离子束溅射制备Co/Pt多层膜的结构和磁性

采用离子束溅射技术制备了Co／Pt多层膜，并研究了多层膜的结构和磁性随Co层厚度（tCo）或Pt层厚度（tPt）的变化关系。结果表明Co层呈现出hcp结构的（002）织构，Pt层表现出fcc结构的（111）织构。当Co层和Pt层都比较薄时，界面有Co-Pt的化合物形成。当tPt=2．4nm而tCo在0．6～2．4nm变化时，样品的磁矫顽力（Hc）随tCo增加而下降，饱和磁化强度（Ms）随tCo增加而增加。当tCo=1．2nm而tPt在1．2～4．8nm变化时，Hc呈现先升后降的变化，Ms随tPt增大而减小。样品的Hc还受调制周期（D）和周期数ny的影响，通过对Co层和Pt层的厚度比、调制周期、周期数的设计，可以获得较大的磁矫顽力。     

Disorder effects in focused-ion-beam-deposited Pt contacts on GaN nanowires

The current-bias (I-V) characteristics at various temperatures, T, of focused-ion-beam (FIB)-deposited Pt contacts on GaN nanowires evolves from low-resistance ohmic (linear I-V) to rectifying as the diameter increases, and both exhibit strongly nonmetallic T-dependence. The small-diameter (66 nm) T-dependent resistance is explained by two-dimensional variable range hopping with a small characteristic energy, ensuring low resistance at 300 K. For large diameters (184 nm), back-to-back Schottky barriers explain the nonlinear I-V at all T values and permit an estimate of doping concentration from the bias-dependent barrier height. Both behaviors can be understood by accounting for the role of FIB-induced amorphization of GaN underneath the contact, as confirmed by cross-sectional transmission electron microscopy.     

Pt浓度对磁控溅射制备Co1-xPtx:C薄膜的影响

采用组合靶,利用磁控共溅射技术制备了Co1-xPtx:C复合纳米颗粒薄膜,研究发现CoPt粒子取向和磁性能与CoPt:C薄膜中的Pt浓度有密切关系,在较高Pt浓度的CoPt：C薄膜中观察到垂直各向异性现象。通过改变Pt浓度,可以获得粒子粒径小于lOnm、矫顽力可控、高的垂直磁晶各向异性能的薄膜。综合考虑,薄膜的最佳成分为Co47Pt53:C,此时矫顽力达到最大。     

Focused ion beam fabrication of novel core-shell nanowire structures

A novel method of indirect deposition by means of a focused ion beam (FIB) is utilized to develop metal/insulator/semiconductor nanowire core-shell structures. This method is based upon depositing an annular pattern centered on a nanowire, with secondary deposition then coating the wire. Typical cross-sectional deposition area increments as a function of ion doses are 1.3 × 10(-2)?μm(2)?nC(-1) for Pt and 3.5 × 10(-2)?μm(2)?nC(-1) for SiO(2). The structures are examined with a transmission electron microscope (TEM) using a new nanowire TEM sample preparation method that allows direct examinations of individually selected core-shell nanowires fabricated under different indirect FIB deposition conditions. Elemental analyses by means of energy dispersive x-ray spectroscopy and electron energy filtered TEM imaging verify the deposition of SiO(2) and Pt layers. Relatively uniform Pt and SiO(2) coatings on individual GaP nanowires can be achieved with overall thickness deviation of about 10% for deposition up to 25-30?nm thick Pt or SiO(2) shells. It should be possible to extend this approach to any nanowire/nanotube system, and to a wide range of coatings in any desired layer sequences.     

Effects of Pt junction on electrical transport of individual ZnO nanorod device fabricated by focused ion beam

The electrical transport of individual ZnO nanorod devices manufactured by focused ion beam (FIB) was investigated by the direct measurement of electrical resistance at electrode junctions of cross-sectioned devices using two nanoprobes. The cathodoluminescence (CL) measurements were also performed to evaluate the crystallinity at the center and edge of the cross-sectioned ZnO nanorods. The electrical transport of the individual ZnO nanorod device depends strongly on the crystallinity of the ZnO nanorod itself and the carbon contents at Pt junctions. The ZnO-Au junction of the device acted as the fastest path for electrical transport.     

