Current-voltage Plots Research Articles

Sensing of Airborne Nanoparticles Using Miniaturized Whipple Double Condenser

We have demonstrated the sensing of airborne nanoparticles using a miniaturized Whipple double condenser (MWDC). Each condenser (17 mm long, 2.2 mm wide, and 1 mm tall) was fabricated using photolithography and copper electroplating. The MWDC was theoretically shown to function within the laminar flow regime and capable of detecting 10- and 20-nm particles at a flow rate of 0.3 LPM. Monodispersed isopropyl alcohol and oleic acid airborne nanoparticles (10 and 20 nm) were generated using a TSI Model 9302 Single Jet Atomizer and TSI 3080 Electrostatic Classifier, and were electrically charged with 85Kr isotope. The calculated and experimental particle pass through ratio (PPR) agreed reasonably well. Using a Keithley 616 electrometer, similar threshold condenser voltage (maximum second condenser current) was observed in both experimental PPR as well as the second condenser current versus condenser voltage plot. The MWDC also displayed characteristic Whipple curves in its experimental I/V versus $\text{k}_{c}$ plots. These data demonstrate the feasibility of the microfabricated double condenser design as the basis of a miniaturized nanoparticle sizing and counting device.

Fabrication of Smart Au/TiO2 Nanotubes/Si Based Schottky-Tunneling Diode Sensors for Electrochemical Detection of Biomarkers

Rapid, point-of-care (POC) disease diagnostics presents several challenges including cost, detection time, equipment portability, and performance. Detection of volatile organic compounds (VOCs) based disease biomarkers from the breath provides a potential solution to the aforementioned problems. One such tuberculosis (TB) biomarker identified from breath is methyl nicotinate. In this regard, development of smart sensor systems can provide an economically feasible solution and pave the way for rapid disease diagnostics. In this paper, we present the fabrication of a smart sensor developed by synthesis of self-organized TiO2 nanotube arrays formed by anodization of thin Ti film deposited on Si wafers by direct current (D.C.) magnetron sputtering. Site-specific interdigitated patterned growth of gold electrode was achieved using photolithography techniques. The gold interdigitated electrodes behave as the working electrode while platinum deposited on the back surface of the Si wafer acts as the back contact. Au on TiO2 presents a Schottky junction due to differences in their work function and can be overcome by light irradiation. On the other hand, an ultra-thin, inherent SiO2 layer on Si aids in tunneling electrons across the TiO2 – Si junction. Thus, Au/TiO2/SiO2/Si behaves as a Schottky tunneling diode junction that electronically couples a VOC oxidation catalyst (Au) to a photovoltaic absorber (Si). A sweep of the bias voltage (-5V to 5V) and associated sensor response at room temperature upon exposure to both air and biomarker vapors (~1000 ppm) was carried out. From the current-voltage plot (I-V), the operating voltage was chosen overcoming the negative differential resistance such that the sensor current response to the biomarker vapor would be maximized under forward bias condition. The sensor current when exposed to the biomarker vapor was higher than that in air. All sensor measurements were carried out under illuminated conditions. The variation in the output current of the sensor biased at the chosen operating voltage (~ 0.7V) at room temperature was observed for the range of 0.01 ppm to 1000 ppm biomarker concentration. The sensor demonstrated a strong response and the results suggest that the sensor is capable of detecting extremely small concentrations of the biomarker in the vapor phase. This smart sensor presents significant enhancement in sensor response over previously reported metal functionalized TiO2 nanotube array based sensing platform developed in our group for electrochemical detection of similar disease biomarkers.

Nanoengineering of a Supramolecular Gel by Copolymer Incorporation: Enhancement of Gelation Rate, Mechanical Property, Fluorescence, and Conductivity.

