Mechanical characterization of Co/Cu multilayered nanowires

The mechanical deformation properties of (110) Co/Cu multilayered nanowires were studied by Molecular Dynamics under uniaxial tensile and compressive stresses. The potential of the immiscible CoCu system was modeled by a second-moment tight-binding approximation. Stress-strain curves at different conditions were obtained and the elastic modulus and yield stress were analyzed. Both magnitudes are approximately independent of the strain rate, except at high values. They decrease linearly with increasing temperature. Below a volume-to-surface-area ratio, their values drastically increase and diverge from the bulk values. If the thickness of the Cu sublayers increases, the Young's modulus and yield stress decrease, although in a different way. The elastic modulus decreases linearly and the yield stress falls steeply whenever Cu is present in the nanowire, since the lattice distortion takes place firstly and fundamentally in Cu sublayers. The change in the axial stress at the interface is little significant on average and rather localized. Unlike, the transverse stress has a non-uniform distribution along the Cu sublayer, especially at the yield point. The Young's modulus and yield stress are larger in tension than in compression. Under tensile stress, nanowires slip via partial dislocation nucleation and propagation. Unlike, compressive deformation of nanowires takes place via both partial and full dislocations.     

Excitation of propagating surface plasmons with a scanning tunnelling microscope

Inelastic electron tunnelling excitation of propagating surface plasmon polaritons (SPPs) on a thin gold film is demonstrated. This is done by combining a scanning tunnelling microscope (STM) with an inverted optical microscope. Analysis of the leakage radiation in both the image and Fourier planes unambiguously shows that the majority (up to 99.5%) of the detected photons originate from propagating SPPs with propagation lengths of the order of 10 μm. The remaining photon emission is localized under the STM tip and is attributed to a tip-gold film coupled plasmon resonance as evidenced by the bimodal spectral distribution and enhanced emission intensity observed using a silver STM tip for excitation.     

Ordered arrays of nanocolumns grown by the oblique angle deposition technique on a self-assembled layer of polystyrene spheres

Ordered arrays of upright nanocolumns of chalcogenide glass were fabricated by combining the oblique angle deposition technique with substrate rotation. Self-assembled close-packed arrays of polystyrene spheres of 200 nm and 500 nm in diameter were used as templates. Our method allows the fabrication of GeSbSe nanocolumns of controlled height, cross-sectional diameter and two-dimensional distribution. Finally, preliminary optical characterization suggests the possible use of the ordered arrays of GeSbSe nanocolumns in optical devices, in particular photonic crystals.     

Fe为过渡层的Co/Cu/Co三明治巨磁电阻效应的研究

用超高真空电子束蒸发方法成功制备了以不同厚度Fe为过渡层的Co/Cu/Co三明治巨磁电阻样品,与以Cr为过渡层的Co/Cu/Co三明治巨磁电阻样品比较,样品的矫顽力大大减小,因而样品的磁灵敏度有了较大地提高。当Fe过渡层的厚度为7nm时样品的磁电阻值最大。另外,温度更强烈地影响以Fe为过渡层样品的磁电阻值,在77K下样品的磁电阻曲线表现出明显的不对称性,它来源于低温下fcc Fe过渡层的反铁磁性转变。     

Tailoring the atomic structure of graphene nanoribbons by scanning tunnelling microscope lithography

The practical realization of nanoscale electronics faces two major challenges: the precise engineering of the building blocks and their assembly into functional circuits. In spite of the exceptional electronic properties of carbon nanotubes, only basic demonstration devices have been realized that require time-consuming processes. This is mainly due to a lack of selective growth and reliable assembly processes for nanotubes. However, graphene offers an attractive alternative. Here we report the patterning of graphene nanoribbons and bent junctions with nanometre-precision, well-defined widths and predetermined crystallographic orientations, allowing us to fully engineer their electronic structure using scanning tunnelling microscope lithography. The atomic structure and electronic properties of the ribbons have been investigated by scanning tunnelling microscopy and tunnelling spectroscopy measurements. Opening of confinement gaps up to 0.5 eV, enabling room-temperature operation of graphene nanoribbon-based devices, is reported. This method avoids the difficulties of assembling nanoscale components and may prove useful in the realization of complete integrated circuits, operating as room-temperature ballistic electronic devices.     

