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Controlling light emission from quantum emitters has important applications, ranging from solid-state lighting and displays to nanoscale single-photon sources. Optical antennas have emerged as promising tools to achieve such control right at the location of the emitter, without the need for bulky, external optics. Semiconductor nanoantennas are particularly practical for this purpose because simple geometries such as wires and spheres support multiple, degenerate optical resonances. Here, we start by modifying Mie scattering theory developed for plane wave illumination to describe scattering of dipole emission. We then use this theory and experiments to demonstrate several pathways to achieve control over the directionality, polarization state and spectral emission that rely on a coherent coupling of an emitting dipole to optical resonances of a silicon nanowire. A forward-to-backward ratio of 20 was demonstrated for the electric dipole emission at 680 nm from a monolayer MoS2 by optically coupling it to a silicon nanowire.

Metasurfaces offer the possibility to shape optical wavefronts with an ultracompact, planar form factor. However, most metasurfaces are static, and their optical functions are fixed after the fabrication process. Many modern optical systems require dynamic manipulation of light, and this is now driving the development of electrically reconfigurable metasurfaces. We can realize metasurfaces with fast (>10⁵ hertz), electrically tunable pixels that offer complete (0- to 2π) phase control and large amplitude modulation of scattered waves through the microelectromechanical movement of silicon antenna arrays created in standard silicon-on-insulator technology. Our approach can be used to realize a platform technology that enables low-voltage operation of pixels for temporal color mixing and continuous, dynamic beam steering and light focusing.

Semiconductor nanoantennas have recently emerged as very promising platforms for light manipulation at the nanoscale. More specifically, Silicon has become very popular among researchers thanks to its strong light-matter interaction features, mature fabrication technology availabilities, potential for serving simultaneous optical and electronic purposes, and significantly lower losses compared to its metallic competitors. In this thesis, we employed two main architectures that help us achieve our ultimate goal of controlling the light emission and scattering properties in the nanoscale. In the first architecture, we utilize Si nanowires as our nanoantennas to control the emission directionality of 2D monolayer MoS2 emitters, where our choice of emitter material was based on the attractive properties and recent popularity of 2D materials emitting in the visible range of the spectrum. In this Si-MoS2 configuration, we demonstrate more than 25 top-to-bottom emission ratio enhancement with Si NWs compared to bare MoS2 emission. By using NWs of different radii, we demonstrated such directionality by two different mechanisms which were fundamentally different in terms of the excited resonances in the NW. While targeting directionality, we also observed strong polarization selectivity and spectral modification of the operation principles which gave us the power to tune the spectral and polarization properties of the dominant top emission of this system. As the next step, we aimed to demonstrate an active and on-demand control of directionality of scattering of plane-waves. To achieve this, we designed, fabricated and characterized a Si MEMS architecture that enabled us to observe more than 30° active control of angular emission with the application of 5 V potential.

Semiconductor nanocrystal quantum dots (QDs) have been found to be very promising for important application areas in optoelectronics and photonics. Their energy band-gap tunability, high performance band-edge emission, decent temperature stabilities, and easy material processing make the QDs attractive for these applications ranging from photovoltaic devices to photodetectors and lasers to light-emitting diodes. For these QDs, the concepts of multi exciton generation (MEG) and recombination (MER) have recently been shown to be important especially because they possibly enable efficiency levels exceeding unity using these QDs in various device configurations. However, understanding multi exciton kinetics in QD solids has been hindered by the confusion of MER with the recombination of carriers in charged QDs. This understanding lacks to date and the spectral-temporal aspects of MER still remain unresolved in solid QD ensembles. In this thesis, we reveal the spectral-temporal behavior of biexcitons (BXs) in the presence of photocharging using near-unity quantum yield core/shell CdSe/CdS QDs. The spectral behavior of BXs and that of excitons (Xs) were obtained for the QD samples with different core sizes, exhibiting the strength-tunability of the X-X interaction energy in these QDs. The extraction of spectrally resolved X, BX, and trion kinetics, which would be spectrally unresolved using conventional approaches, is enabled by our approach introducing the integrated time-resolved fluorescence. Besides the fundamental understanding of MEG and MER concepts, we also explored the possibility of utilizing multi excitons in these QDs for optical gain. In this part of the thesis, tunable, high performance, two-photon absorption (TPA) based amplified spontaneous emission (ASE) from the same QDs is presented. Here, for the first time, in addition to the absolute spectral tuning of the ASE, on the single material system of CdSe/CdS, the relative spectral tuning of ASE peak with respect to spontaneous emission was demonstrated. With the core and shell size adjustments, it was shown that Coulombic X-X interactions can be tuned to be either attractive leading to the red-shifted ASE peak or repulsive leading to the blue-shifted ASE peak and that non-shifting ASE can be achieved with the right core-shell combinations. It was further found here that it is possible to obtain ASE at a specific wavelength from both Type-I-like and Type-II-like CdSe/CdS QDs. In addition to the CdSe/CdS QDs, we showed ASE and Type-tunability features on CdSe/CdS nanorods (NRs), which are particularly promising with their extremely high TPA cross-sections and independent emission/absorption tunabilities. In the final part of the thesis, we report the observation of MEG on CdHgTe QDs, for the first time in the literature, and a novel application of MEG concept in a photosensor device, one of the first examples of real-life photosensing application of MEG concept. We believe that the results provided in this thesis do not only contribute to the fundamental understanding of MEG and MER concepts in the QDs, but also pave the way for the utilization of these concepts in the QD-based lasers, photodetectors and photovoltaic devices.

