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Superparamagnetic nanoparticles with superhigh T2 relaxivity and cellular uptake are strongly desired for ultrasensitive magnetic resonance imaging (MRI). Towards this end, highly monodispersed manganese ferrite nanoparticles (MNPs, 6 nm) with mPEG-g-PEI and PEG coatings as model system are employed in this study to investigate the coating engineering for simultaneously high T2 relaxivity and cellular uptake. The quantitative evaluations of the intracellular uptake indicate that mPEG-g-PEI modified MNPs possess highly efficient cellular uptake, 2.4-fold larger than that with mPEG coating. More significantly, this coating simultaneously leads to a remarkably high T2 relaxivity up to 331.8 mm−1 s−1, which is 4 times larger than that of the mPEG control and the largest value reported for superparamagnetic iron oxides with similar size. Modeling analysis reveals that the superior relaxivity is mainly attributed to the largely reduced diffusivity of water molecules trapped in the mPEG-g-PEI net. Further MRI of MDA-MB-231 breast cancer cells loaded MNPs with mPEG-g-PEI coating demonstrated the strong MR contrast in vitro effect with a T2 relaxivity as high as 92.6 mm−1 s−1, 2.5-folds larger than reported 10 nm MNPs. This study provides a universal strategy of coating engineering of various magnetic nanoparticles for highly sensitive MRI.

Terahertz (THz) technology has been a promising tool for sensing, spectroscopy, imaging, and communication. However, only few devices have shown efficient performance for future THz technology. Herein, we propose a device based on tunable magnetoplasmons in gated monolayer graphene for THz wave modulation and isolation. The relative transmission and the Faraday rotation angle of the device have been calculated by combining the Fresnel method with the voltage-dependent Drude model. Our results suggest that a superior modulation depth and giant Faraday rotation due to the cyclotron effect in the classical regime by intraband transitions in graphene offer an effective, uniform, and flexible tunability for THz wave. And the modulating and isolating manipulations by graphene can range from 0 to 2 THz, with electron-hole asymmetry originating from variable scattering rate of magnetoplasmons. Moreover, the thickness effect of the thin substrate is also studied for better performance of the device, taking advantage of the unavoidable Fabry-Perot (F-P) effect. This work demonstrates a pathway for efficient THz modulator and isolator based on the magneto-optical polarization effect in graphene.

Magnetite nanoring with vortex domain structure may form stable magnetic colloid for biomedical applications due to its weak magnetic interaction without superparamagnetic (SPM) limitation. In the present study, we perform three-dimensional (3 D) Landau-Liftshitz-Gilbert (LLG) micromagnetics simulation for magnetite nanorings. The ground state phase diagram and stable vortex area (SVA) as a function of outer diameter (Dout), thickness (T), and inner to outer diameter ratios (β) within 100 nm are obtained. The influence of notch, eccentricity, and crystallographic orientation are taken carefully into consideration. In the SVA, the vortex state is not only the ground state but also the remanence state after in-plane is fully magnetized. In particular, the results suggest that a 20 nm inter-rings distance for a typical magnetite nanoring (Dout = 70 nm, T = 50 nm, and β = 0.6) can achieve the stable colloid based on vortex domain structure. Furthermore, these simulation results have been confirmed experimentally and demonstrated by using phosphorylated-mPEG modified magnetite nanorings. The optimization of magnetite nanorings from both simulation and experiments in this work pave the way to achieve such novel and stable vortex domain based magnetic suspension for various biomedical applications.

By manipulating the interfacial interactions between the peptide templates and the silicate species derived from TEOS and APTES, a facile biomimetic method was developed for the fabrication of silica nanostructures exhibiting "string-of-beads" and fibrillar morphologies of varied sizes.

Highly monodispersed magnetite nanoparticles with controlled particle size and mPEG surface coating have been successfully synthesized as a model system to investigate the effect of surface coating on the specific absorption rate (SAR) under an alternating magnetic field. Enhanced SAR with decreased surface coating thickness was observed and ascribed to the increased Brownian loss, improved thermal conductivity as well as improved dispersibility. By elaborate optimization of the surface coating and particle size, a significant increase of SAR (up to 74%) could be achieved with a minimal variation of the saturation magnetization (

CdS nanoribbons with various cross sections offer the opportunity to deeply understand the interaction between optical cavity and spontaneous emission. Herein, long tapered nanoribbons with the cross sections gradually changing were synthesized by a simple physical vapour deposition method. Morphology dependent micro-region photoluminescence (PL) spectroscopy is employed to show Purcell effect along different low symmetry cross sections. Spikes on the PL spectra reveal that local density of optical modes increases when the mode match happens between optical cavity and spontaneous emission. Bound exciton complex related amplified spontaneous emission is observed in a single CdS nanoribbon with well-defined elliptical cross sections and optimized width/thickness ratio [similar]1.45. Polarized Raman and TEM confirmed that the nanoribbon with the elliptical cross section adopts the [0002] growth direction with good quality. The results suggest that the cross section resonant cavity would be of importance for both fundamental and practical application of cavity quantum electrodynamics in CdS nanoribbon.

