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Electromagnetic wave absorbing properties and hyperfine interactions of Fe-Cu-Nb-Si-B nanocomposites

Han Man-Gui (韩满贵), Guo Wei (郭韦), Wu Yan-Hui (吴燕辉), Liu Min (刘明), Magundappa L. Hadimani

Chin. Phys. B, 2014, 23 (8): 083301. DOI: 10.1088/1674-1056/23/8/083301

Abstract （571）

PDF （861KB）（507）

The Fe-Cu-Nb-Si-B alloy nanocomposite containing two ferromagnetic phases (amorphous phase and nanophase phase) is obtained by properly annealing the as-prepared alloys. High resolution transmission electron microscopy (HR-TEM) images show the coexistence of these two phases. It is found that Fe-Si nanograins are surrounded by the retained amorphous ferromagnetic phase. Mössbauer spectroscopy measurements show that the nanophase is the D0₃-type Fe-Si phase, which is employed to find the atomic fractions of resonant ⁵⁷Fe atoms in these two phases. The microwave permittivity and permeability spectra of Fe-Cu-Nb-Si-B nanocomposite are measured in the frequency range of 0.5 GHz-10 GHz. Large relative microwave permeability values are obtained. The results show that the absorber containing the nanocomposite flakes with a volume fraction of 28.59% exhibits good microwave absorption properties. The reflection loss of the absorber is less than -10 dB in a frequency band of 1.93 GHz-3.20 GHz.

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High refractive index sensitivity sensing in gold nanoslit arrays

Yuan Jun (袁浚), Kan Qiang (阚强), Geng Zhao-Xin (耿照新), Xie Yi-Yang (解意洋), Wang Chun-Xia (王春霞), Chen Hong-Da (陈弘达)

Chin. Phys. B, 2014, 23 (8): 084201. DOI: 10.1088/1674-1056/23/8/084201

Abstract （640）

PDF （956KB）（524）

The extraordinary optical transmission (EOT) phenomenon of nano-periodic aperture array in metallic film has been widely investigated and used in biosensors. The surface plasmon resonance and cavity mode in some periodic nanostructures, such as nanohole and nanoslit, cause EOTs at certain wavelengths. This resonance wavelength is sensitive to the refractive index on the surface of periodic nanostructures. Therefore, the metallic nanostructures are expected to be good sensing elements. The sensing performances of gold nanoslit arrays are experimentally and theoretically investigated. Three-dimensional finite difference time domain (FDTD) simulations are utilized to explore their transmission spectra and steady-state field intensity distributions. The electron beam evaporation, electron beam lithography, and ion milling are applied to the gold nanoslit arrays with different widths and periods. The sensing performances of the gold nanoslit array are characterized via transmission spectra in four kinds of refractive index samples. The highest sensitivity reaches 726 nm/RIU when the width of the gold nanoslit array is 38.5 nm.

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Synthesis of boron, nitrogen co-doped porous carbon from asphaltene for high-performance supercapacitors

Zhou Ying (周颖), Wang Dao-Long (王道龙), Wang Chun-Lei (王春雷), Jin Xin-Xin (金新新), Qiu Jie-Shan (邱介山)

Chin. Phys. B, 2014, 23 (8): 086101. DOI: 10.1088/1674-1056/23/8/086101

Abstract （860）

PDF （1200KB）（542）

Oxidized asphaltene (OA), a thermosetting material with plenty of functional groups, is synthesized from asphaltene (A) using HNO₃/H₂SO₄ as the oxidizing agent. Boron, nitrogen co-doped porous carbon (BNC-OA) is prepared by carbonization of the mixture of boric acid and OA at 1173 K in an argon atmosphere. X-ray photoelectron spectroscopy (XPS) characterization reveals that the BNC-OA has a nitrogen content of 3.26 at.% and a boron content of 1.31 at.%, while its oxidation-free counterpart (BNC-SA) has a nitrogen content of 1.61 at.% and a boron content of 3.02 at.%. The specific surface area and total pore volume of BNC-OA are 1103 m²·g^-1 and 0.921 cm³·g^-1, respectively. At a current density of 0.1 A·g^-1, the specific capacitance of BNC-OA is 335 F·g^-1 and the capacitance retention can still reach 83% at 1 A·g^-1. The analysis shows that the superior electrochemical performance of the BNC-OA is attributed to the pseudocapacitance behavior of surface heteroatom functional groups and an abundant pore-structure. Boron, nitrogen co-doped porous carbon is a promising electrode material for supercapacitors.

