复旦大学：《纳米线材料和功能器件》课程教学资料_纳米线的合成（一）_Controlled Synthesis of Millimeter-Long Silicon Nanowires with Uniform Electronic Properties

NANO LETTERS Controlled Synthesis of Millimeter-Long VoL 8, No 9 Silicon Nanowires with Uniform 3004-3009 Electronic Properties Won ll Park, *,t Gengfeng Zheng, Xiaocheng Jiang, Bozhi Tian, and Charles M. Lieber*. 5 Division of Materials Science and Engineering, Hanyang University Seoul 133-791, Korea, and Department of Chemistry and Chemical Biology, and School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 Received July 12, 2008; Revised Manuscript Received August 6, 2008 ABSTRACT We report the nanocluster-catalyzed growth of ultralong and highly uniform single-crystalline silicon nanowires( SiNWs)with millimeter-scale lengths and aspect ratios up to approximately 100 000. the average SiNW growth rate using disilane(Si2Hs)at 400C was 31 um/min, while the growth rate determined for silane(SiH) reactant under similar growth conditions was 130 times lower Transmission electron microscopy studies of millimeter-long SiNWs with diameters of 20-80 nm show that the nanowires grow preferentially along the( 110)direction independent of diameter. In addition, ultralong SINWs were used as building blocks to fabricate one-dimensional arrays of field-effect transistors(FETs) onsisting of approximately 100 independent devices per nanowire. Significantly, electrical transport measurements demonstrated that the millimeter-long SiNWs had uniform electrical properties along the entire length of wires, and each device can behave as a reliable FEt with an on-state current, threshold voltage, and transconductance values(average +1 standard deviation) of 1.8+0.3 uA, 6.0+ 1.1 V, 210+60 nS, respectively. Electronically uniform millimeter-long SiNWs were also functionalized with monoclonal antibody receptors and used to demonstrate multiplexed detection of cancer marker proteins with a single nanowire. The synthesis of structurally and electronically unifor ultralong SiNWs may open up new opportunities for integrated nanoelectronics and could serve as unique building blocks linking integrated structures from the nanometer through millimeter length scales Semiconducting nanowires(NWs)- are attractive building thermal evaporation of silicon monoxide 4a and silicon4b blocks for fabricating functional nanodevices with single powders; however, the electronic properties and nanoelec- device demonstrations reported for field-effect transistors tronic device characteristics have not been reported. The (FETs),memories, light emitting diodes, laser diodes, and nanocluster-catalyzed vapor-liquid-solid (VLS)growth biological sensors. o More complex device arrays and simple method is a promising method for the growth of single-crystal circuits, including logic gates, ring oscillators, and NWs with controlled diameter, length, and electronic proper- multiplexed biosensors, have been demonstrated by inter- ties. -The kinetics of SiNW VLS growth have been studied connection of multi-NW devices. A complementary approach recently by several groups. 5. 6 Interestingly, diameter- for device integration would be to employ ultralong NWs independentand diameter-dependent 6 growth rates have with multiple devices on a single NW, assuming that been observed, although in all cases the rates have been materials with uniform structure and electronic properties slower than 1-2 um/min. These reported rates make the could be prepared. Ultralong nanowires could also benefit VLS-based growth of millimeter length SiNWs a significant overall integration by facilitating inter ion of nano- challenge. We note that much larger micrometer-scale electronic device arrays, which are defined on single NWs, diameter Si whiskers have exhibited growth rates reaching to larger scale input/output wires in a system cl um/sec, which would facilitate growth of millimeter Previously, millimeter-long SiNWsl4 with a range of length structures structural properties have been produced by high-temperature To investigate nanocluster-catalyzed VLS synthesis of millimeter-long single-crystal SiNWS, we have considered *Corresponding author. E-mail: wipark @hanyang. ac kr(W1.)and whether the overall growth rate could be increased by f Hanyang University. accelerating the rate-limiting step in the process. 5, 10. 19,20 The Department of Chemistry and Chemical Biology, Harvard University. overall growth process can be broken down into contributions s Division of Engineering and Applied Science, Harvard University (i) catalytic otion of gaseous reactants at the 2063q CCC: $40.75 2008 American Chemical Society Published on Web 08/15

Controlled Synthesis of Millimeter-Long Silicon Nanowires with Uniform Electronic Properties Won Il Park,*,† Gengfeng Zheng,‡ Xiaocheng Jiang,‡ Bozhi Tian,‡ and Charles M. Lieber*,‡,§ DiVision of Materials Science and Engineering, Hanyang UniVersity, Seoul 133-791, Korea, and Department of Chemistry and Chemical Biology, and School of Engineering and Applied Sciences, HarVard UniVersity, Cambridge, Massachusetts 02138 Received July 12, 2008; Revised Manuscript Received August 6, 2008 ABSTRACT We report the nanocluster-catalyzed growth of ultralong and highly uniform single-crystalline silicon nanowires (SiNWs) with millimeter-scale lengths and aspect ratios up to approximately 100 000. The average SiNW growth rate using disilane (Si2H6) at 400 °C was 31 µm/min, while the growth rate determined for silane (SiH4) reactant under similar growth conditions was 130 times lower. Transmission electron microscopy studies of millimeter-long SiNWs with diameters of 20-80 nm show