Surface and in-depth characterization of InGaN compounds synthesized by plasma-assisted molecular beam epitaxy

InGaN layers with multiple quantum wells are widely used as active layers in advanced optoelectronic devices. In the present work, surface properties of some InGaN layers grown on GaN/sapphire substrates by plasma-assisted molecular beam epitaxy were examined. The total indium content incorporated in the crystalline lattice of In_0.165Ga_0.835N and In_0.353Ga_0.647N layers grown with a thickness of 70-200 nm was controlled by the growth temperature, and was determined from X-ray diffraction. Auger electron spectroscopy and X-ray photoelectron spectroscopy analysis reveal relatively smaller concentration of In within the surface area than in the bulk of the InGaN layers. The Ar⁺ XPS depth profile analysis shows the thick InGaN layers to be chemically homogeneous within an analytical area. To determine the electron inelastic mean free path in the layers within the 500-2000 eV range, relative elastic-peak electron spectroscopy measurements with Ni and Au standards were performed. The measured IMFPs were considerably larger than those predicted from the TPP-2M formula. The smallest root-mean-square-deviation and the mean percentage deviation of 9.9 Å and 44.5%, respectively, were found between EPES IMFP data and those predicted for the In_0.353Ga_0.647N layer with respect to the Au standard. This work provided the detailed compositional and chemical changes of InGaN thick layers, and could be useful in solving key issues associated with the growth of high-quality layer with much higher In content.     

The characterization of patina components by X-ray diffraction and evolved gas analysis

Fourteen patinated copper specimens, seven each from the Statue of Liberty, New York Habor and from roofs at AT&T Bell Laboratories in Murray Hill, NJ, ranged in atmospheric exposure from 1 to 100 years. X-ray diffraction showed the presence of cuprite, Cu₂O, and brochantite, Cu₄(SO₄)(OH)₆, in all specimens and antlerite, Cu₃(SO₄)(OH)₄ (up to 0.7 times brochantite), atacamite, Cu₂Cl(OH)₃ (up to 1.6 times brochantite), and/or posnjakite, Cu₄(SO₄)(OH)₆ · 2H₂O (up to 5.2 times brochantite) in some. Posnjakite has been previously reported as a patina component only once during short term exposures in Eurasia. It appears to be an early corrosion product which subsequently converts to brochantite. Mass spectrographic examination of gases emitted from heated patinas provides further information on patina composition, in particular on the presence of both carbonate and oxalate in widely varying ratios.     

X-ray computed tomography for pore-related characterization and simulation of cement mortar matrix

Application of X-ray computed tomography (CT) for pore-related characterization and simulation of cement mortar was explored in this paper. Based on visualization and quantitation of the three-dimensional (3D) morphological features (i.e., appearance, size, volume, shape, and distribution) of pores, the porosity, tortuosity-connectivity, permeability, and molecular diffusion of cement mortar were computed and simulated. The simulation of the permeability and molecular diffusion of cement mortar was carried out on the basis of Darcy's law and Fick's second law, respectively. The dynamical velocity field and concentration field were respectively visualized. It was found that the X-ray CT technique provided a promising non-destructive alternative for both qualitative and quantitative analysis of the pore-related characterizations of cementitious materials. Furthermore, it was possible to use the simulations to replace lab-intensive experimental tests to quickly obtain the permeability and diffusivity parameters of cement mortar for application in engineering design.     

The status of two-dimensional Si/SiGe heterostructures

Silicon has dominated the semiconductor market consistently for decades. Other semiconductors, such as gallium arsenide, have found important niches, but the computer industry has yet to difoplace silicon as its favorite semiconductor. Recently, however, silicon-germanium alloys have been a focus of research, because they offer the option of greatly enhancing the speed and flexibility of silicon and can be integrated with existing silicon technology rather than replacing it. This article reviews some of the exciting new results in Si/SiGe heterostructures.     

X-ray microbeam transmission/fluorescence method for non-destructive characterization of tungsten coated carbon materials

Tungsten erosion, its subsequent transport and redeposition are of great interest, because a full tungsten divertor is foreseen to be used during the deuterium–tritium operational phase of ITER. The erosion of tungsten and carbon marker layers was extensively studied in the outer divertor of ASDEX Upgrade (AUG), and work is currently in progress to completely replace the existing JET CFC tiles with tungsten-coated tiles within the JET ITER-like wall project. The need for fast and non-destructive method which allows the quantitative determination of the thickness of a tungsten coating on a carbon material on large areas led us to evaluate a combined absorption/fluorescence X-ray (XRTF) technique. The method can provide fast analysis, high spatial resolution and a material selective detection of deposited layers and inclusions. It was applied on W coated fine grain graphite (FGG) tiles from AUG's divertor. It is proved that the method is able to provide information about the uniformity of the tungsten coating on a graphite or CFC substrate whilst the technique can be used to determine the thickness of the tungsten and other marker materials coatings. It represents a unique instrument for the post-mortem analysis of the coatings.     