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Enhanced photoluminescence of CdSe quantum dots by the coupling of Ag nanocube and Ag film

Jiang Tong-Tong (蒋童童), Shao Wei-Jia (邵伟佳), Yin Nai-Qiang (尹乃强), Liu Ling (刘玲), Song Jiang-Lu-Qi (宋江鲁奇), Zhu Li-Xin (朱立新), Xu Xiao-Liang (许小亮)

Chin. Phys. B, 2014, 23 (8): 086102. DOI: 10.1088/1674-1056/23/8/086102

Abstract （880）

PDF （556KB）（523）

The coupling of local surface plasmon (LSP) of nanoparticle and surface plasmon (SP) mode produced by metal film can lead to the enhanced electromagnetic field, which has an important application in enhancing the fluorescence of quantum dots (QDs). Herein, the Ag nanocube and Ag film are used to enhance the fluorescence of CdSe QDs. The enhancement is found to relate to the sizes of the Ag nanocube and the thickness of the Ag film. Moreover, we also present the fluorescence enhancement caused by only SP. The result shows that the coupling between metal nanoparticles and metal film can realize larger field enhancement. Numerical simulation verifies that a nanocube can localize a strong electric field around its corner. All the results indicate that the fluorescence of QDs can be efficiently improved by optimizing the parameters of Ag film and Ag cubes.

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Microwave ferromagnetic properties of as-deposited Co₂FeSi Heusler alloy films prepared by oblique sputtering

Cao Xiao-Qin (曹晓琴), Li Shan-Dong (李山东), Cai Zhi-Yi (蔡志义), Du Hong-Lei (杜洪磊), Xue Qian (薛倩), Gao Xiao-Yang (高小洋), Xie Shi-Ming (谢施名)

Chin. Phys. B, 2014, 23 (8): 086201. DOI: 10.1088/1674-1056/23/8/086201

Abstract （584）

PDF （1219KB）（454）

The Co₂FeSi films are deposited on Si (100) substrates by an oblique sputtering method at ambient temperature. It is revealed that the microwave ferromagnetic properties of Co₂FeSi films are sensitive to sample position and sputtering power. It is exciting that the as-deposited films without any magnetic annealing exhibit high in-plane uniaxial anisotropy fields in a range of 200 Oe-330 Oe (1 Oe=79.5775 A·m^-1), and low coercivities in a range of 5 Oe-28 Oe. As a result, high self-biased ferromagnetic resonance frequency up to 4.75 GHz is achieved in as-deposited oblique sputtered films. These results indicate that Co₂FeSi Heusler alloy films are promising in practical applications of RF/microwave devices.

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Adsorptions and diffusions of carbon atoms on the surface and in the subsurface of Co (200)：A first-principles density-functional study

Qiao Liang (乔靓), Wang Shu-Min (王淑敏), Zhang Xiao-Ming (张晓明), Hu Xiao-Ying (胡小颖), Zeng Yi (曾毅), Zheng Wei-Tao (郑伟涛)

Chin. Phys. B, 2014, 23 (8): 086802. DOI: 10.1088/1674-1056/23/8/086802

Abstract （696）

PDF （799KB）（403）

First-principles calculations based on density functional theory are used to investigate the adsorptions and diffusions of carbon atoms on the surface and in the subsurface of Co (200). The preferred site for the carbon atom on the surface is the hollow site, and the preferred site in the subsurface is the octahedral site. There is charge transfer from the surface to the adsorbed carbon atom, and for the most favorable adsorbed structure the charge transfer is largest. Moreover, the energy barriers for the diffusions of carbon atoms on the surface and from the surface into the subsurface and then back to the surface are calculated in detail. The results indicate that the energy barrier for the diffusion of carbon atoms on the surface is comparable to that from the subsurface to the surface. The results imply that both the direct surface nucleation and the surface segregation from Co bulk can be observed in the chemical vapor deposition growth of graphene on Co (200) substrate, which can gain a new insight into the growth mechanism of graphene.

