Grazing Incidence Angle X-ray Diffraction Research Articles

Enhanced tunneling electroresistance effects in HfZrO-based ferroelectric tunnel junctions by high-pressure nitrogen annealing

Greatly improved ferroelectricity with an excellent remanent polarization of 20 μC/cm2 and enhanced tunneling electroresistance (TER) were achieved with TiN/HfZrO(HZO)/p-type Ge ferroelectric tunnel junctions (FTJs) annealed at a high pressure of 200 atmosphere (atm.). We found that the enhanced ferroelectric characteristics can be ascribed to the effective formation of an orthorhombic phase at high pressures. This was verified by the combined study of grazing angle incidence X-ray diffraction, transmission electron microscopy, and hysteresis polarization curve analyses. In addition, using pulse switching measurements, we quantitatively evaluated the interfacial paraelectric capacitance (Ci) of HZO FTJs according to the annealing temperature. HZO films annealed at 550 °C and 200 atm. exhibited an excellent TER effect ratio of 20 due to the extra paraelectric layer between the ferroelectric layer and the bottom electrode and a relatively high remanent polarization.

Ion irradiation induced nucleation and growth of nanoparticles in amorphous silicon carbide at elevated temperatures

Ion irradiation induced crystallization in as-deposited amorphous SiC films is investigated using grazing-angle incidence x-ray diffraction (GIXRD), transmission electron microscopy (TEM) and Raman spectroscopy. Irradiation with 5 MeV Xe to fluence of 1.15 × 1016 Xe/cm2 at 700 K results in a homogenous distribution of 3C-SiC grains with an average crystallite size of ∼5.7 nm over the entire film thickness (∼1 μm). The nucleation and growth processes exhibit a weak dependence on dose in displacements per atom (dpa) in the range from ∼6 dpa at the film surface to ∼20 dpa at the SiC/Si interface. A transformation of homonuclear C-C bonds from sp3 to sp2 hybridization is observed in the irradiated films, which may be partly responsible for the observed grain size saturation. The results from this study may have a significant impact on applications of SiC as structural components of advanced nuclear energy systems.

Constrained crystallization of poly(L-lactic acid) in thin films prepared by dip coating

Dip coating process used at various withdrawing speeds showed a great ability to control the crystalline structure of thin films of poly(L-lactic acid) which can be of great importance for applications where mechanical or optical properties are involved. Thin films were studied by Atomic Force Microscopy and Grazing Incidence Angle X-ray Diffraction. Withdrawing the silicon substrate in the draining regime (at high speeds) led to amorphous films with flat surface whatever the solvent and the molar mass. At low speeds (capillary regime), AFM demonstrated the presence of spherulites or hedrites in the films depending on the solvent and the molar mass. GIXRD showed that spherulites were less crystallized than hedrites. This difference was attributed to solvent evaporation rate.

Effects of high pressure nitrogen annealing on ferroelectric Hf0.5Zr0.5O2 films

The effect of high-pressure nitrogen annealing at up to 50 atmospheres (atm) on Hf0.5Zr0.5O2 films at relatively low temperatures (450 °C) is analyzed using polarization-electric field curves, bipolar switching endurance measurements, grazing angle incidence X-ray diffraction, and piezoelectric force microscopy. Hf0.5Zr0.5O2 films annealed at 450 °C/50 atm have excellent characteristics, including remanent polarizations greater than 20 μC/cm2, a switching speed of 200 ns, and reliability, measured by sustained performance after 1010 bipolar switching cycles. The enhanced device features are attributed to the transition to the orthorhombic-phase from the tetragonal-phase of Hf0.5Zr0.5O2 at high pressure, which is also consistent with the results of “wake-up” analysis, and the variations of the pure polarization curves, extracted from the total displacement field under pressure.

