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1.
Nano Lett ; 19(2): 1204-1209, 2019 02 13.
Artigo em Inglês | MEDLINE | ID: mdl-30682253

RESUMO

Silicon photonics has been a very active area of research especially in the past two decades in order to meet the ever-increasing demand for more computational power and faster device speeds and their natural compatibility with complementary metal-oxide semiconductor. In order to develop Si as a useful photonics material, essential photonic components such as light sources, waveguides, wavelength convertors, modulators, and detectors need to be developed and integrated. However, due to the indirect electronic bandgap of Si, conventional light emission devices such as light-emitting diodes and lasers cannot be built. Therefore, there has been considerable interest in developing Si-based Raman lasers, which are nonlinear devices and require large stimulated Raman scattering (SRS) in an optical cavity. However, due to the low quantum yield of SRS in Si, Raman lasers have very large device footprints and high lasing threshold, making them unsuitable for faster, smaller, and energy-efficient devices. Here, we report strong SRS and extremely high Raman gain in Si nanowire optical cavities in the visible region with measured SRS threshold as low as 30 kW/cm2. At cavity mode resonance, light is confined into a low mode volume and high intensity electromagnetic mode inside the Si nanowire due to its high refractive index, which leads to strong SRS at low pump intensities. Electromagnetic calculations reveal greater than 6 orders of magnitude increase in Raman gain coefficient at 532 nm pump wavelength, compared to the gain value at 1.55 µm wavelength reported in literature, despite the 108 higher losses at 532 nm. Because of the high gain in such small structures, we believe that this is a significant first step in realizing a monolithically integrable nanoscale low-powered Si Raman laser.

2.
Nano Lett ; 18(3): 1620-1627, 2018 03 14.
Artigo em Inglês | MEDLINE | ID: mdl-29406729

RESUMO

Controlled chemical transformation of nanostructures is a promising technique to obtain precisely designed novel materials, which are difficult to synthesize otherwise. We report high-temperature vapor-phase anion-exchange reactions to chemically transform II-VI semiconductor nanostructures (100-300 nm length scale) while retaining the single crystallinity, crystal structure, morphology, and even defect distribution of the parent material via atomic templating. The concept of atomic templating is employed to obtain kinetically controlled, thermodynamically metastable structural phases such as zincblende CdSe and CdS from zincblende CdTe upon complete chemical replacement of Te with Se or S. The underlying transformation mechanisms are explained through first-principles density functional theory calculations. Atomic templating is a unique path to independently tune materials' phase and composition at the nanoscale, allowing the synthesis of novel materials.

3.
Nano Lett ; 16(7): 4404-9, 2016 07 13.
Artigo em Inglês | MEDLINE | ID: mdl-27351823

RESUMO

We demonstrate that optical second harmonic generation (SHG) can be utilized to determine the exact nature of nanotwins in noncentrosymmetric crystals, which is challenging to resolve via conventional transmission electron or scanned probe microscopies. Using single-crystalline nanotwinned CdTe nanobelts and nanowires as a model system, we show that SHG polarimetry can distinguish between upright (Cd-Te bonds) and inverted (Cd-Cd or Te-Te bonds) twin boundaries in the system. Inverted twin boundaries are generally not reported in nanowires due to the lack of techniques and complexity associated with the study of the nature of such defects. Precise characterization of the nature of defects in nanocrystals is required for deeper understanding of their growth and physical properties to enable their application in future devices.

4.
Nano Lett ; 15(11): 7341-6, 2015 Nov 11.
Artigo em Inglês | MEDLINE | ID: mdl-26421441

RESUMO

We demonstrate the utility of optical second harmonic generation (SHG) polarimetry to perform structural characterization of noncentrosymmetric, single-crystalline II-VI semiconducting nanowires, nanobelts, and nanoflakes. By analyzing anisotropic SHG polarimetric patterns, we distinguish between wurtzite and zincblende II-VI semiconducting crystal structures and determine their growth orientation. The crystallography of these nanostructures was then confirmed via transmission electron microscopy measurements performed on the same system. In addition, we show that some intrinsic material properties such as nonlinear coefficients and geometry-dependent optical in-coupling coefficients can also be determined from the SHG experiments in WZ nanobelts. The ability to perform SHG-based structural characterization and crystallographic study of II-VI semiconducting single-crystalline nanomaterials will be useful to correlate structure-property relationships of nanodevices on which transmission electron microscopy measurements cannot be typically performed.

