Paul Ndione - Academia.edu (original) (raw)

Papers by Paul Ndione

Mutation Research/Genetic Toxicology, 1996

N-Propyl-N-nitrosourea (PNU) is shown to be active in male mouse bone marrow micronucleus assays ... more N-Propyl-N-nitrosourea (PNU) is shown to be active in male mouse bone marrow micronucleus assays when dosed at either 100 or 200 mg/kg in saline. Activity was observed following either intraperitoneal (i.p.) injection or oral gavage. This observation is consistent with the demonstration by Murota and Shibuya of the specific-locus mutagenicity caused by PNU in male mouse spermatogonia when dosed at 200 mg/kg by i.p. injection. These data strengthen further the observation that rodent germ cell mutagens are also mutagenic to rodent somatic cells.

Applied Physics Letters, 2007

The electro-optical response of calcium barium niobate ferroelectric thin films is characterized ... more The electro-optical response of calcium barium niobate ferroelectric thin films is characterized using a single beam setup in reflection geometry. Clear evidence of a Pockels response together with an r33 coefficient as high as 130 pm/V is found. This large value and the high Curie temperature of the material under study (>250 °C) can be considered as a promising feature

Photonic Applications in Devices and Communication Systems, 2005

In this study, we report for the first time the epitaxial growth of CBN thin films on Magnesium O... more In this study, we report for the first time the epitaxial growth of CBN thin films on Magnesium Oxide (MgO) substrates for optical device applications. A high deposition temperature (greater than or equal to to 800 oC) is required to obtain the epitaxial growth of CBN films. A parametric study is proposed in order to elaborate CBN thin films with

Photonic Applications in Nonlinear Optics, Nanophotonics, and Microwave Photonics, 2005

Temporal Talbot effect is the time domain counterpart of spatial self imaging phenomenon. When a ... more Temporal Talbot effect is the time domain counterpart of spatial self imaging phenomenon. When a periodic time signal is propagated through a first order dispersive medium, exact replicas of the signal are reproduced at specific distance along the direction of propagation. At other distances, the signal is self imaged with a higher repetition-rate than the original periodic sequence (Fractional Talbot

Digest of the LEOS Summer Topical Meetings, 2005., 2005

The problem of propagation of a periodic optical pulse sequence through a linear dispersive fiber... more The problem of propagation of a periodic optical pulse sequence through a linear dispersive fiber is investigated in the joint time-frequency domain. This study provides a new and deeper insight into the dynamics of formation of the integer and fractional temporal Talbot patterns which are observed along the fiber propagation distance.

2010 35th IEEE Photovoltaic Specialists Conference, 2010

... [7] T. Minami, Thin Solid Films 2008, 516, 5822. [8] AJ Leenheer, JD Perkins, MFAM van Hest, ... more ... [7] T. Minami, Thin Solid Films 2008, 516, 5822. [8] AJ Leenheer, JD Perkins, MFAM van Hest, JJ Berry, RP O'Hayre, and DS Ginley, Phys. Rev. B 2008, 77, 115215. [9] JD Perkins, MFAM van Hest, MP Taylor, and DS Ginley, Int J Nanotechnol 2009, 6, 850. ...

Conference on Lasers and Electro-Optics, 2007, CLEO 2007, 2007

The electro-optical coefficient r 33 of a novel ferroelectric thin film (Calcium Barium Niobate) ... more The electro-optical coefficient r 33 of a novel ferroelectric thin film (Calcium Barium Niobate) is estimated using a single beam set-up in a reflection geometry. Our measures show that the value of r 33 in this material is as large as 100 pm/V.