Restoration of perovskite phase in the top layer of thin BTO film by plasma treatment and annealing

We report a simple method to restore the perovskite phase in the top surface/sub-surface region of a thin film (~100 nm) of barium titanate (BTO) fabricated by pulsed laser deposition on a platinized silicon surface and thus enhance its dielectric and ferroelectric properties. Phase evolution, surface morphology with local chemical composition of as-grown BTO films have been studied as a function of laser fluence. Investigations using x-ray diffraction, grazing-angle incidence x-ray diffraction and depth resolved x-ray photoelectron spectroscopy show that even after achieving a good phase formation there can be a presence of non-perovskite TiO2 phase at the surface and subsurface in such films that degrades its dielectric and ferroelectric response. The restoration of the degraded top layer was done by a combination of low energy Ar plasma treatment followed by an annealing process that enhances Ba content.

Structural and optical properties of silica single-layer films doped with ZnS quantum dots: Photoluminescence monitoring of annealing-induced defects

Zinc Sulfide (ZnS) quantum dots (QDs) embedded in sol-gel silica single-layer films were synthesized by dip-coating and thermal treatment. Nucleation and growth of these QDs occurred during annealing. The effect of annealing temperature on morphological, structural and optical properties of the films was considered in the range (200–500°C). Scanning electron microscopy (SEM), atomic force microscopy (AFM), grazing incident angle X-ray diffraction (GIXD), UV–Visible spectroscopy (UV–Vis) and photoluminescence (PL) were used to characterize the films. The band gap values of the ZnS QDs ranged from 3.83 to 4.03eV corresponding to average radii in the range 1.5–2.1nm. PL revealed different annealing-induced defects in the ZnS QDs. Zn interstices dominate at 400 and 500°C annealing temperatures by the appearance of two excitation bands at 395nm and 404nm respectively. Corresponding emission bands were recorded at 402nm and 408nm. An emission peak (457nm) and an excitation peak (437nm) were also observed at 500°C. These peaks were attributed to S vacancies which might be created by the transformation of ZnS to ZnO. Finally, an overall energy-level diagram showing all the defect states in the gap of ZnS was proposed.

Correlation of surface pressure and hue of planarizable push-pull chromophores at the air/water interface.

It is currently not possible to directly measure the lateral pressure of a biomembrane. Mechanoresponsive fluorescent probes are an elegant solution to this problem but it requires first the establishment of a direct correlation between the membrane surface pressure and the induced color change of the probe. Here, we analyze planarizable dithienothiophene push–pull probes in a monolayer at the air/water interface using fluorescence microscopy, grazing-incidence angle X-ray diffraction, and infrared reflection–absorption spectroscopy. An increase of the lateral membrane pressure leads to a well-packed layer of the ‘flipper’ mechanophores and a clear change in hue above 18 mN/m. The fluorescent probes had no influence on the measured isotherm of the natural phospholipid DPPC suggesting that the flippers probe the lateral membrane pressure without physically changing it. This makes the flipper probes a truly useful addition to the membrane probe toolbox.

A Complementary Metal Oxide Semiconductor Process-Compatible Ferroelectric Tunnel Junction.

In recent years, experimental demonstration of ferroelectric tunnel junctions (FTJ) based on perovskite tunnel barriers has been reported. However, integrating these perovskite materials into conventional silicon memory technology remains challenging due to their lack of compatibility with the complementary metal oxide semiconductor process (CMOS). This communication reports the fabrication of an FTJ based on a CMOS-compatible tunnel barrier Hf0.5Zr0.5O2 (6 unit cells thick) on an equally CMOS-compatible TiN electrode. Analysis of the FTJ by grazing angle incidence X-ray diffraction confirmed the formation of the noncentrosymmetric orthorhombic phase (Pbc21, ferroelectric phase). The FTJ characterization is followed by the reconstruction of the electrostatic potential profile in the as-grown TiN/Hf0.5Zr0.5O2/Pt heterostructure. A direct tunneling current model across a trapezoidal barrier was used to correlate the electronic and electrical properties of our FTJ devices. The good agreement between the experimental and theoretical model attests to the tunneling electroresistance effect (TER) in our FTJ device. A TER ratio of ∼15 was calculated for the present FTJ device at low read voltage (+0.2 V). This study suggests that Hf0.5Zr0.5O2 is a promising candidate for integration into conventional Si memory technology.

