STM induced modification of gold surface in the presence of TMP amine

In this paper we present scanning tunneling microscopy (STM) investigations of gold with 2,2,6,6-Tetramethylpiperidine (TMP) overlayer. During the STM experiments the creation of holes and hills or no changes of the surface were observed depending on the applied bias voltage and polarity. No modifications were observed in the bias range from −0.5 to +0.5 V. The holes were created for the bias voltages greater than +0.5 V and hills for the bias voltages lower than −0.5 V. The observed changes of the surface morphology suggest the presence of electrochemical reaction between the tip and the surface. Additionally, our results suggest that TMP lowers the electrochemical activation energy of gold to +0.5 eV.     

Hydrothermal treatment of ZnO nanostructures

Hydrothermal treatment of ZnO nanostructures involves low temperatures (150-200 °C) and elevated water vapor pressure for the purpose of the improvement in the material properties. Under such moderate conditions, no significant changes in the morphology would be expected. Nevertheless, such treatment results in a significant change of nanostructured morphologies of ZnO. The observed changes are dependent on the starting material properties and the substrate used for the growth. In the case of Si substrate, hydrothermal treatment results in significant Si contamination of the samples. In terms of the optical properties, improvements are observed only in some cases, while samples with excellent starting optical properties are degraded by the treatment. Mechanisms responsible for the observed changes are discussed.     

Selective area growth of GaN nanowires using metalorganic chemical vapor deposition on nano-patterned Si(111) formed by the etching of nano-sized Au droplets

We report on the selective area growth of GaN nanowires (NWs) on nano-patterned Si(111) substrates by metalorganic chemical vapor deposition. The nano-patterns were fabricated by the oxidation of Si followed by the etching process of Au nano-droplets. The size of formed nano-pattern on Si(111) substrate was corresponding to the size of Au nano-droplet, and the diameter of GaN NWs grown was similar to the diameter of fabricated nano-pattern. The interesting phenomenon of using the nano-patterned Si(111) substrates is the formation of very clear substrate surface even after the growth of GaN NWs. However, in the case of GaN NWs grown using Au nano-droplets, there was several nanoparticles including GaN bulk grains on the Si(111) substrates. The smooth surface morphology of nano-patterned Si(111) substrates was attributed to the presence of SiO₂ layer which prevents the formation of unnecessary GaN particles during the GaN NW growth. Therefore, we believe that nano-patterning method of Si(111) which was obtained by the oxidation of Si(111) substrate and subsequent Au etching process can be utilized to grow high-quality GaN NWs and its related nano-device applications.     

Optimized inductively coupled plasma etching for poly(methyl-methacrylate-glycidly-methacrylate) optical waveguide

Optical loss is a crucial quality for the application of polymer waveguide devices. The optimized oxygen inductively coupled plasma etching conditions, including antenna power, bias power, chamber pressure, O₂ flow rate and etching time for the fabrication of smooth vertical poly(methyl-methacrylate-glycidly-methacrylate) channel waveguide were systematically investigated. Atomic force microscopy and scanning electron microscopy were used to characterize the etch rate, surface roughness and vertical profiles. The increment of etch rate with the antenna power, bias power and O₂ flow rate was observed. Bias power and chamber pressure were found to be the main factor affecting the interface roughness. The vertical profiles were proved to be closely related to antenna power, bias power and O₂ flow rate. Surface roughness increment was observed when the etching time increased.     

Template-free mechanochemical route to prepare crystalline and electroactive polydiphenylamine nanostructures

A facile and sustainable mechanochemical route for the synthesis of undoped polydiphenylamine (PDPA) and inorganic acid doped nanostructures are reported. Field emission scanning electron microscopic (FESEM) images highlighted the formation of distinctly different nanostructures for each of the inorganic acid doped PDPA. Elemental analysis carried out for the polymers revealed the presence of more repeating units in their backbone. The X-ray diffraction (XRD) results of the as-prepared PDPA nanostructures indicated the high degree of crystallinity ever reported for PDPA. Spectroscopic profile of the polymers showed that the prepared PDPA is in a doped conducting form. Electrochemical studies performed for the polymeric particles ascertained the redox behaviour and the good electrochemical activity of obtained PDPA samples. The probable mechanistic aspect behind the formation of PDPA nanostructures through this simple and efficient route is discussed.     

