Bound-Ion Pair X-Type Ligation of Cadmium and Zinc Dithiocarbamates on Cadmium Selenide Quantum Belts.

Wurtzite CdSe quantum belts with L-type -octylamine, L-type ammonia, or Z-type Cd(oleate) ligands are exchanged for several metal-dithiocarbamate ligands [M(SCNRR)]: Cd(SCNPhMe), Cd(SCNEt), Zn(SCNPhMe), and Zn(SCNEt). Successful ligand exchange with all M(SCNRR) compounds occurs from {CdSe[Cd(oleate)]} quantum belts (QBs), which induce similar spectral shifts in the absorption spectra of the ligand-exchanged QBs. Spectroscopic data, experimentally determined lattice strains, and ligand exchanges with [Na][EtNCS] and [NH][MePhNCS] establish that the [M(SCNRR)] ligands bind as bound-ion-paired X-type ligands with (SCNRR) groups ligated directly to the QB surfaces and [M(SCNRR)] groups serving as the charge-balancing ion-paired countercations.

Intraband Relaxation Dynamics of Charge Carriers within CdTe Quantum Wires.

The state-to-state intraband relaxation dynamics of charge carriers photogenerated within CdTe quantum wires (QWs) are characterized via transient absorption spectroscopy. Overlapping signals from the energetic-shifting of the quantum-confinement features and the occupancy of carriers in the states associated with these features are separated using the quantum-state renormalization model. Holes generated with an excitation energy of 2.

Excitation Energy Dependence of Photoluminescence Quantum Yields in Semiconductor Nanomaterials with Varying Dimensionalities.

The excitation energy dependence (EED) of the photoluminescence quantum yield (Φ) of semiconductor nanoparticles with varying dimensionalities is reported. Specifically, the EEDs of CdSe quantum dots, CdSe quantum platelets, CdSe quantum belts, and CdTe quantum wires were determined via measurements of individual Φ values and photoluminescence efficiency (PL()) spectra. There is a general trend of overall decreasing efficiency for radiative recombination with increasing excitation energy.

Core-Shell Cadmium Telluride Quantum Platelets with Absorptions Spanning the Visible Spectrum.

CdS and CdSe shells are deposited on wurtzite CdTe quantum platelets (nanoplatelets) by exchanging the initial primary-amine ligation to Cd(OAc) ligation, with subsequent reaction of the Cd(OAc) ligand shell and thiourea or selenourea, respectively. Shell deposition is conducted in a cyclic manner, with 0.21-0.

Isolation of Amine Derivatives of (ZnSe) and (CdTe). Spectroscopic Comparisons of the (II-VI) and (II-VI) Magic-Size Nanoclusters.

The spectroscopically observed magic-size nanoclusters (ZnSe) and (CdTe) are isolated as amine derivatives. The nanoclusters [(ZnSe)( n-octylamine)(di- n-octylamine)] and [(CdTe)( n-octylamine)(di- n-pentylamine)] are fully characterized by combustion-based elemental analysis, UV-visible spectroscopy, IR spectroscopy, and mass spectrometry. Amine derivatives of both (ZnSe) and (CdTe) are observed to convert to the corresponding (ZnSe) and (CdTe) derivatives, indicating that the former are kinetic products and the latter thermodynamic products, under the conditions employed.

Tellurium Precursor for Nanocrystal Synthesis: Tris(dimethylamino)phosphine Telluride.

Preparations of CdTe quantum platelets, magic-size (CdTe) nanoclusters, and CdTe quantum wires are described using (MeN)PTe (with (MeN)P) as a Te precursor. The (MeN)PTe/(MeN)P precursor mixture is shown to be more reactive than mixtures of trialkylphosphine tellurides and the corresponding trialkylphosphines, RPTe/RP, which are commonly employed in nanocrystal syntheses. For syntheses conducted in primary amine solvents, (MeN)PTe and (MeN)P undergo a transamination reaction, affording (MeN) (RHN)PTe and (MeN) (RHN)P (R = n-octyl or oleyl).

Wave Function Engineering in CdSe/PbS Core/Shell Quantum Dots.

The synthesis of epitaxial CdSe/PbS core/shell quantum dots (QDs) is reported. The PbS shell grows in a rock salt structure on the zinc blende CdSe core, thereby creating a crystal structure mismatch through additive growth. Absorption and photoluminescence (PL) band edge features shift to lower energies with increasing shell thickness, but remain above the CdSe bulk band gap.

Role of Precursor-Conversion Chemistry in the Crystal-Phase Control of Catalytically Grown Colloidal Semiconductor Quantum Wires.

