Fundamental Reflections Research Articles

Improving the Linearity of Infrared Diffuse Reflection Spectroscopy Data for Quantitative Analysis: An Application in Quantifying Organophosphorus Contamination in Soil

Diffuse reflection data are presented for ethyl methylphosphonate in a fine Utah dirt sample as a model system for organophosphate-contaminated soil. The data revealed a chemometric artifact when the spectra were represented in Kubelka-Munk units that manifests as a linear dependence of spectral peak height on variations in the observed baseline position (i.e., the position of the observed transmission intensity where no absorption features occur in the sample spectrum). We believe that this artifact is the result of the mathematical process by which the raw data are converted into Kubelka-Munk units, and we developed a numerical strategy for compensating for the observed effect and restoring chemometric precision to the diffuse reflection data for quantitative analysis while retaining the benefits of linear calibration afforded by the Kubelka-Munk approach. We validated our Kubelka-Munk correction strategy by repeating the experiment using a simpler system--pure caffeine in potassium bromide. The numerical preprocessing includes conventional multiplicative scatter correction coupled with a baseline offset correction that facilitates the use of quantitative diffuse reflection data in the Kubelka-Munk formalism for the quantitation of contaminants in a complex soil matrix, but is also applicable to more fundamental diffuse reflection quantitative analysis experiments.

Strained Chirped Fiber Bragg Gratings Based all-fiber Variable Optical Delay Line for Optical Coherence Tomography

We present the novel all-fiber optical delay line that can be realized by exploiting the fundamental distributive reflection characteristics of a chirped fiber Bragg gratings (CFBG). With the assist of a strained CFBG and a designed fiber stretcher, the proposed delay line could perform the function (such as attainment of variable large enough optical delay without dispersion mismatch) of the conventional optical delay line within the optical fiber. While the strained CFBG produced 3.1 mm optical delay, the pair of CFBGs in the opposite direction can manage dispersion imbalance of the delay line. The use of the PZT-based fiber stretcher can enable depth scanning at a high repetition rate for real-time imaging. The performance of the delay element is demonstrated with measured experimental results. OCT system embedded with the all-fiber variable optical delay line showed the axial resolution of 100 μm and the dynamic range of 50 dB. The implemented system was used for the imaging of a biomedical sample, which proves the utility of the proposed delay element as a promising alternative of optical delay line.

Nonlinear diffraction and second-harmonic generation enhancement in silicon-opal photonic crystals

Nonlinear diffraction in three-dimensional silicon-filled photonic crystals of opals is studied. Efficient backward second-harmonic generation (SHG) is observed in the specular direction upon the fundamental radiation reflection from the (111) face of the face-centered-cubic opal lattice. Tuning the fundamental wavelength across the photonic band gap (PBG) results in the 20-times increase of the second-harmonic intensity. The SHG peak has the width of approximately 20nm and is located at the long-wavelength edge of the PBG.

Evidence of L10Type Ordered Structure at an Equiatomic Composition PtCr

Evidence of L1₀Type Ordered Structure at an Equiatomic Composition PtCr

Temperature Dependence of the Order Parameter and of Diffuse Scattering in the Hg[sub 2]Cl[sub 2] Model Ferroelastics

The fundamental and diffuse x-ray reflections from Brillouin zone-edge X points of the paraelastic phase of Hg2Cl2 crystals (whose integrated intensity is related to the order parameter and its fluctuations) were studied. Information was obtained on the temperature dependence of the order parameter and of diffuse scattering, and the critical exponents were determined. The conclusion is drawn that the ferroelastic phase transition in these crystals is close to the tricritical point.

