Crater-like Defects Research Articles

Crater-free monolayer graphene above the 2D Si film on SiC(0001) formed via SiSn cointercalation and Sn deintercalation

When Si atoms are intercalated under the graphene-like zero layer (ZL) generated on the SiC(0001) substrate, the resulting quasi-free-standing monolayer graphene (QFMLG) has lots of crater-like defects due to a strong Si-C reaction. Here, a method for creating crater-free QFMLG above a two-dimensional Si film is investigated using scanning tunneling microscopy and photoemission spectroscopy. The method involves forming a SiSn interfacial film as a precursor via cointercalation performed by sequential Sn and Si deposition on the ZL at room temperature and annealing at 650–700 °C. The Sn atoms prevent reactive Si atoms from directly contacting the ZL, which would otherwise cause SiC defects. The sample is then annealed at 750 °C to selectively remove the Sn atoms from the SiSn interfacial film, leaving a well-ordered Si film. The SiSn film composed of a bottom Si layer and top Sn atoms has a short-range-ordered “2 × 2” or a long-range-ordered 2×7 superstructure depending on the annealing temperature and the Sn coverage. Both the superstructures are semiconducting and induce less n-doped QFMLG than the pure Si film.

Failure Analysis of Inconel 601 Radiant Tubes in Continuous Annealing Furnace of Hot Dip Galvanizing Line

Metallurgical investigation was conducted to establish the genesis of crater-like defects and perforations in Inconel 601 radiant tubes used in Radiant Tube Heating/ Radiant Tube Soaking (RTH/RTS) section of the Continuous Annealing Furnace in Hot Dip Galvanizing Line (HDGL) of an integrated steel plant. The radiant tubes, several of them, had undergone catastrophic damage after only about 70 days of service under mixed gas firing inside the furnace. Visual examination, chemical analysis and secondary electron imaging (SEI) coupled with energy-dispersive x-ray spectrometry (EDS) were concomitantly utilized for the investigation of failed radiant tube samples. Based on the findings, the unprecedented failures were attributed to the high temperature sulphidation attack experienced by the tubes on their inner walls, owing to sulphur dioxide (SO2) resulting from combustion of hydrogen sulphide (H2S) in the mixed gas (2H2S + 3O2 → 2H2O + 2SO2). The investigation also pointed toward the apparent formation of low-melting nickel-nickel sulphide (Ni-Ni3S2) eutectic because of sulphidation, which led to unique spherical manifestations of the defects and served to highlight the deleterious influence of sulphur-bearing compounds on nickel-base alloys at high temperatures. Suitable alternative materials of construction are proposed for the radiant tubes operating under such environments.

Condition of Surface of Titanium after Pulsed X-ray Exposure

The effect of the pulsed soft X-ray flux on the topography of surface the VТ 1-0 titanium alloy has been studied. The radiation energy density on the surface of the sample is ~10 J/cm2 for one pulse. It is found that a corrugated topography is formed on the surface of titanium as a result of melting followed by freezing: a cellular- or mesh-type topography is formed after one X-ray pulse, the mesh-type topography becomes more sharply defined after two pulses, and the surface of titanium is melted and the mesh structure is almost invisible after three pulses. Crater-like defects are not found, but small cracks are formed on the surface of titanium after melting caused by pulsed X-ray exposure followed by fast cooling of the molten metal.

RADIOGRAPHIC PREDICTORS OF BONE EXPOSURE IN PATIENTS WITH STAGE 0 ONJ

Background Osteonecrosis of the jaws (ONJ) is a severe adverse effect of antiresorptive medications. Although the diagnosis of ONJ is based on the presence of necrotic bone in the oral cavity, patients at the initial phase of the disease (stage 0 ONJ) can present without bone exposure.1 Approximately 50% of stage 0 ONJ patients develop bone exposure within 6 to 12 months of initial presentation.2 However, diagnostic predictors of stage 0 ONJ progressing to clinical ONJ are absent. Objectives The aim of this study was to investigate stage 0 ONJ radiographic features associated with subsequent clinical exposure. Materials and Methods Files from 14 patients with stage 0 ONJ (history of antiresorptive medication and nonspecific clinical symptoms) were utilized. Imaging included panoramic radiographs and CBCT scans. Additionally, clinical photos were obtained. Cortical erosion, sclerosis, sequestration, periosteal reaction and crater-like defects were assessed as localized or extensive. Patients were followed up for 6 months to 2 years and absence or presence of clinical exposure was noted. Results Two patients reported a history of recent extraction, 3 were edentulous and 9 were dentate. Of the patients, 50% (7 of 14) presented with cortical erosion, 43% (6 of 14) showed bony sequestration or bony spicules, 50% (7 of 14) demonstrated crater-like defect, 50% (7 of 14) had extensive sclerosis, and 36% (5 of 14) presented with periosteal reaction. In follow-up, 50% (7 of 14) of patients with stage 0 ONJ developed clinical exposure during the observation period. Patients with subsequent exposure presented more frequently with abnormal radiographic findings. Interestingly, 6 of these patients presented with sequestration or bony spicules at the initial appointment. All patients with sequestrum advanced to clinical ONJ. Discussion Our data show an association of radiographic findings, in particular of sequestration, with development of bone exposure, and emphasize the importance of a thorough radiographic assessment in patients with suspected stage 0 ONJ. Currently, we are expanding our patient population to increase the statistical power of our studies.

