Synthesis and characterization of single crystalline SnO<Subscript>2</Subscript> nanorods by high-pressure pulsed laser deposition

Tin oxide (SnO₂) nanorods were grown by high-pressure pulsed laser deposition (PLD). The nanorods were grown without the use of a catalyst but required high background pressure growth in order to realize small grain columnar growth and nanorod formation, with nanorod formation most favored on non-epitaxial substrates. The structures and morphology were characterized by field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). X-ray diffraction and HRTEM analysis indicate that the as-grown SnO₂ nanorods are single crystals with a rutile structure. The nanorods are approximately 50–90 nm in diameters and 1.5 μm in length. This method provides an approach for large area synthesis of one dimensional SnO₂ nanostructure materials. PACS 81.16.Mk; 61.46.-w; 81.07.-b     

Chemical polishing method of GaAs specimens for transmission electron microscopy

A practical method for transmission electron microscopy specimen preparation of GaAs-based materials with quantum dot structures is presented to show that high-quality image observations in high-resolution transmission electron microscopy (HRTEM) can be effectively obtained. Specimens were prepared in plan-view and cross-section using ion milling, followed by two-steps chemical fine polishing with an ammonia solution (NH₄OH) and a dilute H₂SO₄ solution. Measurements of electron energy loss spectroscopy (EELS) and atomic force microscopy (AFM) proved that clean and flat specimens can be obtained without chemical residues. HRTEM images show that the amorphous regions of carbon and GaAs can be significantly reduced to enhance the contrast of lattice images of GaAs-based quantum structure.     

Characterization of carbon nanotubes by scanning probe microscopy

Carbon nanotubes, fabricated by the Ebbesen-Ajayan method, were imaged using scanning tunneling microscopy (STM) and atomic force microscopy (AFM) in air and were compared to images obtained with high-resolution transmission electron microscopy (HRTEM). The HRTEM images revealed an abundance of elongated structures ranging in diameter from 3.0 to 30 nm, and with lengths of up to 0.8 μm. Many of the structures possessed several graphitic shells as if the tubes were nested one in the other. Reproducible images of the tubular structures, typically 20 nm in diameter and with a large variation in length, were obtained with both STM and AFM when the nanotubes were deposited on hydrogen-terminated Si(111), confirming that the nested structures observed with HRTEM do indeed have a tubular morphology. No single-walled, bare nanotubes or spherical fullerenes (typical of the Krätschmer-Huffman process) were observed.     

Experimental study of lattice distortion in ellipsoid-like nano-crystallites of copper

The elastic state of embedded inclusions is of considerable importance to the properties of materials. The non-uniform lattice distortion in the inclusions in which the interfaces are shaped with variable curvature cannot be measured by usual experimental methods. In this paper, the lattice distortions in an ellipsoid-like nano-crystallite of copper were measured by means of the peak finding method in the central part of the HRTEM image. The effects of contrast delocalization are studied by HRTEM image simulations, which show that the measured spacings of peaks in the middle part of the crystallite can be considered approximately equal to the true spacings of columns. With the HRTEM method, our measured results show that the nano-crystallite is expanded in the short axis direction and compressed in the long axis direction. The results calculated with the elasticity theory incorporating interface tension consist with the experimental results of HRTEM.     

Incommensurate modulations in Ba2TiSi2O8, Sr2TiSi2O8, and Ba2TiGe2O8

Incommensurate modulations in Ba₂TiSi₂O₈, Sr₂TiSi₂O₈, and Ba₂TiGe₂O₈ are compared based on their corresponding electron diffraction patterns. The dependence of the modulations on chemical composition provides a suitable model system for the investigation of incommensurations in framework structures using high-resolution transmission electron microscopy (HRTEM). A widening of quantitative HRTEM utilising the concept of rigid units is proposed allowing for a determination of atomistic displacements responsible for the formation of incommensurately modulated structures.     