Controlling light emission from quantum emitters has important applications ranging from solid-state lighting and displays to nanoscale single-photon sources. Optical antennas have emerged as promising tools to achieve such control right at the location of the emitter, without the need for bulky, external optics. Semiconductor nanoantennas are particularly practical for this purpose because simple geometries, such as wires and spheres, support multiple, degenerate optical resonances. Here, we start by modifying Mie scattering theory developed for plane wave illumination to describe scattering of dipole emission. We then use this theory and experiments to demonstrate several pathways to achieve control over the directionality, polarization state, and spectral emission that rely on a coherent coupling of an emitting dipole to optical resonances of a Si nanowire. A forward-to-backward ratio of 20 was demonstrated for the electric dipole emission at 680 nm from a monolayer MoS2 by optically coupling it to a Si nanowire.

Background Bevacizumab is widely used for recurrent high-grade glioma, but the real-world effectiveness of bevacizumab with or without irinotecan remains uncertain. We evaluated outcomes of bevacizumab-based regimens in a large multicenter Turkish cohort. Methods In this retrospective study from 30 centers, adults with recurrent glioblastoma or other primary brain tumors treated with a bevacizumab-containing regimen at first or second progression were included. Patients received bevacizumab monotherapy, bevacizumab plus low-dose weekly irinotecan, or bevacizumab plus standard-dose irinotecan every 14 days. Tumor response, progression-free survival (PFS), overall survival (OS), and toxicity were assessed. Prognostic factors were analyzed using Cox regression. Results A total of 437 patients were included; 78.0% had glioblastoma. Treatment consisted of bevacizumab monotherapy in 9.4%, bevacizumab plus weekly irinotecan in 8.5%, and bevacizumab plus irinotecan every 14 days in 82.2% of patients. The objective response rate was 41.6%, and the disease control rate was 80.1%. Median OS was 10.77, 7.37 and 9.77 months (log-rank p  = 0.024), and median PFS was 5.77, 3.93 and 6.43 months ( p  = 0.005), respectively. On multivariable analysis, glioblastoma histology independently predicted shorter PFS and OS, whereas a higher number of treatment cycles and antiepileptic drug use were associated with longer PFS. For OS, the irinotecan–bevacizumab every-14-day regimen and a higher number of treatment cycles were associated with improved survival compared with bevacizumab monotherapy, while baseline corticosteroid use and discontinuation of bevacizumab-containing therapy were independent adverse prognostic factors. Conclusions In this large real-world cohort, bevacizumab-based therapy achieved meaningful disease control and survival in recurrent primary brain tumors. An irinotecan–bevacizumab regimen administered every 14 days was associated with superior OS at the expense of increased but manageable chemotherapy-related toxicity, supporting its use in appropriately selected patients.

Multilocus Inherited Neoplasia Allele Syndrome (MINAS) describes individuals who harbor pathogenic or likely pathogenic (LP/P) germline variants in two or more distinct cancer predisposition genes. With the broader implementation of next-generation sequencing (NGS) and multigene panel testing, MINAS has been increasingly recognized. We retrospectively evaluated 655 Turkish patients referred for hereditary cancer testing using two validated NGS panels. MINAS was defined as the presence of LP/P variants in at least two different genes. 14 patients (2.13%) met the criteria for MINAS. An additional 156 patients (23.8%) had single-gene LP/P variants. MINAS cases accounted for 8.2% of mutation-positive individuals. These patients showed diverse tumor types. Common gene combinations included and . This is the first MINAS-focused analysis from a Turkish cohort. Although uncommon, MINAS represents a significant subset of genetically high-risk individuals requiring tailored clinical management.

