The hydrostatic pressure coefficients of interband transition energies of a number of single-walled carbon nanotubes with different chiralities were measured. Optical experiments were performed on debundled, single-walled carbon nanotube suspensions with hydrostatic pressure applied by diamond anvil cells. The pressure coefficients of the band-gap energies are negative and dependent on the nanotube structure, while the second van Hove transitions are much less sensitive to hydrostatic pressure. An empirical equation that relates the pressure coefficients to nanotube structure is presented and discussed.

Alloying III–V compounds with small amounts of nitrogen leads to a dramatic reduction of the fundamental band-gap energy in the resulting dilute nitride alloys. The effect originates from an anticrossing interaction between the extended conduction-band states and localized N states. The interaction splits the conduction band into two non-parabolic subbands. The downward shift of the lower conduction subband edge is responsible for the N-induced reduction of the fundamental band-gap energy. The changes in the conduction band structure result in a significant increase in electron effective mass and a decrease in the electron mobility, and lead to a large enhancement of the maximum doping level in GaInNAs doped with group VI donors. In addition, a striking asymmetry in the electrical activation of group IV and group VI donors can be attributed to mutual passivation process through formation of the nearest neighbour group-IV donor nitrogen pairs.

The elastic properties and structural phase transitions of individual VO(2) nanowires were studied using an in situ push-to-pull microelectromechanical device to realize quantitative tensile analysis in a transmission electron microscope and a synchrotron X-ray microdiffraction beamline. A plateau was detected in the stress-strain curve, signifying superelasticity of the nanowire arising from the M1-M2 structural phase transition. The transition was induced and controlled by uniaxial tension. The transition dynamics were characterized by a one-dimensionally aligned domain structure with pinning and depinning of the domain walls along the nanowire. From the stress-strain dependence the Young's moduli of the VO(2) M1 and M2 phases were estimated to be 128 ± 10 and 156 ± 10 GPa, respectively. Single pinning and depinning events of M1-M2 domain wall were observed in the superelastic regime, allowing for evaluation of the domain wall pinning potential energy. This study demonstrates a new way to investigate nanoscale mechanics and dynamics of structural phase transitions in general.

The experimental study of InN and In-rich InGaN by a number of structural, optical and electrical methods is reviewed. Recent advances in thin film growth have produced single crystal epitaxial layers of InN which are similar in structural quality to GaN films made under similar conditions and which can have electron concentrations below 1 × 1018 cm−3 and mobilities exceeding 2000 cm2 (Vs)−1. Optical absorption, photoluminescence, photo-modulated reflectance and soft x-ray spectroscopy measurements were used to establish that the room temperature band gap of InN is 0.67 ± 0.05 eV. Experimental measurements of the electron effective mass in InN are presented and interpreted in terms of a non-parabolic conduction band caused by the k · p interaction across the narrow gap. Energetic particle irradiation is shown to be an effective method to control the electron concentration, n, in undoped InN. Optical studies of irradiated InN reveal a large Burstein–Moss shift of the absorption edge with increasing n. Fundamental studies of the energy levels of defects in InN and of electron transport are also reviewed. Finally, the current experimental evidence for p-type activity in Mg-doped InN is evaluated.

Abstract We report multiwavelength observations and theoretical modeling of the afterglow of gamma-ray burst (GRB) 151027A. The object exhibits a complete evolutionary sequence, including prompt gamma-ray and optical emission, an initial optical onset bump, an optical rebrightening, a late-time supernova bump, an X-ray flare, and two distinct X-ray plateaus. GRB 151027A exhibits nearly all characteristic features observed in GRB afterglows. Such a rich set of features within a single event is exceptionally rare. We show that the first X-ray plateau followed by a rapid decay can be attributed to the collapse of a newly formed magnetar to form a black hole. The second X-ray plateau can be explained by fallback accretion. We find that the energy-injection model successfully reproduces the optical rebrightening of GRB 151027A. The late-time optical bump is well described by a 56 Ni-powered supernova light curve. GRB 151027A presents a complete physical picture for GRB phenomenology, whereas reconstructing such a comprehensive picture previously required the statistical analysis of multiple GRBs.

We report Raman and time-resolved photoluminescence spectroscopic studies of multiwalled BN and B{sub x}C{sub y}N{sub z} nanotubes. The Raman spectroscopy shows that the as-grown B{sub x}C{sub y}N{sub z} charge recombination, respectively. Comparison of the photoluminescence of BN nanotubes to that decay process is characterized by two time constants that are attributed to intra- and inter-BN sheet nanotubes as predicted by theory. nanotubes are radially phase separated into BN shells and carbon shells. The photoluminescence of hexagonal BN is consistent with the existence of a spatially indirect band gap in multi-walled BN.

InN films with free electron concentrations ranging from mid-1017 to mid-1020 cm−3 have been studied using optical absorption, Hall effect, and secondary ion mass spectrometry. The optical absorption edge covers a wide energy range from the intrinsic band gap of InN of about 0.7 to about 1.7 eV which is close to the previously accepted band gap of InN. The electron concentration dependence of the optical absorption edge energy is fully accounted for by the Burstein–Moss shift. Results of secondary ion mass spectrometry measurements indicate that O and H impurities cannot fully account for the free electron concentration in the films.