In the quest to engineer the nanofibrillar morphology of folic acid (F) gel, poly(4-vinylpyridine-co-styrene) (PVPS) is judiciously integrated as a polymeric additive because of its potential to form H-bonding and π-stacking with F. The hybrid gels are designated as F-PVPSx gels, where x denotes the amount of PVPS (mg) added in 2 mL of F gel (0.3%, w/v). The assistance of PVPS in the gelation of F is manifested from the drop in critical gelation concentration and increased fiber diameter and branching of F-PVPSx gels compared to that of F gel. PVPS induces a magnificent improvement of mechanical properties: a 500 times increase of storage modulus and ∼62 times increase of yield stress in the F-PVPS5 gel compared to the F gel. The complex modulus also increases with increasing PVPS concentration with a maximum in F-PVPS5 gel. Creep recovery experiments suggest PVPS induced elasticity in the otherwise viscous F gel. The fluorescence intensity of F-PVPSx gels at first increases with increasing PVPS concentration showing maxima at F-PVPS5 gel and then slowly decreases. Gelation is monitored by time-dependent fluorescence spectroscopy, and it is observed that F and F-PVPSx gels exhibit perfectly opposite trend; the former shows a sigmoidal decrease in fluorescence intensity during gelation, but the latter shows a sigmoidal increase. The gelation rate constants calculated from Avrami treatment on the time-dependent fluorescence data manifest that PVPS effectively enhances the gelation rate showing a maximum for F-PVPS5 gel. The hybrid gel exhibit 5 orders increase of dc conductivity than that of F-gel showing semiconducting nature in the current-voltage plot. The Nyquist plot in impedance spectra of F-PVPS5 xerogel exhibit a depressed semicircle with a spike at lower frequency region, and the equivalent circuit represents a complex combination of resistance-capacitance circuits attributed to the hybrid morphology of the gel fibers.

Memristive behaviour of high‐impedance faults

In this reported work, the analogy between parallel electrical arcs and memristors is extended to high-impedance faults such as carbonised paths and circuit openings. First, it is demonstrated that the conductance from the high-impedance Mayr model behaves like a particular memductance sensitive to the integral of the squared current. Then, the current–voltage plot confirms the memristive behaviour of high-impedance faults, both by simulation and with experimental results.

Principles of a Single-Molecule Rectifier in Electrolytic Environment

The idea of gating the electrical current across a single-chain molecule, confined between and linking two electrodes in electrolytic solution, in order to achieve an asymmetric current–voltage plot, was first put forward and substantiated with a detailed theory by Kornyshev and Kuznetsov (ChemPhysChem, 2006), and Kornyshev, Kuznetsov, and Ulstrup (PNAS, 2006). However, not all aspects of that effect have been studied in those papers. Its experimental confirmation, published by Capozzi et al. (Nature Nanotech., 2015), enthused us to revisit that theory, extending it and exploring all the regimes of system operation. In this article we present such comprehensive analysis, which reveals a set of new features. An important finding is that the introduction of more refined models of the electric double layer (beyond linear response) results in stronger rectification effects, already for relatively dilute electrolyte concentrations. The theory equally applies to electrode systems with and without full electroch...

Characterization of graphene-on-insulator films formed using plasma based surface chemistry

This research explores the surface chemistry of halogen based plasmas on silicon carbide and is aimed at the synthesis of large area graphene-on-insulator films. In these studies, 6H–SiC (0001) substrates were etched using either CF4 and Cl2 based plasmas and then thermally annealed. The resulting surfaces were analyzed using x-ray photoelectron spectroscopy, reflection high energy electron diffraction, atomic force microscopy, and Raman spectroscopy. The analyses showed that the etching process selectively etched silicon to produce carbon rich surface layers on the silicon carbide substrate, and when annealed, these carbon rich layers formed graphene films with halogen- and oxygen-based defects. The thickness of the graphene was controlled by the plasma etch parameters. Two point current–voltage measurements were used to characterize the electrical properties of the films. The current–voltage plots exhibited back-to-back Schottky behavior which suggests that the defects open a band gap in these films. Current-voltage data were used to determine the Schottky barrier height, carrier density, and the upper limit for the film resistivity.

Solution-Processed, Flexible, and Transparent Non-Volatile Memory With Embedded Graphene Quantum Dots in Polymethylsilsesquioxane Layers

Non-volatile memory (NVM) devices using graphene quantum dots (GQDs) as charge trapping sites were fabricated with silver nanowires as top electrodes using solution process. The stacking structure consists of GQDs embedded between polymethylsilsesquioxane layers constructed on transparent flexible substrate. Hysteresis window was observed in the current–voltage plots, and the NVM devices are reprogrammable and stable up to $1\times 10^{4}$ s with a distinct ON/OFF ratio of $10^{4}$ . In addition, the memory device shows the stable hysteresis window without obvious degradation upon bending under different curvature radii.