Amelioration of Aorta Morphology in Spontaneous Hypertensive Rat (SHR) by Syzygium Polyanthum

Background: Prolonged uncontrolled hypertension can lead to vessels damage; manifested as abnormal morphology changes. Sygyzium polyanthum has been shown to has blood pressure lowering effects in SHR rats. Objective: This study was designed to evaluate the improvement effects of S. polyanthum aqueous leave extracts (AESP) on the descending thoracic aorta morphology damaged secondary to hypertension. Material & Methods: Twenty-one rats were used in this study, with 7 rats in each group. Group 1: normotensive Wistar Kyoto (WKY) rat, Group 2: untreated SHR, Group 3: SHR on AESP (2250 mg/kg). AESP was orally administered daily for 3 months. The descending thoracic aorta was harvested at the end of the study. The aorta morphology was evaluated using Hematoxylin and Eosin stain (H&E stain) and Scanning Electron Microscope (SEM). Systolic blood pressure (SBP) were also recorded every 2 weeks during the study. Results: On HE stained, treatment with AESP increased the endothelial cell lining on the surface of aortic tunica intima. The endothelial lining also notably smoother. The elastic laminae were not discontinued and more regular pattern of vascular smooth muscle cells with elongated nuclei. The thickness ratio of tunica media to tunica intima was also reduced. Under SEM, the surface of the aorta was smoother and there were no crater-like defects as compared to untreated SHR. There were also no inflammatory cells or fibrinogen seen as on the aortic surface of untreated SHR. The SBP in AESP-treated SHR was significantly reduced (107.00 + 1.68 mmHg) as compared to untreated SHR (199.75 + 2.86 mmHg, p<0.001). Conclusion: S. polyanthum improves the morphology of aorta and also significantly reduces the blood pressure.

Isolated crater formation by gas cluster ion impact and their use as templates for carbon nanotube growth

Crater-like defects formations with gas cluster ion beams (GCIB) were used as templates for carbon nanotube (CNT) growth. Upon a gas cluster ion impact, dense energy is deposited on a target surface while energy/atom of gas cluster ion is low, which creates crater-like defects. Si and SiO2 were irradiated with Ar-GCIB, subsequently CNTs were grown with an alcohol catalytic CVD using Co and ethanol as catalyst and precursor, respectively. From SEM, AFM and Raman spectroscopy, it was shown that growth of CNT with small diameter was observed on SiO2 with Ar-GCIB irradiation. On Si targets, formation of craters with bottom oxide prevented Co diffusion during CNT growth, as a result, CNT growth was observed only on Si irradiated with high-energy Ar-GCIB. These results showed that isolated defects created by GCIB can be used as templates for nanotube growth.

Novel Endoscopic Finding Associated With Gastrointestinal Hemorrhage in a Post-Stem Cell Transplant Patient With Light Chain Amyloidosis

A 67-year-old woman with a incidental diagnosis of amyloidosis lambda subtype (AL-amyloid) presented with melena after therapy with heparin for an upper extremity deep vein thrombosis. She had undergone induction treatment with bortezomib, cyclophosphamide, weekly dexamethasone, and an autologous stem cell transplant 40 days prior to admission. Laboratory results revealed hemoglobin 5.9 g/dL and prothrombin time (PT) 84.8 seconds. An magnetic resonance imaging (MRI) of the abdomen and pelvis noted circumferential thickening of the duodenum and proximal jejunum. Upper endoscopy revealed multiple circular, shallow, 2–3-mm crater-like defects of the mucosa creating an appearance of a “moon surface mucosa” throughout the duodenum and jejunum (Figure 1). Duodenal biopsies revealed amyloid deposits involving the lamina propria, submucosa, and blood vessels. Congo red stain for amyloid was positive and showed birefringence under cross-polarized light microscopy (Figure 2).

