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Few Layers Thin Film Metallic Glass Enhanced Optical Properties of ZnO Nanostructures Bohr-Ran Huang, Jinn P. Chu, Cheng-Liang Hsu, You-Syuan Chen, and Chia-Hao Chang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b13121 • Publication Date (Web): 24 Oct 2017 Downloaded from http://pubs.acs.org on October 25, 2017

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ACS Applied Materials & Interfaces

Few Layers Thin Film Metallic Glass Enhanced Optical Properties of ZnO Nanostructures Bohr-Ran Huang,† Jinn P. Chu,*,‡ Cheng-Liang Hsu,*,§ You-Syuan Chen,† Chia-Hao Chang‡ †

Graduate Institute of Electro-Optical Engineering and Department of Electronic and Computer

Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan ‡

Department of Materials Science and Engineering, National Taiwan University of Science and

Technology, Taipei 10607, Taiwan §

Department of Electrical Engineering, National University of Tainan, Tainan 700, Taiwan

KEYWORDS ZnO nanowires, ZnO nanotubes, thin film, metallic glass, UV photodetector.

ABSTRACT

ACS Paragon Plus Environment

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The few layers Cu-based (Cu47Zr42Al7Ti4) thin-film metallic glasses (TFMGs) was sputtered on hydrothermally synthesized ZnO nanowires/glass and ZnO nanotubes/glass to fabricate UV photodetectors. The few layers of Cu-based TFMG are ultra-thin at approximately 0.98 nm and have a non-crystalline metal structure according to XRD, Raman, PL and HT-TEM verification. The photoresponse performance of the coated few layers Cu-TFMG samples was enhanced 1680~7700% compared with the non-coated sample. The few layers Cu-TFMG has high transmittance ~90% in the visible band and creates a large capacitor to absorb UV photocurrent and release dark current.

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Introduction Bulk metallic glasses (BMGs) have attracted considerable attention due to their unique characteristics, including high flexibility at higher glass transformation temperatures. BMGs have a non-crystalline metal structure that offers excellent mechanical properties, such as extreme strength, no grain boundary, high corrosion resistance, high ductility, good toughness and large elasticity at room temperature.1-3 In recent decades, BMG research has become an interesting and challenging topic, in which the development has moved toward increased specimen sizes and optimized mechanical properties with a combination of metals. The constitutional components of BMGs consist of many metal elements with distinct atomic radii and chemical affinities.4-5 Up to now, TFMGs have used transition metals, alkali metals, alkaline earth metals, near metalloids and rare earth elements. Moreover, thin film metallic glasses (TFMGs) have gradually attracted more attention in engineering due to TFMG coatings being able to improve the mechanical properties for a wide variety of applications.6 TFMGs have been applied in non-stick syringe needles by smooth-surface morphology and improved the thermoelectric modules via an effective diffusion barrier.7-8 TFMGs also play an important role in micro/nano electromechanical systems (MEMS/NEMS) materials.9 The industrial, military and livelihood industries widely apply UV photodetectors, which are comprised of wide bandgap semiconductor materials, such as SiC, GaN, ZnSe, ZnO, and TiO2.1012

Among these materials, ZnO one-dimensional (1-D) nanostructures (NSs) have received the

most attention, due to their high exciton binding energy (60 meV), large surface-area-to-volume ratio, and variety of morphologies.13 In addition, there are several methods to increase the photoresponse performance of ZnO 1-D NSs UV photodetectors. One common method is to dope various elements to change the photoresponse and electrical properties of the ZnO 1-D


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NSs.14 Some articles have reported the fabrication of p-n ZnO 1-D NSs homojunctions or heterojunctions to improve the UV photoresponse.15-16 The ZnO 1-D NSs have been decorated with various noble metal nanoparticles (NPs) to create the Schottky effect for enhancing the photoresponse.17-19 These methods can significantly reduce the dark current by increasing the photocurrent to dark current ratio.14-19 In this study, a few layers and thin Cu-based TFMG (CuTFMG) is for the first time combined with ZnO nanowires (NWs) and nanotubes (NTs) to fabricate a UV photodetector. The fabrication processes, as well as physical and electrical properties of the Cu-TFMG/ZnO NWs and Cu-TFNG/ZnO NTs photodetectors are discussed in detail.