that the nanowires grow preferentially along the 〈110〉 direction independent of diameter. In addition, ultralong SiNWs were used as building blocks to fabricate one-dimensional arrays of field-effect transistors (FETs) consisting of approximately 100 independent devices per nanowire. Significantly, electrical transport measurements demonstrated that the millimeter-long SiNWs had uniform electrical properties along the entire length of wires, and each device can behave as a reliable FET with an on-state current, threshold voltage, and transconductance values (average (1 standard deviation) of 1.8 ( 0.3 µA, 6.0 ( 1.1 V, 210 ( 60 nS, respectively. Electronically uniform millimeter-long SiNWs were also functionalized with monoclonal antibody receptors and used to demonstrate multiplexed detection of cancer marker proteins with a single nanowire. The synthesis of structurally and electronically uniform ultralong SiNWs may open up new opportunities for integrated nanoelectronics and could serve as unique building blocks linking integrated structures from the nanometer through millimeter length scales. Semiconducting nanowires (NWs)1-5 are attractive building blocks for fabricating functional nanodevices with single device demonstrations reported for field-effect transistors (FETs),6 memories,7 light emitting diodes,8 laser diodes,9 and biological sensors.10 More complex device arrays and simple circuits, including logic gates,11 ring oscillators,12 and multiplexed biosensors,13 have been demonstrated by inter￾connection of multi-NW devices. A complementary approach for device integration would be to employ ultralong NWs with multiple devices on a single NW, assuming that materials with uniform structure and electronic properties could be prepared. Ultralong nanowires could also benefit overall integration by facilitating interconnection of nano￾electronic device arrays, which are defined on single NWs, to larger scale input/output wires in a system. Previously, millimeter-long SiNWs14 with a range of structural properties have been produced by high-temperature thermal evaporation of silicon monoxide14a and silicon14b powders; however, the electronic properties and nanoelec￾tronic device characteristics have not been reported. The nanocluster-catalyzed vapor-liquid-solid (VLS) growth method is a promising method for the growth of single-crystal NWs with controlled diameter, length, and electronic proper￾ties.1-4 The kinetics of SiNW VLS growth have been studied recently by several groups.15,16 Interestingly, diameter￾independent15 and diameter-dependent16 growth rates have been observed, although in all cases the rates have been slower than 1-2 µm/min.17 These reported rates make the VLS-based growth of millimeter length SiNWs a significant challenge. We note that much larger micrometer-scale diameter Si whiskers have exhibited growth rates reaching ∼1 µm/sec,18 which would facilitate growth of millimeter length structures. To investigate nanocluster-catalyzed VLS synthesis of millimeter-long single-crystal SiNWs, we have considered whether the overall growth rate could be increased by accelerating the rate-limiting step in the process.15,16,19,20 The overall growth process can be broken down into contributions from (i) catalytic adsorption of gaseous reactants at the * Corresponding author. E-mail: wipark@hanyang.ac.kr (W.I.P) and cml@cmliris.harvard.edu (C.M.L.). † Hanyang University. ‡ Department of Chemistry and Chemical Biology, Harvard University. § Division of Engineering and Applied Science, Harvard University. NANO LETTERS 2008 Vol. 8, No. 9 3004-3009 10.1021/nl802063q CCC: $40.75  2008 American Chemical Society Published on Web 08/19/2008

End point of this Nw.(c)Dark-field optical image of the same wire Scale bar, 500 um surface of liquid nanoparticles, (ii) diffusion of Si through of 20 scanning SEM images recorded along the length of a the liquid alloy to a sink, and (iii) crystallization at representative ultralong SiNw(Figure 1b)demonstrate liquid-solid interface. 216. 9. The critical importance of steps several important points. First, the length of the ap- (i) and/or (ii) in limiting growth rate has been dis- proximately 30 nm diameter nanowire, 2.3 mm, is almost Our previous studies have shown that single 100 times longer than the SiNWs we typically produce using crystal SiNWs synthesized via gold nanocluster-catalyzed SiH4 reactant. The entire SiNW can also be readily visualized VLS growth proceeds with growth rates of approximately 1 in dark-field optical microscopy images as shown in Figure um/min using silane(SiH4)as gas-phase reactant 7.22 The lc. Second, the Nw diameter is very uniform with the strong temperature dependence of the SiNW growth rate starting and end points of approximately 31 and 33 nm. under optimized conditions suggests that SiH4 decomposition respectively. This uniform diameter indicates (i) that there kinetics are more important than the gas-phase mass trans- is little or no homogeneous deposition of Si2H6 on the port and thus that acceleration of the decomposition step elongating nanowire during the synthesis and(ii) that Au might enhance the observed growth rate. Here, we explore from the catalyst does not incorporate into or diffuse along SinW growth using disilane(Si2H6)since Si2H6 is expected the surface to a substantial amount during growth. Third, to have a higher catalytic decomposition rate due to lower quantitative analysis of the lengths of ultralong SiNWS activation energy for cleavage of Si-Si versus Si-H bonds. 