Lifetime Product Research Articles

Toward achieving cost-effective hexagonal BN semi-bulk crystals and BN neutron detectors via halide vapor phase epitaxy

Presently, thermal neutron detectors fabricated from boron-10 enriched hexagonal boron nitride (h-10BN) ultrawide bandgap semiconductor grown by metal organic chemical vapor deposition (MOCVD) hold the record high detection efficiency among all solid-state detectors at 59%. To overcome the short comings of MOCVD growth, including inherently low growth rate and unavoidable impurities such as carbon in metal organic source, we demonstrate here the growth of natural hexagonal boron nitride (h-BN) semi-bulk wafers using halide vapor phase epitaxy (HVPE), which is an established technique for producing GaN semi-bulk crystals at a high growth rate. Electrical transport characterization results revealed that these HVPE grown materials possess an electrical resistivity of 1 × 1013 Ω cm, and a charge carrier mobility and lifetime product of 2 × 10−4 cm2/V s. Detectors fabricated from a 100 μm thick h-BN wafer have demonstrated a thermal neutron detection efficiency of 20%, corresponding to a charge collection efficiency of ∼60% at an operating voltage of 500 V. This initial demonstration opens the door for mass producing high efficiency h-BN semiconductor neutron detectors at a reduced cost, which could create unprecedented applications in nuclear energy, national security, nuclear waste monitoring and management, the health care industry, and material sciences.

High charge collection efficiency detector based on plasma purified high-quality diamond

Diamond radiation detector is an ideal choice for the next-generation radiation detection in harsh environments, due to its small size, high irradiation resistance and fast response. However, high-purity single crystal diamond is hard to be prepared at the high growth rate due to the inevitable impurity incorporation. In this paper, based on the high-quality high-temperature/high-pressure (HPHT) single crystal diamond substrate, detector-grade single crystal diamonds material with high purity and low defect density were epitaxially grown at growth rate of about 4 μm/h by using plasma environment purification technology. It showed that the full width at half maximum of X-ray rocking curve of high-quality single crystal diamond could reach 0.007°, there was no nitrogen related impurity in PL spectrum, and the substitutional nitrogen content estimated by UV absorption spectrum was less than 10 ppb. After metallization and packaging process, the diamond detectors were prepared and the detector response under irradiation with 241 Am α-particles was realized. For the sample with fewer dislocations, the charge collection efficiency and energy resolution of this detector were 86.8 % and 7.85 % for electrons, and 96.7 % and 2.48 % for holes. The product of mobility and lifetime of electrons and holes were 1.7 × 10 −4 cm 2 V −1 and 3.7 × 10 −4 cm 2 V −1 , respectively. The high performances of the detector indicate that the current diamond detector can meet the application requirements of commercial diamond detectors. • Detector-grade diamond was prepared by plasma environment purification technology. • The high-purity single crystal diamond was grown at growth rate of about 4 μm/h. • The diamond detector with charge collection efficiency of 96.7 % was realized. • The products of mobility and lifetime of electrons and holes were 1.7 × 10 −4 and 3.7 × 10 −4 cm 2 V −1 .

Flexible perovskite scintillators and detectors for X-ray detection.

X-ray detection and imaging technology has been rapidly developed for various fields since 1895, offering great opportunities to scientific and industrial communities. Particularly, flexible X-ray detectors have drawn numerous attention in medical-related applications, solving the uniform issues of traditional rigid X-ray detectors. Out of all the potential materials, metal halide perovskites (MHPs) have been emerged as excellent candidates as flexible X-ray scintillators and detectors owing to the advantages including low temperature solution processable, strong X-ray absorption coefficient, large mobility lifetime product and tunable bandgap. In this review, the recent advances of MHP-based flexible X-ray detectors are comprehensively summarized, focusing on the scalable synthesis technologies of materials and diverse device architectures, and covering both direct and indirect X-ray detection. A brief outlook that highlights the current challenges impeding the commercialization of flexible MHP-based X-ray detectors is also included with possible solutions to those problem being provided.

An inventory model for perishable item with two-stage pricing

The purpose of this study is to determine an optimal inventory policy for perishable item with two-stage pricing mechanism in selling process. Inventory is one of the most important parts in business and industry that affects the profit. Control of inventory affects the costs incurred by the company, therefore the inventory must be balanced with needs. If the inventory is higher than needed, the company will be spending higher storage costs and the risk of damage to inventory, but if the inventory is lower than needed, there will be a production delay and the company will be unable to supply demand on time. This paper deals with fixed lifetime products by using two-stage pricing strategy, especially for agricultural products that are perishable and have a short shelf life. Using the concept of two-stage pricing mechanism in selling process, the mathematical expression for the profit function is derived and a solution procedure is proposed to determine the optimal policy. Finally, a numerical example is provided to illustrate the solution procedure. The results of this research can provide inventory managers with valuable suggestions in making the production policy.