Conference Proceedings of the International Symposium on Signals, Systems and Electronics, 2007

Ca 0.28 Ba 0.72 Nb 2 O 6 (CBN-28) waveguides based on thin film technology were fabricated on SiO... more Ca 0.28 Ba 0.72 Nb 2 O 6 (CBN-28) waveguides based on thin film technology were fabricated on SiO 2 /(100) Si substrates. By using X-ray diffraction, we confirmed the preferential c-axis orientation of the CBN structures. An effective unclamped electro-optic r 33 coefficient of 12 pm/V was measured in CBN thin films by using an ellipsometric technique in reflection geometry. In addition, by means of a Fabry-Perot technique, the propagation losses of our strip loaded waveguides were estimated to be as low as 4.8 dB/cm and 6.5 dB/cm at telecommunication wavelengths for the fundamental TE and TM modes, respectively.

SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference Proceedings, 2007

The electro-optical coefficient r33 of a novel ferroelectric compound (Calcium Barium Niobate) is... more The electro-optical coefficient r33 of a novel ferroelectric compound (Calcium Barium Niobate) is estimated using a single beam set-up in a reflection geometry on thin film samples. The quality of the electrode used to apply the exciting field was estimated as a critical parameter. Following an electrode quality optimization we estimated a lower bound for the r33 coefficient as large

Journal of Applied Physics, 2008

In the present work, we investigate in detail the effect of both the deposition temperature and t... more In the present work, we investigate in detail the effect of both the deposition temperature and the cooling rate on the growth of calcium barium niobate (CBN) thin films on a magnesium oxide (MgO) single crystal substrate. As revealed by x-ray diffraction measurements, epitaxy occurs for films deposited at 800 °C with a slow in situ cooling rate. We have

Thin Solid Films, 2012

Bulk-heterojunction (BHJ) organic photovoltaics (OPV) are very promising thin film renewable ener... more Bulk-heterojunction (BHJ) organic photovoltaics (OPV) are very promising thin film renewable energy conversion technologies due to low production cost by high-throughput roll-to-roll manufacturing, an expansive list of compatible materials, and flexible device fabrication. An important aspect of OPV device efficiency is good contact engineering. The use of oxide thin films for this application offers increased design flexibility and improved chemical

Physical Review B, 2012

We explore the effects of cation off-stoichiometry on structural, electrical, optical, and electr... more We explore the effects of cation off-stoichiometry on structural, electrical, optical, and electronic properties of Co 2 ZnO 4 normal spinel and Co 2 NiO 4 inverse spinel using theoretic and experimental (combinatorial and conventional) techniques, both at thermodynamic equilibrium and in the metastable regime. Theory predicts that nonequilibrium substitution of divalent Zn on nominally trivalent octahedral sites increases net hole density in Co 2 ZnO 4 . Experiment confirms high conductivity and high work function in Co 2 NiO 4 and Zn-rich Co 2 ZnO 4 thin films grown by nonequilibrium physical vapor deposition techniques. High p-type conductivities of Co 2 ZnO 4 (up to 5 S/cm) and Co 2 NiO 4 (up to 204 S/cm) are found over a broad compositional range, they are only weakly sensitive to oxygen partial pressure and quite tolerant to a wide range of processing temperatures. In addition, off-stoichiometry caused by nonequilibrium growth decreases the optical absorption of Co 2 ZnO 4 and Co 2 NiO 4 thin films, although the 500-nm thin films still have rather limited transparency. All these properties as well as high work functions make Co 2 ZnO 4 and Co 2 NiO 4 thin films attractive for technological applications, such as hole transport layers in organic photovoltaic devices or p-type buffer layers in inorganic solar cells.

Physical Review B, 2011

ABSTRACT Holes can be readily doped into small-gap semiconductors such as Si or GaAs, but corresp... more ABSTRACT Holes can be readily doped into small-gap semiconductors such as Si or GaAs, but corresponding p-type doping in wide-gap insulators, while maintaining transparency, has proven difficult. Here, by utilizing design principles distilled from theory with systematic measurements in the prototype A2BO4 spinel Co2ZnO4, we formulate and test practical design rules for effective hole doping. Using these, we demonstrate a 20-fold increase in the hole density in Co2ZnO4 due to extrinsic (Mg) doping and, ultimately, a factor of 104 increase for the inverse spinel Co2NiO4, the x = 1 end point of Ni-doped Co2Zn1−xNixO4.

