Low polarization-sensitive ultra-broadband anti-reflection coatings with improved reliability.

Broader spectra, lower reflectivity and higher reliability are the performance requirements for broadband antireflective (BBAR) films. In this work, a BBAR film structure was proposed, which maintains extremely low reflectivity, ultra-wide spectra, low polarization sensitivity and practical reliability. The BBAR film consists of a dense multilayer interference stack on the bottom and a nano-grass-like alumina (NGLA) layer with a gradient low refractive index distribution on the top. The film was deposited by atomic layer deposition, while the NGLA layer was formed by means of a hot water bath on Al2O3 layer. The top NGLA layer has extremely high porosity and ultra-low refractive index, along with extremely fragile structure. To surmount the fragility of NGLA layer, a sub-nano layer of SiO2 was grown by atomic layer deposition to solidify its structure and also to adjust the refractive index with different thicknesses of SiO2. Finally, in the wide wavelength range of 400-1100 nm, the average transmittance of the double-sided coated fused quartz reaches 99.2%. The absorption, light scattering, reliability and polarization characteristics of BBAR films were investigated. An optimized BBAR film with low polarization-sensitivity and improved reliability was realized, which should be potentially promising for application in optical systems.

Interpretation of Reflection and Colorimetry Characteristics of Indium-Particle Films by Means of Ellipsometric Modeling.

It is of great technological importance in the field of plasmonic color generation to establish and understand the relationship between optical responses and the reflectance of metallic nanoparticles. Previously, a series of indium nanoparticle ensembles were fabricated using electron beam evaporation and inspected using spectroscopic ellipsometry (SE). The multi-oscillator Lorentz-Drude model demonstrated the optical responses of indium nanoparticles with different sizes and size distributions. The reflectance spectra and colorimetry characteristics of indium nanoparticles with unimodal and bimodal size distributions were interpreted based on the SE analysis. The trends of reflectance spectra were explained by the transfer matrix method. The effects of optical constants n and k of indium on the reflectance were demonstrated by mapping the reflectance contour lines on the n-k plane. Using oscillator decomposition, the influence of different electron behaviors in various indium structures on the reflectance spectra was revealed intuitively. The contribution of each oscillator on the colorimetry characteristics, including hue, lightness and saturation, were determined and discussed from the reflectance spectral analysis.

Apatinib for the treatment of metastatic or locoregionally recurrent nasopharyngeal carcinoma after failure of chemotherapy: A multicenter, single-arm, prospective phase 2 study.

BACKGROUND: The authors aimed to investigate the efficacy and safety of apatinib in patients with metastatic or locoregionally recurrent nasopharyngeal carcinoma (NPC). METHODS: A multicenter, single-arm, prospective phase 2 study was conducted on patients (18-70 years of age) with metastatic or recurrent NPC who had failed chemotherapy. Patients with recurrent disease involving vascular structure invasion were excluded. All enrolled patients received apatinib (500 mg daily) in continuous 4-week cycles until disease progression or development of unacceptable toxicity. The primary end point of this study was objective response rate (ORR), and the secondary end points were progression-free survival (PFS), overall survival (OS), and toxicity. This study was registered with ClinicalTrials.gov (NCT03130270). RESULTS: Between January 2017 and June 2018, 33 patients were enrolled. At the end of the data collection (May 20, 2020), the 33 patients had completed a total of 261.2 cycles of apatinib. Although 12 patients achieved a partial response, no patient achieved a complete response; thus, the ORR in the 33 patients was 36.4% (95% CI, 19.0%-53.7%). At the end of follow-up (median, 30 months; 95% CI, 24.9-35.1), median OS and median PFS were 16 months (95% CI, 14.6-17.4 months) and 5.0 months (95% CI, 3.6-6.4 months), respectively. The most common adverse events (grade 1/2) were hand-foot syndrome (18 [54.5%]), hypertension (14 [42.4%]), oral ulcer (8 [24.2%]), and proteinuria (4 [12.1%]). Two patients (1 with diabetes and 1 with hypertension) developed cerebral infarction. Grade 3/4 toxicities were uncommon. CONCLUSIONS: Apatinib shows promising activity, with manageable toxicities, in patients with metastatic or locoregionally recurrent NPC. Further evaluation of apatinib in large-scale studies is warranted. LAY SUMMARY: Clinical studies on vascular endothelial growth factor receptor (VEGFR)-targeted therapy for recurrent or metastatic nasopharyngeal carcinoma (NPC) are limited. A recent preclinical study that evaluated apatinib in models of NPC showed a high objective response rate and a favorable safety profile. Our data further confirmed good efficacy in patients with lung metastasis. Further studies of the efficacy and safety of apatinib combined with immune checkpoint inhibitors or chemotherapy in NPC is warranted.

