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The ability to gradually modify the atomic structures of nanomaterials and directly identify such structural variation is important in nanoscience research. Here, we present the first example of a high-pressure single-crystal X-ray diffraction analysis of atomically precise metal nanoclusters. The pressure-dependent, subangstrom structural evolution of an ultrasmall gold nanoparticle, Au

Upconverting nanoparticles (UCNPs) are an emerging platform for mechanical force sensing at the nanometer scale. An outstanding challenge in realizing nanometer-scale mechano-sensitive UCNPs is maintaining a high mechanical force responsivity in conjunction with bright optical emission. This Letter reports mechano-sensing UCNPs based on the lanthanide dopants Yb(3+) and Er(3+), which exhibit a strong ratiometric change in emission spectra and bright emission under applied pressure. We synthesize and analyze the pressure response of five different types of nanoparticles, including cubic NaYF(4) host nanoparticles and alkaline-earth host materials CaLuF, SrLuF, SrYbF, and BaLuF, all with lengths of 15 nm or less. By combining optical spectroscopy in a diamond anvil cell with single-particle brightness, we determine the noise equivalent sensitivity (GPa/√Hz) of these particles. The SrYb(0.72)Er(0.28)F@SrLuF particles exhibit an optimum noise equivalent sensitivity of 0.26 ± 0.04 GPa/√Hz. These particles present the possibility of robust nanometer-scale mechano-sensing.

Surfaces can significantly alter the optical properties of nanomaterials, but they are difficult to control and their roles are hard to understand in highly reactive materials such as silicon nanomaterials. In this work, we investigate the role of the surface in controlling the optical transitions in highly luminescent silicon-derived nanoparticles. By combining high-pressure and low-temperature experiments, we experimentally correlate the anomalously intense and narrow transitions in the UV range with the surface oxides, while the visible transition and the photoluminescence (PL) are verified to originate from the Si-ligand charge transfer band. We find that the high-pressure absorption and PL depends on the rigidity of the surface ligand. This indicates that the surface plays a dominant role on the optical properties of these silicon-derived nanoparticles, and is different than other semiconductor nanomaterials, in which pressure-dependent optical transitions depend on lattice strain or phase transformations. This work presents a comprehensive understanding of the optical transitions and the effect of surface ligands and surface oxidation in these highly luminescent Si-derived nanoparticles. The new insight into the oxidation-activated and ligand-mediated transitions, and the pressure-dependent PL may help with engineering the band structure of other highly-reactive optical nanomaterials.

Colloidal nanoparticles can be coated with a conformal shell to form multifunctional nanoparticles. For instance, plasmonic, magnetic, and catalytic properties, chemical stability and biocompatibility can be mixed and matched. Here, a facile synthesis for depositing metal boride amorphous coatings on colloidal metallic nanocrystals is introduced. The synthesis is independent of core size, shape, capping ligand, and composition. Shell thickness can be as thin as 3 nm with no apparent pinholes. High pressure studies show that the coatings are highly resistant to crystallization and are strongly bonded to the crystalline core. By choosing either CoB or NiB for the coating, the composite nanoparticles can be either ferromagnetic or paramagnetic at room temperature, respectively.

Currently, a comprehensive understanding of the relationship between atomic structures and optical properties of ultrasmall metal nanoclusters with diameters between 1 and 3 nm is lacking. To address this challenge, it is necessary to develop tools for perturbing the atomic structure and modulating the optical properties of metal nanoclusters beyond what can be achieved using synthetic chemistry. Here, we present a systematic high-pressure study on a series of atomically precise ligand-protected metal nanoclusters. A diamond anvil cell is used as a high-pressure chamber to gradually compress the metal nanoclusters, while their optical properties are monitored