Origin of the Superlattice Reflections in Pb(Fe2/3W1/3)O3

Two types of superlattice reflections have been observed in pressureless-sintered Pb(Fe 2/3 W 1/3 )O 3 perovskite ceramics from selected-area electron diffraction patterns (SADPs). The presence of commensurate superlattice reflections of the {1/2 1/2 1/2} type found in as-sintered samples persisted after prolonged postsintering annealing at 800°C for 300 h. These reflections, conventionally termed the F-spots, represent the existence of the nanoscale cation-ordered domains of cubic perovskite Pb 1-x (Fe 1/2 W 1/2 )O 3 . However, the satellite-type incommensurate superlattice reflections, appearing as sideband spots to the fundamental reflections and occurring only along , (110), and (100), have gradually reduced their intensities and finally disappeared on postsintering annealing at 800°C. Observations via transmission electron microscopy (TEM) suggested that the black dots revealed in bright-field (BF) images have given rise to the incommensurate superlattice sideband spots. These dots of ∼5-10 nm are in fact a different type of nanocrystalline domain whose structure (and chemical composition) differs from those of the disordered Pb(Fe 2/3 W 1/3 )O 3 matrix and the ordered nanoscale Pb 1-x (Fe 1/2 W 1/2 )O 3 domains. The nanocrystalline precipitates containing the paracrystalline phase are pyrochlore (Pb 2 (Fe,W)O 6.5 ) formed during powder preparation via the solid-state mixed-oxide route. They become dispersed in the Pb(Fe 2/3 W 1/3 )O 3 perovskite matrix grain and have also undergone phase transformation to perovskite progressively during sintering and postsintering annealing. It is suggested that the nanocrystalline pyrochlore precipitates are metastable and disappear when chemical composition within the perovskite grains becomes homogenized from solid-state diffusion on postsintering annealing.

In situ transmission electron microscopy study of the electric field-induced transformation of incommensurate modulations in a Sn-modified lead zirconate titanate ceramic

Electric field-induced transformation of incommensurate modulations in a Sn-modified lead zirconate titanate ceramic was investigated with an electric field in situ transmission electron microscopy technique. It is found that the spacing between the (1∕x){110} satellite spots and the fundamental reflections do not change with external electric field, indicating that the modulation wavelength stays constant under applied field. The intensity of these satellites starts to decrease when the field level reaches a critical value. Further increase in the field strength eventually leads to the complete disappearance of the satellite reflections. In addition, the 12{111}-type superlattice reflections showed no response to electrical stimuli.

Compositional dependence of phase separation in InGaN layers

Phase separation in InGaN layers grown by metalorganic chemical vapor deposition on GaN epilayers was investigated using transmission electron microscopy. Layer thicknesses of 220 and 660nm were deposited with InN fractions ranging from 3% to 34%. At InN contents of 3%, plan-view TEM images show a homogeneous microstructure and selected area diffraction (SAD) patterns exhibit no evidence of satellite spots. InN contents of 12% result in a speckled contrast. Satellites close to the fundamental spots belonging to the wurtzite structure are present in SAD patterns and they are indicative of composition modulations lying in the (0001) growth plane. No satellites are observed along the [0001] direction, implying that phase separation is two-dimensional in nature. Samples containing InN fractions of between 22% and 28% have microstructures exhibiting much stronger contrast variations. Satellite spots in SAD patterns are further spaced from the fundamental reflections. This trend continues on increasing InN content to 34%. In addition, cross-sectional TEM images show an absence of contrast from InGaN layers with InN contents above 12%, in the vicinity of the InGaN∕GaN interface, indicating that coherency strain inhibits phase separation. Arguments are developed to rationalize these observations.

A comparative study on microstructure of the plasma-nitrided layers on austenitic stainless steel and pure Fe