Electrochemical corrosion and bioactivity of titanium–hydroxyapatite composites prepared by spark plasma sintering

The corrosion resistance and bioactivity of titanium–hydroxyapatite (Ti–HA) composites prepared by mechanical alloying (MA) followed by spark plasma sintering were investigated. Potentiodynamic polarization tests showed that Ti composites containing 0–10% HA exhibited higher corrosion resistance than commercially pure Ti. An increase in HA concentration (20–30%) decreased corrosion resistance owing to the craterlike defects induced by ceramic particle detachment. Increasing MA time significantly reduced defect density and improved corrosion resistance. Bioactivity test on Ti HA composites in simulated body fluid revealed the growth of a nano-HA layer, which indicates the high potential of Ti–HA composites for application in biomedical implants.

Improved wear resistance of magnesium alloys AZ91 by high current pulsed electron beam treatment

Surface modification of magnesium alloy AZ91 by high current pulsed electron beam (HCPEB) was investigated in the present work. After irradiated by HCPEB, crater-like defects were found scattering on the modified surface, when increasing pulse number, the density of craters sharply reduced. According to XRD analysis, hard intermetallic phase Mg17Al12 would sappear after several pulse of HCPEB treatment that is accordance with the improvement of wear resistance, but more pulses will lead to the solution of Mg17Al12 phase. Ultimately, due to the thickest depth of modified layer, sample treated with 30 pulses and accelerating voltage of 27 kV exhibited the best wear resistance, the depth of wear track decreased from 12.75 µm in initial state to 7.82 μm.

Instability of anodically formed TiO 2 layers (revisited)

On the occasion of the 4th Gerischer Symposium, a remarkable Ti anodising experiment first reported in 1978 by Di Quarto, Doblhofer and Gerischer has been reproduced. The key observation of the original experiment was the presence of a fast cell voltage decay occurring when the current during galvanostatic Ti anodising was decreased below a critical, low threshold value. In order to reveal the origin of this instability, which at the time was suggested to be mechanical in nature, chronopotentiometric data have been combined with high resolution in situ curvature measurements, the latter allowing to monitor the internal stress evolution during anodising. Our synchronised in situ electrochemical and curvature measurements have confirmed for the first time the previously assumed sequence of phenomena underlying the reported instability (O 2-evolution, oxide swelling, oxide delamination and oxide regrowth) through their mechanical consequences (curvature noise, electrostriction jumps and growth stress transitions). However, no evidence could be obtained as to a possible mechanical origin of the instability itself. Instead, based on detailed SEM and TEM inspection, a link with the microstructural evolution has been establised, involving the presence of anatase micro-crystals in the early stages of anodising. Local gas evolution at these anatase crystals is then believed to lead to the gradual appearance of open, crater-like defects on the oxide surface, which in turn allow for electrolyte penetration during the voltage decay when gas evolution at these surface features has stopped.

Preferential Sputtering of DNA Molecules on a Graphite Surface by Ar Cluster Ion Beam

The process of sputtering by bombardment with gas cluster ions was investigated from the perspective of the kinetic energy per constituent atom (E atom ) of an incident cluster ion, which determines the threshold for the formation of craterlike defects by irradiation of an argon gas cluster ion beam (Ar-GCIB) onto a graphite surface. Furthermore, DNA molecules adsorbed on a graphite surface were preferentially sputtered by adjusting E atom of the Ar-GCIB down to this threshold, while the substrate graphite surface retained its carbon lattice structure without the formation of craterlike defects. These results indicate that a GCIB could be used as a primary ion beam for secondary ion mass spectrometry (SIMS), which would enable the preferential analysis of an adsorbed layer on a substrate without causing damage to the substrate.

Biomechanical consequences of progressive marginal bone loss around oral implants: a finite element stress analysis

The purpose of this study was to explore the biomechanical effects of progressive marginal bone loss in the peri-implant bone. Finite element model of a Ø 4.1 x 10 mm Straumann dental implant and a solid abutment was constructed as predefined eight-layers around the implant neck. The implant-abutment complex was embedded in a cylindrical bone model to analyze bone biomechanics regardless of anatomical influences. Angular and circular progressive marginal bone loss was simulated by sequential removal of each layer, resulting crater-like defects and a total of ten finite element models for analysis. Each model was subjected to a vertical and oblique static load of 100 N in separate load cases. Principal stress minimum and maximum, displacement, and equivalent of elastic strain outcomes were compared. Under vertical loading, principal stresses minimum and maximum decreased remarkably as with the increase in bone resorption. Under oblique load simulations, decrease in principal stress maximum and minimum was evident. With progressive bone loss and under oblique load simulations, displacement and equivalent of elastic strain increased considerably in trabecular bone contacting the implant neck. The presence of cortical bone contacting a load-carrying implant, even in a bone defect, improves the biomechanical performance of implants in comparison with only trabecular bone support as a sequel of progressive marginal bone loss.

