papers C. M. Lieber et al SOI substrate op-down hybrid structure 600650 00 Wavelength(nm Figure 6. a)Emission spectrum(solid line) from CdSe QDs excited Figure 5. a)Schematic illustrating the fabrication of hybrid structures. using a p-si/n-Cds NW nanoLED; the QD emission A silicon-on-insulator(So0 substrate is patterned by standard elec- 619 nm. The increasing intensity on the shorter wavelength side of tron-beam or photolithography followed by reactive- ion etching the emission peak corresponds to the tail of the cds nanoLED. The Emissive NWs are then aligned on to the patterned sol substrate to form photonic sources; b) schematic of a single LED fabricated by dashed red line is the spectrum of pure Cdse QDs excited with an the method outlined in(a); c)/v behavior for a crossed p-n junc- Ar-ion laser; b)emission spectrum(solid line) from propidium iodide excited using a p-Si/n-CdS NW nanoLED. The dashed red line is the tion formed between a fabricated p+Si electrode and an n-Cds Nw; emission spectrum of propidium iodide obtained in aqueous so- d)EL spectrum from the forward-biased junction; e) SEM image of a lution(Fluorolog, ISA/Jobin Yvon-Spex) CdS NW assembled over seven p+Si electrodes on a Sol wafer scale bar=3 um); f) EL image recorded from an array consisting of a CdS NW crossing seven p*t-Si electrodes. The image was acquired with +5 V applied to each silicon electrodes while the Cds Nw was Experimental Section blocks. We believe that these studies represent a new path Nanowire synthesis: Compound semiconductor NWs(GaN, way towards integrated nanophotonic systems and could CdS, CdSse, CdSe, InP) were synthesized using laser-assisted impact a number or areas including intra-and inter-chip op- catalytic growth(LCG). tSal The LCG target typically consisted of tical interconnects and communications for the next genera- 95% of the respective semiconductor material and 5%Au tion of computing systems, ultrahigh density optical infor- the catalyst. The fumace temperature was set at 700-900oC mation storage, high-resolution microdisplays, and multi- during growth, and the target was placed at the upstream end of plexed chemical/biological analysis. Our studies demonstrate the furnace. A pulsed(8 ns, 10 Hz) Nd-YAG laser (1064 nm)wa the potential of nanoLEDs in this latter area, and we be- used to vaporize the target. Typically, growth was performed lieve this is especially promising since arrays of different 10 min with NWs collected at the downstream, cool end of olor nanolED sources could be combined with microflui- fumace. SiNWs were synthesized using a Au-nanocluster-cata- analytic systems that might enable applications ranging respectively l g silane and diborane as reactant and dopant, dics in lab-on-a-chip systems to produce highly integrated lyzed process usi from high-throughput screening to medical diagnostics. Assembly of crossed Nw devices: The crossed Nw devices were assembled onto Si/Sio, substrates(600 nm oxide)using a layer-by-layer fluidic directed assembly Electrical contact pat- terns were defined using electron-beam lithography (EOL 6400), 46 O 2005 Wiley-VCH Verlag GmbH& Co KGaA, D-69451Weinheim www.small-lournalcomblocks. We believe that these studies represent a new path￾way towards integrated nanophotonic systems and could impact a number or areas including intra- and inter-chip op￾tical interconnects and communications for the next genera￾tion of computing systems, ultrahigh density optical infor￾mation storage, high-resolution microdisplays, and multi￾plexed chemical/biological analysis. Our studies demonstrate the potential of nanoLEDs in this latter area, and we be￾lieve this is especially promising since arrays of different color nanoLED sources could be combined with microflui￾dics in lab-on-a-chip systems to produce highly integrated analytic systems that might enable applications ranging from high-throughput screening to medical diagnostics. Experimental Section Nanowire synthesis: Compound semiconductor NWs (GaN, CdS, CdSSe, CdSe, InP) were synthesized using laser-assisted catalytic growth (LCG).[15a] The LCG target typically consisted of 95% of the respective semiconductor material and 5% Au as the catalyst. The furnace temperature was set at 700–9008C during growth, and the target was placed at the upstream end of the furnace. A pulsed (8 ns, 10 Hz) Nd-YAG laser (1064 nm) was used to vaporize the target. Typically, growth was performed for 10 min with NWs collected at the downstream, cool end of the furnace. SiNWs were synthesized using a Au-nanocluster-cata￾lyzed process using silane and diborane as reactant and dopant, respectively.[6a, 15c] Assembly of crossed NW devices: The crossed NW devices were assembled onto Si/SiO2 substrates (600 nm oxide) using a layer-by-layer fluidic directed assembly.[13] Electrical contact pat￾terns were defined using electron-beam lithography (JEOL 6400), Figure 5. a) Schematic illustrating the fabrication of hybrid structures. A silicon-on-insulator (SOI) substrate is patterned by standard elec￾tron-beam or photolithography followed by reactive-ion etching. Emissive NWs are then aligned on to the patterned SOI substrate to form photonic sources; b) schematic of a single LED fabricated by the method outlined in (a) ; c) I–V behavior for a crossed p–n junc￾tion formed between a fabricated p+-Si electrode and an n-CdS NW; d) EL spectrum from the forward-biased junction ; e) SEM image of a CdS NW assembled over seven p+-Si electrodes on a SOI wafer (scale bar=3 mm) ; f) EL image recorded from an array consisting of a CdS NW crossing seven p+-Si electrodes. The image was acquired with +5 V applied to each silicon electrodes while the CdS NW was grounded. Figure 6. a) Emission spectrum (solid line) from CdSe QDs excited using a p-Si/n-CdS NW nanoLED ; the QD emission maximum was 619 nm. The increasing intensity on the shorter wavelength side of the emission peak corresponds to the tail of the CdS nanoLED. The dashed red line is the spectrum of pure CdSe QDs excited with an Ar-ion laser; b) emission spectrum (solid line) from propidium iodide excited using a p-Si/n-CdS NW nanoLED. The dashed red line is the emission spectrum of propidium iodide obtained in aqueous so￾lution (Fluorolog, ISA/Jobin Yvon-Spex). 146 < 2005 Wiley-VCH Verlag GmbH & Co. KGaA, D-69451 Weinheim www.small-journal.com small 2005, 1, No. 1 full papers C. M. Lieber et al