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Phase transformation in Mg–Sb₃Te thin films

Li Jun-Jian (李军建), Wang Guo-Xiang (王国祥), Chen Yi-Min (陈益敏), Shen Xiang (沈祥), Nie Qiu-Hua (聂秋华), Lü Ye-Gang (吕业刚), Dai Shi-Xun (戴世勋), Xu Tie-Feng (徐铁锋)

Chin. Phys. B, 2014, 23 (8): 087301. DOI: 10.1088/1674-1056/23/8/087301

Abstract （609）

PDF （509KB）（365）

Mg-doped Sb₃Te films are proposed to improve the performance of phase-change memory (PCM). We prepare Mg-doped Sb₃Te films and investigate their crystallization behaviors, structural, optical and electrical properties. We find that Mg-doping can increase the crystallization temperature, enhance the activation energy, and improve the 10-year data retention of Sb₃Te. Especially Mg_25.19(Sb₃Te)_74.81 shows higher T_c (～ 190 ℃) and larger E_a (～ 3.49 eV), which results in a better data retention maintaining for 10 yr at ～ 112 ℃. Moreover R_a/R_c value is also improved. These excellent properties make Mg-Sb-Te material a promising candidate for the phase-change memory (PCM).

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Exchange interaction between vortex and antivortex

Liu Yan (柳艳), Li Hua-Nan (李化南), Hu Yong (胡勇), Du An (杜安)

Chin. Phys. B, 2014, 23 (8): 087501. DOI: 10.1088/1674-1056/23/8/087501

Abstract （490）

PDF （279KB）（392）

The dynamic properties of interacting vortex-antivortex pairs in thin film are studied by analytical calculations. Analytical expressions for the magnetization vector distribution of vortex-antivortex pairs and the trivortex states are given. The magnetic states of the vortices are treated as having rigid structures, i.e., the vortex maintains its spin distribution when moving. The trajectories of the vortex cores are calculated by the Thiele's equation. It is found that the vortex-antivortex pair rotates around each other when they have opposite polarities, however, vortex and antivortex cores move along straight lines when they have the same polarity. The frequency of the rotation decreases with increasing the distance between the two cores of vortex-antivortex pair, and it has a lower value when a third vortex is introduced.

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Magnetic field control of ferroelectric polarization and magnetization of LiCu₂O₂ compound

Qi Yan (齐岩), Du An (杜安)

Chin. Phys. B, 2014, 23 (8): 087502. DOI: 10.1088/1674-1056/23/8/087502

Abstract （596）

PDF （551KB）（379）

A spin model of LiCu₂O₂ compound with ground state of ellipsoidal helical structure is adopted. Taking into account the interchain coupling and exchange anisotropy, we investigate the magnetoelectric properties in a rotating magnetic field and perform the Monte Carlo simulation on a two-dimensional lattice. A prominent anisotropic response is observed in both the magnetization curve and the polarization curve, qualitatively coinciding with the behaviors that are detected in the experiment. In addition, the influences of the magnetic field with various magnitudes on polarization are also explored and analyzed in detail. As the magnetic field increases, a much smoother polarization of angle dependence is exhibited, indicating the strong correlation between the magnetic and ferroelectric orders.

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Large coercivity and unconventional exchange coupling in manganese-oxide-coated manganese–gallium nanoparticles

Feng Jun-Ning (冯俊宁), Liu Wei (刘伟), Geng Dian-Yu (耿殿禹), Ma Song (马嵩), Yu Tao (余涛), Zhao Xiao-Tian (赵晓天), Dai Zhi-Ming (代志明), Zhao Xin-Guo (赵新国), Zhang Zhi-Dong (张志东)

Chin. Phys. B, 2014, 23 (8): 087503. DOI: 10.1088/1674-1056/23/8/087503

Abstract （501）

PDF （1364KB）（526）

The microstructures and magnetic properties of nanoparticles, each composed of an antiferromagnetic (AFM) manganese-oxide shell and a ferromagnetic-like core of manganese-gallium (MnGa) compounds, are studied. The core-shell structure is confirmed by transmission electron microscope (TEM). The ferromagnetic-like core contains three kinds of MnGa binary compounds, i.e., ferrimagnetic (FI) D0₂₂-type Mn₃Ga, ferromagnetic (FM) Mn₈Ga₅, and AFM D0₁₉-type Mn₃Ga, of which the first two correspond respectively to a hard magnetic phase and to a soft one. Decoupling effect between these two phases is found at 1ow temperature, which weakens gradually with increasing temperature and disappears above 200 K. The exchange bias (EB) effect is observed simultaneously, which is caused by the exchange coupling between the AFM shell and FM-like core. A large coercivity of 6.96 kOe (1 Oe = 79.5775 A·m^-1) and a maximum EB value of 0.45 kOe are achieved at 300 K and 200 K respectively.

