First-principles investigation of graphitic carbon nitride monolayer with embedded Fe atom

Density-functional theory calculations with spin-polarized generalized gradient approximation and Hubbard $U$ correction is carried out to investigate the mechanical, structural, electronic and magnetic properties of graphitic heptazine with embedded $\mathrm{Fe}$ atom under bi-axial tensile strain and applied perpendicular electric field. It was found that the binding energy of heptazine with embedded $\mathrm{Fe}$ atom system decreases as more tensile strain is applied and increases as more electric field strength is applied. Our calculations also predict a band gap at a peak value of 5 tensile strain but at expense of the structural stability of the system. The band gap opening at 5 tensile strain is due to distortion in the structure caused by the repulsive effect in the cavity between the lone pairs of edge nitrogen atoms and $\mathrm{d}_{{xy}}/\mathrm{d}_{x^2-y^2}$ orbital of Fe atom, hence the unoccupied $\mathrm{p}_z$-orbital is forced to shift towards higher energy. The electronic and magnetic properties of the heptazine with embedded $\mathrm{Fe}$ system under perpendicular electric field up to a peak value of 10 $\mathrm{V/nm}$ is also well preserved despite obvious buckled structure. Such properties may be desirable for diluted magnetic semiconductors, spintronics, and sensing devices

Theoretical studies on mechanical and electronic properties of ss-triazine sheet

Mechanical and electronic properties of $s$-triazine are studied using first-principles calculations based on density functional theory. The in-plane stiffness and bulk modulus for $s$-triazine sheet are found to be less than that of heptazine. The reduction can be related to the nature of the covalent bonds connecting the adjacent sheets and the number of atoms per unit cell. The Poisson's ratio of $s$-triazine is half the value to that of graphene. Additionally, the calculated values of the two critical strains (elastic and yielding points) of $s$-triazine sheet are in the same order of magnitude to that for heptazine which was calculated using MD simulations in the literature. It is also demonstrated that $s$-triazine sheet can withstand larger tension in the plastic region. These results established a stable mechanical property for $s$-triazine sheet. We found a linear relationship of bandgap as a function of bi-axial tensile strain within the harmonic elastic region. The reduced steric repulse of the lone pairs ($\mathrm{p}_x$-, $\mathrm {p}_y$-) causes the $\mathrm {p}_z$-like orbital to shift to high energy, and consequently an increase in the bandgap. We find no electronic properties modulation of the $s$-triazine sheet under electric field up to a peak value of 10 V/nm. Such noble properties may be useful in future nanomaterial applications.Comment: Manuscript submitted to Philosophical Magazine Journa

Adsorption of atoms and molecules on s-triazine sheet with embedded manganese atom: First-principles calculations

The mechanical, structural, electronic and magnetic properties of s-triazine sheet (C6N6) with embedded Mn atom (Mn-C6N6) is investigated under the influence of external environment using density functional theory. Our results show that Mn-C6N6 system is structurally and mechanically stable. The binding energy of Mn embedded in C6N6 sheet can be modulated under the influence of symmetric deformation and perpendicular electric field respectively. The semiconducting property of pure C6N6 sheet is maintained upon embedment of Mn atom in the porous site. It is also found that small increment in bi-axial tensile strain enhances the band gap (from 0.630 eV at zero strain to 0.802 eV at 5% strain) while the magnetic moment of the embedded Mn atom is preserved. The electronic and magnetic properties of the Mn-C6N6 systems are maintained up to 10 V/nm in electric field strength. We also explore the geometries, electronic and magnetic properties of Mn-C6N6 with adsorbed atoms and molecules. The Mn-C6N6 with adsorbed O atom and O2 molecule systems shows half-metallic character whereas the remaining systems preserve their semiconducting property. The total magnetic moment per unit cell in most of the systems is found to reduce as compared to that of the Mn-C6N6 sheet. The reduction in magnetic moment can be related to the strong interactions among the Mn atom and the surrounding atoms which lead to the formation of low-spin configurations. Overall, our results indicate that the Mn-C6N6 systems with and without adsorbed atoms and molecules can serve as potential candidates for future spintronics and catalysis applications.Comment: 14 pages, 6 figure

