Natural Bond Orbitals(NBO),Natural Population Analysis,Mulliken Analysis of Atomic Charges of 2-[(2,3-Dimethylphenyl)Amino]Benzoic Acid

The spectroscopic properties of the FT-IR and FT-Raman spectra of the 2-[(2,3-dimethylphenyl)amino]benzoic acid (DMPABA) compound have been recorded in the region 4 000～400 cm-1. The molecular structure, vibrational wavenumbers were calculated using DFT (B3LYP) method with 6-31G(d,p) and 6-311++G(d,p) basis sets. The Geometrical structure, vibrational frequencies, corresponding vibrational assignments of 2-[(2,3-dimethylphenyl)amino]benzoic acid (DMPABA) have been investigated experimentally and theoretically using Gaussian03 software package. The detailed Molecular orbital calculation such as Natural Bond Orbitals (NBO), Natural Population Analysis (NPA) and Mulliken analysis of atomic charges is also calculated.     

Natural Bond Orbital(NBO),Natural Population Analysis and Mulliken Analysis of Atomic Charges of 4-Amino-3-Phenylbutanoic Acid

The Molecular Structure of 4-Amino-3-phenylbutanoic acid conformers have been studied in the gas phase. Natural Bond Orbital Analysis (NBO) and Mulliken analysis of atomic charges of 4-Amino-3-phenylbutanoic acid have been performed by DFT level of theory using B3LYP/6-311++G(d,p) basis set. The atomic charges, electronic exchange interaction and charge delocalization of the molecule have been performed by Natural Bond Orbital(NBO) analysis and Natural Population Analysis(NPA) have been constructed at B3LYP/6-311++G(d,p) level.     

Growth behavior of high k LaAlO3 films on Si by metalorganic chemical vapor deposition for alternative gate dielectric application

LaAlO₃ (LAO) is explored in this work to replace SiO₂ as the gate dielectric material in metal–oxide–semiconductor field effect transistor. Amorphous LAO gate dielectric films were deposited on Si (0 0 1) substrates by low pressure metalorganic chemical vapor deposition using La(dpm)₃ and Al(acac)₃ sources. The effect of processing parameters such as deposition temperature and precursor vapor flux on growth, structure, morphology, and composition of LAO films has been investigated by various analytical methods deeply. The film growth mechanism on Si is reaction limiting instead of mass transport control. The reaction is thermally activated with activation energy of 37 kJ/mol. In the initial growth stage, Al element is deficient due to higher nucleation barrier on Si. The LAO films show a smooth surface and good thermal stability and remain amorphous up to a high temperature of 850 °C. The electrical properties of amorphous LAO ultrathin films on Si have also been evaluated, indicating LAO is suitable for high k gate dielectric applications.     

Structure Stability of LaAlO3 Thin Films on Si Substrates

A series of amorphous and single-crystalline LaAlO3 （LAO） thin films are fabricated by laser molecular-beam epitaxy technique on Si substrates under various conditions of deposition. The structure stability of the LAO films annealed in high temperature and various ambients is studied by x-ray diffraction as well as high-resolution transmission electron microscopy. The results show that the epitaxial LAO films have very good stability, and the structures of amorphous LAO thin films depend strongly on the conditions of deposition and post-annealing. The results reveal that the formation of LAO composition during the deposition is very important for the structure stability of LAO thin films.     

Surface characterisation and interface studies of high-k materials by XPS and TOF-SIMS

High-k dielectric LaAlO₃ (LAO) films on Si(100) were studied by TOF-SIMS and XPS to look for diffusion processes during deposition and additional thermal treatment and for the formation and composition of possible interfacial layers. The measurements reveal the existence of SiO₂ at the LAO/Si interface. Thermal treatment strengthens this effect indicating a segregation of Si. However, thin LAO layers show no interfacial SiO₂ but the formation of a La-Al-Si-O compound. In addition, Pt diffusion from the top coating into the LAO layers occurs. Within the LAO layer C is the most abundant contamination (10²¹ at/cm³). Its relatively high concentration could influence electric characteristics. XPS shows that CO₃²⁻ is intrinsic to the LAO layer and is due to the adsorption of CO₂ of the residual gas in the deposition chamber.     