5.
Nano Lett ; 14(11): 6564-71, 2014 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-25301247

RESUMO

Semiconductor nanostructures such as nanowires and nanoribbons functioning as Fabry-Pérot (F-P)-type optical cavities and nanolasers have attracted great interest not only for their potential use in nanophotonic systems but also to understand the physics of light-matter interactions at the nanoscale. Due to their nanoscale dimensions, new techniques need to be continuously developed to characterize the nature of highly confined optical modes. Furthermore, the inadequacy of typical far-field photoluminescence experiments for characterizing the nanoscale cavity modes such as parity and order has precluded efforts to obtain precise information that is required to fully understand these cavities. Here, we utilize a modified Young's interference method based on angle-resolved microphotoluminescence spectral technique to directly reveal the parity of F-P cavity modes in CdS nanostructures functioning as waveguides and nanolasers. From these analyses, the mode order can be straightforwardly obtained with the help of numerical simulations. Moreover, we show that the Young's technique is a general technique applicable to any F-P type cavities in nanoribbons, nanowires, or other photonic and plasmonic nanostructures.


Assuntos
Compostos de Cádmio/química , Lasers , Nanoestruturas/química , Compostos de Selênio/química , Semicondutores , Desenho de Equipamento , Luz , Nanotecnologia , Nanofios/química , Fótons
6.
Opt Express ; 22(23): 28653-61, 2014 Nov 17.
Artigo em Inglês | MEDLINE | ID: mdl-25402106

RESUMO

We have investigated second harmonic generation (SHG) from Ag-coated LiNbO3(LN) core-shell nanocuboids and found that giant SHG can occur via deliberately designed double plasmonic resonances. By controlling the aspect ratio, we can tune fundamental wave (FW) and SHG signal to match the longitudinal and transverse plasmonic modes simultaneously, and achieve giant enhancement of SHG by 3 × 10(5) in comparison to a bare LN nanocuboid and by about one order of magnitude to the case adopting only single plasmonic resonance. The underlying key physics is that the double-resonance nanoparticle enables greatly enhanced trapping and harvesting of incident FW energy, efficient internal transfer of optical energy from FW to the SHG signal, and much improved power to transport the SHG energy from the nanoparticle to the far-field region. The proposed double-resonance nanostructure can serve as an efficient subwavelength coherent light source through SHG and enable flexible engineering of light-matter interaction at nanoscale.


Assuntos
Nanoestruturas/química , Ressonância de Plasmônio de Superfície/métodos , Modelos Teóricos , Nióbio/química , Análise Numérica Assistida por Computador , Óxidos/química , Processamento de Sinais Assistido por Computador , Prata/química
7.
Small ; 8(9): 1355-9, 2012 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-22378595

RESUMO

Loss issues are fundamentally crucial for the application of surface plasmon polaritons (SPPs). In this study the amplified spontaneous emission (ASE) of SPPs in a typical Kretschmann configuration is observed and shows an unusually broadened angular response with increased pump intensity. Theoretical models are further developed to verify the results and understand the amplification of SPPs in Fourier space.

8.
Cell Immunol ; 278(1-2): 152-7, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-22982671

RESUMO

Adipose tissue-derived stem cells (ADSC) have been shown to possess stem cell properties such as transdifferentiation, self-renewal and therapeutic potential. However, the property of ADSC to accommodate immune system is still unknown. In this study, ADSC were cocultured with allogenetic dendritic cells (DC), and then treated DC were mixed with allogenetic CD4+ T cells. The results demonstrated that ADSC could downregulate costimulatory molecules, including CD80, CD83, CD86, and cytokine secretion such as interleukin (IL)-12 and tumor necrosis factor (TNF)-α, while upregulate indoleamine-2,3-dioxygenase (IDO) of allogenetic DC. In addition, treated DC could inhibit CD4+ T cell activation and naïve T cells toward Th1 polarization. The results suggest that ADSC could negatively modulate immunity and induce immune tolerance, which provide a promising strategy in transplantation or autoimmune disease.