A New Process Performance Index for the Weibull Distribution with a Type-I Hybrid Censoring Scheme

A new life performance index is proposed for evaluating the quality of lifetime products. The maximum likelihood estimation method and the Bayesian approaches using informative and non-informative prior distributions are utilized to infer the parameters of the Weibull distribution and the proposed new life performance index under a Type-I hybrid censoring scheme. Monte Carlo simulation results show that two Bayesian approaches outperform the maximum likelihood estimation method in terms of the measures of relative bias, relative mean square error, and coverage probability for the point and confidence interval estimators, respectively. The Bayesian approach using a non-informative prior distribution is recommended if the knowledge of setting up the hyper-parameters in the informative prior distribution is not available. Two real data sets are provided for illustration.

High‐Quality 0D Cs4PbBr6‐Based Dense Wafer for High‐Sensitivity X‐Ray Detection and High‐Resolution Imaging in Harsh Environment

AbstractThe use of metal halides promotes the development of X‐ray detectors (XDs) owing to their excellent X‐ray absorbance, electrically benign defects, and large mobility−lifetime (µτ) product. Yet the severe baseline drift, size limitation, large dark current, and mediocre stability are still waiting to be solved. Herein, high density size‐scalable Cs4PbBr6 wafer‐based XD is constructed by the hot isostatic‐pressed method for the first time. Meanwhile, different Br− vacancy (VBr) concentration‐based Cs4PbBr6 is realized. The role of VBr in electrical structure and charge transport is highlighted by density functional theory and experimental measurement. Moreover, the further study points the 0D structure endows Cs4PbBr6 with high activation energy for ionic transport (1044 meV) and bandgap (3.88 eV), which finally results in an ultra‐stable baseline and thermal stability. On the basis of efficient response (7068 µC Gyair−1 cm−2), reliable current output, ultra‐low detection limit (1.75 nGyair s−1), high spatial resolution (5.2 lp mm−1 at modulation transfer function = 0.2), fast response speed and radiation stabilities (>1000 Gyair), the high‐resolution X‐ray images under broad energy range (20–160 keV) are realized on both single‐pixel and linear scanning mode, thus holding huge potential for medical diagnosis, safety inspection, and outer space detection.

Effects of annealing in Te2 atmosphere on photoelectric properties and carrier transport properties of CdZnTe films

CdZnTe (CZT) epitaxial films were deposited on GaAs substrates by closed spaced sublimation. In order to reduce the adverse effects of point defects and dislocations in the film on its properties, CZT films were annealed at 400 °C in Te2 atmosphere at different times. The I–V test and energy spectrum show that the resistivity of CZT films increased from 109 Ω cm to 1010 Ω cm, and the electron mobility lifetime product (μτ)e increased from 10−5 cm2 V−1 to 10−4 cm2 V−1. According to the etch pit density and photoluminescence tests, the results show that annealing reduced the dislocation density from 3.28 × 105 cm−2 to 2.52 × 105 cm−2 in the CdZnTe films. In this study, the annealing process which can stably improve the properties of CdZnTe films is obtained, that is, annealing at 400 °C in Te2 atmosphere for 2–4 h.

Performance optimization of CZT thick films by CdTe buffer layers for solar-blind ultraviolet photoelectric detectors

CdZnTe (CZT) thick films with CdTe buffer layers (CZT/CdTe) were studied for high-performance ultraviolet photoelectric detector. CZT thick films were prepared on AlN/Si substrates via close-spaced sublimation (CSS) and CdTe buffer layers were introduced to optimize the interface quality of CZT thick films. Results of x-ray diffraction showed that the full width at half maximum (FWHM) and dislocation density (δ) of interface of optimized samples were 0.156 ° and 2.543 × 1014 lin/m2, respectively. Interface detect analysis of free-standing CZT and CZT/CdTe thick films was studied by x-ray photoelectron spectroscopy (XPS) and low-temperature photoluminescence (PL) spectroscopy, and mechanism of in-situ annealing in CdTe atmosphere to reduce interfacial defect states was discussed. Moreover, the photo-dark current ratio of the CZT/CdTe thick film metal-semiconductor-metal (MSM) structural photodetector was as high as 5530, which was nearly double that of the CZT thick film detector, and the carrier mobility lifetime product could reach 5.59 × 10−4 cm2/V at 100 V bias, confirming the improvement of carrier transport capacity and detection efficiency. CZT-based detectors have inestimable prospect in the field of solar-blind ultraviolet detection with the participation of CdTe buffer layers.