Experimental Methods The schematic illustrated in Figure S1 shows the manufacturing process flow and fabrication steps of the Cu-TFMG/ZnO NTs photodetector. The glass substrate (Corning Inc.) was ultrasonically cleaned with acetone and isopropanol solvent for 30 mins, then immersed in deionized (DI) water and dried with nitrogen. Next, the ZnO seed layer was spin coated on the glass by the sol-gel method, the solution for which consisted of 1.1g zinc acetate [Zn(CH3COO2)·2H2O] and 0.3 ml ethanolamine (C2H7NO) mixed in 50 ml methanol (CH3OH) and heated to 60°C with magnetic stirring for 2 hours. The zinc acetate (Acros organics Inc.) was dissolved in methanol (Nzcali Tesque Inc.), and then ethanolamine (Panreac Inc.) was act a stabilizer to add in the mixed solution. The optimal molar ratio of zinc ions and solvent was maintained at ~1. The crystalline structure of the ZnO seed layer was improved by annealing at 350°C in atmosphere. ZnO NWs were then synthesized on the ZnO seed layer by a hydrothermal


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method, which involved immersing the ZnO/glass in a solution of 60 mM zinc nitrate, 60 mM hexamethylenetetramine (C6H12N4) and 100 ml DI water at 95°C for 3 hours. After the ZnO NWs growth, the 95°C synthesized temperature was cooled to 50°C, allowing self-etching samples to form for 5, 6, 7, and 8 hours, respectively. The ZnO NWs will then self-etch and become ZnO NTs due to the pH of the solution being dependent on the temperature, with a temperature of 50°C causing the preferential chemical dissolution issue.20 Cu-TFMG was then deposited on the ZnO NWs and ZnO NTs with no substrate heating by radio frequency (RF) magnetron sputtering. The optimized deposition conditions were controlled as follows: Ar flow of 20 sccm; working pressure of 3 mtorr; 10 cm working distance; and, 100W sputtering power. The photodetector electrode was fabricated by the lift-off process, and consists of a 5 nm Ni buffer layer and 100 nm Pt layer. The surface morphology, element analysis, and element mapping were measured by field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM). The crystalline phase, optical and physical properties of the ZnO NWs and ZnO NTs were examined with X-ray diffraction (XRD), photoluminescence (PL) and Raman spectroscopy. The wavelength and power density of the UV light was 365 nm and 1 mW/cm2, the excitation source of which was a Xe lamp. The current-voltage (I-V) curves were measured at room temperature under ambient atmospheric conditions via source-measure instruments (Keithley 237).

Results and Discussion Figure S2 shows the top view and cross-sectional FE-SEM images of the ZnO NWs and ZnO NTs with self-etching for 5, 6, 7, and 8 hours. The length and diameter of the hydrothermally


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grown ZnO NWs were 2.663 µm and 100~250 nm, respectively. A hollow structure of Fig. S2(c) has be marked by a red rectangle frame. Although the diameter of the ZnO NTs is similar to the ZnO NWs, the length of ZnO NTs shortens with increasing self-etching time, as shown in Fig. S2(b), Fig. S2(d), Fig. S2(f), Fig. S2(h) and Fig. S2(j). It was found that the 7hr-ZnO NTs sample presented the maximum number of hollow structures on the top of the NTs. Half of the hollow structures of the 8hr-ZnO NTs sample were damaged by over etching. Figure S3 plots the I-V curves of the ZnO NWs and ZnO NTs samples measured in the dark and under UV illumination. As can be seen, the I-V curves are linear, which indicates the electrode contact is ohmic. The dark current of the ZnO NTs decreases with increasing self-etching time due to the shortened NT lengths being similar to the thinner film, thereby causing the low conductivity. Under UV illumination, the 7hr-ZnO NTs performance features the maximum photocurrent. It is speculated that the hollow structure is helpful in absorbing the incident UV light and decreasing the refracted light. The UV photocurrent (IUV) to dark current (IDark) ratios of the ZnO NWs and ZnO NTs with self-etching for 5, 6, 7, and 8 hours are the 2.52×102, 5.42×102, 5.96×102, 2.69×103, and 7.10×102, respectively. The XRD, Raman and PL spectra of the ZnO NWs and ZnO NTs are revealed in Figure S4. The XRD and Raman spectra that dominate the NWs and NTs indicate a crystalline structure and wurtzite structure. The XRD spectrums of these samples have a strong diffraction peak at values of ~34.5°, which is corresponding to the (002) plane can be indexed to a hexagonal wurtzite structure of ZnO (JCPDS card no.36-1451). The Raman E2H peaks of the NTs samples are stronger than those of the NWs, which indicates that the NTs structure has better crystallinity. The E2H of the 7hr-ZnO NTs has the highest peak compared with the other NTs and NWs, which indicates that the 7hr-ZnO NTs has best crystallinity. Based on the PL spectra, the near band