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Influence of magnetic layer thickness on [Fe₈₀Ni₂₀–O/SiO₂]_n multilayer thin films

Wei Jian-Qing (魏建清), Geng Hao (耿昊), Xu Lei (徐磊), Wang Lai-Sen (王来森), Chen Yuan-Zhi (陈远志), Yue Guang-Hui (岳光辉), Peng Dong-Liang (彭栋梁)

Chin. Phys. B, 2014, 23 (8): 087504. DOI: 10.1088/1674-1056/23/8/087504

Abstract （718）

PDF （1494KB）（431）

In the present work, a series of [Fe₈₀Ni₂₀-O/SiO₂]_n multilayer thin films is fabricated using a reactive magnetron sputtering equipment. The thickness of SiO₂ interlayer is fixed at 3 nm, while the thickness values of Fe₈₀Ni₂₀-O magnetic films range from 10 nm to 30 nm. All films present obvious in-plane uniaxial magnetic anisotropy. With increasing the Fe₈₀Ni₂₀-O layer thickness, the saturation magnetization increases slightly and the coercivity becomes larger due to the enlarged grain size, which could weaken the soft magnetic property. The results of high frequency magnetic permeability characterization show that films with thin magnetic layer are more suitable for practical applications. When the thickness of Fe₈₀Ni₂₀-O layer is 10 nm, the multilayer film exhibits the most comprehensive high-frequency magnetic property with a real permeability of 300 in gigahertz range.

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Rational doping for zinc oxide and its influences on morphology and optical properties

Xia Yu-Jing (夏玉静), Guan Zi-Sheng (管自生), He Tao (贺涛)

Chin. Phys. B, 2014, 23 (8): 087701. DOI: 10.1088/1674-1056/23/8/087701

Abstract （495）

PDF （1595KB）（370）

Zinc oxide (ZnO) nanopowders doped with different metal ions (Me, Me = Sn⁴⁺, In³⁺, Mn²⁺, and Co²⁺) are prepared by a simple sol-gel method. Influences of the ion doping on morphology and optical properties of the resulting Zn_xMe_yO are investigated by scanning electron microscopy, X-ray diffraction, UV-vis absorption spectrum, and photoluminescence. The morphology of ZnO can be tailored by ion doping, which is closely related not only to the ionic radii and electronegativities of the doped ions, but also to their oxidation states and electron configurations. The optical band gap and photoluminescence of ZnO can also be modulated by ion doping, which results from a combination of different effects, Burstein-Moss, band tail, charge compensation, sp-d exchange, non-radiative recombination, and blocking barrier. This may offer us a viable approach to tuning the (optical) properties of ZnO-based materials via rational ion doping.

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Thickness dependence of the optical constants of oxidized copper thin films based on ellipsometry and transmittance

Gong Jun-Bo (宫俊波), Dong Wei-Le (董伟乐), Dai Ru-Cheng (代如成), Wang Zhong-Ping (王中平), Zhang Zeng-Ming (张增明), Ding Ze-Jun (丁泽军)

Chin. Phys. B, 2014, 23 (8): 087802. DOI: 10.1088/1674-1056/23/8/087802

Abstract （661）

PDF （770KB）（1450）

Thin oxidized copper films in various thickness values are deposited onto quartz glass substrates by electron beam evaporation. The ellipsometry parameters and transmittance in a wavelength range of 300 nm-1000 nm are collected by a spectroscopic ellipsometer and a spectrophotometer respectively. The effective thickness and optical constants, i.e., refractive index n and extinction coefficient k, are accurately determined by using newly developed ellipsometry combined with transmittance iteration method. It is found that the effective thickness determined by this method is close to the physical thickness and has obvious difference from the mass thickness for very thin film due to variable density of film. Furthermore, the thickness dependence of optical constants of thin oxidized Cu films is analyzed.

