facile one-step synthesis of cds x se 1– x nanobelts with uniform and controllable stoichiometry

Published: September 07, 2011

r 2011 American Chemical Society 19538 dx.doi.org/10.1021/jp205760r | J. Phys. Chem. C 2011, 115, 19538–19545

ARTICLE

pubs.acs.org/JPCC

Facile One-Step Synthesis of CdSxSe1�x Nanobelts with Uniformand Controllable StoichiometryLu Junpeng,† Sun Cheng,‡ Zheng Minrui,† Nripan Mathews,‡ Liu Hongwei,†,§ Chen Gin Seng,†

Zhang Xinhai,§ Subodh G. Mhaisalkar,‡ and Sow Chorng Haur*,†

†Department of Physics, 2 Science Drive 3, National University of Singapore, 117542, Singapore‡School of Materials Science and Engineering, Nanyang Technological University, Blk N4.1, Nanyang Avenue, 639798, Singapore§Institute ofMaterials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 3 Research Link, 117602, Singapore

1. INTRODUCTION

Quasi-one-dimensional (1D) semiconductor nanowires andnanobelts have attracted great attention due to their potential inthe fabrication of nanoscaled novel electronic, photoelectronic,and electromechanical devices. These devices include field-effect transistors,1,2 photodetectors,3,4 solar cells,5,6 and piezonanogenerators.7,8 Recently, II�VI compound semiconductornanowires have been widely investigated because of their abun-dance and promising performance. In terms of optical applica-tion, such as lasers and waveguide, a semiconductor material withtunable physical properties is extremely attractive. In comparisonwith binary compounds, ternary II�VI alloys possess significantadvantages that include continuously tunable band gap andcontrollable physicochemical properties through precise controlof the alloy’s stoichiometries.9,10 Recently, a ternary II�VIcompound semiconductor, CdSxSe1�x alloy, has attracted greatattention.11�14 It has a direct and widely modulated band gapfrom 1.73 to 2.44 eV corresponding to the composition changefrom CdSe to CdS. Ternary CdSxSe1�x nanowires have beenproduced through a pulsed laser deposition (PLD) process,11

and alloy CdSxSe1�x nanoribbons have been synthesized in atube furnace.12�14 Both photoluminescence (PL) with tunablewavelength and lasing properties of alloy CdSxSe1�x nanorib-bons have been demonstrated.13�15 During the growth in tubefurnace, themixedCdS andCdSe source powders are placed in themiddle of the heat zone, and the substrate (1�3 cm in size) ispositioned at a distance away from the source. Products coveringthe entire composition range (x varied from 1 to 0) are typicallyobtained on a single substrate. However, uniformity and selectivity

of stoichiometry have not been obtained through this approach.Products with varied stoichiometry would obscure the character-ization of the samples which ideally should be samples with purestoichiometry. Otherwise one cannot draw strong conclusionabout the physical properties of the alloy. The challenges inachieving uniform composition on the substrate are due to thefact that the composition of the nanostructured CdSxSe1�x ishighly dependent on the local substrate temperature.12,13 Thecomposition value xwould change accordingly with the distance ofthe substrate from the source, changing from 1 to 0within a 1.2 cmlong substrate.14 This limits the application of these 1D ternarysemiconductor nanostructures in areas where uniform composi-tion and tailored physical properties are required. Therefore, it isnecessary to develop an easy and feasible way to synthesize 1Dternary nanostructure with uniform composition on a reasonablylarge substrate. Recently Li et al. employed a complex two-stepsulfurization method through thermal annealing of CdSe nano-ribbons in a H2S�Ar atmosphere15 to fabricate uniform products.However, it is worthwhile to continue to develop simple and facilemethod to synthesize these alloy nanostructures.

In this work, we report a simple and effective one-step approachfor the growth of desirable CdSxSe1�x single crystalline nanobeltswith good uniformity and stoichiometry selectivity on singlesubstrates. Uniform composition over the entire substrate wasconfirmed by energy dispersive X-ray spectroscope (EDS) spectra