Real-world use of trastuzumab deruxtecan for HER2-positive metastatic breast cancer HER2-positive metastatic breast cancer is an aggressive form of breast cancer that often requires multiple lines of treatment. Trastuzumab deruxtecan is a targeted cancer medicine that combines an antibody with a chemotherapy drug, allowing treatment to be delivered directly to cancer cells. Clinical trials have shown that this treatment can be very effective, but patients enrolled in trials may not fully represent those treated in everyday clinical practice. In this study, we examined how trastuzumab deruxtecan performed in real-world settings across Turkiye. We collected and analyzed data from 269 patients treated at 27 cancer centers. This allowed us to understand how well the drug worked and how safe it was outside of clinical trials. We found that many patients experienced meaningful disease control, with most patients showing tumor shrinkage or stabilization. Patients who received trastuzumab deruxtecan earlier in their treatment course tended to benefit the most. Overall survival and the time patients lived without cancer progression were similar to, or better than, results previously reported in clinical trials. Side effects were generally manageable. A small number of patients developed lung inflammation, a known risk of this treatment, highlighting the importance of careful monitoring. In summary, our findings show that trastuzumab deruxtecan is an effective and reasonably safe treatment for HER2-positive metastatic breast cancer in routine clinical care. These results support its use beyond clinical trials and provide valuable evidence from a middle-income country setting, helping doctors and patients make informed treatment decisions.

Sentinel lymph node (SLN) biopsy is the main method in staging the axilla. There are insufficient data available regarding the accuracy of an SLN biopsy in male breast cancer. The aim of this study is to evaluate whether the combination of dye and radiotracer would improve the detection rate of SLNs versus dye alone in male breast cancer patients. From February 2009 to January 2012, our SLN biopsy database was retrospectively reviewed to identify male breast cancer cases. Of the 890 SLN procedures contained in the database, 10 male breast cancer patients were identified. Patient age, body mass index, SLN biopsy technique, SLN identification, number of SLN excised, and pathology reports were reviewed. Mean age was 57.2 (34–85) years with a mean tumor size was 2.2 (1.0–4.0) cm. SLN detection ratios were two in four with blue dye and six in six with the combination technique. Overall, SLNs were identified in 8 of the 10 patients. SLN biopsy is applicable in male breast cancer cases. The addition of a radiotracer to the dye in SLN biopsy increases the detection rate of sentinel nodes in male breast cancer patients.

Background and Aims: During liver transplantation, hepatocellular carcinoma (HCC) recurrence remains a critical challenge for patient survival. Targeted therapies, such as sorafenib and regorafenib, have been utilized to manage relapsed HCC in this unique setting. This study aimed to assess the efficacy of Sorafenib and Regorafenib in patients with HCC who experienced recurrence after liver transplantation. We focused on survival outcomes, treatment responses, and the management of side effects in this patient group. Methods: We conducted a retrospective analysis of 73 patients who experienced HCC recurrence post-liver transplantation between 2012 and 2022 across 11 oncology centers in Turkey. Patients were categorized according to Child–Pugh classification and treated with sorafenib as first-line therapy and Regorafenib in case of progression. Survival rates were analyzed using the Kaplan–Meier method, and risk factors were evaluated using Cox regression analysis. Results: Of the 73 patients included in the study, 62 were male (84.9%), and 11 were female (15.1%), with a mean age of 61.5 ± 10.9 years. All patients received sorafenib as first-line treatment. Among patients who experienced progression with sorafenib or discontinued treatment due to toxicity, 45.2% (n = 33) continued treatment with regorafenib. The median progression-free survival (PFS1) time with sorafenib was 5.6 months, and the one-year survival rate was 24.3%. The median progression-free survival (PFS2) time with regorafenib, which was administered as second-line treatment, was also calculated as 5.9 months. Overall survival (OS) duration was determined as 35.9 months. The most common side effects associated with both drugs included fatigue, hand and foot syndrome, and hypertension. Significantly better survival outcomes were shown in the Child–Pugh A group compared to other patients. Conclusions: These results suggest that Sorafenib and Regorafenib treatments offer a survival advantage in patients with relapsed HCC post-transplantation. However, individualized treatment strategies and close follow-up are crucial for optimizing outcomes. Further studies are needed to refine therapeutic protocols and enhance the care of this specific patient group.