X-ray diffraction characterization of crystallinity and phase composition in plasma-sprayed hydroxyapatite coatings

Orthopedic and dental implants consisting of a metallic substrate plasma spray coated with hydroxyapatite (HA) are currently used in reconstructive surgery. The crystalline phases present in the calcium phosphate ceramic and the degree of crystallinity must be controlled for medical applications. X-ray diffraction (XRD) is routinely employed to characterize the phase composition and percent crystallinity in both biological and sintered HA. However, application of the same XRD methods to plasma-sprayed coatings is complicated by the potential presence of several crystalline contaminant phases and an amorphous component. To overcome the complexities of characterizing plasma-sprayed HA coatings, an external standard method of XRD quantitative analysis has been developed that can be applied nondestructively. Data collection and reduction strategies allowing separation of intensity diffracted from commonly occurring phases and the amorphous fraction are presented. The method is applied to coating samples, and detection limits and sources of error are discussed. Repeability and accuracy are demonstrated with powder mixtures of known composition.     

Synthesis and characterization of novel 2,5-diphenyl-1,3,4-oxadiazole derivatives of anthracene and its application as electron transporting blue emitters in OLEDs

With a general aim to make anthracene derivatives multifunctional (n-type emitter) and also study their suitability as electron transport layers for organic light emitting diodes (OLED), we report the synthesis and characterization of five novel molecules in which the 9 and 10 positions of anthracene have been directly substituted by 2,5-diphenyl-1,3,4-oxadiazole groups. We have carried out detailed characterization of these molecules which include photophysical, electrochemical, thermal, electroluminescent and computational studies. The electron affinity is very high, around 3.7 eV, and the ionization potential is around 6.7–6.8 eV, which is relatively higher than the most commonly used electron transport electroluminescent layer Alq₃. The studies reveal that the new molecules being reported by us, in addition to the high thermal stability, are quite efficient in a two layer unoptimized nondoped device with the device structure ITO/α-NPD/10a–11b/LiF/Al and have an emission in pure blue. They also show very high efficiency as electron transport layer in device structure ITO(120 nm)/α-NPD(30 nm)/Ir(ppy)₃ doped CBP(35 nm)/BCP(6 nm)/10a(28 nm)/LiF(1 nm)/Al(150 nm). From these studies we conclude that these anthracene derivatives also have considerable potential as multifunctional layers and as electron transport layers in OLED.     

Proton-induced X-ray emission (PIXE) characterization of special glasses and multi-coated lenses

The manganese values for the same brand of glass made at the same manufacturing plant were analyzed by PIXE. Manganese impurity levels in A2 and A4 likely result from tin. Enhanced zirconium values on the air side for samples C and D and iron values for sample B were almost 5 times higher on the tin side than the air side. For Rutherford backscattering analysis, the fit to the thickness data by calculations obtained using SIMNRA, was very reasonable. The PIXE technique was proved to be adequate and powerful in characterizing specifications, as well as being a monitor of impurities introduced during the fabrication process, in special glasses and multi-coated lenses. This article based on a presentation made in the symposium “The 1999 KSEA Materials Symposium in Honor of Professor Sang Joo Kim's 70th Anniversary”, held at UCLA, Los Angeles, CA, USA, August 12≈14, 1999 under the auspices of the Korea-US American Scientists and Engineers Association.     

The characterization and interpretation of ductile fracture mechanisms in AL2024-T351 using X-ray and focused ion beam tomography

This paper describes an experimental investigation into the mechanism of ductile fracture in the aluminum alloy AL2024-T351 using a combination of synchrotron X-ray and focused ion beam tomography. Microstructural features that influence fracture at the micro- and nanoscale were characterized in virgin material in three-dimensions. The nature and volume fraction of ductile damage was then quantified as a function of distance below the fracture surfaces of tested notched and fatigue pre-cracked laboratory specimens. In both specimens the ductile fracture process initiates with the brittle fracture of large irregular intermetallic particles at low levels of plastic strain. With increasing plasticity, the resulting voids grow and combine with pre-existing porosity to increase the overall void volume fraction. Once a critical void volume fraction is attained, final failure occurs by the fracture or decohesion of dispersoids from the matrix, initiating a second population of nanoscale voids, which interlinks the larger voids. The critical void volume fraction for coalescence and the distribution of ductile damage below the fracture surface is markedly different between blunt-notched and pre-cracked specimens, with notched specimens exhibiting a significantly lower critical void volume fraction and a more extensive distribution of ductile damage below the fracture surface than is observed in pre-cracked specimens. This observation, related to the gradients in stress triaxiality and plastic strain in each specimen type, has important implications for the calibration of ductile damage mechanics models against notched-specimen data and their use to predict crack behavior in engineering structures.     

