C. F. Dee

Optimization of HNA etching parameters to produce high aspect ratio solid silicon microneedles

High aspect ratio solid silicon microneedles with a concave conic shape were fabricated. Hydrofluoric acid–nitric acid–acetic acid (HNA) etching parameters were characterized and optimized to produce microneedles that have long and narrow bodies with smooth surfaces, suitable for transdermal drug delivery applications. The etching parameters were characterized by varying the HNA composition, the optical masks window size, the etching temperature and bath agitation. An L9 orthogonal Taguchi experiment with three factors, each having three levels, was utilized to determine the optimal fabrication parameters. Isoetch contours for HNA composition with 0% and 10% acetic acid concentrations were presented and a high nitric acid region was identified to produce microneedles with smooth surfaces. It is observed that an increase in window size indiscriminately increases the etch rate in both the vertical and lateral directions, while an increase in etching temperature beyond 35 °C causes the etching to become rapid and uncontrollable. Bath agitation and sample placement could be manipulated to achieve a higher vertical etch rate compared to its lateral counterpart in order to construct high aspect ratio microneedles. The Taguchi experiment performed suggests that a HNA composition of 2:7:1 (HF:HNO3:CH3COOH), window size of 500 µm and agitation rate of 450 RPM are optimal. Solid silicon microneedles with an average height of 159.4 µm, an average base width of 110.9 µm, an aspect ratio of 1.44, and a tip angle and diameter of 19.2° and 0.38 µm respectively were successfully fabricated.

Electrochemically deposited and etched membranes with precisely sized micropores for biological fluids microfiltration

This paper presents simple and economical, yet reliable techniques to fabricate a micro-fluidic filter for MEMS lab-on-chip (LoC) applications. The microporous filter is a crucial component in a MEMS LoC system. Microsized components and contaminants in biological fluids are selectively filtered using copper and silicon membranes with precisely controlled microsized pores. Two techniques were explored in microporous membrane fabrication, namely copper electroplating and electrochemical etching (ECE) of silicon. In the first technique, a copper membrane with evenly distributed micropores was fabricated by electroplating the copper layer on the silicon nitride membrane, which was later removed to leave the freestanding microporous membrane structure. The second approach involves the thinning of bulk silicon down to a few micrometers thick using KOH and etching the resulting silicon membrane in 5% HF by ECE to create micropores. Upon testing with nanoparticles of various sizes, it was observed that electroplated copper membrane passes nanoparticles up to 200?nm wide, while porous silicon membrane passes nanoparticles up to 380?nm in size. Due to process compatibility, simplicity, and low-cost fabrication, electroplated copper and porous silicon membranes enable synchronized microfilter fabrication and integration into the MEMS LoC system.

Formulation and simulation for electrical properties of a (5,3) Single Wall Carbon Nanotube

Carbon Nano Tubes (CNTs) are potential candidate to be used in nano transistors and interconnection inside the ICs. In most of these applications, speed of the carriers is very important. Due to small sizes of CNTs, the mobility of electrons is ballistic. On the other hand because of the superabundant free electrons, most of CNTs are in the degenerate regime, where Boltzmann statistics can not be used. However different CNTs have various characteristics. In this research work we formulate and simulate the behavior of a (5, 3) Single Wall Carbon Nano Tube (SWCNT) by using Fermi-Dirac distribution function. Simulation results are in good agreement with the expected results of theoretical analysis. These results show that the E(k) relation of this SWCNT near the minimum energy is close to parabolic, and (Ef - Ec) is a weak (logarithmic) function of carrier concentration, but varies linearly with temperature in the nondegenerate (ND) regime. However, in degenerate statistics, the Fermi energy is independent of temperature and is a strong function of carrier concentration.

Modelling of the current-voltage characteristics of a carbon nano tube field effect transistor

Working on carbon nanotube field effect transistors (CNTFETs) involving the skill to treat electronic devices at the molecular scale. Nanotubes are being considered as the best candidates for high-speed applications. The charge transport in CNTs is controlled by mobility and saturation velocity. It has also been shown that the high mobility does not always lead to higher carrier velocity. In the high electric field, velocity vectors are changed from randomness to streamline. Velocity approach is applied to the modelling of the current-voltage characteristic of a carbon nanotube field effect transistor. According to the simulation results, in the absence of the quantum capacitance, the short channel effects are arising. However it is foreseeable that if the quantum capacitance takes into consideration, this effect can be improved.

