Reflections In Electron Diffraction Patterns Research Articles

Pulsed laser deposition nickel oxide on crystalline silicon as hole selective contacts

In this work, the authors report the use of pulsed laser deposition to fabricate nickel oxide layers on silicon and assess the applicability of this structure as a hole selective contact. Films were deposited at temperatures of 300, 500, 700, and 900 °C. Results from reflective high energy electron diffraction patterns indicate increasing crystallinity with temperature up to 500 °C. However, layers deposited at 900 °C are amorphous. Nevertheless, results from atomic force microscopy, contact resistance measurements, and photoluminescence lifetime imaging indicate that films deposited at 900 °C have the best film smoothness, lowest specific contact resistivity, and highest lifetimes, and therefore, they are best suited for hole selective contact applications. Kelvin probe force microscopy and x-ray photoelectron spectroscopy were also carried out to study the effects of deposition temperature.

EDIFF: a program for automated unit-cell determination and indexing of electron diffraction data

EDIFFis a new user-friendly software suite for unit-cell determination of three-dimensional nanocrystals from randomly oriented electron diffraction patterns with unknown independent orientations. It can also be used for three-dimensional cell reconstruction from diffraction tilt series. In neither case is exact knowledge of the angular relationship between the patterns required. The unit cell can be validated and the crystal system assigned.EDIFFcan index the reflections in electron diffraction patterns. Thus,EDIFFcan be employed as a first step in reconstructing the three-dimensional atomic structure of organic and inorganic molecules and of proteins from diffraction data. An example illustrates the viability of theEDIFFapproach.

Epitaxial Growth of Si(111)/Er2O3 (111) Structure on Si(111) by Molecular Beam Epitaxy

The Si overlayers are grown by molecular beam epitaxy on atomically smooth Er2O3 (111) films prepared on Si(111) substrates. Single crystalline Si overlayers are achieved and are evident due to the spot-like reflective high energy electron diffraction (RHEED) patterns and x-ray diffraction patterns. The epitaxial relationship of the Si overlayer along the surface with respect to the orientation of Er2O3 and the Si substrate is as follows: overgrown Si(111)//Er2O3(111)//Si(111). The rough surface of Si overlayers, as identified by both RHEED patterns and atomic force microscopy images, indicates a three-dimensional growth mode. The reason for this is based on the interfacial energy argument. Further growth of Er2O3 films on this rough Si overlayer leads to the polycrystalline nature of the topmost Er2O3 layer.

The Non‐Centrosymmetric Borate Oxides, MBi2B2O7 (M: Ca, Sr).

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Strong perpendicular magnetic anisotropy of Fe–Pd nanocrystalline particles enhanced by Co addition

L 1 0 - Pd Co Fe nanoparticles were prepared by vapor deposition of the components and characterized by transmission electron microscopy and by superconducting quantum interference device magnetometry. Co addition to the Fe–Pd nanocrystals resulted in a strong perpendicular magnetic anisotropy and a reduction in the formation temperature of the ordered L10 phase. Formation of the ordered phase was studied by in situ annealing of specimens inside the transmission electron microscope. L10 phase formation started at 698K, as evidenced by the appearance of 110 superlattice reflections in electron diffraction patterns. Co additions enhanced the magnetic easy axis alignment perpendicular to the film plane. The perpendicular maximum coercivity at room temperature was 1.75kOe for L10-PdCoFe nanoparticles with an average size of 8nm, and the magnetic coercivity decreased by increasing the Co concentration in the L10 nanoparticles.

The non-centrosymmetric borate oxides, MBi 2B 2O 7 ( M=Ca, Sr)

Two novel noncentrosymmetric borates oxides, MBi 2B 2O 7 or MBi 2O(BO 3) 2 ( M Ca, Sr), have been synthesized by solid-state reactions in air at temperatures in the 600–700 °C range. Their crystal structures have been determined ab initio and refined using powder neutron diffraction data. CaBi 2B 2O 7 crystallizes in the orthorhombic Pna2 1 space group with a=8.9371(5) Å, b=5.4771(3) Å, c=12.5912(7) Å, Z=4, R wp=0.118, χ 2=2.30. SrBi 2B 2O 7 crystallizes in the hexagonal P6 3 space group with a=9.1404(4) Å, c=13.0808(6) Å, Z=6, R wp=0.115, χ 2=4.15. Large displacement parameters suggest the presence of disorder in SrBi 2B 2O 7 as also revealed by diffuse 2× a superstructure reflections in electron diffraction patterns. Both structures are built of identical (001) neutral layers of corner-sharing BO 3 triangles and MO 6 trigonal prisms forming six-membered rings in which Bi 2O groups are located. Adjacent layers are stacked in a staggered configuration and connected through weak Bi–O bonds. A moderate efficiency for second harmonic generation (SHG) has been measured for a powder sample of CaBi 2B 2O 7 ( d eff=2 d eff(KDP)).