The effect of temperature on the electrical characterization of a poly(phenoxy-imine)/p-silicon heterojunction

AbstractA poly(phenoxy-imine)/p-silicon rectifying device was fabricated and the current-voltage characteristics of the device were examined as a function of temperature in the 40–300 K range. The temperature dependence of the main parameters, namely, the barrier height (Φb), ideality factor (η), reverse current (I0) and series resistance (Rs), were investigated. It was seen that the Φb and the I0 values of the device increased with increasing temperature, while the η and the Rs values decreased. The temperature dependences of the Φb and the η were interpreted by the assumption of a Gaussian distribution of the barrier heights arising from barrier inhomogeneities that prevailed at the interface of the poly(phenoxyimine)/p-silicon. From ln(I0/T2) vs. 1/ηT plot, the values of the activation energy (Ea) and Richardson constant (A*) were calculated as 0.324 eV and 2.84×10-7 A cm-2K-2, respectively. The experimental value of the Rs from the forward current-voltage plots decreased with an increase in the temperature.

Electrodeposition of Cu-Zn-Sn Precursors from an Acidic Solution for Cu2ZnSnS4 Absorber Layers

Low cost and non-toxic Cu2ZnSnS4(CZTS) absorber layers are promising candidates for high performance solar cells due to the high absorption coefficient and a suitable direct band gap [1]. The current world record efficiency is around 12% for CZTS (Se) absorber layer based solar cell [2]. Electrodeposition and annealing (EDA) method is one of the favorable production processes for CZTS solar cells [3,4]. An efficiency of 7% was obtained for CZTSe film prepaired from a sequentially electrodeposited metal stack of Cu, Sn and Zn precursor [3]. The champion efficieny of 8% among the absorber layers manufactored by EDA method was achieved via selenization of metallic Cu-Zn-Sn alloy precursor film [4]. Alloy deposition of Cu-Zn-Sn enables the growth of ternary alloy from a single bath solution. However, the different reduction potentials of metal ions influence the uniformity and morphology of precursor films and the stability of the solution bath [5]. Our aim is to obtain a suitable solution bath for the electrodeposition of Cu-Zn-Sn with complexing agents and surfactants to manufacture compact, uniform and smooth ~ 1 cm2 precursors to form CZTS via sulfurization. Alloy electrodeposition was performed from an acidic solution at room temperature. Cu-Zn-Sn alloy precursor films have a suitable composition to form CZTS with atomic ratios Zn/Sn~ 1 and Cu/(Zn+Sn)~1 [Figure 1]. The electrodeposited Cu-Zn-Sn precursors were sulfurized in a quartz tube in argon atmosphere at 500-550°C for 1-2 hours. The crystal structure of the films was investigated by X-ray diffraction and Raman spectroscopy. XRD patterns after sulfurization of the precursors are shown in Figure 2. These films dominantly show peaks from the CZTS phase with a few reflections from secondary phases. Photoresponse of CZTS films was investigated in 0.1M Eu(NO3)3 solution with pH 2.3 under simulated solar light. The current-voltage plot for the CZTS film with Zn/Sn atomic ratio 1.37 is shown in Figure 3. The cathodic photocurrent increased gradually at more negative potentials, which suggests CZTS film exhibit p-type conductivity. The photocurrent produced around -0.95 V (vs. MSE) is 0.51 mA/cm2. Figure 1 Composition of precursors as a function of deposition potential Figure 2 XRD patterns for precursors after sulfurization at 500°C Figure 3 J-V plot of the photocurrent response of CZTS film in 0.1M Eu(NO3)3solution References [1]A. H. Reshak ,K. Nouneh,I. V. J. Bila, S. Auluck, H. Kamarudin, Z. Sekkat, J Electrochem Sci 9(2014) 955 - 974 [2]W Wang, MT Winkler, O Gunawan, T Gokmen, Teodor K Todorov, Y Zhu, DB Mitzi, Adv. Energy Mater. 4 (2014) 7. [3]L. Guo, Y. Zhu, O. Gunawan, T. Gokmen, V. R. Deline, S.Ahmed, L. T. Romankiw, H. Deligianni, Progr.Photovolt.: Res. Appl. 22 (2014) 1. [4]J.-O. Jeon, K. D. Lee, L. S. Oh, S.-W. Seo, D.-K. Lee, H.Kim, J.-H. Jeong, M. J. Ko, B. Kim, H. J. Son, J. Y.Kim, Chem. Sus. Chem. 7 (2014) 4. [5]D. Colombara, A. Crossay,L. Vauche, A. Crossay, S. Jaime, M. Arasimowicz, P.-P. Grand, P.J. Dale, Phys Status Solidi 212(2015)1 Figure 1

