Interfacial Reconstructed Layer Controls the Orientation of Monolayer Transition-Metal Dichalcogenides.

Growing continuous monolayer films of transition-metal dichalcogenides (TMDs) without the disruption of grain boundaries is essential to realize the full potential of these materials for future electronics and optoelectronics, but it remains a formidable challenge. It is generally believed that controlling the TMDs orientations on epitaxial substrates stems from matching the atomic registry, symmetry, and penetrable van der Waals forces. Interfacial reconstruction within the exceedingly narrow substrate-epilayer gap has been anticipated. However, its role in the growth mechanism has not been intensively investigated. Here, we report the experimental conformation of an interfacial reconstructed (IR) layer within the substrate-epilayer gap. Such an IR layer profoundly impacts the orientations of nucleating TMDs domains and, thus, affects the materials' properties. These findings provide deeper insights into the buried interface that could have profound implications for the development of TMD-based electronics and optoelectronics.

Chlorine-Infused Wide-Band Gap p-CuSCN/n-GaN Heterojunction Ultraviolet-Light Photodetectors.

Copper thiocyanate (CuSCN) is a p-type semiconductor that exhibits hole-transport and wide-band gap (∼3.9 eV) characteristics. However, the conductivity of CuSCN is not sufficiently high, which limits its potential application in optoelectronic devices. Herein, CuSCN thin films were exposed to chlorine using a dry etching system to enhance their electrical properties, yielding a maximum hole concentration of 3 × 1018 cm-3. The p-type CuSCN layer was then deposited onto an n-type gallium nitride (GaN) layer to form a prototypical ultraviolet-based photodetector. X-ray photoelectron spectroscopy further demonstrated the interface electronic structures of the heterojunction, confirming a favorable alignment for holes and electrons transport. The ensuing p-CuSCN/n-GaN heterojunction photodetector exhibited a turn-on voltage of 2.3 V, a responsivity of 1.35 A/W at -1 V, and an external quantum efficiency of 5.14 × 102% under illumination with ultraviolet light (peak wavelength of 330 nm). The work opens a new pathway for making a plethora of hybrid optoelectronic devices of inorganic and organic nature by using p-type CuSCN as the hole injection layer.

Formation and properties of iodine- and acetonitrile-functionalized two-dimensional Si materials: a Density Functional Theory study.

Topotactic transformations of suitable layered three-dimensional precursors are among the most robust methods to prepare two-dimensional (2D) materials based on silicon or germanium. Here we use Density Functional Theory calculations to probe the mechanisms underlying the formation of 2D-Si sheets functionalized with iodine atoms (SiI) or acetonitrile molecules [Si(MeCN)] starting from a layered CaSi2 precursor. We identify the sequence of exothermic surface reactions that enable the adsorption of, not only iodine atoms, but, surprisingly, also of solvent acetonitrile molecules on both sides of the top layer of a Si-terminated CaSi2 surface and its ensuing exfoliation as a standalone 2D sheet. In the acetonitrile case, the as-formed 2D material exhibits intriguing structural and electronic properties with an unusual quasi-one-dimensional substructure of silicon chains and a Dirac-like cone in the energy band diagram. The results elucidate the atomic-scale details of the established experimental technique of topotactic synthesis of functionalized silicene and identify new structural motifs for 2D materials.

Nonlinear tuning of PT symmetry and non-Hermitian topological states.

Topology, parity-time (PT) symmetry, and nonlinearity are at the origin of many fundamental phenomena in complex systems across the natural sciences, but their mutual interplay remains unexplored. We established a nonlinear non-Hermitian topological platform for active tuning of PT symmetry and topological states. We found that the loss in a topological defect potential in a non-Hermitian photonic lattice can be tuned solely by nonlinearity, enabling the transition between PT-symmetric and non-PT-symmetric regimes and the maneuvering of topological zero modes. The interaction between two apparently antagonistic effects is revealed: the sensitivity close to exceptional points and the robustness of non-Hermitian topological states. Our scheme using single-channel control of global PT symmetry and topology via local nonlinearity may provide opportunities for unconventional light manipulation and device applications.

