Low temperature synthesis and electrical characterization of germanium doped Ti-based nanocrystals for nonvolatile memory

Chemical and electrical characteristics of Ti-based nanocrystals containing germanium, fabricated by annealing the co-sputtered thin film with titanium silicide and germanium targets, were demonstrated for low temperature applications of nonvolatile memory. Formation and composition characteristics of nanocrystals (NCs) at various annealing temperatures were examined by transmission electron microscopy and X-ray photon-emission spectroscopy, respectively. It was observed that the addition of germanium (Ge) significantly reduces the proposed thermal budget necessary for Ti-based NC formation due to the rise of morphological instability and agglomeration properties during annealing. NC structures formed after annealing at 500 °C, and separated well at 600 °C annealing. However, it was also observed that significant thermal desorption of Ge atoms occurs at 600 °C due to the sublimation of formatted GeO phase and results in a serious decrease of memory window. Therefore, an approach to effectively restrain Ge thermal desorption is proposed by encapsulating the Ti-based trapping layer with a thick silicon oxide layer before 600 °C annealing. The electrical characteristics of data retention in the sample with the 600 °C annealing exhibited better performance than the 500 °C-annealed sample, a result associated with the better separation and better crystallization of the NC structures.     

The effect of postgrowth annealing on the structure and optical properties of multilayer Ge/Si heterostructures

The effect of the postgrowth laser and thermal annealing on the structure and optical properties of multilayer heterostructures comprising quantum dots of germanium in a silicon matrix has been studied by photoluminescence (PL) and transmission electron microscopy (TEM). The PL spectra of annealed samples reveal a decrease of emission from the quantum dots and display a new emission band as compared to the initial spectra. The TEM measurements show that this effect is related to smearing of the Ge-Si interface and to the appearance of a regular rectangular network of dislocations on the surface of the annealed structure.     

In-situ formation of ultrathin Ge nanobelts bonded with nanotubes

A novel nanostructure of ultrathin Ge nanobelts bonded with nanotubes has been fabricated and characterized. Nanotubes (either carbon or BN) are first coated with amorphous germanium and then heated and observed by an in-situ TEM. The thickness, down to 2 nm, and the width of the Ge nanobelts are determined by the thickness of this amorphous Ge coating and the diameter of nanotubes, respectively.     

Solution-phase synthesis of germanium nanoclusters using sulfur

Sulfur is used to promote the formation of germanium nanocrystals from the robust organometallic precursor, triphenylgermanium chloride, at elevated temperatures (300?°C) in the surfactant/solvent hexadecylamine. Transmission electron microscopy shows that 8?nm germanium nanocrystals are produced that self-assemble into uniform-sized 60?nm germanium nanoclusters after purification. Electron diffraction studies show that the germanium nanoclusters have a diamond germanium crystal structure and energy dispersive x-ray spectroscopy shows that the nanoclusters are primarily composed of pure germanium.     

The role of the structure and surface properties of Sn–Ge melts in the germanium crystallization

By analyzing the local atomic structure using models reconstructed from the experimental structure factor curves by the reverse Monte-Carlo method, we have established that microsegregation in the liquid state takes place in the Sn–Ge system and that tin and germanium atoms form chains with atomic spacings close to the covalent bond in solid state. The increase in the number of germanium atoms participating in cluster formation in diluted melts of germanium noticeably surpasses the increase in the germanium content of the melt, which is the reason for the appearance of extremums in the isotherms of density and surface tension of the Sn–Ge melt that is characterized by small positive deviations of activity from the ideal solution. In parallel with the interfacial energy and supersaturation, the cluster formation of the crystallizing substance with spacings close to the bond of this substance in the solid state contributes to an increase of the crystal growth rate.     