Assuntos
Tecido Adiposo/imunologia , Comunicação Celular/imunologia , Células Dendríticas/imunologia , Tolerância Imunológica , Células-Tronco/imunologia , Tecido Adiposo/citologia , Tecido Adiposo/metabolismo , Adulto , Antígenos CD/genética , Antígenos CD/imunologia , Linfócitos T CD4-Positivos/citologia , Linfócitos T CD4-Positivos/imunologia , Linfócitos T CD4-Positivos/metabolismo , Comunicação Celular/genética , Diferenciação Celular/imunologia , Técnicas de Cocultura , Células Dendríticas/citologia , Células Dendríticas/metabolismo , Regulação da Expressão Gênica , Humanos , Indolamina-Pirrol 2,3,-Dioxigenase/genética , Indolamina-Pirrol 2,3,-Dioxigenase/imunologia , Interleucina-12/genética , Interleucina-12/imunologia , Pessoa de Meia-Idade , Cultura Primária de Células , Transdução de Sinais , Células-Tronco/citologia , Células-Tronco/metabolismo , Fator de Necrose Tumoral alfa/genética , Fator de Necrose Tumoral alfa/imunologia
9.
Opt Lett ; 36(18): 3696-8, 2011 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-21931436

RESUMO

We have demonstrated super quasi-phase matching (QPM) in a super periodically poled lithium niobate (PPLN), which is composed of multiple ordinary PPLN cells. When super QPM is achieved, the slight phase mismatch in each PPLN cell can be further compensated for, and the relevant second harmonic generation is facilitated greatly. This mechanism provides an insightful means to relieve the limitation imposed by sample fabrication inaccuracy and will open up a promising avenue toward highly efficient nonlinear interactions.

10.
Opt Express ; 18(7): 7288-99, 2010 Mar 29.
Artigo em Inglês | MEDLINE | ID: mdl-20389750

RESUMO

A versatile and accurate approach that combines a numerical iteration technique and a transfer-matrix method (TMM) is developed to solve the general problem of second harmonic generation (SHG) with pump depletion in quasi-phase-matched (QPM) nonlinear optical structures. We derive the iterative formulae from the nonlinear coupled wave equations and obtain the intensity distribution of fundamental wave and second harmonic wave by TMM. The approach shows quick numerical convergence of iteration and maintains perfect conservation of total energy. The simulation results show that the model coincides with the one under undepleted pump approximation very well when the SHG efficiency is small (well below 15%) and agrees very well with the effective nonlinear susceptibility model in handling general SHG problems even when the conversion efficiency is high up to 100%. Our method is applicable to general nonlinear optical structures, such as periodic, quasi-periodic, and aperiodic QPM structures, photonic crystals, and micro-cavities that might involve complicated modulation on the linear and nonlinear susceptibility.

11.
Opt Express ; 17(17): 14502-10, 2009 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-19687928

RESUMO

We theoretically investigate second harmonic generation (SHG) in one-dimensional multilayer nonlinear photonic crystal (NPC) structures with distributed Bragg reflector (DBR) as mirrors. The NPC structures have periodic modulation on both the linear and second-order susceptibility. Three major physical mechanisms, quasi-phase matching (QPM) effect, slow light effect at photonic band gap edges, and cavity effect induced by DBR mirrors can be harnessed to enhance SHG. Selection of appropriate structural parameters can facilitate coexistence of these mechanisms to act collectively and constructively to create very high SHG conversion efficiency with an enhancement by up to seven orders of magnitude compared with the ordinary NPC where only QPM works.

12.
Int J Mol Med ; 44(4): 1281-1288, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31432131

RESUMO

Implant­associated infection (IAI), a common condition marked by progressive inflammation and bone destruction, is mentally and financially devastating to those it affects, causing severe morbidity, prolonged hospital admissions, significant hospital costs and, in certain cases, mortality. Aspirin, a popular synthetic compound with a history of >100 years, is antipyretic, anti­inflammatory and analgesic. It is the most active component of non­steroidal anti­inflammatory drugs. However, the effects of aspirin on IAI remain unknown. In the present study, an IAI animal model was used, in which a stainless steel pin coated with Staphylococcus aureus was implanted through the left shaft of the tibia in mice. The animals were then randomized into five groups and subjected respectively to IAI, IAI + 15 mg aspirin treatment, IAI + 30 mg aspirin treatment, IAI + 60 mg aspirin treatment and IAI + 120 mg aspirin treatment groups. Aspirin was injected intraperitoneally twice daily for 11 days. Micro­CT and histological assays were performed to assess the effects of aspirin on IAI. It was found that aspirin reduced osteolysis and periosteal reaction, inhibited the activation of osteoclasts, promoted the activation of osteoblasts and facilitated healing of the infected fracture.