Micro-positron emission tomography imaging of angiogenesis based on 18F-RGD for assessing liver metastasis of colorectal cancer.

BACKGROUND: Positron emission tomography (PET) imaging is a non-invasive method to visualize and quantify the tumor microenvironment. This study aimed to explore the feasibility of 18F-AIF-NOTA-E[PEG4-c(RGDfk)]2 (denoted as 18F-RGD) PET quantitative parameters to distinguish the angiogenesis in colorectal cancer (CRC) mice which has different metastatic potential. METHODS: Twenty LoVo and twenty LS174T of CRC liver metastases animal models were established by implantation of human CRC cell lines via intrasplenic injection. Radiotracer-based micro-PET imaging of animal model was performed and the uptake of 18F-RGD tracer in the tumor tissues was quantified as tumor-to-liver maximum or mean standardized uptake value (SUVmax or SUVmean) ratio. Pearson correlation was used to analyze the relationship between radioactive parameters and tumor markers. RESULTS: The SUVmax and SUVmean ratios of LoVo model were significantly higher than those of LS174T in both liver metastasis and primary tumor lesions (P < 0.05). A significant difference was observed in both vascular endothelial growth factor (VEGF) and Ki67 expressions between LoVo and LS174T primary tumors (P < 0.05). The tumor-to-liver SUVmax or SUVmean ratio of 18F-RGD showed a moderate correlation with VEGF expression (r = 0.5700, P = 0.001 and r = 0.6657, P < 0.001, respectively), but the SUVmean ration showed a weak correlation with Ki67 expression (r = 0.3706, P < 0.05). The areas under the receiver operating characteristic (ROC) curves of 18F-RGD SUVmean ratio, SUVmax ratio for differentiating LoVo from LS174T tumor were 0.801 and 0.759, respectively. CONCLUSIONS: The tumor-to-liver SUVmean ratio of 18F-RGD was a promising image parameter for the process of monitoring tumor angiogenesis in CRC xenograft mice model.

A coma-free super-high resolution optical spectrometer using 44 high dispersion sub-gratings.

Unlike the single grating Czerny-Turner configuration spectrometers, a super-high spectral resolution optical spectrometer with zero coma aberration is first experimentally demonstrated by using a compound integrated diffraction grating module consisting of 44 high dispersion sub-gratings and a two-dimensional backside-illuminated charge-coupled device array photodetector. The demonstrated super-high resolution spectrometer gives 0.005 nm (5 pm) spectral resolution in ultra-violet range and 0.01 nm spectral resolution in the visible range, as well as a uniform efficiency of diffraction in a broad 200 nm to 1000 nm wavelength region. Our new zero-off-axis spectrometer configuration has the unique merit that enables it to be used for a wide range of spectral sensing and measurement applications.

Remarkable quality improvement of as-grown monolayer MoS2 by sulfur vapor pretreatment of SiO2/Si substrates.

Monolayer MoS2 is a direct bandgap semiconductor which is believed to be one of the most promising candidates for optoelectronic devices. Chemical vapor deposition (CVD) is the most popular method to synthesize monolayer MoS2 with a large area. However, many defects are always found in monolayer MoS2 grown by CVD, such as sulfur vacancies, which severely degrade the performance of devices. This work demonstrates a concise and effective method for direct growth of high quality monolayer MoS2 by using SiO2/Si substrates pretreated with sulfur vapor. The MoS2 monolayer obtained using this method shows about 20 times PL intensity enhancement and a much narrower PL peak width than that grown on untreated substrates. Detailed characterization studies reveal that MoS2 grown on sulfur vapor pretreated SiO2/Si substrates has a much lower density of sulfur vacancies. The synthesis of monolayer MoS2 with high optical quality and low defect concentration is critical for both fundamental physics studies and potential practical device applications in the atomically thin limit.