Two-dimensional Mo(SCN)2: a novel MoS2-variant.

Transition metal dichalcogenides (TMDC) are currently among the most studied two-dimensional (2D) materials. Based on first-principles calculations we propose a new family of 2D materials which resemble TMDC's, but contain more complex chemical groups instead of elemental chalcogen atoms. In particular, we identify various stable 2D polymorphs of molybdenum di-thiocyanate, Mo(SCN)2, with structures akin to those of MoS2. The most stable Mo(SCN)2 polymorphs are semiconductors with small energy band gaps, whereas a higher-energy structure is metallic. Since the calculated formation energies of MoS2 and Mo(SCN)2 are comparable, the synthesis of the latter should be feasible.

Chemical routes to modify, uplift, and detach a silicene layer from a metal substrate.

Experimental studies have shown that honeycomb silicene layers can grow on various metal substrates. Here we demonstrate using first-principles calculations that hydrogenation and calcium intercalation can be employed to break bonds between a silicene overlayer and a silver surface. The end result of the former process is the creation of a silicane mono-layer, a wide band-gap semiconductor. In this way, the Si overlayer can eventually be etched away, in agreement with pertinent experiments. Ca intercalation, on the other hand, lifts the silicene sheet up without destroying its sp(2) honeycomb bonding. Both approaches augment thus the functionalities of silicene overlayers by creating two-dimensional materials with distinct properties.

Stability and electronic properties of ultrathin films of silicon and germanium.

Recent studies have examined the possibility of growing honeycomb silicene and germanene, the silicon and germanium analogues of graphene. Here we use first-principles calculations to examine the relative stability of a number of other single-layer structures that are derived from prominent surface reconstructions of group-IV semiconductors. We find that Si single-layers with the geometry of the √3 × âˆš3 reconstruction are more stable than honeycomb silicene. Likewise, honeycomb germanene is less stable than germanium ultrathin films with a √3 × âˆš3 or 7 × 7 arrangement. √3 × âˆš3 Si and Ge single layers are metals with strong peaks at the Fermi level, and, in the case of Ge, they bear a magnetic moment. Overall, the results demonstrate that free-standing Si and Ge nano-sheets differ in key structural and electronic properties from graphene, and may thus provide systems with alternative functionalities.

Markers of bone metabolism in eugonadal female patients with beta-thalassemia major.

Osteoprotegerin (OPG) and receptor activator of NF-kappaB ligand (RANKL) have been recently implicated in the pathogenesis of various types of osteoporosis. The aim of this study was to investigate bone turnover in eugonadal female patients with this disease and characterize the possible role of the OPG/RANKL system in thalassemia-related bone loss. Markers of bone turnover and bone mineral density (BMD) were measured in 16 eugonadal young females with beta-thalassemia major and 18 age- and sex-matched healthy controls. Bone turnover was significantly increased in thalassemic patients compared to controls but OPG was significantly higher in healthy subjects. BMD values negatively correlated with urine markers of bone resorption but not with OPG/sRANKL system.

Circulating osteoprotegerin and receptor activator of NF-kappaB ligand system in patients with beta-thalassemia major.