4 produced following I h growth yielded an average of 1.8 SiNWs were synthesized at 390-410C using gold mm with longest NWs at or exceeding 3.5 mm nanoclusters as catalysts and Si2H6 (3 sccm)as reactant We have compared siNW growth rates using Si2 H6 versus ourcewith other procedures similar to our previous reports SiH4 with other conditions fixed except growth temperature for SiHa-based SiNW growth. 417.22.26 Scanning electron in order to probe the origin of the faster growth rates leading microscopy(SEM) images of the growth wafer(Figure la) to the ultralong SiNWs. Plots of the SiNW length versus show the presence of very long nanowires with varying growth time with Si2H6 at 400C, SiH4 at 400C, and Siha degrees of entanglement. The long SiNWs were transferred at 450C for 30 nm diameter NWs(Figure 2a) show that to clean substrates via a reported shear contact printing the average growth rate for Si H6 at 400C is approximately process, which can extend and align the SiNWs for direct 31 um/min, which is approximately 130 times higher than and unambiguous length mea ents. Analysis of a series that for SiHa at the same temperature(0. 24 um/min) and 31 Nano Let., Vol. 8. No. 9, 2008

surface of liquid nanoparticles, (ii) diffusion of Si through the liquid alloy to a sink, and (iii) crystallization at liquid-solid interface.2,16,19,21 The critical importance of steps (i) and/or (iii) in limiting growth rate has been dis￾cussed.15,16,19,20 Our previous studies have shown that single￾crystal SiNWs synthesized via gold nanocluster-catalyzed VLS growth proceeds with growth rates of approximately 1 µm/min using silane (SiH4) as gas-phase recactant.17,22 The strong temperature dependence of the SiNW growth rate under optimized conditions suggests that SiH4 decomposition kinetics are more important than the gas-phase mass trans￾port23 and thus that acceleration of the decomposition step might enhance the observed growth rate. Here, we explore SiNW growth using disilane (Si2H6) since Si2H6 is expected to have a higher catalytic decomposition rate due to lower activation energy for cleavage of Si-Si versus Si-H bonds.24 SiNWs were synthesized at 390-410 °C using gold nanoclusters as catalysts and Si2H6 (3 sccm) as reactant source25 with other procedures similar to our previous reports for SiH4-based SiNW growth.4,17,22,26 Scanning electron microscopy (SEM) images of the growth wafer (Figure 1a) show the presence of very long nanowires with varying degrees of entanglement. The long SiNWs were transferred to clean substrates via a reported shear contact printing process,27 which can extend and align the SiNWs for direct and unambiguous length measurements. Analysis of a series of 20 scanning SEM images recorded along the length of a representative ultralong SiNW (Figure 1b) demonstrate several important points. First, the length of the ap￾proximately 30 nm diameter nanowire, 2.3 mm, is almost 100 times longer than the SiNWs we typically produce using SiH4 reactant. The entire SiNW can also be readily visualized in dark-field optical microscopy images as shown in Figure 1c. Second, the NW diameter is very uniform with the starting and end points of approximately 31 and 33 nm, respectively. This uniform diameter indicates (i) that there is little or no homogeneous deposition of Si2H6 on the elongating nanowire during the synthesis26 and (ii) that Au from the catalyst does not incorporate into or diffuse along the surface to a substantial amount during growth. Third, quantitative analysis of the lengths of ultralong SiNWs produced following 1 h growth yielded an average of 1.8 mm with longest NWs at or exceeding 3.5 mm. We have compared SiNW growth rates using Si2H6 versus SiH4 with other conditions fixed except growth temperature in order to probe the origin of the faster growth rates leading to the ultralong SiNWs. Plots of the SiNW length versus growth time with Si2H6 at 400 °C, SiH4 at 400 °C, and SiH4 at 450 °C for 30 nm diameter NWs (Figure 2a) show that the average growth rate for Si2H6 at 400 °C is approximately 31 µm/min, which is approximately 130 times higher than that for SiH4 at the same temperature (0.24 µm/min) and 31 Figure 1. (a) SEM image of as-grown ultralong SiNWs synthesized by Si2H6 at 400 °C for 30 min. Scale bar, 20 µm. (b) A series of 20 SEM images of a 2.3 mm- long SiNW transferred on SiO2/Si substrate. Scale bar, 200 µm. Insets, SEM images of starting and end segments of this NW. (c) Dark-field optical image of the same wire. Scale bar, 500 µm. Nano Lett., Vol. 8, No. 9, 2008 3005

the growth axis was( 110), consistent with previous studies of smaller diameter SiNWs.4. 22 In addition. TEM studies of 18 SiNWs with diameters from 15 to 80 nm(Figure 2c and 200 Supporting Information, Figure SIb) all showed single- crystalline structures with a growth axis of (1 10)indep ndent of diameter, where 13/18 of the sampled SiNWS had diameters between 29 to 80 nm. Interestingly, the diameter 1000 independent growth direction observed for the ultralong SiNWs contrasts previous studies where a cross-over to(111) 50 direction at approximately 20 nm was observed. 