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Raman scattering in In/InO_x core–shell structured nanoparticles

Wang Meng (王萌), Tian Ye (田野), Zhang Jian-Ming (张建明), Guo Chuan-Fei (郭传飞), Zhang Xin-Zheng (张心正), Liu Qian (刘前)

Chin. Phys. B, 2014, 23 (8): 087803. DOI: 10.1088/1674-1056/23/8/087803

Abstract （805）

PDF （1347KB）（665）

The properties of Raman phonons are very important due to the fact that they can availably reflect some important physical information. An abnormal Raman peak is observed at about 558 cm^-1 in In film composed of In/InO_x core-shell structured nanoparticles, and the phonon mode stays very stable when the temperature changes. Our results indicate that this Raman scattering is attributed to the existence of incomplete indium oxide in the oxide shell.

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Thermal effect of Ge₂Sb₂Te₅ in phase change memory device

Li Jun-Tao (李俊焘), Liu Bo (刘波), Song Zhi-Tang (宋志棠), Ren Kun (任堃), Zhu Min (朱敏), Xu Jia (徐佳), Ren Jia-Dong (任佳栋), Feng Gao-Ming (冯高明), Ren Wan-Chun (任万春), Tong Hao (童浩)

Chin. Phys. B, 2014, 23 (8): 087804. DOI: 10.1088/1674-1056/23/8/087804

Abstract （540）

PDF （3626KB）（726）

In the fabrication of phase change random access memory (PRAM) devices, high temperature thermal processes are inevitable. We investigate the thermal stability of Ge₂Sb₂Te₅ (GST) which is a prototypical phase change material. After high temperature process, voids of phase change material exist at the interface between Ge₂Sb₂Te₅ and substrate in the initial open memory cell. This lower region of Ge₂Sb₂Te₅ is found to be a Te-rich phase change layer. Phase change memory devices are fabricated in different process conditions and examined by scanning electron microscopy and energy dispersive X-ray. It is found that hot-chuck process, nitrogen-doping process, and lower temperature inter-metal dielectric (IMD) deposition process can ease the thermal impact of line-GST PRAM cell.

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The engineering of doxorubicin-loaded liposome-quantum dot hybrids for cancer theranostics

Bowen Tian (田博文), Wafa' T. Al-Jamal, Kostas Kostarelos

Chin. Phys. B, 2014, 23 (8): 087805. DOI: 10.1088/1674-1056/23/8/087805

Abstract （656）

PDF （591KB）（280）

Many studies have recently attempted to develop multifunctional nanoconstructs by integrating the superior fluorescence properties of quantum dots (QD) with therapeutic capabilities into a single vesicle for cancer theranostics. Liposome-quantum dot (L-QD) hybrid vesicles have shown promising potential for the construction of multifunctional nanoconstructs for cancer imaging and therapy. To fulfil such a potential, we report here the further functionalization of L-QD hybrid vesicles with therapeutic capabilities by loading anticancer drug doxorubicin (Dox) into their aqueous core. L-QD hybrid vesicles are first engineered by the incorporation of TOPO-capped, CdSe/ZnS QD into the lipid bilayers of DSPC:Chol:DSPE-PEG₂₀₀₀, followed by Dox loading using the pH-gradient technique. The loading efficiency of Dox into L-QD hybrid vesicles is achieved up to 97%, comparable to liposome control. All these evidences prove that the incorporation of QD into the lipid bilayer does not affect Dox loading through the lipid membrane of liposomes using the pH-gradient technique. Moreover, the release study shows that Dox release profile can be modulated simply by changing lipid composition. In conclusion, the Dox-loaded L-QD hybrid vesicles presented here constitute a promising multifunctional nanoconstruct capable of transporting combinations of therapeutic and diagnostic modalities.