The design of ductile metallic glasses has been a longstanding challenge. Here, we use colloidal synthesis to fabricate nickel-boron metallic glass nanoparticles that exhibit homogeneous deformation at room temperature and moderate strain rates. In situ compression testing is used to characterize the mechanical behavior of 90-260 nm diameter nanoparticles. The force-displacement curves consist of two regimes separated by a slowly propagating shear band in small, 90 nm particles. The propensity for shear banding decreases with increasing particle size, such that large particles are more likely to deform homogeneously through gradual shape change. We relate this behavior to differences in composition and atomic bonding between particles of different size using mass spectroscopy and XPS. We propose that the ductility of the nanoparticles is related to their internal structure, which consists of atomic clusters made of a metalloid core and a metallic shell that are connected to neighboring clusters by metal-metal bonds.

The interaction of crystalline defects leads to strain hardening in bulk metals. Metals with high stacking fault energy (SFE), such as aluminum, tend to have low strain hardening rates due to an inability to form stacking faults and deformation twins. Here, we use in situ SEM mechanical compressions to find that colloidally synthesized defect-free 114 nm Al nanocubes combine a high linear strain hardening rate of 4.1 GPa with a high strength of 1.1 GPa. These nanocubes have a 3 nm self-passivating oxide layer that has a large influence on mechanical behavior and the accumulation of dislocation structures. Post-compression TEM imaging reveals stable prismatic dislocation loops and the absence of stacking faults. MD simulations relate the formation of dislocation loops and strain hardening to the surface oxide. These results indicate that slight modifications to surface and interfacial properties can induce enormous changes to mechanical properties in high SFE metals., Comment: 10 pages, 7 figures

Demirjian’s original method for forensic dental age estimation has undergone various modifications over the years, owing to the wide discrepancies in age estimates when applied on different population samples. Specific regression formulae were derived upon testing the revised method proposed by Chaillet and Demirjian on an Indian population. The objective of this study was to apply these formulae on a Central Indian sample of 400 healthy subjects, aged between 7–25 years and assess the ability of these formulae to predict age accurately. The study sample consisted of orthopantomograms of 400 subjects, categorized into four groups: Group A (7–16-year-old males), Group B (17–25-year-old males), Group C (7–16-year-old females) and Group D (17–25-year-old females). Based on the radiographic developmental stage of each tooth in the mandibular left quadrant, their respective maturity scores were allotted and a total maturity score for all the 8 teeth was determined for each subject. This value was then substituted in the India specific regression formulae, separately for males and females, to estimate the dental age. Difference between the chronological age and estimated age was then calculated. The mean absolute error for the entire sample was 0.5 years. The mean absolute error ranged between 0.7 ± 2.05 years for males and 0.4 ± 1.86 years for female subjects, implying greater accuracy in females. Further, 78.5 % of the sample showed negligible error of less than ±1 year. In case of male subjects aged between 7–16 years, least mean absolute error of 0.34 years was obtained. Higher error rates in Group B (17–25-year-old males) and Group D (17–25-year-old females) indicated reduced tendency for accurate age prediction in subjects beyond 16 years of age. The results derived in this study, showed improved accuracy of India specific regression formulae in predicting the dental age of the population of central India.

Nanocrystals can exist in multiply twinned structures like the icosahedron, or single crystalline structures like the cuboctahedron or Wulff-polyhedron. Structural transformation between these polymorphic structures can proceed through diffusion or displacive motion. Experimental studies on nanocrystal structural transformations have focused on high temperature diffusion mediated processes. Thus, there is limited experimental evidence of displacive motion mediated structural transformations. Here, we report the high-pressure structural transformation of 6 nm Au nanocrystals under nonhydrostatic pressure in a diamond anvil cell that is driven by displacive motion. In-situ X-ray diffraction and transmission electron microscopy were used to detect the transformation of multiply twinned nanocrystals into single crystalline nanocrystals. High-pressure single crystalline nanocrystals were recovered after unloading, however, the nanocrystals quickly reverted back to multiply twinned state after redispersion in toluene solvent. The dynamics of recovery was captured using transmission electron microscopy which showed that the recovery was governed by surface recrystallization and rapid twin boundary motion. We show that this transformation is energetically favorable by calculating the pressure-induced change in strain energy. Molecular dynamics simulations showed that defects nucleated from a region of high stress region in the interior of the nanocrystal, which make twin boundaries unstable. Deviatoric stress driven Mackay transformation and dislocation/disclination mediated detwinning are hypothesized as possible mechanisms of high-pressure structural transformation., 32 pages, 14 figures, and 1 movie (please open pdf with Adobe Acrobat Reader to see the embedded movie)

