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Nanoscale Res Lett ; 14(1): 276, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31414236


We have studied the characteristics of frequency response at 850-nm GaAs high-speed vertical-cavity surface-emitting lasers (VCSELs) with different kinds of oxide aperture sizes and cavity length using the PICS3D simulation program. Using 5-µm oxide aperture sizes, the frequency response behavior can be improved from 18.4 GHz and 15.5 GHz to 21.2 GHz and 19 GHz in a maximum of 3 dB at 25 °C and 85 °C, respectively. Numerical simulation results also suggest that the frequency response performances improved from 21.2 GHz and 19 GHz to 30.5 GHz and 24.5 GHz in a maximum of 3 dB at 25 °C and 85 °C due to the reduction of cavity length from 3λ/2 to λ/2. Consequently, the high-speed VCSEL devices were fabricated on a modified structure and exhibited 50-Gb/s data rate at 85 °C.

Opt Express ; 27(12): A643-A653, 2019 Jun 10.
Artigo em Inglês | MEDLINE | ID: mdl-31252844


In this work, the size-dependent effect for InGaN/GaN-based blue micro-light emitting diodes (µLEDs) is numerically investigated. Our results show that the external quantum efficiency (EQE) and the optical power density drop drastically as the device size decreases when sidewall defects are induced. The observations are owing to the higher surface-to-volume ratio for small µLEDs, which makes the Shockley-Read-Hall (SRH) non-radiative recombination at the sidewall defects not negligible. The sidewall defects also severely affect the injection capability for electrons and holes, such that the electrons and holes are captured by sidewall defects for the SRH recombination. Thus, the poor carrier injection shall be deemed as a challenge for achieving high-brightness µLEDs. Our studies also indicate that the sidewall defects form current leakage channels, and this is reflected by the current density-voltage characteristics. However, the improved current spreading effect can be obtained when the chip size decreases. The better current spreading effect takes account for the reduced forward voltage.

J Phys Chem Lett ; 8(21): 5430-5437, 2017 Nov 02.
Artigo em Inglês | MEDLINE | ID: mdl-29058902


Chemical reactions at a solid-liquid interface are of fundamental importance. Interfacial chemical reactions occur not only at the very interface but also in the subsurface area, while existing monitoring techniques either provide limited spatial resolution or are applicable only for the outmost atomic layer. Here, with the aid of the time-domain analysis with femtosecond acoustics, we demonstrate a subatomic-level-resolution technique to longitudinally monitor chemical reactions at solid-water interfaces, capable of in situ monitoring even the subsurface area under atmospheric conditions. Our work was proven by monitoring the already-known anode oxidation process occurring during photoelectrochemical water splitting. Furthermore, whenever the oxide layer thickness equals an integer  number of the effective atomic layer thickness, the measured acoustic echo will show higher signal-to-noise ratios with reduced speckle noise, indicating the quantum-like behavior of this coherent-phonon-based technique.

Chemistry ; 23(47): 11261-11271, 2017 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-28497504


A series of semiconducting cluster-incorporated Cu-based coordination polymers, namely, 1D zigzag polymers [{TeFe3 (CO)9 Cu2 }(L)]n (L=1,2-bis(4-pyridyl)ethane (bpea), 1; L=1,2-bis(4-pyridyl)ethylene (bpee), 5), 2D honeycomb-like polymers [{TeFe3 (CO)9 Cu}Cu(L)2.5 ]n (L=bpea, 2; L=bpee, 6), and 2D wave-like cation-anion polymer [{Cu2 (L)4 }({TeFe3 (CO)9 Cu}2 (L))]n (L=1,3-bis(4-pyridyl)propane (bpp), 4), as well as the macrocycle [{TeFe3 (CO)9 Cu2 }2 (bpp)2 ] (3) have been quantitatively synthesized via the liquid-assisted grinding from the pre-designed cluster [TeFe3 (CO)9 Cu2 (MeCN)2 ] with conjugated or conjugation-interrupted dipyridyl linkers. Notably, the most conjugation-interrupted bpp-bridged polymer 4 exhibited extraordinary semiconducting characteristics with an ultra-narrow bandgap of 1.43 eV and a DC conductivity of 1.5×10-2 Ω-1  cm-1 , which violates our knowledge, mainly attributed to the through-space electron transport via non-classical C-H⋅⋅⋅O(carbonyl) hydrogen bonds and aromatic C-H⋅⋅⋅π interactions. The incorporated Te-Fe-CO anions can not only provide numerous possibilities for secondary interactions within these Cu-based polymers but also serve as a redox-active coordination ligand to promote their conductivities. The intriguing structure-property relationships were studied by X-ray and DFT analyses and further demonstrated by significant change in the oxidation state of Cu atoms by XPS and Cu K-edge XANES.

Phys Chem Chem Phys ; 17(22): 14561-8, 2015 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-25969355


We present a comprehensive Raman scattering study of monolayer MoS2 with increasing laser excitation energies ranging from the near-infrared to the deep-ultraviolet. The Raman scattering intensities from the second-order phonon modes are revealed to be enhanced anomalously by only the ultraviolet excitation wavelength 354 nm. We demonstrate theoretically that such resonant behavior arises from a strong optical absorption that forms near the Γ point and ½ΓK of the band structure and an inter-valley resonant electronic scattering by the M-point phonons. These results advance our understanding of the double resonance Raman scattering process in low-dimensional semiconducting nanomaterials and provide a foundation for the technological development of monolayer MoS2 in the ultraviolet frequency range.

J Am Chem Soc ; 130(43): 14114-6, 2008 Oct 29.
Artigo em Inglês | MEDLINE | ID: mdl-18828634


The unprecedented ternary Te-Fe-Cu chain polymers [{Et4N}{TeFe3(CO)9Cu}]infinity and [{TeFe3(CO)9Cu2}(mu-4,4'-dipyridyl)1.5]infinity were prepared from the self-assembly of [Et4N]2[TeFe3(CO)9] with [Cu(MeCN)4][BF4] in THF or in the presence of 4,4'-dipyridyl in THF. These two chain polymers, which can also be constructed from the precursor complex TeFe3(CO)9Cu2(MeCN)2, show semiconducting behaviors with low band gaps of 0.59 and 0.41 eV, respectively. In addition, their conductivity and the effect of the bridging ligand are further elucidated by theoretical calculations.

Cobre/química , Ferro/química , Compostos Organometálicos/química , Polímeros/química , Semicondutores , Telúrio/química , Simulação por Computador , Cristalografia por Raios X , Modelos Químicos , Modelos Moleculares , Estrutura Molecular