Quantitative studies of copper plasma using laser induced breakdown spectroscopy

In the present work, we present the spatial evolution of the copper plasma produced by the fundamental harmonic (1064 nm) and second harmonic (532 nm) of a Q-switched Nd:YAG laser. The experimentally observed line profiles of neutral copper have been used to extract the electron temperature using the Boltzmann plot method, whereas, the electron number density has been determined from the Stark broadening. Besides we have studied the variation of electron temperature and electron number density as a function of laser energy at atmospheric pressure. The Cu I lines at 333.78, 406.26, 465.11 and 515.32 nm are used for the determination of electron temperature. The relative uncertainty in the determination of electron temperature is ≈10%. The electron temperature calculated for the fundamental harmonic (1064 nm) of Nd:YAG laser is 10500–15600 K, and that for the second harmonic (532 nm) of Nd:YAG laser is 11500–14700 K at a Q Switch delay of 40 μs. The electron temperature has also been calculated as a function of laser energy from the target surface for both modes of the laser. We have also studied the spatial behavior of the electron number density in the plume. The electron number densities close to the target surface (0.05 mm), in the case of fundamental harmonic (1064 nm) of Nd:YAG laser having pulse energy 135 mJ and second harmonic (532 nm) of Nd:YAG laser with pulse energy 80 mJ are 2.50×10¹⁶ and 2.60×10¹⁶ cm⁻³, respectively.     

Electron penetration depth in amorphous AlN exploiting the luminescence of AlN:Tm/AlN:Ho bilayers

The penetration depth of electron in amorphous aluminum nitride (AlN) is determined in terms of energy loss per unit length using electron beam in a cathodoluminescence (CL) apparatus. Thin films bilayers of holmium doped aluminum nitride (AlN:Ho) and thulium doped aluminum nitride (AlN:Tm) are deposited on silicon substrates by rf magnetron sputtering method at liquid nitrogen temperatures. The bilayers structure consisted of a 37.8 nm thick AlN:Tm film on the top of a 15.3 nm thick AlN:Ho film. Electron beam of different energies are allowed to penetrate the AlN:Tm/AlN:Ho bilayers film. The spectroscopic properties of AlN:Ho and AlN:Tm, the thickness of the film and the energies of electron beam are used to calculate the penetration depth of electron in amorphous AlN. Electron beam of 2.5 keV energy was able to pass through the 37.8 nm thick AlN:Tm film. The electron penetration depth for AlN is found to be 661.4 MeV/cm.     

Stark broadening measurements of some N(II) and N(III) lines

The Stark widths of seventeen N(II) and ten N(III) spectral lines, emitted from a wall-stabilized arc plasma with electron densities in the range 0.9-2.9 × 10¹⁷ cm^-3, were measured. The arc was run with a 1:1N₂:He mixture, and the electron densities were determined from the Stark widths of He(I) 5876 and 6678 A. The Stark widths of the N lines were found to scale approximately linearly with electron density.     

Large-scale synthesis of SnO2 nanobelts

Tin dioxide (SnO₂) nanobelts have been successfully synthesized in bulk quantity by a simple and low-cost process based on the thermal evaporation of tin powders at 800 °C. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations reveal that the nanobelts are uniform, with lengths from several-hundred micrometers to a few millimeters, widths of 60 to 250 nm and thicknesses of 10 to 30 nm. X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and selected-area electron diffraction analysis (SAED) indicate that the nanobelts are tetragonal rutile structure of SnO₂. The SnO₂ nanobelts grow via a vapor–solid (VS) process. Received: 3 June 2002 / Accepted: 10 June 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-551/559-1434, E-mail: gwmeng@mail.issp.ac.cn     

Li掺杂8-羟基喹啉铝的密度泛函理论研究

采用密度泛函理论研究了Li原子掺杂8-羟基喹啉铝(Alq₃)分子的几何构型、 前线分子轨道及电子转移特性. 研究结果表明, Li原子掺杂Alq₃后, Li原子与Alq₃的O, N原子键合, 形成电子转移复合物. Li原子将部分电子转移到Alq₃的吡啶环上, 在Alq₃的带隙内形成施主能级, 这种n型掺杂结构有效地提高了电子的传输效率; 但过多的Li原子的掺杂会使Alq₃分解, 从而减弱其电子传输能力. 为使Alq₃的电子传输能力达到最高, Li原子的掺杂应保持在2:1左右的比例.     