Effect of ion irradiation on internal stress of amorphic carbon films produced by pulsed laser

Amorphic carbon films either 50 or 160 nm thick were deposited on Si(100) and glass substrates at room temperature in a high-vacuum environment using a Q-switched Nd-YAG pulse laser focused on a graphite target. These films were irradiated with Ti⁺ or C⁺ ions having kinetic energies of 35 and 75 keV, and the changes in internal stresses of the films with varying ion influence were investigated by measuring substrate bending using stylus profilometry. The ion energy and the film thickness were chosen such that the ion penetration depth, R_p, corresponded to either the film thickness or one half of the film thickness. The results indicate that there is an optimum ion fluence leading to a stress-free film for a given ion species and energy. Interpretation of the resulting stress behavior from ion irradiation was made based on the relaxation resulting from damage inside the film together with interfacial mixing. The scanning electron microscopy pictures and surface roughness measurements showed a very smooth surface for both as-deposited and ion-irradiated films. The ion-irradiated films had a Vickers hardness greater than 22 GPa, and were adherent to both Si and glass substrates. An investigation of the film characteristics using Raman scattering and electron-energy loss spectra has revealed that high-energy ion irradiation of an intermediate ion fluence can be utilized successfully to deposit an adherent and hard carbon film with controlled internal stress without changing the film structure significantly.     

Doughnut-shaped hierarchical Cu2ZnSnS4 microparticles synthesized by cyclic microwave irradiation

For the first time, hierarchical doughnut-shaped Cu₂ZnSnS₄ (CZTS) microparticles were synthesized by microwave-assisted solution method. N,N-dimethylformamide and polyvinylpyrrolidone (PVP) were used as solvent and stabilizing agent respectively, and the results showed that PVP played an important role in the formation of hierarchical nanostructures. Structural analysis by X-ray diffraction and Raman studies confirmed the formation of single phase kesterite CZTS. Morphological analysis by scanning electron microscope showed doughnut-shaped CZTS microparticles composed of large number of interpenetrating nanoplates. Optical analysis by UV–Vis diffused reflectance spectra showed strong absorption in the visible region with an optical band gap of 1.54 eV. Asymmetric broad emission bands around 1.55 eV and 1.30 eV were observed in the photoluminescence spectrum. A possible formation mechanism for doughnut-shaped CZTS microparticles was put forward and discussed briefly.     

Subtractive methods to form pyrite and sulfide nanostructures of Fe,Co, Ni,Cu and Zn

The low Z metals Fe, Co, Ni, Cu and Zn are Earth abundant, i.e. inexpensive, and their sulfides are of low toxicity. This makes them appealing candidates for materials applications requiring semiconductors or, in the case of CoS₂, a metal since they can potentially be produced in large quantities and low cost. Though of great potential little work has explored how subtractive methods can be used to form nanostructured and/or porous structures in, e.g. FeS₂, CoS₂, NiS, Cu₂S and ZnS.     

Facile conversion of bulk metal surface to metal oxide single-crystalline nanostructures by microwave irradiation: Formation of pure or Cr-doped hematite nanostructure arrays

We report a method for converting the surfaces of bulk metal substrates (pure iron or stainless steel) to metal oxide (hematite or Cr-doped hematite) nanostructures using microwave irradiation. When microwave radiation (2.45 GHz, single-mode) was applied to a metal substrate under the flow of a gas mixture containing O₂ and Ar, metal oxide nanostructures formed and entirely covered the substrate. The nanostructures were single crystalline, and the atomic ratios of the substrate metals were preserved in the nanostructures. When a pure iron sheet was used as a substrate, hematite nanowires (1000 W microwave radiation) or nanosheets (1800 W microwave radiation) formed on the surface of the substrate. When a SUS410 sheet was used as a substrate, slightly curved rod-like nanostructures were synthesized. The oxidation states of Fe and Cr in these nanorods were Fe³⁺ and Cr³⁺. Quantitative analyses revealed an average Fe/Cr atomic ratio of 9.2, nearly identical to the ratio of the metals in the SUS410 substrate.     

