An In Situ Reflectance Spectroscopic Investigation to Monitor Two-Dimensional MoS2 Flakes on a Sapphire Substrate

In this work, we demonstrate the application of differential reflectance spectroscopy (DRS) to monitor the growth of molybdenum disulfide (MoS₂) using chemical vapor deposition (CVD). The growth process, optical properties, and structure evolution of MoS₂ were recorded by in-situ DRS. Indeed, blue shifts of the characteristic peak B were discussed with the decrease of temperature. We also obtained the imaginary part of the MoS₂ dielectric constant according to reflectance spectra. This method provides an approach for studying the change of two-dimensional (2D) materials’ dielectric constant with temperature. More importantly, our work emphasizes that the DRS technique is a non-destructive and effective method for in-situ monitoring the growth of 2D materials, which is helpful in guiding the preparation of 2D materials.     

Survival of single crystal sapphire implants supporting mandibular overdentures

One hundred and sixteen sapphire (Bioceram, Kyocera) implants were inserted in 30 patients between 1984 and 1991 to support mandibular overdentures. Survival analyses were made on the basis of clinical and radiographic follow-up evaluation for 15 patients with 56 implants. For the 15 patients who were lost to follow-up, 7 of whom were deceased, reviews of records and available radiographs determined outcome and observation time. The resulting Kaplan-Meier cumulative survival rate for the sapphire implants was 68.66%, mean survival time 11.44 years, 95% confidence interval 10.56-12.32 years. Uni- and multivariate analysis using the Cox Regression model, indicated an increased risk of implant failure in patients over 60 years at time of operation, and in patients who smoke. Limited experience in implant surgery were associated with increased implant failure rate. A qualitative analysis of survived implants showed a mean annual bone loss of 0.2 mm, moderate to excellent plaque control, and excellent to good subjective global assessment of the treatment. The long-term results of the sapphire implant system used for mandibular overdenture support are inferior to other implants systems.     

Physical properties of sapphire fibretips for laser angioplasty

The physical properties of sapphire contact probes were examined with respect to their use in laser angioplasty. The rounded and bullet-shaped probes are mechanically atraumatic and provide tactile feedback during laser angioplasty. The optical transmission characteristics of the flat, rounded and bullet-shaped probes were measured and the propagated laser beam profiles photographed in air and water. These properties are largely wavelenght independent in the small part of the spectrum currently used for laser angioplasty. Sapphire contact probes may heat up from direct absorption of laser light at the interfaces, but they probably also heat up by conduction from the heated tissue with which they are in contact. The rounded and bullet shaped probes focus light to a rather diffuse waist in air, but in water this focusing effect is lost. The divergence angle of the bare fibre is reduced in water. Transmittance characteristics depend on surface reflection, absorption, probe shape and surface smoothness. The flat probes transmitted 85% of the incident light, but the rounded and bullet probes absorbed and scattered almost half of the light.     

External drainage of subretinal fluid with a contact Nd:YAG laser

We used a Nd:YAg laser fit with a fiberoptic cord and sapphire tip to drain subretinal fluid externally in patients with rhegmatogenous retinal detachment. The direct contact between the laser and the choroid allowed for controlled cutting and coagulation of the intervening choroidal vasculature. The drainage was successfully achieved with no complication.Supported in part by a grant from Research to Prevent Blindness, Inc., New York City, and by Core grant EY1972 from the National Eye Institute, Bethesda, MD.     

Comparison of tissue effects with sculptured fiberoptic cables and other Nd:YAG laser and argon laser treatments.

The use of a fiber optic cable in contact with tissue results in a complex thermal interaction between the cable and the tissue. The effect of the laser-tissue interaction was investigated using sculptured quartz fiber optic cables, sapphire contact rods, and bare fiber optic cables attached to the Nd:YAG laser. The laser-tissue effects of the Nd:YAG and argon lasers were compared. Examination of treated animals showed there to be a significant difference between immediate and 48-hour thermal effects. The sculptured fibers created significantly less tissue damage than the sapphire contact tips, the 0.6-mm bare fiber, or the argon laser with a 0.3-mm bare fiber either with or without contact. All Nd:YAG laser contact treatments were less damaging than the argon laser treatments.     

Catastrophic injury secondary to the use of coaxial gas-cooled fibers and artificial sapphire tips for intrauterine surgery: a report of five cases

Five women undergoing endometrial ablation with the Nd-YAG laser developed sudden gas embolism. In each case laser intrauterine contact surgery was carried out utilizing coaxial fibers with (three cases) and without (two cases) artificial sapphire tips but commonly cooled by air or nitrogen. Four of the five women died in a sequence of sudden cardiovascular collapse followed by irreversible cardiac arrest. One woman was critically ill and following prolonged hospitalization survived with neurological deficits.     

Laser Raman spectrum of calcified human aorta.

Raman spectra of highly calcified areas of human aorta were obtained using long wavelength excitation at 740 nm to minimize background fluorescence interference. Raman spectra resembling that of hydroxyapatite were obtained for segments of highly calcified aorta that were thawed frozen samples, from which the surface layer had been removed, or were dried. These are the first reported spectra obtained in air or in normal saline solution showing the hydroxyapatite peak in calcified plaque for samples which were untreated except for freezing, which is encouraging for the application of Raman spectroscopy as a method of detection of plaque during laser angioplasty. Spectra obtained from calcified aorta using excitation at 514.5 nm did not show evidence of the hydroxyapatite band because of the severe interference by background fluorescence generated at this wavelength.     

Epitaxial Growth of GaN on Magnetron Sputtered AlN/Hexagonal BN/Sapphire Substrates

Magnetron sputtering is adopted to deposit ~25 nm thick AlN on the surface of hexagonal BN(h-BN)/sapphire substrates, followed by epitaxial GaN growth on top of the AlN/h-BN/sapphire substrate using a metal–organic chemical vapor deposition system. Compared to GaN grown on the h-BN/sapphire surface directly, this method results in a continuous and smooth GaN film with a smaller root mean square roughness. Besides, the introduction of the sputtered AlN layer reduces the dislocation density of GaN by 35.7%. We provide a pathway of GaN epitaxy on the h-BN surface, which significantly improves its surface morphology and crystal quality.