585 nm. The novel nc-Si/SiO x composite nanowires show potentialforapplicationinoptoelectronicdevices. Experimental The growth of the nc-Si/SiO x composite nanowires was carried out in a HF CVDreactor.TheHFCVDsystemconsistsofa35cmdiameterprocesscham- berequippedwithatungstenwireandasubstratestage,whichwereemployed fortheactivationofgasphasereactionsandforindependentcontrolofthesub- stratetemperature,respectively.TheWwirewithadiameterof0.5mm,coiled withadiameterof4mm,andalengthof1.5cm,wasarrangedinparallelwith thesubstrateholderatadistanceof2cmaboveit.Thetemperatureofthewire was 1800C and was monitored by an optical pyrometer through a window of the chamber. A mixture of 5 sccm SiCl 4 and 30 sccm H 2 was introduced into the reactor via a quartz tube and the total pressure was 1 torr during growth. The well-aligned nanowires were synthesized on fused silica and Si(111) sub- strates. 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FacileConversionoftheFace-CenteredCubic Prussian-BlueMaterialK 2 [Mn 2 (CN) 6 ]intothe SpinelOxideMn 3 O 4 attheSolid/Water Interface** By AurØlie Buckelew, JosØ Ramón Galµn-Mascarós ,* and Kim R. Dunbar* Prussian-blue magnets have attracted considerable atten- tion in recent years for a number of reasons, including their relative ease of preparation and the high ordering tempera- tures that they exhibit. [1] It is particularly convenient that the face-centered cubic structural motif is preserved in these ma- terials, irrespective of the composition or the identity of the transition metal ions. This situation provides an opportunity for chemists to tune the electronic structures and magnetic properties. It is now widely known that numerous Prussian- blue analogues exhibit bulk magnetic ordering with Curie temperatures that exceed those of classical inorganic materi- alsaboveroomtemperature. [2] Inaddition,Prussian-blueana- logues hold promise in the area of multi-property materials, especially magneto-optical materials, [3] and have inspired the synthesis of novel cubic molecules based on the use of spe- ciallydesignedcappingligands. [4] Apartfromtheintrinsicinterestinmaterialsbasedonmol- ecules, another general application of these compounds is their use as precursors for solid-state materials. In this ap- proach, molecular materials are used as starting materials to obtain solid-state structures, by removing the organic ligands of coordination upon thermal or chemical treatment. Exam- ples of these methods include the thermal decomposition of oxalatocomplexestoobtainoxides, [5] andthephotochemical- ly induced transformation of oxalate complexes to Prussian- blue phases in the presence of cyanide complexes. [6] Herein we report a very different type of ªdecompositionº reaction ofamaterialproducedfrommolecularprecursors,namelythe facileconversionofacyanidematerialintoametaloxidebya mildsolutionrouteandinessentiallyquantitativeyield. During the preparation in our laboratories of the Prussian- blue analogue K 2 [Mn 2 (CN) 6 ](1), first reported by Girolami etal., [7] weobservedthatacolorchangefromgreentobrown occurred with repeated washing of the product with water. This transformation was also observed in the solid state after thegreensolidwasexposedtomoistlaboratoryairforseveral 1646 Ó 2002WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim 0935-9648/02/2211-1646$17.50+.50/0 Adv. Mater. 2002, 14,No.22,November18 COMMUNICATIONS ± [*] Prof. K. R. Dunbar,A. Buckelew DepartmentofChemistry,TexasA&MUniversity POBox30012,CollegeStation,TX77842-3012(USA) E-mail:dunbar@mail.chem.tamu.edu [*] Dr. J. R. Galµn-Mascarós InstitutodeCienciaMolecular,UniversidaddeValencia Dr.Moliner,50,E-46100Burjasot(Spain) E-mail:jose.r.galan@uv.es [**] The authors thank the National Science Foundation for a Nanoscale Science and Engineering NIRT Grant (DMR-0103455) and a PI Grant (CHE-9906583) and the SQUID magnetometer (NSF-9974899). We also thanktheMICatTexasA&MUniversityfortheSEMwork.