宫颈癌腔内放射治疗的光子运输

子宫颈癌是我国常见的妇科恶性肿瘤之一,每年新发病例为13万左右,对妇女健康构成严重的威胁。目前临床治疗宫颈癌仍是行手术、放疗、化疗三者综合治疗,放疗扮演着重要的角色。只有提高放疗水平,才能提高患者的生存率,而准确的放疗剂量资料,来源于直接测量。由于女姓盆腔及周围组织的解剖学结构复杂,在实施放射测量过程中需要一系列测量设备、实验技术、照射参数等等,测量成本高,工作程序繁琐。本工作采用随机光子跟踪模拟方法,进行宫颈癌腔内放射治疗时组织中光子通量的计算,简单、灵活、准确、受条件影响不大,对复杂的女性盆腔结构、组织参数随能量的剧烈变化及散射各向异性均能很好地处理,值得推广。

校验X刀放射治疗剂量分布的一种简易计算

检验X刀放射治疗剂量分布的实验测量需要利用组织等效模型和系列测量设备、实验技术,测量工作繁琐,费用高[1]。本工作采用统计试验方法[2]。模拟全空间定向X刀射线治疗脑室肿瘤的光输运过程,计算颅内一些选定位置处的能量沉积和对组织吸收剂量的贡献。此方法比较简单灵活,受问题条件的影响不大,对复杂的组织结构、几何条件、各参数随能量的剧烈变化、散射各向异性等情况均易处理,其计算结果准确性好。

Transport Properties of Two Coupled Quantum Dots Under Optical Pumping

Using the Keldysh-Green function,we present a theoretical study on the electron transport properties of two coupled quantum dots under optical pumping. Plateaus in the I-V curve and resonant peaks in the transmission coefficient occur and can be explained by the local electron density of states in the quantum dots. The effects of the optical pumping frequency and intensity on the transport properties of the system are also discussed. The electron dynamical localization phenomenon occurs when the optical pumping frequency is equal to the discrete hole energy level. This result can be used to realize optical control switches.

Towards single-molecule optoelectronic devices

Benefiting from the development of molecular electronics and molecular plasmonics, the interplay of light and electronic transport in molecular junctions has attracted growing interest among researchers in both fields, leading to a new research direction of "single-molecule optoelectronics". Here, we review the latest developments of photo-modulated charge transport,electroluminescence and Raman spectroscopy from single-molecule junctions, and suggest future directions for single-molecule optoelectronics.

Single Photon Scattering Properties in Coupled-Resonator Waveguide Coupling with a Nanocavity Interacting with an External Mirror

We investigate theoretically single photon transport properties in coupled-resonator waveguide coupling with a nanocavity interacting with an external mirror. By using the discrete coordinates approach, transmission and reflection amplitudes of the propagating single photon in the waveguide are obtained. The influence of the coupling strength between the nanocavity and the external mirror on the single photon scattering spectra is discussed. We also extend the results to the waveguide with linear and quadratic form dispersion relations.

Appending triphenyltriazine to 1,10-phenanthroline: a robust electron-transport material for stable organic light-emitting diodes

There has been an increasing demand for high-performance and cost-effective organic electron-transport materials for organic light-emitting diodes （OLEDs）. In this contribution, we present a simple compound 3-（3-（4,6-diphenyl-l,3,5-triazin-2-yl）phenyl）-1,10-phenanthroline through the facile Pd-catalyzed coupling of a triphenyltriazine boronic ester with 3-hromo-1,10-phenanthroline. It shows a high Tg of 112℃. The ultraviolet photoelectron spectroscopy measurements reveal a deep HOMO level of -6.5 eV. The LUMO level is derived as -3.0 eV, based on the optical bandgap. The low-temperature solid-state phosphorescent spectrum gives a triplet energy of -2.36eV. n-Doping with 8-hydroxyquinolatolithium （Liq, 1：1） leads to considerably improved electron mobility of 5.2 × 10 -6 -5.8 × 10 -5 cm2 v-1 S-1 at E=（2-5） × 10 5Vcm -1, in contrast with the triarylphosphine oxide- phenantroline molecular conjugate we reported previously. It has been shown that through optimizing the device structure and hence suppressing polaron-exciton annihilation, introducing this single Liq-doped electron-transport layer could offer high-efficiency and stable phosphorescent OLEDs.