Preparation and characterization of boron nitride coating on silicon carbide fibers based on low-temperature chemical vapor deposition

Boron nitride (BN) has been considered as promising material owing to its unique properties, such as high thermal stability, high chemical stability, high thermal conductivity and thermal shock resistance. Chemical vapor deposition (CVD) is the most popular method for the preparation of BN. However, the side-products (like HF, HCl and HBr) are corrosive and the crystallinity of BN is poor if the deposition temperature is 1300°C. Herein we reported a new method for preparing BN by low-temperature CVD using ammonia borane as precursor on silicon carbide fibers. Ammonia borane was sublimated at 110–130°C using a heating belt, and the sublimated gaseous substance was transported to the deposition region where the silicon carbide fibers were placed at the deposition temperature of 900°C. During the sublimation, a certain quality of ammonia borane was uniformly distributed in the quartz boat with a certain length, and the heating belt moved along the quartz tube with a fixed speed to the end of the boat. Thus the sublimation gas substances could be supplied continually and steadily. Scanning electronic microscopy (SEM), auger electron spectroscopy (AES), Fourier translation infrared spectroscopy (FTIR), and grazing incidence angle X-ray diffraction (GIAXRD) were used to characterize the properties of the coatings, and single fiber electron tensile machine was used to test the tensile strength of silicon carbide fibers without and with different thickness of coatings. The results illustrated that BN coating enwrapped well with the fibers with no defects like voids or cleavages. Meanwhile, the surface of the coating was uniform and dense. And the ratio of B and N was approximate 1: 1. Pure BN coating could be acquired at a relatively low deposition temperature, and microstructure of the BN coating was more ideal with the increasing of deposition temperature. Considering the balance between the coating crystallinity and strength retention of the fiber, 800–1000°C was the optimum deposition temperature range of BN coating on silicon carbide fibers. Compared with previous reports, this method reduced the preparation temperature effectively and could acquire pure BN on relatively low temperature. In this work, we aimed at preparing the ideal interphase of ceramic composite, and reducing the deposition temperature to elevate the fiber strength retention. This work could reduce the deposition temperature by at least 100°C and even 500°C compared with some cases. It would solve the reduction of mechanical properties during long time and high temperature deposition. At 900°C, the strength retention of the fibers retained 92.7%, 83.6% and 77.7%, as the coating thickness was 0.28, 0.51 and 0.82 μ m, respectively. The strength retention of the silicon carbide fiber can meet the requirement of ceramic composite.

Effect of heat treatment on the optical properties of sol–gel-derived, fully dielectric solar control coatings on glass

TiO2 and zeolite were used as high index and low index dielectric materials respectively to generate fully dielectric solar control coatings on glass. TiO2|Zeolite|TiO2 trilayer stacks as well as single layer TiO2 and zeolite coatings were generated on soda lime glass substrates using dip-coating technique. The coatings were densified at 450°C in air using a conventional muffle furnace and a conveyorized belt furnace with a total cycle time of 330 and 30 min, respectively, per layer. The effect of heat-treatment time on the optical properties of multilayered and single-layered coatings was studied. Spectroscopic ellipsometric analysis was carried out on individual layers of the stack to elucidate thickness, roughness, and refractive index data. The ellipsometry data were subsequently used as inputs to simulate the UV–Vis–NIR transmittance spectra of the trilayer stacks generated by TFCalc® software, for comparison with experimentally obtained data. The morphology and phase compositions of the coatings were studied using scanning electron microscopy and grazing angle incidence X-ray diffraction analysis. Different heat treatment schedules were found to result in different optical properties. The results from the present study could be used to recommend suitable heat treatment schedules for generating solar control coatings that could be used for either architectural or automotive applications.