Osteoporosis represents an important cause of morbidity in patients with beta-thalassemia major, and its etiology is multifactorial. Thus, the aim of this study was to characterize the possible role of the osteoprotegerin (OPG) and receptor activator of the NF-kappaB ligand (RANKL) system in thalassemia-related bone loss. Serum concentrations of OPG, soluble RANKL (s-RANKL), markers of bone turnover, and lumbar spine bone mineral density (BMD) were measured in random samples of males (n = 29; mean age +/- SEM, 24.26 +/- 1.29 years; range, 13-41 years) and females (n = 31; age, 24.59 +/- 0.95 years; range, 12-34 years) with beta-thalassemia major and in 30 healthy age-, height-, and weight-matched subjects. Thalassemic patients had significantly lower levels of OPG compared with controls (2.54 +/- 0.12 vs. 3.25 +/- 0.122, respectively; P < 0.05) and higher, albeit not statistically significantly, serum levels of s-RANKL (0.350 +/- 0.03 vs. 0.295 +/- 0.046, respectively; P < 0.05). s-RANKL correlated negatively with age (r = -0.3, P < 0.05), and OPG correlated positively with the duration of the interval between the onset of transfusions and chelation therapy (r = 0.52, P < 0.001). Regarding markers of bone metabolism, plasma values of osteocalcin correlated positively with s-RANKL (r = 0.40, P < 0.05) and negatively with OPG/s-RANKL ratio (r = -0.55, P < 0.01). In multiple regression analysis only cross-linked N-teleopeptide of type I collagen (NTX) significantly accounted for BMD. Although the OPG/RANKL system may have some clinical usefulness as a marker of bone turnover in beta-thalassemia, conventional markers of bone turnover more accurately represent changes in the BMD of these patients.

Medical treatment of acromegaly: comorbidities and their reversibility by somatostatin analogs.

Relief of symptoms can be achieved following surgery for growth hormone (GH)-secreting adenomas, as well as after pharmacological therapy with somatostatin analogs. Recently, long-acting somatostatin analog depot formulations, octreotide LAR and lanreotide SR have become available. Somatostatin analogs control GH/insulin-like growth factor (IGF)-1 excess, induce tumor shrinkage in a high proportion of patients, improve symptoms of acromegaly with relatively limited side effects and are successfully administered in patients not suitable for surgery. Furthermore, preoperative somatostatin analogs have been suggested to improve outcome for tumors with limited invasiveness, while surgical tumor debulking in cases that are, at least partially, somatostatin resistant, increases the achievement of normal IGF-1 levels by postoperative somatostatin analog treatment. Effective control of hypertension, as well as diabetes, is mandatory in order to reduce the increased vascular morbidity/mortality. Control of GH/IGF-1 excess generally improves glucose metabolism. Somatostatin analogs improve insulin sensitivity, exerting, however, a concomitant direct inhibitory effect on insulin secretion, with a net balance leaning towards a deterioration in glucose homeostasis. As a result, oral insulin secretagogues (and/or insulin) should probably be preferred to insulin sensitizers in acromegalic patients developing diabetes while on somatostatin analogs. Nevertheless, glucose tolerance remains normal in most of the nondiabetic acromegalic patients, while diabetic acromegalic patients on insulin are at risk for hypoglycemia during initiation of somatostatin analog therapy. Although successful management of acromegaly has been associated with improvement in morphological and functional parameters of cardiomyopathy, limited and conflicting information is available regarding the effect on blood pressure control. Contradictory results have also been reported regarding sleep hypopnea or apnea in treated acromegalic patients. As acromegalic skeletal abnormalities are rather irreversible, apneic episodes may persist after normalization of hormonal levels. Aggressive therapy, including surgery, pharmacological treatment and, in some cases, pituitary irradiation, aiming at normalization of IGF-1 levels, is required for arthropathy management. Some improvement in pain, crepitus and range of motion has been observed after treatment with somatostatin analogs. Information on the impact of disease control, either by surgery or somatostatin analog treatment, on gonadal function is limited. Finally, the link between the hormonal/biochemical and the psychiatric/psychological features of acromegaly, as well as a potential basis for positive effects of somatostatin analog therapy remain unclear.

Evaluation of bone mineral density of the lumbar spine in patients with beta-thalassemia major with dual-energy x-ray absorptiometry and quantitative computed tomography: a comparison study.

