Effect of thermal annealing on the electrical and structural properties of Au/Y/p-type InP Schottky structure

Dasaradha Rao, L.,Shanthi Latha, K.,Rajagopal Reddy, V.,Choi, C.J. Pergamon Press [etc.] 2015 Vacuum Vol.119 No.-

The effects of rapid thermal annealing on the electrical and structural properties of a fabricated Au/Y/p-InP Schottky barrier diode (SBD) have been investigated. The estimated Schottky barrier heights (SBHs) of the as-deposited and 200 <SUP>o</SUP>C annealed Au/Y/p-InP SBDs are found to be 0.62 eV (I-V)/0.83 eV (C-V) and 0.63 eV (I-V)/0.92 eV (C-V) respectively. However, the SBH increases to 0.65 eV (I-V)/0.96 eV (C-V) upon annealing at 300 <SUP>o</SUP>C. Further, the SBH slightly decreases to 0.59 eV (I-V)/0.78 eV (C-V) for contact annealed at 400 <SUP>o</SUP>C. The SBH, ideality factor and series resistance of the Au/Y/p-InP SBD are estimated by Norde and Cheung's methods. Also, the discrepancy between SBHs estimated from I-V, C-V, Norde and Cheung's methods are described and discussed. It is noted that the interface state density of the Au/Y/p-InP SBD decreases upon annealing at 300 <SUP>o</SUP>C and then slightly increases after annealing at 400 <SUP>o</SUP>C. The AES and XRD measurements have revealed that the formation of Au-In, Au-P and Y-P interfacial phases at the interface may be the reason for the increase and decrease of SBHs upon annealing. The AFM results showed that the surface morphology of the Au/Y Schottky contact is fairly smooth at various annealing temperatures.

Effects of Annealing on Electrical Characteristics and Current Transport Mechanisms of the Y/p-GaN Schottky Diode

Reddy, V. R.,Asha, B.,Choi, C. J. Springer Science + Business Media 2016 Journal of electronic materials Vol.45 No.7

<P>This study investigates the effects of annealing on the electrical properties and current transport mechanism of Y/p-GaN Schottky barrier diodes (SBDs). We found no significant change in the surface morphology of the Y Schottky contacts during the annealing process. The Schottky barrier height (SBH) of the as-deposited Y/p-GaN SBD was estimated to be 0.95 eV (I-V)/1.19 eV (C-V). The SBH increased upon annealing at 400A degrees C and 500A degrees C, and then decreased slightly with annealing at 600A degrees C. Thus the maximum SBH of the Y/p-GaN SBD was achieved at 500A degrees C, with values of 1.01 eV (I-V)/1.29 eV (C-V). In addition, the SBH values were estimated by Cheung's, Norde, and I-s-V plots and were found to be in good agreement with one another. Series resistance (R (S)) values were also calculated by I-V, Cheung's, and Norde functions at different annealing temperatures, with results showing a decrease in the interface state density of the SBD with annealing at 500A degrees C, followed by a slight increase upon annealing at 600A degrees C. The forward-bias current transport mechanism of SBD was investigated by the logI-logV plot at different annealing temperatures. Our investigations revealed that the Poole-Frenkel emission mechanism dominated the reverse leakage current in Y/p-GaN SBD at all annealing temperatures.</P>

Hydrothermally synthesized Na₂Ti₃O₇ nanotube–V₂O₅ heterostructures with improved visible photocatalytic degradation and hydrogen evolution - Its photocorrosion suppression

Vattikuti, S.V. Prabhakar,Reddy, Police Anil Kumar,NagaJyothi, P.C.,Shim, Jaesool,Byon, Chan Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.740 No.-

