Limits...
Growth mechanism and magnon excitation in NiO nanowalls.

Gandhi AC, Huang CY, Yang CC, Chan TS, Cheng CL, Ma YR, Wu SY - Nanoscale Res Lett (2011)

Bottom Line: The nanosized effects of short-range multimagnon excitation behavior and short-circuit diffusion in NiO nanowalls synthesized using the Ni grid thermal treatment method were observed.This study shows that short spin correlation leads to an exponential dependence of the growth temperatures and the existence of nickel vacancies during the magnon excitation.Four-magnon configurations were determined from the scattering factor, revealing a lowest state and monotonic change with the growth temperature.PACS: 75.47.Lx; 61.82.Rx; 75.50.Tt; 74.25.nd; 72.10.Di.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, National Dong Hwa University, Hualien 97401, Taiwan. sywu@mail.ndhu.edu.tw.

ABSTRACT
The nanosized effects of short-range multimagnon excitation behavior and short-circuit diffusion in NiO nanowalls synthesized using the Ni grid thermal treatment method were observed. The energy dispersive spectroscopy mapping technique was used to characterize the growth mechanism, and confocal Raman scattering was used to probe the antiferromagnetic exchange energy J2 between next-nearest-neighboring Ni ions in NiO nanowalls at various growth temperatures below the Neel temperature. This study shows that short spin correlation leads to an exponential dependence of the growth temperatures and the existence of nickel vacancies during the magnon excitation. Four-magnon configurations were determined from the scattering factor, revealing a lowest state and monotonic change with the growth temperature.PACS: 75.47.Lx; 61.82.Rx; 75.50.Tt; 74.25.nd; 72.10.Di.

No MeSH data available.


Related in: MedlinePlus

SEM images of the NiO nanowalls. (a-e) SEM images of the NiO nanowalls with various mean widths <d > which were synthesized at various annealing temperatures. (f) Distributions of mean nanowall width obtained from a portion of the SEM image of NiO nanowalls. The solid lines represent the fitting curves assuming the log-normal function.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3211999&req=5

Figure 1: SEM images of the NiO nanowalls. (a-e) SEM images of the NiO nanowalls with various mean widths <d > which were synthesized at various annealing temperatures. (f) Distributions of mean nanowall width obtained from a portion of the SEM image of NiO nanowalls. The solid lines represent the fitting curves assuming the log-normal function.

Mentions: A series of template-free NiO nanowalls with various grain sizes were fabricated. The samples were prepared by a process where a pure Ni grid (200 mesh) was placed in a ceramic boat inside a quartz tube, which was then evacuated to about 10-3 Torr using a mechanical pump. The samples were then heated in a tube furnace at about 200°C for 2 h for degassing before being heated to various temperatures ranging from 400°C to 800°C for 3 h in a mixed argon (100 sccm) and oxygen (10 sccm) gas. The morphology and structures of the prepared samples were characterized using field-emission scanning electron microscopy (JEOL JSM-6500F, JEOL Ltd., Japan). For the SEM analysis, some of the nanowalls were transferred by gently sliding them onto a commercially available cooper grid with a carbon film. The SEM images in Figure 1a, b, c, d, e shows the surface morphology of NiO nanowalls with various sizes synthesized at TA = 800°C, 700°C, 600°C, 500°C, and 400°C, respectively. It can be seen that the NiO nanowalls form homogeneously on the nickel grid substrate. The mean sizes <d > of the nanowalls were calculated and defined from their width and grain, as shown in Figure 1a, b, c, d, e, respectively. The distribution of the mean width <d > of the NiO nanowalls as seen in Figure 1f is quite asymmetric, assuming a log-normal function distribution. The solid curves represent the fitting curve assuming log-normal distribution function. The log-normal distribution is defined as follows: where <d > is the mean value and σ is the standard deviation of the function. The mean NiO nanowall widths <d >, as determined from the SEM images and described by the fit of the log-normal function, were approximately 32(1), 75(2), 175(4), 239(8), and 416(18) nm, respectively. The corresponding fitting parameters are presented in Table 1. The value of the standard deviation of fitted function which is less than 0.5 for all annealing temperatures indicates that the distribution is confined to a limited range. There is a surprising contrast in sample color. The resultant NiO nanowalls can be either "black" (TA = 400°C and 500°C) or "green" (TA = 600°C-800°C), containing nickel vacancies, depending on the growth temperature and oxygen supplementation given various concentrations of nickel vacancies.