Assuntos
Anti-Inflamatórios não Esteroides/uso terapêutico , Aspirina/uso terapêutico , Próteses e Implantes/efeitos adversos , Infecções Relacionadas à Prótese/tratamento farmacológico , Infecções Relacionadas à Prótese/etiologia , Animais , Modelos Animais de Doenças , Feminino , Humanos , Imuno-Histoquímica , Camundongos , Osteólise , Infecções Relacionadas à Prótese/diagnóstico , Infecções Estafilocócicas/diagnóstico , Infecções Estafilocócicas/tratamento farmacológico , Infecções Estafilocócicas/etiologia , Staphylococcus aureus , Microtomografia por Raio-X
13.
Nat Commun ; 9(1): 186, 2018 01 15.
Artigo em Inglês | MEDLINE | ID: mdl-29335589

RESUMO

Dynamic control of nonlinear signals is critical for a wide variety of optoelectronic applications, such as signal processing for optical computing. However, controlling nonlinear optical signals with large modulation strengths and near-perfect contrast remains a challenging problem due to intrinsic second-order nonlinear coefficients via bulk or surface contributions. Here, via electrical control, we turn on and tune second-order nonlinear coefficients in semiconducting CdS nanobelts from zero to up to 151 pm V-1, a value higher than other intrinsic nonlinear coefficients in CdS. We also observe ultrahigh ON/OFF ratio of >104 and modulation strengths ~200% V-1 of the nonlinear signal. The unusual nonlinear behavior, including super-quadratic voltage and power dependence, is ascribed to the high-field domain, which can be further controlled by near-infrared optical excitation and electrical gating. The ability to electrically control nonlinear optical signals in nanostructures can enable optoelectronic devices such as optical transistors and modulators for on-chip integrated photonics.

14.
Sci Rep ; 6: 26607, 2016 05 23.
Artigo em Inglês | MEDLINE | ID: mdl-27210303

RESUMO

We report the modulation of emission energy, exciton dynamics and lasing properties in a single buckled CdS nanoribbon (NR) by strain-engineering. Inspired by ordered structure fabrication on elastomeric polymer, we develop a new method to fabricate uniform buckled NRs supported on polydimethylsiloxane (PDMS). Wavy structure, of which compressive and tensile strain periodically varied along the CdS NR, leads to a position-dependent emission energy shift as large as 14 nm in photoluminescence (PL) mapping. Both micro-PL and micro-reflectance reveal the spectral characteristics of broad emission of buckled NR, which can be understood by the discrepancy of strain-induced energy shift of A- and B-exciton of CdS. Furthermore, the dynamics of excitons under tensile strain are also investigated; we find that the B-exciton have much shorter lifetime than that of redshifted A-exciton. In addition, we also present the lasing of buckled CdS NRs, in which the strain-dominated mode selection in multi-mode laser and negligible mode shifts in single-mode laser are clearly observed. Our results show that the strained NRs may serve as new functional optical elements for flexible light emitter or on-chip all-optical devices.


Assuntos
Compostos de Cádmio/química , Luminescência , Nanotubos de Carbono/química , Sulfetos/química
15.
Nat Commun ; 5: 5432, 2014 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-25388766

RESUMO

Coherent and tunable nanoscale light sources utilizing optical nonlinearities are required for applications ranging from imaging and bio-sensing to on-chip all-optical signal processing. However, owing to their small sizes, the efficiency of nanostructures even with high nonlinear coefficients is poor, therefore requiring very high excitation energies. Although surface-plasmon resonances of metal nanostructures can enhance surface nonlinear processes such as second-harmonic generation, they still suffer from low conversion efficiencies owing to their intrinsically low nonlinear coefficients. Here we show highly enhanced and directional second-harmonic generation from individual CdS nanowires integrated with silver nanocavities (>1,000 times higher external efficiency compared with bare CdS), in which the lowest-order whispering gallery mode is engineered to concentrate light in the nonlinear material while minimizing Ohmic losses. The directional nonlinear signal is redirected into another waveguide, which is then utilized to configure an optical router that can potentially serve as a tunable coherent light source to enable on-chip signal processing for integrated nanophotonic systems.