Direct observation of radical intermediates during electron transfer between DNA and a ternary copper complex

The photoinduced electron transfer (PET) reaction within a ternary copper complex [Cu(phen)(Htrp)]⁺ (Htrp: l-tryptophanato; phen: 1,10-phenanthroline) (1) and in presence of DNA has been studied in homogeneous buffer medium and in reverse micelles. An intramolecular electron transfer occurs within the photoexcited complex (1) from tryptophan to phen. The copper complex can displace ethidium bromide from DNA backbone and on photoexcitation can oxidize DNA in a deoxygenated environment due to intermolecular electron transfer, although the intramolecular electron transfer is thermodynamically favorable. A prominent magnetic field effect (MFE) has been found even in homogeneous aqueous medium for the triplet born radicals both in case of intra and intermolecular electron transfer reactions. In case of intramolecular electron transfer the observation of MFE is similar to that of linked donor-acceptor system. However the observation of MFE for the intermolecular electron transfer between non-covalently bound complex-DNA systems is rather rare. Some non-covalent weak interaction, e.g. hydrophobic interaction between the phen ligand and DNA base pairs and electrostatic force of attraction between [Cu(phen)(Htrp)]⁺ complex and DNA may lead to partial intercalation of the copper complex within DNA that is responsible for such a rare observation.     

Dielectric mismatch and shallow donor impurities in GaN/HfO2 quantum wells

In this work we investigate electron–impurity binding energy in GaN/HfO₂ quantum wells. The calculation considers simultaneously all energy contributions caused by the dielectric mismatch: (i) image self-energy (i.e., interaction between electron and its image charge), (ii) the direct Coulomb interaction between the electron–impurity and (iii) the interactions among electron and impurity image charges. The theoretical model account for the solution of the time-dependent Schrödinger equation and the results shows how the magnitude of the electron–impurity binding energy depends on the position of impurity in the well-barrier system. The role of the large dielectric constant in the barrier region is exposed with the comparison of the results for GaN/HfO₂ with those of a more typical GaN/AlN system, for two different confinement regimes: narrow and wide quantum wells.     

Photo-Induced Electron Transfer in P3DDT, P3OT, M3EH-PPV Conjugated Polymers Blended with Maleic Anhydride in THF Solution Under UV Flash Photolysis Studied by Means of CW TR ESR

Free-radical signals of positive polarons in conjugated polymer chains and maleic anhydride (MA) anion radicals were registered in poly(3-octylthiophene) P3OT:MA and (poly[2,5-dimethoxy-1,4-phenylene-1,2-ethenylene-2-methoxy-5-(2-ethylhexyloxy)?C(1,4-phenylene-1,2-ethenylene)]) M3EH-PPV:MA blends in tetrahydrofuran (THF) solutions under ultraviolet flash photolysis (308?nm) by continuous-wave time-resolved electron spin resonance. Their emissive chemically induced dynamic electron polarization (CIDEP) originated mainly from excited triplet states (triplet mechanism of CIDEP) and partly by from the radical pair mechanism due to the singlet?Ctriplet mixing states. The observed M3EH-PPV polaron spectrum (g ₀?=?2.0029) supports the supposition that the previously registered CIDEP spectra in P3DDT:MA blends (g ₀?=?2.0021) can be attributed to the polaron signals instead of the possible solvate electron signal one.     

