International Journal of Nanoscience

Nanometer-scale silicon oxide mask was patterned by atomic force microscope (AFM) lithography for fabrication of nanoelectronic devices. The oxide growth mechanism is similar to a well-known local anodic oxidation, which a negative voltage applied to conductive AFM tip in order to grow oxide patterns on silicon layer surface. The surrounding environment is one of the very important parameter on the formation of nanoscale silicon oxide patterns via AFM lithography. Therefore, in this work, the effect of relative humidity (RH) has been studied systematically in the range of 55–72%. Meanwhile, the applied tip voltage, exposure time, and scanning speed were kept constant during lithography process. From AFM topographic analysis on the fabricated nanopatterns found that the oxide width and thickness are significantly depending on the room humidity. These results proved that the room humidity is playing an important role on the fabrication of nanometer-scale oxide patterns by using AFM nanolithography.

Quasi-solid-state dye-sensitized solar cells were fabricated using a high molecular polymer redox electrolyte. Poly(ethylene oxide) (PEO) and Poly(vinylidenefluoride-co-hexafluoropropylene) (P(VDF-HFP)) were used to form a stable quasi-solid structure and a three-dimensional gel polymer network structure. The polymer electrolytes were composed of LiI, I₂, and DMPII in the mixture of propylene carbonate (PC) and γ-butyrolactone (GBL) with different volume ratios. A metal-free organic dye (indoline dye D102) was used as a sensitizer. The ionic conductivity of the gel polymer electrolytes was measured with Electrochemical Impedance Spectroscopy (EIS). The dependence of the ionic conductivity on the volume ratio of PC to GBL was investigated. The volume ratio of the mix solvent, weight ratio of PEO/P(VDF-HFP), and the weight ratio of TiO₂ fillers were optimized. The optimized quasi-solid-state cell exhibited an efficiency of 5.49% at full sunlight (air mass 1.5, 60 mW/cm²) irradiation.

AlGaN/GaN-based heterostructure field-effect transistors (HFETs) with and without Mg-doped semi-insulating carrier confinement layer were simulated by using ISE TCAD software, respectively. The detailed study on the electrical properties of these samples was performed. The effect of inserting Mg-doped GaN layer on the source–drain (S–D) leakage current was investigated. Higher values of drain current and extrinsic transconductance were achieved with conventional HFETs (without Mg-doped). The source-to-drain (S–D) leakage current of conventional HFETs was also higher. However, the S–D leakage current was reduced with the insertion of the Mg-doped semi-insulating carrier confinement layer. Our results are in good agreement with the experimental results obtained by other researchers.

The introduction of new molecular states originating from the anchoring groups has a profound effect on the transport properties of molecular junctions for nanodevice applications. In this work, a bipyridine molecule is anchored via dithiocarbamate, thiocarboxylate, and carboxylate end groups and is analyzed to explore the effect of these anchoring groups on transmission. Also asymmetric anchoring of molecule with Au electrodes is studied. We adopt a transport model for molecular conduction involving an extended Huckel theoretical treatment combined with nonequilibrium Green's function. We observed that the molecule with carbodithiolate linker yields significant broadening of peaks in the transmission spectra and improves significantly electron transport properties of the molecular junction. These theoretical results will help to design and fabricate future molecular devices.

Theoretical understanding of electron transport phenomena through single molecules is of great importance for the design of future devices and materials in molecular electronics. Nonequilibrium Green's function (NEGF) formalism combined with extended Huckel (EHT) theory is used to investigate the electron transport characteristics of Au–benzene–Au, Au–borazine–Au, and Au–BCN–Au systems with selenium (Se) as terminal group. It is observed that the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of borazine ring is higher than the benzene and BCN does. Our result shows that for the terminal group selenium borazine is the best core molecule than benzene and BCN systems.

In situ Raman measurements have been carried out on a thin bundle of single-walled carbon nanotubes (SWNTs) in field effect transistor configuration at various gate voltages. Two excitation lasers with the photon energy of 1.96 eV and 2.41 eV, respectively, are selected to excite the Raman scattering modes of metallic and semiconducting SWNTs in the bundle, respectively. For the metallic SWNTs, the G^- Raman mode is found to shift to higher frequencies and narrow down its line shape at negative gate voltages, but be insensitive to positive gate voltages. These findings confirm that the Kohn anomaly exists in a thin SWNT bundle and that the LO phonon mode changes along with the position of the Fermi level in the metallic SWNTs. In contrast, semiconducting SWNTs do not show any observable changes in the Raman spectra.