Domain configurations of the "incommensurate" structures of 2H-TaSe2 and Bi2Sr2(Ca1-xLn(x))Cu2O8+delta studied by HRTEM

High-resolution transmission electron microscopy (HRTEM) images of the "incommensurate" structures of 2H-TaSe2 and Bi2Sr2Ca1-xLnx Cu2O8+delta (Ln: rare earth metal) are shown. They were taken from a wide specimen area with homogeneous thickness. For the former, a configuration of two domains was found by a scrutiny of HRTEM images. For the latter, many configurations of two domains were extracted from the photometric density distribution in the one-dimensional contrast modulations in HRTEM images. One domain of the two in both configurations is created by a phase slip occurring in the primary atomic displacement longitudinal wave.     

Transmission electron microscopy investigation of the atomic structure of interfaces in nanoscale Cu–Nb multilayers

Multilayers of Cu–Nb have been grown on a Nb seed layer on a Si (100) substrate using a magnetron sputtering technique. The bilayer period (Λ) was varied from 10 to 2.4 nm. Cross-sectional transmission electron microscopy (XTEM) and high-resolution TEM (HRTEM) were used to study the detailed structure as a function of the bilayer period. Although the majority of the structures conformed to a Kurdjumov–Sachs (K–S) orientation relationship between the Cu and Nb layers, the structures exhibit considerable spatial variation. In some local regions, a Nishiyama–Wasserman (N–W) orientation relationship was found. In addition, considerable distortions were observed in both the Cu and Nb regions close to the interface. Using both HRTEM imaging and fast Fourier transform (FFT) of HRTEM images, early stage of the fcc to bcc transition in Cu was detected. The results suggest that, in multilayer structures, the detailed structure of the interface and large local distortions may play an important role in interface-controlled plasticity.     

碲、硒碲合金纳米线的可控合成

"采用一种新的化学溶液法合成了具有不同形貌的碲、硒碲合金纳米线．用十二烷基苯磺酸钠作为表面活性剂实现了对纳米线的可控合成,通过控制反应过程可以弯曲状、"V"字型的硒碲纳米线,利用XRD、TEM以及HRTEM对纳米线的形貌结构特征进行表征;以实验结果为依据讨论了纳米线的生长机理．"     

UV-vis Absorption and PL Properties of Self-Assembled Silicon Nanotubes

Silicon nanotubes （SiNTs） are novel one-dimensional nanomaterials, which have potential applications in nano- photoelectric devices, sensors and field-emission devices. The self-assembled silicon nanotubes have clear structures without metal catalysts. The structures are confirmed by TEM and HRTEM, and the UV-vis absorption spectra with an absorption peak near 685nm and PL spectra with widened strong emission near 436nm are measured by UV-vis spectrometer and spectroftuorophotometer.     

Surface and interfacial structural characterization of MBE grown Si/Ge multilayers

Si/Ge multilayer structures have been grown by solid source molecular beam epitaxy (MBE) on Si (1 1 1) and (1 0 0) substrates and were characterized by high-resolution X-ray diffraction (XRD), atomic force microscopy (AFM), high-depth-resolution secondary ion mass spectroscopy (SIMS) and cross-section high-resolution transmission electron microscopy (HRTEM). A reasonably good agreement has been obtained for layer thickness, interfacial structure and diffusion between SIMS and HRTEM measurements. Epitaxial growth and crystalline nature of the individual layer have been probed using cross-sectional HRTEM and XRD measurements. Surface and interface morphological studies by AFM and HRTEM show island-like growth of both Si and Ge nanostructures.     

Interface roughness of GaAs/AlAs superlattices MBE-grown on vicinal surfaces

The interface morphology of GaAs/AlAs superlattices grown by molecular beam epitaxy on misoriented (001) GaAs substrates has been investigated using X-ray diffraction techniques in addition to high-resolution transmission electron microscopy (HRTEM). We observe that the width and intensity of the satellite peaks are very sensitive to the step-edge orientation. Among the investigated ones ([ 110], [100], [110]), it is the [ 10] step-edge direction which is the most favourable to a regular growth of superlattice structures. Structural models based on HRTEM observations (step distribution at interfaces and local fluctuation of layer thickness) have been constructed, allowing an explanation of the X-ray diagrams.     