<P><B>Abstract</B></P> <P>There is still a need to prepare heterostructure photocatalysts with high activity and recyclability but without using precious metals to reduce the cost of photocatalysts. Thus, a facile and simple method for the synthesis of a Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB> nanotube–V<SUB>2</SUB>O<SUB>5</SUB> heterostructure photocatalyst via hydrothermal synthesis is reported herein. The chemical composition, morphology, and structural features of the photocatalyst were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), N<SUB>2</SUB> adsorption–desorption specific surface area analysis (BET), and diffuse reflectance absorption (DRS) methods. It was observed that the specific surface area of the Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB> nanotube–V<SUB>2</SUB>O<SUB>5</SUB> heterostructure photocatalyst increased with the incorporation of V<SUB>2</SUB>O<SUB>5</SUB>. The Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB> nanotube–V<SUB>2</SUB>O<SUB>5</SUB> heterostructure photocatalyst was then used for the removal of rhodamine B (RhB) under simulated solar light irradiation. The Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB> nanotube–V<SUB>2</SUB>O<SUB>5</SUB> heterostructure photocatalyst revealed excellent photocatalytic activity and photodegradation kinetics as compared to pristine Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB> nanotubes and V<SUB>2</SUB>O<SUB>5</SUB> photocatalysts. Furthermore, both the photoactivity and long-term stability of the Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB> nanotube–V<SUB>2</SUB>O<SUB>5</SUB> heterostructure photocatalyst were superior to those of the pristine Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB> nanotubes and V<SUB>2</SUB>O<SUB>5</SUB> photocatalysts. The excellent photocatalytic performance of the Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB> nanotube–V<SUB>2</SUB>O<SUB>5</SUB> heterostructure photocatalyst can be ascribed to its high specific surface area (283.71 m<SUP>2</SUP>g<SUP>−1</SUP>), mesoporous structure, highly dispersed V<SUB>2</SUB>O<SUB>5</SUB> nanoparticles, and hindrance of electron–hole pair recombination of Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB> due to the V<SUB>2</SUB>O<SUB>5</SUB> incorporation, which is proven by the photoelectrochemical results, including photocurrent and electron impendence spectroscopy results. In addition, during the study of photocatalytic hydrogen evolution, the hydrogen yield of the Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB>/V<SUB>2</SUB>O<SUB>5</SUB> nanocomposite was 1.83 times that of pristine Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB>, which also exhibited excellent photocatalytic activity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Heterojunction of Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB> NTs/V<SUB>2</SUB>O<SUB>5</SUB> NPs was developed via hydrothermal method. </LI> <LI> Visible photocatalytic RhB degradation studies were performed over Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB> NTs/V<SUB>2</SUB>O<SUB>5</SUB> NPs. </LI> <LI> Improved degradation efficiency was observed over Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB> NTs/V<SUB>2</SUB>O<SUB>5</SUB> NPs when compared to pristine Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB> NTs. </LI> <LI> V<SUB>2</SUB>O<SUB>5</SUB> NPs were successfully utilized as cocatalyst for pollutant degradation. </LI> <LI> Charge recombination was diminished in the Na<SUB>2</SUB>Ti<SUB>3</SUB>O<SUB>7</SUB> NTs by the addition of V<SUB>2</SUB>O<SUB>5</SUB> NPs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Electrical and structural properties of tungsten Schottky contacts to p-type InP at different annealing temperatures

Rajagopal Reddy, V.,Sri Silpa, D.,Yun, H.J.,Choi, C.J. Academic Press 2014 Superlattices and microstructures Vol.71 No.-

The electrical and structural properties of a fabricated W/p-InP Schottky barrier diode (SBD) have been investigated as a function of annealing temperature. The W/p-InP SBD exhibits good rectification behavior. The barrier height (BH) and ideality factor of the W/p-InP SBD are determined to be 0.82eV (I-V)/0.98eV (C-V) and 1.34, respectively. However, the BH is increases to 0.87eV (I-V)/1.08eV (C-V) after annealing at 300<SUP>o</SUP>C. When the SBD is annealed at 400<SUP>o</SUP>C, the BH decreases to 0.74eV (I-V)/0.86eV (C-V) and the ideality factor increases to 1.45. Results indicate that a maximum BH is obtained on the W/p-InP SBD at 300<SUP>o</SUP>C. Norde method is also employed to determine BHs of W/p-InP SBD which are in good agreement with those estimated by the I-V method. Further, Cheung method is used to estimate the series resistance of the W/p-InP SBD, and the consistency is checked using the Norde method. Besides, the energy distribution of interface state density is determined from the forward bias I-V data at different annealing temperatures. Auger electron spectroscopy and X-ray diffraction studies revealed that the formation of W-P interfacial phases at the W/p-InP interface may be the cause for the increase of BH upon annealing at 300<SUP>o</SUP>C. AFM results indicated that the overall surface morphology of the W/p-InP SBD did not change significantly at elevated temperatures.