Optics Express, 2009

Ca 0.28 Ba 0.72 Nb 2 O 6 (CBN-28) waveguides based on thin film technology were fabricated on SiO... more Ca 0.28 Ba 0.72 Nb 2 O 6 (CBN-28) waveguides based on thin film technology were fabricated on SiO 2 /(100) Si substrates. By using X-ray diffraction, we confirmed the preferential c-axis orientation of the CBN structures. An effective unclamped electro-optic r 33 coefficient of 12 pm/V was measured in CBN thin films by using an ellipsometric technique in reflection geometry. In addition, by means of a Fabry-Perot technique, the propagation losses of our strip loaded waveguides were estimated to be as low as 4.8 dB/cm and 6.5 dB/cm at telecommunication wavelengths for the fundamental TE and TM modes, respectively.

Journal of Applied Physics, 2012

ABSTRACT The utilization of radio-frequency (RF) superimposed direct-current (DC) magnetron sputt... more ABSTRACT The utilization of radio-frequency (RF) superimposed direct-current (DC) magnetron sputtering deposition on the properties of gallium doped ZnO (GZO) based transparent conducting oxides has been examined. The GZO films were deposited using 76.2 mm diameter ZnO:Ga{sub 2}O{sub 3} (5 at. % Ga vs. Zn) ceramic oxide target on heated non-alkaline glass substrates by varying total power from 60 W to 120 W in steps of 20 W and at various power ratios of RF to DC changing from 0 to 1 in steps of 0.25. The GZO thin films grown with pure DC, mixed approach, and pure RF resulted in conductivities of 2200 {+-} 200 S/cm, 3920 {+-} 600 S/cm, and 3610 {+-} 400 S/cm, respectively. X-ray diffraction showed all films have wurtzite ZnO structure with the c-axis oriented perpendicular to the substrate. The films grown with increasing RF portion of the total power resulted in the improvement of crystallographic texture with smaller full-width half maximum in {chi} and broadening of optical gap with increased carrier concentration via more efficient doping. Independent of the total sputtering power, all films grown with 50% or higher RF power portion resulted in high mobility ({approx}28 {+-} 1 cm{sup 2}/Vs), consistent with observed improvements in crystallographic texture. All films showed optical transmittance of {approx}90% in the visible range.

Journal of Applied Physics, 2009

The influence of surface chemistry in plasma etching of multicomponent oxides was investigated th... more The influence of surface chemistry in plasma etching of multicomponent oxides was investigated through measurements of the ion energy dependence of the etch yield. Using pulsed-laser-deposited CaxBa(1-x)Nb2O6 (CBN) and SrTiO3 thin films as examples, it was found that the etching energy threshold shifts toward values larger or smaller than the sputtering threshold depending on whether or not ion-assisted chemical etching

Applied Physics Letters, 2007

The electro-optical response of calcium barium niobate ferroelectric thin films is characterized ... more The electro-optical response of calcium barium niobate ferroelectric thin films is characterized using a single beam setup in reflection geometry. Clear evidence of a Pockels response together with an r33 coefficient as high as 130 pm/V is found. This large value and the high Curie temperature of the material under study (>250 °C) can be considered as a promising feature

Applied Physics Letters, 1998

Laser-diode heterostructures of InGaAlN containing a third-order diffraction grating for distribu... more Laser-diode heterostructures of InGaAlN containing a third-order diffraction grating for distributed optical feedback have been examined with transmission electron microscopy ͑TEM͒ and scanning electron microscopy ͑SEM͒. The grating was defined holographically and etched by chemically assisted ion-beam etching into the upper GaN confinement layer of the laser structure. After the etch step, it was overgrown with an Al 0.08 Ga 0.92 N upper cladding layer. Threading dislocations were present that initiated at the sapphire substrate, but no new dislocations were observed at the grating/Al 0.08 Ga 0.92 N interface. A comparison of TEM and SEM micrographs reveals that there is a compositional gradient in the AlGaN upper cladding layer; however, calculations show that it did not reduce the optical coupling coefficient of the grating.