Sol–gel derived solar selective coatings on SS 321 substrates for solar thermal applications

Sol–gel derived multilayered solar selective coatings were generated on AISI SS 321 substrates using Ag-TiO2 as the cermet layer, titania and silica as the dielectric layers with high and low refractive indices respectively. The phase compositions of the individual layers were independently confirmed using grazing angle incidence X-ray diffraction, which was corroborated by X-ray photoelectron spectroscopic analysis. Thickness of the layers was measured using variable angle spectroscopic ellipsometry. The solar absorbance was measured over the UV–Vis-NIR wavelength range. Thermal emissivity was determined using FTIR spectroscopic analysis. The durability of the coatings was ascertained using accelerated corrosion testing methods as well as by measuring the optical properties after thermal cycling experiments. The promising nature of hexavalent chrome-free, environmental friendly, multilayered solar selective coating was ascertained with respect to amenability to scale-up.

Formation of α-alumina scales in the Fe–Al(Cr) diffusion coating on China low activation martensitic steel

To study the formation mechanism of stable α-Al2O3 scales, the oxidation behavior of Fe–Al(Cr) diffusion coating on China low activation martensitic steel has been investigated under the oxygen partial pressure ranging from 1 to 20,000Pa at 1253K. A single, continuous Al2O3 scale with the maximum thickness of about 2000nm was formed on the Fe–Al(Cr) diffusion layer. The phase transformation of alumina scales on the surface of Fe–Al(Cr) layer was studied at different oxidation times ranging from 3 to 180min. With the increase in oxygen partial pressure, the phase transformation time of α-Al2O3 is decreased. The metastable γ-Al2O3 and transition α-(Al0.948Cr0.052)2O3 phases were formed in the earlier oxidation process and finally transformed to the stable α-Al2O3 phase, which were detected by grazing incidence angle X-ray diffraction and confirmed by transmission electron microscopy. This implies that Cr shows the third element effect and serves as a template for the nucleation of the stable α-Al2O3.

High proton conductivity in the molecular interlayer of a polymer nanosheet multilayer film.

High proton conductivity was achieved in a polymer multilayer film with a well-defined two-dimensional lamella structure. The multilayer film was prepared by deposition of poly(N-dodecylacryamide-co-acrylic acid) (p(DDA/AA)) monolayers onto a solid substrate using the Langmuir-Blodgett technique. Grazing-angle incidence X-ray diffraction measurement of a 30-layer film of p(DDA/AA) showed strong diffraction peaks in the out-of-plane direction at 2θ = 2.26° and 4.50°, revealing that the multilayer film had a highly uniform layered structure with a monolayer thickness of 2.0 nm. The proton conductivity of the p(DDA/AA) multilayer film parallel to the layer plane direction was 0.051 S/cm at 60 °C and 98% relative humidity with a low activation energy of 0.35 eV, which is comparable to perfluorosulfonic acid membranes. The high conductivity and low activation energy resulted from the formation of uniform two-dimensional proton-conductive nanochannels in the hydrophilic regions of the multilayer film. The proton conductivity of the multilayer film perpendicular to the layer plane was determined to be 2.1 × 10(-13) S/cm. Therefore, the multilayer film showed large anisotropic conductivity with an anisotropic ratio of 2.4 × 10(11).

Thermotropic Phase Transition of Benzodithiophene Copolymer Thin Films and Its Impact on Electrical and Photovoltaic Characteristics

We observed a thermotropic phase transition in poly[3,4-dihexyl thiophene-2,2′:5,6′-benzo[1,2-b:4,5-b′]dithiophene] (PDHBDT) thin films accompanied by a transition from a random orientation to an ordered lamellar phase via a nearly hexagonal lattice upon annealing. We demonstrate the effect of temperature-dependent molecular packing on charge carrier mobility (μ) in organic field-effect transistors (OFETs) and photovoltaic characteristics, such as exciton diffusion length (LD) and power conversion efficiency (PCE), in organic solar cells (OSCs) using PDHBDT. The μ was continuously improved with increasing annealing temperature and PDHBDT films annealed at 270 °C resulted in a maximum μ up to 0.46 cm2/(V s) (μavg = 0.22 cm2/(V s)), which is attributed to the well-ordered lamellar structure with a closer π–π stacking distance of 3.5 Å as shown by grazing incidence-angle X-ray diffraction (GIXD). On the other hand, PDHBDT films with a random molecular orientation are more effective in photovoltaic devices than films with an ordered hexagonal or lamellar phase based on current–voltage characteristics of PDHBDT/C60 bilayer solar cells. This observation corresponds to an enhanced dark current density (JD) and a decreased LD upon annealing. This study provides insight into the dependence of charge transport and photovoltaic characteristics on molecular packing in polymer semiconductors, which is crucial for the management of charge and energy transport in a range of organic optoelectronic devices.

