Implantation and Activation of Phosphorus in Amorphous and Crystalline Germanium Layers

We have investigated phosphorus implantation and activation in amorphous and crystalline Ge layers, deposited on Si substrates. The structure of the Ge layer has only limited influence on the dopant profile and diffusion after annealing. Surprisingly, crystalline Ge layers show better electrical results after implantation and dopant activation. For the amorphous layer, the solid phase epitaxy process is influenced in the neighborhood of P, leading to point defects, which inhibit electrical activation. This result implies that when a crystalline Ge layer is amorphized during implantation of high doses, the dopant activation can be significantly reduced. Reduced temperature ramping improves activation of P in amorphous Ge layers

Intrinsic Point Defects in a-SiO2 with Embedded Si Nanoparticles Probed by ESR.

Using the electron spin resonance (ESR) technique as basic experimentaltool, this PhD thesis is concerned with an elaborate study of, mostly native, point defects in different kinds of structures consisting of nanocrystalline-Si particles embedded in an a-SiO2 matrix. This includes superstructures manufactured through thermal treatment of the as deposited SiO/SiO2 multilayers on Si substrates, and Si+ implanted thermal SiO2 assisted by in situ ultrasound treatment. Additionally, the efforts given to trace the true atomic nature of the illusive E δ defect in a-SiO2 can be seen along these lines. We monitored and characterized the different varieties of point defects in those structures both in the as-produced state as well as after different treatments such as annealing in different ambient gases (N­2, Ar, room ambient, H2) and pre- or post-anneal irradiations (UV, VUV, and γ-rays) to alter the paramagnetic point defect densities, that is, lowering them in the case of nc-Si's but increasing them in the case of E δ defect investigation.As tonc-Si/SiO2 superstructures, an important result attained by combining extensive ESR and photolumenscence (PL) spectroscopies in combination with passivation and depassivation treatments of paramagnetic defects, is the demonstration of the possibility of switching from defect related PL to quantum confinement originating PL and vice versa in the same sample.The superb microscopic Si/SiO2 properties are retained down to the nanoscale . The interfacial Pb(0) type center is traced as main PL quenching center.In a next part, the ESR technique has first been applied to asses the effects of in situ ultrasound treatment (UST) during Si+ ionimplantation of SiO2 on true atomic level, viz., probing of point defects and their behavior over various treatments. This reveals an impressive healing effect of in situ UST, now quantified in detail on atomic level. The effect is retained even after high-T anneal, resulting in the removal of virtually all ESR active centers .A final part intends to asses the atomic structure of the irradiation induced (VUV or γ-ray) E δ point defect in a-SiO2, mainly targeted through focusing on the correct determination of the relative hf structure intensityover various microwave frequencies and a broad temperature range. The results are conclusive in that they exclude the Si dimer (Si­2) atomic model advocated by theory, while definitively establishing the unpaired electron to be in interaction with 4 (5) Si atom sites a conclusion not supported by theory. It reveals a hiat in the current understanding of this illusive point defect, though assumedly classified within the single O-vacancy type point defects in SiO2 (E family).status: publishe

Structure and performance of carbon xerogel molded emitters for micropropulsion applications

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2016.Cataloged from PDF version of thesis.Includes bibliographical references (pages 91-94).Ion electrospray propulsion relies on the transport of propellant to emission sites where ions and/or droplets are extracted to create thrust. The focus of this research is the creation of porous emitter substrates through which the liquid is passively transported. Previous substrates were created subtractively by selectively removing material to reveal emitter tips or arrays. The limitations of the previous substrates are pore size variability, non-uniform emitter tips, and difficulty in creating identical tips. This study investigates the use of carbon xerogels for electrospray applications due to their exceptional properties such as large surface to volume ratio, robustness and pore uniformity. The substrates are created through a synthesis route which is advantageous for reproducibility. Single carbon xerogel emitter tips and emitter arrays are molded on previously synthesized carbon xerogel substrates. Molding is an additive method which allows for parallel processing and batch manufacturing. Initially carbon xerogels substrates are synthesized. Then a carbon xerogel emitter tip is molded on top of a previously synthesized carbon substrate. Finally, an array of resorcinol formaldehyde emitters is molded on top of a carbon substrate. The carbon xerogel substrate with a molded tip is tested for Retarding Potential Analysis and Time of Flight Mass Spectrometry measurements in order to determine fragmentation fractions and beam composition. The results are consistent with the ionic liquid EMI-BF4 fragmentation fractions and pure ionic regime is achieved. The beam is nearly monoenergetic and fragmentation occurs mostly outside the acceleration region which does not affect thruster efficiency.by Iulia Elena Jivanescu.S.M

Effects of a Hydrogel Patch on Denture‐Related Traumatic Ulcers; an Exploratory Study

