Raman scattering of light and IR absorption in carbon nanotubes

Raman light scattering and IR absorption spectra of samples containing multilayer carbon nanotubes in different stages of purification by the selective oxidation technique have been investigated. It was found that the Raman spectra of carbon nanotubes exhibit softening of the mode at 1582 cm⁻¹ corresponding to E _2g vibrations of graphite hexagons and a line at 120 cm⁻¹ due to the radial vibrations of nanotubes. In IR absorption spectra measured in the region of 0.07–0.3 eV, several sets of lines with a spacing of 15 meV (120 cm⁻¹) between lines of each group have been detected. We suggest that each group corresponds to electron transitions generating electron-hole pairs in semiconducting nanotubes and contains a phononless 00-line and its phonon replicas with spacing between them equal to the “breathing” mode energy of 120 cm⁻¹. Measurements of electric conductivity at a frequency of 9300 MHz indicate that, in addition to semiconducting nanotubes, the samples contain nanotubes with properties of a highly disordered semimetal. Zh. éksp. Teor. Fiz. 113, 1883–1891 (May 1998)     

Temperature dependence of electric resistance and magnetoresistance of pressed nanocomposites of multilayer nanotubes with the structure of nested cones

Bulk samples of carbon multilayer nanotubes with the structure of nested cones (fishbone structure) suitable for transport measurements, were prepared by compressing under high pressure (∼25 kbar) a nanotube precursor synthesized through thermal decomposition of polyethylene catalyzed by nickel. The structure of the initial nanotube material was studied using high-resolution transmission electron microscopy. In the low-temperature range (4.2–100 K) the electric resistance of the samples changes according to the law ln R ∝ (T ₀/T)^1/3, where T ₀∼7 K. The measured magnetoresistance is quadratic in the magnetic field and linear in the reciprocal temperature. The measurements have been interpreted in terms of two-dimensional variable-range hopping conductivity. It is suggested that the space between the inside and outside walls of nanotubes acts as a two-dimensional conducting medium. Estimates suggest a high value of the density of electron states at the Fermi level of about 5×10²¹ eV⁻¹ cm⁻³. Zh. éksp. Teor. Fiz. 113, 2221–2228 (June 1998)     

Carbon-nanotube-based saturable absorbers for near infrared solid state lasers

We demonstrate the passive mode-locking of a diode-pumped Nd⁺³:YAG (central wavelength: 1.32 μm; pulse duration: 50 ps; output energy: up to 70 μJ) laser using a polymer film containing single-wall carbon nanotubes. The mode-locking regime is stable at a pump repetition rate of up to 1 kHz. We also investigate the temporal evolution of the light-induced absorption change of the polymer film containing carbon nanotubes in the spectral range of 1.3–1.5 μm by femtosecond time-resolved pump-probe measurements. The measurements reveal that light-induced transmission exhibits fast and slow components that last 280 fs and more than 10 ps, respectively. The third-order susceptibility of the polymer film containing single wall carbon nanotubes is as high as 10⁻¹¹ esu.     

Pulsed laser deposition of Zr–N codoped <Emphasis Type="Italic">p</Emphasis>-type ZnO thin films

Present p-type ZnO films tend to exhibit high resistivity and low carrier concentration, and they revert to their natural n-type state within days after deposition. One approach to grow higher quality p-type ZnO is by codoping the ZnO during growth. This article describes recent results from the growth and characterization of Zr–N codoped p-type ZnO thin films by pulsed laser deposition (PLD) on (0001) sapphire substrates. For this work, both N-doped and Zr–N codoped p-type ZnO films were grown for comparison purposes at substrate temperatures ranging between 400 to 700 °C and N₂O background pressures between 10⁻⁵ to 10⁻² Torr. The carrier type and conduction were found to be very sensitive to substrate temperature and N₂O deposition pressure. P-type conduction was observed for films grown at pressures between 10⁻³ to 10⁻² Torr. The Zr–N codoped ZnO films grown at 550 °C in 1×10⁻³ Torr of N₂O show p-type conduction behavior with a very low resistivity of 0.89 Ω-cm, a carrier concentration of 5.0×10¹⁸ cm⁻³, and a Hall mobility of 1.4 cm² V⁻¹ s⁻¹. The structure, morphology and optical properties were also evaluated for both N-doped and Zr–N codoped ZnO films.     

