nan Khairurrijal

Analytic model of direct tunnel current through ultrathin gate oxides

A theoretical model for tunnel leakage current through 1.65–3.90-nm-thick gate oxides in metal-oxide-semiconductor structures has been developed. The electron effective mass in the oxide layer and the Fermi energy in the n+ poly-Si gate are the only two fitting parameters. It is shown that the calculated tunnel current is well fitted to the measured one over the entire oxide thickness range when the nonparabolic E-k dispersion relationship for the oxide band gap is employed. The electron effective mass in the oxide layer tends to increase as the oxide thickness decreases to less than 2.80 nm presumably due to the existence of compressive stress in the oxide layer near the SiO2/Si(100) interface.

Intense green and yellow emissions from electrospun BCNO phosphor nanofibers

BCNO phosphor nanofibers, composed of polycrystalline-BCN and B2O3 crystal, were prepared by electrospinning followed by calcination at 700 °C. These showed intense green and yellow emissions under UV-light irradiation that could be seen by the naked eye. The prepared nanofibers were uniform, non-agglomerate, thermally resistant, and had a good atomic distribution.

A constant-current electrospinning system for production of high quality nanofibers.

A constant-current electrospinning system has been successfully developed to produce high quality nanofibers. In order to keep at a certain value of the electric current, a proportional integral-derivative (PID) control action was employed, in which the PID parameters were manually tuned. The desired value of electric current was quickly achieved and no overshoot was observed in the system output. The restoration of the electric current due to a disturbance occurred rapidly.Poly(vinyl pyrrolidone) PVP nanofibers have been produced from a precursor solution prepared by dissolution of the PVP powder in a mixture of dimethyl formamide and ethanol using the constant-current electrospinning system. The cone jet shape observed at the end of the needle during the injection of the precursor solution became shorter with increasing electric current. The diameter of the PVP nanofibers was very uniform and reduced with increasing electric current, which is consistent with the model.

High performance electrospinning system for fabricating highly uniform polymer nanofibers.

A high performance electrospinning system has been successfully developed for production of highly uniform polymer nanofibers. The electrospinning system employed a proportional integral-derivative control action to maintain a constant current during the production of polyvinyl acetate (PVAc) nanofibers from a precursor solution prepared by dissolution of the PVAc powder in dimethyl formamide so that high uniformity of the nanofibers was achieved. It was found that the cone jet length observed at the end of the needle during the injection of the precursor solution and the average diameter of the nanofibers decreased with decreasing Q/I, where Q is the flow rate of the precursor solution of the nanofibers and I is the current flowing through the electro spinning system. A power law obtained from the relation between the average diameter and Q/I is in accordance with the theoretical model.

Unified analytic model of direct and Fowler–Nordheim tunnel currents through ultrathin gate oxides

A theoretical model to predict the gate tunnel current in metal–oxide–semiconductor structures has been developed by employing the nonparabolic E-k dispersion for describing the tunneling electron momentum. The tunnel electron effective mass mox and the Fermi energy in the gate have been used to fit the calculated tunnel current to the measured one. It is shown that in the direct tunneling regime the tunnel electron effective mass mox apparently increases with decreasing oxide thickness presumably due to the reduction of Si–O–Si bond angle in the compressively strained layer near the SiO2/Si interface, while in the Fowler–Nordheim tunneling regime mox remains constant at 0.50 m0.

Home‐made PIC 16F877 microcontroller‐based temperature control system for learning automatic control

A closed‐loop temperature control system, which is composed of a thermal plant and a controller, has been developed to support undergraduate students in learning automatic control delivered in the Special Topics in Instrumentation Physics course. The thermal plant was made from a plastic box covering a lamp and a fan, which heats and drains the air in the plastic box, respectively, as well as a temperature sensor. The controller with a proportional control action was realized by employing the PIC 16F877 microcontroller. The control signal updates pulse‐width modulators (PWMs) in which driver circuits turn on or off the lamp and the fan. A mathematical model of the closed‐loop control system was derived and a theoretical transient response was then obtained. It is found that the experimental transient responses were always much lower than the set point and the steady‐state errors were high for the proportional sensitivity (KP) lower than 10. For KP higher than 10, the transient responses tend to approach the set point to cause small steady‐state errors. These characteristics are consistent with the theoretical transient response. Further examination revealed that the closed‐loop system is a higher order system due to the action of the PWMs and the driver circuits.