Enhanced effect of local fields in subwavelength metallic series nanocavities from surface plasmon polaritons

The enhancement and confinement characteristics of the local field in the two-dimensional (2D) subwavelength-size series cavities structure are investigated numerically by using the boundary integral method. The series cavities are built of two pieces of finite silver thin slabs with subwavelength corrugations on their inner boundaries, set in a face-to-face arrangement with a separating space, and the central part is a narrow channel (NC). We calculate the average amplitude of the local field in the NC as a function of the wavelength for exploring the influence of the structural parameters and demonstrate the amplitude distribution of the magnetic field in the structure and the cross-section distributions of the local field in the NC region along both the longitudinal axis direction and the transverse directions. The simulations show that the local field in the NC has significant enhancement, up to 2 orders of magnitude, of the incident light field, and the local light field is confined to a small region less than one fifth of the resonant wavelength in the longitudinal direction and one twentieth of the resonant wavelength in the lateral direction. Replacing the metallic material of the cavity walls with the semiconductor germanium leads to the complete disappearance of the enhancement of the local field. It is clearly shown that surface plasmon polaritons on the metal play a critical role for this enhancement phenomenon. The influences of various geometric parameters on the resonant wavelength and the peak value of the average amplitude of the local field are extensively investigated.     

Smooth germanium nanowires prepared by a hydrothermal deposition process

Smooth germanium nanowires were prepared using Ge and GeO₂ as the starting materials and Cu sheet as the substrate by a simple hydrothermal deposition process. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations show that the germanium nanowires are smooth and straight with uniform diameter of about 150 nm in average and tens of micrometers in length. X-ray diffraction (XRD) and Raman spectrum of the germanium nanowires display that the germanium nanowires are mainly composed of cubic diamond phase. PL spectrum shows a strong blue light emission at 441 nm. The growth mechanism is also discussed.     

Synthesis of crystalline and amorphous germanium nanorods

Crystalline and amorphous germanium nanorods have been synthesized by PVD of germanium powders in flowing Ar/H₂ atmospheres. TEM images show diameters of the nanorods ranging from 20 to 200 nm and length up to 5 μm. Selected area electron diffraction indicates that the crystalline nanorods have tetragonal structure. Their growth process has been considered as VLS mechanism.     

Potential energy of two structures of Σ = 110 1 1 tilt grain boundary in silicon and germanium with empirical potentials and tight-binding methods

Two atomic structures A and B of the Σ = 110 1 1 grain boundary were observed in silicon and germanium. We have performed a complete study of the stability of these two grain boundaries using some empirical potentials and also the semiempirical, tight-binding (TB) method. The TB method has confirmed the experimental observations at low temperatures. The A structure is more stable in silicon whereas for germanium the B structure is obtained. The empirical potentials, such as those of Keating (1966), Baraff et al. (1980) and of Stillinger and Weber (1985), give the A structure as the most stable for both germanium and silicon. The non-ability of these empirical potentials to make a difference between germanium and silicon and the advantage of TB method are discussed.     

Evolution Behaviors of Oxides in Severely Plastic Deformed Region of AISI 52100 Steel during Dry Sliding Wear

Under dry sliding wear, the evolution of oxides in severely plastic deformed(SPD) regions of metals has a great impact on the wear behaviors. To study the evolution behaviors of oxides in the SPD region, an SPD region was prefabricated on the surface of AISI 52100 steel by supersonic ?ne particle bombarding(SFPB) treatment. Dry sliding wear tests were carried out on both of the SFPB-treated and original samples.Wear volume loss of the SPBF-treated samples were compared with those of the original samples at different loads. Microstructure, element composition and oxides distribution in the SPD region were characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM) and an electron probe microanalysis(EPMA). The results show that the evolution behaviors of the oxides in the SPD region change signi?cantly with the load. Under low loads, oxides are usually formed on the contact surface. It inhibits adhesive wear on the steel. However, under high loads, oxides are apt to distribute along the cracks in the subsurface layer. The internal oxidation along the cracks can accelerate the cracks propagation, resulting in severe delamination wear on the steel.     

