Boosting the thermoelectric performance of p-type heavily Cu-doped polycrystalline SnSe via inducing intensive crystal imperfections and defect phonon scattering

In this study, we, for the first time, report a high Cu solubility of 11.8% in single crystal SnSe microbelts synthesized via a facile solvothermal route. The pellets sintered from these heavily Cu-doped microbelts show a high power factor of 5.57 μW cm−1 K−2 and low thermal conductivity of 0.32 W m−1 K−1 at 823 K, contributing to a high peak ZT of ∼1.41. Through a combination of detailed structural and chemical characterizations, we found that with increasing the Cu doping level, the morphology of the synthesized Sn1−xCuxSe (x is from 0 to 0.118) transfers from rectangular microplate to microbelt. The high electrical transport performance comes from the obtained Cu+ doped state, and the intensive crystal imperfections such as dislocations, lattice distortions, and strains, play key roles in keeping low thermal conductivity. This study fills in the gaps of the existing knowledge concerning the doping mechanisms of Cu in SnSe systems, and provides a new strategy to achieve high thermoelectric performance in SnSe-based thermoelectric materials

Correction: Computer-aided design of high-efficiency GeTe-based thermoelectric devices

Correction for ‘Computer-aided design of high-efficiency GeTe-based thermoelectric devices’ by Min Hong et al., Energy Environ. Sci., 2020, DOI: 10.1039/d0ee01004a. The authors regret errors in the author affiliations in the original manuscript. The corrected list of authors and affiliations for this paper is as shown above. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers

Investigation of cracks in GaN films grown by combined hydride and metal organic vapor-phase epitaxial method

Cracks appeared in GaN epitaxial layers which were grown by a novel method combining metal organic vapor-phase epitaxy (MOCVD) and hydride vapor-phase epitaxy (HVPE) in one chamber. The origin of cracks in a 22-μm thick GaN film was fully investigated by high-resolution X-ray diffraction (XRD), micro-Raman spectra, and scanning electron microscopy (SEM). Many cracks under the surface were first observed by SEM after etching for 10 min. By investigating the cross section of the sample with high-resolution micro-Raman spectra, the distribution of the stress along the depth was determined. From the interface of the film/substrate to the top surface of the film, several turnings were found. A large compressive stress existed at the interface. The stress went down as the detecting area was moved up from the interface to the overlayer, and it was maintained at a large value for a long depth area. Then it went down again, and it finally increased near the top surface. The cross-section of the film was observed after cleaving and etching for 2 min. It was found that the crystal quality of the healed part was nearly the same as the uncracked region. This indicated that cracking occurred in the growth, when the tensile stress accumulated and reached the critical value. Moreover, the cracks would heal because of high lateral growth rate

Development of time-gated luminescence bio-imaging instruments

Thesis by publication.Bibliography: Pages 135-138.Chapter 1: Introduction -- Chapter 2: Multi-colour time-gated luminescence microscopy -- Chapter 3: Time-gated animal imaging system -- Chapter 4: Encoder-assisted scanning microscopy -- Chapter 5: Conclusions and perspectivesThe general goal for biosensing is to realize ultra-sensitive, high-contrast, rapid and high throughput detection, localization and quantification of trace amounts of biomolecules and diseased cells of rare types within complex samples. Luminescent probes, such as lanthanidecomplexes and photon upconversion nanomaterials, hold the potential to realize this goal due to their unique optical properties, which include long luminescence lifetimes in the microsecond region and as well sharp spectral emission spectra. Application of the time-gated and time-resolved techniques based on these probes will provide background-free detection conditions. But such a potential has been seriously limited by the availability of suitable instrumentsThe focus of my PhD research program is the development and the design of new instruments to realize time-domain detection towards advanced optical characterizations of luminescent materials and their analytical applications in biosensing and bioimaging. Specifically, my research project aims to advance and translate the time-gated luminescence detection technique into three prototype instruments -the multi-colour microscope, the invivo imaging system, and the high-speed scanning cytometryThe development of the first instrument, a multi-colour microscope, in this work had the specific aims of (a) increasing the detection efficiency, (b) improving the compatibility and stability, and (c) reducing the cost and complexity associated with time-gated luminescence microscopes. These aims were met by designing and engineering a high-efficiency excitation unit that is based on a high power and high repetition rate Xenon flash lamp, to provide broadband illumination for simultaneously exciting multiple lanthanide luminescent probes. The time-gated detection module of this apparatus is optimised by using a fast-rotating optimal chopper with a pinhole on the edge of the chopper blade to realise a high switching speed. The modular design has been proved to offer high compatibility and stability when installed to a commercial inverted microscope, and high-contrast dual-colour imaging has been demonstrated in this work by imaging two types of micro-organisms stained by a red-emitting europium complex and a green-emitting terbium complex, respectively, using this setup.The second instrument, an in-vivo imaging system, extended the time-gated technique usedi n background-free small animal imaging. In this work, the mechanics and optics of the time-gated detection unit of this instrument was re-designed so that this instrument became more suited to the visualization of upconversion nanoparticles when it was used as the optical contrast agents. Their ability to be excited at 980 nm and emit at 800 nm are advantageous for deep-tissue imaging of animal models because near-infrared light lies in the biological transparent window' where haemoglobin and proteins demonstrate a low absorption. In this work, it was shown that an excitation module housing up to eight 980 nm fibre-coupled diode could be engineered, and a synchronization circuit to generate time-delayed pulses with sufficient driving capacity could be designed. Capable of significantly reducing the optical background and the thermal accumulation, the system integrating near-infrared optical imaging and time-gated technique was demonstrated that could visualise upconversion nanoparticles injected into a Kunming mouse in vivo.The third instrument, a high-speed scanning cytometry, aimed to achieve high-precision pinpointing of individual luminescent targets at high sample throughput for quantitative measurements. Based on the orthogonal scanning automated microscopy (OSAM) method previously developed by members of the Author's research group, the next-generation referenced-OSAM (R-OSAM) was further engineered by integrating two linear encoders and an autofocus unit to provide the positional reference and compensate the sample tilt in real time. It has been evaluated using micrometre-scale luminescent beads incorporating down-converting lanthanide complexes or upconversion nanoparticles, crystalline microplates, colour-barcoded microrods, and quantitative suspension array assays.Through the course of this work, a range of device modules have been demonstrated with high detection efficiency, low cost, improved stability and compatibility to modify commercial systems. These create new opportunities for chemistry and biology laboratories to access advanced time-gated luminescence techniques for material characterisation and biosensing applicationsThis work is structured as a thesis by publication. The three result chapters are presentedin the form of four peer-reviewed journal papers.Mode of access: World wide web1 online resource (xviii, 138 pages