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A tunable infrared plasmonic polarization filter with asymmetrical cross resonator

Chen Xi-Yao (陈曦曜), Zhong Yuan-Gang (钟远刚), Jiang Jun-Zhen (蒋俊贞), Zeng Xia-Hui (曾夏辉), Fu Ping (傅平), Qiu Yi-Shen (邱怡申), Li Hui (李晖)

Chin. Phys. B, 2014, 23 (8): 087806. DOI: 10.1088/1674-1056/23/8/087806

Abstract （587）

PDF （514KB）（450）

A tunable infrared plasmonic polarization filter is proposed and investigated in this paper. The filter is based on the sandwich absorption structure which consists of three layers. The top layer is an array of asymmetrical cross resonator. The middle and bottom layers are dielectric spacer and metal film respectively. By absorbing specific wavelength of the incident light perfectly, the reflection spectrum of the structure shows filter performance. The calculated results show that the absorption wavelength is strongly dependent on the length of branch of the asymmetrical cross resonator which is parallel to the light polarization and independent of the length of the vertical one. Therefore, the asymmetrical cross resonator filter structure opens the way for freely tuning the filtering wavelength for a different light polarization. We can fix a resonant wavelength (absorption wavelength) corresponding to one polarization and change the resonant wavelength for the other polarization by adjusting the corresponding branch length of the asymmetrical cross resonator, or change the two resonant wavelengths of both two polarizations at the same time.

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Synthesis of Au nanorods in a low pH solution via seed-media method

Ma Xiao (马晓), Feng Jin-Yang (冯晋阳), You Fang-Fang (游芳芳), Ma Juan (马娟), Zhao Xiu-Jian (赵修建), Wang Moo-Chin (王木琴)

Chin. Phys. B, 2014, 23 (8): 087807. DOI: 10.1088/1674-1056/23/8/087807

Abstract （529）

PDF （999KB）（482）

The gold (Au) nanorods with various aspect ratios are obtained by a seed-media method in low pH growth solution. Transmission electron microscopy (TEM) and UV-visible spectrophotometry are utilized to characterize the Au nanorods, and the longitudinal absorption peak positions of Au nanorods show different shifting trends of the growth evolutions in various low pH (1～ 3) solutions. Other influential factors on the shape of Au nanorod are also systematically studied under low pH reaction condition. The positions of longitudinal peak shift between 600 nm and 900 nm, with the aspect ratios of Au nanorods varying from 2 to 5 both in the simulation and experimental results. The simulation results are in agreement with experimental ones.

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Growth of threaded AlN whiskers by a physical vapor transport method

Wang Jun (王军), Zhao Meng (赵萌), Zuo Si-Bin (左思斌), Wang Wen-Jun (王文军)

Chin. Phys. B, 2014, 23 (8): 088103. DOI: 10.1088/1674-1056/23/8/088103

Abstract （631）

PDF （549KB）（457）

Threaded aluminum nitride (AlN) whiskers are grown by a physical vapor transport method in a radio-frequency induction heating furnace. The resultant whiskers are characterized by X-ray diffraction, Raman scattering, scanning electron microscopy, transmission electron microscopy and photoluminescence. The analysis shows that the whiskers are single-crystalline, wurtzite AlN. The threaded AlN whiskers are 0.5 μm～ 100 μm in diameter and several millimeters in length in the fiber direction, and have lots of tiny sawteeth on the surface. The morphology of this threaded AlN whisker is beneficial for bonding when the whisker is used in composite. The growth of the whiskers is dominated by the vapor-solid (VS) mechanism, and the particular morphology might result from an oscillating condition produced in the radio-frequency induction heating furnace.

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Complete coverage of reduced graphene oxide on silicon dioxide substrates

Huang Jingfeng, Melanie Larisika, Chen Hu, Steve Faulkner, Myra A. Nimmo, Christoph Nowak, Alfred Tok Iing Yoong

Chin. Phys. B, 2014, 23 (8): 088104. DOI: 10.1088/1674-1056/23/8/088104

Abstract （636）

PDF （516KB）（404）

Reduced graphene oxide (RGO) has the advantage of an aqueous and industrial-scale production route. No other approaches can rival the RGO field effect transistor platform in terms of cost (< US$1) and portability (millimetre scale). However the large deviations in the electrical resistivity of this fabricated material prevent it from being used widely. After an ethanol chemical vapor deposition (CVD) post-treatment to graphene oxide with ethanol, carbon islets are deposited preferentially at the edges of existing flakes. With a 2-h treatment, the standard deviation in electrical resistance of the treated chips can be reduced by 99.95%. Thus this process could enable RGO to be used in practical electronic devices.

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