Temperature-gradient Metalorganic Chemical Vapor Deposition was used to deposit In{sub x}Ga{sub 1-x}N/GaN multiple quantum well structures with a concentration gradient of indium across the wafer. These multiple quantum well structures were deposited on low defect density (2 x 10{sup 8} cm{sup -2}) GaN template layers for investigation of microstructural properties and V-defect (pinhole) formation. Room temperature photoluminescence and photomodulated transmission were used for optical characterization which show a systematic decrease in emission energy for a decrease in growth temperature. Triple-axis X-ray diffraction, scanning electron microscopy and cross-section transmission electron microscopy were used to obtain microstructural properties of different regions across the wafer. Results show that there is a decrease in crystal quality and an increase in V-defect formation with increasing indium concentration. A direct correlation was found between V-defect density and growth temperature due to increased strain and indium segregation for increasing indium concentration.

Abstract Supernova (SN) 2025coe at a distance of ∼25 Mpc is the second-closest calcium-strong transient. It was discovered at a large projected offset of ∼34 kpc from its potential host galaxy NGC 3277. Multiband photometry of SN 2025coe indicates the presence of two peaks at day ∼2 and day ∼11 after explosion. Modeling the bolometric light curve, we find that the first peak can be reproduced either by shock cooling of a compact envelope ( R env ≈6–40 R ⊙ ; M env ≈0.1–0.2 M ⊙ ) or by interaction with close-in circumstellar material (CSM; R CSM ≲ 6 × 10 14 cm), or a combination of both. The second peak is dominated by radioactive decay of 56 Ni ( M ej ≈ 0.4–0.5 M ⊙ ; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mrow> <mml:mn>56</mml:mn> </mml:mrow> </mml:msup> <mml:mi mathvariant="normal">Ni</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>1.4</mml:mn> <mml:mo>×</mml:mo> <mml:mn>1</mml:mn> <mml:msup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> M ⊙ ). SN 2025coe rapidly evolves from the photospheric phase dominated by He I P Cygni profiles to nebular phase spectra dominated by strong [Ca ii ] λλ 7291, 7323 and weak [O i ] λλ 6300, 6364 emission lines. Simultaneous line profile modeling of [Ca ii ] and [O i ] at nebular phases shows that an asymmetric core-collapse explosion of a low-mass (≲3.3 M ⊙ ) He-core progenitor can explain the observed line profiles. Alternatively, lack of local star formation at the site of the SN explosion combined with a low ejecta mass is also consistent with a thermonuclear explosion due to a low-mass hybrid He-C/O white dwarf +C/O white dwarf merger.

The direct gap of the In_1-xGa_xN alloy system extends continuously from InN (0.7 eV, in the near IR) to GaN (3.4 eV, in the mid-ultraviolet). This opens the intriguing possibility of using this single ternary alloy system in single or multi-junction (MJ) solar cells. A number of measurements of the intrinsic properties of InN and In-rich In_1-xGa_xN alloys (0 < x < 0.63) are presented and discussed here. To evaluate the suitability of In_1-xGa_xN as a material for space applications, extensive radiation damage testing with electron, proton, and alpha particle radiation has been performed. Using the room temperature photoluminescence intensity as a indirect measure of minority carrier lifetime, it is shown that In_1-xGa_xN retains its optoelectronic properties at radiation damage doses at least 2 orders of magnitude higher than the damage thresholds of the materials (GaAs and GaInP) currently used in high efficiency MJ cells. Results are evaluated in terms of the positions of the valence and conduction band edges with respect to the average energy level of broken-bond defects (Fermi level stabilization energy <i>E_FS</i>). Measurements of the surface electron concentration as a function of <i>x</i> are also discussed in terms of the relative position of <i>E_FS</i>. The main outstanding challenges in the photovoltaic applications of In_1-xGa_xN alloys, which include developing methods to achieve p-type doping and improving the structural quality of heteroepitaxial films, are also discussed.

Ternary and quaternary dilute II–VI oxides were synthesised using a highly non-equilibrium method: the combination of O ion implantation and pulsed-laser melting. CdOxTe1−x thin films have been produced with x up to 0.015 and with the energy gap reduced by 0.15 eV. Optical transitions corresponding to both the lower (E−) and upper (E+) conduction sub-bands, resulting from the anticrossing interaction between the localised O states and the extended conduction states of the matrix, are clearly observed in quaternary Cd0.6Mn0.4OxTe1−x and Zn0.88Mn0.12OxTe1−x layers. These results have important implications for the existing theoretical models of the electronic structure of the highly mismatched alloys. In Zn1−xMnxTe, where the O level lies below the conduction band edge, it was demonstrated that incorporation of a small amount of oxygen leads to the formation of a narrow, oxygen-derived band of extended states located well below the conduction band edge of the ZnMnTe matrix. The three absorption edges of this material (∼0.73, 1.83 and 2.56 eV) cover the entire solar spectrum providing a material envisioned for multiband, single-junction, high-efficiency photovoltaic devices.

We report the synthesis of single-crystalline GeTe nanowires (NWs) and nanohelices (NHs) using a vapor transport method assisted by metal catalysts. The NWs have typical diameters of 65 +/- 20 nm and lengths reaching up to 50 mum, while NHs have an average helix diameter of 135 +/- 30 nm, with widely varying pitches. Electron microscopy and diffraction measurements show that these NWs and NHs are single crystalline and exhibit a rhombohedral structure. The devices incorporating individual GeTe NWs exhibit nonvolatile resistance changes associated with voltage-driven crystalline-amorphous transitions, suggesting that these NWs can be the basis of an electrically driven nonvolatile memory.

A method is proposed and tested which allows for the accurate determination of the carrier collection efficiency and minority carrier diffusion length in Cu(In,Ga)Se2 solar cells using energy dependent electron beam induced current. Gallium composition gradients across the film thickness introduce quasielectric fields that are found to improve collection efficiency when they are located toward the rear of the sample. The quasielectric fields are also shown to reduce the influence of back surface recombination. The strengths and limitations of this technique are discussed and compared with external quantum efficiency measurements.