Morphology evolution in a diblock copolymer film

Morphologies of surface micelles of the diblock copolymer polystyrene-block-poly(4-vinylpyridine) (PS-P4VP) at different concentrations were investigated using TEM. Highly-ordered spherical micelles were observed. The morphology was found to depend strongly on the solution concentration. A transformation from spherical to cylindrical micelles and the formation of multilayers of micelles were observed when the concentration was increased. The evolution of the morphology of the diblock copolymer film cast on Si substrates in the presence of different solvents was also investigated using AFM. We find that there is a discrepancy in the structure obtained using TEM and AFM because of the presence of a selective solvent in the TEM sample. The transformation from cylindrical to spherical micelles was observed for the film prepared under a nitrogen atmosphere. Hexagonally ordered holes were observed in the film prepared in air. The presence of moisture in the air may play an important role in the formation of this structure.     

Synergistic effect of carbon black and nanoclay fillers in styrene butadiene rubber matrix: Development of dual structure

Styrene butadiene rubber (SBR) based hybrid nanocomposites containing carbon black (CB) and organo-modified nanoclay (NC) was prepared. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed the presence of intercalated, aggregated, and partially exfoliated structures. Incorporating 10 phr NC to the control SBR containing 20 phr CB resulted 153% increase in tensile strength, 157% increase in elongation at break and 144% stress improvement at 100% strain, which showed synergistic effect between the fillers. The dynamic modulus reinforcement of nanocomposites was examined by the Guth, Modified Guth, and Halpin–Tsai equations. For predicting CB filled nanocomposite modulus, the contribution of modified intercalated structure of clay and the ‘nano-unit’ (dual structure) comprising CB–NC should be considered.     

大塑性变形工艺制备纳米晶过饱和固溶体的研究进展

合金在大塑性变形过程中能够形成纳米晶过饱和固溶体,呈现出不同于传统粗晶材料的微观结构和独特性能。近年来,纳米晶过饱和固溶体的形成机制及其热稳定性已成为国内外的一个研究热点。综述了大塑性变形工艺(如机械合金化法、高压扭转法等)制备纳米晶过饱和固溶体的研究概况,着重讨论分析了大塑性变形诱导纳米晶形成和固溶度扩展的几种机制及其局限性,简要介绍了纳米晶过饱和固溶体的热稳定性及其影响因素,最后对该领域今后的研究方向做出了分析和展望。     

The effect of constrained groove pressing on grain size,dislocation density and electrical resistivity of low carbon steel

In this research, constrained groove pressing (CGP) technique is used for imposing severe plastic deformation (SPD) on the low carbon steel sheets. Using transmission electron microscopy (TEM), X-ray diffraction (XRD) and optical microscopy, the microstructural characteristics of produced sheets are investigated. The results show that CGP process can effectively refine the coarse-grained structure to an ultrafine grain range. Dislocation densities of the ultrafine grained low carbon steel sheets are quantitatively calculated and it is found that the CGP can effectively enhance the dislocation density of the sheets. Measurements of their electrical resistivity values show that microstructure refinement and increasing the dislocation density can efficiently increase the electrical resistivity of the CGPed sheets up to ∼100%.     

Role of severe plastic deformation on the formation of nanograins and nano-sized precipitates in Fe–Ni–Mn steel

In this research, the effect of severe plastic deformation (SPD) on the formation of nano-scaled grains and precipitation of nano-sized particles which consequently control mechanical properties of Fe–Ni–Mn alloy was investigated. Fe–Ni–Mn martensitic steels show excellent age hardenability but suffer from embrittlement after aging. Discontinuous coarsening of grain boundary precipitates, resulting in the formation of precipitate free zone (PFZ) along prior austenite grain boundaries, has been found as the main source of embrittlement in the previous studies. In this paper, severe plastic deformation has been carried out on the Fe–10Ni–7Mn steel to improve its mechanical properties. It is found that substantial improvement of tensile properties in cold-rolled steels occurs at thickness reductions larger than 60% where formation of ultrafine grains is realized. According to transmission electron microscopy (TEM) observations, formation of nano-scaled grains less than 100 nm along with the copious precipitation of nanometer-sized precipitates take place in the severely-deformed steels.     