Effect of Selenium Compounds on the Damage Induced by Oxysterol on Rat Arterial Walls

Wistar rats were fed Se-deficient (0.017 +/- 0.002 mg Se/kg) and Seadequate (0.32 +/- 0.045 Se mg/kg) diets for 12 mo and then were given 5 mg/kg of cholestane-3beta,5alpha,6beta-triol (3-triol), intravenously. Se compounds (Na(2)SeO(3) and ebselen) were supplemented in different doses and times to the Se-deficient rats. Twenty-four hours after 3-triol infusion, the changes in ultrastructures of rat aorta were examined by scanning electron micrography (SEM) and transmission electron micrography (TEM). SEM examinations showed that 3-triol induced diffused injuries on arterial endothelial urfaces of long-term Se-deficient rat, and a large number of holes or craterlike defects were observed. TEM examinations further showed that 3-triol induced swelling, necrosis, and shedding of endothelial cells, which resulted in the destruction of endothelial integrity. Meanwhile, smooth muscle cells proliferated and migrated toward intimae; the breakage of internal elastic lamina benefited the migration of smooth muscle cells. Supplemented with Na(2)SeO(3) (40 microg/kg, 10 d per continuum) and ebselen (20 mg/kg), respectively, exhibited significant protection from damages induced by 3-triol. It seems that protecting mechanisms were different between Na(2)SeO(3) and ebselen. The present investigation gave visual evidence that both injuries induced by cholesterol oxides and the Se nutritional status contributed to the development of atherosclerosis.

Role of selenium in cytoprotection against cholesterol oxide-induced vascular damage in rats

Wistar rats were fed Se-deficient (0.038 mg/kg diet) and adequate (0.326 mg/kg diet) diets for 13 weeks. The blood Se content, blood and vascular wall glutathione peroxidase (GPx) activity, serum high-density lipoprotein cholesterol (HDL-C) level and plasma prostacyclin (PGI 2) concentration were decreased significantly, and the blood lipid peroxide (LPO) concentration, serum low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC) level and plasma thromboxane A 2 (TXA 2), content were increased significantly in Se-deficient rats compared with Se-adequate group, respectively. Furthermore the Se-deficient and adequate rats were given 5 mg/kg of cholestane-3β, 5α, 6β -triol (3-triol) or vehicle only. Twenty four hours after treatment, the plasma PGI 2 level was decreased in Se-adequate rats infused 3-triol (+3 triol), meanwhile, the level in Se- deficient +3-triol group was much lower than that in Se-adequate +3-triol group. Compared with Se-adequate group, plasma TXA 2 content in Se-adequate +3-triol group had no significantly difference, but in Se- deficient rats infused 3-triol, plasma TXA 2 content was much higher than that in Se-adequate +3-triol group. The plasma ET concentration in Se-deficient group decreased slightly, but the concentration in Se-adequate +3-triol group increased significantly with respect to Se-deficient group. Although plasma ET concentration in Se-deficient group +3-triol did not increase, it was significantly lower than that in Se-adequate +3-triol group. The luminal surfaces of aorta thoracica of experimental rats were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Observed by SEM, the luminal surface of aorta of Se-deficient rats showed few crater-like defects due to the disruption of endothelial cell. Se-adequate +3-triol group showed some crater-like defects on the their aorta luminal surface, but the luminal surface of Se-deficient +3-triol group exhibited numerous crater-like defects and appeared sponge-like as well as platelets adhering followed by thrombus formation in focal area of extensive endothelial damage. TEM studies also showed that the endothelium of aorta of Se deficient +3-triol group had more frequent lesion where endothelial cell plasma were swelling with profuse intracellular edema and some vacuoles were seen in cytoplasm. In severely injured areas, endothelial integrity was completely destroyed and smooth muscle cells were proliferating and migrated to the endomembrane. Thus, we can conclude that Se or selenoproteins in the vascular wall plays an important role in cytoprotection against cholesterol oxide-induced vascular damage in rats.

