Radiation tolerance of GaN: the balance between radiation-stimulated defect annealing and defect stabilization by implanted atoms

Realization of radiation-hard electronic devices able to work in harsh environments requires deep understanding the processes of defect formation/evolution occurring in semiconductors bombarded by energetic particles. In the present work we address such intriguing radiation phenomenon as high radiation tolerance of GaN and analyze structural disorder employing advanced co-irradiation schemes where low and high energy implants with different ions have been used. Channeling analysis revealed that the interplay between radiation-stimulated defect annealing and defect stabilization by implanted atoms dominates defect formation in the crystal bulk. Furthermore, the balance between these two processes depends on implanted species. In particular, strong damage enhancement leading to the complete GaN bulk amorphization observed for the samples pre-implanted with fluorine ions, whereas the co-irradiation of the samples pre-implanted with such elements as neon, phosphorus, and argon ions leads to a decrease of the damage.

On the Possible Nature of Armchair-Zigzag Structure Formation and Heat Capacity Decrease in MWCNTs

Structural disorder and temperature behavior of specific heat in multi walled carbon nanotubes (MWCNTs) have been investigated. The results of X-ray diffractometry, Raman spectroscopy, and transmission electron microscopy (TEM) images are analyzed. The thermodynamic theory of the zigzag-armchair domain structure formation during nanotube synthesis is developed. The influence of structural disorder on the temperature behavior of specific heat is investigated. The size of domains was estimated at ~40 nm. A decrease in heat capacity is due to this size effect. The revealed dependence of the heat capacity of MWCNTs on the structural disorder allows control over thermal properties of nanotubes and can be useful for the development of thermoelectric, thermal interface materials and nanofluids based on them.

Q61 mutant-mediated dynamics changes of the GTP-KRAS complex probed by Gaussian accelerated molecular dynamics and free energy landscapes

Q61 mutants induce structural disorder of the switch domain in KRAS and affect binding of KRAS to effectors.

Низкотемпературная фотолюминесценция монослоя WSe-=SUB=-2-=/SUB=-, полученного механическим слоением с использованием золота

We studied the optical properties of an atomically thin WSe$_2$ film obtained by gold-assisted mechanical exfoliation. Raman scattering spectra, low-temperature photoluminescence, and micro-reflection from large-scale monolayer are investigated. At room temperature, the optical properties of such a film reproduce the properties of WSe$_2$ monolayers obtained by regular mechanical exfoliation. It is shown that at low temperatures, the radiation spectra of the resulting film are determined by standard mechanisms of radiative recombination involving free excitons, bound excitons, and trions. However, in contrast to room temperatures, there is a significant difference in the spectral width and intensity of the lines compared to monolayers WSe$_2$, obtained regular way from the same source material. The differences found, demonstrating a significant increase in background doping and structural disorder when using gold-assisted exfoliation, may be meaningful for a number of optoelectronic applications of atomically thin WSe$_2$ films.

Structural Disorder in Layered Hybrid Halide Perovskites: Types of Stacking Faults, Influence on Optical Properties and Their Suppression by Crystallization Engineering

Layered hybrid halide perovskites (LHHPs) are an emerging type of semiconductor with a set of unique optoelectronic properties. However, the solution processing of high-quality LHHPs films with desired optical properties and phase composition is a challenging task, possibly due to the structural disorder in the LHHP phase. Nevertheless, there is still a lack of experimental evidence and understanding of the nature of the structural disorder in LHHPs and its influence on the optical properties of the material. In the current work, using 2D perovskites (C4H9NH3)2(CH3NH3)n−1PbnI3n+1 (further BA2MAn−1PbnI3n+1) with n = 1–4 as a model system, we demonstrate that deviations in LHHPs optical properties and X-ray diffraction occur due to the presence of continuous defects—Stacking Faults (SFs). Upon analyzing the experimental data and modeled XRD patterns of a possible set of stacking faults (SFs) in the BA2MAPb2I7 phase, we uncover the most plausible type of SFs, featured by the thickness variation within one perovskite slab. We also demonstrate the successful suppression of SFs formation by simple addition of BAI excess into BA2MAn−1PbnI3n+1 solutions.

Linking topological features of the Hofstadter model to optical diffraction figures

In two, three and even four spatial dimensions, the transverse responses experienced by a charged particle on a lattice in a uniform magnetic field are fully controlled by topological invariants called Chern numbers, which characterize the energy bands of the underlying Hofstadter Hamiltonian. These remarkable features, solely arising from the magnetic translational symmetry, are captured by Diophantine equations which relate the fraction of occupied states, the magnetic flux and the Chern numbers of the system bands. Here we investigate the close analogy between the topological properties of Hofstadter Hamiltonians and the diffraction figures resulting from optical gratings. In particular, we show that there is a one-to-one relation between the above mentioned Diophantine equation and the Bragg condition determining the far-field positions of the optical diffraction peaks. As an interesting consequence of this mapping, we discuss how the robustness of diffraction figures to structural disorder in the grating is a direct analogy of the robustness of transverse conductance in the Quantum Hall effect.

Multivariate Analysis of Disorder in Metal–Organic Frameworks

The rational design of disordered frameworks is an appealing route to target functional materials. However, intentional realisation of such materials relies on our ability to readily characterise and quantify structural disorder. Here, we use multivariate analysis of pair distribution functions to fingerprint and quantify the disorder within a series of compositionally identical metal–organic frameworks, possessing different crystalline, disordered, and amorphous structures. We find this approach can provide powerful insight into the kinetics and mechanism of structural collapse that links these materials. Our methodology is also extended to a very different system, namely the melting of a zeolitic imidazolate framework, to demonstrate the potential generality of this approach across many areas of disordered structural chemistry.

Direct observation of one-dimensional disordered diffusion channel in a chain-like thermoelectric with ultralow thermal conductivity

Structural disorder, highly effective in reducing thermal conductivity, is important in technological applications such as thermal barrier coatings and thermoelectrics. In particular, interstitial, disordered, diffusive atoms are common in complex crystal structures with ultralow thermal conductivity, but are rarely found in simple crystalline solids. Combining single-crystal synchrotron X-ray diffraction, the maximum entropy method, diffuse scattering, and theoretical calculations, here we report the direct observation of one-dimensional disordered In1+ chains in a simple chain-like thermoelectric InTe, which contains a significant In1+ vacancy along with interstitial indium sites. Intriguingly, the disordered In1+ chains undergo a static-dynamic transition with increasing temperature to form a one-dimensional diffusion channel, which is attributed to a low In1+-ion migration energy barrier along the c direction, a general feature in many other TlSe-type compounds. Our work provides a basis towards understanding ultralow thermal conductivity with weak temperature dependence in TlSe-type chain-like materials.