Nanocomposite coatings on cotton and silk fibers for enhanced electrical conductivity

Electrically conducting carbon nanofillers like liquid exfoliated graphite (EG), nanographite (NG), carbon nanotube (CNT) and carbon nanofiber (CNF) were dispersed in thermoplastic polyurethane (TPU) matrix. HRTEM images and SAED patterns confirmed exfoliation of graphite and good dispersion of all nanofillers. The polymer dispersions were used to develop nanocomposite coatings on cotton yarn and silk fibers. These nanocomposite coated fibers showed significant improvements in electrical conductivity. Current-voltage (IV) plots indicated linearity for most of the nanocomposite coated fibers. Among the nanofillers, CNF and CNT have strong potential to impart stable conductivity on such fibers. The electrical conductivity of 10 wt% CNF based nanocomposite coated cotton yarn was 2 S/m; while it was more than 12 S/m for silk filament. 2 wt% CNT dispersed nanocomposite coating on silk also showed very good conductivity of 11 S/m. The large void fraction in coated cotton yarn (~12 %) is attributed for such difference in electrical conductivity. Hence, staple yarns are not suitable to develop such nanocomposite coated fibers. Both the resistance and impedance tests were carried out at different test lengths up to 5 cm and resistance and impedance (at 100 Hz, 120 Hz and 1 kHz) per cm was calculated with variable test length. As variations in test results were not very high it can be concluded that the uniformity in electrical conductivity is achieved through these coatings.

Effects of 1,8-cineole on Na+ currents of dissociated superior cervical ganglia neurons

1,8-Cineole is a terpenoid present in many essential oil of plants with several pharmacological and biological effects, including antinociceptive, smooth muscle relaxant and ion channel activation. Also, 1,8-cineole blocked action potentials, reducing excitability of peripheral neurons. The objective of this work was to investigate effects of 1,8-cineole on Na+ currents (INa+) in dissociated superior cervical ganglion neurons (SCG). Wistar rats of both sexes were used (10–12 weeks old, 200–300g). SCG’s were dissected and neurons were enzymatically treated. To study 1,8-cineole effect on INa+, the patch-clamp technique in whole-cell mode was employed. 1,8-Cineole (6.0mM) partially blocked INa+ in SCG neurons. The effect stabilized within ∼150s and there was a partial recovery of INa+ after washout. Current density was reduced from −105.8 to −83.7pA/pF, corresponding to a decrease to ∼20% of control. 1,8-Cineole also reduced the time-to-peak of INa+ activation and the amplitude and decay time constants of INa+ inactivation. Current–voltage plots revealed that 1,8-cineole left-shifted the V1/2 of both activation and inactivation curves by ∼10 and ∼20mV, respectively. In conclusion, we demonstrate that 1,8-cineole directly affects Na+ channels of the SCG by modifying several gating parameters that are likely to be the major cause of excitability blockade.

Biomimetic phosphate assay based on nanopores obtained by immobilization of zirconium(IV) on a film of polyethyleneimine

A biomimetic ion-responsive single nanopore sensor was constructed by immobilizing zirconium(IV) ion on a film of poly(ethylene terephthalate) whose surface was modified with polyethyleneimine (PEI) to form nanopores. PEI is an excellent metal-chelating ligand that was initially modified on the surface of the membrane through amidation. The Zr-chelated nanopore responds to inorganic phosphate by a change in the ion current–voltage plot. This is due to a reversal of the charge from positive to negative after binding of the phosphate to the tip of the ion channel. Inorganic phosphate can be quantified by measurement of the extent of rectification. The limit of detection of the method is 118 nM, and response is linear in the 0 to 40 μM phosphate concentration range. The formation of the Zr(IV)/phosphate system on the surface was corroborated by X-ray photoelectron spectroscopy and current–voltage characterization. The single synthetic nanopore display excellent selectivity, high sensitivity and a wide response range for phosphate. The accuracy of the method and applicability of the nanopore-based detection scheme was proven by the successful determination of inorganic phosphate in (spiked) lake water and a cola drink.