CsPbBrI perovskites with low energy loss for high-performance indoor and outdoor photovoltaics

Over the years,the efficiency of inorganic perovskite solar cells(PSCs)has increased at an unprecedented pace.However,energy loss in the device has limited a further increase in efficiency and commercialization.In this work,we used(NH4)2C2O4·H2O to treat CsPbBrI2 perovskite film during spin-coating.The CsPbBrI2 underwent secondary crystallization to form high quality films with micrometer-scale and low trap density.(NH4)2C2O4·H2O treatment promoted charge transfer capacity and reduced the ideal factor.It also dropped the energy loss from 0.80 to 0.64 eV.The resulting device delivered a power conversion efficiency(PCE)of 16.55%with an open-circuit voltage(Voc)of 1.24 V,which are largely improved compared with the reference device which exhibited a PCE of 13.27%and a Voc of 1.10 V.In addition,the optimized treated device presented a record indoor PCE of 28.48%under a fluorescent lamp of 1000 lux,better than that of the reference device(19.05%).

CH_2,NH,and O heteroatom substitution effects on the electronic,optical,and charge transport properties of a 2,1,3-benzothiadiazole-based derivative:Insights from theory

A set of CH2-,NH-,and O-substituted 2,1,3-benzothiadiazole(BTD)-based derivatives have been investigated theoretically in order to explore their electronic,optical,and charge transport properties.The calculation results show that the electronic and optical properties of the pristine molecule can be easily tuned through changing the S substituent in the central aromatic ring.Based on the calculated maximum emission wavelength,we predict that CH2-,NH-,and O-substituted BTD-based derivatives could be used as red,green,and orange light-emitting materials,respectively.After CH2-,NH-or O-substitution,the oscillator strengths of the emission spectra are enhanced with respect to that of the pristine molecule,implying that these compounds have larger fluorescence intensity.Finally,it can be deduced that CH2-,NH-,and O-substituted BTD-based derivatives may act as hole transport materials in organic light-emitting diodes.

Optical and photo-carrier characterization of ultra-shallow junctions in silicon

Spectroscopic ellipsometry (SE), photocarrier radiometry (PCR) and photoluminescence (PL) techniques were employed to measure the ultra-shallow junction (USJ) wafers. These USJ wafers were prepared by As+ ion implantation at energies of 0.5-5 keV, at a dose of 1×1015 As+ /cm 2 and spike annealing. Experimentally the damaged layer of the as-implanted wafer and the recrystallization and activation of the post-annealed wafer were evaluated by SE in the spectral range from 0.27 to 20 m. The PCR amplitude decreased monotonically with the increasing implantation energy. The experimental results also showed that the PCR amplitudes of post-annealed USJ wafers were greatly enhanced, compared to the non-implanted and non-annealed substrate wafer. The PL measurements showed the enhanced PCR signals were attributed to the band-edge emissions of silicon. For explaining the PL enhancement, the electronic transport properties of USJ wafers were extracted via multi-wavelength PCR experiment and fitting. The fitted results showed the decreasing surface recombination velocity and the decreasing diffusion coefficient of the implanted layer contributed to the PCR signal enhancement with the decreasing implantation energy. SE, PCR and PL were proven to be non-destructive metrology tools for characterizing ultra-shallow junctions.

A first-principles study of dihydroazulene as a possible optical molecular switch

By applying nonequilibrium Green's function formalism combined with first-principles density functional theory, we investigate the electronic transport properties of the dihydroazulene optical molecular switch. Three kinds of adsorption sites including the hollow, bridge and top sites are studied. The two forms of this molecule, namely the open form and the closed form, can reversibly switch from each other upon photoexcitation. Their transmission spectra are remarkably distinctive. Theoretical results show that the current of the closed form is always significantly larger than that of the open form for all three adsorption sites, which promises this system as possibly one of the good candidates for optical switches due to its unique advantage, and which may have some potential applications in the future molecular circuit.

