Change In D-spacing Research Articles

Effects of Operating Conditions on Membrane Electrode Assembly Saturation and Hydration Revealed By Operando Small- & Wide-Angle X-Ray Scattering

Operando scanning small- and wide-angle X-ray scattering (SAXS&WAXS) at the cSAXS beamline of the Swiss Light Source was employed in this study to examine the water saturation of polymer electrolyte fuel cell (PEFC) component, particularly in the nanoscale pore space of catalyst layers (CL) and the membrane hydration state. A small beam size (≈7x30 microns) and ≈0.6 microns through-plane step size enabled to resolve of the bulk CLs (Pt/C Ketjen Black based, 0.1 mgPt/cm2; ≈7 microns thick) separated by a 15-micron membrane. Additionally, it allows for precise registration in case of membrane swelling during operation, which is a prerequisite for the analysis of the operando scattering data. Due to the difference in electron density variation between solid-void and solid-liquid interfaces, any change in CL saturation results in different scattering intensity profiles, which can be quantified by Invariant calculations (see Fig. 1a & b).The presentation will give insights into CL saturation evolution concerning relative humidity, operating pressure and current density. Differences in the CL saturation, and membrane hydration indicated by a change in d-spacing of the ionomer peak (1), were observed between wet nitrogen flushing and cell operation (see Fig. 1c & d). However, the cathode microporous layer (MPL) saturation seems to be unaffected for a Li100-based MPL on a Freudenberg H14 gas diffusion layer (GDL) substrate. The length scale-specific scattering data will provide a better understanding of mass transport in PEFC’s materials and allow us to push material design development forward. We acknowledge the Paul Scherrer Institut, Villigen, Switzerland for provision of synchrotron radiation beamtime at beamline cSAXS of the Swiss Light Source.

Atomistic Insights into the Interlayer Cation and Water Structures of Na-, K-, and Cs-Birnessite

Birnessite is a key mineral involved in the geochemical cycles of trace metals through its high cation sorption capacity. Information about cation and water structures in the interlayer regions, as well as about the layer spacing and associated changes, is essential to understanding the cation exchange mechanism. However, this fundamental knowledge is lacking for birnessite due to the complexity of its structure and the insufficient ability to probe the interlayer species, water molecules in particular. In this study, we performed molecular dynamics (MD) computer simulations of Na-, K-, and Cs-birnessite as a function of the interlayer hydration state and cation exchange ratio. As the monolayer hydrate state transitioned to a bilayer hydrate state, the d-spacing of Na-birnessite increased from ∼7 to ∼10 Å, Na+ cations maintained a position at the midplane of the interlayer, and water molecules were reoriented to form intermolecular H-bonds rather than H-bonds with birnessite surfaces. In the bilayer hydrate states of K- and Cs-birnessite, the interlayer cations were positioned near the birnessite surface rather than the midplane of the interlayer. As the K+ ratio increased in Na0.29–xKxMnO2·0.75H2O, the d-spacing contracted in the initial stage of cation exchange but increased in the subsequent stage. In Na0.29–xCsxMnO2·0.75H2O, the d-spacing expanded continuously with an increasing Cs+-to-Na+ ratio. In our MD simulations, interlayer water molecules needed to be deintercalated during cation exchange to reproduce the experimentally observed trends in d-spacing changes of Na-birnessite during cation exchange. These results suggest the important role of interlayer water in the cation sorption of birnessite that is often neglected in understanding the birnessite reactivity.

Novel P2-Type Na0.6Fe0.5Mn0.5-2xCuxVxO2 Cathode Material for Improved Sodium Ion Batteries

