Controlled wrinkling of single-layer graphene (1-LG) at nanometer scale was achieved by introducing monodisperse nanoparticles (NPs), with size comparable to the strain coherence length, underneath the 1-LG. Typical fingerprint of the delaminated fraction is identified as substantial contribution to the principal Raman modes of the 1-LG (G and G’). Correlation analysis of the Raman shift of the G and G’ modes clearly resolved the 1-LG in contact and delaminated from the substrate, respectively. Intensity of Raman features of the delaminated 1-LG increases linearly with the amount of the wrinkles, as determined by advanced processing of atomic force microscopy data. Our study thus offers universal approach for both fine tuning and facile quantification of the graphene topography up to ~60% of wrinkling.

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We have investigated the magnetic response of residual metal catalyst in the raw and super purified HiPco single wall carbon nanotubes (HiPco_raw and HiPco_SP SWCNTs). It has been shown that the residual metal catalyst is in the form of nanoparticles, even in the HiPco_SP SWCNTs that should contain a minimal amount of the metal. M€ ossbauer spectroscopy of the HiPco_raw SWCNTs proved the catalyst nanoparticles are in the form of Fe 3 C. Analysis of the synchrotron X-ray diffraction data provided an average diameter of nanoparticles about 1.9 nm. Magnetic studies by means of temperature dependence of magnetization, magnetization isotherms and susceptibility suggested that the nanoparticles obey the behavior of weakly interacting superparamagnetic systems in both samples. Further analysis of the data revealed a coreÀshell structure of the nanoparticles in the HiPco_raw nanotubes, with a magnetically oriented core and a paramagnetic shell, which is almost removed in the case of the HiPco_SP catalyst nanoparticles.

This work aims to emphasize that the magnetic response of single-domain magnetic nanoparticles (NPs) is driven by the NPs' internal structure, and the NP size dependencies of magnetic properties are overestimated. The relationship between the degree of the NPs' crystallinity and magnetic response is unambiguously demonstrated in eight samples of uniform maghemite/magnetite NPs and corroborated with the results obtained for about 20 samples of spinel ferrite NPs with different degrees of crystallinity. The NP samples were prepared by the thermal decomposition of an organic iron precursor subjected to varying reaction conditions, yielding variations in the NP size, shape and relative crystallinity. We characterized the samples by using several complementary methods, such as powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), high resolution TEM (HR-TEM) and Mössbauer spectroscopy (MS). We evaluated the NPs' relative crystallinity by comparing the NP sizes determined from TEM and PXRD and further inspecting the NPs' internal structure and relative crystallinity by using HR-TEM. The results of the structural characterization were put in the context of the NPs' magnetic response. In this work, the highest saturation magnetization (M) was measured for the smallest but well-crystalline NPs, while the larger NPs exhibiting worse crystallinity revealed a lower M. Our results clearly demonstrate that the NP crystallinity level that is mirrored in the internal spin order drives the specific magnetic response of the single-domain NPs.