Fate and fouling characteristics of fluorescent dissolved organic matter in ultrafiltration of terrestrial humic substances

Quang, V.L.,Kim, H.C.,Maqbool, T.,Hur, J. Pergamon Press 2016 CHEMOSPHERE - Vol.165 No.-

Ultrafiltration (UF) membrane fouling caused by terrestrial input of dissolved organic matter (DOM), especially during high flood periods, is poorly understood. In this study, we examined the fouling characteristics of three different terrestrial humic substances (HS) on regenerated cellulose (RC) UF membranes with the pore sizes of 30 k-3 kDa via conventional bulk HS measurements as well as an advanced fluorescence spectroscopy. The fluorescence excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) identified one protein-like (C1) and three humic-like fluorescent components (C2-C4) from soil and leaf-derived HS. The fate of the different fluorescent components was individually tracked for the UF processes. The higher removal rates were found generally on the order of high molecular weight (HMW) C1 to smaller sized humic-like components (C4 > C3 > C2) regardless of the HS sources, implying the importance of HS molecular sizes on the UF operation. Among the humic-like components, C2 was the most associated with irreversible fouling, while other two humic-like components contributed more to reversible fouling. For soil-derived HS, C4 can be suggested as a good surrogate for membrane fouling, as evidenced by the highest correlation between the removal rates and the total fouling indices among the tested HS variables including conventional bulk parameters. Our study demonstrated a promising application of EEM-PARAFAC for probing membrane fouling of terrestrial DOM, which provided additional insight into the fate of different fluorescent components on the UF processes.

First observation ofγγ→pp¯K+K−and search for exotic baryons inpKsystems

Shen, C. P.,Yuan, C. Z.,Adachi, I.,Aihara, H.,Asner, D. M.,Aulchenko, V.,Aushev, T.,Ayad, R.,Babu, V.,Badhrees, I.,Bakich, A. M.,Barberio, E.,Behera, P.,Bhardwaj, V.,Bhuyan, B.,Biswal, J.,Bobrov, A.,B American Physical Society 2016 Physical review. D Vol.93 No.11

<P>The process gamma gamma -> p (p) over barK(+)K(-) and its intermediate processes are measured for the first time using a 980 fb(-1) data sample collected with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. The production of p (p) over barK(+)K(-) and a Lambda(1520)(0) ((Lambda) over bar (1520)(0)) signal in the pK(-) ((p) over barK(+)) invariant mass spectrum are clearly observed. However, no evidence for an exotic baryon near 1540 MeV/c(2), denoted as Theta(1540)(0) ((Theta) over bar (1540)(0)) or Theta(1540)(++) (Theta(1540)(--)), is seen in the pK(-) ((p) over barK(+)) or pK(+) ((p) over barK(-)) invariant mass spectra. Cross sections for gamma gamma -> p (p) over barK(+)K(-), Lambda(1520)(0)(p) over barK(+) + c.c. and the products sigma(gamma gamma -> Theta(1540)(0)(p) over barK(+) + c.c.)B(Theta(1540)(0) -> pK(-)) and sigma(gamma gamma -> Theta(1540)(++)(p) over barK(-) + c.c.)B(Theta(1540)(++) -> pK(+)) are measured. We also determine upper limits on the products of the chi(c0) and chi(c2) two-photon decay widths and their branching fractions to p (p) over barK(+)K(-) at the 90% credibility level.</P>

Activated T Cells Secrete an Alternatively Spliced Form of Common γ-Chain that Inhibits Cytokine Signaling and Exacerbates Inflammation

Hong, C.,Luckey, Megan A.,Ligons, Davinna L.,Waickman, Adam T.,Park, J.Y.,Kim, Grace Y.,Keller, Hilary R.,Etzensperger, R.,Tai, X.,Lazarevic, V.,Feigenbaum, L.,Catalfamo, M.,Walsh, Scott T.R.,Park, J. Cell Press 2014 Immunity Vol.40 No.6

The common γ-chain (γc) plays a central role in signaling by IL-2 and other γc-dependent cytokines. Here we report that activated T cells produce an alternatively spliced form of γc mRNA that results in protein expression and secretion of the γc extracellular domain. The soluble form of γc (sγc) is present in serum and directly binds to IL-2Rβ and IL-7Rα proteins on T cells to inhibit cytokine signaling and promote inflammation. sγc suppressed IL-7 signaling to impair naive T cell survival during homeostasis and exacerbated Th17-cell-mediated inflammation by inhibiting IL-2 signaling upon T cell activation. Reciprocally, the severity of Th17-cell-mediated inflammatory diseases was markedly diminished in mice lacking sγc. Thus, sγc expression is a naturally occurring immunomodulator that regulates γc cytokine signaling and controls T cell activation and differentiation.

