Low-Temperature Wafer-Scale Deposition of Continuous 2D SnS2 Films

Semiconducting 2D materials, such as SnS2, hold immense potential for many applications ranging from electronics to catalysis. However, deposition of few-layer SnS2 films has remained a great challenge. Herein, continuous wafer-scale 2D SnS2 films with accurately controlled thickness (2 to 10 monolayers) are realized by combining a new atomic layer deposition process with low-temperature (250 degrees C) postdeposition annealing. Uniform coating of large-area and 3D substrates is demonstrated owing to the unique self-limiting growth mechanism of atomic layer deposition. Detailed characterization confirms the 1T-type crystal structure and composition, smoothness, and continuity of the SnS2 films. A two-stage deposition process is also introduced to improve the texture of the films. Successful deposition of continuous, high-quality SnS2 films at low temperatures constitutes a crucial step toward various applications of 2D semiconductors.Peer reviewe

Asymptotic conditions of motion for radiating charged particles

Approximate asymptotic conditions on the motion of compact, electrically charged particles are derived within the framework of general relativity using the Einstein- Infeld-Hoffmann (EIH) surface integral method. While superficially similar to the Abraham-Lorentz and Lorentz-Dirac (ALD) equations of motion, these conditions differ from them in several fundamental ways. They are not equations of motion in the usual sense but rather a set of conditions which these motions must obey in the asymptotic future of an initial value surface. In addition to being asymptotic, these conditions of motion are approximate and apply, as do the original EIH equations, only to slowly moving systems. Also, they do not admit the run- away solutions of these other equations. As in the original EIH work, they are integrability conditions gotten from integrating the empty-space (i.e., source free) Einstein-Maxwell equations of general relativity over closed two-surfaces surrounding the sources of the fields governed by these equations. No additional ad hoc assumptions, such as the form of a force law or the introduction of inertial reaction terms, needed to derive the ALD equations are required for this purpose. Nor is there a need for any of the infinite mass renormalizations that are required in deriving these other equations.Comment: 15 page

Speech rhythm: a metaphor?

Is speech rhythmic? In the absence of evidence for a traditional view that languages strive to coordinate either syllables or stress-feet with regular time intervals, we consider the alternative that languages exhibit contrastive rhythm subsisting merely in the alternation of stronger and weaker elements. This is initially plausible, particularly for languages with a steep ‘prominence gradient’, i.e. a large disparity between stronger and weaker elements; but we point out that alternation is poorly achieved even by a ‘stress-timed’ language such as English, and, historically, languages have conspicuously failed to adopt simple phonological remedies that would ensure alternation. Languages seem more concerned to allow ‘syntagmatic contrast’ between successive units and to use durational effects to support linguistic functions than to facilitate rhythm. Furthermore, some languages (e.g. Tamil, Korean) lack the lexical prominence which would most straightforwardly underpin prominence alternation. We conclude that speech is not incontestibly rhythmic, and may even be antirhythmic. However, its linguistic structure and patterning allow the metaphorical extension of rhythm in varying degrees and in different ways depending on the language, and that it is this analogical process which allows speech to be matched to external rhythms

Band gap temperature-dependence and exciton-like state in copper antimony sulphide, CuSbS2

The temperature-dependence of the band gap of the proposed photovoltaic absorber copper antimony sulphide (CuSbS2) has been studied by Fourier-transform infrared spectroscopy. The direct gap rises from 1.608 to 1.694 eV between 300 and 4.2 K. Below 200 K an exciton-like feature develops above the absorption edge at 1.82 eV. First-principles calculations evaluate band structure, band symmetries, and dipole selection rules, suggesting distinctly enhanced absorption for certain excitonic optical transitions. Striking consistency is seen between predicted dielectric and absorption spectra and those determined by ellipsometry, which reveal rapidly strengthening absorption passing 105 cm−1 at 2.2 eV. These results suggest beneficial photovoltaic performance due to strong optical absorption arising from unusually strong electron–hole interactions in polycrystalline CuSbS2 material

Band line-up investigation of atomic layer deposited TiAlO and GaAlO on GaN

A comprehensive study of the band alignments of TixAl1−xOy (with x = 9%, 16%, 25%, 36%, 100%) and GaxAl1−xOy (x = 5%, 20%, 80% and 95%) fabricated using atomic layer deposition on GaN has been presented using X-ray photoelectron spectroscopy and variable angle spectroscopic ellipsometry. The permittivity, k, has been found to be enhanced from ~10 for 9% Ti in TixAl1−xOy to 76 for TiO2, however TiO2 brings an unfavorable band alignment and a small conduction band offset (<0.1 eV) with GaN. The latter has been observed for all studied TixAl1−xOy films deposited on GaN. On the other hand, GaxAl1−xOy films show a substantial increase of the band gap from 4.5 eV for Ga2O3 to 5.5 eV for x = 20% Ga and 6.0 eV for x = 5% Ga. A strong suppression of leakage current in associated GaxAl1−xOy-based metal insulator semiconductor capacitors has also been observed, showing promise for device applications