Synthesis and Characterization of Chemically Pure Nanometer-Thin Zero-Valent Iron Films and Their Surfaces

The synthesis and characterization of 15, 25, 50, and 70 nm thin iron films having chemical impurities below the detection limit of various analytical techniques is reported. As established herein, the films are chemically pure and formed by electron beam deposition from inexpensive and readily available iron sources of 3N5 purity. Chemical purity of the thin films was achieved using mean deposition rates of 0.3 nm/s or higher, at which point the melting point of iron is reached at the iron source surface and a shutter is opened, from which point on the rate of transfer of impurities present in the source to the target is low enough that they are not observed in the film as confirmed via X-ray photoelectron spectroscopy (XPS), reported here for energies between 0 and 1200 eV. Nanoindentation measurements indicate the iron films to be 14 times harder than bulk iron. The iron films are shown by XPS to be coated with a 3 nm thin overlayer of Fe3+, which is possibly present in the form of Fe3O4, even though other forms of iron oxide are likely to be present as well, as indicated by Raman and XPS spectroscopy. Grazing incidence angle X-ray diffraction experiments indicate the presence of crystalline Fe0 with low index faces exposed but no crystallinity of the iron oxide overlayer. Atomic force microscopy of the iron film surfaces indicates narrowing and shifts to lower heights in the height distribution of nanoscale features formed during the film deposition process as the film thickness decreases. Second harmonic generation is then used to determine that the interfacial charge density of the thinnest iron film is −0.007(3) C/m2 at pH 7.

Naphtho[2,1-b:3,4-b']dithiophene-based bulk heterojunction solar cells: how molecular structure influences nanoscale morphology and photovoltaic properties.

Organic bulk heterojunction photovoltaic devices based on a series of three naphtho[2,1-b:3,4-b']dithiophene (NDT) derivatives blended with phenyl-C71-butyric acid methyl ester were studied. These three derivatives, which have NDT units with various thiophene-chain lengths, were employed as the donor polymers. The influence of their molecular structures on the correlation between their solar-cell performances and their degree of crystallization was assessed. The grazing-incidence angle X-ray diffraction and atomic force microscopy results showed that the three derivatives exhibit three distinct nanoscale morphologies. We correlated these morphologies with the device physics by determining the J-V characteristics and the hole and electron mobilities of the devices. On the basis of our results, we propose new rules for the design of future generations of NDT-based polymers for use in bulk heterojunction solar cells.

Influence of annealing temperature on the nanostructure and performance of polymer: Polymer solar cells

Here we report the influence of thermal annealing temperature on the nanostructure and the performance of polymer:polymer solar cells. The active layer was prepared with bulk heterojunction (BHJ) films of poly(3-hexylthiophene) (P3HT) and of poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) doped with (1S)-(+)-10-camphorsulfonic acid (CSA) (F8BT-CSA). The change in the nanostructure of the P3HT:F8BT-CSA films with thermal annealing temperature was investigated by employing a synchrotron radiation grazing-incidence-angle X-ray diffraction (GIXD) technique. Results showed that the power conversion efficiency (PCE) of the P3HT:F8BT-CSA solar cells was noticeably improved by thermal annealing at 150 °C, which could be attributed to the optimized nanostructure in the BHJ film at 150 °C, as suggested by the GIXD measurements.