Perpendicular exchange bias in IrMn/Pt/[Co/Pt]3 multilayers with cone magnetization

The perpendicular exchange bias and magnetic anisotropy were investigated in IrMn/Pt/[Co/Pt]₃ multilayers through the analysis of in-plane and out-of-plane magnetization hysteresis loops. A phenomenological model was used to simulate the in-plane curves and the effective perpendicular anisotropies were obtained employing the area method. The canted state anisotropy was introduced by taking into account the first and second uniaxial anisotropy terms of the ferromagnet with the corresponding uniaxial anisotropy direction allowed to make a nonzero angle with the film's normal. This angle, obtained from the fittings, was of approximately 15° for IrMn/[Co/Pt]₃ film and decreases with the introduction of Pt in the IrMn/Pt/ [Co/Pt]₃ system, indicating that the Pt interlayer leads to a predominant perpendicular anisotropy. A maximum of the out-of-plane anisotropy was found between 0.5 and 0.6 nm of Pt, whereas a maximum of the perpendicular exchange bias was found at 0.3 nm. These results are very similar to those obtained for IrMn/Cu/[Co/Pt]₃ system; however, the decrease of the exchange bias with the spacer thickness is more abrupt and the enhacement of the perpendicular anisotropy is higher for the case of Cu spacer as compared with that of Pt spacer. The existence of a maximum in the perpendicular exchange bias as a function of the Pt layer thickness was attributed to the predominance of the enhancement of exchange bias due to more perpendicular Co moment orientation over the exponential decrease of the ferromagnetic/antiferromagnetic exchange coupling and, consequently, of the exchange-bias field.     

Pt Content Dependence of Magnetic Properties of CoPt/Ru Patterned Films

The magnetic properties of dot arrays made of CoPt/Ru perpendicular films (20 nm thickness) were examined as a function of Pt content. The CoPt dot arrays with a dot size D of 140 nm showed a single domain state, after removal of the applied field equal to H_r. H_r decreased from 5.2 kOe to 3.0 kOe as the Pt content decreased from 20 at% to 14 at%. The angular dependence of H_r for these dot arrays indicated coherent rotation of the magnetization during nucleation. The effective magnetic anisotropy, including the demagnetizing energy due to the dot shape, K_u ^eff, decreased as the Pt content decreased, resulting in the H_r reduction. The values of the switching volume for nucleation, V_sw , evaluated from the stabilizing energy barrier E₀, were a few percent of the dot volume. The switching diameter for nucleation, D_sw, increased slightly as the Pt content decreased, which was qualitatively in good agreement with the increase in the exchange length of magnetization. The value of E₀/k _BT (k_B is the Boltzmann constant and T is the absolute temperature) reduced as the Pt content decreased; however, E ₀/k_BT still had a high of 440 even at 14 at% Pt content. We successfully demonstrated the reduction of H_r for CoPt/Ru patterned films on reducing the Pt content, while simultaneously maintaining a high thermal stability. A calculation based on the experimental results suggested the potential recording density of CoPt/Ru dot arrays used for patterned media to be over 1 Tb/in²      

Nanostructure and chemical characterisation of individual NiFe/Pt multilayer nanowires

NiFe/Pt multilayer nanowires have been successfully fabricated by pulse electrodeposition into the channels of porous anodic aluminum oxide (AAO) templates, and characterized at the nanoscale. Individual nanowires have uniform structure and regular periodicity. The NiFe and Pt layers are polycrystalline, with random orientation fcc lattice structure crystallites and grain sizes 3-10 nm, and the average layer growth rate is 30 nm/s for NiFe and 4 nm/s for Pt. Nanoscale chemical analysis of individual NiFe/Pt nanowires by EDX and EELS shows that they contain alternating NiFe and Pt layers, with a small approximately 1% inclusion of Pt in the NiFe layer due to electrochemical co-deposition.     

Rapid synthesis of cubic Pt nanoparticles and their use for the preparation of Pt nanoagglomerates

We report the synthesis of hexadecyltrimethylammonium bromide (CTAB)-stabilized cubic Pt nanoparticles by NaBH4 reduction of H2PtCl6 in aqueous CTAB solution. These Pt nanoparticles (average size of 7 nm) were well dispersed in aqueous solution and stable at least for 2 months. Addition of a trace amount of AgNO3 can alter the morphology of these Pt nanoparticles. More interestingly, the as-prepared uniform Pt nanoparticles were further developed into bigger Pt nanoagglomerates (approximately 20 to 47 nm) by a seed-mediate growth process. Dentritic and spherical Pt nanoagglomerates can be synthesized by altering the incubation time and their size can be tuned by controlling the amount of the seeds added.     