用FTMS方法制备Co／Cu巨磁阻超晶格多层薄膜

本文用双靶相对磁控溅射法（ＦＴＭＳ）在云母单晶基板上原位生长了巨磁阻Ｃｏ／Ｃｕ超晶格薄膜，研究了放电气压及背景真空对薄膜结构和电磁性质的影响。     

Magnetoresistance and microstructure evolution upon rapid thermal annealing of giant magnetoresistive Co/Cu/Co/CoNbZr multilayers

The magnetoresistance (MR) variation of Co/Cu/Co/CoNbZr spin valves as a result of rapid thermal annealing has been investigated. MR ratio of 3.8% was obtained in the as-deposited sample and a considerable increase to 6.86% was observed in the 450°C×60 s treated sample. Microstructure studies show that the enhancement of MR ratio is a consequence of the nano-crystallization of amorphous CoNbZr soft layer. The nano-crystallized CoNbZr possess fine and dense microstructure and excellent electrical and soft magnetic properties which leads to the MR enhancement. With increasing annealing temperature or annealing time, interface roughness caused by rapid grain growth decrease the MR ratio rapidly. XRD studies imply that the interfusion of Cu atom into the Co layer is another possible degradation mechanism of Co/Cu/Co/CoNbZr spin valves at annealing temperature beyond 550°C.     

A scanning tunnelling microscope study of groove structures in polycarbonate optical discs

The groove structure in polycarbonate substrates, commonly used in the fabrication of optical discs, has been studied with the scanning tunnelling microscope. Comparative studies of the same structures were also performed using more conventional scanning electron microscopy and transmission electron microscopy techniques. These studies illustrate the ability to characterize the shape of man-made structures that are commonly recorded in these polymer-based materials. The scanning tunnelling microscope images show the superiority of this technique for detailed cross-sectional studies of the profiles of structures with typical dimensions 500 nm in width by 50 nm in depth.     

Interface strength of structured nanocolumns grown by glancing angle deposition

In order to investigate the mechanics of interfacial fracture in structured nano-elements grown by glancing angle deposition (GLAD), fracture experiments were conducted on oblique Ti nanocolumns grown on a Si substrate using a micro-brick specimen. Two types of specimens, a Forward specimen (loading with the column tilt direction) and a Reverse specimen (loading against the column tilt), were prepared to clarify the effect of an asymmetric nanostructure on the interface strength. The specimens fractured at the interface or near the interface between the Ti nanocolumns and the Si substrate for both specimens. The critical force and displacement at fracture in the Forward specimens were about 2.0 times and 1.6 times as large as those in the Reverse specimens, respectively, showing clear anisotropy in the interface strength. The local stress distribution along the interface in the single nanocolumn at fracture was analyzed by finite element analysis. While the stress singularity in the Reverse specimen was greater than that in the Forward specimen, the normal stresses in a region 1–3 nm near the interface edge were almost identical regardless of the loading direction, suggesting that intensified stress in the nanoscale region dominated fracture.     

Measurement of the divergence angle of the electron microprobe of a scanning electron microscope

A method of measuring the divergence angle of the electron microprobe of a scanning electron microscope is developed. The method has been tested on the model PHI-650 scanning electron microscope. The divergence angle of the microprobe amounts to 1.4±0.2 mradian. Translated from Izmeritel'naya Tekhnika, No. 12, pp. 26–28, December, 1996.     

Observations of slip patterns on the surface of fatigued gold using the scanning tunnelling microscope

Observations of fatigue-induced slip patterns on the surface of polycrystalline gold (+99.9%) using the scanning tunnelling microscope (STM) are presented. The samples were cycled in four-point bending between zero and 0.0025 strain for 250 and 2500 cycles. STM observations of the sample fatigued for 250 cycles revealed broad slip bands 0.38–0.69 m wide containing narrow slip bands 0.015–0.123 m wide and fine slip lines 0.006 m wide. The depth of these features are 20–57 nm for broad slip bands, 3–7 nm for narrow slip bands, and approximately 2–4 nm for fine slip lines. The sample fatigued for 2500 cycles showed similar values for the width of the slip bands and slip lines except that their depth was increased by a factor of between 2 and 4 times for the narrow slip bands and the fine slip lines. Apparent persistent slip bands (PSBs) spaced 2.4 m, 300–500 nm deep were also observed. These results demonstrate that STM is a significant new tool for observing and distinguishing various types of fatigue-induced surface slip patterns on suitably prepared samples. The vertical resolution obtained with STM is vastly superior to current SEM and TEM methods.     

