Search query: n-type colloidal semiconductor nanocrystals Nature， 2000，407,981-983

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abstract: Colloidal semiconductor nanocrystals combine the physical and chemical properties of molecules with the optoelectronic properties of semiconductors. Their colour is highly controllable, a direct consequence of quantum confinement on the electronic states. Such nanocrystals are a form of 'artificial atoms' (ref. 4) that may find applications in optoelectronic systems such as light emitting diodes and photovoltaic cells, or as components of future nanoelectronic devices. The ability to control the electron occupation (especially in n type or p type nanocrystals) is important for tailoring the electrical and optical properties, and should lead to a wider range of practical devices. But conventional doping by introducing impurity atoms has been unsuccessful so far: impurities tend to be expelled from the small crystalline cores (as observed for magnetic impurities) and thermal ionization of the impurities (which provides free carriers) is hindered by strong confinement. Here we report the fabrication of n type nanocrystals using an electron transfer approach commonly employed in the field of conducting organic polymers. We find that semiconductor nanocrystals prepared as colloids can be made n type, with electrons in quantum confined states.
author_names: Moonsub Shim

Philippe Guyot-Sionnest
title: n type colloidal semiconductor nanocrystals
venue: Nature
year: 2000

abstract: SSNanoparticles of metallic copper (Cu 0 and copper I oxide (Cu2O) have been prepared through a new nonhydrolytic precursor approach by applying template mineralization of self assembled anisotropic double chained cationic lipids (2C12 18NMe2OH) in the presence of pyruvylated xanthan (0.0001% w/w) in the presence of a suitable redox system. The controlled formation of defined inorganic cationic lipid composites by using the self assembled vesicles (spherical, rod like or tubular) as templates lead to the formation of defined nanocrystals of Cu 0 or Cu2O in astonishing shape dependent manner as shown by small angle X ray scattering, transmission electron microscopy (TEM) and light scattering methods. Spherical, rodshaped nanocrystals could be obtained, particularly for Cu2O which is very light sensitive (at~580 nm) and can act as a p type semiconductor. The formed and isolated nanoparticles have average sizes of 6.0 12.0 nm in diameter for Cu2O and of 7.0 12.0 nm in diameter for the metallic Cu 0 nanocrystals as determined from small angle X ray scattering, transmission electron microscopy and powder diffraction, respectively. The formation of nanoclusters of zerovalent copper of sizes between 7 and 12 nm show a surface plasma bond at 561 566 nm. The reduction of the copper salts to colloidal copper in the presence of the glycolipids A B can be enhanced through addition of less than 10 molecules of didocyldimethylammonium hydroxide per biosurfactant micelle in the presence of l0 mM (R* R* 1,4 dimercapto 2,3 dibutandiol. The addition of the cationic surfactant induced a strong increase in the size and in the yield as observed by TEM, small angle X ray scattering and light scattering measurements. Due to the low CMC of the double chained cationic lipids including their very low surface tension which is significantly affected by the nature of the counterions enables one to produce large quantities of Cu nano clusters having different shapes. The nature of the counterions are also found to be crucial in the synthesis of zero valent copper nano clusters.
author_names: H Henrich Paradies

Michael Thies

Ulrike Hinze
title: TEMPLATE MINERALIZATION OF ORDERED NANOMATERIALS OF METALLIC COPPER AND COPPER I OXIDES IN THE PRESENCE OF DOUBLE CHAINED CATIONIC LIPIDS (Ill)
year: 2000

abstract: The Redox Potentials of n Type Colloidal Semiconductor Nanocrystals
author_names: Gerard Michael Carroll
title: The Redox Potentials of n type Colloidal Semiconductor Nanocrystals
year: 2016

