Journal of Nano Research Vol. 4

Abstract: Frequency modulation atomic force microscopy (FM-AFM) has been a powerful tool for imaging atomic-scale structures and properties of various materials including metals, semiconductors, metal oxides, alkali halides and organic systems. Whilst the method has been used mainly in ultrahigh vacuum environments, recent progress in FM-AFM instrumentation made it possible to apply this technique also to investigations in liquid. This technological innovation opened up a variety of applications of FM-AFM in biology and electrochemistry. To date, the improved FM-AFM instrument and technique have been applied to investigations of several biological materials, providing novel information that has not been accessible with other imaging techniques. In this review, I will summarize the recent progress in FM-AFM instrumentation and biological applications in liquid.

Abstract: In this work, we report the fabrication of porous silicon multilayers using lightly doped, p-type, silicon wafers (resistivity: 14-22 Ω-cm) by pulsed anodic etching. The optical properties have been found to be strongly dependent on the duty-cycle and frequency of the applied current. Less than 50 % of duty-cycle, at low frequencies, is found to show very rough porous silicon – crystalline silicon (PS-cSi) interface. Use of duty cycle above 50 %, in a certain range of frequencies, is found to make the interface smooth. The optical properties of the photonic devices are investigated for 50 % and 75 % of duty-cycle, for different frequencies in the range of 0-1000 Hz, using the current densities of 10, 90 and 150 mA/cm2. The possibility of fabricating rugate filter with this resistivity is also explored.

Abstract: Zinc oxide (ZnO) nanorods on Au patterned Si substrates were fabricated using vapor transport method. The XRD pattern showed the ZnO nanorods were highly c-axis oriented similar to ZnO thin films. The photoluminescence spectrum at 77 K of ZnO nanorods was consisting of the fundamental near band edge emission of ZnO in the UV region along with a broad defect induced emission around green band. The field emission properties of the nanorods showed a current density of 1mA/cm2 at an applied field of 10V/m, which is comparable to other reported values of ZnO nanorods. The patterned gold island formed by self-assembly of polystyrene ball on Si substrate acted as a catalyst in the growth of nanorods as well as stable ohmic contact for field emission.

Abstract: Sintering of a ZnO-MgO powder mixture under argon flow leads to the growth of elongated Mg doped ZnO structures such as stacks of nanoplates and rods with secondary nanowires in a comb-like arrangement. The nanoplates grow perpendicular to a central axis and have a six-fold symmetry. The hierarchical growth is related to the presence of Mg. Cathodoluminescence (CL) in the scanning electron microscope shows a blue-shift of the ZnO exciton peak as well as changes in the deep level bands due to the influence of Mg.

Abstract: Functionalization of CNFs with silane coupling agents (SCAs) has been studied in this work. APS silane has been used in order to study the influence of temperature and reaction time on the silanization process. Thermal analysis and surface area measurements have revealed that reaction times higher than 1 min. and temperature reaction higher than 25°C do not increase the amount of adsorbed silane on CNFs surface. Silanization process carried with different SCAs (APS, AMO, DMO and GMO) has allowed the study of the concentration and silane structure influence. It has been observed that differences in SCA adsorption are related to the silane structure. Aminosilanes APS and AMO show a very similar behaviour because they have the same functional group. However, the diaminosilane DMO shows lower interaction with CNFs surface due to the length of the diamine chain, that avoid further silane adsorption on the coated CNFs surface. The epoxysilane GMO shows a similar behaviour to other SCAs at low concentrations, while for high silane concentrations epoxysilane GMO forms multilayers.

Abstract: Multiwalled carbon nanotubes (MWNTs) were fabricated by thermal chemical vapor deposition (CVD) using monometallic and bimetallic Co and Ni on MgO as the catalyst. The mixture of H2/C2H2 gas was used as carbon source. The prepared CNTs have different sizes/shapes and morphologies with minimal formation of carbon particles. The maximum yield of CNTs was obtained with 50% Co catalyst at 600 oC. The morphology of the CNTs with 50% Co loading generates curved structure while 50% Ni results in the formation of linear structure with aligned graphene walls. Intensity ratio of D and G-peaks (ID/IG) was measured from Raman spectra. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) was done for the structural analysis of the prepared MWNTs.

Abstract: Various gold nanowires with very small cross-sections (few atoms) have been studied using the Gupta potential. Gold nanowire icosa structure is found to be most stable among structures studied. The values of cohesive energy, Young’s modulus and shear modulus have been computed and all the values (except poisson ratio) are more than that of bulk gold. Another striking observation about gold nanostructures is that the Young’s modulus increases with tube radius whereas shear modulus decreases.

Abstract: Inorganic semiconductors have properties that are notoriously difficult to control due to the deleterious impact of crystalline imperfections, and this is especially so in solar cells. In this work, it is demonstrated that materials grown using wet chemistry processes for the preparation of nanocristalline precursors can achieve the same performance as the best state of the art, namely conversion efficiencies above 11% with CuInS2. Interestingly, due to the growth process, the active material inherit a porous morphology that is shown to play a part in the performance and functionality of the active material. The new device morphology leads to a device operation closer to that of nanoscale organic interpenetrated solar cells or dye sensitized solar cells than to those of standard polycrystalline ones.

Abstract: Tin oxide nanoparticle was successfully prepared by the chemical digestion method from the starting material as SnCl2. The SnO2 material was characterized by X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM) and Selected Area Electron Diffraction (SAED). The SnO2 was an n-type material preferred to humidity sensing property towards the moisture. The response and recovery time of sensor was calculated as 129sec and 206sec respectively. It has exhibited better efficiency compared with the bulk SnO2 material. Additional Weight loss, EDS, FT-IR and resistivity measurements were also presented.

Abstract: Amorphous silicon on amorphous carbon (a-Si/a-C) multilayers was deposited by RadioFrequency (RF) sputtering. These multilayers were obtained by alternate deposition of a-C and a-Si layers, respectively from graphite and silicon targets of high purity, on crystalline silicon substrates. The RF power and the argon pressure, during the pulverization, were maintained respectively at 250W and 10-2 mbar. The annealing effects, at temperatures of 450°C and 750°C, on the deposited structures were investigated by X-ray reflectometry. The a-Si/a-C interfaces are abrupt before and after annealing at 450°C. The annealing at 750°C leads to a net decrease of both the upper a-Si layer thickness and the total multilayer thickness with a net enhancement of the interfaces reactivity. The upper silicon layer is crystallized after annealing at 750°C.