共查询到20条相似文献,搜索用时 156 毫秒
1.
Subramaniam C Sreeprasad TS Pradeep T Pavan Kumar GV Narayana C Yajima T Sugawara Y Tanaka H Ogawa T Chakrabarti J 《Physical review letters》2007,99(16):167404
We show that single-walled carbon nanotube (SWNT) bundles emit visible fluorescence in the presence of noble metal nanoparticles and nanorods in the solid state. Conductivity measurements with metallic nanotubes, isolated from pristine SWNTs, show that they become semiconducting in the presence of the metal nanoparticles. Nanoparticle binding increases the defects in the nanotube structures which is evident in the Raman spectra. The metal-semiconductor transition removes the nonradiative decay channels of the excited states enabling visible fluorescence. Nanotube structures are imaged using this emission with resolution below the classical limits. 相似文献
2.
Tae Kyu Shim Myoung Hee Lee Doseok Kim Hyun Sung Kim Kyung Byung Yoon 《Journal of fluorescence》2012,22(6):1475-1482
Fluorescence characteristics of hemicyanine dye molecules isolated from neighboring molecules and strongly restricted inside nanosized pores of zeolite (silicalite-1) crystal were investigated. For samples in which the molecules were sufficiently far away from the others, the fluorescence decay lifetime of the molecules was about 2.2?ns. As the intermolecular distance was reduced, the steady-state fluorescence peak shifted toward the longer wavelength and the fluorescence efficiency decreased markedly. The fluorescence decay lifetime also decreased to 0.8?ns for a sample with the smallest intermolecular distance of 2.1?nm. These results were explained in terms of a dipole-dipole interaction between pairs of dye molecules. From the relation between the intermolecular distances and the fluorescence decay lifetimes of the molecules, the radius of energy transfer of hemicyanine donor-acceptor pair in zeolite matrix was determined to be 2.2?nm, in fair agreement with the calculated F?rster radius between dye molecules of the same species. 相似文献
3.
Wang F Sfeir MY Huang L Huang XM Wu Y Kim J Hone J O'Brien S Brus LE Heinz TF 《Physical review letters》2006,96(16):167401
The electronic properties of single-walled carbon nanotubes (SWNTs) are altered by intertube coupling whenever bundles are formed. These effects are examined experimentally by applying Rayleigh scattering spectroscopy to probe the optical transitions of given individual SWNTs in their isolated and bundled forms. The transition energies of SWNTs are observed to undergo redshifts of tens of meVs upon bundling with other SWNTs. These intertube coupling effects can be understood as arising from the mutual dielectric screening of SWNTs in a bundle. 相似文献
4.
Masao Ichida Satoshi Sakoda Yumie Kiyohara Singo Saito Yasumitsu Miyata Hiromichi Kataura Ken-ichi Mizuno Hiroaki Ando 《Journal of luminescence》2008,128(5-6):952-955
We have studied 1D exciton relaxation dynamics in semiconducting single-walled carbon nanotubes (SWNTs) by femtosecond pump–probe experiments. The time evolution of change in transmittance ΔT/T induced by photo-excitation varies depending on the tube diameter. The decay time decreases with a decrease in the tube diameter. Pressure measurements have been conducted to explore the relaxation mechanism. The deformation potential estimated from the pressure dependence of photoluminescence spectra increases with decreasing tube diameter. This means that the exciton–phonon interaction becomes stronger in the smaller diameter tubes. The diameter dependences of decay time and deformation potential suggest that the exciton–phonon interaction plays an important role in exciton nonradiative relaxation process in semiconducting SWNTs. 相似文献
5.
Infrared fluorescence from vibrational levels of matrix isolated CN- ions has been studied in the temperature range of 300 K to 600 K. At 300 K the variation in the fluorescence lifetime from host to host is compatible with a multiphonon decay mechanism, but the measured temperature dependence does not agree with thermally induced multiphonon decay. 相似文献
6.