In the present study, 0.05 wt.% of Ni-coated multi-walled carbon nanotubes (Ni-CNTs) were successfully incorporated into the 95.8Sn–3.5Ag–0.7Cu solder using the powder metallurgy technique, to synthesize a new lead-free composite solder. Its mechanical property (in terms of hardness) was investigated at room temperature using the nanoindentation method. The results revealed that the nanoindentation hardness increased by 14.3% with the incorporation of 0.05 wt.% of Ni-coated CNTs. This observation is in good agreement with the microhardness test results. Moreover, the addition of Ni-CNTs improved the creep resistance of the composite solder. The test results established that nanotechnology coupled with composite technology in electronics solders can result in the enhancement of mechanical properties. These advanced interconnect materials will thus benefit the microelectronics assembly and packaging industry.

Atomic force microscope (AFM) nanolithography was performed to create nanowire transistor pattern via local anodic oxidation process on surface of silicon-on-insulator (SOI) wafer. This nanoscale oxide pattern is used as a mask system for chemical etching to produce silicon nanowire transistor. The device with component structures of a silicon nanowire (SiNW) as channel with source, drain, and gate pads had been drawn at 9 V tip voltage, 6 μm/s writing speed with humidity 55.8–68.9%RH. The designed device was etched with tetramethylammonium hydroxide (TMAH) to remove uncovered silicon layer but oxide pattern remains. In order to obtain SiNW transistor, sample was etched using hydrogen fluoride (HF) to remove oxide layer. From the AFM and field emission scanning electron microscope (FESEM) observation found that the SiNW transistor with wire size of 92.65 nm in wire thickness, 90.83 nm wire width and 10.30 μm in length with contact pads size of about 5 μm × 5 μm has been successfully fabricated.

Thermosetting polymer gel electrolytes (TPGEs) based on poly(acrylic acid)-poly(ethylene glycol) (PAA-PEG) hybrid were prepared and applied to fabricate dye-sensitized solar cells (DSCs). N-methylpyrrolidone (NMP) and γ-butyrolactone (GBL) were used as solvents for liquid electrolytes and LiI and KI as iodide source, separately. The microstructure of PAA-PEG shows a well swelling ability in liquid electrolyte and excellent stability of the swollen hybrid. The TPGE was optimized in terms of the liquid electrolyte absorbency and ionic conductivity photovoltaic performance. Quasi-solid-state DSCs containing TPGE with optimized KI electrolyte show higher efficiency, voltage, fill factor, and lower photocurrent than those with LiI electrolyte. The related mechanism was discussed. A quasi-solid-state DSC fabricated with optimized polymer gel electrolyte obtained an overall energy conversion efficiency of 4.90% under irradiation of 100 mW/cm² (AM1.5).

The titanium dioxide nanotubes (TiNTs) were directly prepared from commercial P25 TiO₂ powder via alkali hydrothermal transformation. The fabricated nanotubes had an average outer diameter of 8–10 nm and the inner diameter of 4–6 nm with several hundred nanometers in length. The prepared nanotubes were added into TiO₂ nanoporous electrodes for the fabrication of dye-sensitized solar cells (DSCs). The photoelectrochemical characteristics and dye-adsorption properties were investigated by varying the proportion of the nanotubes incorporated into TiO₂ working electrodes. The electron transport resistance, electron life time, and dye adsorption properties were evaluated in terms of electrochemical impedance spectra and photovoltaic characteristics of the solar cells. Compared to DSCs based on TiO₂ nanoparticles, the fill factor, open-voltage, and photocurrent based on TiNT/P25 hybrid increased significantly. High conversion efficiency of light-to-electricity of 7.41% under illumination of simulated AM 1.5 sunlight (100 mW/cm²) was achieved for DSCs using optimized proportions of TiO₂ nanotubes incorporated into TiO₂ electrodes. The studies provided a promising method for the development of high efficiency and low cost DSCs.

We have studied the preparation of hybrid organic–inorganic polymers and the fabrication of distributed feedback grating using those hybrid polymers. The hybrid polymer precursors were prepared from ester-modified silicon alkoxide by using sol–gel technique. The gel precursor can be then polymerized into a solid film by photo-polymerization. The gratings were fabricated by interference laser technique by employing Lloyd's mirror configuration. The Atomic Force Microscopy (AFM) image shows the formation of corrugated grating structure. Although the grating depth is relatively shallow compared to the thickness of the layer, the photo-pumped lasing action has been observed in those structures. In a film without grating structure, only Amplified Spontaneous Emission (ASE) was observed.