HRTEM image contrast of short range order in Ni4Mo

The high resolution transmission electron microscope (HRTEM) imaging of short range order (SRO) in Ni4Mo was investigated by means of multi-slice image simulations. The HRTEM images of Ni4Mo exhibit locally bright dot patterns corresponding to the [001] projections of the N2M2-type (chalcopyrite-like) structure. The multi-slice simulations revealed that the N2M2 patterns are rationalized as the projection patterns of the SRO structure which consists of subunit cell clusters of D1a, D022 and Pt2Mo structures. The N2M2-type image contrast appears when both the fundamental fcc lattice reflections and the 1 1/2 0 diffuse scattering of SRO contribute enough to imaging. This suggests that a good coincidence in intensity distribution between the Fourier power spectra of HRTEM images and the electron diffraction patterns is one of the conditions for the image contrast of SRO to be interpreted in terms of the projection contrast.     

HRTEM and EELS study of Y2O3/MgO thin films

Y2O3 thin films deposited on (001)-MgO substrate have been investigated by high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy. Digital processing of the HRTEM images reveals the presence of grains with a crystallographic structure different from that of the rest of the film (Ia3). The spectrum imaging technique has been applied in vicinity of the Y2O3/MgO interface to get a better knowledge of the phases nucleated on the substrate surface. Fine structures of the O K-edge have been studied in detail; actually two kinds of spectra have been detected in the yttrium oxide thin film. These spectra have been compared to self-consistent full multiple scattering calculations (SC-FMS). One family of spectra has then been associated to the well-known Ia3 structure. The other family of spectra has been compared to calculations performed for the other known structures (such as hexagonal or monoclinic) of Y2O3 with a little success. We have finally compared these spectra to calculations performed with a particular atomic arrangement (octahedral) of Y and O atoms, which leads to a good match between experimental and calculated spectra. Our results emphasize the benefit of coupling several techniques such as HRTEM, EELS and SC-FMS for the determination of structures at the nanometric scale.     

Domain structures in rutile in ultrahigh-pressure metamorphic rocks from Dabie Mountains, China

According to the HRTEM study, the UHP jadeite-quartzite mineral (Rutile, TiO(2)) in Anhui Province, Dabie Mountains, China, has ultrastructures such as 011 two-dimensional commensurable modulated structures or superstructures, [011] twin domain structures, dislocations and crystal deformations. The SAED patterns and HRTEM images indicate the existence of the deformations and stacking faults on the interface of [011] twin crystal of rutile and its two-dimensional commensurate modulated structures with repetition period 0.753 nm (3d(011)) has tetragonal symmetry, cell parameters a = 3a0 = 1.377 nm (a0 = 0.459 nm), c = c0 = 0.3 nm. The modulated structures of rutile were probably caused by the isomorphic replacement of Ti(4+) and position modulation or occupation modulation of oxygen atoms in different degree; the deformation structures reveal that during the process of crystallization and mineralization, this mineral may be affected by the geological environment (such as temperature, pressure and stress), metamorphism and deformation.     

Crystallographic aspects related to the high pressure–high temperature phase transformation of boron nitride

Crystallographic relations between different forms of boron nitride (BN) appearing at the high pressure–high temperature structural phase transformation have been revealed by high-resolution transmission electron microscopy (HRTEM). As starting materials, crystalline hexagonal BN (hBN) with different degrees of crystallinity, or with defects intentionally introduced, were used. Cubic BN (cBN) is formed only as a minor component, the rest consisting of different forms of sp ² bonded BN: hBN, compressed, monoclinic deformed hBN, or turbostratic BN (tBN). The small cBN crystallites (300–400?nm) contain many defects such as twins, stacking faults and nanoinclusions of other BN forms: tBN, rhombohedral BN (rBN) and wurtzite BN (wBN). The cBN phase grows epitaxially on the basal plane of hBN. The nucleation sites for cBN are revealed by HRTEM. They consist of nanoarches (sp ³ hybridized, highly curved nanostructures), frequently observed at the edges of the hBN crystallites in the starting materials. Based on HRTEM observations of specimens not fully transformed, a nucleation and growth model for cBN is proposed which is consistent with existing theoretical and experimental models.     