Metallic/semiconducting ratio of carbon nanotubes in a bundle prepared using CVD technique

We present an investigation of the nature of single-walled carbon nanotubes (SWCNTs) in a bundle by resonant Raman spectroscopy. The calculation has been done for the three peak positions in radial breathing mode (RBM) spectra obtained by using a laser excitation wavelength (γ) of 633 nm from He-Ne laser on SWNT bundle sample prepared by chemical vapor deposition (CVD) technique using iron catalyst at 800°C. The detailed analysis in the present study is focused on peak positions 162 cm⁻¹, 186 cm⁻¹, and 216 cm⁻¹. The firs step of the analysis is to construct a list of possible (n, m) pairs from the diameters calculated from the RBM peak positions. The parameters of SWNTs studied gives in-depth understanding of many symmetry, resonance and characteristic properties of SWNT bundles. Our results indicate that the contribution of metallic SWNTs in the bundle is small at RBM peak positions 162 cm⁻¹, 186 cm⁻¹ and in agreement with pervious results at peak position 216 cm⁻¹.     

One-pot fabrication and enhanced thermoelectric properties of poly(3,4-ethylenedioxythiophene)-Bi<Subscript>2</Subscript>S<Subscript>3</Subscript> nanocomposites

Bi₂S₃ nanotubes and de-doped poly(3,4-ethylenedioxythiophene) (PEDOT) composite nanopowders were synchronously synthesized by a one-pot self-assembly method. The powders were characterized by X-ray powder diffraction, infrared spectroscopy, and transmission electron microscopy, respectively. Thermoelectric properties of the Bi₂S₃–PEDOT composite nanopowders with different Bi₂S₃ contents after being cold pressed into pellets were measured at room temperature. The sample with 36.1 wt% Bi₂S₃ has a highest power factor of 2.3 μWm⁻¹K⁻², which is higher than that of both pure PEDOT (0.445 μWm⁻¹K⁻²) and Bi₂S₃ (1.94 μWm⁻¹K⁻²).     

Theoretical analysis of impurity distributions in crystalline silicon

Calculations of the total energy of oxygen and carbon impurities in silicon at T=0 K are presented. The equilibrium position of point defects is determined for low (10⁻³–10⁻² at. %) concentrations. Fiz. Tverd. Tela (St. Petersburg) 39, 2001–2002 (November 1997)     

Controllable one-step synthesis of magnetite/carbon nanotubes composite and its electrochemical properties

Magnetite nanocrystals are deposited on carbon nanotubes by a reflux method in diethylene glycol. The morphological characterization proves that magnetite nanocrystals are decorated on the external surfaces of carbon nanotubes. The crystal size of magnetite nanocrystals can be readily tuned by adjusting the content of sodium acetate, but the content of sodium acetate has little effect on the amount of magnetite. The magnetite/carbon nanotubes composites exhibit an initial capacity as high as 840 mAh g⁻¹ and an excellent cycling performance for lithium storage. The reversible capacity, as high as 390 mAh g⁻¹, can be maintained after 75 charge/discharge cycles. The research has potential implications for the application of magnetite/carbon nanotubes composites as anode materials of lithium ion batteries.     

Four-wave mixing spectroscopy of aqueous suspensions of single-wall carbon nanotubes in the ranges of 0.1–10 and 100–250 cm<Superscript>−1</Superscript>

Distinctive optical properties of single-wall carbon nanotubes (SWNT) are highly sensitive to variations in the environment. Here, we have studied SWNT in aqueous suspensions at a low (less than 0.1 μg ml⁻¹) concentration by four-wave mixing (FWM) spectroscopy in the spectral bands of 0.1 to 10 cm⁻¹ (≈300 GHz) and 100 to 250 cm⁻¹ (3 to 7.5 THz). We directly investigated the hydration layers around SWNT. A comparison of the FWM spectra of an SWNT aqueous suspension and Milli-Q water shows a considerable increase in the intensity of low-frequency Raman modes, which are attributed to the rotational transitions of H₂O₂ and H₂O molecules. We explain the observed phenomenon by the hydrogen peroxide production and formation of a low-density depletion layer at the water-nanotube interface. We have observed several SWNT radial breathing modes ω _RBM =118.5, 164.7, and 233.5 cm⁻¹ in an SWNT aqueous suspension and estimated the corresponding SWNT diameters as ≈2.0, 1.5, and 1 nm.     