High scintillation yield and fast response to alpha particles from thin perovskite films deposited by pulsed laser deposition

Although the field of solar cells is the most popular application of perovskite materials, their use in radiation detection applications is emerging. The success of perovskites as radiation detectors rests partly on the same material properties that have led to successful optoelectronics applications, meaning that other specific properties, like large stopping power, high mobility lifetime product, fast response, and large bulk resistance, play a role. In this respect, inorganic perovskites are attracting a lot of attention as scintillator materials with performances sensitive to material shape (single crystals, nanocrystals, and thin films) and growth methods. In this study, we report on the morphological, structural, and optical response of thin CsPbBr3-based perovskite films, deposited by Pulsed Laser Deposition (PLD) and post-growth annealed at 350°C in air, following excitation by different particle sources. The annealing treatment resulted in a prompt structural refinement, grain growth, and oxygen bonding to the Pb phase together with an enrichment of the surface in chemo-adsorbed oxygen probably due to Cs–O interactions, as evidenced by X-ray photoelectron spectroscopy. The film behavior under 2 MeV H+ ion beam irradiation at different fluences was analyzed together with its scintillation properties following an interaction with α particles from an Am-241 radioactive source demonstrating a very fast response for an inorganic material (∼5ns) and a photoelectron yield of about ∼47% with respect to a commercial CsI:Tl scintillator.

Jointly Rayleigh lifetime products in the presence of competing risks model

Abstract In this article, we are applying the competing risks model of product from two different lines of production. So, the comparative life test is done under type-II censoring scheme with consideration of only two independent causes of failure. The statistical analysis procedures are developed considering joint sample of production and its life distributed with the Rayleigh lifetime distribution. The point estimation and the corresponding asymptotic confidence interval of the model parameters under maximum likelihood are constructed. Two bootstrap confidence intervals, bootstrap- p p , and bootstrap- t t , are discussed. Also, Bayesian approach to estimate point and credible interval is constructed. The estimation results are discussed through data set analyses. The validity of theoretical results is assessed and compared through Monte Carlo study. Finally, some of the points are reported as a brief comment.

Charge Transport and Photoconductivity in a Hybrid Uranium(IV) Halide Perovskite.

Hybrid metal halide perovskites are extensively synthesized using p- and d-elements. However, the properties of hybrid halide perovskites involving 5f-elements are still elusive. Herein, we first report the semiconductive property of a uranium-bearing hybrid halide perovskite, [N(C2H5)4]2UCl6 (EAUCl). Single crystal X-ray crystallography demonstrates that EAUCl adopts a zero-dimensional molecular structure consisting of isolated [UCl6]2- anions and organic cations. The intrinsically semiconductive property endows EAUCl with obvious charge transport and photoconductivity, with a high carrier mobility lifetime (μτ) product of 9.91 × 10-4 cm2/V and a photocurrent on-off ratio of 380 under X-ray excitation. Theoretical calculations corroborate that the U 5f orbitals are involved in electron transitions and the formation of band structure.

Effect of low-temperature rapid annealing on structural and electrical properties of electroless platinum contacts on CdZnTe detectors

In this work, platinum (Pt) electrodes were deposited on CdZnTe wafers by electroless H2PtCl4 solution and subsequently annealed at different temperature from 323 K to 473 K. Focused ion beam (FIB) imaging, transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), current-voltage (I–V) analysis and energy spectra under 241Am irradiation were adopted to investigate the effect of low-temperature rapid annealing on interface structure, electrical and carrier transport properties of Pt/CdZnTe samples. Single-crystal PtTe layer with [100] orientation and thickness of 20 nm was found in the interface between electroless Pt and CdZnTe wafer. The leakage current of the Pt/CdZnTe detectors at 200 V decreased from 212 nA cm−2 to 101 nA cm−2 after low-temperature rapid annealing, due to a decrease of voltage drop across the PtTe interface layer. The energy spectra and carrier transport performance of Pt/CdZnTe detectors suggested that the optimal annealing temperature was 423 K. The energy spectra of Pt/CdZnTe detector under 241Am showed that the FWHM was improved from 23.3% to 14.4%, while the full charge collection and mobility lifetime product of electrons increasing from 611 to 625 and 3.17 × 10−3 to 3.76 × 10−3 cm2 V−1 s−1, respectively.