Room temperature ferromagnetism has been experimentally observed in TiO2:N films prepared by pulse laser deposition under N2O atmosphere. The ferromagnetism appears when the N2O partial pressure is higher than 10−5 Torr. XPS study has revealed that N substitutes O at the partial pressure of 10−5 Torr, whereas additional N atoms occupy interstitial sites besides substituting N at higher N2O partial pressures. Our study indicates that the origin of the ferromagnetism is the O substitution with N. Each substituted N has a magnetic moment of approximately 0.9 μB. The substitution of O also resulted in p-type behavior, accompanied with magnetoresistance and anomalous Hall effect.

Unique bismuth telluride nanostructures, tri-wing nanoribbons, are controllably synthesized on a large scale by a facile one-pot hydrothermal method. The length of the nanoribbon is up to tens of micrometres, and the wing of the nanoribbon is very thin with an average thickness of about 20 nm. During the synthesis process, tri-wing Te nanoribbons are first formed and act as the template, highly crystalline tri-wing Bi(2)Te(3) nanoribbons are then obtained through a surface-directing diffusion process. An elaborate TEM study reveals a quasi-periodic rough surface with sequential (1 (1) over bar5) and ((1) over bar 05) planes along the Bi(2)Te(3) nanoribbon, which is ascribed to the coherent growth of Bi(2)Te(3) crystals during the surface-directing diffusion process. The successful synthesis of Bi(2)Te(3) nanoribbons with rough surfaces opens up the opportunities of developing high performance nanoscale thermoelectrics as well as studying the surface state of Bi(2)Te(3) nanoribbons as potential topological insulators.

We address the room-temperature (RT) carbon ferromagnetism by considering the magnetic states of low-dimensional carbons linked by sp-hybridized carbon atoms. Based on the spin-polarized density functional theory calculations, we find that the sp(*) orbitals of carbon atoms can bring magnetic moments into different carbon allotropes which may eventually give rise to the long-range ferromagnetic ordering at room temperature through an indirect carrier-mediated coupling mechanism. The fact that this indirect coupling is Fermi-level-dependent predicts that the individual magnetism of diverse carbon materials is governed by their chemical environments. This mechanism may help to illuminate the RT magnetic properties of carbon-based materials and to explore the new magnetic applications of carbon materials.

Highly-textured n-type ZnO:Cu films with room-temperature ferromagnetism have been hydrothermally grown in aqueous solution at 90 °C using PLD-derived ZnO seed layers on different substrates (quartz, silicon, glass and sapphire). The crystallinity of the ZnO seed layers on different substrates plays an important role in the microstructure of the subsequently grown ZnO:Cu films. Better crystallinity and texture of the seed layers is favourable to the growth of continuous films. Thick Zn0.98Cu0.02O films (ca. 1.2 μm) exhibit high value of magnetic moment (0.40 μB per Cu), comparable to the previously reported value of thin films, indicating that thick ZnO:Cu films with high magnetization can be synthesized via this hydrothermal route. The incorporation of hydrogen into the ZnO lattice plays a dominant role in ferromagnetism in this ZnO:Cu system.

In this work, we demonstrate room temperature ferromagnetism of ZnO nanocrystals (NCs) embedded in alumina-based amorphous matrix. Our study has shown that solid solution occurred for lower Al concentration [≤x=0.09 for (Zn1−x,Alx)O]. No ferromagnetism appears in Al-doped ZnO with x≤0.09. With higher Al concentration, alumina-based amorphous structure appeared and fully amorphous was found in the composition of (Zn0.30,Al0.70)O. Ferromagnetism was found in (Zn1−x,Alx)O with a threshold of 16 mol % of Al. The room temperature ferromagnetism was found to be attributed to ZnO NCs in an alumina-based amorphous ZnO–Al2O3 matrix. Ferromagnetism reached a maximum with a volume percentage of ZnO NCs to be ∼27 vol %. The detailed investigations (transmission electron microscopy, x-ray photoelectron spectroscopy, and superconducting quantum interference device) show that the optimized size of these NCs is in the range of 4–5 nm. No ferromagnetism appears if the sample contains a fully amorphous structure.