Simultaneous optical and electrical modeling of plasmonic light trapping in thin-film amorphous silicon photovoltaic devices

Rapid prototyping of photovoltaic (PV) cells requires a method for the simultaneous simulation of the optical and electrical characteristics of the device. The development of nanomaterial enabled PV cells only increases the complexity of such simulations. Here, we use a commercial technology-computer-aided-design (TCAD) software, Silvaco Atlas, to design and model plasmonic gold nanoparticles integrated in optoelectronic device models of thin film amorphous silicon (a-Si:H) PV cells. Upon illumination with incident light, we simulate the optical and electrical properties of the cell simultaneously, and use the simulation to produce current-voltage (J-V) and external quantum efficiency (EQE) plots. Light trapping due to light scattering and localized surface plasmon resonance interactions by the nanoparticles has resulted in the enhancement of both the optical and electrical properties due to the reduction in the recombination rates in the photoactive layer. We show that the device performance of the modeled plasmonic a-Si:H PV cells depends significantly on the position and size of the gold nanoparticles, which leads to improvements either in optical properties only, or in both optical and electrical properties. The model provides a route to optimize the device architecture, by simultaneously optimizing the optical and electrical characteristics, which leads to a detailed understanding of plasmonic PV cells from a design perspective and offers an advanced tool for rapid device prototyping.

Growth And Properties Of Pulsed Laser Deposited Al-doped ZnO Thin Film

Al-doping of 1.5% by weight, in ZnO (Al:ZnO), thin films are deposited on glass substrates at temperature 400 °C and varying oxygen gas pressure (PO2) from 1.33 Pa to 5.32 Pa via Pulsed Laser Deposition (PLD) technique. The single crystalline nature of the thin films is confirmed from the X-ray diffraction (XRD) pattern. The evaluated crystallite size is found to be <15 nm. Atomic Force Microscopy (AFM) study reveals the columnar grain formation in the thin films, with low surface roughness. The surface morphology of the grown thin films is significantly affected by PO2. Optical measurements depict that the thin films are highly transparent in the visible region with transmittance up to 80%. The optical band gap calculated from Tauc’s plot evinced that Al-doping results in band edge bending in Al:ZnO thin films, a red shift in the band gap is observed with increase in PO2 that is due to the contributing electrons from oxygen ions. Photoluminescence (PL) spectra of films indicate the visible emission peaks originating from defect states. Optical properties of the thin films confirm their applicability for optoelectronic devices. The room temperature, current-voltage (I-V) plots indicate low resistivity in the thin films ~ 10 -2 (Ω-cm).

Probing the nanoscale Schottky barrier of metal/semiconductor interfaces of Pt/CdSe/Pt nanodumbbells by conductive-probe atomic force microscopy.

The electrical nature of the nanoscale contact between metal nanodots and semiconductor rods has drawn significant interest because of potential applications for metal-semiconductor hybrid nanostructures in energy conversion or heterogeneous catalysis. Here, we studied the nanoscale electrical character of the Pt/CdSe junction in Pt/CdSe/Pt nanodumbbells on connected Au islands by conductive-probe atomic force microscopy under ultra-high vacuum. Current-voltage plots measured in contact mode revealed Schottky barrier heights of individual nanojunctions of 0.41 ± 0.02 eV. The measured value of the Schottky barrier is significantly lower than that of planar thin-film diodes because of a reduction in the barrier width and enhanced tunneling probability at the interface.

Molecular Dynamics Simulations Describe the Mechanism of K Block in Bacterial Nav Channels

Although extensive electrophysiological characterization is available for eukaryotic voltage-gated Na+ channels (Nav), no high-resolution structures of these channels are available. Crystal structures of several bacterial Nav channels have been published and molecular dynamics simulations of ion permeation through these channels are consistent with many electrophysiological properties of the eukaryotic channels. Unlike eukaryotic Nav channels, however, the bacterial Nav channels are strongly outwardly rectifying, and the mechanism of this rectification has not previously been described. We used step-wise pulling protocols to implement Jarzynski's Equality in non-equilibrium molecular dynamics simulations of ion permeation through the bacterial NavAb channel to obtain a mechanistic description of this outward rectification. Results of the simulations indicate that two or three extracellular K+ ions bind tightly at the same z-coordinate along the selectivity filter of NavAb and can effectively block the channel in the presence of modest voltages or concentration driving forces. The configuration with two potassium ions located at the same z-coordinate is also found in the two-dimensional potential of mean forces generated from umbrella sampling and weighted histogram analysis. In contrast to K+, three Na+ ions move through the selectivity filter together as a unit in a “knock-on” mechanism of permeation. Differences in the amount of work required to move three Na+ ions through the selectivity filter of NavAb compared to three K+ ions predict the large negative reversal potentials observed for bacterial Nav channels in instantaneous current-voltage plots. The results of the simulations suggest that the block of bacterial voltage-gated Na+ channels by extracellular K+ does not occur in eukaryotic voltage-gated Na+ channels because of differences in the amino acids present in the selectivity filters of the different channels.

