Cryogenic spectroscopy of ultra-low density colloidal lead chalcogenide quantum dots on chip-scale optical cavities towards single quantum dot near-infrared cavity QED

We present evidence of cavity quantum electrodynamics from a sparse density of strongly quantum-confined Pb-chalcogenide nanocrystals (between 1 and 10) approaching single-dot levels on moderately high-Q mesoscopic silicon optical cavities. Operating at important near-infrared (1500-nm) wavelengths, large enhancements are observed from devices and strong modifications of the QD emission are achieved. Saturation spectroscopy of coupled QDs is observed at 77K, highlighting the modified nanocrystal dynamics for quantum information processing.Comment: * new additional figures and text * 10 pages, 5 figure

Colored semi-transparent Cu-Si oxide thin films prepared by magnetron sputtering

Colored semi-transparent Cu-Si oxide thin films have been prepared by reactive magnetron sputtering from a single cathode of copper-silicon composition. Thin films of different composition and optical response were obtained by changing process parameters like the relative amount of copper in the target and the O2/Ar mixture of the reactive plasma gas. The film characteristics were analyzed by several techniques. Their optical properties (refractive index, absorption coefficient, color) have been correlated with the process parameters used in the film preparation as well as with the film stoichiometry and chemistry.Ministerio de Ciencia e Innovación CEN-20072014, MAT2010-18447, MAT2010-21228, CSD2008–00023Junta de Andalucía P09-TEP5283, CTS-518

Investigation of Optical and Structural Properties of GeSn Heterostructures

Silicon (Si)-based optoelectronics have gained traction due to its primed versatility at developing light-based technologies. Si, however, features indirect bandgap characteristics and suffers relegated optical properties compared to its III-V counterparts. III-Vs have also been hybridized to Si platforms but the resulting technologies are expensive and incompatible with standard complementary-metal-oxide-semiconductor processes. Germanium (Ge), on the other hand, have been engineered to behave like direct bandgap material through tensile strain interventions but are well short of attaining extensive wavelength coverage. To create a competitive material that evades these challenges, transitional amounts of Sn can be incorporated into Ge matrix to form direct bandgap GeSn alloys that have led to the increasing possibility of engineering a suite of low-cost, light emission sources that applies to a wide range of infrared photonics and optoelectronics systems. Hence, the importance of studying the structural and optical properties of these GeSn heterostructures cannot be overemphasized. The first part of this dissertation investigates the structural and optical properties of SiGeSn/GeSn/SiGeSn quantum wells (QWs) where the photoluminescence (PL) behaviors of thick (22 nm in well) and thin (9 nm in well) GeSn QW samples are compared. Using PL results from two excitation lasers (532 nm and 1550 nm lasers) as well as studying their respective optical transitions, the result reveals that the thicker well sample shows i) a more direct bandgap outcome in addition to a much lower ground energy Г valley; ii) a higher carrier density within the well, and iii) an increased barrier height coupled with improved carrier confinement. All of these resulted in a significantly enhanced emission that allows for the first-ever estimation of GeSn QWs quantum efficiency (QE) while also suggesting a path towards efficient mid-infrared devices. To further improve the carrier confinement while also reducing the carrier leakage in the thicker well design, a SiGeSn/GeSn/GeSn/SiGeSn separate confinement heterostructure (SCH) is introduced. The sample is characterized and the optical properties are compared with the previously reported 9 nm and 22 nm well non-SCH samples. Based on the optical transition analysis, the SCH QW also shows significantly higher carrier confinement compared to reference samples. In addition to these studies, an attempt is made to investigate advanced quantum well structures through an all-inclusive structural and optical study of SiGeSn/GeSn/SiGeSn multi-quantum wells (MQWs). The resulting analysis shows evidence of intermixing diffusion during growth. The second part of this work provides insights into the behavior of annealed GeSn bulk samples near the indirect-to-direct transition point. The study attempts to provide connections between the strain, composition, and defect densities before and after annealing. The result reveals the impact of annealing on a sample may either i) lower the strain giving rise to an increased PL while reducing the energy separation or ii) introduce misfit dislocation/ surface roughness leading to an affected or decreased PL. Finally, this work also explores the low-temperature capability of our in-house plasma-enhanced ultra-high vacuum chemical vapor deposition system through the growth of Si-on-Ge epitaxy and pressure-dependent growth of GeSn bulk heterostructures