Sodium ion batteries (SIB’s) have become a popular area of research in recent years due to their low cost and high sustainability compared to the current lithium-ion technology. The abundance of sodium on Earth makes sodium-based batteries a viable option for portable electronic devices, electric vehicles, and in grid sized energy storage applications. Although, SIB’s are a good alternative to lithium ion batteries (LIB’s) there are still improvements that need to be made before commercially produced (SIB’s) can compete with the overall performance of (LIB’s). The improvements needed include an increase in the capacity, in the cycle life, and in the voltage of the batteries. Improvements in these areas can be realized through the development of high-performance sodium-based cathode materials, specifically sodium transition metal oxide materials. The research presented here deals with cobalt-free Na0.6Fe0.5Mn0.5O2 (NFM) based cathode materials and a number of copper and vanadium doped variations. The focus of this research is on improving the electrochemical performance of sodium ion batteries through the stabilization of the transition metal oxide cathode structure. The main areas of improvement that are achieved in this research is minimizing the effects of Jahn-Teller distortion on the transition metal oxide layers and increasing the distance between the transition metal oxide layers by doping with copper and vanadium. Alleviating the Jahn-Teller distortion will improve the structural stability of the P2-type cathode material and promote higher cyclability in the battery. Multiple structural analysis tools and techniques were used to determine how the copper and vanadium doping effected the P2-type structure of the cathode material. The material characterization was performed using the Rigaku Ultima IV diffractometer with an ultra-high-speed detector over the range from 10˚ to 80˚ at a scan speed of 2˚/min with Cu Kα radiation (power setting 40kV, 44mA). Rietveld refinements on the XRD patterns as well as a thorough analysis of the lattice parameters and d-spacing were performed to determine the effects of the Cu and V doping (1%, 2%, 3%, and 5%) with respect to the pristine NFM cathode material. The pristine NFM cathode material resulted in a P2-type crystal structure with lattice parameters of a=b=2.9170Å and c=11.3032Å which resulted in the d-spacings of 2.043Å in the transition metal oxide layer and 3.607Å in the sodium layer. The 1% doped cathode material resulted in an increase in the d-spacing of the transition metal oxide layer and a decrease in the d-spacing of the sodium layer. The 2% doped cathode material resulted in a decrease in the d-spacing of the transition metal oxide layer and an increase in the d-spacing of the sodium layer with respect to the 1% doped cathode material. This change in d-spacing could show a trend with respect to a higher percentage of doping with Cu and V. Morphological assessment of the pristine and doped NFM cathode materials were performed using scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDAX). All the synthesized samples had prismatic hexagonal shaped particles conforming to the space group P63/mmc and having an average size in the range of 1-5µm. The elemental mapping results verified a homogeneous distribution of Cu and V throughout the cathode material. It was observed that all the elements were evenly dispersed throughout the surface, confirming uniform doping into the crystal structure.

Improved analysis methods to study the behavior of potassium ions in the interlayer of montmorillonite

The behavior of potassium chloride (KCl) as a main mud shale inhibitor remains poorly defined in the interlayer of montmorillonite (Mt). In this paper, a new analysis method of transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) was established. The distribution of K+ in the interlayer of Mt and the processes surrounding d-spacing shifts in Mt were investigated through X-ray diffraction and TEM-EDS. The experimental results revealed shoulder peaks in the diffraction patterns at KCl concentrations between 11% and 19%. The distribution of K+ varied in the inner and outer layers of Mt with different KCl concentrations. It could be concluded that the distribution of K+ and the changes in d-spacing of Na are determined by two factors: negative charge sites and concentration difference. When the KCl concentration was below 8%, both factors cause the outer layer of Mt to adsorb more K+ than the inner layer, with all layers exhibiting d-spacings within the 1.50nm state. At an 8% KCl concentration, all negative charge sites were occupied by K+. As the KCl concentration rose above 8%, the outer layer of Mt adsorbed more K+ than the inner layer due to the concentration difference. With a further increase in the KCl concentration, the d-spacing shifted linearly to 1.30nm from the outer to the inner layer of Mt. All layers of Mt exhibited a d-spacing of 1.30nm at KCl concentrations of up to 23%. These results demonstrate the benefits and capabilities of the proposed method in investigating the intercalating mechanisms of Mt.

Study of thermal and structural characteristics of mechanically milled nanostructured Al-Cu-Fe quasicrystals

Single phase nanostructured Al-Cu-Fe quascrystalline powders, with various grain sizes, were synthesized by low intensity mechanical milling of spray deposited icosahedral quasicrystals. Structural evolution as a function of temperature was studied in-situ using high energy synchrotron X-ray diffraction. Coefficient of thermal expansion was calculated using the change in d-spacing. The diffraction results revealed a change in the lattice parameter, grain size and quasi-lattice strain with increasing temperature. During heating, onset of appreciable grain growth in different nanostructured quascrystalline powders was observed at a certain critical temperature, which was closely related with the milling time. Quasicrystalline powders milled for 1 and 80 h exhibited appreciable grain coarsening at 923 and 573 K, respectively. For all the samples, the activation energy for grain growth (Egg) was ~30–35 kJ/mol. In addition, the β Al(Cu,Fe) phase with B2-type structure evolved during heating of powder samples milled for 10 h. Onset temperature for β phase formation showed an inverse relationship with the milling time.