Received: June 20, 2011Revised: September 4, 2011

ABSTRACT:We present a simple yet effective one-step approach with a speciallydesigned substrate holder to synthesize single crystalline ternary CdSxSe1�x

nanobelts with uniform chemical stoichiometry and accurately controllable com-positions (0 e x e 1). The micromorphologies and detailed structures of thesenanobelts were studied by scanning electron microscopy, high-resolution transmis-sion electron microscopy, X-ray diffraction, micro-Raman spectra, and energy-dispersive X-ray spectroscopy. The elements distribution was explored usingelemental mapping. All the characteristic results indicate that the nanobelts exhibithigh quality single crystalline wurtzite structure. Photoluminescence spectra obtained from these nanobelts show that the near-band-edge energy can be systematically modulated in the range of 1.73 to 2.44 eV. Functional electrical application of thesenanobelts was achieved by a fabricated CdSxSe1�x nanonet-field effect transistor (FET). A lower threshold voltage and a muchhigher ON�OFF ratio than pure CdS- and CdSe-based FET were obtained. These nanonet-FETs also show potential asphotosensors with rapid photoelectrical response to light illuminations.

19539 dx.doi.org/10.1021/jp205760r |J. Phys. Chem. C 2011, 115, 19538–19545

The Journal of Physical Chemistry C ARTICLE

and elemental mapping at different random points from thesubstrate. With good stoichiometry control and coupled withdetail knowledge of composition value in CdSxSe1�xwe can arriveat conclusive and decisive description of the physical properties ofthese ternary compounds. Notably one could provide furtherinsight into the correlation between the physical properties ofthe alloy compound and its stoichiometry. As an illustration of thisconcept, Raman spectra of 1D CdSxSe1�x nanostructures withdifferent x values are studied in this work. PL measurements ondifferent samples synthesized proved that the composition range(0 e x e 1) can be fully controlled, and tunable band-edgeemissions from 507 to 713 nm were achieved.

In addition, most of the previous studies focused their attentionon the tunnable optical properties,12�14 and few of the applicabledevices were reported except a single nanowire electrical one.15 Inthis work, a large-scale 1D nanostructure network field effecttransistor (FET) from CdSxSe1�x nanobelts was fabricated usinga photolithography-free method.16,17 To the best of our knowledge,no prior studies involving the use of CdSxSe1�x ternary alloyednanobelts network at such large scale for field-effect transistorapplications exist. And this also is the first report for potentialphotosensor application of CdSxSe1�x nanobelts based on largescale electrical device.

2. EXPERIMENTAL SECTION

Sample Synthesis.CdSxSe1�x nanobelts with highly uniformcomposition were synthesized through a VLS approach with CdS(99.995%, Sigma Aldrich) and CdSe (99.99%, Sigma Aldrich)mixed powder as the precursor. The growth was carried outin a single-heating-zone horizontal tube furnace as shown inFigure 1a with He (99.9%) as the carrier gas. A ceramic boatloaded with 0.1 g mixed powder was inserted into the end of ahalf-sealed quartz tube with diameter of about 1.5 cm. A sapphirewafer sputter-coated with a thin (∼1 nm) Au layer was loadedinside the quartz tube 15—20 cm away from the source powder.To obtain large area samples with highly uniform composition, aspecially designed substrate holder (Figure 1c) was used. Withthis holder, substrate could be slotted vertically with the plane of

the substrate facing the incoming flux of CdSxSe1�x vapor duringthe growth. The vertically positioned substrate was maintained ata fixed temperature during the growth. In this case, all of thenanobelts were grown at the same growth temperature, andsamples with highly uniform composition covering a large areawere obtained. The quartz tube was then placed inside theceramic tube with the precursor end located at the high-temperature zone of the furnace. The system was first pumpeddown to a base pressure of 8.0� 10�3 Torr before theHe gas wasintroduced into the ceramic tube at a constant flow rate of 20sccm with the pressure regulated and maintained at 1 Torr. Afteran hour of He flow to purge away the oxygen, the furnacetemperature was ramped to 850 �C at a rate of 60 �C/min, andthe system was maintained at this temperature for 30 min beforecooling down to room temperature naturally. Samples withdifferent composition were obtained by changing the molar ratioof CdS and CdSe powder. The pure binary CdS and CdSenanobelts were synthesized under the same growth conditionsexcept only the CdS or CdSe powder was used as the precursor.Morphology and Crystalline Characterizations. The mor-

phology, structure, and composition of the as-grown pro-ducts were characterized using field emission scanning electronmicroscopy (FESEM, JEOL JSM-6700F), X-ray diffractometry(X’PERT MPD, Cu Kα (1.5406 Å) radiation), and transmissionelectron microscopy (TEM, Philips CM300) with built-in en-ergy-dispersive spectroscopy (EDS), respectively.Optical Measurements. A He�Cd laser (centered at 325 nm)

