Key Engineering Materials Vols. 326-328

Abstract: This paper discusses possibilities to extract elastic-plastic properties of nano-scale materials using combined nano-indentation tests with FE simulations. One interesting finding is that FE simulations of nano-indentation with a number of different plastic properties give same load-displacement response, which suggests that plastic properties cannot be determined from simulating load-depth curves from nano-indentation tests. However, careful examination of possible plastic properties suggests a concept of the reference strain, which makes it possible to effectively determine plastic properties from nano-indentation tests with FE simulations.

Abstract: TiO2 colloids prepared by sol-gel method were autoclaved and then deposited onto a transparent conducting oxide substrate by screen-printing. The TiO2 films electrode was characterized by XRD, SEM, AFM and Alpha-Step profilometer and then sensitized by zinc phthalocyanine (ZnPc), 2,9,16,23-tetracarboxy zinc phthalocyanine (ZnTCPc) and ZnTCPc/lauric acid respectively. Photocurrent density (I) and photovoltage (V) of the electrode were measured with the solar simulator. The ZnTCPc-sensitized electrode was found the best performance with the short-circuit photocurrent density (Isc) 16.66 3A/cm2, the open-circuit photovoltage (Voc) 277.9 mV and the fill factor (FF) 0.39. And the ZnPc-sensitized electrode was found the worst performance with Voc 114.2 mV, Isc 2.26 3A/cm2 and FF 0.31. It was also found that lauric acid promoted Voc of the the ZnTCPc sensitized system.

Abstract: Based on the CaCO3-B4C-C system to prepare calcium hexaboride (CaB6) powder, the influence of B4C size on the CaB6 powder was investigated in this paper, in which micro-sized B4C in various size and nano-sized CaCO3 were as main raw materials. XRD and SEM were used to characterize the phase pattern, size and morphology of CaB6 powder particles respectively. Laser particle size analyzer was employed to determine the size distribution of CaB6 particles. It was found that the size of B4C had a dominant effect on the size and distribution of CaB6 powder particles. When B4C particles were much coarser than CaCO3, the CaB6 synthesized appeared as aggregates which size relied on B4C, however, the size of every CaB6 particle was determined by CaCO3. When B4C particles size was fine to several microns, the CaB6 particles synthesized were dispersive and the size of them has great relation to B4C. Synthesis models were also established to describe various reaction processes.

Abstract: This paper reports the scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) studies of porous Zn (p- Zn) prepared by electrochemical etching. Further, the post annealing of the p- Zn is carried out and STM/STS investigations are also performed. STM studies of these samples reveal the porous structure and display small, pseudo-spherical shaped crystals in the range of 2 and 100 nm, 2 and 50 nm, and similar average corrugation of 9 nm for p- Zn and oxidized p-Zn. STS analysis of freshly prepared p- Zn shows a band gap of 2.4 eV along with metallic conductance behavior. However, oxidized p- Zn reveals a distinct wide band gap (3 eV) and shows shallow donor states near the conduction band.

Abstract: Atomic force microscopy (AFM) is widely used in many fields, because of its outstanding force measurement ability in nano scale. Some coating layers are used to enhance the signal intensity, but these coating layers affect the spring constant of AFM cantilever and the accuracy of force measurement. In this paper, the spring constants of rectangular cantilever with different coating thickness were quantitatively measured and discussed. The finite element method was used to analyze the nonlinear force-displacement behavior from which the cantilever’s normal and torsional spring constants could be determined. The experimental data and the numerical results were also compared with the results from other methods. By considering the influence of coating layers and real cantilever geometries, the more accurate force measurements by AFM cantilever can be obtained.

Abstract: Nickel-Iron nanocrystalline alloys with different grain sizes were fabricated by electrodeposition technique. In this study, influence of the grain size nanocrystalline NiFe deposits on saturation magnetization Ms and coercivity Hc was investigated. Alternating gradient magnetometer (AGM) with up to 10 kOe applied magnetic field was used to study the magnetic properties of NiFe film. The results showed that saturation magnetization Ms and coercivity Hc were affected by grain size variation. Increase in grain size increased the saturation magnetization. The largest grain size of 18.6 nm showed the highest Ms of 138 emu/g, while the smallest grain size of 7.2 nm showed Ms of 94 emu/g. Minimum coercivity of 3.847 Oe was observed for sample with 7.2 nm grain sizes. The coercivities decreased for smaller grain sizes.