Elemental partitioning in medium Mn steel during short-time annealing: An in-situ study using synchrotron x-rays

In this study, high energy synchrotron radiation was used to perform an in-situ diffraction experiment in medium Mn Fe-6Mn-0.5C-1Al alloy to study the elemental partitioning and consequent austenite phase evolution at different stages, namely, during heating, holding and cooling. It has been observed that the austenite phase fraction significantly increases on annealing at the inter-critical annealing temperature and remains stable at room temperature. The austenite phase stability at room temperature is due to the rapid partitioning of manganese (Mn) and carbon (C) during annealing. The relative change in d-spacing (Δd/d) during heating-cooling confirms the partitioning of alloying elements during inter-critical annealing.

Effects of Various Graphite Cathodes on Self-Discharge Behavior of Rechargeable Aluminum Batteries

Renewable energy technologies, such as wind power and solar energy, have become great importance in modern society [1]. Unfortunately, the intermittent nature of these energies leads to a huge barrier in energy generation and stabilization in electricity supply [2]. The rechargeable batteries received a lot of attention due to high energy density and satisfactory cycle life. Rechargeable aluminum batteries (RABs) gain a great amount of research interest in recent times due to the low cost of aluminum compared to that of lithium. Aluminum, being the most abundant metal in the earth crust, has three-electron transfer characteristic, high volumetric capacity, and great safety, which make RABs suitable for large-scale energy storage [3]. However, problems like low discharge voltage, high corrosion of electrolyte, serious self-discharge impede the growth and development of RABs. Jiao’s group demonstrated self-discharge phenomena for Ah-level RABs, where self-discharge rate was about 6%/day [4]. Their research only presented the self-discharge phenomena, but not studied the factors affecting self-discharge behavior. Self-discharge is an important issue for practical applications. The self-discharge rate of RABs is much higher than that of commercial lithium-ion batteries, whose self-discharge rate is approximately 5%/month. It is thus necessary to investigate the factors affecting self-discharge properties of RABs. In this work, effects of various types of graphite cathodes on charge-discharge properties and self-discharge behavior in ionic liquid electrolyte are studied. The results demonstrate that the changes in d-spacing and morphology of the graphite are crucial. The phase transformation of the graphite cathode during charging/discharging and self-discharge is examined using in-situ X-ray diffraction (performed at National Synchrotron Radiation Research Centre, Taiwan). The reaction mechanism is discussed in details.

Rapid Elemental Partitioning in Medium Mn Steel During Short Time Annealing: An In-Situ Study Using Synchrotron X-Rays

High energy synchrotron radiation was used to perform an in-situ diffraction experiment in medium Mn Fe-6Mn-0.5C-1Al alloy to study the elemental partitiong and austenite phase evolution at different heating, holding and cooling stages. It has been observed that austenite phase fraction increases at inter-critical annealing temperature significantly and it remains stable at room temperature. Austenite phase stability at room temperature is due to rapid partitioning of Mn and C during annealing. The relative change in d-spacing (Δd/d) during heating-cooling indicates partitioning of alloying elements during inter-critical annealing.

Clay-organic intumescent hybrid system for the synergetic flammability of polymer nanocomposites

A polyethylene vinyl acetic acid (EVA) nanocomposite comprising of an intumescent agent that incorporates ammonium phosphate monobasic, mono-pentaerythritol, and melamine with a cationic nanoclay was set up through solution blending and melt blending to assess the fire retardancy utilizing a cone calorimeter. The results demonstrated that there was a significant reduction in the peak heat release rate of 70% contrasted with pure EVA. The fire retardancy of the clay-organic intumescent mixture framework composite was more successful than a same amount of additional nanoclay and intumescent agent. To check these outcomes, the residues of cone calorimeter samples were assessed alongside clay d-spacing changes amid utilization.

