A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre. More generally, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less and an unconstrained length. At these scales, quantum mechanical effects are important—which coined the term "quantum wires".
Quantum dots (QDs) are semiconductor particles a few nanometres in size, having optical and electronic properties that differ from larger particles due to quantum mechanics. They are a central topic in nanotechnology. When the quantum dots are illuminated by UV light, an electron in the quantum dot can be excited to a state of higher energy. In the case of a semiconducting quantum dot, this process corresponds to the transition of an electron from the valence band to the conductance band. The excited electron can drop back into the valence band releasing its energy as light. This light emission (photoluminescence) is illustrated in the figure on the right. The color of that light depends on the energy difference between the conductance band and the valence band, or the transition between discretized energy states when band structure is no longer a good definition in QDs.
Nanomaterials describe, in principle, materials of which a single unit is sized between 1 and 100 nm.
A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 100 nm in only two directions. At the lowest range, metal particles smaller than 1 nm are usually called atom clusters instead.
Cadmium selenide is an inorganic compound with the formula CdSe. It is a black to red-black solid that is classified as a II-VI semiconductor of the n-type. Much of the current research on this compound is focused on its nanoparticles.
Hybrid solar cells combine advantages of both organic and inorganic semiconductors. Hybrid photovoltaics have organic materials that consist of conjugated polymers that absorb light as the donor and transport holes. Inorganic materials in hybrid cells are used as the acceptor and electron transporter in the structure. The hybrid photovoltaic devices have a potential for not only low-cost by roll-to-roll processing but also for scalable solar power conversion.
Germanium telluride (GeTe) is a chemical compound of germanium and tellurium and is a component of chalcogenide glasses. It shows semimetallic conduction and ferroelectric behaviour.
Bis(trimethylsilyl)amine (also known as hexamethyldisilazane and HMDS) is an organosilicon compound with the molecular formula [(CH3)3Si]2NH. The molecule is a derivative of ammonia with trimethylsilyl groups in place of two hydrogen atoms. An electron diffraction study shows that silicon-nitrogen bond length (173.5 pm) and Si-N-Si bond angle (125.5°) to be similar to disilazane (in which methyl groups are replaced by hydrogen atoms) suggesting that steric factors are not a factor in regulating angles in this case. This colorless liquid is a reagent and a precursor to bases that are popular in organic synthesis and organometallic chemistry. Additionally, HMDS is also increasingly used as molecular precursor in chemical vapor deposition techniques to deposit silicon carbonitride thin films or coatings.
A nanocrystalline (NC) material is a polycrystalline material with a crystallite size of only a few nanometers. These materials fill the gap between amorphous materials without any long range order and conventional coarse-grained materials. Definitions vary, but nanocrystalline material is commonly defined as a crystallite (grain) size below 100 nm. Grain sizes from 100–500 nm are typically considered "ultrafine" grains.
A quantum dot solar cell (QDSC) is a solar cell design that uses quantum dots as the absorbing photovoltaic material. It attempts to replace bulk materials such as silicon, copper indium gallium selenide (CIGS) or cadmium telluride (CdTe). Quantum dots have bandgaps that are tunable across a wide range of energy levels by changing their size. In bulk materials, the bandgap is fixed by the choice of material(s). This property makes quantum dots attractive for multi-junction solar cells, where a variety of materials are used to improve efficiency by harvesting multiple portions of the solar spectrum.
Bis(trimethylsilyl) sulfide is the chemical compound with the formula ((CH3)3Si)2S. Often abbreviated (tms)2S, this colourless, vile-smelling liquid is a useful aprotic source of "S2−" in chemical synthesis.
In solar cell research, carrier multiplication is the phenomenon wherein the absorption of a single photon leads to the excitation of multiple electrons from the valence band to conduction band. In the theory of a conventional solar cell, each photon is only able to excite one electron across the band gap of the semiconductor, and any excess energy in that photon is dissipated as heat. In a material with carrier multiplication, high-energy photons excite on average more than one electron across the band gap, and so in principle the solar cell can produce more useful work.