45.22 Previously, Schmidt et al. proposed a model based on he free energy, which is influenced by the interplay of the Time(min) liquid-solid interfacial tension with Si surface edge tension, to explain consistently diameter dependent growth in SiNWS Within the context of this model, a larger critical cross-over diameter from(110) to(111)would be observed for an interfacial thickness that increased with crystallization rate We speculate that the faster growth rates used to achieve the ultralong siNWs might lead to an increase of the interfacial thickness parameter, although future studies of critical diameter versus growth rate will be required to clarify this point. Regardless of the detailed origin, we believe these observations suggest that it will be interesting to explore and possibly exploit kinetic effects as a means to controlling growth directions for NWs produced by the nanocluster- catalyzed VLs process The ultralong SiNWs represent potentially attractive build ing blocks for nanoelectronics because it would be possible to define a large nu facilitating integration as shown schematically in Figure 3a. In addition, the fabrication and characterization of multipl devices on a single Nw could provide important information addressing doping and electronic uniformity of these nano structures. To address these issues, we have prepared ultralong boron-doped SiNWs, aligned the NWs on sub Figure 2.(a)Plot of SiNW length versus growth time for Si2H6 strate by shear contact printing, 7and defined arrays of FETs 400°C( black), SiHg at400°c( red) and Sih4450°C(blue) by electron beam lithography. 0a.11.2628 A representative (b)Lattice-resolved TEM image recorded along(111) zone axis of a 18 nm diameter ultralong SiNw; scale bar is 5 nm.(c) optical image(Figure 3b) highlights the large number of Lattice-resolved TEM image of a 78 nm diameter ultralon addressable fets defined on the ultralong sinws. SiNW; scale bar is 5 nm. Inset is a lower magnification image Electrical transport measurements showed that more than of the siNw 90%o devices behaved as good p-type devices. Specifically, source-drain current(p) versus source-drain voltage(VD) times higher than for SiHa at our optimal growth temperature curves at small V were linear, which demonstrates good f 450C(1.0 um/min). Using the temperature-dependent contacts across the Nw. The decrease in /p with increasingly gas phase decomposition rate data for Si2H6 and SiH4, we positive VG(Figure S2)also showed that devices were p-type Si2H6(400C): SiH4(400 and 450C) of ap- depletion mode FETs In addition, we have assessed and ately 170 and 10, respectively. These values are compared quantitatively key transistor characteristics, includ to the experimental ratios of growth rates and thus ing on-state current, Ion, peak transconductance, GM, and uggest that reactant decomposition kinetics is important in threshold voltage, Vuh, as a function of position across the determining the observed SiNW growth rates. single SiNW array. Notably, the lon(Figure 3c), GM(Figure The structural characteristics of the ultralong SiNWs were 3d), and Vuh(Figure 3e) show very reproducible values across also investigated by transmission electron microscopy (TEM). the entire array spanning almost I mm in length with average Lattice-resolved images of an approximately 18 nm diameter +l standard deviation values of 1. 77+0.33 uA, 213+ 61 SiNW(Figure 2b) show that the SinW is a single-crystalline nS, and 6.0+ 1.1 V, respectively. Previous studies of structure despite the fact that growth occurred at rates at least individual nanowire FETsa.y have exhibited larger variations 10 times greater than previous studies. 4.5-7, 9.22 The TEM in key FET properties, with variations in threshold voltage image and two-dimensional Fourier transform analysis(Sup. of 35-135% versus 20% and transconductance of 58-76% porting Information, Figure Sla) further demonstrated that versus 30%. This comparison indicates that the ultralong Nano Lett., Vol. 8. No. 9, 2008

times higher than for SiH4 at our optimal growth temperature of 450 °C (1.0 µm/min). Using the temperature-dependent gas phase decomposition rate data for Si2H6 and SiH4, 24 we estimate Si2H6 (400 °C):SiH4 (400 and 450 °C) of ap￾proximately 170 and 10, respectively. These values are similar to the experimental ratios of growth rates and thus suggest that reactant decomposition kinetics is important in determining the observed SiNW growth rates. The structural characteristics of the ultralong SiNWs were also investigated by transmission electron microscopy (TEM). Lattice-resolved images of an approximately 18 nm diameter SiNW (Figure 2b) show that the SiNW is a single-crystalline structure despite the fact that growth occurred at rates at least 10 times greater than previous studies.4,15-17,19,22 The TEM image and two-dimensional Fourier transform analysis (Sup￾porting Information, Figure S1a) further demonstrated that the growth axis was 〈110〉, consistent with previous studies of smaller diameter SiNWs.4,22 In addition, TEM studies of 18 SiNWs with diameters from 15 to 80 nm (Figure 2c and Supporting Information, Figure S1b) all showed single￾crystalline structures with a growth axis of 〈110〉 independent of diameter, where 13/18 of the sampled SiNWs had diameters between 29 to 80 nm. Interestingly, the diameter￾independent growth direction observed for the ultralong SiNWs contrasts previous studies where a cross-over to 〈111〉 direction at approximately 20 nm was observed.4,5,22 Previously, Schmidt et al.5 proposed a model based on the free energy, which is influenced by the interplay of the liquid-solid interfacial tension with Si surface edge tension, to explain consistently diameter dependent growth in SiNWs. Within the context of this model, a larger critical cross-over diameter from 〈110〉 to 〈111〉 would be observed for an interfacial thickness that increased with crystallization rate. We speculate that the faster growth rates used to achieve the ultralong SiNWs might lead to an increase of the interfacial thickness parameter, although future studies of critical diameter versus growth rate will be required to clarify this point. Regardless of the detailed