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In Situ Raman Spectroscopy of Solution-Gated Graphene on Copper

100%
Binder J., Stępniewski R., Strupiński W., Wysmołek A.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
360-363
EN
We present a solution-gated in situ Raman spectroscopy approach, which enables the electrical characterization of graphene on a copper substrate without the need of a transfer process. The application of a voltage across the solution resulted in a shift of the Raman G-band without a significant shift of the 2D band. This observation allowed for the separation of the effects of strain and doping. Based on the G and 2D band shifts we show that we can manipulate the n-type carrier concentration of graphene directly on the copper substrate in a range from about 8× 10¹² cm¯² to about 1.5× 10¹³ cm¯².
2
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Absorption and Emission Properties of Light Emitting Diode Structures Containing GaInN/GaN QWs

76%
Binder J., Korona K., Borysiuk J., Wysmołek A., Baeumler M., Köhler K., Kirste L.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
918-920
EN
In this work we present measurements of GaInN/GaN light emitting diodes (LEDs) with an active layer consisting of three quantum wells made of Ga_{0.9}In_{0.10}N that have different widths (1.8 nm, 2.7 nm, 3.7 nm). A comparison of emission and absorption (photocurrent) on the same sample revealed a shift in energy, with the emission energy being significantly lower. The shifts are about 0.02 eV, 0.03 eV, and 0.04 eV for the quantum wells having the widths of 1.8 nm, 2.7 nm, and 3.7 nm, respectively. This can be explained by a shift of the ground state energy caused by the quantum confined Stark effect. Calculations show that due to the spontaneous polarization and the piezoelectric effect a strong electric field of the order of 1 MV/cm was present in the GaInN quantum wells. Simulations of ground-state energies in the model of an infinite square well under the influence of an electric field with a matched effective well width were performed and used to interpret the experimental results.
3
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Photoluminescence Dynamics of GaN/Si Nanowires

76%
Korona K., Zytkiewicz Z., Perkowska P., Borysiuk J., Binder J., Sobanska M., Klosek K.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1001-1003
EN
In this work we present analysis of carriers dynamics in samples of GaN nanowires grown on silicon. The samples exhibit bright luminescence of bulk donor-bound excitons at 3.472 eV, surface defect-bound excitons at 3.450 eV (SDX) and a broad (0.05 eV) band centered at 3.47 eV caused probably by single free exciton and bi-exciton recombination. The SDX emission has long lifetime τ = 0.6 ns at 4 K and can be observed up to 50 K. At higher temperatures luminescence is dominated by free excitons. The broad excitonic band is best visible under high excitation, and reveals fast, non-exponential dynamics. We present mathematical model assuming exciton-exciton interaction leading to the Auger processes. The model includes n^2 (Langevin) term and describes well the non-exponential dynamics of the excitonic band.
4
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Graphene Based Flow Sensors

76%
Kaźmierczak P., Binder J., Boryczko K., Ciuk T., Strupiński W., Stępniewski R., Wysmołek A.
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vol. 126
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issue 5
1209-1212
EN
We report on attempts to produce a graphene based liquid flow sensor. Our results indicate that modifications of the electric double layer, formed in the vicinity of the graphene surface, dominate over mechanisms responsible for liquid flow-induced voltage/current generation. Several graphene structures were tested in different measurement configurations, aimed to maximize the generated signal amplitude and its stability. Some realizations of working devices in water as well as in aqueous solutions of NaCl or HCl are presented.
5
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Optical Properties of Molybdenum Disulfide (MoS_2)

64%
Gołasa K., Grzeszczyk M., Korona K., Bożek R., Binder J., Szczytko J., Wysmołek A., Babiński A.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
849-851
EN
Research of a monolayer and a bulk MoS_2 is reported. The room temperature Raman spectra of the natural MoS_2 crystals for the both resonant (632.8 nm) and the non-resonant (532 nm) excitation are presented. The apparent differences observed in the spectra from the bulk and the one monolayer MoS_2 are discussed. In particular, the feature due to a first order scattering involving the LA(M) phonon in the resonance Raman spectrum of the one monolayer MoS_2 was observed and explained in terms of the disorder in the natural crystal. The disorder is also documented by the line-shape of the room-temperature photoluminescence spectra observed from both the bulk and the one monolayer MoS_2.
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