Influence of growth temperature on SnO2 nanowires

Abstract Tin oxide (SnO2) nanowires have been synthesised using a thermal evaporation approach on quartz (SiO2) substrates in nitrogen atmosphere with a mixture of milled SnO2 powder and graphite as reactants. The substrates were placed vertically right above the reactants during the growth at 850, 900, 950 and 1000°C. A SnO2 thin film layer has been used as the nucleation site which is different from the conventional methods of using metal catalyst as seed for growth. SnO2 thin films have self-catalysed to form SnO2 nanowires at 950°C. At 850 and 900°C, plenty of SnO2 clusters landed on the substrates which were originated from the non-vaporised SnO2 powder. An optimum range of temperature was obtained for growth of clean SnO2 nanowires which were free from metal catalysts and non-vaporised SnO2 clusters.

Simulation for deposition of ZnO thin film layer by kinetic Monte Carlo method

Abstract Kinetic Monte Carlo method was used to simulate the deposition of ZnO thin film layers. For this simulation, parameters for atom absorption, desorption and surface diffusion were incorporated to perform more realistic model of deposition. A new approach was used where the diffusion process was integrated as part of the deposition process. Simulations were carried out at different substrate temperatures. Two- and three-dimensional growth mechanisms were simulated using this model. Surface roughness can be estimated from the ratio of the atoms at the edge of the islands to the total surface sites. The number of Zn and O adatoms on the surface as a time function was analysed.

Synthesis and characterization of sn doped ZnO nanowires

This paper reports on synthesis and characterizations of Sn doped ZnO nanowires. Sn doped ZnO nanowires was successfully been grown using carbothermal reduction method. Morphological and structures were characterized using FESEM, revealed that nanowires grown on random direction with diameter around 30 – 60 nm. EDX analysis was used to confirm composition element, Sn element was found in the nanowires in less than 1% of total composition. XRD was applied to examine structure quality of Sn doped ZnO nanowires, XRD spectra shown the structure have high crystallinity and it is wurtzite structure. No contrast different were found between pure and Sn doped ZnO nanowires. I-V measurement shown that using Sn as dopant may decrease the resistance of ZnO nanowires.

Synthesis and characterisation of Zn–Sn–In–O quaternary nanostructure system

Abstract This paper reports the synthesis and characterisation of a quaternary nanostructure system of Zn–Sn–In–O. This quaternary system has been synthesised using the vapour thermal method. Three distinct shapes of nanostructures out of this quaternary system were obtained. All three elements formed their own oxide nanostructures according to SEM observation. The effect of segregation among these three materials seemed to dominate and influence the growth process, which caused separative growth of three different nanostructures. The hierarchical growth of the nanostructures on top of each other could also be observed in the SEM images. The presence of all the elements was confirmed using EDX. The X-ray diffraction results proved and revealed the high crystallinity of these nanostructures.

Analysis and simulation of carriers statistic for semiconducting single wall carbon nanotube

Abstract In scaling down to 10 nm, the electron transportation is predominantly ballistic. Moreover, in most of the doped nanoscale devices, the carrier density is in the degenerate regime. In these cases the failure of Boltzmann statistic has led the research to new explanations. In this paper the authors formulate and simulate the carrier concentration in a semiconducting single wall carbon nanotube using the Fermi-Dirac distribution function. It was shown that the band structure of semiconducting single wall carbon nanotube nearby the minimum energy is parabolic and density of state is proportional to the Fermi-Dirac distribution. In the non-degenerate regime, Fermi energy is a weak logarithmic function of carrier concentration and varies linearly with temperature, but for strongly degenerate statistics, the Fermi energy is a strong function of carrier concentration and is independent of temperature.

Study of the contact properties of ZnO nanowires with Ag and Au/Ag

Zinc oxide (ZnO) nanowires have been synthesized using thermal evaporation approach on quartz (SiO2) substrates in nitrogen atmosphere with a mixture of milled ZnO and graphite powder as reactants. Ohmic behavior has been obtained for both Ag and Au/Ag contact to ZnO nanowires. The samples were re-examined after annealing at 300degC, 400degC and 500degC. The optimum annealing temperature for obtaining minimum resistance of Ag and Au/Ag contact with ZnO nanowires are 400degC and 300degC respectively. The contact is dominated by Metal-Zinc bonds rather than Metal-Oxygen bonds which cause the formation of ohmic behavior.