Acellular dermal matrix collagen responds to strain by intermolecular spacing contraction with fibril extension and rearrangement.

Acellular dermal matrix (ADM) materials are used as scaffold materials in reconstructive surgery. The internal structural response of these materials in load-bearing clinical applications is not well understood. Bovine ADM is characterized by small-angle X-ray scattering while subjected to strain. Changes in collagen fibril orientation (O), degree of orientation as an orientation index (OI) (measured both edge-on and flat-on to the ADM), extension (from d-spacing changes) and changes to intermolecular spacing are measured as a result of the strain and stress in conjunction with mechanical measurements. As is already well established in similar systems, when strained, collagen fibrils in ADM can accommodate the strain by reorienting by up to 50° (as an average of all the fibrils). This reorientation corresponds to the OI increasing from 0.3 to 0.7. Here it is shown that concurrently, the intermolecular spacing between tropocollagen decreases by 10% from 15.8 to 14.3Å, with the fibril diameter decreasing from 400 to 375Å, and the individual fibrils extending by an average of 3.1% (D-spacing from 63.9 to 65.9nm). ADM materials can withstand large strain and high stress due to the combined mechanisms of collagen reorientation, individual fibril extension, sliding and changes in the molecular packing density.

A Study of Carbonate Formation Kinetics and Morphological Effects Observed on OH- Form of Pfaem When Exposed to Air Containing CO2

For AEMFC OH- form of membrane reacts with CO2 when exposed to air leading to loss in conductivity. The data published by Yanagi et.al.[1] suggest that OH species reacts to form Carbonate/bicarbonate in few minutes and after 2 h the membrane only consists of carbonate and bicarbonate. Although this is an important data to consider the reaction kinetics, morphological properties and equilibrium concentrations are still unknown at different environmental conditions. We have attempted to study the CO2 kinetics and its transient effect on conductivity, water-uptake (or lambda) and morphology when the OH- form of PFAEM membrane is exposed to air which has approx. 400 ppm of CO2. The kinetics was studied by exposing the membrane to controlled environment and titrating it using Warder and Winkler titration methods. We have studied transient change in small angle x-ray scattering patterns when the films are exposed to air at different conditions to study the change in d-spacing of the ionic domains. From SAXS analysis it can be concluded that the intensity of spectrum drops over time and the time of equilibration is higher at higher humidity. It takes few hours for the conductivity to drop to carbonate/bicarbonate level. Ultimately we want to understand the effect of CO2 on membrane from every aspect and possibly help us think about strategies to mitigate the problem. Keywords: Anionic exchange membrane, Carbonate,bicarbonate,carbon-dioxide, small angle x-ray scattering Ref: [1]Yanagi and Fukuta, ECS transactions,16(2008). Figure 1

Physical and chemical mechanisms affecting electrical conductivity in reduced graphene oxide films

This article focuses on the influence of surface topography (roughness), surface chemistry (carbon and oxygen functional groups) and physical (film thickness) parameters on the electrical conductivity of graphene oxide (GO) and reduced graphene oxide (rGO) films. This study was carried out to understand how changes in chemistry, roughness and film thickness, arising from the reduction process, alter the electrical properties of the films. Improved understanding is needed to control and optimise these parameters in graphene/rGO films for future applications where targeted property performance is needed. Films with smooth surfaces, measured using confocal imaging, and lower thicknesses have been shown to possess higher electrical conductivity. X-ray diffraction patterns shows minor changes in d-spacing, though improvements in crystal perfection, orientation and crystallinity could be concluded. X-ray photoelectron spectroscopy shows a significant decrease in the oxygen present at the surface as the films are exfoliated to reduce their thickness. Conductivity improves as the materials become increasingly defect-free, achieved by careful control of reduction and post-processing techniques. Ideal practical conductivity is achieved for films of 4μm thickness: beyond this point, no practical gains are made (about 25 exfoliation trials from the bulk cast film).

