Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

GaInP 2 QDs from a plot of the square of the absorbance times photon energyversus photon energy indicates a value of about 2.7 eV; this value is blueshiftedfrom the bulk value of 1.8–2.0 eV.4. Colloidal GaAs Quantum DotsGaAs quantum dots can be formed by first reacting Ga(III) acetylacetonateand As[Si(CH 3 ) 3 ] 3 at reflux (216jC) in triethylene glycol dimethyl ether(triglyme) [25–28]. This produces an orange-brown turbid slurry that can befiltered through a 700-Å ultrafilter to produce the GaAs colloidal QDsolution. A TEM image of GaAs QDs prepared in this way, except thatquinoline was used instead of triglyme, shows perfectly spherical QDs withvery well-resolved lattice planes [27]. Electron diffraction data show clear hklzinc-blende GaAs patterns of (111), (220), (311), and (422). The observedlattice plane spacing of 3.2 A˚ in TEM images corresponds to the d(111) ofGaAs. Optical absorption spectra of the GaAs QDs shows an onset ofabsorption at about 600 nm; a shallow rise with decreasing wavelengthsteepens at about 470 nm and peaks at about 440 nm [25–28]. The particlesizedistribution of the GaAs QDs was not sufficient to observe excitonictransitions in the absorption or emission spectra [25–28].5. Colloidal GaN Quantum DotsWells and co-workers [29,30] first showed that nanosize GaN can be synthesizedby pyrolysis of {Ga(NH) 3/2 } n at high temperature. The lack of anyorganic substituents in the precursor makes {Ga(NH) 3/2 } n a good candidatefor the generation of carbon-free gallium nitride. To produce colloidaltransparent solutions of isolated GaN QDs, a method was used which issimilar to that described earlier for the preparation of III–V phosphide QDs.Dimeric amidogallium Ga[N(CH 3 ) 2 ] 6 was synthesized by mixing anhydrousGaCl 3 with LiN(CH 3 ) 2 in hexane according to the published method [31].This dimer was then used to prepare polymeric gallium imide {Ga(NH) 3/2 } nby reacting Ga 2 [N(CH 3 ) 2 ] 6 with gaseous NH 3 at room temperature for 24 h.Details of the preparation are given in Refs. 29 and 30. To produce GaN QDs,the resulting {Ga(NH) 3/2 } n (0.2 g) was slowly heated in trioctylamine (TOA)[boiling point (b.p. 365jC, 4 mL)] at 360jC over 24 h and kept at thistemperature for 1 day. Ammonia flow at ambient pressure was maintainedduring this heat treatment and while the solution cooled to room temperature.The solution was cooled to 220jC and a mixture of TOA (2 mL) andhexadecylamine (HDA) (b.p. 330jC, 2g) was added and stirred at 220jCfor 10 h; the HDA improved hydrophobic capping of the GaN surfacebecause HDA is less sterically hindered and creates a more dense surfacecap. After that, the solution was cooled over several hours.Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.