Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session B54: Optical Properties of Semiconductor Nanostructures IIIndustry
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Sponsoring Units: FIAP DMP Chair: Alexander Efros, Naval Research Lab Room: Hilton Baltimore Holiday Ballroom 5 |
Monday, March 14, 2016 11:15AM - 11:27AM |
B54.00001: Experimental evidence of $\alpha$$\rightarrow$$\beta$ phase transformation in SiC quantum dots and their size-dependent luminescence Xiaoxiao Guo, Dejian Dai, Baolu Fan, Jiyang Fan Silicon carbide (SiC) quantum dots (QDs) have attracted great interest due to their wide application in photonics, optoelectronics, and life sciences. SiC is an outstanding wide-bandgap semiconductor for applications in high power, high temperature, and high frequency electronic devices owing to its superior physical and mechanical properties. As a wide-bandgap semiconductor, SiC has over 250 crystalline structures, and some polytypes have been found in the presolar meteorites. Phase transformation can occur among different SiC polytypes under extreme conditions such as high pressure or high temperature. It remains unknown whether phase transformation can occur under normal conditions. We demonstrate that the $\alpha$$\rightarrow$$\beta$ phase transformation can occur at ambient temperature and pressure in nanoscale SiC. The microstructural characterization and light absorption and emission spectroscopy demonstrate the occurrence of this phase transformation. It is found that the quantum-confinement luminescence dominates in larger SiC QDs and the surface-defect luminescence dominates in ultrasmall SiC QDs. The rare phenomenon of photon absorption accompanied by emission or absorption of multiple phonons has been observed, demonstrating the indirect-bandgap nature of the SiC QDs. [Preview Abstract] |
Monday, March 14, 2016 11:27AM - 11:39AM |
B54.00002: Two-photon absorption in 3-100nm diameter Silicon nanocrystals in solution Brandon Furey, Michael Downer, Yixuan Yu, Brian Korgel Silicon nanocrystals (nc-Si) exhibit efficient photoluminescence (PL) that has applications in non-toxic bio-imaging. Two-photon absorption (TPA) is an important process for exciting PL in the tissue transparency spectral window, but absolute TPA coefficients have not been measured as a continuous function of nc size or excitation wavelength. Previous TPA studies have focused on nc-Si embedded in an oxide matrix or on porous Si surfaces at selected discrete wavelengths [1]. However, recently free standing, ligand-stabilized nc-Si with diameters ranging from 3 to 100 nm that are soluble in liquids, including water, and suitable for bio-imaging have become available [3]. We will present calibrated TPA spectra for free standing nc-Si over a wide range of nc diameters, based on measurements with tunable femtosecond laser pulses. We will compare indirect TPA measurements based on collection and detection of PL with direct TPA measurements based on attenuation of the incident beam. [1] P. Zhang, Z. Zhang, K. Chen et al., Nanoscale Res. Lett. 9 (28), 1 (2014) [2] C.M. Hessel, J. Wei, B. Korgel et al., Chem. Mater. 24 (2), 393 (2012) [Preview Abstract] |
Monday, March 14, 2016 11:39AM - 11:51AM |
B54.00003: ABSTRACT WITHDRAWN |
Monday, March 14, 2016 11:51AM - 12:03PM |
B54.00004: \textbf{Stimulated emission and lasing from all-inorganic perovskite quantum dots} Handong Sun, Yue Wang, Xiaoming Li, Zeng Haibo We present superior optical gain and lasing properties in a new class of emerging quantum materials, the colloidal all-inorganic cesium lead halide perovskite quantum dots (IPQDs) (CsPbX$_{\mathrm{3}}$, X $=$ Cl, Br, I). Our result has indicated that such material system show combined merits of both colloidal quantum dots and halide perovskites. Low-threshold and ultrastable stimulated emission was demonstrated under atmospheric condition. The flexibility and advantageous optical gain properties of these CsPbX$_{\mathrm{3\thinspace }}$IPQDs were manifested by demonstration of an optically pumped micro-laser. The nonlinear optical properties including the multi-photon absorption and resultant photoluminescence of the CsPbX$_{\mathrm{3}}$ nanocrystals were investigated. A large two-photon absorption cross-section of up to \textasciitilde 1.2\texttimes 105 GM is determined from 9 nm-sized CsPbBr$_{\mathrm{3}}$ nanocrystals. Moreover, low-threshold frequency-upconverted stimulated emission by two-photon absorption was observed from the thin films of close-packed CsPbBr$_{\mathrm{3}}$ nanocrystals. We further realize the three-photon pumped stimulated emission in green spectra range from colloidal IPQD. [Preview Abstract] |