abstract: In the present work, we demonstrate crystallographically textured n type Bi2Te3 xSe x nanomaterials with exceptional thermoelectric figures of merit produced by consolidating disk shaped Bi2Te3 xSe x colloidal nanocrystals (NCs) Crystallographic texture was achieved by hot pressing the asymmetric NCs in the presence of an excess of tellurium. During the hot press, tellurium acted both as lubricant to facilitate the rotation of NCs lying close to normal to the pressure axis and as solvent to dissolve the NCs approximately aligned with the pressing direction, which afterward recrystallize with a preferential orientation. NC based Bi2Te3 xSe x nanomaterials showed very high electrical conductivities associated with large charge carrier concentrations, n. We hypothesize that such large n resulted from the presence of an excess of tellurium during processing, which introduced a high density of donor TeBi antisites. Additionally, the presence in between grains of traces of elemental Te, a narrow band gap semiconductor with a work function well below Bi2Te3 xSe x, might further contribute to increase n through spillover of electrons, while at the same time blocking phonon propagation and hole transport through the nanomaterial. NC based Bi2Te3 xSe x nanomaterials were characterized by very low thermal conductivities in the pressing direction, which resulted in ZT values up to 1.31 at 438 K in this direction. This corresponds to a ca. 40% ZT enhancement from commercial ingots. Additionally, high ZT values were extended over wider temperature ranges due to reduced bipolar contribution to the Seebeck coefficient and the thermal conductivity. Average ZT values up to 1.15 over a wide temperature range, 320 to 500 K, were measured, which corresponds to a ca. 50% increase over commercial materials in the same temperature range. Contrary to most previous works, highest ZT values were obtained in the pressing direction, corresponding to the c crystallographic axis, due to the predominance of the thermal conductivity reduction over the electrical conductivity difference when comparing the two crystal directions.
author_names: Yupu Liu

Yuanwei Zhang

Khak Ho Lim

Maria Ibanez

Silvia Ortega

Mengyao Li

Jeremy David

Sara Marti-Sanchez

Ka Ming Ng

Jordi Arbiol

Maksym V Kovalenko

Doris Cadavid

Andreu Cabot
title: High Thermoelectric Performance in Crystallographically Textured n Type Bi2Te3 xSe x Produced from Asymmetric Colloidal Nanocrystals.
venue: ACS nano
year: 2018

author_names: Robertson Ansah Bill
title: Electron Transfer Produces n Type Colloidal Semiconductor Nanocrystals
year: 2001

abstract: Assemblies of colloidal semiconductor nanocrystals (NCs) in the form of thin solid films leverage the size dependent quantum confinement properties and the wet chemical methods, vital for the development of the emerging solution processable electronics, photonics and optoelectronics technologies. The ability to control the charge carrier transport in the colloidal NC assemblies is fundamental for altering their electronic and optical properties for the desired applications. Here we demonstrate a strategy to render the solids of narrow bandgap NC assemblies exclusively electron transporting by creating type II heterojunction via shelling. Electronic transport of molecularly cross linked PbTe@PbS core@shell NC assemblies is measured using both conventional solid gate transistor and electric double layer transistor, as well as compared with those of core only PbTe NCs. In contrast to the ambipolar characteristics demonstrated by many narrow bandgap NCs, the core@shell NCs exhibit exclusive n type transport; i.e. drastically suppressed contribution of holes to the overall transport. The PbS shell that forms type II heterojunction assists the selective carrier transport by heavy doping of electrons into the PbTe core conduction level, and simultaneously strongly localize the holes within the NC core valence level. This strongly enhanced n type transport makes these core@shell NCs suitable for applications where ambipolar characteristics should be actively suppressed; in particular, for thermoelectric and electron transporting layer in photovoltaic devices.
author_names: Retno Miranti

Daiki Shin

Ricky Dwi Septianto

Maria Ibanez

Maksym V Kovalenko

Nobuhiro Matsushita

Yoshihiro Iwasa

Satria Zulkarnaen Bisri
title: Exclusive Electron Transport in Core@Shell PbTe@PbS Colloidal Semiconductor Nanocrystal Assemblies.
venue: ACS nano
year: 2020

abstract: Precise control over the shape and elemental composition of colloidal nanocrystals (NCs) is challenging, especially for anisotropic growth. While the most studied nanocrystal syntheses involve homogenous nucleation and growth, the solution based approach involving heterogenous growth from ion conductive seeds has proved to be very efficient yet less explored. The static nature and superionic conductivity of the seeds enable rapid cation transport for catalysis of defect free, phase pure NC growth. This review aims to explain the significance of ion conductive solid seed based synthesis from a mechanistic point of view to produce 1D and quasi 1D NCs for applications such as photocatalysis, photovoltaics, and photodetectors. We highlight the significant synthetic information reported for heterostructure and alloyed metal chalcogenide NCs synthesized via solution solid solid and diffusion controlled growth based on several kinetic and thermodynamic growth parameters. We also provide a perspective on the areas that hold promise and are in need of further development.
author_names: Nilotpal Kapuria