Bright Room-Temperature Single Photon Emission from Defects in Gallium Nitride

Single photon emitters play a central role in many photonic quantum technologies. A promising class of single photon emitters consists of atomic color centers in wide-bandgap crystals, such as diamond silicon carbide and hexagonal boron nitride. However, it is currently not possible to grow these materials as sub-micron thick films on low-refractive index substrates, which is necessary for mature photonic integrated circuit technologies. Hence, there is great interest in identifying quantum emitters in technologically mature semiconductors that are compatible with suitable heteroepitaxies. Here, we demonstrate robust single photon emitters based on defects in gallium nitride (GaN), the most established and well understood semiconductor that can emit light over the entire visible spectrum. We show that the emitters have excellent photophysical properties including a brightness in excess of 500x10^3 counts/s. We further show that the emitters can be found in a variety of GaN wafers, thus offering reliable and scalable platform for further technological development. We propose a theoretical model to explain the origin of these emitters based on cubic inclusions in hexagonal gallium nitride. Our results constitute a feasible path to scalable, integrated on-chip quantum technologies based on GaN

Civil space technology initiative

The Civil Space Technology Initiative (CSTI) is a major, focused, space technology program of the Office of Aeronautics, Exploration and Technology (OAET) of NASA. The program was initiated to advance technology beyond basic research in order to expand and enhance system and vehicle capabilities for near-term missions. CSTI takes critical technologies to the point at which a user can confidently incorporate the new or expanded capabilities into relatively near-term, high-priority NASA missions. In particular, the CSTI program emphasizes technologies necessary for reliable and efficient access to and operation in Earth orbit as well as for support of scientific missions from Earth orbit