Monday, March 14, 2016 12:03PM - 12:15PM |
B54.00005: Control of Photo- and Electro-generated Excited States of Colloidal Quantum Dots Xiaogang Peng Colloidal semiconductor nanocrystals (quantum dots) as solution-processible photo- and electro-excited emitters are promising and may impact many industrial sectors. Both photoluminescence and electroluminescence are based on generation and relaxation of the excited states. Thus, properties of excited states should be the key for design, synthesis, understanding, and applications of emitters. Specifically, as promising emissive materials, colloidal quantum dots rely heavily on their excited-state properties, instead of solely the ground-state properties. [Preview Abstract] |
Monday, March 14, 2016 12:15PM - 12:27PM |
B54.00006: Self-assembled single-mode micro-lasers of "giant" CdSe/CdS core/shell quantum dots Chen Liao, Jiayu Zhang So-called “giant” quantum dots (g-QDs) as optical gain media have attracted much attention due to their near elimination of nonradiative Auger effects. In the present work, phase-pure wurtzite CdSe/CdS core/shell QDs with controlled shell thickness are successfully synthesized, and the threshold of amplified spontaneous emission (ASE) of the films of this series of QDs is measured. The threshold of ASE is decreased dramatically with the CdS shell growth towards 11 monolayers (MLs) (21 $\mu $J/cm$^{2})$, but increased with the further shell growth. The effects of the overlap degree of electron and hole wave functions, surface states, and absorption cross-section are discussed to explain the ASE properties of the QDs. Moreover, the low-threshold gain of the CdSe/CdS core/shell (11 MLs) g-QDs is exploited to fabricate micro-lasers solely by deposition of small droplets of QDs solution onto glass substrates. The evaporation dynamics of the droplets are governed by the “coffee-ring effect” which leads to the formation of well defined micron-size rings. The self-assembled coffee-ring micro-lasers display single-mode operation and a very low threshold of 3 $\mu $J/cm$^{2}$. Herein, an innovative, simple and reliable method to produce micro-lasers based on CdSe/CdS g-QDs is presented. [Preview Abstract] |
Monday, March 14, 2016 12:27PM - 12:39PM |
B54.00007: Red shift in the photoluminescence of colloidal carbon quantum dots induced by photon reabsorption Wenxia Zhang, Jiyang Fan We synthesize the colloidal carbon/graphene quantum dots 1-9 nm in diameter through a novel alkaline-assisted method and deeply studied their photoluminescence properties. Surprisingly, the luminescence properties of a fixed collection of carbon dots can be systematically changed as the concentration varies. A model based on photon reabsorption is proposed which explains well the experiment. Infrared spectral study indicates that the surfaces of the carbon dots are totally terminated by three bonding-types of oxygen atoms, which result in their ultra-high hydrophilicity. Our result clarifies the mystery of distinct emission colors in carbon dots and indicates that photon reabsorption can strongly affect the luminescence properties of colloidal nanocrystals.This mechanism can be generalized to help understand the complex luminescence properties of other colloidal quantum dots. and should be seriously considered,otherwise, distinct conclusions may be drawn if different concentrations of quantum dots have been utilized in studying their luminescence properies. [Preview Abstract] |
Monday, March 14, 2016 12:39PM - 12:51PM |
B54.00008: Tunable Emission in Inverted Type-I CdS/CdSe Core/Crown Semiconductor Nanoplatelets Pedro Ludwig Hernandez-Martinez, Savas Delikanli, Burak Guzelturk, Talha Erdem, Yusuf Kelestemur, Murat Olutas, Mehmet Zafer Akgul, Hilmi Volkan Demir In this work, we present the tunable optical properties of an inverted Type-I core/crown nanoplatelet heterostructure. We show that the emission peak of the resulting CdS/CdSe hetero-nanoplatelets can be tuned continuously between the peak emission wavelengths of the core only CdS nanoplatelets (421 nm) and CdSe nanoplatelets (515 nm). In these inverted Type-I nanoplatelets, the unique continuously tunable emission is enabled by adjusting the lateral width of the CdSe crown, around the core CdS nanoplatelet. As a proof-of-concept, we generate white light by using color conversion concept with CdS/CdSe hetero-nanoplatelets, which have finely tuned thin crowns. This results in a color rendering index of 80. [Preview Abstract] |
Monday, March 14, 2016 12:51PM - 1:03PM |