[Influence of acupuncture plus moxibustion on changes of synaptic structure and expression of synaptic skeleton related genes and proteins in prefrontal cortex of heroin re-addicted rats].

OBJECTIVE: To observe the effect of acupuncture plus moxibustion on the synaptic ultrastructure and expression of synaptic skeleton related proteins in the prefrontal cortex (PFC) of heroin re-addicted rats, so as to reveal its mechanisms underlying improvement of heroin addiction. METHODS: Twenty-four Wister rats (half male and half female) were randomly divi-ded into normal control, model and acupuncture groups (n＝8 in each group). The heroin re-addicted model was established by muscular injection of heroin into the hind limbs for 8 days (incremental 0.8-3.6 mg, once daily for 6 days, and twice daily for 2 days), followed by conventional breeding for 5 days (detoxification), the procedure (addition－detoxification) was repeated 3 cycles. For rats of the acupuncture group, "Baihui" (GV20) was needled with filiform needles which were retained for 30 min, and moxibustion was then applied to bilateral "Shenshu" (BL23) for 30 min. The treatment was conducted once daily during the deto-xification. On the 39th day of experiment, the bilateral prefrontal cortex tissues were sampled for examining the ultrastructure by using transmission electron microscope (TEM) after fixative solution immersion and for determining the expression of genes and proteins of activity-regulated cytoskeleton-associated protein (Arc), microtubule-asso-ciated protein-2 (MAP-2) and microtubule-associated protein Tau (Tau) with quantitative real-time PCR and Western blot, respectively. RESULTS: After modeling, the expression levels of Arc mRNA and protein were significantly up-regulated, and those of MAP-2 and Tau mRNA and proteins ob-viously down-regulated in the model group relevant to the normal control group (P<0.05). Following the intervention, the up-regulated Arc protein and mRNA and the down-regulated MAP-2 and Tau were obviously reversed relevant to the model group (P<0.05). Outcomes of TEM showed unclear pre- and post-membranes of the synapses, narrowing of the synaptic gap and non-uniform of the density of the thickened dense plaque after modeling, which was relatively milder in the acupuncture group. CONCLUSION: Acupuncture plus moxibustion can improve changes of synaptic ultrastructure in heroin re-addicted rats, which may be related to their effect in regulating the expression of some synaptic skeleton proteins and genes.

Gemcitabine plus cisplatin versus fluorouracil plus cisplatin as a first-line concurrent chemotherapy regimen in nasopharyngeal carcinoma: a prospective, multi-institution, randomized controlled phase II study.

BACKGROUND: The objective of this study was to evaluate the efficacy and safety of gemcitabine plus cisplatin concurrent chemoradiotherapy (CCRT) in patients with nasopharyngeal carcinoma. METHOD: Patients with NPC were randomly assigned to the gemcitabine plus cisplatin (GP) group or fluorouracil plus cisplatin (PF) group. Primary end-point was disease-free survival (DFS); secondary endpoints: overall survival, distant metastasis-free survival (DMFS), locoregional relapse-free survival, and treatment-related adverse events. RESULTS: Seventy-six patients were prospectively enrolled and the median follow-up time was 41 months (9-61 months). Three-year DFS were similar between the GP and PF groups (73.7% vs. 60.5%, HR 0.66, 95% CI 0.30-1.44; P = 0.30). Distant metastasis was the most common failure form in PF compared with GP (P = 0.034). Three-year DMFS was significantly better in the GP group than PF group (89.5% vs. 71.1%, P = 0.045). Grade 3-4 gastrointestinal toxicities (vomiting and diarrhea) were significantly more common in the PF group; grade 3-4 neutropenia and thrombocytopenia were more common in the GP group. CONCLUSION: Gemcitabine plus cisplatin could be used as an alternative regimen in CCRT for nasopharyngeal carcinoma.