A nanoscale thin film of niobium oxide on a platinum substrate was evaluated for its influence on the electronic and chemical properties of the underlying platinum towards the oxygen reduction reaction with applications to proton exchange membrane fuel cells. The nanoscale thin film of niobium oxide was deposited using atomic layer deposition onto the platinum substrate. A film of niobium oxide is a chemically stable and electronically insulating material that can be used to prevent corrosion and electrochemical degradation when layers are several nanometers thick. These layers can be insulating if sufficiently thick and may not be sufficient to protect the platinum from corrosion if too thin. An ∼3 nm thin film of niobium oxide was fabricated on the platinum surface to determine its influence on the electronic and chemical properties at the interface of these materials. The atomic layer deposition process enabled a precise control over the material composition, structure, and layer thickness. The niobium oxide film was evaluated using cyclic voltammetry and electrochemical impedance spectroscopy to evaluate whether a balance could be found between the inhibition of platinum degradation and electronic insulation of the platinum for use in proton exchange membrane fuel cells. The 3 nm thin niobium oxide film was found to be sufficiently thin to permit electronic conductivity while reducing the incidence of platinum dissolution.

Background Assessment of an age of an individual whether living or dead through teeth is one of the most reliable and simple method to calculate age than skeletal remains especially when they are in poor conditions. Objectives The study was carried out with aim of (i) to evaluate reliability of dental age assessment through two different methods for adults i.e. tooth coronal index and pulp/tooth ratio using digital panoramic radiographs and (ii) to compare these methods for their accuracy in age determination. Materials and methods The digital panoramic radiographs of 180 subjects of Chhattisgarh aged 15–70 years were selected for the study. The measurements were performed on the JPEG images of selected panoramic radiographs by using Adobe Acrobat 7.0 professional software. For tooth coronal index (TCI), height of the crown i.e. coronal height (CH) and the height of the coronal pulp cavity i.e. coronal pulp cavity height (CPCH) of mandibular second premolars and first molars was measured in millimeter (mm) and then TCI was calculated for each tooth and calculated age was compared with chronological age. For pulp/tooth ratio, the measurements of pulp chamber height (PCH) and crown root trunk height (CRTH) were performed on the mandibular first and second molar teeth, the pulp chamber crown root trunk height ratios (PCTHR) of selected tooth were calculated. The acquired data were subjected to Pearson correlation test, unpaired t test and Analysis of Variance (ANOVA) analysis. Results Results suggested that TCI (mandibular first molar r = −0.178), second premolar (r = −0.187) and PCTHR(mandibular first molar r = −0.921, second molar r = −0.901) correlated negatively with chronological age suggesting decrease in size of pulp cavity. Mandibular first molar was found to be most reliable tooth to estimate dental age. Conclusion The study showed that both PCTHR and TCI have negative association with chronological age. PCTHR showed slightly higher negative correlation and proved as a better tool for age estimation than TCI. Statistically significant differences were observed between chronological and calculated age by both methods thus emphasizing the need for future clinical trials.