Multiwalled carbon nanotubes effect on the bioavailability of artemisinin and its cytotoxity to cancerous cells

Artemisinin regarded as one of the most promising anticancer drugs can bind to DNA with a binding constant of 1.04 × 10⁴ M⁻¹. The electrochemical experiments indicated that for longer incubation time periods, the reduction peak current of artemisinin on carbon nanotube modified electrode increases. Therefore, the uptake of drug molecules from a solution into CNTs will be achieved automatically by adsorption of 88.7% of artemisinin onto carbon nanotubes surface without alteration in drug properties. Hence, capability of carbon nanotubes to have synergistic effect on the bioavailability of artemisinin was investigated. Experimental tests on K562 cancer cell lines growth by MTT assay proved that multi-walled carbon nanotubes can enhance the cytotoxity of artemisinin to the targeted cancer cells with unprecedented accuracy and efficiency. The IC₅₀ values were 65 and 35 μM for artemisinin and artemisinin loaded on multi-walled carbon nanotubes, respectively; demonstrating that artemisinin loaded on multi-walled carbon nanotubes is more effective in inhibition of cancer cell lines growth.     

Nuclear Spin-Lattice Relaxation of 82BrFe

The field dependence of the nuclear spin-lattice relaxation (SLR) of cold implanted ⁸²Br (T ≤ 25 mK) in α-Fe single crystals was investigated with nuclear magnetic resonance of oriented nuclei (NMR/ON) at low temperatures as experimental technique. The SLR at the lattice sites with the hyperfine fields found by earlier NMR/ON experiments was measured as a function of the applied external magnetic field B _ext parallel to the three principle axes [100], [110] and [111] of the iron single crystal. The data were evaluated with the full relaxation formalism in the single impurity limit and for comparison also with the often employed model of a single exponential function with an effective relaxation time T ₁′. With a phenomenological model the high field values of the relaxation rates r _{∞, [100]′} = 6.6(2) · 10⁻¹⁵ T²sK⁻¹, r _{∞, [110]} = 5.4(2) · 10⁻¹⁵ T²sK⁻¹ and r _{∞, [111]} = 5.2(1) · 10⁻¹⁵ T²sK⁻¹ were obtained.     

Fluorescent Method for the Determination of Sulfide Anion with ZnS:Mn Quantum Dots

Water-soluble Mn²⁺-doped ZnS quantum dots (QDs) were prepared using mercaptoacetic acid as the stabilizer. The optical properties and structure features were characterized by X-Ray, absorption spectrum, IR spectrum and fluorescence spectrum. In pH 7.8 Tris-HCl buffer, the QDs emitted strong fluorescence peaked at 590 nm with excitation wavelength at 300 nm. The presence of sulfide anion resulted in the quenching of fluorescence and the intensity decrease was proportional to the S²⁻ concentration. The linear range was from 2.5 × 10⁻⁶ to 3.8 × 10⁻⁵ mol L⁻¹ with detection limit as 1.5 × 10⁻⁷ mol L⁻¹. Most anions such as F⁻, Cl⁻, Br⁻, I⁻, CH₃CO₂ ⁻, ClO₄ ⁻, CO₃ ²⁻, NO₂ ⁻, NO₃ ⁻, S₂O₃ ²⁻, SO₃ ²⁻ and SO₄ ²⁻ did not interfere with the determination. Thus a highly selective assay was proposed and applied to the determination of S²⁻ in discharged water with the recovery of ca. 103%.     

The nonlinear optical property and photoinduced anisotropy of?a?novel azobenzene-containing fluorinated polyimide

A novel azobenzene-containing fluorinated polyimide was synthesized. The nonlinear optical property and photoinduced birefringence of a polyimide thin film were investigated. Large third-order nonlinear refraction (n ₂=−4.49×10⁻¹¹ cm²/W) was observed in the polyimide thin film by carrying out Z-scan measurement. The polyimide thin film exhibited larger nonlinear refraction than that of a mono-azo dye doped PMMA thin film (n ₂=−1.63×10⁻¹² cm²/W). The photoinduced birefringence of the polyimide thin film (▵ n∼10⁻²) under different pump intensities was investigated; it was much larger than that of the mono-azo dye doped PMMA thin film (▵ n∼10⁻³). Moreover, the time constants for birefringence growth and relaxation processes were determined.     