Perubahan kualiti air bawah tanah di negeri Kelantan pada tahun 2010 hingga 2012

Air bawah tanah adalah satu badan penting kepada yang terdapat di dalam bumi. Penerobosan air laut telah memberi kesan terhadap kualiti air bawah tanah. Kajian ini dilakukan adalah bagi menganalisis tahap kualiti air bawah tanah dalam konteks kemasinan dan kandungan klorida di beberapa lokasi jajahan negeri Kelantan daripada tahun 2010 hingga tahun 2012. Selain itu, parameter lain yang diukur dalam kajian ini adalah kandungan logam berat yang terdapat di dalam air bawah tanah. Metod kajian ini adalah mengukur min bagi setiap parameter. Penilaian turut dibuat terhadap kualiti air tanah berdasarkan kepada had piawai dalam Garis Panduan Kebangsaan bagi Kualiti Air Mentah untuk Minuman, 2000 (NGRDWQ) dan Standard Kualiti Air Minum. Hasil daripada data yang diperolehi mendapati tahap kemasinan air adalah berada pada tahap kurang daripada 2 ppt. Namun bagi kandungan klorida yang terdapat dalam air bawah tanah tersebut pula adalah melebihi daripada 250 mg/l. Ini mendapati tahap air adalah berada pada tahap air payau. Manakala bagi parameter logam berat pula didapati terdapat beberapa jenis logam yang melebihi piawai ditetapkan seperti AS (0.062 mg/l), Cr (0.0213 mg/l), Fn (10.0 mg/l) dan Mn (1.0 mg/l). Hasil daripada kajian ini menunjukkan tahap kualiti air bawah tanah di negeri Kelantan masih lagi berada pada tahap yang baik walaupun kualiti air telah berubah akibat daripada penerobosan air laut

Fabrication And Electrical Characterization Of Silicon Bipolar Transistors In A O.5µm Based BiCMOS Technology.

Bipolar transistors are well known for its high current driving capability and current gains, while CMOS transistors are dominant in the integrated circuit market because of its low power consumption and small size advantage. The combination of both types of transistor on the same chip provides a high performance circuit with a high packing density. In this work 0.5-µm BiCMOS technology is fully utilized to realize silicon bipolar transistors with optimized performance. Preliminary electrical results are presented on bipolar transistors fabricated for the first time in Malaysia. Significant improvements in electrical device performance can be achieved by optimizing the emitter drive-in temperature and choice of annealing system

Low temperature characterization of Si bipolar junction transistors and Si1-xGex heterojunction bipolar transistors

This thesis investigates the low temperature characterization of Si bipolar junction transistors and Si1-xGex heterojunction bipolar transistors. Device characteristics are measured between 300K and 200K, and a new analysis method is used for extracting the bandgap narrowing in the base from the temperature dependence of the collector current. Applying the analysis method to Si BJTs with mean base doping concentrations of 1.6x1018cm-3 and 6.3x1018cm-3 gives bandgap narrowing values of 37meV and 47meV due to heavy doping in the base. These values compare with the predicted values of 35meV and 54meV for the model of Klaassen et al. Applying the analysis method to a Si0.88Ge0.12 HBT and a Si0.87Ge0.13 HBT gives bandgap narrowing values of 119meV and 125meV due to the presence of the 12% and 13% Ge respectively. These values compare with the predicted values of 123meV and 128meV for the model of People.One problem in npm SiGe HBTs is boron out-diffusion from the base. Boron dopant that out-diffuses into the emitter and the collector during SiGe growth or subsequent heat treatment results in the formation of parasitic energy barriers at the emitter/base and base/collector junctions. These barriers suppress the injection of electrons from the emitter to the collector which results in reduced collector current. Undoped SiGe spacers can be incorporated at the emitter/base and base/collector junction to contain boron diffusion within the SiGe base, thus eliminating the formation of the parasitic energy barriers. Investigations have been carried out on SiGe HBTs with 5, 10 and 15nm undoped SiGe spacers. The SiGe HBTs with 15nm spacers showed the highest collector current compared to those with 5 and 10nm spacers. This is explained by increasing amounts of boron out-diffusion as the base spacer thickness is reduced. It is also shown that boron out-diffusion is almost completely eliminated in devices with 15nm base spacers but this is not the case for devices with 5 and 10nm spacers. The size of the parasitic energy barrier at the emitter/base and base/collector junctions is quantified. The results show that boron out-diffusion is more critical at the base/collector junction than at the emitter/base junction due to the lower doping concentration in the collector (1x1016cm-3) than in the emitter (1x1018cm-3).</p