Self-assembly of gold nanoparticles into chain-like structures and their optical properties

Au nanoparticles with diameters of ca. 15 nm were synthesized according to the well-developed citrate reduction method. It was found that the nanoparticles tended to attach and fuse into each other to form chain-like structures with the removal of the stabilizing agents. UV–Vis absorption and HRTEM characterizations provided solid evidence for the fused features. On the basis of the HRTEM observations, we believed the decreased surface energy as well as the dipole–dipole interaction is responsible for the formation of the chain-like structures. SERS activity investigation indicated that the intensities of the b2-type bands have close relation with the concentration of the probing molecules, which further confirmed the chemical effect character of the b2-type scatterings.     

Au, Ge, and AuGe nanoparticles fabricated by laser ablation

A eutectic AuGe target immersed in distilled water was ablated by pulsed ultraviolet laser light. The structure of the ablated material was investigated by high-resolution transmission electron microscopy (HRTEM). The images show formation of nanowire structures of AuGe up to 100 nm in length, with widths of 5–10 nm. These nanostructures have Ge content significantly lower than the target material. Electron diffraction demonstrates that they crystallize in the α-AuGe structure. For comparison, laser ablation of pure Au and pure Ge targets was also performed under the same conditions. HRTEM shows that Ge forms spherical nanoparticles with a characteristic size of ~30 nm. Au forms spherical nanoparticles with diameters of ~10 nm. Similar to AuGe, it also forms chainlike structures with substantially lower aspect ratio.     

单晶ZnO纳米棒的H2O2辅助水热法制备与表征

以二水醋酸锌和氢氧化钠为起始原料,采用H2O2辅助水热法制备了粒径分布均匀的ZnO纳米棒,用XRD、FTIR、FESEM、HRTEM和SEAD等手段对其进行了表征.结果表明,制备的ZnO纳米棒是单晶体,具有六边形截面并沿[0001]晶体方向生长.光致发光谱(PL)测试结果表明,添加H2O2制得的ZnO纳米棒在390nm...     

Preparation and characterizations of SiO2-coated nanoparticles of Mn0.4Zn0.6Fe2O4

Core/shell nanoparticles consisting of a magnetic core of zinc-substituted manganese ferrite (Mn_0.4Zn_0.6Fe₂O₄) and a shell of silica (SiO₂) are prepared by a sol-gel method using tetraethyl orthosilicate (TEOS) as a precursor material for silica and salts of iron, manganese and zinc as the precursor of the ferrite. Three weight percentages of the shell materials of SiO₂ are used to prepare the coated nanoparticles. The X-ray diffractograms (XRD) of the coated and uncoated magnetic nanoparticles confirmed that the magnetic nanoparticles are in their mixed spinel phase in an amorphous matrix of silica. Particles sizes of the samples annealed at different temperatures are estimated from the width of the (3 1 1) line of the XRD pattern using the Debye-Sherrer equation. The information regarding the crystallographic structure together with the particles sizes extracted from the high-resolution transmission electron microscopy (HRTEM) of a few selected samples are in agreement with those obtained from the XRD. HRTEM observations revealed that particles are coated with silica. The calculated thickness is in agreement with that obtained from the HRTEM pictures. Hysteresis loops observed in the temperature range 300 down to 5 K and Mössbauer spectra at room temperature indicate superparamagnetic relaxation of the nanoparticles.