B54.00009: Nonradiative Auger recombination of biexcitons in CdSe/CdS core-shell nanocrystal quantum dots Roman Vaxenburg, Anna Rodina, Efrat Lifshitz, Alexander Efros Semiconductor nanocrystals are known for their applicative potential as light-emitting components in lasers and LEDs, as well as light absorbers in solar cells. The performance of these nanocrystal-based devices, however, strongly depends on the dissipative nonradiative Auger recombination. The study of dynamics of the Auger processes is therefore of key importance in connection with the performance of nanocrystals devices. Here we report on a theoretical study of the Auger recombination dynamics of biexcitons in CdSe/CdS core-shell nanocrystals. Biexcitons can decay by the Auger process via negative or positive trion recombination channels. We study the dependence of the rate of each one of these channels on the angular momentum of the initial biexciton state, nanocrystal geometry, and temperature. We observe that the overall dependence of the rates of both channels is strongly oscillating with nanocrystal geometry, indicating large differences in the Auger rates in nanocrystals of similar size. We find that the rate of the negative trion channel is independent of the initial biexciton angular momentum and is generally slower than the rate of the positive trion channel, which, in contrast, is sensitive to the biexciton angular momentum. Further, we demonstrate that by variation of temperature the Auger rate can be varied across a wide range of values. [Preview Abstract] |
Monday, March 14, 2016 1:03PM - 1:15PM |
B54.00010: Dangling Bond Magnetic Polaron in CdSe nanocrystals Alexander Efros, Anna Rodina In this work we study theoretically the effect of the spins of the surface dangling bonds on the PL of CdSe nanocrystals (NCs). [1] We show that spins of dangling bonds open new recombination channels for the dark exciton recombination which is connected with flip-flip and flip-flop spin-assisted recombination of the dark exciton. Calculations show that at low temperatures the interaction between dangling bonds and NC excitons leads to the dynamical polarization of the dangling bond spins along the anisotropic axis following by the formation of a dangling bond magnetic polaron. An increase of the temperature, or of the external magnetic field perpendicular to the anisotropic axis, destroys the polaron state. This results in a shift of the transition energy and an increase of its recombination rate. Thus thermal depolarization of the polaron state may explain the small activation energies observed in the temperature dependences of the exciton lifetimes in CdSe NCs. The exchange interaction of the electron spin with spins of the surface dangling bonds explains also radiative recombination of the dark excitons in nanowires, nanorods and nanoplatelets. [1] A. Rodina and Al. L. Efros, Nano Lett. v. 15, 4214-4222 (2015) [Preview Abstract] |
Monday, March 14, 2016 1:15PM - 1:27PM |
B54.00011: Superradiance in Spherical Layered Nanostructures Serguei Goupalov We propose a design of a spherically symmetric nanostructure consisting of alternate concentric semiconductor and dielectric layers. The exciton states in different semiconductor layers of such a structure interact via the common electro-magnetic field of light. We show that, if the exciton states in $N$ semiconductor layers are in resonance with one another, then superradiant states can emerge under optical excitation of such a structure. We discuss the conditions under which superradiance can be observed and show that they strongly depend on the valence-band structure of the semiconductor layers. [Preview Abstract] |
Monday, March 14, 2016 1:27PM - 1:39PM |
B54.00012: Macrocrystals of Colloidal Quantum Dots in Anthracene: Exciton Transfer and Polarized Emission Zeliha Soran-Erdem, Talha Erdem, Pedro Ludwig Hernandez-Martinez, Mehmet Zafer Akgul, Nikolai Gaponik, Hilmi Volkan Demir We systematically investigate the exciton energy transfer from anthracene host (donor) to quantum dots (acceptor) in a centimeter-scale macrocrystal of nonpolar colloidal quantum dots incorporated into anthracene. The decrease in photoluminescence lifetime of the donor anthracene indicate a strong energy transfer with increasing quantum dot concentration in the macrocrystals. In addition, anisotropic emission from the isotropic quantum dots in anthracene macrocrystals was observed. The quantum dots inside the anthracene host acquired a polarization ratio of $\sim $1.5 at 0 degree collection angle, and this increases to $\sim $2.5 at the collection angle of 60 degree. Finally, a proof-of-concept application of these excitonic macrocrystals as tunable color converters was employed in light-emitting diodes. [Preview Abstract] |