was used as the light source for the room temperature micro-photoluminescence (Renishaw inVia) measurements. The micro-Raman measurements were carried out via the same setup exceptthat a 785-nm laser was used as the excitation source.Nanonet-FET Fabrication. The CdSxSe1�x nanonet FET de-

vices were fabricated following the method reported previously.16,17

Briefly, a precleaned Si3N4 (200 nm)/Si wafer worked as theacceptor substrate and the source was the as-grown nanobelts.Through unidirectional sliding with light pressure, the CdSxSe1�x

nanobelts were transferred and formed a network onto the Si3N4

gate dielectric. The device fabrication was completed by depositing100 nm thick Al source-drain electrodes by thermal evapora-tion through a shadow mask with channel width about 100 μm.A halogen lamp source was used to examine the photosensitivity ofthe large-scale CdSxSe1�x FET.

3. RESULTS AND DISCUSSION

Structural Characterization. In this work, we adopted amodified approach to make use of a tube furnace with mixedCdS and CdSe source powders to synthesize CdSxSe1�x alloy.A schematic of the setup is shown in Figure 1a. Details of thegrowth conditions are given in the method sections. Figure 1bshows an optical picture of the as-grown sample when thesubstrate was placed horizontally. Evidently, the substrate ex-hibited a range of colors. This indicated that the sample wascovered with nanobelts with different stoichiometries. Thus toavoid nanobelts with wide-ranging composition, the substratewas vertically inserted into the slits of a newly designed sampleholder (Figure 1c). In doing so, we were able to grow CdSxSe1�x

alloy with uniform chemical stoichiometry. Optical pictures offive representative samples with different S and Se concentrationwere shown in Figure 1d. Visibly, these samples showed singleand unique colors with good uniformity across the substrate. Theyellow sample on the left corresponds to the pure CdS nanobelts

Figure 1. (a) Schematic diagram of alloyed nanobelts growth reactorsetup. (b) Nanobelts grown on horizontally placed substrate showingdifferent colors from left to right, indicating wide composition range inthe alloyed compounds. (c) Design model of substrate holder. (d)Optical images of five samples with different composition grown on thesubstrates. Sulfur concentration decreasing from left to right.



with wide band gap (2.44 eV). The black sample on the rightcorresponds to the pure CdSe sample with a narrower band gap(1.73 eV). The 3 samples in the middle correspond to sampleswith different proportion of S and Se in the nanobelts.Panels a�e of Figure 2 show the SEM images of these as-

grown samples. Evidently from the SEM images, all of them arequasi-one-dimensional nanobelts with similar morphologies.The nanobelts have an average length of about several tens ofmicrometers, 10�30 nm in thickness, and ∼100�200 nm inwidth. The corresponding in situ EDS are shown in curves f�j ofFigure 2, respectively. The results indicate the samples com-prised of Cd, S, and Se elements, and the atomic ratio of S/Cd,namely, the x value gradually reducing from 1 to 0 correspondingto samples a�e. The values are in good agreement with thosecalculated using Vegard’s law from the X-ray diffraction (XRD)patterns (details will be discussed later). It should be notedthat more EDS spectra were taken from randomly selectednanobelts to confirm that the whole large area sample hasuniform chemical composition. Moreover, the elements of Sand Se were distributed homogeneously in the individual nano-belts, which was supported by the EDS elemental mapping(panels k�o of Figure 2).

The detailed microstructures of these 1D samples were furtherstudied by TEM. The typical TEM images, high-resolution TEM(HRTEM), and corresponding selected area electron diffraction(SAED) pattern of two representative samples with the x valuesof 0.8 and 0.2 are shown in Figure 3. Parts a and b of Figure 3display the low magnification TEM images of CdS0.8Se0.2 andCdS0.2Se0.8 nanobelts, respectively. The corresponding HRTEMimages are shown in parts c and d of Figure 3. Evidently, the as-synthesized nanobelts are high quality single crystalline withhexagonal structure. For CdS0.8Se0.2, the fringe spacings betweenadjacent lattice planes were measured to be 0.355 and 0.674 nmcorresponding to the (010) and (001) interplanar distance,respectively. The corresponding values are 0.361 and 0.688 nmfor CdS0.2Se0.8. Their SAED patterns are shown in the inserts ofparts a and b of Figure 3, which further confirm the nanobeltsare typical wurtzite hexagonal structure with lattice parameters ofa = 0.41 nm and c = 0.67 nm for CdS0.8Se0.2 and a = 0.42 nm andc = 0.68 nm for CdS0.2Se0.8, respectively.The XRD patterns of five CdSxSe1�x (0e xe 1) samples are

shown in Figure 4. All diffraction peaks can be indexed tohexagonal wurtzite structure. In reference to Joint Committee