Crystal-phase control is one of the most challenging problems in nanowire growth. We demonstrate that, in the solution-phase catalyzed growth of colloidal cadmium telluride (CdTe) quantum wires (QWs), the crystal phase can be controlled by manipulating the reaction chemistry of the Cd precursors and tri-n-octylphosphine telluride (TOPTe) to favor the production of either a CdTe solute or Te, which consequently determines the composition and (liquid or solid) state of the BiCdTe catalyst nanoparticles. Growth of single-phase (e.

Cadmium Bis(phenyldithiocarbamate) as a Nanocrystal Shell-Growth Precursor.

Cadmium bis(phenyldithiocarbamate) [Cd(PTC)] is prepared and structurally characterized. The compound crystallizes in the monoclinic space group P2/n. A one-dimensional polymeric structure is adopted in the solid state, having bridging PTC ligands and 6-coordinate pseudo-octahedral Cd atoms.

Reversible Exchange of L-Type and Bound-Ion-Pair X-Type Ligation on Cadmium Selenide Quantum Belts.

CdSe quantum belts of composition {CdSe[n-octylamine]} and protic acids HX (X = Cl, Br, NO, acetate (OAc), and benzoate (OBz)) react to exchange the L-type amine ligation to bound-ion-pair X-type ligation. The latter ligation has X anions bound to the nanocrystal surfaces and closely associated LH counter-cations (protonated n-octylamine or tri-n-octylphosphine (TOP) to balance the surface charges. The compositions of the exchanged QBs are {CdSe[Br][n-octylammonium]}, {CdSe[NO][TOPH]}, {CdSe[OBz][n-octylammonium][TOPH]}, and {CdSe[OAc][n-octylammonium][TOPH]}.

Spectroscopic Properties of Phase-Pure and Polytypic Colloidal Semiconductor Quantum Wires.

We report ensemble extinction and photoluminesence spectra for colloidal CdTe quantum wires (QWs) with nearly phase-pure, defect-free wurtzite (WZ) structure, having spectral line widths comparable to the best ensemble or single quantum-dot values, to the single polytypic (having WZ and zinc blende (ZB) alternations) QW values, and to those of two-dimensional quantum belts or platelets. The electronic structures determined from the multifeatured extinction spectra are in excellent agreement with the theoretical results of WZ QWs having the same crystallographic orientation. Optical properties of polytypic QWs of like diameter and diameter distribution are provided for comparison, which exhibit smaller bandgaps and broader spectral line widths.

Solution-Liquid-Solid Synthesis, Properties, and Applications of One-Dimensional Colloidal Semiconductor Nanorods and Nanowires.

The solution-liquid-solid (SLS) and related solution-based methods for the synthesis of semiconductor nanowires and nanorods are reviewed. Since its discovery in 1995, the SLS mechanism and its close variants have provided a nearly general strategy for the growth of pseudo-one-dimensional nanocrystals. The various metallic-catalyst nanoparticles employed are summarized, as are the syntheses of III-V, II-VI, IV-VI, group IV, ternary, and other nanorods and nanowires.

Crystal-Phase Control by Solution-Solid-Solid Growth of II-VI Quantum Wires.

A simple and potentially general means of eliminating the planar defects and phase alternations that typically accompany the growth of semiconductor nanowires by catalyzed methods is reported. Nearly phase-pure, defect-free wurtzite II-VI semiconductor quantum wires are grown from solid rather than liquid catalyst nanoparticles. The solid-catalyst nanoparticles are morphologically stable during growth, which minimizes the spontaneous fluctuations in nucleation barriers between zinc blende and wurtzite phases that are responsible for the defect formation and phase alternations.

Large Exciton Energy Shifts by Reversible Surface Exchange in 2D II-VI Nanocrystals.

Reaction of n-octylamine-passivated {CdSe[n-octylamine](0.53±0.06)} quantum belts with anhydrous metal carboxylates M(oleate)2 (M = Cd, Zn) results in a rapid exchange of the L-type amine passivation for Z-type M(oleate)2 passivation.

Influence of the Nanoscale Kirkendall Effect on the Morphology of Copper Indium Disulfide Nanoplatelets Synthesized by Ion Exchange.

CuInS2 nanocrystals are prepared by ion exchange with template Cu2-xS nanoplatelets and InX3 [X = chloride, iodide, acetate (OAc), or acetylacetonate (acac)]. The morphologies of the resultant nanocrystals depend on the InX3 precursor and the reaction temperature. Exchange with InCl3 at 150 °C produces CuInS2 nanoplatelets having central holes and thickness variations, whereas the exchange at 200 °C produces intact CuInS2 nanoplatelets in which the initial morphology is preserved.

