite nanosheet to be 2.9 ± 0.2 eV and optically allowed transitions above 3.8 ± 0.2 eV (optical band gap). The spatial resolution of the measurements is about 9 nm, taking into account 50% of the excitations when illuminating with an incident electron beam of 1 nm diameter. Our investigations reveal that the band gap of an individual nanosheet is not changed significantly compared to the bulk phase, which is confirmed by UV–vis data. This is rationalized by the quasi-2D electronic structure of the bulk material being preserved upon delamination.

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Section: Resultsmentioning

confidence: 99%

Band Gap Extraction from Individual Two-Dimensional Perovskite Nanosheets Using Valence Electron Energy Loss Spectroscopy

et al. 2016

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“…This solely relies on the improvement of energy-resolution ( Figure 4), which now can be achieved on an advanced EM. 148 The in situ TEM can also reveal some dynamic structural information on catalysts in gas or liquid environments. 149,150 Dynamic Behaviors and Catalytic Data.…”

Section: Advanced Information That a Modern Tem/stem Can Providementioning

confidence: 99%

“…Synchrotron radiation-based methods are able to explore the fine chemical and structural variation within solid catalysts, also under reaction conditions. , The advanced electron microscope equipped with aberration corrector and monochromator can provide some equivalent information. This solely relies on the improvement of energy-resolution (Figure ), which now can be achieved on an advanced EM . The in situ TEM can also reveal some dynamic structural information on catalysts in gas or liquid environments. , …”

Section: Role Of Electron Microscopy For the Characterization Of Soli...mentioning

confidence: 99%

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Electron Microscopy of Solid Catalysts—Transforming from a Challenge to a Toolbox

2015

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“…In a thin film of zinc oxide (ZnO) with embedded Au nanodots [2], the material properties are anisotropic due to the ZnO wurtzite crystal structure and vary in three-dimensions as dictated by changes in the film's composition and crystallographic orientation. Recently, researchers have used EELS spectroscopy to explore effects of size and crystal orientation on the electronic structure of ZnO nanowires and nanobelts [3][4][5]. Crystallographic effects were reported as systematic differences in low-loss and core-loss structure when spectra were obtained with the electron beam parallel and perpendicular to the c-axis of the ZnO [5].…”

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4D STEM/EELS Characterization of Au Nanodots in a ZnO Thin Film

2008

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Nanostructured thin films can be engineered during synthesis [1-2] to yield unique structure-property relationships. In a thin film of zinc oxide (ZnO) with embedded Au nanodots [2], the material properties are anisotropic due to the ZnO wurtzite crystal structure and vary in three-dimensions as dictated by changes in the film's composition and crystallographic orientation. Recently, researchers have used EELS spectroscopy to explore effects of size and crystal orientation on the electronic structure of ZnO nanowires and nanobelts [3][4][5]. Crystallographic effects were reported as systematic differences in low-loss and core-loss structure when spectra were obtained with the electron beam parallel and perpendicular to the c-axis of the ZnO [5]. The authors also show that these differences vary off-axis but do not explore this variation systematically. In this study we used a combination of FIB nanofabrication and STEM/EELS nanoanalysis to determine morphology and arrangement of the Au nanodots in the ZnO film and collect data on optoelectronic properties of this nanomaterial composite. We report the VEELS spectra of ZnO as mapped in three-dimensions by acquiring a series of STEM/EELS spectrum images at regular sampling intervals during a 360° rotation.Nanofabrication with a FIB was used to prepare a pillar of ZnO with final dimensions measuring ~5um in length and ~140nm thickness. Imaging and analysis was performed in a 200kV Hitachi HD-2300A STEM equipped with a Gatan Enfina EELS spectrometer. HAADF and phase contrast imaging were used to document the Au nanodot size, arrangement and morphology. Direct threedimensional probing of the low-loss electronic structure was made possible by utilizing the STEM's high probe-current and an improved EELS spectrum detection speed to achieve read-out speeds of greater than 100 spectra/sec [6]. Gold nanodots embedded in the ZnO thin film matrix, with diameters on the order of ~30nm, are seen as regions of bright contrast in the cross section micrograph of FIG. 1A. The pillar for 360˚ rotation was nanofabricated from the approximate region indicated by the red box in FIG. 1B and is shown at low magnification (FIG. 2A) and higher magnifications (FIG. 2B and 2C) to better resolve the Au nanodots. The 360˚ image data was tiled together in sequential order to make movies allowing simple interpretation of Au nanodot arrangement in the thin film. The systematic variation in EELS low-loss spectra as a function of rotation angle is shown in FIG 3. The spectra taken with the beam on and near the film's c-axis shows a small peak at 13eV labeled "B" in the figure which dissappears when the beam is aligned close to the film's a-axis. The origin of this feature is still under investigation and is believed to be either due to surface plasmon excitation or the anisotropic properties of the nanomaterial. Diffraction patterns obtained during the same analysis (also shown in FIG. 3) clearly illustrate the ability of this 4D STEM-EELS technique to probe the same sample with the beam both parall...

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Nanomaterial electronic structure investigation by valence electron energy loss spectroscopy—An example of doped ZnO nanowires

Cited by 6 publications

References 25 publications

Band Gap Extraction from Individual Two-Dimensional Perovskite Nanosheets Using Valence Electron Energy Loss Spectroscopy

Band Gap Extraction from Individual Two-Dimensional Perovskite Nanosheets Using Valence Electron Energy Loss Spectroscopy

Electron Microscopy of Solid Catalysts—Transforming from a Challenge to a Toolbox

4D STEM/EELS Characterization of Au Nanodots in a ZnO Thin Film

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