Excited-state lifetimes of isolated single-walled semiconducting carbon nanotubes (SWNTs) have been measured for the first time; these excited states, observed over the 400- to 1800-nm spectral domain, possess lifetimes that range from several ps to more than 100 ps. Sub-ps to ps decay components are assigned to relaxation in SWNT bundles. Interrogation of the samples with different SWNT mean diameters further confirms the dependence of the excited-state lifetime on roll-up vector. The ratio of fast and slow decaying component contributions in the first van Hove band can be viewed as a measure of the bundle content. PACS 78.67.Ch; 78.47.+p; 61.46.+w; 73.22.-f 相似文献
7.
Selection of isolated and individual single-walled carbon nanotube from a film and its usage in nanodevices
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Individual and isolated single-walled carbon nanotubes (SWNTs) are important for fabricating relevant nanode- vices and studying the properties of the SWNT devices. In this work, we demonstrate that individual and isolated SWNT can be selected and obtained from a film containing a huge number of SWNTs. By using both the polymethyl-methacrylate (PMMA) as a negative resist and the electron beam lithography, the selected SWNT can be fixed on a substrate, while the other SWNTs in the film can lift off. The selected SWNT can be used to fabricate nanodevice and a gas sensor of oxygen is demonstrated in this work. 相似文献
8.
A. V. Okotrub L. G. Bulusheva A. V. Gusel’nikov 《Journal of Experimental and Theoretical Physics》2004,99(6):1244-1252
A carbonaceous material containing single-wall carbon nanotubes (SWNTs) has been synthesized by arc-discharge evaporation of graphite with a catalytic additive of nickel and cobalt powders. The synthesized SWNTs were purified from an amorphous carbon component (soot) and the catalyst particles by boiling in nitric acid. A comparison of the X-ray fluorescence spectra measured before and after this treatment showed that acid etching significantly decreased the content of soot in the material. The material enriched with SWNTs is characterized by a reduced threshold for the appearance of the field emission current, which is explained by a decrease in the screening effect of soot. The current-voltage characteristics of SWNTs exhibit a hysteresis, which is suggested to be due to the adsorption of molecules and radicals on the surface and at the ends of carbon nanotubes. 相似文献
9.
D. A. Kolosov M. I. Deryabin I. A. Dobrovol’skaya I. V. Gadzhialieva 《Journal of Applied Spectroscopy》2011,78(4):601-604
We studied the annihilation kinetics for triplet excitations in isolated pairs of organic molecules and their delayed fluorescence
decay using a new mathematical model for the process. According to this model, the intensity of delayed annihilation fluorescence
(DAF) for isolated pairs is directly proportional to the number of pairs in which both molecules are found in the excited
triplet state. We show that the decrease in such pairs and the decay of their delayed annihilation fluorescence occur according
to an exponential law in the absence of random scatter in the deactivation rate constants for the triplet excitations. The
results of an experimental study of the DAF decay kinetics for 1,12-benzoperylene in n-hexane at 77 K, where triplet–triplet
annihilation occurs in isolated pairs, confirm the validity of the theoretical conclusions. 相似文献
10.
Kinetics study of ultrafast electron transfer from sensitized dyes to silver halide microcrystals 总被引:1,自引:0,他引:1
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Spectral sensitization micromechanism of cyanine dyes J-aggregate adsorbed
on the tabular and cubic AgBr microcrystals with different dye
concentrations
is studied by using picosecond time-resolved fluorescence spectroscopy, and
the dependences of electron transfer and spectral efficiency sensitization
on different conditions are analysed in detail. With the steady
spectroscopy, the wavelengths of absorption and fluorescence of J-aggregate
adsorbed on AgBr microcrystals are found to shift to red relative to dye
monomer. The spectrum of fluorescence has a red shift relative to the
absorption peak. With the time-resolved fluorescence spectroscopy, the
fluorescence decay curves of cyanine dyes J-aggregate adsorbed on the
tabular and cubic AgBr grains are found to be fitted well by a
double-exponential decay function. The fitting curves consist of a fast and
a slow component. Because of the large amplitude of the fast component, this
fast decay should be attributable mainly to the electron transfer from
J-aggregate of dye to a conduction band of AgBr. 相似文献
11.