Microstructural and electrical properties of BaTiO3 epitaxial films on SrTiO3 substructures with a LaNiO3 conductive layer as a template

BaTiO3 (BTO) films have been epitaxially grown on SrTiO3(001) and SrTiO3(111) substrates with a LaNiO3 conductive layer as a template using pulsed laser deposition. X-ray diffraction θ–2θ and ψ scanning reveal that the epitaxial relationship for these samples fabricated at 600 °C and 700 °C are BTO[001]//LNO[001]//STO[001] and BTO[111]//LNO[111]//STO[111], respectively. Ex situ reflective high energy electron diffraction patterns also clearly confirm this epitaxial relationship. The epitaxial growth can be more easily realized on LNO-inserted STO(001) substrates at a relatively wide range of temperatures. From C–V measurements, the dielectric constant of the epitaxial (001)BTO film is determined as 159.5, which is larger than the value 89.6 of (111)BTO film. The remanent polarization (2Pr) of the epitaxial BTO(001) thin film on the LNO-coated (001)STO substrate is 39.8 µC cm−2, which is much larger than that of the BTO(111) film on the LNO-coated STO(111) substrate. The result is also consistent with the direct observation made by piezoresponse force microscopy investigation. Thus, with the epitaxial LNO electrode template layers, the epitaxial BaTiO3(001) ferroelectric films exhibit high-quality structure and good electrical properties.

Pulsed laser deposition of InP thin films on sapphire(1 0 0 0) and GaAs(1 0 0)

Indium phosphide thin films were deposited on sapphire and GaAs(1 0 0) substrates by pulsed laser deposition using a XeCl excimer laser in argon background gas and in high vacuum. The grown film structure and morphology were observed by reflection high-energy electron diffraction, scanning electron microscopy, and atomic force microscopy. The films were grown on sapphire produced a reflection electron diffraction pattern of a disordered film. Introduction of an argon gas background enhanced the particulate formation. Epitaxial InP(1 0 0) film with oriented polyhedral islands were grown on hydrogen-cleaned GaAs(1 0 0) at a substrate temperature of ∼573 K at 1×10 −8 Torr background pressure. By varying the deposition parameters, relatively smooth InP films with average surface roughness of about 4–12 nm were obtained.

Domain variance and superstructure across the antiferroelectric/ferroelectric phase boundary in Pb1−1.5xLax(Zr0.9TiM0.1)O3

Transmission electron microscopy, x-ray diffraction, relative permittivity as a function of temperature, and polarization versus field loops were used to study the antiferroelectric/ferroelectric (AFE/FE) phase boundary in Pb1–1.5xLaxZr0.9Ti0.1O3 (PLZT, 100x/90/10) ceramics. X-ray diffraction and electrical measurements indicated a FE rhombohedral (R) to AFE tetragonal (T) phase transition between PLZT 2/90/10 and 4/90/10. Both phases exhibited superstructure reflections in electron-diffraction patterns at ½{hkl} positions consistent with rotations of the octahedra in antiphase. Previously, neutron diffraction suggested that the FER has an a−a−a− tilt system (Glazer notation), in agreement with its macroscopic symmetry. By analogy, it is proposed that the AFET phase has an a0a0c− tilt system. The AFE phase was also characterized by incommensurate superstructure along pseudocubic 〈110〉p directions, whereas the FE phase had extra commensurate superlattice reflections at 1/2{hk0}p positions. 1/2{hk0}p reflections are forbidden in both tilt systems, but their presence is explained by Pb ion displacements averaged along 〈111〉 but with short coherence antiparallel components along 〈110〉 directions. The antiparallel Pb displacements are coupled to an a−b−b− (a ≈ b) monoclinic tilt system in the vicinity of the AFE/FE boundary.