Nanocrystal solar cells are solar cells based on a substrate with a coating of nanocrystals. The nanocrystals are typically based on silicon, CdTe or CIGS and the substrates are generally silicon or various organic conductors. Quantum dot solar cells are a variant of this approach, but take advantage of quantum mechanical effects to extract further performance. Dye-sensitized solar cells are another related approach, but in this case the nano-structuring is part of the substrate.
Photon upconversion (UC) is a process in which the sequential absorption of two or more photons leads to the emission of light at shorter wavelength than the excitation wavelength. It is an anti-Stokes type emission. An example is the conversion of infrared light to visible light. Upconversion can take place in both organic and inorganic materials, through a number of different mechanisms. Organic molecules that can achieve photon upconversion through triplet-triplet annihilation are typically polycyclicaromatic hydrocarbons (PAHs). Inorganic materials capable of photon upconversion often contain ions of d-block or f-block elements. Examples of these ions are Ln3+, Ti2+, Ni2+, Mo3+, Re4+, Os4+, and so on.
Core–shell semiconducting nanocrystals (CSSNCs) are a class of materials which have properties intermediate between those of small, individual molecules and those of bulk, crystalline semiconductors. They are unique because of their easily modular properties, which are a result of their size. These nanocrystals are composed of a quantum dot semiconducting core material and a shell of a distinct semiconducting material. The core and the shell are typically composed of type II–VI, IV–VI, and III–V semiconductors, with configurations such as CdS/ZnS, CdSe/ZnS, CdSe/CdS, and InAs/CdSe Organically passivated quantum dots have low fluorescence quantum yield due to surface related trap states. CSSNCs address this problem because the shell increases quantum yield by passivating the surface trap states. In addition, the shell provides protection against environmental changes, photo-oxidative degradation, and provides another route for modularity. Precise control of the size, shape, and composition of both the core and the shell enable the emission wavelength to be tuned over a wider range of wavelengths than with either individual semiconductor. These materials have found applications in biological systems and optics.
Carbon quantum dots are small carbon nanoparticles with some form of surface passivation.
Quantum dots (QDs) are semiconductor nanoparticles with a size less than 10 nm. They exhibited size-dependent properties especially in the optical absorption and the photoluminescence (PL). Typically, the fluorescence emission peak of the QDs can be tuned by changing their diameters. So far, QDs were consisted of different group elements such as CdTe, CdSe, CdS in the II-VI category, InP or InAs in the III-V category, CuInS2 or AgInS2 in the I–III–VI2 category, and PbSe/PbS in the IV-VI category. These QDs are promising candidates as fluorescent labels in various biological applications such as bioimaging, biosensing and drug delivery.
Stefanie Dehnen is a German chemist. She is a full professor for inorganic chemistry at the University of Marburg.
Uri Banin is an Israeli chemist and a professor at the Hebrew University of Jerusalem, currently holding the Alfred & Erica Larisch Memorial Chair at the Institute of Chemistry. He is recognized as one of the pioneers of nanoscience in Israel. Banin is an associate editor of Nano Letters.
Silicon quantum dots are metal-free biologically compatible quantum dots with photoluminescence emission maxima that are tunable through the visible to near-infrared spectral regions. These quantum dots have unique properties arising from their indirect band gap, including long-lived luminescent excited-states and large Stokes shifts. A variety of disproportionation, pyrolysis, and solution protocols have been used to prepare silicon quantum dots, however it is important to note that some solution-based protocols for preparing luminescent silicon quantum dots actually yield carbon quantum dots instead of the reported silicon. The unique properties of silicon quantum dots lend themselves to an array of potential applications: biological imaging, luminescent solar concentrators, light emitting diodes, sensors, and lithium-ion battery anodes.