What Makes You Can also Break You, Part III: Mitochondrial Permeability Transition Pore Formation by an Uncoupling Channel within the C-Subunit Ring of the F1FO ATP Synthase?

What Makes You Can also Break You, Part III: Mitochondrial Permeability Transition Pore Formation by an Uncoupling Channel within the C-Subunit Ring of the F1FO ATP Synthase?

A variety of microstructural defects in crystalline silicon solar cells

Abstract The performance and lifetime of solar cells critically depends on bulk and surface defects. To improve performance of solar cells, localization and characterization of defects on the microscale is an important issue. This paper describes a variety of microstructural defects in crystalline silicon solar cells which appear during the cell processing steps. The set of defects have been investigated and localized using visible light emission under reversed bias voltage. A light beam induced photocurrent method allows localization of defects having impact on the sample current–voltage plot and reversed bias light emission characteristics. These are shown together with the micrographs of defective surface areas. As a result, particular defects which induce nonlinearity and local breakdown in the current–voltage plot were identified in tested solar cell structures. Furthermore, measurements at various temperatures allows to identify the breakdown mechanism of the investigated defects. An interesting result of the investigation is that the majority of defects are associated with surface inhomogeneities, but not all surface inhomogeneities act as defects.

Calcium Flux Through AvGluR1: A Glutamate Receptor with a Potassium Channel Selectivity Sequence

A glutamate receptor found in the freshwater bdelloid rotifer Adineta vaga was proposed to be an evolutionary link between prokaryotic and eukaryotic iGluR receptor classes (Janovjak et al., 2011). Like GluR0 and some related bacterial iGluRs, the pore loop of AvGluR1 has a K+ channel selectivity filter sequence, TXVGYG. However, electrophysiological experiments revealed permeability to both Na+ and K+ but with no permeability to calcium (Janovjak et al., 2011). Surprisingly, during the course of experiments in Xenopus oocytes designed to evaluate the ligand binding and gating properties of AvGluR1 (Lomash et al., 2013), we found that following attenuation of desensitization by the lectin concanavalin A, or by AvGluR1 Cys mutants that cross link ligand binding domain dimer assemblies, inward current responses to glutamate had a large biphasic transient component that varied from cell to cell. Several lines of evidence suggest that this is due to calcium influx through AvGluR1, and subsequent activation of a Ca dependent chloride current. (i) When the membrane potential was depolarized, the biphasic response to glutamate reverted to a non desensitizing ‘square’ outward current response. (ii) Substitution of barium for extracellular calcium blocked the transient component of the AvGluR1 inward current response recorded at negative membrane potentials. (iii) Current voltage plots revealed a large depolarizing shift in the reversal potential for AvGluR1 responses to glutamate, when extracellular calcium was replaced by magnesium. Thus, despite the presence of the TXVGYG signature sequence, AvGluR1 is a non selective cation channel with permeability to both monovalent and divalent cations.Janovjak H, Sandoz G, Isacoff EY (2011) Nature Comm 2: 232.Lomash S, Chittori S, Brown P, Mayer ML (2013) Structure 21: 414-425

Influence of Localized Structural Defects on the PN Junction Properties

Local defects, as micro-fractures, precipitates and other material inhomogeneities in solar cell structure, evidently modify electrical and photoelectrical behavior of the latter. To improve the efficiency and lifetime of existing solar cells, it is important to localize these defects which influence the p-n properties, and assign them corresponding electrical characteristics. Although the electric breakdown can be evident in current-voltage plot, the localization of local defects in the sample, that generate this breakdown, is not so easy task. It has to be done by microscopic investigations and measurement of light emission from defects under electrical bias conditions. Thus to contribute to this end, the structure of defects is microscopically investigated and consequently, the defects can be removed by focused ion beam milling. The experimental results obtained from samples before and after milling are also discussed.