中华人民共和国机械行业标准工业X射线探伤机性能测试方法

(上接第 3期 2 9页 )2 .1 0 .2　试验程序2 .1 0 .2 .1　根据 2 .1 0 .1 .2的要求选择 R1和 R2 。2 .1 0 .2 .2　在管电压的起末点和中间点分别依次给X射线管加高压 ,同时观察并记录千伏表指示值电压 U3(电阻器 R2 上的电压 )和 X射线机控制器上千伏表指示值 U2 。2 .1 0 .3　结果处理2 .1 0 .3.1　根据下式计算管电压实测值 U1　 U1=KU3f ( 7)式中　 U1—管电压实测值 ;　 K—分压器电阻分配系数 ;　 f—有效值与峰值换算系数。纹波系数小于 1 0时 ,f =1 .0 0 ;纹波系数小于 2 5大于 1 0时 ,f =0 .95 ;纹波系数大于 2 5时 ,f…     

金属材料X射线散射比的测定

通过实验对铁、铝材料经X线射透照时产生的散射X射线进行了测量,得出了透照焦距与散射比的关系曲线,管电压和散射比、板厚与散射比的关系曲线。最后提出了在实际探伤时散射X射线的防护措施。     

分子束外延生长InGaN量子点及其结构和光学特性

采用射频等离子体辅助分子束外延 (RF-MBE)技术在蓝宝石衬底上,外延生长了发光波长位于407 nm的InGaN量子点结构,研究了InN成核层技术对其结构和光学特性的影响。材料生长过程中采用反射式高能电子衍射 (RHEED)进行了在位检测,通过原子力显微镜 (AFM),光致发光 (PL)等测试手段表征了InGaN量子点材料的结构和光学特性。结果表明,相对于直接在GaN层上自组织生长InGaN量子点,通过InN成核层技术可以获得高密度、高质量的InGaN量子点结构,量子点尺寸分布更加均匀,主要集中在35~45 nm之间;量子点的密度更高,可以达到3.2×1010/cm2;InN成核层上生长的InGaN量子点的PL发光峰强度为直接在GaN层上生长的InGaN量子点的2倍,发光峰的半高宽较窄,为10 nm     

Three-dimensional characterization of fatigue cracks in Ti-6246 using X-ray tomography and electron backscatter diffraction

In the present study, fatigue crack propagation was imaged non-destructively in three dimensions during in situ fatigue loading of Ti-6246 using X-ray microtomography on beam line ID19 at the European Synchrotron Radiation Facility. Phase contrast enabled the visualization of the two-phase microstructure and in combination with absorption contrast the crack chronology was recorded in situ during the fatigue experiment. In order to obtain the crystallographic orientation of individual grains along the crack path, a 3D electron backscatter diffraction volume was subsequently recorded. By combining both techniques it was possible to identify the role of prior β grain boundaries and the crystallographic orientation of the α lamellae on the crack path. It is shown that a near-surface crack that cuts across a prior β grain boundary is often diverted and crack bifurcation takes place. This results in local retardation of crack propagation and a first-order undulation of the crack front. In addition, the lamellar grain orientation and morphology causes a second-order crack front undulation with the tendency of large misorientations between α lamellae preferably orientated for prismatic a slip or pyramidal c + a slip deflecting the crack path.     

X-ray photoelectron spectroscopy and electrochemical characterization of a FeCrMoNiRu alloy in 0.5 M HCl solution

The spontaneous passivation behaviour of a Fe-22Cr-3Mo-5Ni alloy system containing small amounts of ruthenium in 0.5 M HCl solution has been investigated by means of immersion tests, electrochemical measurements and the XPS technique. The weight loss and electrochemical measurements show that increasing amounts of ruthenium (up to 0.3 wt%) in Fe-22Cr-3Mo-5Ni substantially improve resistance to attack by hydrochloric acid. The XPS results show that the spontaneously formed passive film on this alloy with ruthenium mainly consists of Cr and Mo oxyhydrox-ides. Molybdenum is incorporated as Mo⁴⁺ and Mo⁶⁺, while neither ruthenium nor nickel are found in the passive film. The effects of ruthenium additions on the spontaneous passivation of FeCrMoNi alloys are discussed.     

Lattice rotations of individual bulk grains: Part I: 3D X-ray characterization

Three-dimensional X-ray diffraction has been applied to characterise the plastic deformation of individual grains deeply embedded in a 99.6% pure aluminium specimen. The specimen is 4 mm thick with an average grain size of 75 μm. The average lattice rotation for each grain as well as the degree of internal orientation spread within the grain is measured in-situ during 6% elongation. The rotation paths for 95 grains with nearly random initial orientations are reported. The quality of this data set is sufficient to make distinctions between plasticity models. The rotation paths exhibit a clear dependence on the initial orientation, while the influence of grain interaction is relatively small. All grains deform plastically. Averaged over grains and reflections the rotation of the tensile axis and the FWHM of the internal spread is 2.0 and 0.8°, respectively, at 6% strain.     

Programs for X-ray analysis of polycrystals

Conclusions The developed set of programs realizes standard and original methods for processing polycrystalline spectra, namely, qualitative and quantitative phase analysis, determination of the parameters of the fine crystalline structure and macrostresses, and determination of the crystal structure by a diffractogram of a polycrystal. The use of these programs simplifies considerably and accelerates the performance of structural research. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 16–19, August, 2000.