Uma V Ghorpade

Maria Zubair

Mohini Mishra

Shalini Singh

Kevin M Ryan
title: Metal chalcogenide semiconductor nanocrystals synthesized from ion conducting seeds and their applications
year: 2020

abstract: Optically bright colloidal semiconductor nanocrystals (CSNCs) are important nanomaterials because of their potential applications such as cellular imaging and solid state lighting. The optoelectronic properties of CSNCs are strongly controlled by the chemical nature of the surface passivating ligands that are introduced during their synthesis. However, the existing LaMer growth model does not provide a clear understanding of the stage when ligands become attached onto the CSNC surface. Herein, apart from the three stage formation mechanism of CSNCs (supersaturation, nucleation, and growth) an entirely new stage solely involving surface ligand attachment onto fully grown CSNCs is now reported that controls their photoluminescence properties. Furthermore, we also demonstrate a fundamentally new surface modification approach using partially passivated CSNCs to introduce a variety of functional groups (azide, alkene, and siloxane) including photoisomerizable molecular machines (e.g. azobenzene) without th.
author_names: Meghan B Teunis

Thakshila Liyanage

Sukanta Dolai

Barry B Muhoberac

Rajesh Sardar

Mangilal Agarwal
title: Unraveling the Mechanism Underlying Surface Ligand Passivation of Colloidal Semiconductor Nanocrystals: A Route for Preparing Advanced Hybrid Nanomaterials
year: 2017

abstract: Heterovalent doping in colloidal semiconductor nanocrystals (CSNCs) with provisions of extra electrons (n type doping) or extra holes (p type doping) could enhance their performance of optical and electronical properties. In view of the challenges imposed by the intrinsic self purification, self quenching, and self compensation effects of CSNCs, we outline the progress on heterovalent doping in CSNCs, with particular focus on the cation exchange enabled tuning of dopant luminescence and electronic impurities. Thus, the well defined substitutional or interstitial heterovalent doping in a deep position of an isolated nanocrystal has been fulfilled. We also envision that new coordination ligand initiated cation exchange would bring about more choices of heterovalent dopants. With the aid of high resolution characterization methods, the accurate atom specific dopant location and distribution could be confirmed clearly. Finally, new applications, some of the remaining unanswered questions, and future directions of this field are presented.
author_names: Jiatao Zhang

Qiumei Di

Jia Liu

Bing Bai

Jian Liu

Meng Xue Xu

Jiajia Liu
title: Heterovalent Doping in Colloidal Semiconductor Nanocrystals: Cation Exchange Enabled New Accesses to Tuning Dopant Luminescence and Electronic Impurities.
venue: The journal of physical chemistry letters
year: 2017

abstract: Colloidal semiconductor quantum wells have emerged as a promising material platform for use in solution processable lasers. However, applications relying on their optical gain suffer from nonradiative Auger decay due to multi excitonic nature of light amplification in II VI semiconductor nanocrystals. Here, we show sub single exciton level of optical gain threshold in specially engineered CdSe/CdS@CdZnS core/crown@gradient alloyed shell quantum wells. This sub single exciton ensemble averaged gain threshold of N g 0.84 (per particle) resulting from impeded Auger recombination, along with a large absorption cross section of quantum wells, enables us to observe the amplified spontaneous emission starting at an ultralow pump fluence of 800 nJ cm 2 at least three folds better than previously reported values among all colloidal nanocrystals. Finally, using these gradient shelled quantum wells, we demonstrate a vertical cavity surface emitting laser operating at a low lasing threshold of 7.5 mJ cm 2 These results represent a significant step towards the realization of solution processable electrically driven colloidal lasers. Colloidal quantum wells are highly promising for applications of solution processed lasers, but their performance is limited by multi excitonic nature of the materials. Here, the authors demonstrate optical gain in graded alloy core/shell CdSe/CdS@CdZnS quantum wells at less than one exciton per particle resulting in ultralow thresholds.
author_names: Nima Taghipour

Savas Delikanli

Sushant Shendre

Mustafa Sak

Mingjie Li

Furkan Isik

Ibrahim Tanriover

Burak Guzelturk

Tze Chien Sum

Hilmi Volkan Demir
title: Sub single exciton optical gain threshold in colloidal semiconductor quantum wells with gradient alloy shelling
venue: Nature Communications
year: 2020