STM/STS investigations of titanium oxide nanostructures on au substrate

Au substrate was prepared by Au evaporation on Si(111) surface. Au surface was composed of Au grains with typical diameter of about 50 nm with atomically flat terraces. TiO₂ nanostructures were created by electron gun evaporation of Ti while simultaneous dosing of high purity O₂ gas. The pressure of oxygen was kept at 5 · 10^− 8 mbar and controlled by means of residual gas analyzer (RGA). Scanning tunneling microscopy (STM) images showed that TiO₂ nanocrystallites had grown between Au grains in cavities between them. This may suggest that such spots are preferred TiO₂ nucleation sites. I-V curves measured above Au showed metallic properties while those measured above TiO₂ exhibit energy gap characteristics for semiconducting material.     

Patterning of porous silicon nanostructures and eliminating microcracks on silicon nitride mask using metal assisted chemical etching

A method for selective formation of reproducible, high fidelity and controllable nano and micrometer size porous Si areas over n-type Si wafers is provided. A 400 nm thick Silicon Nitride layer was used as the mask layer while Platinum and Palladium nanoparticles were deposited over the unprotected areas to obtain porous areas through metal assisted chemical etching process. Nanoparticles were deposited by electroless plating solutions containing H₂PtCl₆ and PdCl₂. Good controls over pore size and depth were obtained with well defined and sharp edges of the patterned areas. The results were compared to porous structures obtained via electrochemical etching process, indicating the superiority of metal assisted etching in terms of its simplicity as well as the ability of Silicon Nitride layer acting as the mask layer.     

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.     

HDDR NdFeB磁粉的表面缺陷与成因

利用扫描电子显微术和Ｘ射线衍射分析技术研究了ＨＤＤＲＮｄＦｅＢ磁粉的表面缺陷与成因,发现ＨＤＤＲＮｄＦｅＢ磁粉的表面缺陷主要是表面微裂纹,其形成原因主要是Ｎｄ２Ｆｅ１４Ｂ化合物在氢化一歧化过程中体积膨胀所导致的内应力。     

Catalyst-referred etching of silicon

A Si wafer and polysilicon deposited on a Si wafer were planarized using catalyst-referred etching (CARE). Two apparatuses were produced for local etching and for planarization. The local etching apparatus was used to planarize polysilicon and the planarization apparatus was used to planarize Si wafers. Platinum and hydrofluoric acid were used as the catalytic plate and the source of reactive species, respectively. The processed surfaces were observed by optical interferometry, atomic force microscopy (AFM) and scanning electron microscopy (SEM). The results indicate that the CARE-processed surface is flat and undamaged.     

Crystalline and amorphous carvedilol-loaded nanoemulsions: formulation optimisation using response surface methodology

This study aimed to evaluate the crystalline and amorphous carvedilol along with their lipidic mixtures using various instrumental techniques and to use response surface methodology in conjunction with factorial design to establish the functional relationships between operating variables (capmul GMS 50?K and cremophor RH 40).

The response variables selected are spectroscopic absorbance (Y ₁), mean particle size in distilled water (Y ₂) and in phosphate buffer pH 6.8 (Y ₃), polydispersibility index (PDI) (Y ₄) and zeta potential (Y ₅).

The optimal formulations of crystalline and amorphous carvedilol-loaded nanoemulsions were composed of fixed levels, ?0.41 and ?0.42, of capmul GMS 50?K and cremophor RH 40, respectively. The predicted and observed values of Y ₁–Y ₅ for blank nanoemulsions showed the percentage bias error of ?12.12%, ?10.25%, ?18.47%, +14.81 and ?2.89, respectively. The bias percent ranged between ?2.70% and ?29.41% for the responses Y ₁–Y ₄ for both crystalline and amorphous carvedilol-loaded nanoemulsions, indicating high degree of prognosis. However, the bias percent values for the response variable Y ₅ were 294.2% and 262.6%, for the crystalline and amorphous carvedilol-loaded nanoemulsions, respectively, possibly due to cationisation of emulsion droplets. The transmission electron microscopy of selected optimal nanoemulsions showed the spherical shape of globules with no signs of coalescence and precipitation of drug.