18F-fluoromisonidazole positron emission tomography may be applicable in the evaluation of colorectal cancer liver metastasis.

BACKGROUND: Positron emission tomography (PET) imaging is a non-invasive functional imaging method used to reflect tumor spatial information, and to provide biological characteristics of tumor progression. The aim of this study was to focus on the application of 18F-fluoromisonidazole (FMISO) PET quantitative parameter of maximum standardized uptake value (SUVmax) ratio to detect the liver metastatic potential of human colorectal cancer (CRC) in mice. METHODS: Colorectal liver metastases (CRLM) xenograft models were established by injecting tumor cells (LoVo, HT29 and HCT116) into spleen of mice, tumor-bearing xenograft models were established by subcutaneously injecting tumor cells in the right left flank of mice. Wound healing assays were performed to examine the ability of cell migration in vitro. 18F-FMISO uptake in CRC cell lines was measured by cellular uptake assay. 18F-FMISO-based micro-PET imaging of CRLM and tumor-bearing mice was performed and quantified by tumor-to-liver SUVmax ratio. The correlation between the 18F-FMISO SUVmax ratio, liver metastases number, hypoxia-induced factor 1α (HIF-1α) and serum starvation-induced glucose transporter 1 (GLUT-1) was evaluated using Pearson correlation analysis. RESULTS: Compared with HT29 and HCT116, LoVo-CRLM mice had significantly higher liver metastases ratio and shorter median survival time. LoVo cells exhibited stronger migration capacity and higher radiotracer uptake compared with HT29 and HCT116 in in vitro. Moreover, 18F-FMISO SUVmax ratio was significantly higher in both LoVo-CRLM model and LoVo-bearing tumor model compared to models established using HT29 and HCT116. In addition, Pearson correlation analysis revealed a significant correlation between 18F-FMISO SUVmax ratio of CRLM mice and number of liver metastases larger than 0.5 cm, as well as between 18F-FMISO SUVmax ratio and HIF-1α or GLUT-1 expression in tumor-bearing tissues. CONCLUSIONS: 18F-FMISO parameter of SUVmax ratio may provide useful tumor biological information in mice with CRLM, thus allowing for better prediction of CRLM and yielding useful radioactive markers for predicting liver metastasis potential in CRC.

Black silicon Schottky photodetector in sub-bandgap near-infrared regime.

Sub-bandgap near-infrared silicon (Si) photodetectors are key elements in integrated Si photonics. We demonstrate such a Si photodetector based on a black Si (b-Si)/Ag nanoparticles (Ag-NPs) Schottky junction. This photodetector synergistically employs the mechanisms of inner photoemission, light-trapping, and surface-plasmon-enhanced absorption to efficiently absorb the sub-bandgap light and generate a photocurrent. The b-Si/Ag-NPs sample was prepared by means of wet chemical etching. Compared to those of a planar-Si/Ag thin-film Schottky photodetector, the responsivities of the b-Si/Ag-NPs photodetector were greatly enhanced, being 0.277 and 0.226 mA/W at a reversely biased voltage of 3 V for 1319- and 1550-nm light, respectively.

Evolution of optical properties and electronic structures: band gaps and critical points in MgxZn1-xO (0 ≤ x ≤ 0.2) thin films.

MgxZn1-xO (ZMO) thin films with tunable Mg content were deposited by atomic layer deposition (ALD) on silicon substrates at 190 °C. The elemental and structural properties were acquired by X-ray photoelectron spectroscopy, transmission electron microscopy, atomic force microscopy and X-ray diffraction. Spectroscopic ellipsometry measurements were performed to reveal the evolution of the dielectric functions and critical points in the ZMO thin films by point-by-point fit in the photon energy range of 1.2-6.0 eV. The dependence of the dielectric functions on doping content is clearly demonstrated and physically explained. The critical point energies and the types of interband optical transitions were extracted from standard lineshape analysis of the second derivatives of the dielectric functions. The critical point features were discussed in terms of band structure modification and structural homogeneity arisen by introducing the Mg dopant into the films. Controlling these transitions by changing the doping content will be of practical significance in emerging ZMO-based thin-film photonic and optoelectronic devices.