Monday, March 14, 2016 1:39PM - 1:51PM |
B54.00013: Optical Properties of the Defect State Luminescence of Zn2SnO4 Nanowires Baichhabi Yakami, Uma Paudyal, Shashank Nandyala, Gaurab Rimal, Jason K. Cooper, Jiajun Chen, TeYu Chien, Wenyong Wang, Jon M Pikal Nanowires (NWs) are a promising option for sensitized solar cells, sensors {\&} display technology. Most of the work thus far has focused on binary oxides for these NWs, but ternary oxides have advantages in additional control of optical and electronic properties. Here we report on the diffuse reflectance, Low Temperature (LT) and Room Temperature (RT) photoluminescence (PL), PL excitation and Time Resolved PL (TRPL) of Zinc Tin Oxide (ZTO) NWs grown by Chemical Vapor Deposition. Our results show two broad peaks centered at 640 nm {\&} 450 nm. The complex emission spectra was studied by Time Resolved Emission Spectroscopy (TRES) and Intensity dependent PL. The intensity dependent TRPL shows that 640 nm states decay much slower than the 450 nm states. We propose an energy band model for the NWs containing donor and acceptor states in the band gap with the associated transitions between these states that are consistent with our results. The effect of annealing in air and vacuum is carried out to study the origin of defect states in these NWs. . [Preview Abstract] |
Monday, March 14, 2016 1:51PM - 2:03PM |
B54.00014: Photoluminescence of Sequential Infiltration Synthesized ZnO nanostructures. Leonidas Ocola, David Gosztola, Angel Yanguas-Gil, Aine Connolly We have investigated a variation of atomic layer deposition (ALD), called sequential infiltration synthesis (SiS), as an alternate method to incorporate ZnO and other oxides inside polymethylmethacrylate (PMMA) and other polymers. Energy dispersive spectroscopy (EDS) results show that we synthesize ZnO up to 300 nm inside a PMMA film. Photoluminescence data on a PMMA film shows that we achieve a factor of 400X increase in photoluminescence (PL) intensity when comparing a blank Si sample and a 270 nm thick PMMA film, where both were treated with the same 12 alternating cycles of H2O and diethyl zinc (DEZ). PMMA is a well-known ebeam resist. We can expose and develop patterns useful for photonics or sensing applications first, and then convert them afterwards into a hybrid polymer-oxide material. We show that patterning does indeed affect the photoluminescence signature of native ZnO. We demonstrate we can track the growth of the ZnO inside the PMMA polymer using both photoluminescence and Raman spectroscopy and determine the point in the process where ZnO is first photoluminescent and also at which point ZnO first exhibits long range order in the polymer. [Preview Abstract] |
Monday, March 14, 2016 2:03PM - 2:15PM |
B54.00015: X-ray Analysis of Self-assembled Nano-Dielectrics Li Zeng, Riccardo Turrisi, Jonathan Emery, Mark Hersam, Tobin Marks, Michael Bedzyk Organic thin-film transistors (OTFTs) are viewed as the new generation thin-film transistors (TFT) for future low-cost, printable, flexible electronics. A class of materials called self-assembled nano-dielectrics (SAND) with phosphoric acid-based-electron (PAE) building blocks sandwiched between ultrathin layers of high-$k$ inorganic oxide materials has been synthesized. These materials show exceptional large capacitance, insulating properties, and are also suitable for ambient atmosphere fabrication. The hybrid nature of these materials combines the distinct properties of both the organic and inorganic components and can be incorporated into the low-operating voltage semiconductor-based OTFT. Despite the great performance and flexibility of SANDs, fundamental aspects of dielectric behavior remain unexplored. Particularly, the behaviors of the Br counteranions that exist within PAE building blocks are poorly understood. Therefore, long-period X-ray Standing Wave (LP-XSW), which is a powerful technique sensitive to heavy atom distributions, was used to characterize SAND deposited on synthetic Si/Mo multilayer substrates. The elemental distributions of Br and reference elements were extracted from the analysis of XSW data. These accurate measurements are important for better understanding of counteranions distributions, charge transportation, dipole-semiconductors interactions, and future device modeling and engineering. [Preview Abstract] |
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