T. I. Syrejshchikova Yu. A. Gryzunov N. V. Smolina A. A. Komar M. G. Uzbekov E. J. Misionzhnik N. M. Maksimova 《Laser Physics》2010,20(5):1074-1078
The efficiency of the therapy of psychiatric diseases is estimated using the fluorescence measurements of the conformational
changes of human serum albumin in the course of medical treatment. The fluorescence decay curves of the CAPIDAN probe (N-carboxyphenylimide
of the dimethylaminonaphthalic acid) in the blood serum are measured. The probe is specifically bound to the albumin drug
binding sites and exhibits fluorescence as a reporter ligand. A variation in the conformation of the albumin molecule substantially
affects the CAPIDAN fluorescence decay curve on the subnanosecond time scale. A subnanosecond pulsed laser or a Pico-Quant
LED excitation source and a fast photon detector with a time resolution of about 50 ps are used for the kinetic measurements.
The blood sera of ten patients suffering from depression and treated at the Institute of Psychiatry were preliminary clinically
tested. Blood for analysis was taken from each patient prior to the treatment and on the third week of treatment. For ten
patients, the analysis of the fluorescence decay curves of the probe in the blood serum using the three-exponential fitting
shows that the difference between the amplitudes of the decay function corresponding to the long-lived (9 ns) fluorescence
of the probe prior to and after the therapeutic procedure reliably differs from zero at a significance level of 1% (p < 0.01). 相似文献
12.
用巨正则蒙特卡罗分子模拟方法研究了单壁纳米碳管中的微孔即单壁纳米碳管基本孔-内管腔和管间孔对单壁纳米碳管储氢性能的影响.与低温下氮气吸附实验结果的比较发现单壁纳米碳管的内管腔是吸附的主要位置.分析单壁纳米碳管内管腔中吸附势的叠加和利用效率,发现管径为2nm左右时单壁纳米碳管内管腔的储氢容量最高.当单壁纳米碳管阵列的管间距增加时,单壁纳米碳管的管间孔也会成为有效的氢吸附位.
关键词:
Monte Carlo方法
单壁纳米碳管
储氢
微孔 相似文献
13.
Individual single-walled carbon nanotubes (SWNTs) in aqueous suspension are visualized directly by fluorescence video microscopy. The fluorescent tagging is simple, biocompatible, and does not modify the SWNTs. The dynamics of individual SWNTs in water are observed and quantified for the first time. We measure the confined rotational diffusion coefficient and find it in reasonable agreement with predictions based on confined diffusion of dilute Brownian rods. We determine the critical concentration at which SWNTs in suspensions start interacting. By analyzing the fluctuating shape of SWNTs in the 3 to 5 microm range, we determine that their persistence length ranges between 32 and 174 microm, in agreement with theoretical estimates; thus, commonly available SWNTs in liquids can be considered as rigid Brownian rods in the absence of imposed external fields or self-attractive forces. 相似文献
14.
J. Gao M. A. Loi 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,75(2):121-126
Single-walled carbon nanotubes (SWNTs) are successfully dispersed in two conjugated polymer poly(9,9-dioctylfluorenyl-2,7-diyl)
(PFO) and poly[2-methoxy-5- (2’-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEHPPV) solutions. Steady-state and time-resolved
photoluminescence spectroscopy in the near-infrared and visible spectral regions are used to study the interaction of the
dispersed carbon nanotube and the wrapped polymer in the
nano-hybrids. The SWNTs infrared emission is the signatures of the separation of single semiconducting tubes, the lifetime
of the photoluminescence of these tubes is bi-exponential with the first component varying from 6 ps (in MEHPPV wrapped SWNTs)
to 14 ps (in PFO wrapped SWNTs), while the second component of the decay for all samples is in the range of 30-40 ps, revealing
the intrinsic lifetime of the SWNTs. The study of the photoluminescence of the nano-hybrids in the visible spectral range
shows, in the case of the PFO, a relatively strong quenching, the photoluminescence lifetime for the hybrid is more than 100 ps
shorter than the one of the pristine polyfluorene solution. For the MEHPPV-SWNT hybrid an opposite behavior is revealed with
the photoluminescence lifetime surprisingly longer than the polymer solution. The possible mechanism for the interaction of
the two conjugated polymers and the SWNTs is discussed in terms of their electronic band structure. 相似文献
15.