Effects of plasma and gas flow conditions on the structures and photoluminescence of carbon nanomaterials

In this work, we demonstrate the conversion of amorphous to crystalline carbon nanomaterials through the synthesis of carbon nanomaterials on silicon substrates coated with gold films in CH4-N2-H2 environment and CH4-N2-H2 plasma by hot filament chemical vapor deposition, respectively. The characterization results indicate that the flow rate of methane and plasma lead to the structural conversion and the change of composition of carbon nanomaterials, which are related to the conversion of hydrocarbon radicals to benzene molecules on the gold nanoparticles and the incorporation of nitrogen in the carbon nanomaterials caused by the plasma. Furthermore, the isothermal absorption theory was applied to study the structural conversion of amorphous to crystalline carbon nanomaterials in the CH4-N2-H2 plasma. The studies suggest that the change of surface tension caused by the dissolution of different carbon species in gold nanoparticles plays a key role for the structural conversion of the carbon nanomaterials. The photoluminescence properties of synthesized carbon nanomaterials were investigated at room temperature. The results exhibit that the carbon nanomaterials can generate the ultraviolet, blue, green and red light due to the functional groups on the surfaces of carbon nanomaterials and they are expected to emit white light after the functional groups are adjusted. The outcomes of this work are significant to control the structures of carbon nanomaterials and contribute the development of white light emission devices

The complete chloroplast genome of Chamaesium paradoxum

Chamaesium paradoxum H. Wolff is an endemic species naturally distributed in China. The complete chloroplast genome sequence of C. paradoxum was generated by de novo assembly using whole genome next generation sequencing data. The complete chloroplast genome of C. paradoxum is 153,512 bp in length, consisting of a pair of inverted repeats (IRs, 25,987 bp) separated by a large single-copy region (LSC, 84,162 bp) and a small single-copy region (SSC, 17,376 bp). There are 129 genes annotated, including 84 coding genes, 37 transfer RNA genes (tRNA), and eight ribosomal RNA genes (rRNA)

Nanocarbon phase transformations controlled by solubility of carbon species in gold nanoparticles

The hybrid structures of carbon nanomaterials reveal the excellent properties and open new windows for the applications of carbon-based nanomaterials. However, the structural transformation of carbon nanomaterials should be better understood to design the new hybrid carbon nanomaterials. For this reason, we explore the growth of carbon nanorods composed of nanocrystalline graphite sheets and amorphous carbon nanoparticles by plasma enhanced hot filament chemical vapor deposition using Au film as the catalyst. The results indicate that the carbon nanorods are a hybrid structure of nanocrystalline graphite sheets and amorphous carbon nanoparticles formed via the large Au nanoparticles. The studies of transformation mechanism indicate that the solubility of C2 and C3 carbon species in the Au nanoparticles plays an important role in the conversion between graphite carbon and amorphous carbon. Moreover, the solubility of C, C2 and C3 carbon species in the Au nanoparticles can control the graphitic nanostructure and morphology. Furthermore, the study on the photoluminescence of carbon nanorods indicates the synthesized carbon nanorods emit the ultraviolet and green light at room temperature, which originates from the hydrocarbon radicals on the carbon nanorods and the transition between π* and π bands of sp2 carbon clusters in the carbon nanorods, respectively. The results enable us not only to control the structure of carbon nanomaterials but also develop the next-generation optoelectronic devices based on carbon nanomaterials

Controlling the non-linear emission of upconversion nanoparticles to enhance super-resolution imaging performance

Upconversion nanoparticles (UCNPs) exhibit unique optical properties such as photo-emission stability, large anti-Stokes shift, and long excited-state lifetimes, allowing significant advances in a broad range of applications from biomedical sensing to super-resolution microscopy. In recent years, progress on nanoparticle synthesis led to the development of many strategies for enhancing their upconversion luminescence, focused in particular on heavy doping of lanthanide ions and core–shell structures. In this article, we investigate the non-linear emission properties of fully Yb-based core–shell UCNPs and their impact on the super-resolution performance of stimulated excitation-depletion (STED) microscopy and super-linear excitation-emission (uSEE) microscopy. Controlling the power-dependent emission curve enables us to relax constraints on the doping concentrations and to reduce the excitation power required for accessing sub-diffraction regimes. We take advantage of this feature to implement multiplexed super-resolution imaging of a two-sample mixture