Upconverting luminescent materials for solar energy conversion

As attractive energy converters, solar cells are considered to play a vital role in covering the constantly increasing energy demands in the future. Despite the strong success in the field, a variety of solar cells including the commercially available ones are utilizing mainly the visible region of the solar spectrum, and thus are lacking the capacity to exploit effectively the infrared region. This issue gives a possibility to improve the solar cell efficiencies by using the unutilized energy of the infrared radiation. One solution to overcome this issue is to use upconverting luminescent materials which are capable of converting infrared radiation to visible by stacking photons. However, despite the potential, the rather weak conversion efficiency still limits the use of these materials. On the other hand, even small portions of this converted radiation would have significant effect on the solar cell efficiency which is why the development of these materials is desirable. The main aims of this thesis work were to investigate and develop different fabrication methods and properties of the upconverting materials that could be used in solar cells. These methods included the co-precipitation method to prepare crystalline inorganic upconverting fluoride materials, the atomic and the molecular layer deposition techniques to fabricate upconverting oxide and hybrid thin films, and the direct particles doping method for preparation of upconverting luminescent glasses. In addition, another goal was to study the possibilities to enhance the upconversion luminescence which was done by adding transition metal ions (Cr3+ or Mnn+) into the Yb3+ and Er3+ doped fluoride material. Improvement in the upconversion luminescence intensity was obtained by using Cr3+ ions. Another enhancement possibility is to use efficient NIR absorbers together with a strong upconverting lanthanide ion. The combined ALD/MLD technique was shown to enable the combination of NIR harvesting organic moiety and upconverting lanthanide ions to form a hybrid thin film. The ALD and the combined ALD/MLD techniques were demonstrated to be well suitable for upconverting thin film fabrication. Moreover, the direct particles doping method was shown to offer a promising way to introduce a variety of crystalline luminescent materials into different glass matrices.Käänteisviritteiset luminoivat materiaalit aurinkoenergian hyödyntämisessä Aurinkoenergian tarjoamia mahdollisuuksia pidetään yhtenä lupaavimmista vaihtoehdoista kasvavien energiatarpeiden täyttämisessä tulevaisuudessa. Aurinkokennot ovat kehittyneet paljon viime aikoina, mutta silti suurin osa tutkituista ja kaupallisesti saatavilla olevista aurinkokennoista pystyy hyödyntämään auringon spektristä vain näkyvän valon alueen jättäen infrapuna-alueen lähes kokonaan hyödyntämättä. Tämä ongelma tarjoaa mahdollisuuden parantaa aurinkokennojen tehokkuutta. Yksi tapa hyödyntää infrapunasäteilyn energiaa on käyttää käänteisviritteisiä luminoivia materiaaleja, jotka pystyvät muuntamaan infrapunasäteilyä näkyväksi valoksi pinoamalla fotoneja. Tämän prosessin heikko teho rajoittaa toistaiseksi materiaalien käyttöä. Toisaalta, jopa pienellä IR-säteilyn muuntomäärällä on mahdollisuus vaikuttaa merkittävästi aurinkokennon tehokkuuteen, minkä vuoksi materiaalien kehittäminen on herättänyt kiinnostusta. Väitöskirjatyön tavoitteena oli tutkia ja kehittää aurinkokennoissa mahdollisesti käytettävien käänteisviritteisten materiaalien ominaisuuksia ja valmistusmenetelmiä. Menetelmiin kuului kerasaostusmenetelmä, jolla valmistettiin kiteisiä fluoridimateriaaleja; atomi- ja molekyylikerroskasvatusmenetelmät, joilla valmistettiin kiteisiä oksidi ja amorfisia hybridiohutkalvoja; sekä seostusmetelemä luminoivien lasien valmistukseen. Lisäksi tavoitteena oli tutkia mahdollisuuksia parantaa käänteisviritteistä luminesenssia käyttämällä siirtymämetalli-ioneja (Cr3+ ja Mnn+). Käänteisviritteisen luminesenssin intensiteettiä kasvatettiin lisäämällä Cr3+ - ioneja fluoridimateriaaliin, joka oli seostettu Yb3+ ja Er3+ -ioneilla. Käänteisviritteisen luminesenssin tehostamisessa voidaan hyödyntää myös tehokkaasti NIR-säteilyä absorboivan orgaanisen osan yhdistämistä käänteisviritteisesti luminoivaan lantanidi-ioniin. Näiden osien yhdistäminen todettiin olevan mahdollista yhdistetyllä ALD/MLD -tekniikalla, jolla valmistettiin hybridikalvoja. Tämän yhdistetyn tekniikan ja ALD-tekniikan osoitettiin olevan hyvin käyttökelpoisia käänteisviritteisten kalvojen valmistuksessa. Lasimateriaaleilla tutkitun seostusmenetelmän osoitettiin olevan lupaava menetelmä erilaisten luminoivien kiteisten materiaalien lisäämisessä lasiin

The NASA SBIR product catalog

The purpose of this catalog is to assist small business firms in making the community aware of products emerging from their efforts in the Small Business Innovation Research (SBIR) program. It contains descriptions of some products that have advanced into Phase 3 and others that are identified as prospective products. Both lists of products in this catalog are based on information supplied by NASA SBIR contractors in responding to an invitation to be represented in this document. Generally, all products suggested by the small firms were included in order to meet the goals of information exchange for SBIR results. Of the 444 SBIR contractors NASA queried, 137 provided information on 219 products. The catalog presents the product information in the technology areas listed in the table of contents. Within each area, the products are listed in alphabetical order by product name and are given identifying numbers. Also included is an alphabetical listing of the companies that have products described. This listing cross-references the product list and provides information on the business activity of each firm. In addition, there are three indexes: one a list of firms by states, one that lists the products according to NASA Centers that managed the SBIR projects, and one that lists the products by the relevant Technical Topics utilized in NASA's annual program solicitation under which each SBIR project was selected