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edge (NBE) peak of the NWs and NTs is sharp, while the deep level emissions (DLE) peak is broad. The intensity INBE/IDLE ratio of the 7hr-ZnO NTs is also the highest ~10.12, which means that the defect density of the 7hr-ZnO NTs is the lowest. In general, the increasing defect density of ZnO NWs can improve the gas sensing preformance,21 owing to that dangling-bond of ZnO defect increases the gas capture ability. According the previous research,22 the ZnO NTs was reveals the lower defect density and higher crystalline quality compared with ZnO NWs, due to the selfetching process is easier begins at the defects places.22 This implies that defects in the ZnO NWs were removed by the self-etching process, which sufficiently reduced the defects in the ZnO NTs. The INBE/IDLE ratio of the 8hr-ZnO NTs is smaller than 7hr-ZnO NTs. Speculated the over etching to cause the half hollow structures and increase the defect density. Because the 7hr-ZnO NTs featured the highest photocurrent/dark current ratio, the Raman and PL peaks had high intensity. Accordingly, follow-up experiments will use the 7hr-ZnO NTs in combination with TFMG to enhance the photoresponse. The 3, 6, 10, 15 nm Cu-TFMG samples were sputtered onto the ZnO NWs and 7hr-ZnO NTs, the top-view FE-SEM images of which are shown in Figures 1(a)-(h). Because these Cu-TFMG layers are ultra-thin, they cannot be observed and analyzed via the FE-SEM images. Thicker CuTFMG 200 nm was deposited on glass and examined by energy dispersive X-ray analytics (EDS) of SEM, and analyzed by electron probe micro-analyzer (EPMA). The EDS and EPMA measures shows that the Cu-TFMG is comprised of Cu = 46.45 atom. %, Zr = 42.27 atom. %, Al = 7.34% atom. %, Ti=3.94% atom. % and Cu = 48 atom. %, Zr = 42 atom. %, Al = 6% atom. %, Ti=4% atom. %, respectively. The EDS and EPMA demonstrated that the major element in TFMG is Cu, with second-most abundant element being Zr.