Interfacial structure and electrical properties of LaAlO3 gate dielectric films on Si by metalorganic chemical vapor deposition

LaAlO₃ (LAO) gate dielectric films were deposited on Si substrates by low-pressure metalorganic chemical vapor deposition. The interfacial structure and composition distribution were investigated by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), secondary-ion mass spectroscopy (SIMS), and Auger-electron spectroscopy (AES). HRTEM confirms that there exists an interfacial layer between LAO and Si in most samples. AES, SIMS, and XPS analyses indicate that the interfacial layer is compositionally graded La–Al silicate and the Al element is severely deficient close to the Si surface. Electrical properties of LAO films were evaluated. No evident difference in electrical properties between samples with and without native SiO₂ layers was observed. The electrical properties are discussed in terms of LAO growth mechanisms, in relation to the interfacial structure. PACS 73.40.Qv; 81.15.Gh; 77.55.+f; 68.35.-p     

LaAlO_3/SrTiO_3界面增强光伏效应

探索LaAlO_3/SrTiO_3(LAO/STO)界面产生的新奇物理特性对理解关联电子系统中多自由度耦合和设计功能材料器件具有重要的价值.本文通过脉冲激光沉积方法在SrTiO_3基底上制备了LAO/STO薄膜,研究了正面照射LAO/STO膜面和侧面照射LAO/STO界面时的光伏效应,探讨了LAO/STO界面对光伏效应的影响.研究结果表明,在同样光照能量下侧面照射LAO/STO界面产生的光电压远高于正面照射LAO/STO膜面产生的光电压,说明LAO/STO界面对光伏效应有明显的增强作用.通过偏压调控可以进一步增强照射LAO/STO界面产生的光电压,当偏压为60 V时, LAO/STO样品的位置探测灵敏度达到了36.8 mV/mm.这些研究结果为设计场调控位置敏感探测器等新型光电子器件提供了新的思路.     

Electric gating of the multichannel conduction in LaAlO_3/SrTiO_3 superlattices

The electric gating on the transport properties of two-dimensional electron gas(2DEG) at the interface of LaAlO₃/SrTiO₃(LAO/STO) heterostructure has attracted great research interest due to its potential application in fieldeffect devices. Most of previous works of gate effect were focused on the LAO/STO heterostructure containing only one conductive interface. Here, we systematically investigated the gate effect on high-quality LAO/STO superlattices(SLs)fabricated on the TiO₂-terminated(001) STO substrates. In addition to the good metallicity of all SLs, we found that there are two types of charge carriers, the majority carriers and the minority carriers, coexisting in the SLs. The sheet resistance of the SLs with a fixed thickness of the LAO layer increases monotonically as the thickness of the STO layer increases. This is derived from the dependence of the minority carrier density on the thickness of STO. Unlike the LAO/STO heterostructure in which minority and majority carriers are simultaneously modulated by the gate effect, the minority carriers in the SLs can be tuned more significantly by the electric gating while the density of majority carriers is almost invariable. Thus, we consider that the minority carriers may mainly exist in the first interface near the STO substrate that is more sensitive to the back-gate voltage, and the majority carriers exist in the post-deposited STO layers. The SL structure provides the space separation for the multichannel conduction in the 2 DEG, which opens an avenue for the design of field-effect devices based on LAO/STO heterostructure.     

Characteristics of SrBi2Ta2O9 ferroelectric films on Si using LaAlO3 thin film as an insulator

Metal–ferroelectric–insulator–semiconductor structures using LaAlO₃ (LAO) layers as an insulating barrier have been investigated. LAO films were deposited on n-Si substrates by low-pressure metalorganic chemical vapor deposition (MOCVD). SrBi₂Ta₂O₉ (SBT) films were prepared as ferroelectric layers at a low processing temperature of 650 °C by a metalorganic decomposition method. The MOCVD-derived LAO buffer layer shows an amorphous structure, relatively high dielectric constant, and good electrical properties. Au/SBT/LAO/n-Si exhibits a larger counterclockwise C–V memory window of 3.7 V and a lower leakage-current density of 2.5×10^-8 A/cm² at an applied voltage of 10 V. It has been confirmed that the hysteresis loop is caused by ferroelectricity. The Auger electron spectrometry depth profile indicates that the introduction of the LAO buffer layer prevents the interfacial diffusion between SBT and the Si substrate effectively and improves the interface quality. PACS 77.84.Dy; 81.15.Fg     

n-ZnO/LaAlO3/p-Si heterojunction for visible-blind UV detection

A visible-blind UV photodetector (PD) using a double heterojunction of n-ZnO/LaAlO3 (LAO)/p-Si was demonstrated. Inserted LAO layers exhibit electrical insulating properties and serve as blocking layers for photoexcited electrons from p-Si to n-ZnO, leading to an enhanced rectification ratio and a visible-blind UV detectivity of the n-ZnO/LAO/p-Si PDs due to the high potential barrier between LAO and p-Si layers (~2.0 eV). These results support the use of n-ZnO/LAO/p-Si PDs in the visible-blind UV PDs in a visible-light environment.     