Osteoporosis is a common, multifactorial cause of morbidity in patients with beta-thalassemia. The present study was performed to compare bone mineral density (BMD) results in the lumbar spine of thalassemic patients measured by both dual-energy x-ray absorptiometry (DEXA) and quantitative computed tomography (QCT), and to determine their correlations with the markers of bone turnover. BMD was measured in the lumbar spine of 13 regularly transfused patients with beta-thalassemia major by both DEXA and QCT. Blood and urine samples were obtained for the determination of biochemical and hormonal profiles. Both T-scores and Z-scores were higher when measured by QCT (T-score = -0.41 +/- 1.31, Z-score = -0.56 +/- 1.08, mean +/- SD) compared with the values given by DEXA (T-score = -2.57 +/- 0.88, Z-score = -2.32 +/- 1.11, P = 0.0005). In comparison to DEXA, QCT T-scores were more closely correlated with age (r = -0.19 vs. r = -0.70, P = 0.0068). Strong negative correlation was found between QCT values and age (r = -0.67, P = 0.01). In comparison to DEXA T-scores, QCT T-scores were more closely correlated with osteocalcin, urine N-telopeptide cross-links of type I collagen, and deoxypyridinoline, but without statistical significance. DEXA T-scores were better correlated only with urine C-terminal telopeptides of type I collagen, but again without statistical significance. These results imply that the two methods cannot be used interchangeably in assessing BMD in thalassemic patients. However, which one of these two techniques more precisely determines the overall strength of vertebrae in patients with beta-thalassemia remains to be investigated.

Hypoparathyroidism in transfusion-dependent patients with beta-thalassemia.

Hypoparathyroidism is thought to be a rare consequence of iron overload seen in beta-thalassemic transfused patients. This study was conducted to determine the prevalence of hypoparathyroidism in a large number of beta-thalassemic patients, and its potential correlation with the presence of other endocrinopathies caused by iron overload. Serum and urine biochemical parameters were measured in 243 thalassemic patients (136 females and 107 males) in order to determine the prevalence of hypoparathyroidism and evaluate bone turnover. The patients were divided into two groups according to the presence of hypoparathyroidism. We compared the prevalence of other endocrinopathies and disease complications in the two groups. Hypoparathyroidism was detected in 13.5% of the patients (33 subjects; 17 males and 16 females). Serum-intact parathyroid hormone, and total and ionized calcium were significantly lower, while phosphorus was significantly higher in thalassemic patients with hypoparathyroidism. The reduction in BMD was more prominent in normal thalassemic patients (Z score = -2.246 +/- 0.97) compared with those with hypoparathyroidism (Z score = -1.975 +/- 0.89), although the difference was not statistically significant. Disturbed glucose metabolism was more common in patients with hypoparathyroidism (P < 0.05). In addition, heart dysfunction was statistically more frequent in this group (odds ratio = 2.51, P < 0.05). Hypoparathyroidism is a not infrequently observed complication in thalassemic patients. Since the concentration of ferritin is not a valuable tool in the prediction of the development of hypoparathyroidism, parathyroid function should be tested periodically, particularly when other iron overload-associated complications occur.

Endocrine pancreatic insufficiency in chronic pancreatitis.

Chronic pancreatitis (CP) is considered to be a rare cause of diabetes mellitus. However, in both the developed and developing world, there is an increasing number of patients suffering from pancreatitis probably due to lifestyle changes, which is partially associated with both social factors and the poor health status of immigrants. Owing to these circumstances, CP has evolved with one of the possible causes of diabetes in a selected group of patients and should be included in the differential diagnosis of diabetes. Several studies have shown that the long-term rate of diabetic complications in patients with CP and insulin-dependent diabetes is similar to that in patients with type 1 diabetes of equal duration. The hypothesis that early diagnosis of CP should result in better prognosis is not validated and may complicate the issue, since the risk of diabetes has been shown to increase significantly only once pancreatic calcification has developed. Accumulative evidence suggests that the risk of diabetes is not influenced by elective pancreatic surgical procedures other than distal pancreatectomy. The lack of contemporary data points to the urgent need for large prospective studies in order to accurately evaluate the special characteristics of disorders in glucose homeostasis in patients with CP.