Growth and characterization of detector-grade CdMnTeSe

The Cd0.95Mn0.05Te0.98Se0.02 (CMTS) ingot was grown by the vertical Bridgman technique at low pressure. All wafers showed high resistivity, which suggests potential as a room-temperature semiconductor detector. The resistivity of the CMTS planar detector was 1.47 × 1010 Ω· cm and mobility lifetime product of electrons was 1.29 × 10−3 cm2/V. The spectroscopic property with Am-241 and Co-57 was evaluated. The energy resolution about 59.5 keV gamma-ray of Am-241 was 11% and the photo-peak of 122 keV gamma-ray from Co-57 was clearly distinguished. The result shows the first detector-grade CMTS in the world and proves CMTS’s potential as a radiation detector operating at room temperature.

Socially-aware and energy-efficient resource allocation and power control for D2D multicast content distribution

Nowadays, a significant portion of the base station's traffic is dedicated to the increasing demand for the same multimedia content in local area services. Device-to-device (D2D) multicast communications are considered an effective and practical approach for tackling such a challenge in 4G/5G cellular networks. Due to the limited power source of the devices, this paper aims to jointly maximize their energy efficiency and lifetime while satisfying the quality of service (QoS) and the minimum battery power of users. To accomplish this aim, D2D multicast clusters are first formed considering the information of the physical distance, the social distance, and the energy levels of the devices' batteries. Then, cluster-head selection, power control, and resource allocation are carried out to maximize the product of energy efficiency and lifetime, which converts the multi-objective problem to a single-objective one. This optimization problem is non-convex and nonlinear; thus, it is divided into two convex sub-problems. In the first sub-problem, for each candidate cluster-head and corresponding cellular user, the power allocation is performed to maximize energy efficiency. Then, the resource allocation and the cluster-head selection are performed by solving the second sub-problem using the one-to-one Hungarian matching algorithm to maximize the life-energy efficiency. Results of extensive evaluation show that our proposed scheme improves energy efficiency and increases the cluster-head life in D2D multicast services.

Short lifetime product supply chain coordination and social benefit considering cannibalization effect and market segmentation

Short lifetime product retailers often face the challenge of cannibalization between new and old products, which can negatively impact their profitability. They attempt to influence consumers’ choices through price differentiation, resulting in internal competition regarding products’ age and price. The pricing decisions affect market demand, sales volume, and as a result, the whole supply chain (SC) profit. This paper coordinates inventory and pricing decisions in a short lifetime product supply chain (SLPSC), considering the cannibalization effect. The investigated SLPSC includes a supplier and a retailer operating in a segmented market. Firstly, the optimal decisions of the SLPSC members are obtained under decentralized and centralized decision-making structures. Then, a new coordination contract named wholesale price and double compensation (WPDC) is designed to motivate the SC members to shift from the decentralized structure to the centralized one. The findings indicate that the coordinated model creates more economic profitability for the whole SLPSC than the decentralized one. Furthermore, the proposed WPDC contract is more beneficial for the SLPSC from a social viewpoint, as it increases consumer surplus. The results also demonstrate that when consumers are more sensitive to the product’s freshness, a price differentiation policy is more profitable than the same pricing.

Life time and mobility product of injected charge carriers in copper II phthalocyanine thin films with different phase structure

Using near-field scanning microwave microprobe (NSMM) method we have observed thedistribution of injected charge carriers along conductivity channel in CuPc thin film on dependence ofapplied bias. From scan data were calculated diffusion length and product fi-r for injected charges fromAu electrode to CuPc thin film. By scanning electron microscopy method were investigated morphologyproperties of CuPc thin films, which explains the difference of product /n-r for injected charge carriers inCuPc thin films with different crystal phase structure.

Effect of unmanned aerial vehicle (drone) delivery on blood product delivery time and wastage in Rwanda: a retrospective, cross-sectional study and time series analysis