The microstructure of the plasma-nitrided layer on austenitic stainless steel and pure Fe was studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the nitrided layer on pure Fe is composed of equilibrium phases ε-Fe 2–3N and γ′-Fe 4N, which have lamellar microstructure. The superlattice reflections appear in XRD pattern and electron diffraction pattern, which correspond to the ordered γ′-Fe 4N. The nitrided layer on austenitic stainless steel is composed of a metastable supersaturated nitrogen solid solution, whose XRD pattern and electron diffraction patterns show that it has an expanded fcc structure and its lattice parameter is much larger than that of the γ-austenite, even larger than that of γ′-Fe 4N. The superlattice reflections similar to ones of γ′-Fe 4N resulting from the nitrogen atoms at octahedral holes of cubic center can be observed in its electron diffraction pattern although no superlattice reflections were detected in its XRD pattern. However, the diffracted intensity of the superlattice reflections is weaker than that of the γ′-Fe 4N formed on pure Fe. Calculation of the structure factor of the supersaturated solid solution suggests that weaker diffracted intensity of the superlattice reflections is attributed to the nitrogen atoms at octahedral holes of the edges in fcc lattice. Their fundamental electron diffraction reflections show intense diffuse scattering effect resulting from the clustered Cr–N. The results indicate that the supersaturated nitrogen solid solution is based on γ′-Fe 4N and nitrogen atoms supersaturated in γ′-Fe 4N are in form of the clustered Cr–N. A lot of slip bands are formed on the layer of austenitic steel due to the strain resulting from supersaturating nitrogen.

Commensurate-incommensurate magnetic phase transition in magnetoelectric single crystal LiNiPO(4).

Neutron scattering studies of single crystal LiNiPO4 reveal a spontaneous first-order commensurate-incommensurate magnetic phase transition. Short- and long-range incommensurate phases are intermediate between the high temperature paramagnetic and the low temperature antiferromagnetic phases. The modulated structure has a predominant antiferromagnetic component, giving rise to satellite peaks in the vicinity of the fundamental antiferromagnetic Bragg reflection, and a ferromagnetic component, giving rise to peaks at small momentum transfers around the origin at (0,+/-Q,0). The wavelength of the modulated magnetic structure varies continuously with temperature. It is argued that the incommensurate short- and long-range phases are due to spin-dimensionality crossover from a continuous to the discrete Ising state.

Electron microscopy characterization of Ba(Cd1/3Ta2/3)O3 microwave dielectrics with boron additive

The microstructure of Ba(Cd1/3Ta2/3)O3 ceramics with boron additive was investigated by high-resolution and analytical electron microscopy. Superlattice reflections were present at positions of (h ± 1/3, k ± 1/3, l ± 1/3) away from the fundamental reflections in the [110] zone diffraction pattern for the pseudocubic perovskite unit cell. Lattice images showed a well-ordered structure with hexagonal symmetry. No boron segregation and amorphous phase was observed along grain boundaries. An amorphous phase rich in boron-oxide was observed to form pockets partially penetrating along multiple grain junctions.

Structural Analysis of a Complex Oxide Eu<sub>2</sub>Mn<sub>2/3</sub>Nb<sub>4/3</sub>O<sub>7</sub> with a Pyrochlore-Related Structure

The complex oxide Eu2Mn2/3Nb4/3O7 structurally characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results of XRD structure analysis shown that the X-ray diffraction profile calculated with monoclinic C2/c model is in a good agreement with the observed X-ray diffraction patterns. In addition to fundamental reflection peaks, super lattice lines could be also assigned with C2/c symmetry. Therefore, it is derived that Eu2Mn2/3Nb4/3O7 phase has not a pyrochlore structure but has a zirconolite-type structure (pyrochlore-related structure) with a C2/c space group. Eu2Mn2/3Nb4/3O7 has two kinds of distorted MO6 octahedra and HTB layers, which deviates from the regular forms. The microstructure of Eu2Mn2/3Nb4/3O7 investigated by TEM also proved the results of XRD structural analysis. It was viewed that HRTEM image of a characteristic twin structure in Eu2Mn2/3Nb4/3O7 which a zirconolite-type structure has.