An effective surface-enhanced Raman scattering (SERS) template based on a 3D hybrid Ag nanocluster (NC)-decorated ZnO nanowire array was fabricated through a simple process of depositing Ag NCs on ZnO nanowire arrays. The effects of particle size and excitation energy on the Raman scattering in these hybrid systems have been investigated using rhodamine 6G as a standard analyte. The results indicate that the hybrid nanosystem with 150 nm Ag NCs produces a larger SERS enhancement factor of 3.2 x 10(8), which is much higher than that of 10 nm Ag NCs (6.0 x 10(6)) under 532 nm excitation energy. The hybrid nanowire arrays were further applied to obtain SERS spectra of the two-photon absorption (TPA) chromophore T7. Finite-difference time-domain simulations reveal the presence of an enhanced field associated with inter-wire plasmon coupling of the 150 nm Ag NCs on adjacent ZnO nanowires; such a field was absent in the case of the 10 nm Ag NC-coated ZnO nanowire. Such hybrid nanosystems could be used as SERS substrates more effectively than assembled Ag NC film due to the enhanced light-scattering local field and the inter-wire plasmon-enhanced electromagnetic field.

Raman and photoluminescence (PL) studies of wurtzite alloy ZnxCd1?xSe (x = 0.2) quantum dots (QDs) with size ~4.7?nm were carried out under hydrostatic pressure up to 130?kbar using the diamond anvil cell technique. The structural phase transition from wurtzite to rock-salt was observed at 71?kbar, indicated by the disappearance of both PL and Raman peaks. In addition, the abrupt change of PL pressure coefficient and Raman peak splitting were observed at about 25.8?kbar, which may indicate a new unidentified structural phase transition of the alloy QDs. This new unidentified phase transition was discussed and possible explanations were proposed. The results of alloyed ZnCdSe QDs differ greatly from that of bare CdSe or ZnSe QDs as well as the corresponding bulk materials, implying that the quantum size effect plays an important role in the structural stability of the alloy QDs.

Orientation dependent electron phonon (EP) coupling on single wurtzite CdS nanowires with average diameter of 60nm has been studied using polarized Raman spectroscopy. The Raman spectra of nanowires are compared with those of bulk ribbon. Different from the bulk sample, the EP coupling of the nanowires is polarized along the longitudinal axis of wire and the diametral coupling strength exhibits a minimum due to the finite size effect of the Frohlich potential. These results show that the highly anisotropic geometry of CdS nanowires is a dominant factor in determining the anisotropy of EP coupling.

Well-crystallized Mn-doped ZnO nanowires were synthesized by a high-temperature chemical reduction method. The microscopic and macroscopic photoluminescence (PL) spectra of these Mn-doped ZnO nanowires were studied. Both the free-exciton emission band and the second-order longitude optical (2LO) phonon-assisted emission band were observed in the microscopic PL spectra. Furthermore, from the power dependent macroscopic PL spectra, the stimulated emission was observed around the 2LO phonon-assisted emission band with an increase in pump fluence, which relates to the strong exciton–phonon couplings along the c-axis in these Mn-doped ZnO nanowires. The nonresonant micro-Raman scattering spectrum demonstrates the strong 2LO phonon mode, which is enhanced by Mn doping. Resonant micro-Raman scattering shows multi-LO modes, due to the strong exciton–phonon coupling via a deformation potential induced by the Mn ions in these Mn-doped ZnO nanowires. Moreover, the low-temperature UV PL band is discussed to demonstrate the activity of phonons in the Mn-doped ZnO nanowires.

Photoluminescence (PL) and Raman spectroscopies of CdSe∕ZnS core/shell quantum dots (QDs) were studied under hydrostatic pressure (0–160kbars) at room temperature. Two phase transitions, at 69 and 79kbars, respectively, were observed, which correspond to wurtzite-rocksalt and rocksalt-cinnabar structural transformations. The full width at half maximum of PL peaks was found to decrease anomalously approximately 30% with pressure. These experimental data show significant difference between the CdSe∕ZnS core/shell QDs and simple bare CdSe QDs or bulk CdSe, implying the ZnS shell plays a dominant role in structural stability and electronic state of such system.

Two-dimensional carbon nanowalls (CNWs) were prepared by microwave plasma-enhanced chemical-vapor deposition and scanning electron microscopy was used to observe their morphologies. The Raman observations of different sample orientations and polarizations show that CNWs are well crystallized. Micro-Raman scattering measurements were also carried out with different excitation laser lines (325, 488, 514, 532, and 633 nm). The D band shows a very strong shift of 46.19 cm(-1)eV with excitation laser energy and this has been explained by the double resonance effect. The decreasing intensity ratios IDIG and ID'/IG with increasing laser excitation energy were detected and discussed.