Ion-induced craters on the surface of benzoyl glycine single-crystals studied by scanning force microscopy

Crater-like defects on the surface of ion-irradiated organic single-crystals of benzoyl glycine (BG, hippuric acid) are imaged by scanning force microscopy (SFM). The crystals are irradiated by Xe, Pb, Bi and U with specific kinetic energy 11.4 MeV/u and fluences 5×10 9 and 1×10 10 ions/cm 2 . In this energy range, the energy loss along the projectile trajectory is almost exclusively electronic. The areal density of the craters matches with the ion fluence confirming that each crater is the result of a single ion impact. The mean crater diameters range from 25 to 50 nm and exhibit a linear dependence on the ion energy loss. Assuming that the shape of the craters is a section of a sphere, mean crater volumes are calculated using the mean diameters and depths extracted from SFM images. These volumes are of order 1 – 5×10 3 nm 3 and have a steep dependence on the energy loss. On average, 10 4 molecules have been ejected from each crater.

Assessment of Silicon Wafer Material for the Fabrication of Integrated Circuit Sensors

The influence of process induced defects on the surface quality of wet anisotropically etched cavities in silicon wafers is investigated. Localized thinning of silicon substrates using cavities of this kind is a common method for fabricating, e.g., diaphragms for silicon pressure sensors. Wafers with four different concentrations of interstitial oxygen varying from to were exposed to a thermally simulated complementary metal oxide semiconductor process and subsequently anisotropically etched with potassium hydroxide or tetramethylammonium hydroxide solution. Crystal defects caused by oxygen precipitation, such as stacking faults, punching systems, and dislocations, were found to be the origin of large craterlike defects in the sidewalls of the cavities. Wafer material with an initial concentration of interstitial oxygen between and exhibits a very low density of small precipitate‐dislocation complexes and, thus, etched cavities of good surface quality are obtained. In wafers with interstitial oxygen concentrations higher than bulk stacking faults were observed and the surface quality of the cavity sidewalls diminishes. The microscopic morphology of the craterlike defects in the {111} sidewalls of the etched cavities is explained using a computer simulation of the etching process. An influence of process induced defects on the surface quality of wet anisotropically etched {100} surfaces was not found. © 2000 The Electrochemical Society. All rights reserved.

MeV-ion-induced defects in organic crystals

We present scanning force microscope images of crater-like defects induced by MeV atomic ions incident on single-crystal L-valine surfaces. For grazing incidence ions, the craters are elongated alongthe ion azimuth of incidence and are followed by raised tails in the surface above the ion track. Craters formed by off-normal ions are wider than craters formed by nrmally incident ions. The crater volume is highly nonlinear in (dE/dx) e. We discuss our observations qualitatively in terms of thermal-spike and pressure-pulse/shock-wave models for the sputtering of organic solids.

Scanning-force-microscopy study of MeV-atomic-ion-induced surface tracks in organic crystals.

We present scanning force microscope images of craterlike defects induced by individual 78.2-MeV [sup 127]I ions incident on organic single-crystal [ital L]-valine surfaces. For grazing incidence ions, the craters are elongated along the ion azimuth of incidence and display a raised tail in the surface above the ion track. This permanent plastic deformation of the surface indicates that a hydrodynamic pressure-pulse phenomenon occurs in response to the electronically deposited energy.

A molecular dynamics study of radiation induced electrostatic disruption of insulator surfaces

We apply a molecular dynamics simulation to study radiation induced electrostatic disruption of insulator surfaces. With a scaled Lennard-Jones potential, we construct a model for 600 atoms in a 2D surface surrounded by the bulk of the solid. Electrostatic disruption is initiated by placing single positive charges on two to five neutral atoms in the surface region. We identify three stages of the disruption process. First, rapid ejection of several atoms (5 to 15) occurs at ~ 0.5–2.0 ps, compared to the Debye period 0.1 ps. Next, after 1 to 5 ps many atoms in the vicinity of the charged region are greatly disturbed. Crater-like defects and voids are generated by the Coulomb explosion, and atoms are piled up at the surface. Third, the temperature of the region near the explosion becomes higher than the background temperature and enhances sublimation and annealing of atoms in this region even at much longer times. It is shown that fluxes and density of ionization for high-energy protons in the space environment are such that electrostatic disruption may produce considerable damage of exposed surfaces of good insulators.

Thermostability and photodesorption of Langmuir-Blodgett films

We report on thermodesorption and photodesorption studies of cadmium and magnesium arachidate Langmuir-Blodgett films using a newly developed optical reflection technique and Nomarsky light microscopy. The mechanism of thermodesorption can be described as a process where only those parts of a monolayer desorb that are exposed to air in the normal direction. However, molecules in the inner monolayers can also be removed by photodesorption. This is understood within a model of defect-mediated desorption where the action of light is twofold: it creates defects and provides energy to overcome binding. The model explains the sigmoidal desorption kinetics and the independence of this kinetics on film thickness and is supported by the observation of grain structure during the desorption process. The latter indicates that crater-like defects are generated throughout the entire depth of the film.