PQQ ameliorates D-galactose induced cognitive impairments by reducing glutamate neurotoxicity via the GSK-3ß/Akt signaling pathway in mouse.

Oxidative stress is known to be associated with various age-related diseases. D-galactose (D-gal) has been considered a senescent model which induces oxidative stress response resulting in memory dysfunction. Pyrroloquinoline quinone (PQQ) is a redox cofactor which is found in various foods. In our previous study, we found that PQQ may be converted into a derivative by binding with amino acid, which is beneficial to several pathological processes. In this study, we found a beneficial glutamate mixture which may diminish neurotoxicity by oxidative stress in D-gal induced mouse. Our results showed that PQQ may influence the generation of proinflammatory mediators, including cytokines and prostaglandins during aging process. D-gal-induced mouse showed increased MDA and ROS levels, and decreased T-AOC activities in the hippocampus, these changes were reversed by PQQ supplementation. Furthermore, PQQ statistically enhanced Superoxide Dismutase SOD2 mRNA expression. PQQ could ameliorate the memory deficits and neurotoxicity induced by D-gal via binding with excess glutamate, which provide a link between glutamate-mediated neurotoxicity, inflammation and oxidative stress. In addition, PQQ reduced the up-regulated expression of p-Akt by D-gal and maintained the activity of GSK-3ß, resulting in a down-regulation of p-Tau level in hippocampus. PQQ modulated memory ability partly via Akt/GSK-3ß pathway.

Optical Properties of Al-Doped ZnO Films in the Infrared Region and Their Absorption Applications.

The optical properties of aluminum-doped zinc oxide (AZO) thin films were calculated rapidly and accurately by point-by-point analysis from spectroscopic ellipsometry (SE) data. It was demonstrated that there were two different physical mechanisms, i.e., the interfacial effect and crystallinity, for the thickness-dependent permittivity in the visible and infrared regions. In addition, there was a blue shift for the effective plasma frequency of AZO when the thickness increased, and the effective plasma frequency did not exist for AZO ultrathin films (< 25 nm) in the infrared region, which demonstrated that AZO ultrathin films could not be used as a negative index metamaterial. Based on detailed permittivity research, we designed a near-perfect absorber at 2-5 µm by etching AZO-ZnO alternative layers. The alternative layers matched the phase of reflected light, and the void cylinder arrays extended the high absorption range. Moreover, the AZO absorber demonstrated feasibility and applicability on different substrates.

Prediction of tumor biological characteristics in different colorectal cancer liver metastasis animal models using 18F-FDG and 18F-FLT.

BACKGROUND: Positron emission tomography (PET) is a noninvasive method to characterize different metabolic activities of tumors, providing information for staging, prognosis, and therapeutic response of patients with cancer. The aim of this study was to evaluate the feasibility of 18F-fludeoxyglucose (18F-FDG) and 3'-deoxy-3'-18F-fluorothymidine (18F-FLT) PET in predicting tumor biological characteristics of colorectal cancer liver metastasis. METHODS: The uptake rate of 18F-FDG and 18F-FLT in SW480 and SW620 cells was measured via an in vitro cell uptake assay. The region of interest was drawn over the tumor and liver to calculate the maximum standardized uptake value ratio (tumor/liver) from PET images in liver metastasis model. The correlation between tracer uptake in liver metastases and VEGF, Ki67 and CD44 expression was evaluated by linear regression. RESULTS: Compared to SW620 tumor-bearing mice, SW480 tumor-bearing mice presented a higher rate of liver metastases. The uptake rate of 18F-FDG in SW480 and SW620 cells was 6.07% ±â€¯1.19% and 2.82% ±â€¯0.15%, respectively (t = 4.69, P = 0.04); that of 18F-FLT was 24.81% ±â€¯0.45% and 15.57% ±â€¯0.66%, respectively (t = 19.99, P < 0.001). Micro-PET scan showed that all parameters of FLT were significantly higher in SW480 tumors than those in SW620 tumors. A moderate relationship was detected between metastases in the liver and 18F-FLT uptake in primary tumors (r = 0.73, P = 0.0019). 18F-FLT uptake was also positively correlated with the expression of CD44 in liver metastases (r = 0.81, P = 0.0049). CONCLUSIONS: The uptake of 18F-FLT in metastatic tumor reflects different biological behaviors of colon cancer cells. 18F-FLT can be used to evaluate the metastatic potential of colorectal cancer in nude mice.