Channel waveguides have been fabricated in x-cut lithium niobate (LiNbO₃) by proton exchange (PE) method and optically measured. The thickness and the optical constants of the thin PE layer were characterized using a prism coupling technique. The PE area was plasma etched and a 2.775-μm total etching depth was achieved. The measured average etching rate is 92.5 nm/min. One- and two-dimensional dense arrays of LiNbO₃ nanostructures have also been fabricated by using interference lithography (IL) and inductively coupled plasma reactive ion etching (ICP-RIE) techniques.

ZnO nanowires (NWs), grown by hydrothermal and vapor phase transport (VPT) methods, were employed as the channel layers to fabricate single nanowire Field Effect Transistors (NWFETs) with a p⁺-silicon as the bottom gate. The FET employing hydrothermal grown ZnO NWs shows n-type depletion mode with a field mobility of 18.27 cm²/V⋅s, an on/off ratio of 10⁶, and a threshold voltage of -48.5 V. In comparison, the device using VPT grown NWs operates in n-type depletion mode with a field effect mobility of 36.94 cm²/V⋅s, a drain current on/off ratio of 10⁵, and a threshold voltage of -14 V. The reason for the difference of threshold voltage and the mobility by two methods was discussed in this paper.

Two sets of multilayer structures consisting of 44 alternating layers of a-SiN_x:H (~ 4 nm and 6 nm) and SiO₂ (5 nm) have been fabricated using the plasma-enhanced chemical vapor deposition (PECVD) technique. The a-SiN_x:H that has a lower bandgap forms the well layer, while the large bandgap SiO₂ forms the barrier layer. A single bulk layer of a-SiN_x:H has also been grown to serve as a reference for comparison with the multilayer structures. The samples were studied using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), spectroscopic ellipsometry (SE), and photoluminescence (PL) techniques. The SE data have been successfully fitted, and the complex refractive indices of the a-SiN_x:H in the bulk and multilayers have been determined. The effects of quantum confinement on the optical bandgap and refractive indices of a-SiN_x:H have been investigated. The results are correlated to the PL spectra of the samples.

Based on ab initio formulation and using nonequilibrium Green's function (NEGF) formalism, electronic transport in the presence of electron–phonon interactions in strained-engineered nanoscale transistors is presented. Ab initio methods are applied to treat the metal/semiconductor interface properly. NEGF formalism is applied as quantum transport and phonon scattering are the dominant factors in devices under realistic operating voltages. Local self-energy functions for electron–phonon scattering have been obtained using deformation potential theory. This approach is applied to the study of electronic transport in strain-engineered nanowire transistors. Electron–phonon interactions on broadening of local density of states are also reported.

Nanoscaled zinc oxides were grown on a polycrystalline Zn metal sheet by using an atmospheric-pressure plasma jet (APPJ) with pure oxygen as the reaction gas in an ambient environment. The initial growth formed nanoparticles on the polycrystalline Zn substrate. The nanoscaled ZnO growth process was as follows: nanoparticles, nanocrystal clusters, and then nanocrystal columns with increasing plasma treatment times. The morphologies of nanoscaled ZnO resembled bulbs, long-legged tetrapods, and multipods. The morphologies and structures of the nanoscaled ZnO thus obtained were investigated by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and grazing-incidence X-ray diffraction (GIXRD). The possible growth mechanisms of nanoscaled ZnO are discussed in this paper.

The effect of laser energy fluence and substrate heating on the annealing of boron-implanted silicon–germanium epitaxial layers on silicon was investigated. By making use of the difference in the melting points of silicon–germanium and silicon, a process window in the laser energy fluence can be found such that the meltdepth was confined within the silicon–germanium. Pre-heating of the substrate to 300°C was done to reduce the laser fluence required and improve the surface morphology. Cross-sectional transmission electron microscopy showed that there were no end-of-range defects due to ion implantation at the silicon–germanium/silicon interface after the laser annealing.

The absorption spectra of semiconductor quantum dots (QDs) are expected to be a series of δ-function-like discrete lines due to the nature of the density of states. In a realistic III–V QD system, the absorption spectra is the superimposition of the contribution from each individual dot and the overall behavior is modeled by considering a Gaussian size distribution. In this paper, we study and present the dependence of the Gaussian nature of the absorption spectra of In_XGa_1-XN/GaN QD systems on the dot size distribution and some fundamental parameters such as bowing effect of the band gap, band offset ratio, and so on. It is observed that the absorption spectra depend strongly on the dot size distribution. The results presented helps to get a better insight of the optical properties of In_XGa_1-XN/GaN QD systems.