Magic-size II-VI nanoclusters as synthons for flat colloidal nanocrystals.

Five new, discretely sized, magic-size II-VI nanoclusters are synthesized in primary-amine bilayer templates and are isolated as the derivatives [(CdS)(34)(n-butylamine)(18)], [(ZnS)(34)(n-butylamine)(34)], [(ZnSe)(13)(n-butylamine)(13)], [(CdTe)(13)(n-propylamine)(13)], and [(ZnTe)(13)(n-butylamine)(13)]. The nanoclusters are characterized by elemental analysis, UV-visible absorption spectroscopy, laser-desorption-ionization mass spectrometry, and transmission electron microscopy. Four of the nanocluster precursors are converted to wurtzitic CdS, ZnS, and ZnSe quantum platelets and CdTe quantum belts, respectively, under mild conditions.

Two-dimensional semiconductor nanocrystals: properties, templated formation, and magic-size nanocluster intermediates.

CONSPECTUS: Semiconductor nanocrystals having an extended length dimension and capable of efficiently transporting energy and charge would have useful applications in solar-energy conversion and other emerging technologies. Pseudocylindrical semiconductor nanowires and quantum wires are available that could potentially serve in this role. Sadly, however, their defective surfaces contain significant populations of surface trap sites that preclude efficient transport.

Excitation Energy Dependence of the Photoluminescence Quantum Yields of Core and Core/Shell Quantum Dots.

The photoluminescence (PL) intensity of semiconductor quantum dots (QDs) is routinely monitored to track the chemical and physical properties within a sample or device incorporating the QDs. A dependence of the PL quantum yields (QYs) on the excitation energy could lead to erroneous conclusions but is commonly not considered. We summarize previous evidence and present results from two methodologies that confirm the possibility of a dependence of the PL QYs on the excitation energy.

Silver chloride as a heterogeneous nucleant for the growth of silver nanowires.

Various additives are employed in the polyol synthesis of silver nanowires (Ag NWs), which are typically halide salts such as NaCl. A variety of mechanistic roles have been suggested for these additives. We now show that the early addition of NaCl in the polyol synthesis of Ag NWs from AgNO3 in ethylene glycol results in the rapid formation of AgCl nanocubes, which induce the heterogeneous nucleation of metallic Ag upon their surfaces.

Preparation of primary amine derivatives of the magic-size nanocluster (CdSe)13.

Four [(CdSe)13(RNH2)13] derivatives (R = n-propyl, n-pentyl, n-octyl, and oleyl) are prepared by reaction of Cd(OAc)2·2H2O and selenourea in the corresponding primary-amine solvent. Nanoclusters grow in spontaneously formed amine-bilayer templates and are characterized by elemental analysis, IR spectroscopy, UV-vis spectroscopy, TEM, and low-angle XRD. Derivative [(CdSe)13(n-propylamine)13] is isolated as a yellowish-white solid (MP 98 °C) on the gram scale.

Bright core-shell semiconductor quantum wires.

Colloidal CdTe quantum wires are reported having ensemble photoluminescence efficiencies as high as 25% under low excitation-power densities. High photoluminescence efficiencies are achieved by formation of a monolayer CdS shell on the CdTe quantum wires. Like other semiconductor nanowires, the CdTe quantum wires may contain frequent wurtzite-zinc-blende structural alternations along their lengths.

Bound 1D Excitons in Single CdSe Quantum Wires.

Photogenerated electron-hole pairs are observed to be bound as 1D excitons in CdSe quantum wires (QWs) at room temperature. Microscopy experiments performed on dilute samples of CdSe QWs prepared on coverslips with patterned electrodes reveal that there is no change in either the overall photoluminescence (PL) intensity or the distribution of the PL intensity with the application of an external electric field. Changes in the PL intensity, and thus evidence for separate charge carriers within the QWs, are observed only for concentrated samples.

Morphology control of cadmium selenide nanocrystals: insights into the roles of di-n-octylphosphine oxide (DOPO) and ucid (DOPA).

Di-n-octylphosphine oxide (DOPO) and di-n-octylphosphinic acid (DOPA), as two of impurities found in commercial tri-n-octylphosphine oxide (TOPO), generate significant differences in the outcomes of CdSe-nanocrystal (NC) syntheses. Using n-tetradecylphosphonic acid (TDPA) as the primary acid additive, quantum dots (QDs) are grown with DOPO added, whereas quantum rods (QRs) are grown in the presence of DOPA. While using oleic acid (OA) as the primary acid additive, QDs are generated and the QDs produced with DOPA exhibit larger sizes and size distributions than those produced with DOPO.