Effects of Bilayer Thickness on the Morphological, Optical, and Electrical Properties of Al2O3/ZnO Nanolaminates.

This report mainly focuses on the investigation of morphological, optical, and electrical properties of Al2O3/ZnO nanolaminates regulated by varying bilayer thicknesses. The growth mechanism of nanolaminates based on atomic layer deposition and Al penetration into ZnO layer are proposed. The surface roughness of Al2O3/ZnO nanolaminates can be controlled due to the smooth effect of interposed Al2O3 layers. The thickness, optical constants, and bandgap information of nanolaminates have been investigated by spectroscopic ellipsometry measurement. The band gap and absorption edge have a blue shift with decreasing the bilayer thickness on account of the Burstein-Moss effect, the quantum confinement effect and the characteristic evolution of nanolaminates. Also, the carrier concentrations and resistivities are found to be modified considerably among various bilayer thicknesses. The modulations of these properties are vital for Al2O3/ZnO nanolaminates to be used as transparent conductor and high resistance layer in optoelectronic applications.

Structure-Dependent Optical Properties of Self-Organized Bi2Se3 Nanostructures: From Nanocrystals to Nanoflakes.

Bismuth selenide (Bi2Se3), with a wide bulk band gap and single massless Dirac cone at the surface, is a promising three-dimensional topological insulator. Bi2Se3 possesses gapless surface states and an insulator-like bulk band gap as a new type of quantum matter. Different Bi2Se3 nanostructures were prepared using electron beam evaporation with high production efficiency. Structural investigations by energy-dispersive X-ray analysis, scanning electron microscopy, and X-ray diffraction revealed the sample stoichiometries and the structural transition mechanism from nanocrystals to nanoflakes. The optical properties systematically probed and analyzed by spectroscopic ellipsometry showed strong dependence on the nanostructures and were also predicted to have structure-modifiable technological prospects. The optical parameters, plasma frequencies, scattering rates of the free electrons, and optical band gaps were related to the topological properties of the Bi2Se3 nanostructures via light-matter interactions, offering new opportunities and approaches for studies on topological insulators and spintronics. The high-quality Bi2Se3 nanostructures provide advantages in exploring novel physics and exploiting prospective applications.

Regulation of the endoplasmic reticulum stress response and neuroprotective effects of acupuncture on brain injury caused by heroin addiction.

OBJECTIVES: To evaluate regulation of the endoplasmic reticulum stress (ERS) response by acupuncture and to investigate its neuroprotective effect on brain injury caused by heroin addiction. METHODS: A total of 48 male Sprague-Dawley rats were randomly divided into a healthy control group (Control), an untreated heroin exposed group (Heroin) and a heroin exposed group receiving electroacupuncture (EA) treatment at GV14 and GV20 (Heroin+acupuncture) with n=16 rats per group. A rat model of heroin addiction was established by intramuscular injection of incremental doses of heroin for 8 consecutive days. A rat model of heroin relapse was established according to the exposure (addiction) → detoxification method. Apoptotic changes in nerve cells in the hippocampus and ventral tegmental area (VTA) were evaluated in each group of rats using terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay. PERK, eIF2a, CHOP, IRE1 and JNK gene expression and protein expression were measured using quantitative real-time PCR (RT-qPCR) assay and immunohistochemical assay, respectively. RESULTS: The total number of positive nerve cells in the hippocampus and VTA was significantly lower in the Heroin+acupuncture group than in the Heroin group (p<0.01). Compared with the Heroin group, mRNA and protein expression of PERK, eIF2a, CHOP, IRE1 and JNK in the hippocampus and VTA were significantly downregulated in the Heroin+acupuncture group (p<0.05). CONCLUSION: The acupuncture-regulated ERS response appears to mediate the neuroprotective effect of acupuncture in heroin-addicted rats with brain injury. Inhibition of CHOP and JNK upregulation and reduction of nerve cell apoptosis may be the main mechanisms underlying the effects of acupuncture on heroin addiction-induced brain injury.