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Figures 2 and 3 display the XRD, Raman and PL spectra of the ZnO NWs and 7hr-ZnO NTs coated with 3, 6, 10, and 15 nm Cu-TFMG. As seen, all XRD peaks of the Cu-TFMG/NWs and Cu-TFMG/NTs are observed to have the ZnO crystalline phase. It is speculated that the CuTFMG is non-crystalline, which is not easily detected by XRD. The XRD peak intensity of the Cu-TFMG/NWs and Cu-TFMG/NTs decreases with the increasing thickness of Cu-TFMG. The 3nm-Cu-TFMG/NWs and 3nm-Cu-TFMG/NTs present the strongest XRD intensity for the ZnO, which is due to the 3nm-Cu-TFMG being the thinnest, which may attributed to discontinuous Cu-TFMG film, thereby revealing ZnO. It should be noted that the sputtering process yields poor step coverage for the NWs and NTs due to their morphologies having a high aspect ratio. Moreover, the side walls of the NWs and NTs are difficult to deposit uniform Cu-TFMG. The Raman peaks of the Cu-TFMG/NWs and Cu-TFMG/NTs still show the ZnO characteristics, but the Raman peaks of the Cu-TFMG samples are obviously smaller than the NWs and NTs samples due to the Cu-TFMG layer blocking or reflecting the incident Raman light. The PL peaks intensity and intensity INBE/IDLE ratios of the Cu-TFMG/NWs and Cu-TFMG/NTs decay with increasing Cu-TFMG thickness. Under the same TFMG thickness, the INBE/IDLE ratio of CuTFMG/NTs is higher than Cu-TFMG/NWs by around 2~3-fold, which is attributable to the NTs having a smaller defect density, thereby causing the IDLE of Cu-TFMG/NTs to be 2~3-fold smaller than Cu-TFMG/NWs. Figure 4 displays the TEM, HR-TEM, EDS mapping and selected-area electron diffraction (SAED) images of the 3nm-Cu-TFMG/NW sample. As shown in Figs. 4(a)-(c), the thicker CuTFMG is coated on the top portion of the NWs while the ultra-thin Cu-TFMG is discontinuously distributed on the NW side walls. The ZnO NWs is single crystal and has c-axis preferredorientation growth by HR-TEM and SAED observation. Compared with the NWs side walls of


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Cu-TFMG, the deposited Cu-TFMG on the top portion of the NWs is thicker at ~2.67nm, which approaches the 3nm-thickness of the Cu-TFMG directly sputtered on the glass substrate. Based on the EDS mapping analysis, the Zn and O elements are distributed throughout the NWs. The elements of the Cu-TFMG have high spot density on the NWs top portion, which is due to the 2.67nm thickness. Moreover, the Cu-TFMG is comprised of Cu, Zr, Al and Ti, which is consistent with the EDS of SEM and EPMA analysis. The TEM, HR-TEM, and EDS mapping analyses of the 3nm-Cu-TFMG/NT sample are presented in Figure 5. According to the TEM images in Fig.5 (a)-(b), the thickness of the CuTFMG layer is obviously thinner than the 3nm-Cu-TFMG/NW. The HR-TEM images demonstrate that the ZnO NTs is single crystal, and that the Cu-TFMG thickness of the top portion of the 3nm-Cu-TFMG/NT is only 0.98~1.23 nm, which is approximately a few atomic layers. This result suggests that the morphology of the hollow structure provided the larger surface area, which caused the sputtered Cu-TFMG to be thinner. The 3nm-Cu-TFMG/NT is composed of Zn, O, Cu, Zr, Al and Ti by EDS mapping analysis. These element spots are distributed throughout the entire NTs and do not have a clear high-concentration area, which indicates that the Cu-TFMG layer is uniformly deposited on the ZnO NTs. Figures 6 and 7 plot the I-V curves of the Cu-TFMG/NW and Cu-TFMG/NT samples in the dark, under UV illumination, and with the UV-lamp switched on/off. The dark currents of the uncoated TFMG samples is 10~103-fold larger than those of the coated TFMG samples. The CuTFMG contacting the ZnO builds a Schottky barrier in the TFMG/ZnO interface, which creates a depletion region that decays the conductivity of the samples. The minimum dark current was found to be from the 3nm-Cu-TFMG coated NWs and NTs samples; apparently, this was due to the ultra-thin and discontinuous side walls of the NWs and NTs sputtered Cu-TFMG, which