CoFe/Cu多层膜巨磁阻效应的研究

采用直流磁控溅射制备了多层膜Ta/缓冲层/[Co95Fe5/Cu]×12/Co95Fe5/Ta。实验发现,多层膜的磁阻性能受到缓冲层材料、各子层厚度以及退火处理的影响。采用优化的多层膜结构:Ni65Fe15Co20缓冲层厚8 nm、CoFe层厚1.55 nm、Cu层厚2.4nm,沉积态薄膜GMR值达到7.6%;而在外加磁场79.6×103A/m下,250℃保温2 h退火处理后,多层膜的GMR值进一步提高到11.9%,磁滞从18.7×102A/m降低到796 A/m。     

Advantage of the scanning tunnelling microscope in documenting changes in carbon fibre surface morphology brought about by various surface treatments

The scanning tunnelling microscope (STM) was used to examine the surfaces of P-55 pitch-based carbon fibres before and after they had experienced various surface treatments (to < 1% weight loss), which included treatment in an argon plasma, as well as oxidation in air at elevated temperature, oxygen plasma at room temperature, nitric acid bath, and an electrochemical bath. The effects of these surface treatments on the filaments could be differentiated from the micrometre scale down to the nanometre scale. The STM has been shown to be a valuable tool for viewing the surface morphology of these 10 μm filaments non-destructively in air down to the atomic scale.     

Evolution of structure and fabrication of Cu/Fe multilayered composites by a repeated diffusion-rolling procedure

Cu/Fe multilayered laminated composite was fabricated by a repeated diffusion-rolling procedure. With diffusion bonding initially, thinner layer was fabricated by rolling, and this procedure was repeated. The evolution of structure and properties of Cu/Fe multilayered composite was investigated. The low inter-solubility interface was examined by using high angle annular dark field (HAADF) imaging mode in scanning transmission electron microscopy (STEM). The interfacial strength of Cu/Fe was enhanced by the plastic deformation after rolling. Parallelism of interfaces can almost be achieved when the thickness of layer is above 25 μm or total reduction ratio is lesser than 99%. An inter diffusion area with about 25 nm in width was present at the interface. HR-TEM and FFT investigations at the interface region revealed that disordered substitutional solid solution of Cu and Fe occurred during the procedure.     

Direct imaging of the atomic structure inside a nanowire by scanning tunnelling microscopy

Semiconductor nanowires are expected to be important components in future nano-electronics and photonics. Already a wide range of applications has been realized, such as high-performance field-effect transistors, bio/chemical sensors, diode logics and single-nanowire lasers. As nanowires have small cross-sections and large surface-to-bulk ratios, their properties can be significantly influenced by individual atomic-scale structural features, and they can have properties or even atomic arrangements with no bulk counterparts. Hence, experimental methods capable of directly addressing the atomic-scale structure of nanowires are highly desirable. One such method is scanning tunnelling microscopy (STM), which, by direct imaging of the atomic and electronic structure of surfaces has revolutionized the perception of nanoscale objects and low-dimensional systems. Here we demonstrate how combining STM with an embedding scheme allows us to image the interior of semiconductor nanowires with atomic resolution. Defect structures such as planar twin segments and single-atom impurities are imaged inside a GaAs nanowire. Further, we image an intriguing GaAs nanowire that is separated into two distinct nanocrystallites along the growth direction of the wire.     

Structural and magnetic characterization of electrochemically deposited Co–Cu multilayer nanowires

The template-assisted electrodeposition technique has been utilized to synthesize highly ordered, well-aligned, and dense Co–Cu multilayer nanowires. The electrochemical impedance spectroscopy has been carried out to study the in situ growth process of multilayer nanowires at different electrodeposition times. Scanning electron microscopy revealed well defined multilayer interfaces. X-ray diffraction investigations of Co–Cu multilayer nanowires showed that the Cu as well as Co deposits exhibit the face centered cubic texture. Magnetic measurements of these multilayer nanowires were also done for the fields applied parallel and perpendicular to the wires axes.     

Growth types and surface topography of Co, Cu and Co/Cu multilayers studied by AES and STM/SFM

A thin film of cobalt, copper and Co/Cu multilayers deposited on Si(1 0 0) has been studied by an in situ combination of Auger electron spectroscopy and scanning tunnelling/scanning force microscopy. We show that thickness-dependent Auger peak intensity measurements, taken in situ during deposition of constituents of Co/Cu multilayers, combined with microscopy can bring valuable information about growth type of the system components.     

Current-perpendicular-to-plane giant magnetoresistance in Co/Cu multilayered nanocylinders electrodeposited into anodized aluminum oxide nanochannels with ultra-large aspect ratio

Journal of Materials Science: Materials in Electronics - An anodized aluminum oxide (AAO) thick film with numerous nanochannels was synthesized by a cathodic exfoliation technique from a metallic...