Properties of Hg implanted Hg1? x Cd x Te infrared detectors

Experimental performance parameters of Hg implanted Hg_1−x Cd _x Te photovoltaic detectors are analyzed. At 77K, for 8–14 μm band, a comparison is made between performances and theoretical ultimate diffusion limits in low frequency direct detection. Experimental features are well-explained by a model based on the Auger band-to-band process for carrier recombination. Peak detectivities exceeding 10¹¹ cm Hz^1/2W⁻¹, external quantum efficiencies as high as 90%, and zero-bias resistance-area products better than 1 Ω·cm² have been achieved in devices with 12 μm cutoff wavelengths. In the 3–5 μm band performances are far from the diffusion limit. Notwithstanding, at 77K zero-bias resistance-area products are better than 10⁴Ω·cm² and detectivities of the order of 10¹² cm Hz^1/2W⁻¹ were observed at 5 μm. Predominant generation-recombination contribution are present at room temperature in 1–1.3 μm photodiodes whose detectivities, primarily limited by the Johnson noise, at 1.3 μm are higher than 10¹¹ cm Hz^1/2W⁻¹ at 300 K. The high frequency response of the photodiodes is also discussed. Response times as low as 0.5 ns are reached despite some limitations arising from the implanted layer sheet resistance. Work supported by CNR-CISE contract No. 73.01435.     

Synthesis and electrical characterisation of the perovskite niobate-titanates,Sr1−x/2Ti1−xNbxO3−δ

The synthesis and electrical characterisation over a range of oxygen partial pressures (10⁻²⁰ to 1 atm) are reported for the cubic perovskite niobate-titanates Sr_1−x/2Ti_1−xNb_xO_3−δ, which are proposed as potential anode materials for solid oxide fuel cells. Single phase samples were observed for 0≤x≤0.4, and phase purity was retained on annealing at both high and low oxygen partial pressures. Good electrical conductivity was observed on reduction in low oxygen partial pressures, with a maximum for the sample with 25% Nb (x=0.25), σ=5.6 Scm⁻¹ at 930°C (P (O₂)=10⁻¹⁸ atm). For dense samples the higher the Nb content the more resistant the reduced sample was to reoxidation as the oxygen partial pressure was increased. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

A Highly Sensitive and Selective Fluorescent Chemodosimeter for Hg<Superscript>2+</Superscript> in Neutral Aqueous Solution

A fluorescent assay of Hg²⁺ in neutral aqueous solution was developed using N-[p-(dimethylamino)benzamido]-N′-phenylthiourea (1). 1’s fluorogenic chemodosimetric behaviors towards various metal ions were studied and a high sensitivity as well as selectivity was achieved for Hg²⁺. It was because of a strongly fluorescent 1,3,4-oxadiazoles which was produced by the Hg²⁺ promoted desulfurization reaction. The spectra of ESI mass and IR provided evidences for this reaction. According to fluorescence titration, a good linear relationship ranging from 1.0 × 10⁻⁷ to 2.0 × 10⁻⁵ mol l⁻¹ was obtained with the limit of detection as 3.1 × 10⁻⁸ mol l⁻¹. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

High vacuum ionization chamber with high spatial resolution for monitoring synchrotron radiation beams

The possibility of using an ionization chamber with a cutting collectorin vacuum (10⁻⁴–10⁻⁵ Pa) for online monitoring of the position of a synchrotron radiation (SR) beam is studied experimentally The possibility of measuring the vertical position of the SR beam with a precision of up to several micrometers is demonstrated in the high vacuum conditions of an open channel in the VEPP-4M storage ring (in the absence of a beryllium window). Two such ionization chambers operating synchronously and situated one after another can serve as a basis for the SR beam stabilization system in neighboring channels.     

Absolute cross sections of electron attachment to molecular clusters. Part II: Formation of (H2O) N? , (N2O) N? , and (N2) N?