Effect of different electrolytes on porous GaN using photo-electrochemical etching

This article reports the properties and the behavior of GaN during the photoelectrochemical etching process using four different electrolytes. The measurements show that the porosity strongly depends on the electrolyte and highly affects the surface morphology of etched samples, which has been revealed by scanning electron microscopy (SEM) images. Peak intensity of the photoluminescence (PL) spectra of the porous GaN samples was observed to be enhanced and strongly depend on the electrolytes. Among the samples, there is a little difference in the peak position indicating that the change of porosity has little influence on the PL peak shift, while it highly affecting the peak intensity. Raman spectra of porous GaN under four different solution exhibit phonon mode E2 (high), A1 (LO), A1 (TO) and E2 (low). There was a red shift in E2 (high) in all samples, indicating a relaxation of stress in the porous GaN surface with respect to the underlying single crystalline epitaxial GaN. Raman and PL intensities were high for samples etched in H2SO4:H2O2 and KOH followed by the samples etched in HF:HNO3 and in HF:C2H5OH

Characterization of Ge nanostructures embedded inside porous silicon for photonics application

In this work we prepared germanium nanostructures by means of filling the material inside porous silicon (PS) using conventional and cost effective technique, thermal evaporator. The PS acts as patterned substrate. It was prepared by anodization of silicon wafer in ethanoic hydrofluoric acid (HF). A Ge layer was then deposited onto the PS by thermal evaporation. This was followed by deposition of Si layer by thermal evaporation and anneal at 650°C for 30 min. The process was completed by Ni metal deposition using thermal evaporator followed by metal annealing of 400°C for 10 min to form metal semiconductor metal (MSM) photodetector. Structural analysis of the samples was performed using energy dispersive x-ray analysis (EDX), scanning electron microscope (SEM), X-ray diffraction (XRD) and Raman spectroscopy (RS). EDX spectrum suggests the presence of Ge inside the pores structure. Raman spectrum showed that good crystalline structure of Ge can be produced inside silicon pores with a phase with the diamond structure by (111), (220) and (400) reflections. Finally current-voltage (I- V) measurement of the MSM photodetector was carried out and showed lower dark currents compared to that of Si control device. Interestingly the device showed enhanced current gain compared to Si device which can be associated with the presence of Ge nanostructures in the porous silicon

ICP-RIE dry etching using Cl2-based on GaN

In this study, the plasma characteristics and GaN etch properties of inductively coupled Cl2/Ar and Cl2/H2 plasmas were investigated. Our results showed that inductively coupled plasma (ICP) etching of gallium nitride by using Cl2/Ar and Cl2/H2 were possible to meet the requirements (anisotropy, high etch rate and high selectivity). We have investigated the etching rate dependency on the percentage of argon and hydrogen in the gas mixture and the DC voltage. Surface morphology of the etched samples was checked by SEM and AFM. It was found that the etched surface was anisotropic and the smoothness of the etched surface is comparable to that of polished wafer. As results, gas mixture using Cl2/Ar, we obtained highest etching rates; 5000 Å/min and ~0.5 nm rms roughness for n-GaN and for p-GaN, the etching rates was 3300 Å/min and ~0.7 nm for rms roughness. Meanwhile, for gas mixture using Cl2/H2, the etching was 1580 Å/min for n-GaN and 950 Å/min for p-GaN