origin, we believe these observations suggest that it will be interesting to explore and possibly exploit kinetic effects as a means to controlling growth directions for NWs produced by the nanocluster￾catalyzed VLS process. The ultralong SiNWs represent potentially attractive build￾ing blocks for nanoelectronics because it would be possible to define a large number of devices on a single NW, thus facilitating integration as shown schematically in Figure 3a. In addition, the fabrication and characterization of multiple devices on a single NW could provide important information addressing doping and electronic uniformity of these nano￾structures. To address these issues, we have prepared ultralong boron-doped SiNWs,25 aligned the NWs on sub￾strate by shear contact printing,27 and defined arrays of FETs by electron beam lithography.10a,11,26,28 A representative optical image (Figure 3b) highlights the large number of addressable FETs defined on the ultralong SiNWs. Electrical transport measurements showed that more than 90% devices behaved as good p-type devices. Specifically, source-drain current (ID) versus source-drain voltage (VD) curves at small VD were linear, which demonstrates good contacts across the NW. The decrease in ID with increasingly positive VG (Figure S2) also showed that devices were p-type depletion mode FETs. In addition, we have assessed and compared quantitatively key transistor characteristics, includ￾ing on-state current, Ion, peak transconductance, GM, and threshold voltage, Vth, as a function of position across the single SiNW array. Notably, the Ion (Figure 3c), GM (Figure 3d), and Vth (Figure 3e) show very reproducible values across the entire array spanning almost 1 mm in length with average (1 standard deviation values of 1.77 ( 0.33 µA, 213 ( 61 nS, and 6.0 ( 1.1 V, respectively. Previous studies of individual nanowire FETs6a,29 have exhibited larger variations in key FET properties, with variations in threshold voltage of 35-135% versus ∼20% and transconductance of 58-76% versus ∼30%. This comparison indicates that the ultralong Figure 2. (a) Plot of SiNW length versus growth time for Si2H6 at 400 °C (black), SiH4 at 400 °C (red) and SiH4 450 °C (blue). (b) Lattice-resolved TEM image recorded along 〈111〉 zone axis of a 18 nm diameter ultralong SiNW; scale bar is 5 nm. (c) Lattice-resolved TEM image of a 78 nm diameter ultralong SiNW; scale bar is 5 nm. Inset is a lower magnification image of the SiNW. 3006 Nano Lett., Vol. 8, No. 9, 2008

i 回1e c9989≈ d &agp Position (um) igure 3.(a) Schematic of multiple FET array on a single ultralong p-siNw.(b)Dark-field optical image of multiple FETs defined by electron beam lithography. The p-siNW is horizontal in the image and the vertical lines crossing the nw correspond to S/D electrodes with um width/2 um separation; scale bar is 100 um. The dashed white rectangle corresponds to a similar area shown schematically in(a).(c) Position vs Ip at VD=1 Vand VG=-10 V measured from the multiple FETs defined on the single p-SiNW in the image.(d) Position vS Gm at VD =1 v(e)Position vs vth. b 1300 (1) (3) 1200 1100 1000 2000400060008000 Figure 4.(a) Optical image of a multiple sensor array with similar source-drain dimensions as in Figure 3b; scale bar, 100 um. The red blue, and green circles highlight regions from which sensing data were recorded. (b)Conductance-versus-time data measured simultaneously from three Fet devices from the red, blue, and green regions of the device array. The sinw FET array was functionalized with mAb for PSA, and the data were recorded by alternating delivery of target solutions(PSA or BSA)and buffer solution where vertical arrows correspond to the delivery of (1)20 pg/ml PSA, (2)500 pg/ml PSA, (3)10 ng/ml PSA, (4)10 ug/ml BSA, and (5)20 pg/ml PSA solutions. The functionalization and measurement procedures were the same as reported previously 3 SiNWs are electrically homogeneous and yield device porated in a uniform manner during nanocluster-catalyzed reproducibility higher than achieved from single Nw-based VLS growth FETs. Last, these measurements also suggest that the active The ability to define large numbers of functional FETs boron dopant yielding the p-type behavior must be incor- along single ultralong NWs can open up new opportunities ano Lett, Vol. 8, No. 9, 2008

SiNWs are electrically homogeneous and yield device reproducibility higher than achieved from single NW-based FETs. Last, these measurements also suggest that the active boron dopant yielding the p-type behavior must be incor￾porated in a uniform manner during nanocluster-catalyzed VLS growth. The ability to define large numbers of functional FETs along single ultralong NWs can open up new opportunities Figure 3. (a) Schematic of multiple FET array on a single ultralong p-SiNW. (b) Dark-field optical image of multiple FETs defined by electron beam lithography. The p-SiNW is horizontal in the image and the vertical lines crossing the NW correspond to S/D electrodes with 2 µm width/2 µm separation; scale bar is 100 µm. The dashed white rectangle corresponds to a similar area shown schematically in (a). (c) Position vs ID at VD ) 1 V and VG ) -10 V measured from the multiple FETs defined on the single p-SiNW in the image. (d) Position vs GM at VD ) 1 V. (e) Position vs Vth. Figure 4. (a) Optical image of a multiple sensor array with similar source-drain dimensions as in Figure 3b; scale bar, 100 µm. The red, blue, and green circles highlight regions from which sensing data were recorded. (b) Conductance-versus-time data measured simultaneously from three FET devices from the red, blue, and green regions of the device array. The SiNW FET array was functionalized with mAb for PSA, and the data were recorded by alternating delivery of target solutions (PSA or BSA) and buffer solution where vertical arrows correspond to the delivery of (1) 20 pg/ml PSA, (2) 500 pg/ml PSA, (3) 10 ng/ml PSA, (4) 10 µg/ml BSA, and (5) 20 pg/ml PSA solutions. The functionalization and measurement procedures were the same as reported previously.13,17 Nano Lett., Vol. 8, No. 9, 2008 3007

