Inorganic, Organic, and Perovskite Halides with Nanotechnology for High-Light Yield X- and γ-Ray Scintillators

Trends in scintillators that are used in many applications, such as medical imaging, security, oil-logging, high energy physics and non-destructive inspections are reviewed. First, we address traditional inorganic and organic scintillators with respect of limitation in the scintillation light yields and lifetimes. The combination of high–light yield and fast response can be found in Ce 3+ , Pr 3+ and Nd 3+ lanthanide-doped scintillators while the maximum light yield conversion of 100,000 photons/MeV can be found in Eu 3+ doped SrI 2 . However, the fabrication of those lanthanide-doped scintillators is inefficient and expensive as it requires high-temperature furnaces. A self-grown single crystal using solution processes is already introduced in perovskite photovoltaic technology and it can be the key for low-cost scintillators. A novel class of materials in scintillation includes lead halide perovskites. These materials were explored decades ago due to the large X-ray absorption cross section. However, lately lead halide perovskites have become a focus of interest due to recently reported very high photoluminescence quantum yield and light yield conversion at low temperatures. In principle, 150,000–300,000 photons/MeV light yields can be proportional to the small energy bandgap of these materials, which is below 2 eV. Finally, we discuss the extraction efficiency improvements through the fabrication of the nanostructure in scintillators, which can be implemented in perovskite materials. The recent technology involving quantum dots and nanocrystals may also improve light conversion in perovskite scintillators

A study of external patterning and internal forces in nanostructure growth

Uniform and orderly arranged gallium arsenide (GaAs) islands on GaAs(100) substrate are demonstrated by the combination of external patterning in the form of nanosphere lithography and internal forces in the form of catalytic effects and facet formation. The substrate was patterned with an array of 210nm diameter silica nanodisks arranged in a hexagonal fashion with periodicity of 280nm. GaAs islands were found to grow from underneath the silica nanodisks, evolving from disk shape into eventually a pyramidal shape, resulting in the toppling of the supported silica nanodisks. The resulting GaAs islands were observed to follow the size and the arrangement of the silica nanodisks closely. The phenomenon occurred consistently for each nanodisk across a large area of ~50 x 50 μm2. The demonstrated island shape evolution also shows the potential for the growth mechanism to be used to obtain island shape tunability.MASTER OF ENGINEERING (EEE

Controlling Spontaneous Emission from Perovskite Nanocrystals with Metal–Emitter–Metal Nanostructures

We show the increase of the photoluminescence intensity ratio (PLR) and the emission rate enhancement of perovskite cesium lead bromide (CsPbBr3) and formamidinium lead bromide (FAPbBr3) nanocrystals (NCs) in the presence of single and double gold layer cavities, which we refer to as Metal-Emitter (ME) and Metal-Emitter-Metal (MEM) nanostructures. Up to 1.9-fold PLRs and up to 5.4-fold emission rate enhancements were obtained for FAPbBr3 NCs confined by double gold layers, which are attributed to plasmonic confinement from the gold layers. The experimentally obtained values are validated by analytical calculations and electromagnetic simulations. Such an effective method of manipulation of the spontaneous emission by simple plasmonic nanostructures can be utilized in sensing and detection applications

Demonstration of low-loss on-chip integrated plasmonic waveguide based on simple fabrication steps on silicon-on-insulator platform

We report the experimental realization of a robust silicon-based plasmonic waveguide structure which can theoretically provide sub-wavelength confinement for Ex- and Ey-polarized surface plasmon polariton modes. Our waveguides exhibit propagation loss as low as 0.2 dB/lm with 50% coupling efficiency.Published versio

The role of cold sonicated development scenarios for achieving ultradense and high aspect ratio for optical metamaterial applications

We present a systematic study of different sonicated cold development scenarios for the purpose of achieving high density optical metamaterial. High aspect ratio sub-15-nm dots at pitch as small as 40 nm are successfully demonstrated for 110-nm thick resist at low exposure dose. Some of the key results include sub-15-nm gold nanodots at 40-nm pitch and high density optical metamaterial (with only ~30nm separation between two adjacent resonators)

Large contrast enhancement by sonication assisted cold development process for low dose and ultrahigh resolution patterning on ZEP520A positive tone resist

The authors demonstrate a robust, low dose, high contrast, and ultrahigh resolution patterning process based on sonication assisted development of ZEP520A positive tone resist in both room and cold temperature. The contrast as high as γ ∼ 25 and γ ∼ 9.14 can readily be achieved in 6 °C and room temperature development, respectively, in diluted n-amyl acetate solution. The high contrast is demonstrated on 90 nm thick ZEP resist at 20 kV acceleration voltage, from which 20 nm thick titanium lift-off of 60 nm pitch lines and 50 nm pitch dots can be successfully achieved.Published versio

Characteristics of defect modes in side-coupled and mutually coupled microresonator arrays

We present both theoretically and experimentally the existence of defect modes in side-coupled and mutually coupled microresonator arrays. The qualitative difference between the two types of defect modes is investigated. The Qfactor of both defect modes for varying defect sizes is characterized, and an enhancement of ∼30×relative to individual loaded resonators is demonstrated. The defect modes are then compared with coupled resonator–induced transparency (CRIT), indicating that the defect modes based on side-coupled microresonator arrays are actually the extension of the CRIT resonance in two-resonator structures.Published versio

Numerical and experimental studies of coupling-induced phase shift in resonator and interferometric integrated optics devices

Coupling induced effects are higher order effects inherent in waveguide evanescent coupling that are known to spectrally distort optical performances of integrated optics devices formed by coupled resonators. We present both numerical and experimental studies of coupling-induced phase shift in various basic integrated optics devices. Rigorous finite difference time domain simulations and systematic experimental characterizations of different basic structures were conducted for more accurate parameter extraction, where it can be observed that coupling induced wave vector may change sign at the increasing gap separation. The devices characterized in this work were fabricated by CMOS-process 193nm Deep UV (DUV) lithography in silicon-on-insulator (SOI) technology.Published versio

Sub-100-nm sized silver split ring resonator metamaterials with fundamental magnetic resonance in the middle visible spectrum

Split ring resonator (SRR) metamaterials working in the visible spectrum have great potential applications, but their fabrication is challenging due to the stringent requirements in the feature size and critical dimension. This paper reports fabrication and systematic characterization of silver SRRs with sub-100-nm sizes that can have magnetic resonance entering into the visible frequency spectrum. SRR size as small as ∼60 nm and fundamental magnetic resonance (LC-resonance) as short as ∼604 nm have been successfully demonstrated, which to the best of our knowledge represent the smallest fabricated SRR and the shortest LC-resonance based on SRR geometry. The resonance wavelengths of the LC and plasmon modes of the sub-100-nm SRRs are found to linearly decrease with SRR size. Excellent agreement between LC-model and experimental data is obtained when the capacitance of the sub-100-nm SRRs is interpreted as capacitance between two spheres instead of between two parallel plates

Light–matter interaction of single quantum emitters with dielectric nanostructures

Single quantum emitters are critical components for many future quantum information technologies. Novel active material systems have been developed and transitioned into engineering efforts at nanoscale. Here, we review recent progress of diverse quantum emitters and their optical properties, including fluorescent point defect in bulk and single nanocrystal, two-dimensional materials, and quantum dots (QDs). Remarkable progress has also been made in controlling spontaneous emission by utilizing the local density of optical states in dielectric photonic nanostructures. We focus on the enhanced light–matter interaction between the emitter and cavity, enabling the realization of efficient and fast single photon sources.MOE (Min. of Education, S’pore)Published versio