In-situ residual stress analysis during annealing treatments using neutron diffraction in combination with a novel furnace design

A method for in-situ monitoring of residual strain/stress evolution during annealing treatments has been developed using a new induction heating setup designed for neutron strain-scanning instruments. First, time-of-flight neutron diffraction was used for determining the location and level of maximum residual stresses induced by quenching in disc shape samples of Ni-base superalloy Inconel 718. These were found to be in the centre of the samples being 700MPa in tension in radial/hoop directions and −300MPa in axial direction. Subsequently, an in-situ annealing experiment was undertaken at 750°C for 8h in order to monitor the d-spacing evolution in this particular location in the three principal directions and in an attached stress-free sample. The measurements revealed that most stress relaxation occurs during the heating stage as a result of a combination of plasticity and early stage creep relaxation. During the isothermal stage the d-spacing changes measured in the stressed sample were dominated by the evolution of the stress-free d-spacing resulting in only very limited further stress relaxation. Ex-situ measurements after annealing confirmed the in-situ observations at the 8h mark of 60% residual stress reduction validating the in-situ experimental protocol.

Improvements In Electronic Structure And Properties Of Graphene Derivatives

This article focuses on the reduction of graphene oxides using different reductants and conditions systematically varying the chemical and physical structure, surface topography and chemistry and film thickness of reduced graphene oxide (rGO) films, with a focus on how these influence the property of most interest: electrical conductivity. The reduction process restores graphene oxide to a graphene-like structure, improving electrical conductivity while creating changes such as increased roughness, film thickness and new surface functionality. Films with smooth surfaces and minimal thicknesses have been shown to possess higher electrical conductivity. There have been minor changes in d-spacing and improvements in crystal perfection and orientation could be concluded from XRD patterns. Through XPS analysis, a significant decrease in the amount of oxygen functional groups at the surface has been noticed as the films get thinned. Copyright © 2016 VBRI Press.

A study of crystallisation of poly (ethylene oxide) and polypropylene on graphene surface

Crystallisation behaviour of poly (ethylene oxide) (PEO) and isotactic polypropylene (iPP) on graphene surface was investigated by means of polarized microscopy, wide angle X-ray diffraction (WAXD), and Raman techniques. Results indicated that graphene influences the crystallisation and crystal structure of iPP and PEO. WAXD peaks shifting toward lower diffraction angle, i.e. increase in d-pacing, was observed in both PEO and iPP crystallised on the surface of graphene. The change of d-spacing of both PEO and iPP could result from the compressive stress caused by graphene. A shift of 2D band in graphene was observed from Raman spectra. The Raman spectra indicated the big shift in the 2D band is due to the presence of stress induced strain in the polymer attached graphene. The residual stress was generated during crystallization of the polymers on the surface of graphene. Due to the interactions between the graphene and the polymers, the stress was transferred to the graphene which leads to a strain of the graphene. Raman spectra proved the presence of stress generated by the crystallization of the polymers on the surface of graphene.

Effect of microdomain structure on the mechanical behavior of binary blends

The relationship between microphase structure and mechanical response of the binary blends consisting of polystyrene-block-polyisoprene-block-polystyrene copolymer and low molecular weight polystyrene has been investigated. Low molecular weight polystyrene was chosen to obtain uniformly solubilized nano-blends without macrophase separation. The specimens were solution-cast by adding different amounts of homo-polystyrene to acquire different microphase structures. Small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and atom force microscopy (AFM) have been used to study the microdomain and grain structure. It is observed that the structural changes in d-spacing and grain size on account of different amounts of polystyrene alter the mechanical behavior in both monotonic tensile and cyclic tests. The elastic and the Mullins effects are strongly sensitive to the changes in d-spacing and grain sizes. Moreover, the sample with bi-continuous structure shows the largest tensile strength and Mullins effect. In addition, the Mooneye-Rivlin phenomenological model was used to evaluate and explore the relationship between the polymer topological networks and the rubber elasticity of these styrenic nano-blends.

Effect of grinding time on fabricating a stable methylene blue/palygorskite hybrid nanocomposite

The nanoscale dispersion of the crystal bundles or aggregates of natural palygorskite (PAL) is the key factor to prepare a stable PAL-based hybrid nanocomposite. The appropriate grinding process can effectively disaggregate the crystal bundles of PAL as dispersed nanorods and promote its interaction with organic molecules. In this study, a series of methylene blue/palygorskite (MB/PAL) hybrid nanocomposites were prepared by a facile mortar grinding process, and the effects of grinding time on their structure and stability were intensively investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectra, Brunauer–Emmett–Teller (BET), thermal gravimetric analysis (TGA) and UV–vis techniques, as well as the resistance tests to acid, heat and UV-light. It was found that the control of grinding time is the key point affected the stability of hybrid structure, because it greatly influenced the removal of the water molecules, the change of d-spacing of (110) crystal plane and the organic/inorganic interaction between MB molecules and PAL. The aggregates of PAL crystals were highly dispersed as individual nanorods after being ground for 30min, and the MB molecules are more easily to be adsorbed on the nanorods of PAL or be encapsulated in their channels, so the thermal stability, acid and UV-light resistance of the nanocomposites were evidently enhanced.