for integrated nanoelectronics. To demonstrate this concept, exploited to demonstrate a new approach to multiplexed we have explored multiplexed protein detection using mono- detection of cancer marker proteins with a single nanowire clonal antibody(mAb) functionalized SiNW FETs( Figure The synthesis of structurally and electronically uniform 4a). In previous studies, we have demonstrated multiplexed ultralong SiNWs may open up new opportunities for detection using mAb functionalized devices, but in this case, integrated nanoelectronics and could serve as unique building ch device was from an individual SiNW thus necessitating blocks linking integrated structures from the nanometer well-defined assembly to achieve the FET array Demonstra- through millimeter length scales tion of multiplexed measurements from independently ad- dressable FETs defined on a single ultralong sinw has not Acknowledgment. We thank J. Xiang for helpful discus- been previously achieved using either nanowires or carbon sion. W.L. P acknowledges support from the Korea Research nanotubes. However, this approach could have substantial Foundation Grant funded by the Korean Government(MOE impact on the biosensor area 0a. 3 because it(i) simpl HRD. Basic Research Promotion Fund: KRF-2007-331 DO0194) C. M.L. acknowledges support of this work through the greater device homogeneity for FETs defined on a single a contract from National Institutes of Health, MITRE ultralong SiNW,(ii)opens up the opportunity to assess nsing reproducibility in device arrays where device-to- Supporting Information Available: Two-dimensional device variability should not be the dominating factor Fourier transforms and source-drain current versus gate Conductance versus time data recorded from three distinct voltage curves. This material is available free of charge via FetSdefinedonthesingleultralongSinw,whichwastheInternetathttp://pubs.acs.org functionalized uniformly with the mAb for prostate specific antigen(PSA), showed several key features. First, the devices References exhibited well-defined and reversible conductance increases (1)Morales, A: Lieber, C. M. associated with the binding and unbinding of the specific 2)(a) Lieber, C. M. Wang, Z. L. MRS Bull. 2007. 32. 99.(b) Xia,Y Yang, P. Sun, Y: u. Y: Mayers. B: Gates, B. Yin, Y. Kim. F target PSA. Second, the conductance change was proportional Yan, H. Adu. Mater. 2003. 15. 353. (c) Thelander, C. Agarwal, P to the PSa concentration, as expected for equilibrium bindin Brongersma, S: Eymery, J. Feiner, L. F; Forchel, A Scheffler, M. Riess. W: Ohlsson. B. J: Gosele U: Samuelson, L. Mater. Today response. Third, the concentration-dependent conductance 2006.9,28 change recorded in the distinct FEt elements which were ()Schmidt, V: Gosele, U. Science 2007, 316. 698. separated by >100 um, was similar and testifies to the u,Y; Cui, Y: Huynh, L. Barrelet. C J. Bell, D. C. Lieber, C.M. Nano Lett. 2004. 4. 433 electronic uniformity of the ultralong SiNWs and the uniform (5)Schmidt, V: Senz, S: Gosele, U. Nano Lett. 2005. 5. 931 mAb functionalization Fourth we note that addition bovine(6)(a) Cui, Y ; Zhong, Z. H. Wang, D. L: Wang, w. U. Lieber, C M serum albumin at 1000 times higher concentration showed H: Lieber, C. M. Nature 2006, 441, 489.(c)Ng, H. T: Han,J. no response, demonstrating good selectivity. lAst Yamada, T. Nguyen, P. Chen, Y. P: Meyyappan, M. Nano Lett. reproducible conductance change from each of the addres- 2004. 4. 1247.(d) Park, w.l.: Kim J.S.: Yi, G.-C: Lee, H. J. Adu. sable devices is consistent with the homogeneous device Mater.2005,17,1393 (7)Lu. W: Lieber, C. M. Nat. Mater. 2007, 6, 841 characteristics demonstrated in Figure 3. While the present )(a)Duan, X. Huang, Y: Cui, Y. Wang. J. Lieber, C. M. Natu measurements represent a relatively simple demonstration 2001, 409, 66.(b)Zhong. Z; Qian. F; Wang, D: Lieber. C. M. Nano of multiplex protein detection, they do demonstrate a new Lett. 2003, 3. 343.(c) Huang. Y; Duan. X. Lieber, C. M. Small 2005 1, 142.(d) Qian, F. Li, Y. Gradeeak, S: Barrelet, C. J. Wang. D approach for multiplexing that could be extended in the future Lieber, C. M. Nano Lett. 2004. 4. 1975 to include parallel, real-time measurements from a larger (9)Duan, X. Huang. Y: AgarwaL, R. Lieber, C M Nature 2003, 42/ number of devices functionalized with diverse mAb recep- (10)(a)Cui, Y. Wei, Q: Park, H. Lieber, C M. Science 2001, 293, 1289. (b)Hahm, J; Lieber, C. M. Nano Lett. 2004. 4, 51(c)Shim, M In we have demonstrated the nanocluster- Kam, N. w.S.: Chen. R.J.: Li, Y M. Dai. H.J. Nano Lett. 2002. 2 catalyzed growth of millimeter-long and highly uniform (11) Huang. Y: Duan, X Cui. Y: Lauhon, L J. Kim, K: Lieber, C.M. ngle-crystalline SiNWs with lence2001,294,1313 proximately 100 000. The average Sinw growth rates using (12)Friedman, R. S: McAlpine, M. C; Ricketts, D. S: Ham, D; Lieber C.M. Nature2005,434,1085 Si2H6 reactant were 30-130 times faster than previous rates (13) Zheng, G. Patolsky, F;Cui,Y:Wang. W.U.Lieber, CM.Nat observed using SiHa reactant under similar growth conditions. Biotechnol. 2005. 23. 