The accessibility of blood and blood products remains challenging in many countries because of the complex supply chain of short lifetime products, timely access, and demand fluctuation at the hospital level. In an effort to improve availability and delivery times, Rwanda launched the use of drones to deliver blood products to remote health facilities. We evaluated the effect of this intervention on blood product delivery times and wastage. We studied data from 20 health facilities between Jan 1, 2015, and Dec 31, 2019, in Rwanda. First, we did a cross-sectional comparison of data on emergency delivery times from the drone operator collected between March 17, 2017, and Dec 31, 2019, with two sources of estimated driving times (Regional Centre for Blood Transfusion estimates and Google Maps). Second, we used interrupted time series analysis and monthly administrative data to assess changes in blood product expirations after the commencement of drone deliveries. Between March 17, 2017, and Dec 31, 2019, 12 733 blood product orders were delivered by drones. 5517 (43%) of 12 733 were emergency orders. The mean drone delivery time was 49·6 min (95% CI 49·1 to 50·2), which was 79 min faster than existing road delivery methods based on estimated driving times (p<0·0001) and 98 min faster based on Google Maps estimates (p<0·0001). The decrease in mean delivery time ranged from 3 min to 211 min depending on the distance to the facility and road quality. We also found a decrease of 7·1 blood unit expirations per month after the start of drone delivery (95% CI -11·8 to -2·4), which translated to a 67% reduction at 12 months. We found that drone delivery led to faster delivery times and less blood component wastage in health facilities. Future studies should investigate if these improvements are cost-effective, and whether drone delivery might be effective for other pharmaceutical and health supplies that cannot be easily stored at remote facilities. Canadian Institutes for Health Research.

Coordinated inventory control and pricing policies for online retailers with perishable products in the presence of social learning

During the period of COVID-19, restrictive social distancing measures have stimulated retailers to increasingly turn to online selling platforms and apply social technologies in marketing even for food and grocery products. Social technologies create opportunities for online retailers to effectively facilitate word-of-mouth communication by allowing consumers to share their consumption experiences. It makes consumers’ behavior more observable to potential customers and leads to social learning. Social learning has a notable impact on purchasing decisions of potential customers, influencing the demand for the product. In this regard, this paper aims to examine the coordinated dynamic pricing and inventory control problem for a perishable product under social learning. The idea is that online retailers who sell a perishable product under Expiration Date-Based Pricing (EDBP) policy counteract the negative quality inference of this practice through social learning. To formulate the problem, a mathematical model is developed and its structural properties are analyzed for a two-period lifetime product. Furthermore, numerical analysis is conducted in a real case study to derive some managerial insights. The obtained results show that the online retailer can promote the EDBP by adopting a consumer-generated online review system. As well, to better exploit the system, the online retailer should adjust the product pricing and inventory control policies with the evolution of consumers’ ratings. Finally, the firm’s profit and waste avoidance are improved by incorporating consumers’ social learning behavior into the pricing and inventory policies.

Ultralow Detection Limit and Robust Hard X-ray Imaging Detector Based on Inch-Sized Lead-Free Perovskite Cs3Bi2Br9 Single Crystals.

Halide perovskites are promising candidates for soft X-ray detection (<80 keV) owing to their high X-ray absorption coefficient, resistivity, and mobility lifetime product. However, the lack of large high-quality single crystals (SCs) renders it challenging to manufacture robust hard X-ray imaging systems (>100 keV) with a low detection limit and stable dark current. Herein, high-quality inch-size two-dimensional (2D) Cs3Bi2Br9 (CBB) single crystals are grown from a melt via the Bridgman method. The crystal quality is enhanced by eliminating inclusions of CsBr-rich phases and restraining the trap-state density, leading to an enhanced resistivity of 1.41 × 1012 Ω cm and a mobility lifetime product of 8.32 × 10-4 cm2 V-1. The Au/CBB/Au single-crystal device exhibits a high sensitivity of 1705 μC Gyair-1 cm-2 in all-inorganic bismuth-based perovskites and an ultralow detection limit of 0.58 nGyair s-1 in all of the bismuth-based perovskites for 120 keV hard X-ray detection. The CBB detector exhibits high work stability with an ultralow dark current drift of 2.8 × 10-10 nA cm-1 s-1 V-1 and long-term air environment reliability under a high electric field of 10 000 V cm-1 owing to the ultrahigh ionic activation energy of the 2D structure. The proposed robust imaging system based on CBB SC is a promising tool for X-ray medical imaging and diagnostics.

Profit Optimization with a Power-Law Adjustable Coefficient for Zero Ending Inventories Dynamic Pricing Model, Stochastic Demand, and Fixed Lifetime Product

We consider a single product with a fixed lifetime and price sensitive intensity of a Poisson customers flow. A model with a power adjustable coefficient of a dynamic retail price control through the intensity of the demand is considered providing almost surely zero ending inventories at the end of the product's lifetime. To obtain probabilistic characteristics of the selling process and the expected profit, the diffusion approximation of the stock level process is used. The task of the expected profit maximization with respect to the adjustable coefficient for a linear approximation of the intensity-of-price dependence is solved.