Sr掺杂对La_(1-x)Sr_xMnO_3/LaAlO_3/SrTiO_3界面电子结构的影响

采用基于密度泛函理论的第一性原理计算方法,系统地研究了La_(1-x)Sr_xMnO_3层中Sr的掺杂方式和掺杂量对4La_(1-x)Sr_xMnO_3/3LaAlO_3/4SrTiO_3(LSMO/LAO/STO)异质结构原子和电子结构的影响.结果表明:对于相同的Sr掺杂量,掺杂方式的差异对体系电子结构的影响微弱,不会导致体系发生金属-绝缘体转变;掺杂量的不同对体系电子结构有着显著的影响,当Sr的掺杂量较少时,LAO/STO界面处存在着准二维电子气,当Sr的掺杂量高于1/3时,LAO/STO界面处准二维电子气消失.我们相信,Sr的引入以及通过Sr掺杂量的改变可以对LSMO覆盖层极化进行调控,这也是导致体系LAO/STO界面处金属-绝缘体转变的可能原因,进一步为极化灾变机制导致的界面处电子重构提供了证据.     

The value of single-shot black-blood MR imaging for mapping of the coronary arteries: a comparison of four different orientations during breath-holding and free breathing

The value of ECG-gated single-shot black-blood MR imaging for rapid visualization of the origin and course of the coronary arteries was investigated. The study population included 28 patients with known or suspected cardiac disease. ECG-gated single-shot black-blood MR acquisitions were acquired in the transverse, coronal, sagittal and LAO orientations, during free breathing and breath-holding. The origin of the left coronary artery was most frequently visualized in the coronal and LAO orientations and the origin of the right coronary artery was most frequently visualized in the LAO orientation. Overall, no significant difference was found for the visualization of the coronary artery segments and the overall image quality among acquisitions during breath-holding and free breathing. ECG-gated single-shot black-blood MR imaging (HASTE) appears to be a time-efficient and robust method for mapping of the entire coronary artery tree, without the need for breath-holding. The LAO orientation provides the most consistent visualization of the origins and major coronary artery segments.     

Gate‐controlled metal–insulator transition in the LaAlO3/SrTiO3 system with sub‐critical LaAlO3 thickness

We studied the electrical conduction in the LaAlO₃/SrTiO₃ (LAO/STO) interface electron system with a sub‐critical LAO layer thickness of ～3.5 unit cells (uc). It was found that the true dividing point between metallic and insulating behaviour without gating lies near the LAO thickness of 3.5 uc. Our marginally metallic 3.5 uc sample showed a sharp transition to insulating state at temperatures which strongly depended on the applied negative back‐gate voltage. The superior gate‐controllability of the sample was attributed to its sheet carrier density which was an order of magnitude lower than those of conducting LAO/STO samples with 4 uc or more of LAO layers. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interfacial structures of LaAlO<Subscript>3</Subscript> films on Si(100) substrates

This paper investigates the interfacial characteristics of LaAlO₃ (LAO) and LaAlO_xN_y (LAON) films deposited directly on silicon substrates by the pulsed-laser deposition technique. High-resolution transmission electron microscopy (HRTEM) pictures indicate that an interfacial reaction between LAO and Si often exists. The interfacial layer thickness of LAO films deposited in a nitrogen ambient atmosphere is smaller than that of LAO films deposited in an oxygen ambient atmosphere. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were used to study the composition of the interfacial layer. The shift of the La 3d photoelectron peak to a higher binding energy compared to LaAlO₃, the shift of the Al 2p peak to a higher binding energy compared to LaAlO₃, the shift of the Si 2p peak to a lower binding energy compared to SiO₂ and the intermediate location of the O 1s peak compared to LaAlO₃ and SiO₂ indicate the existence of a La–Al–Si–O bonding structure, which was also proved by the AES depth profile of LAO films. It can be concluded that the interfacial layer is not simply SiO₂ but a compound of La–Al–Si–O. PACS 77.84.Bw; 77.84.-s; 77.55.+f     

In situ investigation of conducting interface formation in LaAlO3/SrTiO3 heterostructure

The high-mobility conducting interface (CI) between LaAlO₃ (LAO) and SrTiO₃ (STO) has revealed many fascinating phenomena, including exotic magnetism and superconductivity. But, the formation mechanism of the CI has not been conclusively explained. Here, using in situ angle-resolved photoemission spectroscopy, we elucidated the mechanisms for the CI formation. In as-grown samples, we observed a built-in potential (V_bi) proportional to the polar LAO thickness starting from the first unit cell (UC) with CI formation appearing above 3 UCs. However, we found that the V_bi is removed by synchrotron ultraviolet (UV)-irradiation; The built-in potential is recovered by oxygen gas (O₂(g))-exposure. Furthermore, after UV-irradiation, the CI appears even below 3UC of LAO. Our results demonstrate not only the V_bi-driven CI formation in as-grown LAO/STO, but also a new route to control of the interface state by UV lithographic patterning or other surface modification.     