Fabrication of discrete gallium nanoislands on the surface of a Si(001) substrate using a focused ion beam

A gallium focused ion beam (FIB) has been used to implant Ga at specific sites on the surface of undoped Si(001) substrates. Upon annealing at 600?°C, discrete nanoscale surface islands form within the FIB patterned regions when the total Ga ion dose, or fluence, is greater than 1.0 × 10(16) ions cm( - 2). The number of islands depends on the size of the irradiated region and a single island can be achieved for a FIB milled region that is 100 nm × 100 nm. The average sizes of the islands were found to range from 24.5 nm when exposed to a total ion dose of 1.2 × 10(16) ions cm( - 2) to 45 nm for a dose of 3.0 × 10(16) ions cm( - 2). We have confirmed that these surface islands are metallic Ga by performing a selective chemical etch that removes the islands and by transmission electron microscopy characterization. These patterned Ga surface templates could serve as nucleation sites for the lateral arrangement of discrete quantum dot structures.     

Selective growth of silica nanowires in silicon catalysed by Pt thin film

Selective growth of amorphous silica nanowires on a silicon wafer deposited with Pt thin film is reported. The mechanism of nanowire growth has been established to follow the vapour liquid solid (VLS) model via the PtSi phase acting as the catalyst. Nanowires grow with diameters ranging from 50 to 500?nm. These bottom-up grown nanowires exhibit photoluminescence with a stable emission of blue light at 430?nm under excitation. The effect of varying the seed layer thickness (Pt film) from 2 to 100?nm has been studied. It is observed that, above 10?nm thickness, a continuous layer of Pt(2)Si re-solidifies on the surface, inhibiting the growth of nanowires. The selectivity to the Pt thickness has been exploited to create regions of nanowires connected to conducting silicide (Pt(2)Si) simultaneously in a single furnace treatment. This novel approach has opened the gateways for realizing hybrid interconnects in silicon for various nano-optical applications such as the localization of light, low-dimensional waveguides for functional microphotonics, scanning near-field microscopy, and nanoantennae.     

Fabrication of ultralight 3D graphene/Pt aerogel via in situ gamma-ray irradiation and its application for the catalytic degradation of methyl orange

Abstract

In this work, we reported a facile and environmentally friendly approach for the preparing of 3D graphene/Pt aerogel by gamma irradiation at room temperature. Graphene oxide (GO) and platinum ion are simultaneously reduced and self-assembled into a three-dimensional (3D) macro porous structure. Pt NPs with diameter between 2.3 and 5.5?nm were homogeneously attached onto the graphene sheets of the 3D network structure. The catalytic efficiency towards the degradation of methyl orange (MO) of the 3D GA/Pt composite is 108 times higher than that of the pure Pt NPs under the same experimental conditions.     

Interdiffusion in Fe/Pt Multilayers: In Situ High Temperature Synchrotron Radiation Reflectivity Study

Thermal annealing of Fe/Pt multilayers (ML) is reported to reduce significantly the formation temperature of FePt hard magnetic thin films. The transformation mechanisms of [Fe 1.38 nm/Pt 2.24 nm]₅₀ ML, prepared by magnetron sputtering, is investigated in the present communication by high temperature X‐ray reflectivity using synchrotron radiation. Complete degradation of the ML periodic structure is observed at about 610 K. The variation with annealing temperature of the intensity of the first Bragg peak, the correlated vertical roughness, and the lateral correlation length of the ML show that the ML transform in two stages with a cross‐over temperature of about 515 ± 15 K. This behavior cannot be simply explained by the change in the measured interdiffusion coefficient below and above the cross‐over temperature, suggesting the formation of FePt nanograins along the interfaces.     

Fabrication and characterization of RF nanoantenna on a nanoliter-scale 3D microcontainer

We report the design and fabrication of a nanoantenna structure on the surface of a 3D nanoliter-scale container for the development of communicable nanoliter-scale chemical delivery systems. The porous container was self-assembled, after which the nanoantenna was fabricated on the top of the microcontainer using focused ion beam (FIB) ion-induced metal deposition. The nanoantenna was structured as a rectangular metal coil composed of platinum (Pt) nanowires (70?nm in width). The response of the nanoantenna structure was simulated using finite element software and showed a strong resonant feature at 10.8?GHz, which was confirmed by high frequency measurements.     

Rectifying switching characteristics of Pt/ZnO/Pt structure based resistive memory

40 nm thick amorphous ZnO thin films were deposited by radio frequency magnetron sputtering at room temperature and asymmetric electrical switching characteristics are observed in the macroscopic symmetric Pt/ZnO/Pt structure. The crystal structure was examined by X-ray diffraction (XRD). The chemical bonding states of ZnO resistive switching layer was investigated by X-ray photoelectron spectroscopy (XPS). Keithley 4200 semiconductor characterization system was used to measure the current-voltage (I-V) characteristics of the fabricated devices. The results reveal that a reversible resistive switching behavior between the high resistance state and the low resistance state with rectifying effects can be repeated for more than 100 dc cycles. This asymmetric electrical behavior is thought to be related to the naturally self-formed PtOx between ZnO film and the Pt bottom electrode, which introduces an energy barrier when electrons flow from top electrode towards the bottom electrode. The model of Pt/ZnO/Pt memory cell is expected to be able to alleviate the misreading error in cross-point array for high density integrations.     