Magnetic and structural studies on nanostructured Gd/Cr multilayer films

Investigations of magnetic phases, transition temperatures and coercivity were performed in multilayered Gd/Cr films as a function of the crystalline state and morphology of the Gd layers. The films were deposited by dc magnetron sputtering at three substrate temperatures, Ts, (room temperature, 300 and 500°C). The Gd and Cr thicknesses were of 10 and 30nm, respectively. Two series of three films were prepared. In one of the series, the films had a single Gd/Cr bilayer; in the other, 15 bilayers. The discontinuous or granular nature of the Gd layers was revealed by scanning electron microscopy Grazing incidence angle x-ray diffraction was used to investigate the crystalline state of the Gd and Cr layers. These techniques revealed that grain average size and crystalline order increase with increasing Ts. From dc magnetic measurements, the co-existence of ferromagnetic and superferromagnetic phases in the Gd layers was observed, and Curie transition temperatures, TC, were determined. High coercive fields at low temperature (2K) were measured in hysteresis cycles. Field-cooled and zero field-cooled magnetizations as functions of temperature curves exhibited, for some of the samples, a low temperature peak suggesting a freezing transition to a cluster glass state. This was confirmed by complementary ac-susceptibility measurements carried out as a function of temperature, for various frequencies of the ac field. Some results of this work – the decline in TC for decreasing Gd grain size, the high coercive field and its dependence on particle size, and the behavior of the magnetization at low temperatures for the sample deposited at room temperature – are discussed in terms of finite size and surface effects in nanosized particles.

Oxygen “Getter” Effects on Microstructure and Carrier Transport in Low Temperature Combustion-Processed a-InXZnO (X = Ga, Sc, Y, La) Transistors

In oxide semiconductors, such as those based on indium zinc oxide (IXZO), a strong oxygen binding metal ion ("oxygen getter"), X, functions to control O vacancies and enhance lattice formation, hence tune carrier concentration and transport properties. Here we systematically study, in the IXZO series, the role of X = Ga(3+) versus the progression X = Sc(3+) → Y(3+) → La(3+), having similar chemical characteristics but increasing ionic radii. IXZO films are prepared from solution over broad composition ranges for the first time via low-temperature combustion synthesis. The films are characterized via thermal analysis of the precursor solutions, grazing incidence angle X-ray diffraction (GIAXRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy (STEM) with high angle annular dark field (HAADF) imaging. Excellent thin-film transistor (TFT) performance is achieved for all X, with optimal compositions after 300 °C processing exhibiting electron mobilities of 5.4, 2.6, 2.4, and 1.8 cm(2) V(-1) s(-1) for Ga(3+), Sc(3+), Y(3+), and La(3+), respectively, and with I(on)/I(off) = 10(7)-10(8). Analysis of the IXZO TFT positive bias stress response shows X = Ga(3+) to be superior with mobilities (μ) retaining >95% of the prestress values and threshold voltage shifts (ΔV(T)) of <1.6 V, versus <85% μ retention and ΔV(T) ≈ 20 V for the other trivalent ions. Detailed microstructural analysis indicates that Ga(3+) most effectively promotes oxide lattice formation. We conclude that the metal oxide lattice formation enthalpy (ΔH(L)) and metal ionic radius are the best predictors of IXZO oxygen getter efficacy.

Corrosion study of ZrN deposited on 304L stainless steel

The ZrN films were deposited on type 304L stainless steel using dc magnetron sputtering technique at different substrate temperatures from room temperature up to 600°C. The ZrN films have been analysed for their composition, microstructure, surface morphology and their corrosion resistance in different nitric acid concentrations. The grazing incidence angle X-ray diffraction analysis showed the texture orientation of (111) or (200) plane depending on the substrate temperature. The atomic force microscopy analysis reveals the formation of ZrN agglomerates with no visible cracks or pores. However, increase in grain size (10–20 nm) and roughness (10–50 nm) with increase in the substrate temperature was observed. The potentiodynamic polarisation and electrochemical impedance spectroscopy results indicated that the corrosion resistance of different ZrN films, although high in 1 mol L−1 HNO3, suffered a marked decrease in 8 mol L−1 HNO3 concentration.