1294 TEM studies showed that the ultralong SiNWs grow (14)(a)Shi, w.S.; Peng. H. Y. Zheng, Y. F; Wang, N; Shang, N. G Pan, Z. W: Lee, C.S.: Lee, S. T. Adu. Mater. 2000, 12, 1343.(b) preferentially along the(110)direction, independent of Shi. Y: Hu, Q; Araki, H. Suzuki, H: Gao. H: Yang, W: Noda, T. diameter, and suggest that kinetic effects may be used as a Appl. Phys. A: Mater. Sci. Process. 2005, 80, 1733 means for controlling growth directions in NWs produced (15)Kodambaka, S: Tersoff, J Reuter. M. C. Ross, F. M. Phys. ReD. Le.2006.96.09610 by the nanocluster-catalyzed VLs process. In addition, (16) Schmidt, V; Senz, S. Gosele, U. Phys. Reu. B 2007,, 045335 ultralong sinws were used as building blocks to fabricate (17) Patolsky, F; Zheng, G: Lieber, C. M. Nat. Protocols 2006, 1, 1711 one-dimensional FET arrays that exhibit high-degree of (18)Nebol'sin, V. A: Shchetinin, A. A Dolgachev, A. A: Komneeva V Inorg. Mater. 2005, 41, 125 device uniformity over millimeter dimensions and testify to (19) Givargizov, E I J. Cryst. Growth 1975,, 20 the electrical/doping homogeneity of SiNWs produced by Bootsma. G. A; Gassen, H. J.J. Cryst. Growth 1971, 10, 223 (21)Wu, Y: Yang, P J. A. Chem. Soc. 2001. 123, 3165 nanocluster-catalyzed VLS growth. Lastly, the uniform (22)Cui, Y: Lauhon, L.J.; Gudiksen, M.S.: Wang.J: Lieber, C.M.Appl. device properties of nal FET arrays were Phys.Let2001,78,2214 Nano Lett., Vol. 8. No. 9, 2008

for integrated nanoelectronics. To demonstrate this concept, we have explored multiplexed protein detection using mono￾clonal antibody (mAb) functionalized SiNW FETs (Figure 4a). In previous studies,13 we have demonstrated multiplexed detection using mAb functionalized devices, but in this case, each device was from an individual SiNW thus necessitating well-defined assembly to achieve the FET array. Demonstra￾tion of multiplexed measurements from independently ad￾dressable FETs defined on a single ultralong SiNW has not been previously achieved using either nanowires or carbon nanotubes. However, this approach could have substantial impact on the biosensor area10a,13 because it (i) simplifies fabrication of multiplexed sensor device arrays and, given the greater device homogeneity for FETs defined on a single ultralong SiNW, (ii) opens up the opportunity to assess sensing reproducibility in device arrays where device-to￾device variability should not be the dominating factor. Conductance versus time data recorded from three distinct FETs defined on the single ultralong SiNW, which was functionalized uniformly with the mAb for prostate specific antigen (PSA), showed several key features. First, the devices exhibited well-defined and reversible conductance increases associated with the binding and unbinding of the specific target PSA. Second, the conductance change was proportional to the PSA concentration, as expected for equilibrium binding response. Third, the concentration-dependent conductance change recorded in the distinct FET elements, which were separated by >100 µm, was similar and testifies to the electronic uniformity of the ultralong SiNWs and the uniform mAb functionalization. Fourth, we note that addition bovine serum albumin at 1000 times higher concentration showed no response, demonstrating good selectivity.13 Last, the reproducible conductance change from each of the addres￾sable devices is consistent with the homogeneous device characteristics demonstrated in Figure 3. While the present measurements represent a relatively simple demonstration of multiplex protein detection, they do demonstrate a new approach for multiplexing that could be extended in the future to include parallel, real-time measurements from a larger number of devices functionalized with diverse mAb recep￾tors. In summary, we have demonstrated the nanocluster￾catalyzed growth of millimeter-long and highly uniform single-crystalline SiNWs with aspect ratios up to ap￾proximately 100 000. The average SiNW growth rates using Si2H6 reactant were 30-130 times faster than previous rates observed using SiH4 reactant under similar growth conditions. TEM studies showed that the ultralong SiNWs grow preferentially along the 〈110〉 direction, independent of diameter, and suggest that kinetic effects may be used as a means for controlling growth directions in NWs produced by the nanocluster-catalyzed VLS process. In addition, ultralong SiNWs were used as building blocks to fabricate one-dimensional FET arrays that exhibit high-degree of device uniformity over millimeter dimensions and testify to the electrical/doping homogeneity of SiNWs produced by nanocluster-catalyzed VLS growth. Lastly, the uniform device properties of one-dimensional FET arrays were exploited to demonstrate a new approach to multiplexed detection of cancer marker proteins with a single nanowire. The synthesis of structurally and electronically uniform ultralong SiNWs may open up new opportunities for integrated nanoelectronics and could serve as unique building blocks linking integrated structures from the nanometer through millimeter length scales. Acknowledgment. We thank J. Xiang for helpful discus￾sion. W.I.P acknowledges support from the Korea Research Foundation Grant funded by the Korean Government (MOE￾HRD, Basic Research Promotion Fund; KRF-2007-331- D00194). C.M.L. acknowledges support of this work through a contract from National Institutes of Health, MITRE Corporation, and Samsung Electronics. Supporting Information Available: Two-dimensional Fourier transforms and source-drain current versus gate voltage curves. This material is available free of charge via the Internet at http://pubs.acs.org. References (1) Morales, A.; Lieber, C. M. Science 1998, 279, 208. (2) (a) Lieber, C. M.; Wang, Z. L. MRS Bull. 2007, 32, 99. (b) Xia, Y.; Yang, P.; Sun, Y.; Wu, Y.; Mayers, B.; Gates, B.; Yin, Y.; Kim, F.; Yan, H. AdV. Mater. 