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Synthesis of freestanding HfO2 nanostructures.

Kidd T, O'Shea A, Boyle K, Wallace J, Strauss L - Nanoscale Res Lett (2011)

Bottom Line: This simple process resulted in the formation of nanometer scale crystallites of HfO2.The thinnest sheets appeared transparent when viewed in a scanning electron microscope.These results present new routes to create freestanding nanostructured hafnium dioxide.PACS: 81.07.-b, 61.46.Hk, 68.37.Hk.

View Article: PubMed Central - HTML - PubMed

Affiliation: Physics Department, University of Northern Iowa, Cedar Falls, IA 50614, USA. tim.kidd@uni.edu.

ABSTRACT
Two new methods for synthesizing nanostructured HfO2 have been developed. The first method entails exposing HfTe2 powders to air. This simple process resulted in the formation of nanometer scale crystallites of HfO2. The second method involved a two-step heating process by which macroscopic, freestanding nanosheets of HfO2 were formed as a byproduct during the synthesis of HfTe2. These highly two-dimensional sheets had side lengths measuring up to several millimeters and were stable enough to be manipulated with tweezers and other instruments. The thickness of the sheets ranged from a few to a few hundred nanometers. The thinnest sheets appeared transparent when viewed in a scanning electron microscope. It was found that the presence of Mn enhanced the formation of HfO2 by exposure to ambient conditions and was necessary for the formation of the large scale nanosheets. These results present new routes to create freestanding nanostructured hafnium dioxide.PACS: 81.07.-b, 61.46.Hk, 68.37.Hk.

No MeSH data available.


Related in: MedlinePlus

Model and measured XRD pattern for aged powder sample. The model is composed of a mixture of "macroscopic" (>50 nm) and nanometer scale HfO2 particles. The marked peaks indicate MnTe impurities not accounted for in the model.
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Figure 6: Model and measured XRD pattern for aged powder sample. The model is composed of a mixture of "macroscopic" (>50 nm) and nanometer scale HfO2 particles. The marked peaks indicate MnTe impurities not accounted for in the model.

Mentions: Another interesting feature of the powder XRD pattern is the appearance of the background in the spectra. It appears as if there are a large number of extremely broad states that underlie the sharp Bragg peaks in the spectrum of the powder sample. To better understand this phenomenon, the powder was left exposed to air for some time, which resulted in all traces of the HfTe2 disappearing from the sample. The XRD pattern of this aged powder is shown in Figure 6. The only peaks remaining, aside from the anomalous background, can be attributed to HfO2 and the MnTe impurity phase. The model is actually a simple mixture of a simulated XRD pattern composed of 5% "macroscopic" and 95% nanometer scale HfO2 particles with a mean diameter of 2 nm. In this case, "macroscopic" means only that the material is sufficiently large (>50 nm) so that the peaks are not overly broadened as compared to the sharp features in the data. The model is quite simple, ignoring all broadening effects aside from particle size. The features are essentially too broad for other parameters, such as strain, to be of much significance. The model does not include any attempts to actually fit the data by introducing background effects, orientation, or any other parameters. Instead, it is meant to show that the major features of the data can be well reproduced by assuming the powder a mixture composed mainly of randomly oriented HfO2 particles with nanometer scale sizes along with some larger HfO2 particles. The only features that are not accounted for in the model are those associated with MnTe impurities. The impurities are the source of sharp peaks near 36.7°, 43.7°, and 48° as well as the enhancement of the HfO2 peak near 28.3°. The success of this model supports the SEM findings that the freestanding HfO2 sheets are extremely anisotropic materials with nanometer scale thicknesses.


Synthesis of freestanding HfO2 nanostructures.

Kidd T, O'Shea A, Boyle K, Wallace J, Strauss L - Nanoscale Res Lett (2011)

Model and measured XRD pattern for aged powder sample. The model is composed of a mixture of "macroscopic" (>50 nm) and nanometer scale HfO2 particles. The marked peaks indicate MnTe impurities not accounted for in the model.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211360&req=5

Figure 6: Model and measured XRD pattern for aged powder sample. The model is composed of a mixture of "macroscopic" (>50 nm) and nanometer scale HfO2 particles. The marked peaks indicate MnTe impurities not accounted for in the model.
Mentions: Another interesting feature of the powder XRD pattern is the appearance of the background in the spectra. It appears as if there are a large number of extremely broad states that underlie the sharp Bragg peaks in the spectrum of the powder sample. To better understand this phenomenon, the powder was left exposed to air for some time, which resulted in all traces of the HfTe2 disappearing from the sample. The XRD pattern of this aged powder is shown in Figure 6. The only peaks remaining, aside from the anomalous background, can be attributed to HfO2 and the MnTe impurity phase. The model is actually a simple mixture of a simulated XRD pattern composed of 5% "macroscopic" and 95% nanometer scale HfO2 particles with a mean diameter of 2 nm. In this case, "macroscopic" means only that the material is sufficiently large (>50 nm) so that the peaks are not overly broadened as compared to the sharp features in the data. The model is quite simple, ignoring all broadening effects aside from particle size. The features are essentially too broad for other parameters, such as strain, to be of much significance. The model does not include any attempts to actually fit the data by introducing background effects, orientation, or any other parameters. Instead, it is meant to show that the major features of the data can be well reproduced by assuming the powder a mixture composed mainly of randomly oriented HfO2 particles with nanometer scale sizes along with some larger HfO2 particles. The only features that are not accounted for in the model are those associated with MnTe impurities. The impurities are the source of sharp peaks near 36.7°, 43.7°, and 48° as well as the enhancement of the HfO2 peak near 28.3°. The success of this model supports the SEM findings that the freestanding HfO2 sheets are extremely anisotropic materials with nanometer scale thicknesses.

Bottom Line: This simple process resulted in the formation of nanometer scale crystallites of HfO2.The thinnest sheets appeared transparent when viewed in a scanning electron microscope.These results present new routes to create freestanding nanostructured hafnium dioxide.PACS: 81.07.-b, 61.46.Hk, 68.37.Hk.

View Article: PubMed Central - HTML - PubMed

Affiliation: Physics Department, University of Northern Iowa, Cedar Falls, IA 50614, USA. tim.kidd@uni.edu.

ABSTRACT
Two new methods for synthesizing nanostructured HfO2 have been developed. The first method entails exposing HfTe2 powders to air. This simple process resulted in the formation of nanometer scale crystallites of HfO2. The second method involved a two-step heating process by which macroscopic, freestanding nanosheets of HfO2 were formed as a byproduct during the synthesis of HfTe2. These highly two-dimensional sheets had side lengths measuring up to several millimeters and were stable enough to be manipulated with tweezers and other instruments. The thickness of the sheets ranged from a few to a few hundred nanometers. The thinnest sheets appeared transparent when viewed in a scanning electron microscope. It was found that the presence of Mn enhanced the formation of HfO2 by exposure to ambient conditions and was necessary for the formation of the large scale nanosheets. These results present new routes to create freestanding nanostructured hafnium dioxide.PACS: 81.07.-b, 61.46.Hk, 68.37.Hk.

No MeSH data available.


Related in: MedlinePlus