Figure 2. (a�e) SEM images of five CdSxSe1�x samples with differentcompositions. The scale bar is 2 μm. (f�j) Respective EDS of these as-synthesized CdSxSe1�x nanobelts. x value decreasing from 1 to 0 fromf�j. (k�o) Elemental mappings of these samples. Cd, S, and Seelements distributions are homogeneous.

Figure 3. TEM images of CdSxSe1�xwith x values about (a) 0.8 and (b)0.2. Inserts are their corresponding SAED patterns. HRTEM images ofCdSxSe1�x nanobelts with x values of (c) 0.8 and (d) 0.2.

Figure 4. NormalizedXRDpatterns ofCdSxSe1�x nanobelts (0e xe 1).Spectra a and e are for CdS and CdSe, respectively. Spectra b�d are forCdSxSe1�x samples with different x values.



on PowderDiffraction Standards (JCPDS) cardNo. 77-2306 and77-2307, spectra in parts a and e of Figure 4 are pure CdS andCdSe phase, respectively. Their respective lattice constants canbe calculated to be a = 0.4112 nm and c = 0.6717 nm for CdS anda = 0.4276 nm and c = 0.6971 nm for CdSe. The peak positions ofCdSxSe1�x alloy are located in the region between CdS andCdSe. From spectra b�d, the diffraction peaks shift graduallytoward smaller 2θ angles, indicating the lattice constants increasewith decreasing S concentration (i.e., decreasing x value). Since thelattice constants depend on the composition, the composition x ofthese CdSxSe1�x nanobelts can be determined by using the c-axislattice constants calculated from the XRD data and employVegard’s law: Cx = CCdSx + CCdSe(1 � x), where Cx, CCdS, andCCdSe are lattice constants along the c axis of CdSxSe1�x, CdS, andCdSe crystals, respectively. For spectra b�d in Figure 4, thecalculated x values are 0.87, 0.65, and 0.29. The results indicate wecan successfully synthesize alloyed samples with modulated anduniform composition covering the full range from CdS to CdSe.Raman Spectra. To further characterize these ternary products,

micro-Raman spectra of four samples with x values of 1, 0.65, 0.29,and 0 were obtained under room temperature. Analysis of theRaman spectra was performed by the peak fitting as shown inFigure 5. From CdS Raman spectra (Figure 5a), the peaks at 236,256, and 307 cm�1 are three first-order Raman peaks, and they areassigned to A1 (TO), E2

H, and LO modes, respectively, whereas thepeaks at 215, 326, 350, 367, and 600 cm�1 (2LO) arise frommultiphonon scattering18 and additions of optical phonons give abroad band around 590 cm�1. The broad and weak peak at299.5 cm�1 comes from surface optical mode.19 FromCdSeRamanspectra (Figure 5d), the peaks at 212 and 419 cm�1 are assigned to

LO and 2LO modes. The weak peaks at 175, 203.5, and 235 cm�1

are attributed to TO, surface mode, and vibrational mode of�Se�Se�Se� chains.20 CdSxSe1�x is classified as an alloy withtwo-mode behavior. That means the first-order Raman spectra ofthe alloyed ternary crystals exhibit both CdS- and CdSe-likephonons.19 As seen from the spectra (parts b and c of Figure 5),the alloyed nanobelts exhibit CdS-like LO1 and CdSe-like LO2

modes at ∼200 and ∼300 cm�1. In addition, 2LO2 peak at∼600 cm�1 is observed. Furthermore, the asymmetric and broadpeak near 480 cm�1 is assigned to the LO1 + LO2 band. With theS-fraction in the alloy increasing from x = 0.29 to x = 0.65, the LO2

phonon intensity decreases and the peak shifts downward from 204to 197 cm�1, while the LO1 phonon intensity increases and peakposition shifts upward from 289 to 298 cm�1. Similar results areobserved from the 2LO spectra, while the 2LO2 band intensity ofCdS0.65Se0.35 spectra is too weak to be seen. Simultaneously, theLO1+LO2 band peak shifts a bit from 487 to 485 cm�1. Thisbehavior of Raman lines shifts is due to the variation of the chemicalcomposition.21 Moreover, the peaks labeled ahead of the LO peaksare assigned to surface optical modes for CdS andCdSe. Finally, thesurface optical peaks at 180.8 cm�1 in Figure 5b and 194.5 cm�1 inFigure 5c become prominent, which has been explained by theincreasing role of surface phonons.22,23