Influence of hydrogen treatment of CdTe crystals on the reflectivity spectra

The measurements of the reflection coefficient of the strongly hydrogenated CdTe crystals with various hydrogen contents have been performed in the wavelength range 190÷1400nm. Two different types of integrating spheres (the Ulbricht balls) and an automatic double-beam reflectometer have been used for optical measurements. The maxima related to the interband transitions at the centre of the Brillouin zone (E0 transitions), at Λ critical points (E1, E1+Δ1 transitions) and in the volume of the Brillouin zone (E2) have been observed. A high-intensity, wide reflectivity maximum appears at 966nm, i.e. for the photon energy (1.28eV) smaller than the energy gap. The height of this maximum depends on the hydrogen content in the CdTe crystals. The differences observed in the fundamental reflectivity spectra are coherent with the results of atomic force microscopy (AFM) measurements. The experimental results indicate considerable influence of strong hydrogenation on the process of crystallization of CdTe from the vapour.

Distribution of electronic states in amorphous Cd–As thin films on the basis of optical measurements

Transmission and fundamental reflectivity studies, completed on amorphous Cd–As thin films, allowed us to obtain parameters describing the fundamental absorption edge, i.e. the optical pseudogap E G opt, Urbach energy E U and exponential edge parameter E T. All these data, together with the results of earlier transport measurements, have been utilized in developing simple models of electronic structure (distribution of electronic states) for amorphous Cd–As thin films of various compositions.

Culture and Entrepreneurship – Remarks on Transculturality as Practice

ABSTRACTThe most recent media debate about a new ‘Turkish entrepreneurship’ in Germany triggered off the fundamental reflections on the necessarily critical conceptualisation of the relation between ‘culture’ and entrepreneurial action. The dominating concepts in the field of ‘ethnic business’, in which questions of cultural orientation in entrepreneurial action have been a central issue for some time, can serve as a starting point for this analysis. For understanding the term culture and the conceptualisation of culture in conjunction with entrepreneurial action, a few critical remarks and a shift in perspective are necessary. Contributions of economic geography inspired by the ‘cultural turn’, which shows alternative ways of thinking about the connection between culture and economy by using a new understanding of culture may be utilised here. Focusing on the group of ‘German‐Turkish entrepreneurs’ and bearing in mind the idea of ‘transculturality in practice’ this paper will conclude with an outline of a number of conceptual considerations for action‐oriented research on the relation between culture and entrepreneurial action.

TEM study of superstructure in a perovskite lead lanthanum zirconate stannate titanate ceramic

The superstructure of an antiferroelectric Pb 0.97La 0.02(Zr 0.66Sn 0.25Ti 0.09)O 3 phase, whose composition is near the morphotropic-phase boundary, was characterized. Systematic selected-area diffraction revealed that there were two kinds of superlattice reflections in the pseudocubic reciprocal lattice, i.e. 1 2 hk l superlattice reflections ( h, k, l all odd), and g± 1 7.24 a ∗ +b ∗ one-dimensional incommensurate superlattice reflections, where g denotes the vectors of fundamental or 1 2 hk l superlattice reflections. Convergent-beam electron diffraction disclosed that the average structure of the phase was rhombohedral with space group of R 3m . Based on the rhombohedral reciprocal lattice, the 1 2 hk l reflections were no longer superlattice but fundamental reflections, and the reciprocal vector of the one-dimensional incommensurate reflections was re-expressed as H=ha ∗ +kb ∗ +lc ∗ ± 1 7.24 a ∗ +b ∗ , where h, k, l are integers and (− h + k + l) = 3 n. In the light of the average structure and the reflection condition, the superspace Bravais class of the phase with one-dimensional incommensurate structure was determined to be P 11 R 3m in a (3 + 1)-dimensional space. In addition, the origins of the superlattice reflections were also examined and discussed.

Precursor state in a Ti50Pd34Fe16alloy studied by advanced transmission electron microscopy

Peculiar diffuse scattering and microstructures, which occur prior to the onset of a B2 → 4H transformation in a Ti 50 Pd 34 Fe 16 alloy, have been intensively studied by energy-filtered electron microscopy and high-resolution electron microscopy. Two types of diffuse scattering, i.e., rod-like diffuse scattering emanating from the fundamental reflection and a satellite at the tip of the rod, were observed. The rod-like diffuse scattering appeared to be due to well-known tweed microstructures, while the satellite to characteristic microdomains as discovered in a Ti 50 Ni 48 Fe 2 alloy. A dark-field image showed a trend of regular array of the microdomains along directions. This array is likely to correspond to striations observed in the tweed microstructures.