Absolute cross sections σ⁻(E, N) of electron attachment to clusters (H₂O) _N , (N₂O) _N , and (N₂) _N for varying electron energy E and cluster size N are measured by using crossed electron and cluster beams in a vacuum. Continua of σ⁻(E) are found that correlate well with the functions of electron impact excitation of molecules’ internal degrees of freedom. The electron is attached through its solvation in a cluster. In the formation of (H₂O) _N ⁻ , (N₂O) _N ⁻ , and (N₂) _N ⁻ , the curves σ⁻(N) have a well-defined threshold because of a rise in the electron thermalization and solvation probability with N. For (H₂O)₉₀₀, (N₂O)₃₅₀, and (N₂)₂₆₀ clusters at E = 0.2 eV, the energy losses by the slow electron in the cluster are estimated as 3.0 × 10⁷, 2.7 × 10⁷, and 6.0 × 10⁵ eV/m, respectively. It is found that the growth of σ⁻ with N is the fastest for (H₂O) _N and (N₂) _N clusters at E → 0 as a result of polarization capture of the s-electron. Specifically, at E = 0.1 eV and N = 260, σ⁻ = 3.0 × 10⁻¹³ cm² for H₂O clusters, 8.0 × 10⁻¹⁴ cm² for N₂O clusters, and 1.4 × 10⁻¹⁵ cm² for N₂ clusters; at E = 11 eV, σ⁻ = 9.0 × 10⁻¹⁶ cm² for (H₂O)₂₀₀ clusters, 2.4 × 10⁻¹⁴ cm² for (N₂O)₃₅₀ clusters, and 5.0 × 10⁻¹⁷ cm² for (N₂)₂₆₀ clusters; finally, at E = 30 eV, σ⁻ = 3.6 × 10⁻¹⁷ cm² for (N₂O)₁₀ clusters and 3.0 × 10⁻¹⁷ cm² for (N₂)₁₂₅ clusters. Original Russian Text ? A.A. Vostrikov, D.Yu. Dubov, 2006, published in Zhurnal Tekhnicheskoĭ Fiziki, 2006, Vol. 76, No. 12, pp. 1–15.     

Investigation of thin film all-solid-state lithium ion battery materials

All-solid-state thin film batteries are feasible by employing Al as anode and LiPON as electrolyte which are subsequently deposited by sputtering. The lithium ion conductivity of ∼ 10⁻⁶ S/cm for the thin film LiPON is in agreement with data reported for bulk material. The high voltage cathode Li₂CoMn₃O₈ could be prepared by forming the compound by the combustion method andsubsequent e-beam evaporation of this material with the addition of 20 wt.-% LiNO₃ at an oxygen partial pressure of 10⁻⁵ mbar. The thin film cells could be operated between 3 and 5 V vs. Al, LiAl. The chemical diffusion coefficient was found to be in the range from 10⁻¹³ to 10⁻¹² cm²/s at room temperature by employing the GIT-technique for the composition x of Li_2-xCoMn₃O₈ in the range from 0.1 to 1.6. Impedance studies of the complete battery system revealed a charge transfer resistance of 290 Θ, a double layer capacity of ∼ 45–70 μF for an electrode area of 6.7 cm² and a rate determining chemical diffusion coefficient in the range from 10⁻¹² to 10⁻¹¹ cm²/s. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15–21, 2002.     

Thermomechanical and conductivity studies of doped niobium titanates as possible current collector material in the SOFC anode

In the reducing atmosphere of the SOFC anode at operating temperatures of 800 °C and above Nb₂TiO₇ is reduced to Nb_1.33Ti_0.67O₄. This material displays very high electronic conductivity of >100 Scm⁻¹, suitable for use in such applications as a current collector. It has a low thermal expansion coefficient of 3 × 10⁻⁶ K⁻¹, however, which may cause problems due to mismatch with other SOFC components, e.g. YSZ. Doping with Fe₂O₃ successfully increased the thermal expansion to a maximum of 6 × 10⁻⁶ K⁻¹. A conductivity of 140 Scm⁻¹ at 900 °C in dry 5% H₂/Ar, with an activation energy of 0.18 eV, was achieved for the Nb_1.344Ti_0.642Fe_0.014O₄, making it suitable for the use as a current collector. Conductivity runs in wet 5%H₂/Ar showed lower conductivities of 15–18 Scm⁻¹ and lower activation energies of 0.08 − 0.09 eV. Single cell tests of Nb_1.33Ti_0.67O₄ showed power outputs of 5.5 − 7.2 mW·cm⁻² at 850 °C, lower than for Ni with 150 − 200 mW·cm⁻² at 850 °C, however, this material displayed much better stability at high temperatures than Ni. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002.