Micro-PL Spectroscopy.While both CdS and CdSe are directband gap materials with excellent optical properties, CdSxSe1�x

alloys are expected to have high PL yield.12 In this work, the as-grown CdSxSe1�x alloyed nanobelts exhibit strong PL propertyat room temperature. Figure 6a shows the normalized micro-PLspectra of CdSxSe1�x alloys of different compositions. Evidently,the nanobelts synthesized in this work exhibit near-band-edge

Figure 5. Raman spectra of four typical samples excited with 785-nm laser excitations. Experimentally obtained data (red boxes) were offset for clarity.Results of the peak fitting were represented by the colored lines.



emission peak with narrow line-width and no defect-emissionappeared in the spectra. This indicates that the synthesizedCdSxSe1�x alloyed nanobelts are high-quality single crystal withfew defects such as dislocations and stacking faults. Obviously,with x decreasing, the near-band-edge emission peak positionscontinuously red-shifts from 507 nm (pure CdS) to 713 nm(pure CdSe) due to the decreasing band gap. Figure 6b shows aplot of band gaps of CdSxSe1�x alloys, calculated from the PLpeak positions, vs the composition value x. As reported,24 thevariation of the band gaps with x can be fitted by a quadraticfunction

EgðxÞ ¼ ECdSe þ ðECdS � ECdSe � bÞx þ bx2 ð1Þ

whereECdS,ECdSe, and Eg(x) indicate the band gap of CdS, CdSe,and CdSxSe1�x alloys, respectively. b is an additional bowingparameter. The best fitting curve yields b = 0.58 eV. This value isvery close to that reported by Hill et al.26 but different from thatreported by Adachi.25 The bowing parameter is a measure ofcrystal field fluctuation or the nonlinear effect caused by aniso-tropic binding.26,27 The relatively small value of b indicates thatthe synthesized CdSxSe1�x alloy nanobelts have goodmiscibility.Large-Scale Nanonet-FET. A contact printing method was

employed to fabricate wafer-scale device with aligned 1D nano-material arrays at controllable densities.28 Highly ordered net-works can be obtained even though the as-synthesized nanobeltson the donor substrates are randomly aligned.16 Figure 7a showsthe SEM image of the horizontal aligned nanonet-FET fabricatedfrom CdS0.8Se0.2 nanobelts with the schematic shown at theinsert. The red dotted-line indicates the interface of nanowire

network and aluminum electrode. The typical Ids�Vds curves areshown in Figure 7b, with Vgs increasing from 5 to 30 V in steps of5 V. In agreement with previous reports on single CdSxSe1�x

nanoribbon field-effect transistors,29 the nanonet-FET exhibitsan obvious gating effect and shows typical n-channel depletionmode behavior with good saturation. The measured thresholdvoltage (Table 1) is lower than those based on pure individualCdS nanoribbons30 and CdSe naonribbons,31 while the ON�OFF ratio is much higher than that reported for CdS and CdSenanoribbons. The photoresponse (or photocurrent) behavior isrevealed by Figure 7c. In this figure, the Ids vsVgs curves (Vds = 20V)under different light intensities (1, 3, 5 W/m2) are shown. It isobvious that the threshold voltage (Vth) left-shifted significantlywith the increase of the illumination intensities (Figure 7cand Table 1). In spite of the increase of the saturation currentwith the intensities, the ON-OFF ratio declined from 5.8 �105 to 2.9 � 104 since the increase of OFF current is moreprominent.For the electron mobility calculation, a parallel plate capacitor

model is assumed to estimate the gate capacitance. From theSEM images, a nanobelt coverage of about 15% was esti-mated. Following the approach reported by Dattoli and co-workers,29 the normalized effective capacitance of about 60%was used for the subsequent mobility calculation usingfollowing equation

μsat ¼2IDSL

0:6CiWðVG � VthÞ2ð2Þ

where L and W represent the channel length and width,respectively, and Ci indicates the gate capacitance per unitarea. After substituting in the measured capacitance of Si3N4

