Limits...
Resolving transitions in the mesoscale domain configuration in VO2 using laser speckle pattern analysis.

Seal K, Sharoni A, Messman JM, Lokitz BS, Shaw RW, Schuller IK, Snijders PC, Ward TZ - Sci Rep (2014)

Bottom Line: The configuration and evolution of coexisting mesoscopic domains with contrasting material properties are critical in creating novel functionality through emergent physical properties.However, current approaches that map the domain structure involve either spatially resolved but protracted scanning probe experiments without real time information on the domain evolution, or time resolved spectroscopic experiments lacking domain-scale spatial resolution.Our straightforward analysis of laser speckle patterns across the first order phase transition of VO2 can be generalized to other systems with large scale phase separation and has potential as a powerful method with both spatial and temporal resolution to study phase separation in complex materials.

View Article: PubMed Central - PubMed

Affiliation: 1] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA [2] Department of Physics &Astronomy, University of Tennessee, Knoxville, TN 37996, USA.

ABSTRACT
The configuration and evolution of coexisting mesoscopic domains with contrasting material properties are critical in creating novel functionality through emergent physical properties. However, current approaches that map the domain structure involve either spatially resolved but protracted scanning probe experiments without real time information on the domain evolution, or time resolved spectroscopic experiments lacking domain-scale spatial resolution. We demonstrate an elegant experimental technique that bridges these local and global methods, giving access to mesoscale information on domain formation and evolution at time scales orders of magnitude faster than current spatially resolved approaches. Our straightforward analysis of laser speckle patterns across the first order phase transition of VO2 can be generalized to other systems with large scale phase separation and has potential as a powerful method with both spatial and temporal resolution to study phase separation in complex materials.

No MeSH data available.


Related in: MedlinePlus

(a) Normalized variance and (b) normalized mean intensity of intensity plotted for three illumination wavelengths, 488 nm, 633 nm and 800 nm for increasing temperature. Plots focus on region near the TMIT showing the variation of the transition point. The normalization was implemented by setting the maximum and minimum value of the variance or mean intensity observed in the full temperature range to 1 and 0, respectively. Color bars indicate temperature range of observed transition for each wavelength. (c) Surface roughness ratio σΔ for the three wavelengths showing a peak at the transition point.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4151099&req=5

f3: (a) Normalized variance and (b) normalized mean intensity of intensity plotted for three illumination wavelengths, 488 nm, 633 nm and 800 nm for increasing temperature. Plots focus on region near the TMIT showing the variation of the transition point. The normalization was implemented by setting the maximum and minimum value of the variance or mean intensity observed in the full temperature range to 1 and 0, respectively. Color bars indicate temperature range of observed transition for each wavelength. (c) Surface roughness ratio σΔ for the three wavelengths showing a peak at the transition point.

Mentions: Importantly, the speckle pattern allows us to glean information about the configuration of metallic and insulating domains in the sample. This is clear from a number of observations. First, across the MIT, the variance decreases by 2%, 4%, and 15% under illuminations of 488 nm, 633 nm, and 800 nm, respectively. This increase is produced by the higher sensitivity of our experiment to surface dielectric features having length scales on the order of the wavelength used. The larger change in variance for longer wavelengths therefore indicates that the temperature dependent domain configurations on the VO2 surface are dominated by correlation lengths which are closer in magnitude to the longer laser wavelengths. Second, the increased width of the transition region at 488 nm as compared to the longer wavelengths (Fig. 2) indicates that the smaller correlation lengths in the insulating and metallic domains making up the dielectric landscape exist in a larger temperature range around the transition, while larger sized domains are dominant in the middle of the transition, consistent with domain nucleation and growth914. Note that this persistence to higher temperatures also confirms that the low photon flux used in this experiment does not cause a photon-induced decrease in transition temperature as it would then be expected that the transition would be completed at progressively lower temperatures for decreasing wavelengths. Third, a comparison of the temperature dependent MI of the speckle pattern intensity in Fig. 3, demonstrates that the onset of the transition in the MI increases whereas its transition width decreases with increasing wavelength.