Model of a tunneling current in an anisotropic Si/Si1−xGex/Si heterostructure with a nanometer-thick barrier including the effect of parallel–perpendicular kinetic energy coupling

A theoretical model of an electron tunneling current in an anisotropic Si/Si1−xGex/Si heterostructure was developed. The parallel and perpendicular kinetic energies were coupled and the coupling was included in expressing the electron transmittance through the anisotropic heterostructure. The model was applied to the anisotropic Si(1 1 0)/Si0.5Ge0.5/Si(1 1 0) heterostructure with a 25 nm thick strained Si0.5Ge0.5 potential barrier, in which each layer of the heterostructure has three valleys (valleys 1, 2 and 3) with different inverse effective mass tensors and a conduction band discontinuity of 216 meV. The Si(1 1 0)/SiGe structure implies that only the four equivalent valleys (valleys 1 and 2) are considered in calculations. It was found that the transmittance for valley 1 is the same as that for valley 2 due to the same barrier height. The transmittance decreases as the electron phase velocity increases because the electron phase velocity enhances the barrier height. Moreover, the total tunneling current density for the phase velocity higher than 3 × 105 m s−1 differs significantly from that obtained without including the kinetic energy coupling. As the electron phase velocity gets higher, the total tunneling current density lowers. This implies that the coupling effect cannot be ignored for electrons with high phase velocity.

A simple spectrophotometer using common materials and a digital camera

A simple spectrophotometer was designed using cardboard, a DVD, a pocket digital camera, a tripod and a computer. The DVD was used as a diffraction grating and the camera as a light sensor. The spectrophotometer was calibrated using a reference light prior to use. The spectrophotometer was capable of measuring optical wavelengths with a theoretical accuracy as high as 0.2 nm. Using this spectrophotometer, wavelengths are determined via image processing.

Preparation of Polyacrylonitrile Nanofibers with Controlled Morphology Using a Constant-Current Electrospinning System for Filter Applications

Polyacrylonitrile (PAN) fibers with average diameters in the range 100 nm with beaded morphology were prepared by a constant current electrospinning system. The fiber morphology could be easily varied by controlling the flow rate and electric current during the electrospinning process without changing the precursor solution. It was found that the use of lower flow rates resulted in more beaded fibers while the number of beads increases. The electric current could control the fiber morphology in which the beaded number (the number of beads or the beaded fibers) decreased as the electric current increased. It was also found that diameter and length of the beaded fibers increases as the electric current increases. Therefore, these results are able to be applied to find optimal conditions in obtaining high performance filter media.

Enhancement Performance of Dye-Sensitized Solar Cells from Black Rice as Dye and Black Ink as Counter Electrode with Inserting Copper on the Space between TiO2 Particle’s by Using Electroplating Method

In this study, we report well performance of Dye Sensitized Solar Cell (DSSC) coated with copper (Cu) by using the electroplating method. The Cu nanoparticle was impregnated into the pore of the titanium dioxide (TiO2) thin film. Particle contact between Cu and TiO2 plays important role to reduce the recombination effect of the electron and also lead to increase the electron transport in DSSC cell. Here, we used natural dye extracted from black rice and carbon from black ink as counter electrode. It is found that efficiency of DSSC coated with Cu nanoparticle is higher than pure DSSC which is obtained from I-V characterization. It shows that efficiency of DSSC is about 0.019% without coating Cu and enhanced about 0.105% after coating Cu. The analysis of internal resistance of DSSC was measured from Electrochemical Impedance Spectroscopy (EIS) characterization.