The conventional way to form a multicomponent alloy requires mixing individual elements in a single step. Phase formation, therefore, is governed by inherent thermodynamic and kinetic factors of the system. We propose here a new approach for multicomponent alloy synthesis, which involves step by step addition of constituent elements. In the present work, this is illustrated through the formation of nanocrystalline equiatomic AlCoCrFeNi by mechanical alloying. For example, first, binary CoNi is formed by milling elemental Co and Ni powders. In the subsequent steps, Fe, Cr and Al are added to form ternary (CoNiFe), quaternary (CoNiFeCr) and quinary (CoNiFeCrAl) alloy, respectively.Three different classes of binaries have been selected as initial phases, namely, B2 (AlNi, AlCo and AlFe), BCC (FeCr) and FCC (CoNi and FeNi). Remaining constituent elements are added step-wise in varying sequences and equiatomic AlCoCrFeNi is obtained in the concluding step. The final AlCoCrFeNi alloy at the end of each sequence has varied fractions of BCC and FCC phases. For instance, AlNi+Co+Fe+Cr sequence is single phase BCC, whereas the sequence FeNi+Co+Cr+Al results in a mixture of BCC (75%) and FCC (25%) phases. The extent to which a particular element stabilizes a structure (BCC/B2/FCC) has also been elucidated. Keywords: High entropy alloys, Mechanical alloying, X-ray diffraction, Nanocrystalline, Sequential alloying

High entropy alloys (HEAs) have drawn considerable attention owing to their unique properties such as high fracture toughness, good strength–ductility combination and enhanced corrosion resistance. In this study, the corrosion resistance dependence on the crystal structure and grain size of AlCoCrFeNi HEA is investigated. AlCoCrFeNi HEA with different mixture of body centered cubic (BCC) and face centered cubic (FCC) phases is produced using sequential alloying and tested for corrosion resistance in 3.5 wt% NaCl solution. CoNi+Fe+Cr+Al (84% BCC), FeCr+Ni+Al+Co (62% BCC) and AlNi+Co+Cr+Fe (38% BCC) alloy sequences have corrosion potential of −454, −299 and −524 mV (vs. SCE), and corrosion current of 14, 0.4 and 12 µA, respectively. FCC is a tight binding lattice with higher packing fraction than BCC which made it better for corrosion resistance, but FCC is rich in elements like Co, Ni, and Fe which are easily corroded. These two competing effects lead to a nearly optimum corrosion resistance for FeCr+Ni+Al+Co alloy sequence with 62% BCC and 32% FCC. It is also observed that an increase in grain size improves corrosion resistance. The influence of different chemical elements, crystal structure and microstructure (coarse vs. nanocrystalline) on corrosion resistance is discussed.

As circuitry approaches single nanometer length scales, it is important to predict the stability of metals at these scales. The behavior of metals at larger scales can be predicted based on the behavior of dislocations, but it is unclear if dislocations can form and be sustained at single nanometer dimensions. Here, we report the formation of dislocations within individual 3.9 nm Au nanocrystals under nonhydrostatic pressure in a diamond anvil cell. We used a combination of x-ray diffraction, optical absorbance spectroscopy, and molecular dynamics simulation to characterize the defects that are formed, which were found to be surface-nucleated partial dislocations. These results indicate that dislocations are still active at single nanometer length scales and can lead to permanent plasticity., Comment: 33 pages, 12 figures

Background Tobacco is a leading preventable cause of deaths worldwide; the situation is particularly serious in the developing countries. Tobacco use amongst the children and adolescents is already a pandemic and they are vulnerable targets of tobacco industry. This is also the case in India. Objectives 1) Document and monitor the prevalence of tobacco use including smoked, smokeless and other forms of tobacco; 2) Understand studentknowledge and attitudes related to tobacco use and its health impact; 3) Assess the impact of tobacco on the oral health status of school-going children in India. Materials and methods The sample was 1,500 school children of the age group 12-15 years age. A pretested, close ended questionnaire was administered in the form of extensive face to face interview to understand student knowledge, attitudes and behavior related to tobacco use and its health impact and to assess the prevalence of tobacco use including smoked, smokeless and other forms of tobacco. Oral health status was assessed using the Community Periodontal Index (CPI). Frequency distribution, Chi-square tests and Odd's ratio was calculated. Results Prevalence of tobacco usage amongst the prevalence was 20.4%: 9.2% reported smoking, 15.8% used tobacco in the chewable form and 25.3% children were involved in consuming betel nut/areca nuts. The OR (Odd's ratio) for calculus formation was highest for guthka chewers (OR=14.322), paan masala chewers had the highest odds of developing bleeding on probing when compared to the others. Conclusions There is an urgent need to launch school-based tobacco prevention programs for community awareness of children and the public, as preventing the initiation of a habit is far easier than stopping it.