Growth of homoepitaxial diamond doped with nitrogen for electron emitter

Although we had reported the remarkable low threshold emission from polycrystalline diamond heavily doped with nitrogen (N) [Nature 381 (1996) 140], the problems caused by polycrystallinity still remain for understanding the electron emission mechanism. This paper describes the growth of N-doped homoepitaxial diamond film {100}, {111} and {110}, and their electron emission properties. N-doped homoepitaxial diamond is grown on synthetic diamond by hot filament chemical vapor deposition. Urea [(NH 2) 2CO] is used as a dopant for N. Atomic force microscope (AFM) observations indicate that the relatively smooth surface morphologies are obtained for all the films. The epitaxial growth of all the film is confirmed using reflective high energy electron diffraction (RHEED) patterns. Reflective electron energy loss spectra (REELS) indicate that the very surfaces of {100} and {111} are diamond while {110} is graphite rather than diamond. Raman spectra suggest that the bulk of the obtained films are diamond. The resistivities of the films are found to be much higher than the detection limit of the system. The relatively low threshold emission was observed even from the smooth surface and the threshold voltage is confirmed to depend on the crystal orientation. It is speculated from the film characterizations and the electron emission properties that the low threshold emission is due to high resistance rather than rough surface and/or grain boundaries.

Microstructural Observations in Barium Calcium Magnesium Niobate

Microstructural studies on (1 −x)Ba(Mg1/3Nb2/3)O3–xCa(Mg1/3Nb2/3)O3 (BCMN) complex perovskite compounds, which are mixtures of Ba(Mg1/3Nb2/3)O3 (BMN) and Ca(Mg1/3Nb2/3)O3 (CMN), were conducted using scanning electron microscopy, transmission electron microscopy, and X‐ray diffractometry. Pure BMN and CMN both have a 1:2 ordered structure, via the chemical ordering of B‐site cations; however, the tilting of oxygen octahedra is involved in pure CMN, whose structure has a 1:2 ordered monoclinic unit cell that is characterized by (±1/6,±1/6,±1/6)‐type superlattice reflections in electron diffraction patterns along the [110] zone axis that is based on a simple cubic perovskite. Studies of the morphologic differences have indicated two types of inhomogeneities in a mixture of the BCMN system: (i) a rather large‐scale segregation (i.e., grain sizes of several micrometers), where the grains are separated compositionally as being barium‐rich or calcium‐rich, and (ii) fine‐scale lamellar‐type segregations 20 nm wide and 200 nm long. The segregation that is caused by Ba and Ca ions can be identified by the difference of superlattice modulations from high‐resolution transmission electron microscopy lattice images.

Effect of group-V species exchange at the interfaces of InGaAs/AlAsSb superlattice

The effect of growth interruption times combined with selective group-V species exposure of InGaAs/AlAsSb short-period superlattice structure was investigated with photoluminescence, X-ray diffraction, reflection high-energy electron diffraction. X-ray data show no superlattice structural dependence on the used growth treatment. While reflection electron diffraction patterns strongly depend on the exposure time and species type exposure. A shift in the photoluminescence peak position from samples grown under different species type exposure is observed. The samples with Sb- and As-terminated interfaces, respectively, indicate lower- and higher-energy peaks compared to the ones grown without interruption. This is interpreted in terms of increased incorporation of Sb in the InGaAs layer that leads to a change in the quantum well profile.

Charge Density Wave Transitions Induced in Nb3Se4and Nb3S4by Indium Intercalation

The family of crystals Nb3X4(X=Te,Se,S) are isostructural, quasi one-dimensional tunnel structures. The telluride exhibits a charge density wave below room temperature, but no such transition occurs in the selenide or sulfide. A variety of foreign atoms can be intercalated into the tunnels of these structures and it is known that thallium intercalation in Nb3Te4causes dramatic changes in the charge density wave characteristics, due to changes in the Fermi surface and density of states resulting from the electrons being transferred to the host crystal from the intercalated atoms. In this paper it is shown that indium intercalation in Nb3Se4and Nb3S4gives rise to superlattice reflections in electron diffraction patterns, which are interpreted as being due to charge density waves. The unusual variations of the charge density wave vectors with intercalate concentration are discussed and a model to account for them is proposed.

Investigation on structural properties of ZnSe, CdTe, and ZnTe films grown by ionized cluster beam epitaxy

Epitaxial films of ZnSe, CdTe, and ZnTe were grown, on GaAs(1 0 0) substrates by ionized cluster beam epitaxy (ICBE). Streaky reflective high energy electron diffraction (RHEED) patterns indicated good crystallinity and surface flatness of the epitaxial ZnSe, CdTe, and ZnTe films. It was found that the crystalline quality of the epilayers depended on the kinetic energy of the clusters and the substrate temperature. The minimum X-ray rocking curve peak widths of the ZnSe, CdTe, and ZnTe epilayers were determined to be 160, 630, and 110 arc sec, respectively.

