Luminescent Properties of ZnO/MgO Nanocrystal/Polymer Composite Structure

Gennady N. Panin,Andrey N. Baranov,Irina A. Khotina,Tae W. Kang 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5

We report on cathodoluminescence (CL) studies of the composite nanostructure obtained by spin coating of a mixture of chemically-deposited ZnO/MgO nanocrystals and a solution processable polymer (PDPV) on a Si substrate with patterned gold electrodes. The effect of an electric field on the CL of the nanostructure was studied at various bias voltages on the electrodes. A positive voltage suppressed the blue-green emission and shifted the emission maximum to the red region. The emission maximum returned to the blue-green region after the eld had been turned off. A model of the electric-field-induced color switching in the ZnO/polymer-based nanostructure is proposed. The bias-voltage-induced interface band bending and the deactivation of the radiative centers, in particular, singly-ionized oxygen vacancies in ZnO nanocrystals, are suggested to govern the relative changes of the blue-green-red emissions. We report on cathodoluminescence (CL) studies of the composite nanostructure obtained by spin coating of a mixture of chemically-deposited ZnO/MgO nanocrystals and a solution processable polymer (PDPV) on a Si substrate with patterned gold electrodes. The effect of an electric field on the CL of the nanostructure was studied at various bias voltages on the electrodes. A positive voltage suppressed the blue-green emission and shifted the emission maximum to the red region. The emission maximum returned to the blue-green region after the eld had been turned off. A model of the electric-field-induced color switching in the ZnO/polymer-based nanostructure is proposed. The bias-voltage-induced interface band bending and the deactivation of the radiative centers, in particular, singly-ionized oxygen vacancies in ZnO nanocrystals, are suggested to govern the relative changes of the blue-green-red emissions.

Spatially-Resolved Study of Magnetic Properties of Mn-Doped ZnO Quantum Wires

Gennady Panin,Andrey Baranov,Hyun Jeong Kim,Seung Ki Min,강태원 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.6

ZnO nanowires prepared by thermal growth following direct chemical synthesis and doped by Mn and by Mn and Sn impurities were investigated. The nanowires show a single crystal structure and a strong blue shift of the near band edge luminescence, which is attributed to the quantum confinement effect. The magnetic susceptibility of the quantum wires as a function of temperature demonstrated a Curie-Weiss behavior. Hysteresis with a coercive field $<$200 Oe was clearly observed in the magnetization versus field curves at 300 K. Increasing the Mn concentration by Mn and Sn co-doping significantly increased the magnetic hysteresis and the ferromagnetic behavior of the nanowires. Magnetic force microscopy measurements with high spatial resolution revealed a magnetic domain structure in the individual wires. The magnetic domains align perpendicular to the surface and can be controlled by using an external magnetic field.

Novel Green Luminescent and Phosphorescent Material: Semiconductive Nanoporous ZnMnO with Photon Confinement

Lee, Sejoon,Lee, Youngmin,Panin, Gennady N. American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.24

<P>A novel green luminescent and phosphorescent material of semiconductive nanoporous ZnMnO was synthesized by the thermal nucleation of nanopores in the 20-period Zn0.93Mn0.07O/Zn0.65Mn0.35O multilayer structure. Nanoporous ZnMnO showed an n-type semiconducting property and exhibited an extremely strong green light emission in its luminescence and phosphorescence characteristics. This arises from the formation of the localized energy level (i.e., green emission band) within the energy band gap and the confinement of photons. The results suggest nanoporous ZnMnO to have a great potential for the new type of semiconducting green phosphors and semiconductor light emitting diodes with lower thresholds, producing an efficient light emission. In-depth analyses on the structural, electrical, and optical properties are thoroughly examined, and the formation mechanism of nanoporous ZnMnO and the origin of the strong green light emission are discussed.</P>

Formation of self-assembled nanoscale graphene/graphene oxide photomemristive heterojunctions using photocatalytic oxidation

Kapitanova, Olesya O,Panin, Gennady N,Cho, Hak Dong,Baranov, Andrey N,Kang, Tae Won IOP 2017 Nanotechnology Vol.28 No.20