PurposeThe aim of this exploratory study was to evaluate the effects of hydrogel patch wound dressing on healing time and pain level of denture‐related lesions of the oral mucosa in edentulous individuals.Materials and MethodsTwenty‐three adults with newly fabricated complete sets of dentures who subsequently developed at least two ulcerative lesions related to their complete dentures were included in the study. For each participant, the smaller lesion (control lesion) was allocated to usual care, that is, adjustment of the denture's margins, whereas the larger lesion (test lesion) was assigned to receive usual care plus application of a hydrogel patch. In the latter, a patch was applied directly on the affected area three times within the first 24 hours, followed by application of three additional patches, namely one during each of the following 3 days. Participants were monitored until complete healing of all ulcers. The primary outcome measures were changes since baseline in each lesion's greatest dimension at days 1 and 7, as well as improvement in ulcer‐related pain experienced.ResultsParticipants were on average about 70 years old, about half were women, and just over 40% had type 2 diabetes. Lesions treated with the hydrogel patch extended between 4.3 and 10.2 mm (mean 7.1 mm) in their greatest dimension, and the smaller lesions receiving usual care were initially 4 mm on average, ranging from 2.0 to 7.0 mm. The hydrogel patch lesions attained 25% to 75% reductions in their greatest lesion extent from baseline to days 1 and 7, respectively, compared to 10% and just over 50% reduction in the lesions that received usual care. Healing rates were similar in patients with and without diabetes. The participants reported significant improvement in pain level 1 day following treatment initiation for 30% of the control lesions, compared to 65% of the lesions treated with the hydrogel patch.ConclusionsThe results of this exploratory study suggest that application of hydrogel patches may represent a novel, effective treatment for accelerating the healing process and pain reduction in mucosal lesions associated with complete dentures also in people with type 2 diabetes; however, larger studies need to confirm these findings.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110761/1/jopr12186.pd

Can Dental Office Lighting Intensity Conditions Influence the Accuracy of Intraoral Scanning?

The aim of this study was to evaluate the influence of different settings of ambient light intensity inside the dental office on the accuracy (trueness and precision) of an intraoral scanner (IOS). A full crown preparation was conducted on a resin molar which was scanned using a high resolution extraoral scanner to obtain a reference model. Six light settings were chosen based on the most clinically relevant light conditions inside the workspace, and the preparation was scanned using an intraoral scanner (PlanScan, Planmeca). The obtained data was analyzed using a professional 3D quality control software (Geomagic Control X). There was no statistically relevant difference between the groups when regarding trueness, although a slight influence of the light intensity could be observed on the trueness values. Regarding precision, the best results were obtained in the 3800 lux group, with the other groups presenting close values, excepting the extreme values (400 lux and 11 000 lux) groups that proved to be the most deficient

Multi-frequency ESR analysis of the E′

A multifrequency electron spin resonance study of the E′δ defect in six SiO2 glasses irradiated by UV, VUV, or 60Co γ-rays, points to an electronically rigid structure with no dynamic rearrangement occurring in the temperature range T ≥ 4.2 K. Reassuringly coinciding over all frequencies and T's applied, the average intensity ratio of the 100 G 29Si hyperfine doublet to the central Zeeman signal points to delocalization of the unpaired spin over n = 4 or 5 equivalent Si sites, thus refuting the Si dimer model. A noteworthy revelation is that E′δ is only observed in those (3) silica types studied also showing the Al E′ center in the as γ-irradiated state. This may signify some indirect role of charge compensators/traps in activating/stabilizing E′δ centers, relevant to further theoretical modeling

Functionality of thermally hydrogen-passivated interfaces of oxidized crystalline arrays of Si nanowires on (100)Si

Electron spin resonance studies have been performed on arrays of single-crystalline Si nanowires (NWs), 375 nm long and of top diameter of about 5 nm, fabricated on (100)Si by top-down etching and final thinning by thermal oxidation in dry O2/N2 at $1150\ ^{\circ}\text{C}$ . The SiO2/SiNW interfaces, showing a density of inherent electrically detrimental $P_{b0}\ (\text{Si}_{3}\equiv{}\text{Si}^{\bullet})$ defects substantially exceeding that of standard technological (100)Si/SiO2, are of inferior electrical quality. An extensive study of the passivation kinetics in H2 and forming gas ambient reveals that, even under optimized conditions, the defect system cannot be inactivated to device grade (at best, $40\times$ improvement in H2), due to the excessive interface stress as exposed by the enhanced spread in activation energy for hydrogen passivation kinetics. The data reveal the inability, of intrinsic nature, to sufficiently suppress $P_{b0}$ defects, preventing to reach device-grade functioning of solar cells using single-crystalline NW arrays on (100)Si in the current state of manufacturing

Size dependence of P

Size-controlled Si nanocrystals (nc's) of ∼ 2 to 5 nm diameter embedded in amorphous (a-)SiO2 are extensively studied by electron spin resonance (ESR) and photoluminescence (PL). The PL quenching Pb-type (Si dangling bond) interface defects ––Pb(0) and Pb1 centers–– are investigated as a function of Si nc's size and effective interface area with the embedding SiO2. It is shown that the effective areal Pb-type defect density at the nc-Si/SiO2 interface remains approximately constant, indifferent of the nc size. While Si nc's larger than ≈3.5 nm are found to house, on average, at least one PL quenching Pb-type defect, about 75% of the as-annealed 2 nm Si nc's appear Pb-free. Additional study on the effect of heat treatment in H2 indicates this step to be more efficient in inactivating Pb(0) than Pb1 for all Si nc sizes

Scanning Distance Influence on the Intraoral Scanning Accuracy—An In Vitro Study

Intraoral scanners (IOS) have reached a point where their impact in the dental office cannot be denied. The distance between the tip of the IOS and the preparation may have implications on the accuracy of the digital model. The objective of this study was to evaluate the differences in accuracy between digital impressions in the scenario of different scanning distances. Twenty consecutive scans were performed at five predetermined distances: 5 mm, 10 mm, 15 mm, 20 mm and 23 mm by a single operator. The scanning distance of 10 mm displayed the best accuracy with an overall trueness value of 23.05 μm and precision value of 4.2 μm. The drawn conclusion was that increased scanning distances can decrease the accuracy of a digital impression