Vacancy and Doping States in Monolayer and bulk Black Phosphorus.

The atomic geometries and transition levels of point defects and substitutional dopants in few-layer and bulk black phosphorus are calculated. The vacancy is found to reconstruct in monolayer P to leave a single dangling bond, giving a negative U defect with a +/- transition level at 0.24 eV above the valence band edge. The V(-) state forms an unusual 4-fold coordinated site. In few-layer and bulk black P, the defect becomes a positive U site. The divacancy is much more stable than the monovacancy, and it reconstructs to give no deep gap states. Substitutional dopants such as C, Si, O or S do not give rise to shallow donor or acceptor states but instead reconstruct to form non-doping sites analogous to DX or AX centers in GaAs. Impurities on black P adopt the 8-N rule of bonding, as in amorphous semiconductors, rather than simple substitutional geometries seen in tetrahedral semiconductors

Phosphorene: Fabrication, Properties and Applications

Phosphorene, the single- or few-layer form of black phosphorus, was recently rediscovered as a twodimensional layered material holding great promise for applications in electronics and optoelectronics. Research into its fundamental properties and device applications has since seen exponential growth. In this Perspective, we review recent progress in phosphorene research, touching upon topics on fabrication, properties, and applications; we also discuss challenges and future research directions. We highlight the intrinsically anisotropic electronic, transport, optoelectronic, thermoelectric, and mechanical properties of phosphorene resulting from its puckered structure in contrast to those of graphene and transition-metal dichalcogenides. The facile fabrication and novel properties of phosphorene have inspired design and demonstration of new nanodevices; however, further progress hinges on resolutions to technical obstructions like surface degradation effects and non-scalable fabrication techniques. We also briefly describe the latest developments of more sophisticated design concepts and implementation schemes that address some of the challenges in phosphorene research. It is expected that this fascinating material will continue to offer tremendous opportunities for research and development for the foreseeable future.Comment: invited perspective for JPC

Liquid exfoliation of solvent-stabilized few-layer black phosphorus for applications beyond electronics

Few-layer black phosphorus (BP) is a new two-dimensional material which is of great interest for applications, mainly in electronics. However, its lack of environmental stability severely limits its synthesis and processing. Here we demonstrate that high-quality, few-layer BP nanosheets, with controllable size and observable photoluminescence, can be produced in large quantities by liquid phase exfoliation under ambient conditions in solvents such as N-cyclohexyl-2-pyrrolidone (CHP). Nanosheets are surprisingly stable in CHP, probably due to the solvation shell protecting the nanosheets from reacting with water or oxygen. Experiments, supported by simulations, show reactions to occur only at the nanosheet edge, with the rate and extent of the reaction dependent on the water/oxygen content. We demonstrate that liquid-exfoliated BP nanosheets are potentially useful in a range of applications from ultrafast saturable absorbers to gas sensors to fillers for composite reinforcement

Comparison of New Accuracy Degree and Tanaka Johnson Formulae for Prediction of Mesiodistal Width of Unerupted Permanent Canines and Premolars

Introduction: It is important to predict mesiodistal crown width of the unerupted permanent canine and premolars in the mixed dentition, which helps to better determine malocclusion and its further development. Methods: In this study, 120 pair of dental study casts, belonged to subjects aged between 12-30 years, were selected and measured in the most mesiodistal width of permanent canines and premolars of both jaws, lower permanent incisors, and first upper permanent molars with the accuracy of 0/01 mm. Mesiodistal width of permanent canine and premolars in upper and lower jaws were estimated by new formula based on the permanent first upper molars and lower central incisors and then were compared with Tanaka-johnson formula. Results: The actual mean for sum of the mesiodistal width of permanent canines and premolars in the upper jaw was 21/22 mm and in the lower was 20/98 mm. The mean for sum of mesiodistal permanent canine and premolars were estimated by new formula in upper and lower jaw as 21/64 mm and 21/69 mm respectively. On the other hand, via Tanaka-Johnson formula, the predictions in upper and lower jaw were 22/41 mm and 21/92 mm respectively. Statistical analyses by means of ANOVA and Pearson correlation test revealed significant differences (P<0.001, r = 0.701). Conclusion: Sum of mesiodistal width of unerupted permanent canines and premolars teeth in the Iranian race (in Yazd) was estimated better using the new formula than applying the Tanaka Johnson formula, because of two following reasons: first, the new formula can be used at an earlier age and second, it has a higher accuracy

Investigating Hyoid Bone Position in 7-11 Year Children with Ankyloglossia in Lateral Cephalometic Radiographs

Introduction: Ankyloglossia is an anatomic developmental anomaly determined with thick and short fibrotic ferenum. Hyoid bone plays an important role in tongue physiology and tongue changes, in turn, have sever effects on malocclusion. Taking in to account the effects of tongue position on oropharyngeal structures and relation of hyoid position with different types of malocclusion, this study aimed to investigate the hyoid position in children aged 7-11 years with ankyloglossia in lateral cephalometric radiographs. Methods: 30 radiographs of children with ankyloglossia with mean age of 9.8 were chosen. In addition, 30 other radiographs were selected as the control group and were matched with the experimental (study)group in regard with age, sex, class of malocclusion and growth pattern. The measurements of hyoid position were (C3-RGN, C3-H, H-RGN, HP) analysed via the paired t-test. Results: The means of C3-RGN, C3-H, H-RGN, HP were respectively 66.2, 30.9, 33.4, 3.2 in ankyloglossia group (study), whereas those of control group were 7.45, 36.8, 34.1, 68.6 respectively. A statistically significant decrease was observed in all measurements (p-value<0.05). Conclusion: Size and position of hyoid in the study group demonstrated more posterior- superior position than the controls

Investigating Hyoid Bone Position in 7-11 Year Children with Ankyloglossia in Lateral Cephalometic Radiographs

Introduction: Ankyloglossia is an anatomic developmental anomaly determined with thick and short fibrotic ferenum. Hyoid bone plays an important role in tongue physiology and tongue changes, in turn, have sever effects on malocclusion. Taking in to account the effects of tongue position on oropharyngeal structures and relation of hyoid position with different types of malocclusion, this study aimed to investigate the hyoid position in children aged 7-11 years with ankyloglossia in lateral cephalometric radiographs. Methods: 30 radiographs of children with ankyloglossia with mean age of 9.8 were chosen. In addition, 30 other radiographs were selected as the control group and were matched with the experimental (study)group in regard with age, sex, class of malocclusion and growth pattern. The measurements of hyoid position were (C3-RGN, C3-H, H-RGN, HP) analysed via the paired t-test. Results: The means of C3-RGN, C3-H, H-RGN, HP were respectively 66.2, 30.9, 33.4, 3.2 in ankyloglossia group (study), whereas those of control group were 7.45, 36.8, 34.1, 68.6 respectively. A statistically significant decrease was observed in all measurements (p-value<0.05). Conclusion: Size and position of hyoid in the study group demonstrated more posterior- superior position than the controls