<P>Photocatalytic oxidation of graphene with ZnO nanoparticles was found to create self-assembled graphene oxide/graphene (G/GO) photosensitive heterostructures, which can be used as memristors. Oxygen groups released during photodecomposition of water molecules on the nanoparticles under ultraviolet light, oxidized graphene, locally forming the G/GO heterojunctions with ultra-high density. The G/GO nanostructures have non-linear current–voltage characteristics and switch the resistance in the dark and under white light, providing four resistive states at room temperature. Photocatalytic oxidation of graphene with ZnO nanoparticles is proposed as an effective method for creating two-dimensional memristors with a photoresistive switching for ultra-high capacity non-volatile memory.</P>

Shear Exfoliation and Photoresponse of 2D-Layered Gallium Selenide Nanosheets

Chan, A. Sattar,Fu, Xiao,Panin, Gennady N.,Cho, Hak Dong,Lee, Dong Jin,Kang, Tae Won Wiley (John WileySons) 2018 Physica status solidi. PSS-RRL. Rapid Research Let Vol.12 No.10

Multicolor Emission from Poly(<i>p</i>-Phenylene)/Nanoporous ZnMnO Organic–Inorganic Hybrid Light-Emitting Diode

Lee, Sejoon,Lee, Youngmin,Kim, Deuk Young,Panin, Gennady N. American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.51

<P>The voltage-tunable multicolor emission was realized in a poly(p-phenylene)/nanoporous ZnMnO organic inorganic hybrid light-emitting diode. Red, green, and blue (RGB) colors sequentially appeared with increasing magnitude of the bias voltage (i.e., R -> RG -> RGB with V up arrow). At a higher voltage (>2.4 V), eventually, the device emitted the visible light with a mixture of colors including RGB. These unique features may move us a step closer to the application of organic inorganic hybrid solid-state lighting devices for the full-color display and/or the electrical-to-optical data converter for multivalue electronic signal processes. In-depth analyses on electrical and optical properties are presented, and voltage-controllable multicolor-emission mechanisms are discussed.</P>

Highly efficient low-voltage cathodoluminescence of semiconductive nanoporous ZnMnO green phosphor films

Lee, Sejoon,Lee, Youngmin,Kim, Deuk Young,Panin, Gennady N. Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.470 No.-

<P><B>Abstract</B></P> <P>The low voltage-operational thin-film type of the high-quality nanoporous ZnMnO (Mn: ∼18 at.%) green phosphor was fabricated by grain boundary engineering <I>via</I> the thermal nucleation of the well-crystallized columnar ZnMnO thin film. Vertically-aligned nanopores were observed to be formed throughout the whole area of the ZnMnO phosphor film; and the impact excitation of Mn<SUP>2+</SUP> centers and the defect-mediated optical transition in nanoporous ZnMnO significantly enhanced green light emission in the nanoporous cavity. The results suggest nanoporous ZnMnO to hold promise for the next-generation color-field panels as a new type of the thin-film phosphor. The material characteristics, including the structural, electrical, and optical properties, are meticulously examined, and the formation mechanism of nanoporous ZnMnO and the origin of its low-voltage strong-green-cathodoluminescence are described.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nanoporous ZnMnO was fabricated by thermal nucleation using a columnar ZnMnO film. </LI> <LI> Nanoporous ZnMnO showed a low-voltage cathodoluminescence of strong green emission. </LI> <LI> Green emission originates from both Mn<SUP>2+</SUP>- and V<SUB>O</SUB>-related optical transitions. </LI> <LI> Nanocavities in nanoporous ZnMnO significantly enhances the light emission intensity. </LI> <LI> Nanoporous ZnMnO holds great potential as a low voltage-operational green phosphor. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Influence of the Quantum Well Structure and Growth Temperature on a Five-Layer InGaMnAs Quantum Well with an InGaAs Buffer Layer

Yoon, Im Taek,Lee, Sejoon,Roshchupkin, Dmitry V.,Panin, Gennady N. American Scientific Publishers 2018 Journal of nanoscience and nanotechnology Vol.18 No.6