Enhanced brightness of organic light-emitting diodes based on Mg:Ag cathode using alkali metal chlorides as an electron injection layer

Different thicknesses of cesium chloride (CsCl) and various alkali metal chlorides were inserted into organic light-emitting diodes (OLEDs) as electron injection layers (EILs). The basic structure of OLED is indium tin oxide (ITO)/N,N′-diphenyl-N,N′-bis(1-napthyl-phenyl)-1.1′-biphenyl-4.4′-diamine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq₃)/Mg:Ag/Ag. The electroluminescent (EL) performance curves show that both the brightness and efficiency of the OLEDs can be obviously enhanced by using a thin alkali metal chloride layer as an EIL. The electron injection barrier height between the Alq₃ layer and Mg:Ag cathode is reduced by inserting a thin alkali metal chloride as an EIL, which results in enhanced electron injection and electron current. Therefore, a better balance of hole and electron currents at the emissive interface is achieved and consequently the brightness and efficiency of OLEDs are improved.     

Time-related luminescence spectroscopic investigation of electron trapping and recombination in infrared stimulated luminescence

Infrared stimulated luminescence (ISL) occurred in CaS:Eu,Sm due to formation of luminescent centres Eu²⁺ and electron trapping centres Sm³⁺. The electron trapping centres Sm³⁺ became occupied (forming Sm²⁺ by trapping excited electrons) in photoluminescence (PL) excitation (PLX) process causing simultaneous ionization of luminescent centres Eu²⁺ (leaving Eu³⁺ by losing an electron or capturing a hole). In this paper, the electron trapping in PLX and the recombination in ISL were examined by the time-related PL and ISL spectra of CaS:Eu,Sm. The spectroscopic evidence confirmed that the ISL in CaS:Eu,Sm was produced due to recombination of de-trapped electrons and previously ionized luminescent centres (Eu³⁺). It was believed that the electron trapping occurred concurrently as occurrence of the PL of Eu²⁺ in PLX process. However, the recombination of de-trapped electrons and previously ionized luminescent centres took about 10 s or even more to occur after infrared irradiation. PACS 78.55.-m; 78.45.+h     

热电子、双离子成分对离子漂移迴旋不稳定性的影响

分析了热电子、温(热)离子成分对离子漂移迴旋不稳定性的影响。给出了临界稳定热电子成分值α与温(热)离子成分值、离子温度比和离子抗磁漂移速度的关系;讨论了热电子、温(热),冷离子成分对不稳定性各谐频分支的影响;分析了热电子成分稳定作用的物理机制。     

电子迴旋激射不稳定性

本文分析了下述情况下的电子迴旋波的激射不稳定性:当相对性的单能高能电子斜向注入具有背景等离子体的磁场区域内,并且在电子等离子体频率与电子迴旋频率可以比拟时,考虑了背景等离子体密度远大于单能的高能电子的密度,以及与前者相反的两种情况。当单能的高能电子具有弱相对论性效应时,在电子迴旋频率的基频和二次谐波附近,分别有ο模和χ模的不稳定性存在。文中计算了这两种模的增长率,并作了讨论。 关键词：     

Investigation of ageing characteristics and identification of surface chemical changes on SrGa2S4:Ce display phosphor under electron beam bombardment

Cathodoluminescent ageing characteristics of SrGa₂S₄:Ce³⁺ under prolonged electron beam bombardment was studied and the data are presented. The cathodoluminescent intensity with an increasing Coulomb loading was observed to degrade under different primary electron beam voltages. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to monitor the surface chemical changes during electron beam bombardment and after the degradation process. Auger peak to peak heights monitored during the ageing process suggest a loss in S and C and an initial increase in oxygen concentration on the surface. XPS results indicate the formation of a SrO overlayer due to electron stimulated surface chemical reactions (ESSCRs).     

Characterization of boron carbon nitride film modified by excimer laser annealing

Boron carbon nitride (BCN) shows promise as a field emitter material because of its mechanical hardness, chemical inertness, and low electron affinity. This study investigated the modification of a BCN film with an amorphous area using KrF excimer laser (wavelength: 248 nm, photon energy: 5.0 eV) annealing without substrate heating. This achieved significant variation in characteristics, such as an increase in bandgap energy and decrease in electron affinity. Laser annealing reduced electron affinity from 0.7 to 0.3 eV. The results indicate that the modification of the BCN film by KrF excimer laser annealing achieves characteristics similar to hexagonal BN (h-BN) film without losing the desirable properties of the BCN film, such as physical stability.     