The change in attitude of patients with emphasis on being involved and informed of every aspect of care is not only apparent in adults but also when providing care for children and young adults. It is important for the dentist to be well informed of the fundamental process of informed consent, which exists under the law in order to provide care within the legal framework. The important issue when obtaining consent is competence of the patients to give consent. The burden is on the dental professional to ensure that the patient understands the treatment options. Informed consent decreases the practitioners liability from claims associated with miscommunication. It does not shift the whole responsibility to the patient but should be a partnership between a clinician and a patient in which each has rights and defined responsibilities.

Background: Prisoners represent a population group that is disadvantaged, socially deprived and underprivileged, needing particular attention with regard to provision of necessary oral health care, health promotion and motivation and tobacco cessation. Considering the situation in prisons, smoking and tobacco chewing are burning issues related to health deterioration and economic loss that seem to be overlooked by the public health sectors. Aim: To assess prisoners’ perception of tobacco use and cessation in Chhatisgarh, India. Materials and Methods: A pre-tested, close ended questionnaire was administered in the form of extensive face to face interviews, to assess perceptions regarding tobacco use and cessation in the central jail of Durg District of Chhattisgarh state, India. Results: Prevalence of tobacco usage amongst the prisoners was found to be 61%. Some 27% reported smoking, 44% used tobacco in the chewable form and 29% indulged in consuming tobacco in both forms i.e. smoked as well as chewed. Results suggest several recommendations for policy relevance such as provision of a prison dentist, a tobacco cessation counseling program and targeted eradication of oral cancer by educating the prisoners. Conclusions: Health is a fundamental human “right of everyone to the enjoyment of the highest attainable standard of physical and mental well-being”. This applies to prisoners just as it does to every other human being. The alarming findings in the study suggest the need for dental treatment facilities and tobacco cessation counseling in prisons.

Background: The objective of the study was to determine the knowledge, attitude and behaviors of the practicing dentists regarding tobacco cessation counseling (TCC) in Chhattisgarh state and also the barriers that prevent them from doing so. Materials and Methods: The study was conducted among dental practitioners of Raipur district, Chhattisgarh state (India). The sampling frame was registration with the State Dental Council and practicing in Raipur district. A questionnaire was personally administered and the practitioners were given explanations regarding how to complete it. Only descriptive statistics were calculated (SPSS version 16 for Windows). Results: Based on the responding dentists’ self reports, 76% were not confident in TCC, 48% did not assume TCC to be their responsibility, 17% considered that it might have a negative impact on their clinical practice, whereas 24% considered it might take away precious time from their practice, 25% considered TCC by dentists to be effective to a considerable extent and 80% considered TCC activities are not effective due to lack of formal training, 69% considered dental clinics as an appropriate place for TCC but 82% thought there must be separate TCC centre and 100% of the dentists wanted TCC training to be a part of practice and that it should be included in dental curriculum. Some 95% of them were of the view that tobacco products should be banned in India and 86% responded that health professionals must refrain from tobacco habits so to act as role models for society. Conclusions: Dental professionals must expand their armamentarium to include TCC strategies in their clinical practice. The dental institutions should include TCC in the curriculum and the dental professionals at the primary and the community health care level should also be trained in TCC to treat tobacco dependence.