(Ci = 18.83 nF/cm2, 1 MHz), channel width (length of Alelectrodes, 3000 μm) and channel length (distance betweentwo electrodes, 100 μm), the mobility can be estimated. Thecalculated values at different illumination conditions arelisted in Table 1. As the result implies, the increase of thelight intensity will enhance the electrical performance ofthe FET due to the increase of the free electrons. However,the performance did not increase all the way with theintensities but became less promising with the OFF currentincreased by two orders while the saturation current onlyincreased by a factor of 2, the carrier mobility was alsoweakened. The high number of photogenerated electronsunder intensified illumination made the gate voltage effectless dominant which resulted in a less steep curve in theIds�Vgs figure, reducing the device mobility.Figure 7d shows the photoresponse of the CdS0.8Se0.2 nanonet

to the normal white light source as a function of time. The biasvoltage was fixed at 20 V, and the applied light illumination was50 W/m2. Evidently, the photocurrent increases dramatically to2.8 μA in a very short time (<2 s) after the sensor was exposed tothe light source while the current was only at the level of nano-amperes under dark conditions. Both FETs performance andphotoresponse properties of samples with different stoichiome-try were studied. We found that all the ternary alloyed nanobeltsFETs exhibited similar performance. An example of the nanonet-FET performance of another ternary sample with x value of about0.65 is shown in parts e�g of Figure 7. There was no obvioustrend on the dependence of the performance of the nanonet-FETon the composition of the ternary compound. However, com-pared with the results (shown in Figure 8) of pure binary CdS

Figure 6. (a) Normalized PL spectra of as-synthesized CdSxSe1�x

nanobelts of different compositions. (b) Composition dependence ofnear-band-edge emission energy.



Figure 7. (a) Schematic illustration (inset) and SEM image of the horizontal aligned CdSxSe1�x nanonet-FET. IDS�VDS curves of CdS0.8Se0.2 (b) andCdS0.65Se0.35 (e) at Vgs from 5 to 30 V. Transfer characteristics of CdS0.8Se0.2 (c) and CdS0.65Se0.35 (f) nanonet-FET under different light illumination.Photosensitive behavior of CdS0.8Se0.2 (d) and CdS0.65Se0.35 (g) nanonet.

Table 1. Summary of Device Behavior at Different Light Illumination Conditions

light illumination mobility (cm2/(V s)) Vth (V) ON (A) OFF (A) ON/OFF

no illumination 0.04 15.6 1.56� 10�6 2.7� 10�12 5.8� 105

1 W/m2 0.049 15 1.96� 10�6 10.5� 10�12 1.9� 105

3 W/m2 0.034 7.8 2.42� 10�6 27.0� 10�12 9.0� 104

5 W/m2 0.0315 �1.3 2.93� 10�6 100.0� 10�12 2.9� 104



(parts a�c of Figure 8) and CdSe (parts d�f of Figure 8)compound, the alloyed nanobelts exhibited more significantgating effect and produced higher photocurrent upon irradiationof light. All these results indicate that CdSxSe1�x nanobelts havea potential in electronic and photoelectronic applications.

’CONCLUSION

A facile one-step vapor deposition method was employed tosynthesize CdSxSe1�x nanobelts. A simple modification wasdeveloped to remove the influence of the temperature gradienton the uniformity of the composition of the 1D ternary alloyednanostructure. This approach enables the synthesis of singlecrystal CdSxSe1�x nanobelts with accurately controlled compo-sition. This simple and yet effective approach is expected to beuseful in the synthesis of other type of 1D ternary alloys. Alloyedfeatures are studied by Raman spectra. The CdS- and CdSe-likeLO phonon frequency is dependent on the S concentration.Strong and narrow near-band-edge PL with wavelength tunableemissions from 507 to 713 nm was observed. Large-scaleCdSxSe1�x nanonet-FET device shows obvious gating effectand pronounced photosensitivity. The measured thresholdvoltage is lower than those based on pure individual CdSnanoribbon30 and CdSe nanoribbon,31 and the ON�OFF ratiois much higher than that reported for CdS nanoribbon andCdSe nanoribbon. The CdSxSe1�x nanonet-based photosensor

exhibits fast response to normal and weak white light. TheCdSxSe1�x ternary alloyed nanobelts with tunable optical prop-erties have potential application in photoelectronic devices.

’AUTHOR INFORMATION

Corresponding Author*E-mail: [email protected].

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