Reduction of Charging in Biological Electron Cryomicroscopy

Abstract High resolution imaging in electron cryomicroscopy of biological macromolecules is strongly affected by beam-induced charging1. Charging is often expressed in frozen or glucose-embedded specimens as an increase in apparent mass-thickness of the irradiated area. Another obvious effect of charging is blurring of both the unscattered beam and reflections in electron diffraction patterns recorded from crystalline specimens. Coating of ice-embedded specimens with a carbon layer helps to improve the stability of the ice and probably reduce charging of the specimen. Coating in a Gatan ion-beam coater (model 681) of glucose-embedded specimens with thin layers of various conductive materials did reduce charging but the specimens were damaged by the high energy ions used for the coating. In general, coating resulted in much weaker reflections in electron diffraction patterns obtained from coated crystals and faster resolution fall-off. We modified the Gatan coater by outfitting it with a new chamber that replaced the ion-beam deposition capability for thermal evaporation of carbon rods (Fig. 1).

Correlation of reflection electron diffraction patterns, Raman spectra and compositions in “CuInSe2” films

Abstract Quantitative analysis was performed on epitaxial or oriented “CuInSe2” grown on (0 0 1) GaAs (or GaP), which gave five types of reflection electron diffraction (RED) patterns. The compositions of “CuInSe2” could be grouped into four classes corresponding to the types of RED patterns observed. CuInSe2 satisfying stoichiometry belonged to the cubic system (space group, P43m). The RED pattern of “CuInSe2” including Se above 68 mol% could be explained by the superimposition of the RED patterns due to chalcopyrite-type CuInSe2 (s.g., I42d) and an unknown tetragonal crystal (s.g., I42c). The RED pattern of CuInSe2 defined as chalcopyrite-type (0 0 1) CuInSe2 accompanied a non-allowed (0 0 6) spot along the [1 0 0] azimuth.

Comparison of calculated and observed dynamical diffraction from purple membrane: implications

We show that the magnitude and direction of the observed differences in intensities of Friedel-related reflections in electron diffraction patterns from two-dimensional crystals of bacteriorhodopsin (purple membrane) are accounted for by dynamical scattering as well as by Ewald sphere curvature. We suggest how the observed Friedel differences might be used to refine structure factor phases.

Intercalation of vacuum deposited silver into 1T-TaS2 and its influence on charge density waves

It is shown that silver vapour deposited onto (00.1) faces of 1T-TaS2 crystals at 300–500 K starts to intercalate into van der Waals gaps of the host crystal already during the deposition process, even at room temperature deposition. This is demonstrated by superstructure reflections in electron diffraction patterns. The intercalated silver also lowers the transition temperatures among various 1T-TaS2 CDW phases. These effects show that the octahedral coordination of Ta atoms changes into the trigonal prismatic one. In crystals with silver deposited above 500 K, where the transformation of 1T-TaS2 into the stable 2Ha form takes place, the observed superstructures are in agreement with the literature results for electrochemically silver intercalated 2Ha-TaS2 crystals.

Electrical transport in amorphous Se1−xSbx thin films

Amorphous Se1−xSbx (x=0.1, 0.15 and 0.2) films of different thicknesses were prepared by the electron gun evaporation technique. Their structure was studied using reflection or transmission electron diffraction patterns. The d.c. electrical conductivity, thermoelectric power and magnetoresistance measurements, were made in the temperature range 80–300 K. These measurements confirm intrinsic conduction in the entire range of investigation, and were found to be independent of the film thickness. The effect of antimony impurity on electrical transport properties of selenium is understood in terms of the reduction of the Se8 ring population.

Preparation and properties of Bi4Ti3O12 single-crystal thin films by atmospheric pressure metalorganic chemical vapor deposition

Bismuth titanate (Bi4Ti3O12) thin films have been grown on (100) silicon substrates at 550 °C by atmospheric pressure metalorganic chemical vapor deposition using Bi (C6H5)3 and Ti (OC4H9)4 as the source materials. The x-ray diffraction analysis and reflection electron diffraction pattern revealed that the film is a single crystal with a (100) orientation. Ferroelectric properties were confirmed by polarization hysteresis curve observation. The remanent polarization and coercive field were found to be 38 μC/cm2 and 45 kV/cm, respectively. The measured dielectric constant and loss tangent were 93 and 0.05, respectively, at room temperature.