Thermal stability of core-shell nanoparticles: A combined in situ study ...
SUPPORTING ONLINE INFORMATION Thermal stability of core-shell nanoparticles: A combined in situ study by XPS and TEM Cecile S. Bonifacio1, Sophie Carenco2, Cheng Hao Wu3, Stephen D. House1, Hendrik Bluhm,2 and Judith C. Yang1,4* 1
Department of Chemical and Petroleum Engineering, and 4Physics, University of Pittsburgh, 4200 Fifth Ave, Pittsburgh, PA, USA, 15260
2
Chemical Science Division, Lawrence Berkeley National Lab., 1 Cyclotron Road, Berkeley, CA, USA, 94720
3
Department of Chemistry, University of California, Berkeley, CA, USA, 94720
*Corresponding Author: [email protected]
a.
b.
Figure S1- EDS elemental map (a) of the Ni-Co core-shell nanoparticles (NPs) with associated spectrum (b) from the marked area in (a). Elemental map in a shows the distribution of Ni (green) and Co (red) within each NP. Spectrum shows presence of oxygen species inherent to the NP sample while silicon and carbon are from the SiC layer of the MEMS device. S1
Figure S2- EDS elemental map (a) and the associated Co K EDS map (b) showing Co of varying thickness covering the nanoparticles. The numbered EDS line scans (c) corresponding to the marked nanoparticles in (a and b) indicate a core-shell distribution of Co(red) and Ni(green), respectively.
S2
Figure S3- Selected area electron diffraction (SAED) patterns and acquired during the in situ TEM annealing at room temperature (RT), 280°C, 320°C, 440°C , 550°C and 600°C. Before annealing, the Ni-Co core-shell nanoparticles (NPs) had a FCC polycrystalline structure (planes marked with *) with identifiable (111) and (220) planes for CoO surface oxide. From RT to 320°C, the SAED patterns were observed to have double rings as in the (200) plane (marked with the arrows and labelled in the magnified image of the SAED pattern) which correspond to the core and shell structure of the NPs. These rings diminished to a single ring starting at 440°C indicating an onset of the core-shell structure reconfiguration. Further annealing to 550°C and above resulted to ordering of the structure, i.e., increase in diffraction spots, which correspond to the formation of the uniform Ni-Co mixed alloy from the EDS results. S3
Figure S4- Particle size distributions (PSD) of the measured Ni-Co core-shell nanoparticles (NPs) and the corresponding dark-field images(DF) and EDS maps acquired from Area 1 (a-c) and 2 (d-f) during annealing at 25°C-320°C and 440°C-600°C, respectively. The same NPs (singly dispersed, spherical shape and in the field of view) for each Area were selected and measured. The 47 (a-c) and 5 (d-f) distinct NPs present in all DF/map sets were selected for size analysis from Areas 1 and 2, respectively. The PSD was obtained by processing the EDS maps using ImageJ by manually measuring the NP area. These NPs were manually segmented, using Sobel edge-detection (via ImageJ) and the corresponding EDS maps to guide the outline placement. The projected areas were determined for each NP and converted into an equivalent diameter for a circular particle. The average of the diameter of the NPs, dave, was calculated for each annealing step. For accuracy, some areas were disregarded in the analysis. Such is the region from Area 1 where the electron beam was positioned (cross marked as beam). S4
a. 440°C
b. 500°C
Neck
c. 550°C
d. 650°C
Neck growth
Figure S5- EDS elemental maps acquired during the in situ TEM annealing at 440°C (a), 500°C (b), 550°C (c) and 650°C (d) showing sintering of the Ni-Co core-shell NPs. At 440°C, particles (marked with arrows in (a)) were initially in contact. Starting at 500°C (b), a neck between the two marked particles in (a) is observed. Further heating led to the growth of the neck at 550°C(c) and subsequently consolidation of the NPs was observed at 650°C (d).
S5
Department of Chemical and Petroleum Engineering, and 4Physics, University of Pittsburgh, 4200 Fifth Ave, Pittsburgh, PA, USA, 15260
2
Chemical Science Division, Lawrence Berkeley National Lab., 1 Cyclotron Road, Berkeley, CA, USA, 94720
3
Department of Chemistry, University of California, Berkeley, CA, USA, 94720
*Corresponding Author: [email protected]
a.
b.
Figure S1- EDS elemental map (a) of the Ni-Co core-shell nanoparticles (NPs) with associated spectrum (b) from the marked area in (a). Elemental map in a shows the distribution of Ni (green) and Co (red) within each NP. Spectrum shows presence of oxygen species inherent to the NP sample while silicon and carbon are from the SiC layer of the MEMS device. S1
Figure S2- EDS elemental map (a) and the associated Co K EDS map (b) showing Co of varying thickness covering the nanoparticles. The numbered EDS line scans (c) corresponding to the marked nanoparticles in (a and b) indicate a core-shell distribution of Co(red) and Ni(green), respectively.
S2
Figure S3- Selected area electron diffraction (SAED) patterns and acquired during the in situ TEM annealing at room temperature (RT), 280°C, 320°C, 440°C , 550°C and 600°C. Before annealing, the Ni-Co core-shell nanoparticles (NPs) had a FCC polycrystalline structure (planes marked with *) with identifiable (111) and (220) planes for CoO surface oxide. From RT to 320°C, the SAED patterns were observed to have double rings as in the (200) plane (marked with the arrows and labelled in the magnified image of the SAED pattern) which correspond to the core and shell structure of the NPs. These rings diminished to a single ring starting at 440°C indicating an onset of the core-shell structure reconfiguration. Further annealing to 550°C and above resulted to ordering of the structure, i.e., increase in diffraction spots, which correspond to the formation of the uniform Ni-Co mixed alloy from the EDS results. S3
Figure S4- Particle size distributions (PSD) of the measured Ni-Co core-shell nanoparticles (NPs) and the corresponding dark-field images(DF) and EDS maps acquired from Area 1 (a-c) and 2 (d-f) during annealing at 25°C-320°C and 440°C-600°C, respectively. The same NPs (singly dispersed, spherical shape and in the field of view) for each Area were selected and measured. The 47 (a-c) and 5 (d-f) distinct NPs present in all DF/map sets were selected for size analysis from Areas 1 and 2, respectively. The PSD was obtained by processing the EDS maps using ImageJ by manually measuring the NP area. These NPs were manually segmented, using Sobel edge-detection (via ImageJ) and the corresponding EDS maps to guide the outline placement. The projected areas were determined for each NP and converted into an equivalent diameter for a circular particle. The average of the diameter of the NPs, dave, was calculated for each annealing step. For accuracy, some areas were disregarded in the analysis. Such is the region from Area 1 where the electron beam was positioned (cross marked as beam). S4
a. 440°C
b. 500°C
Neck
c. 550°C
d. 650°C
Neck growth
Figure S5- EDS elemental maps acquired during the in situ TEM annealing at 440°C (a), 500°C (b), 550°C (c) and 650°C (d) showing sintering of the Ni-Co core-shell NPs. At 440°C, particles (marked with arrows in (a)) were initially in contact. Starting at 500°C (b), a neck between the two marked particles in (a) is observed. Further heating led to the growth of the neck at 550°C(c) and subsequently consolidation of the NPs was observed at 650°C (d).
S5