AFM nanooxidation process - Technology perspective for mesoscopic structures

We study the technology of local anodic oxidation (LAO) by the AFM tip applied to semiconductor heterostructures with two-dimensional electron gas. The aim is to design mesoscopic rings with persistent current and one subband occupied. For this purpose the need is to oxidize narrow lines that represent energy barriers high enough. Using the electrostatic model, we explain the electric field distribution in the system tip-sample just before LAO starts. We study the influence of the conductivity of the cap layer on LAO and explain the origin of the saddle-like profile lines, observed in the experiment. Using Monte Carlo simulation we show that the carrier redistribution in the system with LAO energy barriers effectively lowers the barrier height. In the experimental part we have grown InGaP/AlGaAs/GaAs heterostructures by organometalic vapor phase epitaxy with an active layer only 31 nm below the surface. We have prepared oxide lines on the heterostructures by LAO and characterized them by the temperature-dependent transport measurement.     

A study on the microwave responses of YBCO and TBCCO thin films by coplanar resonator technique

YBa₂Cu₃O₇(YBCO) thin films have been prepared by thermal coevaporation on LaAlO₃(LAO) substrates, and Tl₂Ba₂CaCu₂O₈(TBCCO) thin films are synthesized by magnetron sputtering method on LAO substrates. The transition temperature T_c is 90\,K for YBCO/LAO and 104\,K for TBCCO/LAO. Microwave responses of the films are studied systematically by coplanar resonator technique. Energy gaps of the films obtained are {\it\Delta}₀=1.04k_BT_c for YBCO films and ${\it\Delta}_0=0.84k_BT_c for TBCCO films by analysing the temperature dependence of resonant frequencies of coplanar resonator. Penetration depth at 0\,K \lambda ₀=198nm for YBCO films and \lambda₀ =200nm for TBCCO films could also be obtained by using the weak coupling theory and two fluid theory. Results of penetration depth and energy gap confirm the weak coupling properties of the films. In addition, microwave surface resistances R_s of YBCO/LAO and TBCCO/LAO are also investigated by analysing the quality factor and insert loss of the coplanar resonator. Surface resistance of TBCCO/LAO is less than that of YBCO/LAO, so that TBCCO/LAO films may have more potential applications.     

Characteristics of the crystalline and luminescence properties of a-plane GaN films grown on γ-LiAlO_2(302) substrates

A-plane GaN films are deposited on(302) γ-LiAlO 2 substrates by metalorganic chemical vapor deposition(MOCVD) . The X-ray diffraction(XRD) results indicate that the in-plane orientation relationship between GaN and LAO substrates is [010] LAO [0001] GaN and [203] LAO [1100] GaN with 0.03% and 2.85% lattice mismatch,respectively. Raman scattering results indicate that the strain in the films decreases along with the increase in the thickness of the films. In addition to the band edge emission at 3.42 eV,defects-related luminescence at 3.35 eV is observed in the photoluminescence(PL) spectra. The cathodoluminescence(CL) spectra indicate that the 3.35-eV emission is related to the V pits.     

Analysis of Natural Phytoplankton Populations by Pattern Recognition of Two-Dimensional Fluorescence Spectra

Two-dimensional Fourier-transform-based pattern recognition is used to characterize natural populations of marine algae by their two-dimensional, in vivo fluorescence spectra. The two dimensional fluorescence spectrum, termed an excitation-emission matrix (EEM), is acquired using a portable, multichannel fluorescence spectrophotometer (PMFS). Natural populations in the Gulf of Mexico south of Louisiana and the coastal area near Savannah, Georgia are characterized by their measurement of in situ fluorescence. Characterization of unknown populations is achieved by comparing the unknown EEMs to a collection of standard EEMs acquired from 23 species (6 classes) of marine algae. Pattern recognition results from data collected along the Georgia coast indicating diatom populations were confirmed by microscopic examination of selected samples.     

Natural Bond Orbital (NBO),Natural Population Analysis (NPA)and Non Linear Optical Properties of (1S,2R)-2-amino-1-phenylpropan-1-ol Using DFT Method

The molecular structure of (1S,2R)-2-amino-1-phenylpropan-1-ol (abbreviated as 2APPO) conformers have been studied in the gas phase. Natural Bond Orbital Analysis and Non Linear Optical properties of 2APPO have been performed by DFT level of theory using B3LYP/6-311++G(d,p) basis set. The atomic charges, electronic exchange interaction and charge delocalization of the molecule have been performed by Natural Bond Orbital (NBO) analysis, Natural Population Analysis (NPA) and Non Linear Optical (NLO) properties have been constructed at B3LYP/6-311++G(d,p) level to understand the optical properties.