This study demonstrates the use of factorial design for the preparation of nanoemulsions of crystalline and amorphous carvedilol. The desirable goals can be obtained by systematic formulation approach in the shortest possible time.     

Wood cellulose biocomposites with fibrous structures at micro- and nanoscale

High-strength composites from wood fiber and nanofibrillated cellulose (NFC) were prepared in a semi-automatic sheet former. The composites were characterized by tensile tests, dynamic mechanical thermal analysis, field-emission scanning electron microscopy, and porosity measurements. The tensile strength increased from 98 MPa to 160 MPa and the work to fracture was more than doubled with the addition of 10% NFC to wood fibers. A hierarchical structure was obtained in the composites in the form of a micro-scale wood fiber network and an additional NFC nanofiber network linking wood fibers and also occupying some of the micro-scale porosity. Deformation mechanisms are discussed as well as possible applications of this biocomposites concept.     

Nanometer-scale electronic and microstructural properties of grain boundaries in Cu(In,Ga)Se2

Despite many recent research efforts, the influence of grain boundaries (GBs) on device properties of CuIn_1−xGa_xSe₂ solar cells is still not fully understood Here, we present a microscopic approach to characterizing GBs in polycrystalline CuIn_1−xGa_xSe₂ films with x = 0.33. On samples from the same deposition process we applied methods giving complementary information, i.e., electron backscatter diffraction (EBSD), electron-beam induced current measurements (EBIC), conductive atomic force microscopy (c-AFM), variable-temperature Kelvin probe force microscopy (KPFM), and scanning capacitance microscopy (SCM). By combining EBIC with EBSD, we find a decrease in charge-carrier collection for non-∑3 GBs, while ∑ 3 GBs exhibit no variation with respect to grain interiors. In contrast, a higher conductance of GBs compared to grain interiors was found by c-AFM at low bias and under illumination. By KPFM, we directly measured the band bending at GBs, finding a variation from − 80 up to + 115 mV. Depletion and even inversion at GBs was confirmed by SCM. We comparatively discuss the apparent differences between the results obtained by various microscopic techniques.     

The effect of carbon content on the microstructure of hydrogen-free physical vapour deposited titanium carbide films

Titanium carbide (TiC) coatings for tribological applications were deposited on high speed steel. Several coatings with different titanium to carbon ratio were deposited by means of physical vapour deposition in which titanium was evaporated and carbon was sputtered. The coatings were characterised using analytical electron microscopy. It was observed that the change in titanium to carbon ratio significantly changed the microstructure of the coatings. The low carbon containing coatings consisted of columnar grains exhibiting a preferred crystallographic orientation whereas the coating with highest carbon content consisted of randomly ordered TiC grains in an amorphous carbon matrix. Energy filtered transmission electron microscopy revealed a change in Ti/C ratio as the distance from the substrate increased. The titanium to carbon ratio was observed to increase with distance from the substrate until a stable level was reached. This is due to a variation in the titanium evaporation during the early stages of film growth. This change of the titanium to carbon ratio affected the columnar growth in the initial stage of coating growth for the coatings with low carbon content.     

Temperature and pH dependence of the electroless Ni–P deposition on silicon

The sensitization, activation, nucleation and growth of electroless Ni–P deposition on silicon in an acid plating bath with sodium hydrophosphite as reducing agent and sodium succinate as complexing agent were studied by transmission electron microscopy, field emission scanning electron microscopy and atomic force microscopy. The results show that a continuous polycrystalline SnCl₂ film was formed on the silicon surface in the sensitization process, and small crystalline Pd particles were dispersedly produced on SnCl₂ film in the activation process. In the initial deposition stage, the small Ni–P particles had already emerged on the silicon surface in a deposition time of less than 2 s. When Ni–P particles grew, their size increased but their number decreased, and they later developed into a columnar structure. The deposition rate of the electroless Ni–P deposit increased as the pH value and the temperature of the plating bath increased (from 1.36 to 29.66 μm/h). The activation energy of the electroless Ni–P deposition on silicon increased as the pH value of the plating bath decreased (from 68.8 to 79.4 kJ/mol).