Exercise prevents β-aminopropionitrile-induced morphological changes to type I collagen in murine bone

This study evaluated the effects of reduced enzymatic crosslinking, exercise and the ability of exercise to prevent the deleterious impact of reduced crosslinking on collagen D-spacing. Eight-week-old female mice were divided into four weight-matched groups receiving daily injections of either phosphate-buffered saline (PBS) or 300 mg kg(-1) β-aminopropionitrile (BAPN) while undergoing normal cage activity (Sed) or 30 min per day of treadmill exercise (Ex) for 21 consecutive days. BAPN caused a downward shift in the D-spacing distribution in Sed BAPN compared with Sed PBS (P<0.001) but not in Ex BAPN (P=0.429), indicating that exercise can prevent changes in collagen morphology caused by BAPN. Exercise had no effect on D-spacing in PBS control mice (P=0.726), which suggests that exercise-induced increases in lysyl oxidase may be a possible mechanism for preventing BAPN-induced changes in D-spacing. The D-spacing changes were accompanied by an increase in mineral crystallinity/maturity due to the main effect of BAPN (P=0.016). However, no changes in nanoindentation, reference point indentation or other Raman spectroscopy parameters were observed. The ability of exercise to rescue BAPN-driven changes in collagen morphology necessitates further research into the use of mechanical stimulation as a preventative therapy for collagen-based diseases.

Poisson's ratio of collagen fibrils measured by small angle X-ray scattering of strained bovine pericardium

Type I collagen is the main structural component of skin, tendons, and skin products, such as leather. Understanding the mechanical performance of collagen fibrils is important for understanding the mechanical performance of the tissues that they make up, while the mechanical properties of bulk tissue are well characterized, less is known about the mechanical behavior of individual collagen fibrils. In this study, bovine pericardium is subjected to strain while small angle X-ray scattering (SAXS) patterns are recorded using synchrotron radiation. The change in d-spacing, which is a measure of fibril extension, and the change in fibril diameter are determined from SAXS. The tissue is strained 0.25 (25%) with a corresponding strain in the collagen fibrils of 0.045 observed. The ratio of collagen fibril width contraction to length extension, or the Poisson's ratio, is 2.1 ± 0.7 for a tissue strain from 0 to 0.25. This Poisson's ratio indicates that the volume of individual collagen fibrils decreases with increasing strain, which is quite unlike most engineering materials. This high Poisson's ratio of individual fibrils may contribute to high Poisson's ratio observed for tissues, contributing to some of the remarkable properties of collagen-based materials.

Surface modification of platinum by laser-produced X-rays

Laser-induced plasma is used as an X-ray source for the growth of hillocks like nanostructures on platinum surface. To generate X-rays, plasma is produced by Nd:YAG laser, which is operated at second harmonics (λ = 532 nm, E = 400 mJ). Analytical grade 5 N pure Al, Cu and W are used as laser targets for X-rays production. X-rays produced from Al, Cu and W plasmas are used to irradiate three analytical grade (5 N pure) platinum substrates, respectively, under the vacuum ∼10−4 torr. XRD analysis shows considerable structural changes in the exposed platinum. The decrement in reflection intensities, increment in dislocation line density, change in d-spacing and disturbance in the periodicity of planes evidently prove these structural changes. Atomic force microscope AFM topographic analysis of the platinum exposed to X-rays emitted from Al, Cu and W targets showed that nanometer-size hillocks are produced on the platinum surface irrespective of the source. It has also been observed that due to these hillocks, the roughness of the surface has increased. Conductivity of hillocks produced from X-rays produced by Al, Cu and W targets is compared and it is shown that the hillocks produced by Al target X-rays have better conductivity compared to the hillocks produced by X-rays from Cu and W targets.