Assuntos
Nanofios , Semicondutores , Impedância Elétrica , Luz , Nanoestruturas
16.
Cell Transplant ; 21(12): 2711-21, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-22963757

RESUMO

The ideal cells for tissue engineering should have the following characteristics: easy obtainment, safety, immune privilege, the capability of self-renewal, and multipotency. Adipose-derived stem cells (ADSCs) are a promising candidate. However, the immunogenicity of allogeneic mesenchymal stem cells limits their long-term benefits. In this study, we introduced human cytomegalovirus US2/US3 gene into the ADSCs to decrease the expression of MHC I protein of ADSCs and reduce the activation of T-cells of the recipient animals. Moreover, the biosafety and biological characteristics of ADSCs transfected with the US2/US3 genes (ADSCs-US2/US3) were similar to normal ADSCs. Then we took ADSCs-US2/US3 to construct a tissue-engineered bone for repairing bone defects in pigs and found that there were no great differences in repair effects or healing time between the allogeneic ADSCs-US2/US3 group and the autologous ADSC group. These results suggest that allogeneic ADSCs-US2/US3 have the advantages of biological safety, low immunogenicity, and effective osteogenesis. Such barely immunogenic ADSCs will be crucial for the success of future tissue-regenerative approaches.


Assuntos
Adipócitos/citologia , Doenças Ósseas/terapia , Transplante de Células-Tronco Mesenquimais , Células-Tronco Mesenquimais/citologia , Engenharia Tecidual , Animais , Doenças Ósseas/induzido quimicamente , Doenças Ósseas/diagnóstico por imagem , Diferenciação Celular , Citomegalovirus/metabolismo , Glicoproteínas/genética , Humanos , Proteínas Imediatamente Precoces/genética , Proteínas de Membrana/genética , Células-Tronco Mesenquimais/imunologia , Camundongos , Camundongos Nus , Osteogênese , Coelhos , Radiografia , Ratos , Ratos Sprague-Dawley , Suínos , Linfócitos T/imunologia , Linfócitos T/metabolismo , Tomografia Computadorizada de Emissão de Fóton Único , Transplante Homólogo , Ulna/diagnóstico por imagem , Proteínas do Envelope Viral/genética
17.
Tissue Eng Part A ; 17(19-20): 2369-78, 2011 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-21548841

RESUMO

Currently, the main hurdle in the tissue engineering field is how to provide sufficient blood supply to grafted tissue substitutes in the early post-transplanted period. For three-dimensional, cell-dense, thick tissues to survive after transplantation, treatments are required for hypoxia, nutrient insufficiency, and the accumulation of waste products. In this study, a biomacromolecular layer-by-layer coating process of chitosan/heparin onto a decellularized extracellular bone matrix was designed to accelerate the blood perfusion and re-endothelialization process. The results of in vitro measurements of the activated partial thromboplastin time supported the theory that the combination of chitosan and heparin could bring both anticoagulation and hemocompatibility to the scaffold. A rabbit bone defect model was established for further evaluation of the application of this kind of surface-modified scaffold in vivo. The final results of computed tomography (CT) perfusion imaging and histological examination proved that this facile coating approach could significantly promote blood perfusion and re-endothelialization in the early post-transplanted period compared with an acellular bone matrix due to its much-improved anticoagulation property.


Assuntos
Matriz Óssea/irrigação sanguínea , Quitosana/farmacologia , Materiais Revestidos Biocompatíveis/farmacologia , Heparina/farmacologia , Neovascularização Fisiológica/efeitos dos fármacos , Engenharia Tecidual/métodos , Alicerces Teciduais/química , Animais , Matriz Óssea/efeitos dos fármacos , Matriz Óssea/patologia , Matriz Óssea/ultraestrutura , Implantes Experimentais , Perfusão , Espectroscopia Fotoeletrônica , Coelhos , Sus scrofa , Fatores de Tempo
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