Dielectric functions and critical points of crystalline WS2 ultrathin films with tunable thickness.

Centimeter-scale WS2 ultrathin films were synthesized on sapphire substrates, and they showed highly oriented crystallographic growth along the c axis. Afterwards, the as-grown samples were systematically characterized using various detection methods. Reliable values of the roughness layer thickness and the film thickness were extracted using both atomic force microscopy (AFM) and spectroscopic ellipsometry (SE), and identified using Raman spectroscopy as well. The expansion and tensile strain along the [001] direction were discovered using X-ray diffraction (XRD) measurements. Accurate dielectric functions of WS2 films were derived from the point-by-point fitting results. The critical points (CPs) of WS2, which have not been reported so far, are precisely extracted from the standard critical point (SCP) model. Their origins are uniquely assigned to different interband electronic transitions in the Brillouin zone, including some novel optical structures above 3 eV, which were not investigated in earlier studies. In this work, it is found that dielectric functions are thickness-dependent, while CPs have an opposite nature, and their intrinsic mechanisms are revealed. The as-obtained results can be expected to help people develop more extensive applications of WS2.

Optical Constants and Band Gap Evolution with Phase Transition in Sub-20-nm-Thick TiO2 Films Prepared by ALD.

Titanium dioxide (TiO2) ultrathin films with different thicknesses below 20 nm were grown by atomic layer deposition (ALD) on silicon substrates at 300 °C. Spectroscopic ellipsometry (SE) measurements were operated to investigate the effect of thickness on the optical properties of ultrathin films in the spectra range from 200 to 1000 nm with Forouhi-Bloomer (F-B) dispersion relation. It has been found that the refractive index and extinction coefficient of the investigated TiO2 ultrathin film increase while the band gap of TiO2 ultrathin film decreases monotonically with an increase in film thickness. Furthermore, with the purpose of studying the temperature dependence of optical properties of TiO2 ultrathin film, the samples were annealed at temperature from 400 to 900 °C in N2 atmosphere. The crystalline structure of deposited and annealed films was deduced by SE and supported by X-ray diffraction (XRD). It was revealed that the anatase TiO2 film started to transform into rutile phase when the annealing temperature was up to 800 °C. In this paper, a constructive and effective method of monitoring the phase transition in ultrathin films by SE has been proposed when the phase transition is not so obvious analyzed by XRD.

High photon-to-heat conversion efficiency in the wavelength region of 250-1200 nm based on a thermoelectric Bi2Te3 film structure.

In this work, 4-layered SiO2/Bi2Te3/SiO2/Cu film structures were designed and fabricated and the optical properties investigated in the wavelength region of 250-1200 nm for their promising applications for direct solar-thermal-electric conversion. A typical 4-layered film sample with the structure SiO2 (66.6 nm)/Bi2Te3 (7.0 nm)/SiO2 (67.0 nm)/Cu (>100.0 nm) was deposited on a Si or K9-glass substrate by magnetron sputtering. The experimental results agree well with the simulated ones showing an average optical absorption of 96.5%, except in the shorter wavelength region, 250-500 nm, which demonstrates the superior absorption property of the 4-layered film due to the randomly rough surface of the Cu layer resulting from the higher deposition power. The high reflectance of the film structure in the long wavelength region of 2-20 µm will result in a low thermal emittance, 0.064 at 600 K. The simpler 4-layered structure with the thermoelectric Bi2Te3 used as the absorption layer may provide a straightforward way to obtain solar-thermal-electric conversion more efficiently through future study.