Abstract: The flexible organic thin film transistor(OTFT) array to use as a switching device for an organic light emitting diode(OLED) was designed and fabricated in the nanocontact printing and low-temperature process. The gate, source, and drain electrode patterns of OTFT were fabricated by nanocontact printing process. And dielectric layer of parylene and organic active semiconductor layer of pentacene formed at room temperature or at a temperature lower than 40
. The nanocontact printing process using SAM and PDMS stamp made it possible to fabricate OTFT arrays with channel lengths down to even submicron size, and reduced the fabrication process by 10 steps compared with photolithography. Since the process was done in room temperature, there was no pattern shrinkage, transformation, and bending problem appeared. Also, it was possible to improve electric field mobility, to decrease contact resistance, to increase close packing of molecules by SAM, and to reduce threshold voltage by using a parylene.

Abstract: As copper technology moves from pilot to volume manufacturing, semiconductor fabrication is focused on methods to improve device yield. In especially semiconductor manufacturing, electrochemically deposited copper is the material of choice for advanced interconnect applications. Electrochemical deposition (ECD) employs copper plating electrolytes with organic additives to achieve bottom-up filling of small vias and trench with high aspect-ratios. However, for features with small aspect-ratios, the ECD process yields conformal layers because the additives and the bottom-up fill mechanism are not operative in such large features. So, ECD process does not achieve within-die and within-wafer planarity of the deposited copper layer. For planarization of large features and obtaining globally and locally flat films, an electro-chemical mechanical deposition (ECMD) method has been employed. ECMD process is a novel technique that has ability to deposit planar conductive films on non-planar substrate surfaces. Technique involves simultaneous ECD roles and mechanical sweeping of the substrate surface. Copper layer deposited by the ECMD process grows preferentially in cavities on the wafer surface yielding flat profiles and much reduced overburden thickness. Preferential deposition into the cavities on the substrates surface may be achieved through two different mechanisms. The first mechanism is more mechanical in nature and it involves material removal from the top surface. The second mechanism is more chemical in nature and it involves enhancing deposition into the cavities where mechanical sweeping does not reach, and reducing deposition onto surfaces that are swept. Planar layers obtained by the ECMD technique are suitable for low stress material removal processes. Planar layers also yield improved parametric results in device structures after the material removal step. In this study, we demonstrate mechanical role of pad gives effects in ECMD process. So we evaluate gap-filling and planarization between ECMD and ECD.

Abstract: The structure and morphology of the electrospun nanofiber depend on the parameters such as the physical properties of polymer, the applied voltages, tip to collector distance and ambient condition. Until now, most of studies have been focused on the effects of the above mentioned parameters for electrospinning process. But the study on vacuum conditions in electrospinning process almost not exists. The goal of this study is to investigate the effects of vacuum conditions in electrospinning process. The setup of electrospinning device is installed within homemade vacuum chamber. The polymer jets are ejected from a multi-spinneret connected with a microsyringe pump towards the collector located at fixed distance from the needle tip under a vacuum condition. The nanofiber mats are fabricated using a rotating collector. The visualization and imaging system of electrospinning process are consisted of a green laser devices, microscope, CCD camera and image recording device. During the electrospinning process, the behaviors of nanofiber are visualized and analyzed by this system. The morphologies and dimensions of electrospun fiber mat are measured with SEM. As a final result, the vacuum conditions of electrospinning process influence the behaviors of nanofiber.

Abstract: The spark processing of metallic Sn yields a powder, which is a mixture of nanosize Sn and crystalline SnO2. This paper reports the characteristics of nanosize Sn powders. Scanning tunneling microscopy (STM) and transmission electron microscopy (TEM) studies reveal an existence of spherical shaped nanocrystals ranging from 2 to 5 nm in size. In contrast the measured surface area of spark processed Sn (sp-Sn) powders by BET is 27.7 m2/g and calculated average size of sp- Sn is about 31 nm, which is close to one order of magnitude larger than the observed size. Further, the characteristics of sp-Sn powders are studied by Raman, and differential thermal analysis (DTA).