Magnetic Resonance Imaging study of cross-sectional area of the cervical extensor musculature in an asymptomatic cohort

Magnetic Resonance Imaging (MRI) can be regarded as the gold standard for muscle imaging; however there is little knowledge about in vivo morphometric features of neck extensor muscles in healthy subjects and how muscle size alters across vertebral segments. It is not known how body size and activity levels may influence neck muscle cross-sectional area (CSA) or if the muscles differ from left and right. The purpose of this study was to establish relative CSA (rCSA) data for the cervical extensor musculature with a reliable MRI measure in asymptomatic females within a defined age range and to determine if side-side and vertebral level differences exist. MRI of the cervical spine was performed on 42 asymptomatic female subjects within the age range of 18-45. The rCSA values for the cervical extensor muscles were measured from axial T1-weighted images. We found significant side-side rCSA differences for the rectus capitis posterior minor, major (P \u3c 0.001), multifidus (P = 0.002), and the semispinalis cervicis/capitis (P = 0.001, P \u3c 0.001). There were significant vertebral level differences in rCSA of the semispinalis cervicis/capitis, multifidus, splenius capitis, and upper trapezius (P \u3c 0.001). Activity levels were shown to impact on the size of semispinalis cervicis (P = 0.027), semispinalis capitis (P = 0.003), and the splenius capitis (P = 0.004). In conclusion, measuring differences in neck extensor muscle rCSA with MRI in an asymptomatic population provides the basis for future study investigating relationships between muscular atrophy and symptoms in patients suffering from persistent neck pain. © 2005 Wiley-Liss, Inc

"Turning back the clock" on serial-stimulus sign tracking.

Two experiments examined the effects of a negative (setback) response contingency on key pecking engendered by a changing light-intensity stimulus clock (ramp stimulus) signaling fixed-time 30-s food deliveries. The response contingency specified that responses would immediately decrease the light-intensity value, and, because food was delivered only after the highest intensity value was presented, would delay food delivery by 1 s for each response. The first experiment examined the acquisition and maintenance of responding for a group trained with the contingency in effect and for a group trained on a response-independent schedule with the ramp stimulus prior to introduction of the contingency. The first group acquired low rates of key pecking, and, after considerable exposure to the contingency, those rates were reduced to low levels. The rates of responding for the second group were reduced very rapidly (within four to five trials) after introduction of the setback contingency. For both groups, rates of responding increased for all but 1 bird when the contingency was removed. A second experiment compared the separate effects of each part of the response contingency. One group was exposed only to the stimulus setback (stimulus only), and a second group was exposed only to the delay of the reinforcer (delay only). The stimulus-only group's rates of responding were immediately reduced to moderate levels, but for most of the birds, these rates recovered quickly when the contingency was removed. The delay-only groups's rates decreased after several trials, to very low levels, and recovery of responding took several sessions once the contingency was removed. The results suggest that (a) sign-tracking behavior elicited by an added clock stimulus may be reduced rapidly and persistently when a setback contingency is imposed, and (b) the success of the contingency is due both to response-dependent stimulus change and response-dependent alterations in the frequency of food delivery. The operation of the contingency is compared with the effects of secondary reinforcement and punishment procedures

Dynamic changes in the transcriptome and methylome of Chlamydomonas reinhardtii throughout its life cycle

The green alga Chlamydomonas reinhardtii undergoes gametogenesis and mating upon nitrogen starvation. While the steps involved in its sexual reproductive cycle have been extensively characterized, the genome-wide transcriptional and epigenetic changes underlying different life cycle stages have yet to be fully described. Here, we performed transcriptome and methylome sequencing to quantify expression and DNA methylation from vegetative and gametic cells of each mating type and from zygotes. We identified 361 gametic genes with mating type-specific expression patterns and 627 genes that are specifically induced in zygotes; furthermore, these sex-related gene sets were enriched for secretory pathway and alga-specific genes. We also examined the C. reinhardtii nuclear methylation map with base-level resolution at different life cycle stages. Despite having low global levels of nuclear methylation, we detected 23 hypermethylated loci in gene-poor, repeat-rich regions. We observed mating type-specific differences in chloroplast DNA methylation levels in plus versus minus mating type gametes followed by chloroplast DNA hypermethylation in zygotes. Lastly, we examined the expression of candidate DNA methyltransferases and found three, DMT1a, DMT1b, and DMT4, that are differentially expressed during the life cycle and are candidate DNA methylases. The expression and methylation data we present provide insight into cell type-specific transcriptional and epigenetic programs during key stages of the C. reinhardtii life cycle