Phase Change Random Access Memory (PCRAM) is one of the next-generation nonvolatile memories with the most potential. A transient measurement method has been developed to link the transient phase change effect to its crystallization kinetics. The flexibility of this measurement method was demonstrated in this paper. This method was first applied to study scaling effects in phase change devices and it was found that scaling not only lowers programming current requirement, but also increases the phase change speed of the device. This suggests that high density and high speed phase change memory devices through scaling are achievable. The same method was applied to study the physical model of phase change and the evidence suggests that phase change in these devices does not proceed solely by nucleation, supporting the hypothesis of filament formation during phase change. This transient method would be an important analysis technique of novel phase change devices and materials.

TiO₂ thin films have been deposited onto well cleaned glass substrates by sol–gel spin coating method. The prepared TiO₂ films have been annealed at different temperatures (350°C, 450°C and 550°C). The structural properties of the films have been studied using X-ray diffraction method and High Resolution Transmission Electron Microscope (HRTEM). The as-deposited films have been found to be amorphous in nature. The crystalline quality has been observed to improve with annealing temperature. The annealed TiO₂ films have been found to exhibit anatase phase. The optical properties have been studied using transmittance spectrum.

Surface plasmon polariton is surface electromagnetic waves that propagate parallel along a metal/dielectric interface through a 1D or 2D periodic structures. Since the polaritons wave is confined at interface, the surface plasma polariton (SPP) is very sensitive to any changes on this boundary that directly change the effective refractive index of the system. This enables us to do some variations to control the SPP, i.e., modifying the metallic nanostructure of the plasmonic crystal (PCL) to vary the effective refractive index. Interference lithography has been widely used to produce different orders of periodic/array of nanostructures. It also has been used as the most economist and efficient way to provide 1D and 2D plasmonic crystals over large area. However, this method suffers from nonlinear processes involved in the manufacture of nominally sinusoidal surface relief diffraction gratings that can introduce distortions. Such distortions may dramatically affect both the specular reflectivity and diffracted efficiencies from plasmonic crystals. Therefore, the quality of surface profile and some geometrical parameters need to be controlled in order to optimize the coupling condition. This will lead us to the understanding of the fundamental geometrical contribution to obtain the field enhancement and variety of profile qualities.

Square-wave cathodic current modulation was used to electrodeposit fine-grained iron from citric acid bath. The effect of pulse on-time, off-time, peak current density, and total plating time on the grain size, surface morphology, and crystal orientation was determined. X-ray diffraction analysis and modified Williamson–Hall relation were used to determine the average grains size of the coatings. The experimental results showed that an increase in peak current density resulted in considerable refinement in crystal size of the deposits. An increase in the pulse off-time at constant on-time and peak current density resulted in a progressive increase in crystal size. However, the crystal orientation remained unaffected with increasing off-time. The design of the pulse deposition parameters is described in terms of the transport limitations through the diffusion layer and electrochemical interface stability.

Formation of carbon nanoclusters in a laser-pulse created plume expanding in vacuum and in a noble gas environment at various pressures was studied. Experiments were performed with carbon nanoclusters formed by laser ablation of graphite targets with 12-picosecond 532 nm laser pulses at MHz-range repetition rate in a broad range of ambient He, Ar, Kr, and Xe gas pressures from 2 × 10^-2Torr to 1500 Torr. The experimental results confirmed our theoretical prediction that the average size of the nanoparticles depends weakly on the type of the ambient gas, and is determined exclusively by the single-laser pulse parameters. The most important finding relates to the fact that in vacuum the cluster size is mainly determined by hydrodynamic expansion of the plume, while in the ambient gas it is controlled by atomic diffusion in the gas.

We report on the fabrication of carbon nanotube field effect transistors (CNTFETs) from dispersed single-walled CNTs using OCMC (O-Carboxymethylchitosan) as the surfactant. The as-prepared devices exhibit p-type as well as ambipolar characteristics due to oxygen adsorption at the metal/nanotube contacts. The Raman scattering from the SWCNTs shows that OCMC disperses CNTs efficiently. Rapid thermal annealing (RTA) at 400°C for 5 min is found to partially remove OCMC from the surface of SWCNTs.