Resolving transitions in the mesoscale domain configuration in VO2 using laser speckle pattern analysis.

Seal K, Sharoni A, Messman JM, Lokitz BS, Shaw RW, Schuller IK, Snijders PC, Ward TZ - Sci Rep (2014)

(a) Normalized variance and (b) normalized mean intensity of intensity plotted for three illumination wavelengths, 488 nm, 633 nm and 800 nm for increasing temperature. Plots focus on region near the TMIT showing the variation of the transition point. The normalization was implemented by setting the maximum and minimum value of the variance or mean intensity observed in the full temperature range to 1 and 0, respectively. Color bars indicate temperature range of observed transition for each wavelength. (c) Surface roughness ratio σΔ for the three wavelengths showing a peak at the transition point.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4151099&req=5

f3: (a) Normalized variance and (b) normalized mean intensity of intensity plotted for three illumination wavelengths, 488 nm, 633 nm and 800 nm for increasing temperature. Plots focus on region near the TMIT showing the variation of the transition point. The normalization was implemented by setting the maximum and minimum value of the variance or mean intensity observed in the full temperature range to 1 and 0, respectively. Color bars indicate temperature range of observed transition for each wavelength. (c) Surface roughness ratio σΔ for the three wavelengths showing a peak at the transition point.
Mentions: Importantly, the speckle pattern allows us to glean information about the configuration of metallic and insulating domains in the sample. This is clear from a number of observations. First, across the MIT, the variance decreases by 2%, 4%, and 15% under illuminations of 488 nm, 633 nm, and 800 nm, respectively. This increase is produced by the higher sensitivity of our experiment to surface dielectric features having length scales on the order of the wavelength used. The larger change in variance for longer wavelengths therefore indicates that the temperature dependent domain configurations on the VO2 surface are dominated by correlation lengths which are closer in magnitude to the longer laser wavelengths. Second, the increased width of the transition region at 488 nm as compared to the longer wavelengths (Fig. 2) indicates that the smaller correlation lengths in the insulating and metallic domains making up the dielectric landscape exist in a larger temperature range around the transition, while larger sized domains are dominant in the middle of the transition, consistent with domain nucleation and growth914. Note that this persistence to higher temperatures also confirms that the low photon flux used in this experiment does not cause a photon-induced decrease in transition temperature as it would then be expected that the transition would be completed at progressively lower temperatures for decreasing wavelengths. Third, a comparison of the temperature dependent MI of the speckle pattern intensity in Fig. 3, demonstrates that the onset of the transition in the MI increases whereas its transition width decreases with increasing wavelength.

Bottom Line: The configuration and evolution of coexisting mesoscopic domains with contrasting material properties are critical in creating novel functionality through emergent physical properties.However, current approaches that map the domain structure involve either spatially resolved but protracted scanning probe experiments without real time information on the domain evolution, or time resolved spectroscopic experiments lacking domain-scale spatial resolution.Our straightforward analysis of laser speckle patterns across the first order phase transition of VO2 can be generalized to other systems with large scale phase separation and has potential as a powerful method with both spatial and temporal resolution to study phase separation in complex materials.

View Article: PubMed Central - PubMed

Affiliation: 1] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA [2] Department of Physics &Astronomy, University of Tennessee, Knoxville, TN 37996, USA.

ABSTRACT
The configuration and evolution of coexisting mesoscopic domains with contrasting material properties are critical in creating novel functionality through emergent physical properties. However, current approaches that map the domain structure involve either spatially resolved but protracted scanning probe experiments without real time information on the domain evolution, or time resolved spectroscopic experiments lacking domain-scale spatial resolution. We demonstrate an elegant experimental technique that bridges these local and global methods, giving access to mesoscale information on domain formation and evolution at time scales orders of magnitude faster than current spatially resolved approaches. Our straightforward analysis of laser speckle patterns across the first order phase transition of VO2 can be generalized to other systems with large scale phase separation and has potential as a powerful method with both spatial and temporal resolution to study phase separation in complex materials.

No MeSH data available.


Related in: MedlinePlus