Mutation Research/Genetic Toxicology, 1996

N-Propyl-N-nitrosourea (PNU) is shown to be active in male mouse bone marrow micronucleus assays ... more N-Propyl-N-nitrosourea (PNU) is shown to be active in male mouse bone marrow micronucleus assays when dosed at either 100 or 200 mg/kg in saline. Activity was observed following either intraperitoneal (i.p.) injection or oral gavage. This observation is consistent with the demonstration by Murota and Shibuya of the specific-locus mutagenicity caused by PNU in male mouse spermatogonia when dosed at 200 mg/kg by i.p. injection. These data strengthen further the observation that rodent germ cell mutagens are also mutagenic to rodent somatic cells.

Applied Physics Letters, 2007

The electro-optical response of calcium barium niobate ferroelectric thin films is characterized ... more The electro-optical response of calcium barium niobate ferroelectric thin films is characterized using a single beam setup in reflection geometry. Clear evidence of a Pockels response together with an r33 coefficient as high as 130 pm/V is found. This large value and the high Curie temperature of the material under study (>250 °C) can be considered as a promising feature

Photonic Applications in Devices and Communication Systems, 2005

In this study, we report for the first time the epitaxial growth of CBN thin films on Magnesium O... more In this study, we report for the first time the epitaxial growth of CBN thin films on Magnesium Oxide (MgO) substrates for optical device applications. A high deposition temperature (greater than or equal to to 800 oC) is required to obtain the epitaxial growth of CBN films. A parametric study is proposed in order to elaborate CBN thin films with

Photonic Applications in Nonlinear Optics, Nanophotonics, and Microwave Photonics, 2005

Temporal Talbot effect is the time domain counterpart of spatial self imaging phenomenon. When a ... more Temporal Talbot effect is the time domain counterpart of spatial self imaging phenomenon. When a periodic time signal is propagated through a first order dispersive medium, exact replicas of the signal are reproduced at specific distance along the direction of propagation. At other distances, the signal is self imaged with a higher repetition-rate than the original periodic sequence (Fractional Talbot

Digest of the LEOS Summer Topical Meetings, 2005., 2005

The problem of propagation of a periodic optical pulse sequence through a linear dispersive fiber... more The problem of propagation of a periodic optical pulse sequence through a linear dispersive fiber is investigated in the joint time-frequency domain. This study provides a new and deeper insight into the dynamics of formation of the integer and fractional temporal Talbot patterns which are observed along the fiber propagation distance.

2010 35th IEEE Photovoltaic Specialists Conference, 2010

... [7] T. Minami, Thin Solid Films 2008, 516, 5822. [8] AJ Leenheer, JD Perkins, MFAM van Hest, ... more ... [7] T. Minami, Thin Solid Films 2008, 516, 5822. [8] AJ Leenheer, JD Perkins, MFAM van Hest, JJ Berry, RP O'Hayre, and DS Ginley, Phys. Rev. B 2008, 77, 115215. [9] JD Perkins, MFAM van Hest, MP Taylor, and DS Ginley, Int J Nanotechnol 2009, 6, 850. ...

Conference on Lasers and Electro-Optics, 2007, CLEO 2007, 2007

The electro-optical coefficient r 33 of a novel ferroelectric thin film (Calcium Barium Niobate) ... more The electro-optical coefficient r 33 of a novel ferroelectric thin film (Calcium Barium Niobate) is estimated using a single beam set-up in a reflection geometry. Our measures show that the value of r 33 in this material is as large as 100 pm/V.

Conference Proceedings of the International Symposium on Signals, Systems and Electronics, 2007

Ca 0.28 Ba 0.72 Nb 2 O 6 (CBN-28) waveguides based on thin film technology were fabricated on SiO... more Ca 0.28 Ba 0.72 Nb 2 O 6 (CBN-28) waveguides based on thin film technology were fabricated on SiO 2 /(100) Si substrates. By using X-ray diffraction, we confirmed the preferential c-axis orientation of the CBN structures. An effective unclamped electro-optic r 33 coefficient of 12 pm/V was measured in CBN thin films by using an ellipsometric technique in reflection geometry. In addition, by means of a Fabry-Perot technique, the propagation losses of our strip loaded waveguides were estimated to be as low as 4.8 dB/cm and 6.5 dB/cm at telecommunication wavelengths for the fundamental TE and TM modes, respectively.

SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference Proceedings, 2007

The electro-optical coefficient r33 of a novel ferroelectric compound (Calcium Barium Niobate) is... more The electro-optical coefficient r33 of a novel ferroelectric compound (Calcium Barium Niobate) is estimated using a single beam set-up in a reflection geometry on thin film samples. The quality of the electrode used to apply the exciting field was estimated as a critical parameter. Following an electrode quality optimization we estimated a lower bound for the r33 coefficient as large

Journal of Applied Physics, 2008

In the present work, we investigate in detail the effect of both the deposition temperature and t... more In the present work, we investigate in detail the effect of both the deposition temperature and the cooling rate on the growth of calcium barium niobate (CBN) thin films on a magnesium oxide (MgO) single crystal substrate. As revealed by x-ray diffraction measurements, epitaxy occurs for films deposited at 800 °C with a slow in situ cooling rate. We have

Thin Solid Films, 2012

Bulk-heterojunction (BHJ) organic photovoltaics (OPV) are very promising thin film renewable ener... more Bulk-heterojunction (BHJ) organic photovoltaics (OPV) are very promising thin film renewable energy conversion technologies due to low production cost by high-throughput roll-to-roll manufacturing, an expansive list of compatible materials, and flexible device fabrication. An important aspect of OPV device efficiency is good contact engineering. The use of oxide thin films for this application offers increased design flexibility and improved chemical

Physical Review B, 2012

We explore the effects of cation off-stoichiometry on structural, electrical, optical, and electr... more We explore the effects of cation off-stoichiometry on structural, electrical, optical, and electronic properties of Co 2 ZnO 4 normal spinel and Co 2 NiO 4 inverse spinel using theoretic and experimental (combinatorial and conventional) techniques, both at thermodynamic equilibrium and in the metastable regime. Theory predicts that nonequilibrium substitution of divalent Zn on nominally trivalent octahedral sites increases net hole density in Co 2 ZnO 4 . Experiment confirms high conductivity and high work function in Co 2 NiO 4 and Zn-rich Co 2 ZnO 4 thin films grown by nonequilibrium physical vapor deposition techniques. High p-type conductivities of Co 2 ZnO 4 (up to 5 S/cm) and Co 2 NiO 4 (up to 204 S/cm) are found over a broad compositional range, they are only weakly sensitive to oxygen partial pressure and quite tolerant to a wide range of processing temperatures. In addition, off-stoichiometry caused by nonequilibrium growth decreases the optical absorption of Co 2 ZnO 4 and Co 2 NiO 4 thin films, although the 500-nm thin films still have rather limited transparency. All these properties as well as high work functions make Co 2 ZnO 4 and Co 2 NiO 4 thin films attractive for technological applications, such as hole transport layers in organic photovoltaic devices or p-type buffer layers in inorganic solar cells.

Physical Review B, 2011

ABSTRACT Holes can be readily doped into small-gap semiconductors such as Si or GaAs, but corresp... more ABSTRACT Holes can be readily doped into small-gap semiconductors such as Si or GaAs, but corresponding p-type doping in wide-gap insulators, while maintaining transparency, has proven difficult. Here, by utilizing design principles distilled from theory with systematic measurements in the prototype A2BO4 spinel Co2ZnO4, we formulate and test practical design rules for effective hole doping. Using these, we demonstrate a 20-fold increase in the hole density in Co2ZnO4 due to extrinsic (Mg) doping and, ultimately, a factor of 104 increase for the inverse spinel Co2NiO4, the x = 1 end point of Ni-doped Co2Zn1−xNixO4.

