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Advanced materials: preparation of novel magnetic nanomaterials by quasi epitaxial growth method

wallpapers News 2020-12-11
The physical chemical properties of

metal nanomaterials are closely related to their crystal structure so the phase engineering of nanomaterials (pen) is attracting more more scientific research interests. For example CO nanomaterials with different crystalline phases exhibit different magnetic properties. CO in HCP phase is usually hard magnetic while CO in FCC Ɛ phase is usually soft magnetic. It is well known that epitaxial growth method can effectively prepare metal nanomaterials with novel crystalline phases by using nanomaterials with unconventional crystalline phases as templates. In wet chemical method a key condition for epitaxial growth between two metals is that their lattice mismatch is usually less than 5%. Therefore epitaxial growth of magnetic metals (e.g. Fe Co Ni) on noble metal nanomaterials (e.g. Au nanoribbons in 4H phase Au nanoflakes in 2H phase) is very challenging because the lattice mismatch of these two metals is much greater than 5%. However a new idea is provided for the formation of irregular dislocation phase which may lead to the formation of irregular dislocation phase.

recently Professor Zhang Hua's team of City University of Hong Kong Gu Lin's research fellow of Institute of physics Chinese Academy of Sciences Professor Wang Jinlan of Southeast University reported the crystal phase control of CO Ni nanostructures by quasi epitaxial growth. Using 4H Au nanoribbons as templates CO can be epitaxial grown on Au surface 4H-Au@14H-Co Nanostructures. Due to the large lattice mismatch between Au Co the ordered misfit dislocations are formed at the Au / CO interface. Along the growth direction of Au nanobelts the spacing of every 6 Au planes is equivalent to that of every 7 co planes that is to say every 6 Au planes form a dislocation. Considering the stacking sequence of 4H Au there are two different dislocations so in the epitaxial growth of CO Nanodendrites the stacking sequence period is 14 resulting in a new phase of CO namely 14h. Interestingly with the increase of surface lig content in wet chemical reaction the epitaxial growth of CO nanorods gradually becomes shorter resulting in the formation of only a very thin uniform coating layer the maintenance of 14h phase 4H-Au@14H-Co Nanobelt structure. In addition the period of dislocations at the Au / CO interface can be changed by different wet chemical synthesis methods. Therefore the epitaxial growth of Co coating can form 2H phase 4H-Au@2H-Co Nanobelt structure. High resolution lens analysis shows that the lattice mismatch between 2H CO Au is smaller than that of 14h Co so the 2H Co coating is thicker than that of 14h Co coating. This method can also be used for epitaxial growth of Ni coating with 2H phase 4H-Au@2H-Ni Nanobelt structure. Due to the difference of crystal plane spacing between CO Ni the dislocation periods at the interface of 4H Au / 2H CO 4H Au / 2H Ni are also different. The hysteresis loops of

indicate that there are two kinds of CO nanostructures with new phases i.e 4H-Au@14H-Co Both nanobranches nanobelts exhibit ferromagnetism the same Curie temperature at room temperature. The difference is that the FC curve of 14h Co nanobranches remains unchanged with the decrease of temperature which is rare in magnetic nanomaterials. It may be due to the contribution of volume fluctuation the strong interaction between CO nanobranches.

this study overcomes the large lattice mismatch between the two metals uses the quasi epitaxial growth method to prepare new crystal structures containing ordered dislocations which is a new synthesis strategy in crystal phase engineering (pen) of nanomaterials opens up a way for the preparation of novel crystal structures the study of crystal phase effects in physical chemical properties.


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