Surface blistering of low temperature annealed hydrogen and helium co-implanted germanium and its application to splitting of bonded wafer substrates

Applications involving transfer of germanium layers to silicon-based substrates often require a process involving a restricted thermal budget. The use of relatively low temperatures has a major advantage in reducing stresses when thermal splitting of implanted germanium wafers bonded to silicon-based substrates is used to create germanium-on-oxide (GeOI) layers. The present study investigates the phenomenon of blistering of hydrogen and helium co-implanted germanium over the temperature range 250–400 °C, optical microscopy being used to detect the initial appearance of the blisters. Results showed that plots of Ln(time) vs. blister initiation temperature consisted of several straight-line regions yielding an activation energy for each region. The plots showed similarities to those observed in previous work with silicon co-implanted and annealed under similar conditions. At temperatures below the blister initiation temperature, transmission electron microscopy (TEM), revealed the presence of spherical bubbles at a depth below the surface estimated to be approximately that of the hydrogen implant projected range. GeOI layers were produced by thermal splitting of co-implanted germanium wafers bonded to oxide-coated silicon substrates wafers at a temperature of 300 °C. The RMS roughness of the split germanium surface measured by atomic force microscopy (AFM) was about 11 nm averaged over the wafer surface. In addition there were isolated and randomly distributed regions of 27 nm roughness covering about 20% of the total surface area of the wafer.     

Nucleation of the diamond phase in aluminium-solid solutions

Precipitation was studied from f c c solid solutions with silicon, germanium, copper and magnesium. Of all these elements only silicon and germanium form diamond cubic (d c) precipitates in f c c Al. Nucleation of the d c structure is enhanced if both types of atom are dissolved in the f c c lattice. This is interpreted as due to atomic size effects in the pre-nucleation stage. There are two modes of interference of fourth elements with nucleation of the d c phase in Al + Si, Ge. The formation of the d c phase is hardly affected if the atoms (for example, copper) are rejected from the (Si, Ge)-rich clusters. If additional types of atom are attracted by silicon and/or germanium, d c nuclei are replaced by intermetallic compounds (for example Mg₂Si).     

Photoluminescence of carbon-induced Ge islands in silicon

Reducing the size of germanium islands improves their optical properties. The spatially strong localised holes in the islands are more uncertain in momentum and thereby the probability of direct optical transitions is enhanced. Carbon predepositon onto Si has been shown to reduce the size of germanium islands. We have studied such islands grown by molecular beam epitaxy. The germanium islands show an intense PL-signal, which is typically more than one order of magnitude larger in intensity than the PL from silicon–germanium quantum wells. Reducing the amount of Ge from 3.4 monolayer (ML) to 1.0 ML results in a PL blueshift from 0.81 to 1.08 eV in conjunction with a narrowing of the PL peak. The blueshift indicates a reduction in the size of the germanium islands, which was confirmed by TEM. Increasing the C coverage from 0.2 to 0.3 ML leads to a red shifted PL. This is attributed to a change in the aspect ratio of the islands with the result of an increased vertical island height.     

非连续增强金属基复合材料剧烈塑性变形行为研究进展

综述了非连续增强金属基复合材料剧烈塑性变形(SPD)行为的研究进展,系统阐述了等径弯曲通道变形(ECAP)、高压扭转(HPT)、多向锻造(MF)、累积叠轧(ARB)和循环挤压压缩(CEC)5种SPD的加工原理和方法。集中介绍了这些方法在铝基、镁基、铜基和钛基等金属基复合材料方面应用的研究进展。重点介绍了金属基复合材料SPD的微观组织演化和变形力学行为,详细阐明了金属基复合材料SPD机制以及超细晶形成机理,指出了金属基复合材料在SPD中存在的深层次问题及发展趋势,展望了利用SPD方法制备超细晶非连续增强金属基复合材料的应用前景。     

Investigation of ductile damage development in ferritic steel subject to uniaxial deformation

The object of this investigation is the influence of uniaxial deformation on both the formation of voids and ductile damage in ferritic steel. Specimens are prepared by means of a method which, to a large extent, is free of manipulation and permits the crystal's interior to be observed. These specimens were investigated using a scanning electron microscope (SEM). Anisotropic void formation and growth behaviour were exhibited which is correlated with the material texture using an EBSD investigation. Observing the crystalline structure by means of transmission electron microscopy (TEM) enables the effects of the pore formation and growth to be examined in more detail.