16.
Xiaoying Yang Zhuohan Zhang Zunfeng Liu Yanfeng Ma Rongcun Yang Yongsheng Chen 《Journal of nanoparticle research》2008,10(5):815-822
Multi-functionalized single walled carbon nanotubes (SWNTs) were prepared and applied as tumor cell targeting biological transporters.
A positive charge was introduced on SWNTs to get high loading efficiency of fluorescein (FAM) labeled short double strands
DNA (20 base pairs). The SWNTs were encapsulated with the folic acid modified phospholipids for active targeting into tumor
cell. The tumor cell-targeting properties of these multi-functionalized SWNTs were investigated by active targeting into mouse
ovarian surface epithelial cells. The experimental results show that these multi-functionalized SWNTs have good tumor cell
targeting property. 相似文献
17.
Jorio A Pimenta MA Souza Filho AG Samsonidze GG Swan AK Unlü MS Goldberg BB Saito R Dresselhaus G Dresselhaus MS 《Physical review letters》2003,90(10):107403
Resonance Raman studies on single wall carbon nanotubes (SWNTs) show that resonance with cross polarized light, i.e., with the E(mu,mu+/-1) van Hove singularities in the joint density of states needs to be taken into account when analyzing the Raman and optical absorption spectra from isolated SWNTs. This study is performed by analyzing the polarization, laser energy, and diameter dependence of two Raman features, the tangential modes (G band) and a second-order mode (G' band), at the isolated SWNT level. 相似文献
18.
The motion and equilibrium distribution of water molecules adsorbed inside neutral and negatively charged singlewalled carbon nanotubes (SWNTs) have been studied using molecular dynamics simulations (MDSs) at room temperature based on CHARMM (Chemistry at HARvard Molecular Mechanics) potential parameters. We find that water molecules have a conspicuous electropism phenomenon and regular tubule patterns inside and outside the charged tube wall. The analyses of the motion behaviour of water molecules in the radial and axial directions show that by charging the SWNT, the adsorption efficiency is greatly enhanced, and the electric field produced by the charged SWNTs prevents water molecules from flowing out of the nanotube. However, water molecules can travel through the neutral SWNT in a fluctuating manner. This indicates that by electrically charging and uncharging the SWNTs, one can control the adsorption and transport behaviour of polar molecules in SWNTs for using as a stable storage medium or long transport channels. The transport velocity can be tailored by changing the charge on the SWNTs, which may have a further application as modulatable transport channels. 相似文献
19.
本文开展了基于单光子调制频谱测量量子点荧光寿命动力学特性的研究.在脉冲激光激发下,对探测到的量子点单光子荧光信号进行频谱分析以获得荧光调制频谱,研究发现特征频谱信号幅值与荧光寿命之间存在确定的非线性对应关系.这种单光子调制频谱方法能有效消除背景噪声和单光子探测器暗计数的影响,用于分析量子点荧光寿命动力学特性时在准确度以及时间分辨率方面都较目前普遍采用的荧光衰减曲线寿命拟合方法呈现出明显优势:当涨落误差为5%时,寿命测量准确度提高了一个数量级;当涨落误差和偏离误差均为5%时,对动力学测量效率以及时间分辨率提高了四倍以上.因此单光子调制频谱可以作为获取量子点在短时间尺度内激发态动力学信息的一种有效技术手段. 相似文献
20.
Fagan JA Simpson JR Landi BJ Richter LJ Mandelbaum I Bajpai V Ho DL Raffaelle R Walker AR Bauer BJ Hobbie EK 《Physical review letters》2007,98(14):147402
We report measurements of the full intrinsic optical anisotropy of isolated single-wall carbon nanotubes (SWNTs). By combining absorption spectroscopy with transmission ellipsometry and polarization-dependent resonant Raman scattering, we obtain the real and imaginary parts of the SWNT permittivity from aligned semiconducting SWNTs dispersed in stretched polymer films. Our results are in agreement with theoretical predictions, highlighting the limited polarizability of excitons in a quasi-1D system. 相似文献