Growth mechanism and magnon excitation in NiO nanowalls.

Gandhi AC, Huang CY, Yang CC, Chan TS, Cheng CL, Ma YR, Wu SY - Nanoscale Res Lett (2011)

SEM images of the NiO nanowalls. (a-e) SEM images of the NiO nanowalls with various mean widths <d > which were synthesized at various annealing temperatures. (f) Distributions of mean nanowall width obtained from a portion of the SEM image of NiO nanowalls. The solid lines represent the fitting curves assuming the log-normal function.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211999&req=5

Figure 1: SEM images of the NiO nanowalls. (a-e) SEM images of the NiO nanowalls with various mean widths <d > which were synthesized at various annealing temperatures. (f) Distributions of mean nanowall width obtained from a portion of the SEM image of NiO nanowalls. The solid lines represent the fitting curves assuming the log-normal function.
Mentions: A series of template-free NiO nanowalls with various grain sizes were fabricated. The samples were prepared by a process where a pure Ni grid (200 mesh) was placed in a ceramic boat inside a quartz tube, which was then evacuated to about 10-3 Torr using a mechanical pump. The samples were then heated in a tube furnace at about 200°C for 2 h for degassing before being heated to various temperatures ranging from 400°C to 800°C for 3 h in a mixed argon (100 sccm) and oxygen (10 sccm) gas. The morphology and structures of the prepared samples were characterized using field-emission scanning electron microscopy (JEOL JSM-6500F, JEOL Ltd., Japan). For the SEM analysis, some of the nanowalls were transferred by gently sliding them onto a commercially available cooper grid with a carbon film. The SEM images in Figure 1a, b, c, d, e shows the surface morphology of NiO nanowalls with various sizes synthesized at TA = 800°C, 700°C, 600°C, 500°C, and 400°C, respectively. It can be seen that the NiO nanowalls form homogeneously on the nickel grid substrate. The mean sizes <d > of the nanowalls were calculated and defined from their width and grain, as shown in Figure 1a, b, c, d, e, respectively. The distribution of the mean width <d > of the NiO nanowalls as seen in Figure 1f is quite asymmetric, assuming a log-normal function distribution. The solid curves represent the fitting curve assuming log-normal distribution function. The log-normal distribution is defined as follows: where <d > is the mean value and σ is the standard deviation of the function. The mean NiO nanowall widths <d >, as determined from the SEM images and described by the fit of the log-normal function, were approximately 32(1), 75(2), 175(4), 239(8), and 416(18) nm, respectively. The corresponding fitting parameters are presented in Table 1. The value of the standard deviation of fitted function which is less than 0.5 for all annealing temperatures indicates that the distribution is confined to a limited range. There is a surprising contrast in sample color. The resultant NiO nanowalls can be either "black" (TA = 400°C and 500°C) or "green" (TA = 600°C-800°C), containing nickel vacancies, depending on the growth temperature and oxygen supplementation given various concentrations of nickel vacancies.

Bottom Line: The nanosized effects of short-range multimagnon excitation behavior and short-circuit diffusion in NiO nanowalls synthesized using the Ni grid thermal treatment method were observed.This study shows that short spin correlation leads to an exponential dependence of the growth temperatures and the existence of nickel vacancies during the magnon excitation.Four-magnon configurations were determined from the scattering factor, revealing a lowest state and monotonic change with the growth temperature.PACS: 75.47.Lx; 61.82.Rx; 75.50.Tt; 74.25.nd; 72.10.Di.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, National Dong Hwa University, Hualien 97401, Taiwan. sywu@mail.ndhu.edu.tw.

ABSTRACT
The nanosized effects of short-range multimagnon excitation behavior and short-circuit diffusion in NiO nanowalls synthesized using the Ni grid thermal treatment method were observed. The energy dispersive spectroscopy mapping technique was used to characterize the growth mechanism, and confocal Raman scattering was used to probe the antiferromagnetic exchange energy J2 between next-nearest-neighboring Ni ions in NiO nanowalls at various growth temperatures below the Neel temperature. This study shows that short spin correlation leads to an exponential dependence of the growth temperatures and the existence of nickel vacancies during the magnon excitation. Four-magnon configurations were determined from the scattering factor, revealing a lowest state and monotonic change with the growth temperature.PACS: 75.47.Lx; 61.82.Rx; 75.50.Tt; 74.25.nd; 72.10.Di.

No MeSH data available.


Related in: MedlinePlus