Optics Express, 2009

Ca 0.28 Ba 0.72 Nb 2 O 6 (CBN-28) waveguides based on thin film technology were fabricated on SiO... more Ca 0.28 Ba 0.72 Nb 2 O 6 (CBN-28) waveguides based on thin film technology were fabricated on SiO 2 /(100) Si substrates. By using X-ray diffraction, we confirmed the preferential c-axis orientation of the CBN structures. An effective unclamped electro-optic r 33 coefficient of 12 pm/V was measured in CBN thin films by using an ellipsometric technique in reflection geometry. In addition, by means of a Fabry-Perot technique, the propagation losses of our strip loaded waveguides were estimated to be as low as 4.8 dB/cm and 6.5 dB/cm at telecommunication wavelengths for the fundamental TE and TM modes, respectively.

Journal of Applied Physics, 2012

ABSTRACT The utilization of radio-frequency (RF) superimposed direct-current (DC) magnetron sputt... more ABSTRACT The utilization of radio-frequency (RF) superimposed direct-current (DC) magnetron sputtering deposition on the properties of gallium doped ZnO (GZO) based transparent conducting oxides has been examined. The GZO films were deposited using 76.2 mm diameter ZnO:Ga{sub 2}O{sub 3} (5 at. % Ga vs. Zn) ceramic oxide target on heated non-alkaline glass substrates by varying total power from 60 W to 120 W in steps of 20 W and at various power ratios of RF to DC changing from 0 to 1 in steps of 0.25. The GZO thin films grown with pure DC, mixed approach, and pure RF resulted in conductivities of 2200 {+-} 200 S/cm, 3920 {+-} 600 S/cm, and 3610 {+-} 400 S/cm, respectively. X-ray diffraction showed all films have wurtzite ZnO structure with the c-axis oriented perpendicular to the substrate. The films grown with increasing RF portion of the total power resulted in the improvement of crystallographic texture with smaller full-width half maximum in {chi} and broadening of optical gap with increased carrier concentration via more efficient doping. Independent of the total sputtering power, all films grown with 50% or higher RF power portion resulted in high mobility ({approx}28 {+-} 1 cm{sup 2}/Vs), consistent with observed improvements in crystallographic texture. All films showed optical transmittance of {approx}90% in the visible range.

Journal of Applied Physics, 2009

The influence of surface chemistry in plasma etching of multicomponent oxides was investigated th... more The influence of surface chemistry in plasma etching of multicomponent oxides was investigated through measurements of the ion energy dependence of the etch yield. Using pulsed-laser-deposited CaxBa(1-x)Nb2O6 (CBN) and SrTiO3 thin films as examples, it was found that the etching energy threshold shifts toward values larger or smaller than the sputtering threshold depending on whether or not ion-assisted chemical etching

Applied Physics Letters, 2007

The electro-optical response of calcium barium niobate ferroelectric thin films is characterized ... more The electro-optical response of calcium barium niobate ferroelectric thin films is characterized using a single beam setup in reflection geometry. Clear evidence of a Pockels response together with an r33 coefficient as high as 130 pm/V is found. This large value and the high Curie temperature of the material under study (>250 °C) can be considered as a promising feature

Applied Physics Letters, 1998

Laser-diode heterostructures of InGaAlN containing a third-order diffraction grating for distribu... more Laser-diode heterostructures of InGaAlN containing a third-order diffraction grating for distributed optical feedback have been examined with transmission electron microscopy ͑TEM͒ and scanning electron microscopy ͑SEM͒. The grating was defined holographically and etched by chemically assisted ion-beam etching into the upper GaN confinement layer of the laser structure. After the etch step, it was overgrown with an Al 0.08 Ga 0.92 N upper cladding layer. Threading dislocations were present that initiated at the sapphire substrate, but no new dislocations were observed at the grating/Al 0.08 Ga 0.92 N interface. A comparison of TEM and SEM micrographs reveals that there is a compositional gradient in the AlGaN upper cladding layer; however, calculations show that it did not reduce the optical coupling coefficient of the grating.