溅射工艺条件对TbFeCo/Pt薄膜磁性能的影响

采用射频磁控溅射法在玻璃基片上成功制得了TbFeCo/Pt非晶垂直磁化膜,系统研究了溅射工艺参数对TbFeCo薄膜磁性能的影响.振动样品磁强计测量结果表明:Tb含量在补偿成分点附近,采用较低的溅射氩气压与Pt底层,有利于提高TbFeCo薄膜的磁性能;当Tb含量为0.24,溅射功率为300W,溅射气压为0.53Pa,薄膜厚度为140nm时,TbFeCo/Pt薄膜矫顽力达到476kA/m,饱和磁化强度为151kA/m,剩磁矩形比超过0.8,该薄膜有望用作高密度光磁混合记录介质.     

Solid-state dewetting of Pt on (100) SrTiO3

Continuous thin films of Pt on (100) SrTiO₃ substrates were dewetted to form Pt particles at 1,150 °C, using an oxygen partial pressure of 10^?20 atm. After retraction of thick (50 or 100 nm) Pt films, SrTiO₃ anisotropic rods, slightly depleted in Ti, were found on the surface of the substrate. Rods did not form after dewetting of thinner (10 nm) Pt films. After dewetting, a ~10 nm thick interfacial phase was found between the Pt and the SrTiO₃. The interfacial phase, based on Sr and containing ~25 at% oxygen, is believed to be a transient state, formed due to Ti depletion from the substrate, resulting in a Pt(Ti) solution in the particles. The interfacial phase forms due to the low oxygen partial pressure used to equilibrate the system, and is expected to influence the electrical properties of devices based on Pt–SrTiO₃.     

Perpendicular magnetic anisotropy in amorphous ferromagnetic CoSiB/Pt multilayers

Magnetic anisotropy properties of amorphous ferromagnetic CoSiB/Pt multilayers with perpendicular magnetic anisotropy (PMA, K(u)) were systematically investigated as a function of CoSiB layer thickness (t(coSiB)) and Pt layer thickness (t(Pt)). In two series of [CoSiB t(coSiB)Pt t(P1)]5 multilayers, the perpendicular coercivity (H(c)) increased to reach a maximum and then decreased with further increase in both t(coSiB) and t(Pt), due to intermixing of CoSiB/Pt interfaces. Particularly, using the amorphous soft magnetic CoSiB, the coercivity became very sensitive to the CoSiB thickness. These multilayer films exhibited a high K(u) of 2 x 10(6) erg/cc and a high H(c) of 360 Oe with marked squareness. It was found that even after annealing at 350 degrees C, the CoSiB/Pt multilayers had a high PMA and their H(c) increased.     

Interstitial Pt in crystalline Si under thin (<12 nm) overlayers of Pt and PtSi

The Rutherford backscattering flux focusing effect is utilized to specifically detect interstitial Pt in Si. Measurements are performed on Si wafers after Pt evaporation at substrate temperatures of room temperature and 200 C, and for silicide formation after a subsequent 450 C anneal. We observe a high concentration, of the order of 3 at %, of interstitial Pt in crystalline Si for those conditions where Pt rapidly reacts with Si to form silicide. The interstitial Pt concentration is reduced when the suicide reaction is blocked in the metal film. We conclude that the high concentration of interstitial Pt in crystalline Si in the immediate (< 10nm) interface region to a metal or suicide overlayer may be crucial for the reaction of 3d transition metals with Si to form a suicide at low temperatures.     

New method for synthesis of Pt nanoparticles embedded in a carbon matrix

Platinum (Pt) nanoparticles embedded in a carbon matrix were synthesized for the first time in benzene by an electric plasma discharge generated in the cavitation field of benzene due to an ultrasonic horn. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to study the particle size, structure and morphology of the synthesized nanoparticles. The Pt nanoparticles have FCC bulk Pt crystal structure. On the average Pt nanoparticle diameter ranged from 8 nm to 40 nm when synthesized at 4.1 kV and from 5 nm to 25 nm when synthesized at 3.4 kV. X-ray photoelectron Spectroscopy (XPS) and Energy dispersive X-ray Spectroscopy (EDX) were used to study the chemical composition of the synthesized nanoparticles. A cost effective new method for carbon supported Pt nanoparticles will be of potential interest in fuel cell and catalysis applications.