<P>The influence of quantum well structure and growth temperature on a synthesized multilayer system composed of a five-layer InMnGaAs quantum well with an InGaAs buffer layer grown on semi-insulating (100)-oriented substrates prepared by low temperature molecular beam epitaxy was studied. The magnetization measurements using a superconducting quantum interference device indicated the existence of ferromagnetism with a Curie temperature above room temperature in the five-layer InGaMnAs quantum well structure with an InGaAs buffer layer in a GaAs matrix. X-ray diffraction and secondary ion mass spectroscopy measurements confirmed the second phase formation of ferromagnetic GaMn clusters. The ferromagnetism that exists in the five-layer of the InMnGaAs quantum well with the InGaAs buffer layer results from a superposition of the ferromagnetism of the low temperature region from the substitutional Mn ions into Ga sites or interstitial Mn ions as well as the presence of manganese ions dopant clusters such as GaMn clusters.</P>

Tunable UV-visible absorption of SnS2layered quantum dots produced by liquid phase exfoliation

Fu, Xiao,Ilanchezhiyan, P.,Mohan Kumar, G.,Cho, Hak Dong,Zhang, Lei,Chan, A. Sattar,Lee, Dong J.,Panin, Gennady N.,Kang, Tae Won The Royal Society of Chemistry 2017 Nanoscale Vol.9 No.5

<P>4H-SnS2 layered crystals synthesized by a hydrothermal method were used to obtain via liquid phase exfoliation quantum dots (QDs), consisting of a single layer (SLQDs) or multiple layers (MLQDs). Systematic downshift of the peaks in the Raman spectra of crystals with a decrease in size was observed. The bandgap of layered QDs, estimated by UV-visible absorption spectroscopy and the tunneling current measurements using graphene probes, increases from 2.25 eV to 3.50 eV with decreasing size. 2-4 nm SLQDs, which are transparent in the visible region, show selective absorption and photosensitivity at wavelengths in the ultraviolet region of the spectrum while larger MLQDs (5-90 nm) exhibit a broad band absorption in the visible spectral region and the photoresponse under white light. The results show that the layered quantum dots obtained by liquid phase exfoliation exhibit wellcontrolled and regulated bandgap absorption in a wide tunable wavelength range. These novel layered quantum dots prepared using an inexpensive method of exfoliation and deposition from solution onto various substrates at room temperature can be used to create highly efficient visible-blind ultraviolet photodetectors and multiple bandgap solar cells.</P>

Direct growth of graphene film on piezoelectric La₃Ga_5.5Ta_0.5O₁₄ crystal

Brzhezinskaya, Maria,Irzhak, Artemii,Irzhak, Dmitry,Kang, Tae Won,Kononenko, Oleg,Matveev, Viktor,Panin, Gennady,Roshchupkin, Dmitry WILEY‐VCH Verlag Berlin GmbH 2016 Physica Status Solidi. Rapid Research Letters Vol.10 No.8

<P>For the first time, a few layer graphene was grown on the surface of the polar <I>X</I> ‐cut (110) of a piezoelectric La<SUB>3</SUB>Ga<SUB>5.5</SUB>Ta<SUB>0.5</SUB>O<SUB>14</SUB> crystal by the CVD method. This polar <I>X</I> ‐cut is characterized by a good matching of the crystal lattice parameters of La<SUB>3</SUB>Ga<SUB>5.5</SUB>Ta<SUB>0.5</SUB>O<SUB>14</SUB> and two‐dimensional graphene crystal, as well as the presence of piezoelectric fields on the surface of the substrate, which could affect the graphene growth process. Raman spectroscopy investigation has shown the ability for direct growth of graphene on the piezoelectric crystal. The NEXAFS spectroscopy studies of the film grown on the surface of the <I>X</I> ‐cut of an La<SUB>3</SUB>Ga5<SUB>.5</SUB>Ta<SUB>0.5</SUB>O<SUB>14</SUB> crystal also confirmed that the grown film is graphene. Moreover, the NEXAFS spectra enable the conclusion that additional electron states are formed as a result of chemical bonding between the atoms of graphene and the substrate which proceeds through hybridization of the valence electron states of the substrate and graphene atoms. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)</P>