Regulation of excitation transit ons by molecular design endowing full-color-tunable emissions with unexpected high quantum yields for bioimaging application

Organic fluorophores are indispensible in chemical/biological imaging. The conjugated fluorescent molecules simultaneously possessing highly tunable emission, high quantum yield in solvents of different polarities, and large Stokes shift are quite rare. Herein, we report a new category of fluorophores based on diarylated thieno[3,4-b]thiophenes efficiently synthesized by direct C-H arylation reaction. TbT-Fluors showed full-color-tunable emissions with large Stokes shifts. Intriguingly,the fluorescence quantum yields of TbT-Fluors are barely sensitive to solvent polarities, approaching 100%. Based on photophysical and theoretical investigations, we found that the enhanced oscillator strength of the S_1-S_0 transition and increased T2-S1 energy difference can sufficiently compensate the negative effect from the decreased energy gap and increased reorganization energy in dimethyl sulfoxide(DMSO). Bioimaging applications revealed that some TbT-Fluors can penetrate the cell membrane and are superior for imaging in terms of high photochemical stability and low cytotoxicity. Furthermore, TbT-PhF exhibits specific colocalization with mitochondria in living cells.

Slow Light in One-Dimensional Coupled-Resonator Waveguide Controlling by an Electric Field

The photon transport properties in one-dimensional coupled-resonator waveguide embedded with a quantum dot molecule are investigated. The calculations reveal that one can control the photon transport by using a gate electric field. The phase shift and group velocity delay of the transmitted single photon are discussed. This research may be found applications in integrated optoelectronic devices and solid quantum devices.

Hole mobility of strained Si/(001)Si_(1-x)Ge_x

The hole mobility of strained silicon along the <110> orientation on (001) Si1?xGex is obtained by solving collision term in the Boltzmann transport equation. The analytical model is proposed that considers the effect of strain-induced splitting at valence band valleys in silicon, doping dependence and three scattering mechanisms, i.e., ionized impurity scattering, acoustic phonon scattering and non-polar optical phonon scattering. The hole occupancy at top band indicates a non-monotonic variation under biaxial tensile strain at low temperature (77 K). What's more, a non-monotonic variation of hole mobility at room temperature (300 K) is presented. Compared with the room temperature hole mobility, the low temperature hole mobility is affected greatly by ionized impurity scattering at lower impurity concentration. At the same time, the room temperature hole mobility is lower than that of electron with the same germanium content and doping concentration. If the parameters are correctly chosen, the model can also be used to calculate the hole mobility of other crystal faces with arbitrary orientation. So, it lays a useful foundation for strained silicon devices and circuits.

Particle acceleration and transport in the inner heliosphere

In the solar system, our Sun is Nature's most efficient particle accelerator. In large solar flares and fast coronal mass ejections(CMEs), protons and heavy ions can be accelerated to over ~GeV/nucleon. Large flares and fast CMEs often occur together. However there are clues that different acceleration mechanisms exist in these two processes. In solar flares, particles are accelerated at magnetic reconnection sites and stochastic acceleration likely dominates. In comparison, at CME-driven shocks,diffusive shock acceleration dominates. Besides solar flares and CMEs, which are transient events, acceleration of particles has also been observed in other places in the solar system, including the solar wind termination shock, planetary bow shocks, and shocks bounding the Corotation Interaction Regions(CIRs). Understanding how particles are accelerated in these places has been a central topic of space physics. However, because observations of energetic particles are often made at spacecraft near the Earth,propagation of energetic particles in the solar wind smears out many distinct features of the acceleration process. The propagation of a charged particle in the solar wind closely relates to the turbulent electric field and magnetic field of the solar wind through particle-wave interaction. A correct interpretation of the observations therefore requires a thorough understanding of the solar wind turbulence. Conversely, one can deduce properties of the solar wind turbulence from energetic particle observations. In this article I briefly review some of the current state of knowledge of particle acceleration and transport in the inner heliosphere and discuss a few topics which may bear the key features to further understand the problem of particle acceleration and transport.