Anisotropic optical response of InP self-assembled quantum dots studied by pump-probe spectroscopy

Transient anisotropic reflectivity change spectra of InP quantum dots have been observed by means of two-color pump-probe spectroscopy. The results show a fast decay component with a lifetime of 100–200 ps which depends on the probe energy, followed by the slow decay component of ~1 ns. The reflectivity change spectra have a dispersive shape having a maximum on the higher energy side of the photoluminescence (PL) band by 80 meV, and a dip located at the maximum of the PL band. Interestingly, the reflectivity change signals observed for the [1[overline 1]0] and [110] polarizations have the opposite sign when the probe energy is set between the first and second exciton states. The temporal change of spectra is simulated by means of a Monte Carlo method, and the model is found to well reproduce the experimental result. Further, the model enables us to evaluate the microscopic exciton parameters of single quantum dots by macroscopic observations. The oscillator strengths along the [110] and [1[overline 1]0] directions at the PL peak energy are evaluated to be fx=0.37 and fy=0.71, respectively. The oscillator strength is about five times smaller than simple theoretical estimates. This suggests a small overlap of the envelope functions which is consistent with the existence of a permanent dipole moment observed in these QDs

Developing 1D nanostructure arrays for future nanophotonics

There is intense and growing interest in one-dimensional (1-D) nanostructures from the perspective of their synthesis and unique properties, especially with respect to their excellent optical response and an ability to form heterostructures. This review discusses alternative approaches to preparation and organization of such structures, and their potential properties. In particular, molecular-scale printing is highlighted as a method for creating organized pre-cursor structure for locating nanowires, as well as vapor–liquid–solid (VLS) templated growth using nano-channel alumina (NCA), and deposition of 1-D structures with glancing angle deposition (GLAD). As regards novel optical properties, we discuss as an example, finite size photonic crystal cavity structures formed from such nanostructure arrays possessing highQand small mode volume, and being ideal for developing future nanolasers

C8-substituted pyrido[3,4-d]pyrimidin-4(3H)-ones: Studies towards the identification of potent, cell penetrant Jumonji C domain containing histone lysine demethylase 4 subfamily (KDM4) inhibitors, compound profiling in cell-based target engagement assays

Residues in the histone substrate binding sites that differ between the KDM4 and KDM5 subfamilies were identified. Subsequently, a C8-substituted pyrido[3,4-d]pyrimidin-4(3H)-one series was designed to rationally exploit these residue differences between the histone substrate binding sites in order to improve affinity for the KDM4-subfamily over KDM5-subfamily enzymes. In particular, residues E169 and V313 (KDM4A numbering) were targeted. Additionally, the conformational restriction of the flexible pyridopyrimidinone C8-substituent was investigated. These approaches yielded potent and cell-penetrant dual KDM4/5-subfamily inhibitors including 19a (KDM4A and KDM5B Ki = 0.004 and 0.007 μM, respectively). Compound cellular profiling in two orthogonal target engagement assays revealed a significant reduction from biochemical to cell-based activity across multiple analogues; this decrease was shown to be consistent with 2OG competition, and suggest that sub-nanomolar biochemical potency will be required with C8-substituted pyrido[3,4-d]pyrimidin-4(3H)-one compounds to achieve sub-micromolar target inhibition in cells

Flash Radiotherapy: Innovative Cancer Treatment

Flash radiotherapy (Flash-RT) is an innovative technique used in radiotherapy for cancer treatment because it delivers an extremely high dose of radiation (>40 Gy/s) to the tumour in a very short period of time, typically within a fraction of a second. This ultra-fast delivery of radiation distinguishes Flash-RT from conventional radiotherapy, which typically involves the delivery of radiation over a longer time period, often several minutes. Studies conducted in cell and preclinical models suggested that Flash-RT may spare normal tissues from radiation-related side effects, such as skin toxicity, gastrointestinal complications, and damage to organs-at-risk. This is believed to be due to the unique normal tissue response to the ultra-high dose rate. Nevertheless, while Flash-RT shows promising results in preclinical and early clinical studies, one should note that the technique is still in the early stages of development. This entry provides a comprehensive exploration of the immense potentials of Flash-RT, covering its background, mechanisms, radiation sources, recent experimental findings based on cell and preclinical models, and future prospects. It aims to provide valuable insights into this innovative radiotherapy technology for anyone interested in the subject

Laser-assisted etching for micropatterning of InP

We report on XeCl excimer (308 nm) laser-assisted dry etching ablation (LADEA) of InP in a Cl2/He atmosphere. The InClx layer produced by the chlorination process was ablated for laser fluences below 80 mJ/cm2; this was determined to be the ablation threshold of InP for our experimental conditions. We studied the influence of Cl2/He mixture pressure, laser fluence and number of pulses on the etch rate of InP. Experiments were carried out with 5% and 10% concentrations of chlorine and at a laser repetition rate of 5 Hz. Employing linearly polarized light with an appropriate choice of experimental parameters (based on the afore mentioned studies), gratings were patterned by laser-induced coherent modulation of the beam at the semiconductor surface. We have also, for the first time, combined diffraction with LADEA to develop regular shaped features on semiconductor surfaces. Using this technique, 0.3-0.5 micrometers gratings were developed on the InP surfaces by an array of rectangular apertures. This approach offers the potential for fabrication of damage-free micro- or nano-structures, as well as substrates with patterns suitable for selective area deposition/epitaxy.NRC publication: Ye

Sensing Responses Based on Transfer Characteristics of InAs Nanowire Field-Effect Transistors

Nanowire-based field-effect transistors (FETs) have demonstrated considerable promise for a new generation of chemical and biological sensors. Indium arsenide (InAs), by virtue of its high electron mobility and intrinsic surface accumulation layer of electrons, holds properties beneficial for creating high performance sensors that can be used in applications such as point-of-care testing for patients diagnosed with chronic diseases. Here, we propose devices based on a parallel configuration of InAs nanowires and investigate sensor responses from measurements of conductance over time and FET characteristics. The devices were tested in controlled concentrations of vapour containing acetic acid, 2-butanone and methanol. After adsorption of analyte molecules, trends in the transient current and transfer curves are correlated with the nature of the surface interaction. Specifically, we observed proportionality between acetic acid concentration and relative conductance change, off current and surface charge density extracted from subthreshold behaviour. We suggest the origin of the sensing response to acetic acid as a two-part, reversible acid-base and redox reaction between acetic acid, InAs and its native oxide that forms slow, donor-like states at the nanowire surface. We further describe a simple model that is able to distinguish the occurrence of physical versus chemical adsorption by comparing the values of the extracted surface charge density. These studies demonstrate that InAs nanowires can produce a multitude of sensor responses for the purpose of developing next generation, multi-dimensional sensor applications