TEM investigation of the structure of deformation-induced antiphase boundary faults inNi3Al

Transmission electron microscopy (TEM) methods were used to analyze the deformation-induced antiphase boundary (APB) tubes in a ${\mathrm{Ni}}_{3}\mathrm{Al}$ single crystal. A high density of tubes is observed after room-temperature deformation showing strong contrasts in some fundamental reflections. This is not expected from a hard sphere model of the APB faults bounding the tubes since in this case the APB faults are just chemical faults (displacement vector ${R}_{C}\ensuremath{\rightarrow}=1/2〈110〉).$ The TEM analysis shows unambiguously that the APB faults contain a small additional structural displacement vector ${R}_{S}\ensuremath{\rightarrow}.$ ${R}_{S}\ensuremath{\rightarrow}$ lies in the plane of the fault and is perpendicular to ${R}_{C}\ensuremath{\rightarrow}.$

Atomic model of anti-phase boundaries in a face-centred icosahedral Zn–Mg–Dyquasicrystal

An atomic model in the physical space for an anti-phase boundary (APB) inthe ordered face-centred icosahedral Zn–Mg–Dy quasicrystal phase ispresented, based on a six-dimensional model suggested by Ishimasa andShimizu (2000 Mater. Sci. Eng. A 294–296 232, Ishimasa 2001 privatecommunication). The physical space atomic positions of the defectedstructure were used for the calculation of the corresponding exit-planewavefunction and high-resolution transmission electron microscopy images. Theanalysis of the defect by inverse Fourier transformation reveals that whensuperstructure reflection spots are used for back-transformation, then at theAPB, bright lattice fringes are found to turn into dark ones, and viceversa. When fundamental reflections are used, the APB is not visible. Thisphenomenon is the same as the corresponding experimental study recentlypublished by Heggen et al(2001a Phys. Rev. B 64 014202). Based on thisatomic model it is found that the APB perpendicular to a fivefold axis A5(APB-A5) is a non-conservative boundary, while the APB perpendicularto a pseudo-twofold axis A2P (APB-A2P) is a conservative one. Thisfact is consistent with the experimental observation (Heggen et al2002 J.Alloys Compounds 342 330) that the frequency of occurrence of APB-A5 is90% in the heat-treated samples compared with that in the deformedsamples (45%), while the frequency of occurrence of APB-A2P is 34% in thedeformed samples compared with that in the heat-treated samples.

Diffuse scattering from an Al72Ni20Co8decagonal quasicrystal on an order–disorder transformation

Non-uniform distortion induced by superstructure domains hasbeen observed during the ordering process of an order–disordertransformation in a single decagonal quasicrystal of Al72Ni20Co8.The full width at half maximum (FWHM) of the fundamentalreflections increased below the transformation temperature,Tc. Atthe same time, the integrated intensity of the fundamental reflections varied drasticallyat Tc. Asmall hysteresis was also observed in the temperature dependences of both the FWHMand the integrated intensity of the fundamental reflections. Peak broadening of thefundamental reflections is predominantly dependent on |G∥ | belowTc. Inaddition, the weak dependence of the peak broadening with |G⊥ |is extracted from the observed FWHM of the fundamental reflections.After deconvolution, the FWHM of the fundamental reflectionsappears to be a linear combination of |G∥ | and |G⊥ |.Coexistence of the non-uniform distortion and of the randomphason strain contributes to the ordering process belowTc.The diffuse scattering from atomic short-range order (SRO) was distributedaround the ideal positions of the superstructure reflections. The SROdiffuse scattering disappeared completely above Tc + 10 K.In addition, a small hysteresis of the SRO diffuse scattering was found in thetemperature cycle.