2003, 15, 353. (c) Thelander, C.; Agarwal, P.; Brongersma, S.; Eymery, J.; Feiner, L. F.; Forchel, A.; Scheffler, M.; Riess, W.; Ohlsson, B. J.; Gosele, U.; Samuelson, L. Mater. Today 2006, 9, 28. (3) Schmidt, V.; Go¨sele, U. Science 2007, 316, 698. (4) Wu, Y.; Cui, Y.; Huynh, L.; Barrelet, C. J.; Bell, D. C.; Lieber, C. M. Nano Lett. 2004, 4, 433. (5) Schmidt, V.; Senz, S.; Go¨sele, U. Nano Lett. 2005, 5, 931. (6) (a) Cui, Y.; Zhong, Z. H.; Wang, D. L.; Wang, W. U.; Lieber, C. M. Nano Lett. 2003, 3, 149. (b) Xiang, J.; Lu, W.; Hu, Y.; Wu, Y.; Yan, H.; Lieber, C. M. Nature 2006, 441, 489. (c) Ng, H. T.; Han, J.; Yamada, T.; Nguyen, P.; Chen, Y. P.; Meyyappan, M. Nano Lett. 2004, 4, 1247. (d) Park, W. I.; Kim, J. S.; Yi, G.-C.; Lee, H. J. AdV. Mater. 2005, 17, 1393. (7) Lu, W.; Lieber, C. M. Nat. Mater. 2007, 6, 841. (8) (a) Duan, X.; Huang, Y.; Cui, Y.; Wang, J.; Lieber, C. M. Nature 2001, 409, 66. (b) Zhong, Z.; Qian, F.; Wang, D.; Lieber, C. M. Nano Lett. 2003, 3, 343. (c) Huang, Y.; Duan, X.; Lieber, C. M. Small 2005, 1, 142. (d) Qian, F.; Li, Y.; Gradee`ak, S.; Barrelet, C. J.; Wang, D.; Lieber, C. M. Nano Lett. 2004, 4, 1975. (9) Duan, X.; Huang, Y.; Agarwal, R.; Lieber, C. M. Nature 2003, 421, 241. (10) (a) Cui, Y.; Wei, Q.; Park, H.; Lieber, C. M. Science 2001, 293, 1289. (b) Hahm, J.; Lieber, C. M. Nano Lett. 2004, 4, 51. (c) Shim, M.; Kam, N. W. S.; Chen, R. J.; Li, Y. M.; Dai, H. J. Nano Lett. 2002, 2, 285. (11) Huang, Y.; Duan, X.; Cui, Y.; Lauhon, L. J.; Kim, K.; Lieber, C. M. Science 2001, 294, 1313. (12) Friedman, R. S.; McAlpine, M. C.; Ricketts, D. S.; Ham, D.; Lieber, C. M. Nature 2005, 434, 1085. (13) Zheng, G.; Patolsky, F.; Cui, Y.; Wang, W. U.; Lieber, C. M. Nat. Biotechnol. 2005, 23, 1294. (14) (a) Shi, W. S.; Peng, H. Y.; Zheng, Y. F.; Wang, N.; Shang, N. G.; Pan, Z. W.; Lee, C. S.; Lee, S. T. AdV. Mater. 2000, 12, 1343. (b) Shi, Y.; Hu, Q.; Araki, H.; Suzuki, H.; Gao, H.; Yang, W.; Noda, T. Appl. Phys. A: Mater. Sci. Process. 2005, 80, 1733. (15) Kodambaka, S.; Tersoff, J.; Reuter, M. C.; Ross, F. M. Phys. ReV. Lett. 2006, 96, 096105. (16) Schmidt, V.; Senz, S.; Go¨sele, U. Phys. ReV. B 2007, 75, 045335. (17) Patolsky, F.; Zheng, G.; Lieber, C. M. Nat. Protocols 2006, 1, 1711. (18) Nebol’sin, V. A.; Shchetinin, A. A.; Dolgachev, A. A.; Korneeva, V. V. Inorg. Mater. 2005, 41, 1256. (19) Givargizov, E. I. J. Cryst. Growth 1975, 31, 20. (20) Bootsma, G. A.; Gassen, H. J. J. Cryst. Growth 1971, 10, 223. (21) Wu, Y.; Yang, P. J. Am. Chem. Soc. 2001, 123, 3165. (22) Cui, Y.; Lauhon, L. J.; Gudiksen, M. S.; Wang, J.; Lieber, C. M. Appl. Phys. Lett. 2001, 78, 2214. 3008 Nano Lett., Vol. 8, No. 9, 2008

(23)Masi, M. Cavallotti. C: Carra, S. In Silicon-Bas (27) Javey. A: Nam, S; Friedman, R.S.; Yan, H; Lieber, C M. Nano Devices: Nalwa, H. S. Eds: Academic Press: San Diego, 200 Let.2007,7,773. (28) The SiNWs were transferred to the oxide surface of doped (resistivity (24)Roenigk, K F; Jensen, K. F: Carr, R. w.J. Phys. Chem. 1987, 91, 0.005 Q2cm) silicon substrates(Silicon Valley Microelectronics, Inc. 5732. San Jose, CA), multiple source-drain electrodes were defined by (25) SiNWs were synthesized at 390-410C using well-dispersed gold electron beam lithography, and then Ni contacts (70 nm thick)were nanoclusters(10-80 nm diameter) as catalysts, H2 as carrie deposited by thermal evaporation. The contacts were annealed at 280 (10 cm at standard temperature and pressure, STM min min in forming gas (10% H2 in H and Si2H6(3 STM min-i)as reactant source at 10 torr. Boron (29)(a)Jin, S: Whang, D: McAlpine, M. C; Friedman, R. S: Wu, Y. doped p-type SiNWs were synthesized using 100 ppm B2H6 as Lieber, C. M. Nano Lett. 2004. 4. 915(b)Hong. W.K.: Kim, B..J oping source with a Si2Hs/B2H6 ratio of 105-2 x 105: 1(Si/B Kim. T -W: Jo. G. Song. S: Kwon, S.-S: Yoon. A: Stach, E. A Lee, T Colloid Surf, A 2008, 313, 378 (26) Yang, C. Zhong, Z: Lieber, C. M. Science 2005, 310, 130 NL802063Q Nano Let., Vol. 8. No. 9, 2008

(23) Masi, M.; Cavallotti, C.; Carra`, S. In Silicon-Based Materials and DeVices; Nalwa, H. S., Eds.; Academic Press: San Diego, 2001; Ch. 4. (24) Roenigk, K. F.; Jensen, K. F.; Carr, R. W. J. Phys. Chem. 1987, 91, 5732. (25) SiNWs were synthesized at 390-410 °C using well-dispersed gold nanoclusters (10-80 nm diameter) as catalysts, H2 as carrier gas (10 cm3 at standard temperature and pressure, STM min-1) and Si2H6 (3 STM min-1) as reactant source at 10 torr. Boron￾doped p-type SiNWs were synthesized using 100 ppm B2H6 as doping source with a Si2H6/B2H6 ratio of 105-2 × 105:1 (Si/B ) 105-2 × 105:1). (26) Yang, C.; Zhong, Z.; Lieber, C. M. Science 2005, 310, 1304. (27) Javey, A.; Nam, S.; Friedman, R. S.; Yan, H.; Lieber, C. M. Nano Lett. 2007, 7, 773. (28) The SiNWs were transferred to the oxide surface of doped (resistivity <0.005 Ω·cm) silicon substrates (Silicon Valley Microelectronics, Inc., San Jose, CA), multiple source-drain electrodes were defined by electron beam lithography, and then Ni contacts (70 nm thick) were deposited by thermal evaporation. The contacts were annealed at 280 °C for 1 min in forming gas (10% H2 in He). (29) (a) Jin, S.; Whang, D.; McAlpine, M. C.; Friedman, R. S.; Wu, Y.; Lieber, C. M. Nano Lett. 2004, 4, 915. (b) Hong, W.-K.; Kim, B.-J.; Kim, T.-W.; Jo, G.; Song, S.; Kwon, S.-S.; Yoon, A.; Stach, E. A.; Lee, T. Colloid. Surf., A 2008, 313, 378. NL802063Q Nano Lett., Vol. 8, No. 9, 2008 3009