Magnetically confined discharge CO laser

Under the condition of magnetic confinement, the paper analyzes the following discharge processes from CO gas: (1) the variation of electron energy distribution; (2) the impact excitation rates of electron for the vibrational CO molecules; and (3) the vibrational-state population of CO molecule and small-signal gain. Our results show that, by adding magnetic field, the electron density increases greatly in the energy region corresponding to the maximum electron cross sections of CO molecule, while the electron impact on excitation rates also increases. At the same time, the vibrational-state population of CO molecule and the laser small-signal gain of every vibrational level are also higher than that without magnetic field.     

Dynamic nuclear polarisation via the integrated solid effect I: theory

In the hyperpolarisation method known as dynamic nuclear polarisation (DNP), a small amount of unpaired electron spins is added to the sample containing the nuclear spins and the polarisation of these unpaired electron spins is transferred to the nuclear spins by means of a microwave field. Traditional DNP uses weak continuous wave (CW) microwave fields, so perturbation methods can be used to calculate the polarisation transfer. A much faster transfer of the electron spin polarisation is obtained with the integrated solid effect (ISE) which uses strong pulsed microwave fields. As in nuclear orientation via electron spin locking, the polarisation transfer is coherent, similar to the coherence transfer between nuclear spins. This paper presents a theoretical approach to calculate this polarisation transfer.

ISE is successfully used for a fast polarisation transfer from short-lived photo-excited triplet states to the surrounding nuclear spins in molecular crystals. These triplet states are strongly aligned in the photo-excitation process and do not require the low temperatures and strong magnetic fields needed to polarise the electron spins in traditional DNP. In the following paper, the theory is applied to the system naphthalene-h₈ doped with pentacene-d₁₄ which provides the photo-excited triplet states, and compared with experimental results.     

Electron g-factor in quantum wire in the presence of Rashba effect and magnetic field

In this paper, we study the electron effective Landé g-factor in the InAs quantum wire under an applied magnetic field and the Rashba effect. For this goal, we first present an analytic solution to one-particle Schrödinger equation in the presence of both magnetic field and spin-orbit interaction (SOI). Then, using the obtained energy levels, we study the electron effective Landé g-factor. It is found that: (i) The effective Landé g-factor decreases when magnetic field increases. (ii) By increasing the confinement length l₀, the electron g-factor decreases. (iii) By increasing the strength of SOI, the electron g-factor increases.     

FABRICATION AND CHARACTERIZATION OF THE SIZE-CONTROLLED AND PATTERNED nc-Si DOTS

A new method of phase-modulated excimer laser crystallization is adopted to fabricate the patterned nanometer-sized crystalline silicon (nc-Si) dots within the sandwiched structure (a-SiN_x:H/a-Si:H/a-SiN_x:H) films. The results of transmission electron microscopy, electron diffraction and Raman scattering show the ultra-thin and single-layer nc-Si films were patterned in the lateral direction and the size of crystallites is controlled by the thickness of as-deposited a-Si film in the longitudinal direction. The effects of the laser energy density on the structures of the samples and the crystallization mechanism are discussed.     

High-Field Phenomena of Qubits

Electron and nuclear spins are very promising candidates to serve as quantum bits (qubits) for proposed quantum computers, as the spin degrees of freedom are relatively isolated from their surroundings and can be coherently manipulated, e.g., through pulsed electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR). For solid-state spin systems, impurities in crystals based on carbon and silicon in various forms have been suggested as qubits, and very long relaxation rates have been observed in such systems. We have investigated a variety of these systems at high magnetic fields in our multifrequency pulsed EPR/ENDOR (electron nuclear double resonance) spectrometer. A high magnetic field leads to large electron spin polarizations at helium temperatures, giving rise to various phenomena that are of interest with respect to quantum computing. For example, it allows the initialization of both the electron spin as well as hyperfine-coupled nuclear spins in a well-defined state by combining millimeter and radio-frequency radiation. It can increase the T ₂ relaxation times by eliminating decoherence due to dipolar interaction and lead to new mechanisms for the coherent electrical readout of electron spins. We will show some examples of these and other effects in Si:P, SiC:N and nitrogen-related centers in diamond.