Electrical Properties and Carrier Transport Mechanism of Au/n-GaN Schottky Contact Modified Using a Copper Pthalocyanine (CuPc) Interlayer

Janardhanam, V.,Jyothi, I.,Lee, J.-H.,Kim, J.-Y.,Reddy, V.R.,Choi, C.-J. JAPAN INSTITUTE OF METALS 2014 MATERIALS TRANSACTIONS Vol.55 No.5

We investigated the electrical characteristics of Au/n-GaN Schottky rectifier incorporating a copper pthalocyanine (CuPc) interlayer using current voltage (I-V), capacitance voltage (C-V) and conductance voltage (G-V) measurements. The barrier height of the Au/CuPc/n-GaN Schottky contact was higher than that of the Au/n-GaN Schottky diode, indicating that the CuPc interlayer influenced the space charge region of the n-GaN layer. The series resistance of Au/CuPc/n-GaN Schottky contact extracted from the C-V and G-V methods was dependent on the frequency. In addition, the series resistance obtained from C V and G V characteristics was comparable to that from Cheung's method at sufficiently high frequencies and in strong accumulation regions. The forward log / log V plot of Au/CuPc/n-GaN Schottky contact exhibited four distinct regions having different slopes, indicating different conduction mechanisms in each region. In particular, at higher forward bias, the trap-filled space-charge-limited current was the dominant conduction mechanism of Au/CuPc/n-GaN Schottky contact, implying that the most of traps were occupied by injected carriers at high injection level.

A systematic investigation of the thermoelectric stability of Pt–Rh thermocouples between 1300 °C and 1500 °C

Pearce, J V,Edler, F,Elliott, C J,Greenen, A,Harris, P M,Izquierdo, C Garcia,Kim, Y-G,Martin, M J,Smith, I M,Tucker, D,Veltcheva, R I BUREAU INTERNATIONAL DES POIDS ET MESURES 2018 METROLOGIA -BERLIN- Vol.55 No.4

<P>By using a simple model to relate the electromotive force drift rate of Pt–Rh thermoelements to d<I>S</I>/d<I>c</I>, i.e. the sensitivity of the Seebeck coefficient, <I>S</I>, to rhodium mass fraction, <I>c</I>, the composition of the optimal pair of Pt–Rh wires that minimizes thermoelectric drift can be determined. The model has been applied to four multi-wire thermocouples each comprising 5 or 7 Pt–Rh wires of different composition. Two thermocouples were exposed to a temperature of around 1324 °C, one thermocouple to around 1492 °C, i.e. the melting points of the Co–C and Pd–C high temperature fixed points, respectively, and one thermocouple to a series of temperatures between 1315 °C and 1450 °C. The duration of exposure at each temperature was several thousand hours. By performing repeated calibrations <I>in situ</I> with the appropriate fixed point during the high temperature exposure, the drift performance has been quantified with high accuracy, entirely free from errors associated with thermoelectric homogeneity. By combining these results it is concluded that the Pt-40%Rh versus Pt-6%Rh is the most stable at the temperatures investigated. A preliminary reference function was determined and is presented.</P>

Enhanced photocatalytic activity of Ag/g-C₃N₄ composite

Nagajyothi, P.C.,Pandurangan, M.,Vattikuti, S.V.P.,Tettey, C.O.,Sreekanth, T.V.M.,Shim, J. Elsevier Science B.V 2017 Separation and purification technology Vol.188 No.-

Silver-graphite carbon nitride (Ag/g-C<SUB>3</SUB>N<SUB>4</SUB>) was designed and synthesized through a simple green chemical route. The photocatalyst was comprehensively characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), High-resolution transmission electron microscopy (HR-TEM), and X -ray photoelectron spectroscopy (XPS). The HR-TEM results indicate that the synthesized Ag spherical-like nanoparticles were randomly loaded on the surface of graphitic carbon nitride (g-C<SUB>3</SUB>N<SUB>4)</SUB>. In addition, the Ag/g-C<SUB>3</SUB>N<SUB>4</SUB> nanocomposites exhibited 2.5 times higher photocatalytic activity than pristine g-C<SUB>3</SUB>N<SUB>4</SUB> for the degradation of malachite green (MG) dye under UV irradiation.