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cause the low conductivity. The thicker Cu-TFMG coated samples formed continuously thin films on side walls of the NWs and NTs, which increase the conductivity for higher dark current. The UV photocurrent of the uncoated TFMG samples is larger than the coated TFMG samples by around 101~102-fold. The UV photocurrent decreases with increasing thickness of the TFMG layer. It us speculated that the TFMG layer blocks or reflects the incident light to decay the UV absorption of ZnO. The UV photoresponse of the 3, 6, 10, and 15 nm Cu-TFMG/NWs and the 3, 6, 10, and 15 nm Cu-TFMG/NTs are (1.94×104, 5.08×103, 2.87×102, 5.67×101) and (4.52×104, 6.78×103, 2.07×103, 1.71×102), respectively. These 3nm Cu-TFMG/NTs samples featured the maximum UV photoresponse. The current of the 3nm-Cu-TFMG/NWs and 3nm-Cu-TFMG/NTs were measured at a 5V bias with a UV-lamp switched on/off. The initial dark currents of these 3nm Cu-TFMG samples was measured to be 0.26~0.50 nA. The dynamic UV photoresponses of the 3nm-Cu-TFMG/NWs and 3nm-Cu-TFMG/NTs were measured to be only ~60 and ~310 with the UV-lamp switched on/off. These dynamic UV photoresponses are lower than previous static UV photoresponses. Because the dynamic dark currents of the 3nm-Cu-TFMG/NWs and 3nm-Cu-TFMG/NTs are respectively 288-fold and 40-fold larger than their initial dark currents, the resulting dynamic UV photoresponses are low. More noteworthy is that the photoresponse time and recovery time is ~70 and ~60 sec, which is very slow compared with previous reports. Figure 8 shows the equivalent circuit and schematic illustration of the ZnO NTs and 3nm-CuTFMG/NTs in the dark and under UV illumination. In general, the oxygen absorbs an electron from the surface of the ZnO NTs, which creates a depletion region on the ZnO surface, the reaction for which is O2(gas) + e－(ZnO) → O2－(ads). The sputtered 3nm-Cu-TFMG on the ZnO NTs


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involved isolated oxygen from the atmosphere to reduce the O2－ concentration. The Schottky barrier of the TFMG/ZnO interface degraded the conductivity of the sample, which suggests that the Schottky barrier caused the lower dark current. The equivalent circuit RZnO_NTs_Schottky is also higher than RZnO_NTs by around 3 orders. The RTFMG of the ultra-thin TFMG is very high due to the film being non-continuous. The thick TFMG has a lower RTFMG owing to its continuous and thicker film. The resistance of the photodetector can be estimated by calculating RZnO_NTs_Schottky in parallel with RTFMG. In this study, the resistances of the ultra-thin TFMG samples can ignore RTFMG due to RTFMG being very high. This means that the photodetector resistance is dominated by RZnO_NTs_Schottky. Under UV illumination, the photons generated numerous electrons (e－) and hole (h+) pairs to enhance conductivity, which decreased the RZnO_NTs_Schottky by around 5 orders. Because the photoresponse time and recovery time are long, the dynamic dark current is ~10-fold still higher than the initial dark current after turning-off the UV light for 10 mins. It is speculated that the 3nm-Cu-TFMG/NTs sample has a larger capacitor CTFMG to absorb the photocurrent and release current in the dark. As such, the response and recovery time delay should be impacted by high RTFMG and CTFMG. The transmittances of the sputtered 3, 6, 10, and 15 nm Cu-TFMG on glass were measured by UV–VIS–NIR spectrophotometry, as shown by the results in Figure 9(a). As seen, the transmittances of these Cu-TFMG samples did not change significantly in the visible and infrared bands. The visible band transmittance of the 3 nm Cu-TFMG is ~90%, which makes replacement of the transparent conductive oxide (TCO) application possible. The transmittances of the 3, 6, 10, and 15 nm Cu-TFMG are 81.8%, 65.9%, 48.3%, and 42.1% at an incident light wavelength of 365 nm. Because the Cu-TFMG layer thickness of the 3nm-Cu-TFMG/NTs sample is only ~1 nm, the transmittance of its Cu-TFMG layer is higher than 81.8%.


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Accordingly, the high photocurrent performance of the 3nm-Cu-TFMG/NTs could be due to the high transmittance of the ultra-thin Cu-TFMG and ZnO NTs morphology. It is well known that conductivity of metal is higher than TCO materials several decade folds. The 3 nm Cu-TFMG was deposited on glass substrate for measured the resistivity (ρ) = 133~144 µΩ-cm, which is also much lower than indium-tin oxide (ITO) films (ρ = 500~1000 µΩ-cm). The 3 nm Cu-TFMG reveals high conductivity and transmittance to replace the ITO. Because of resistivity of the Cu (ρ = 1.68 µΩ-cm), Al (ρ = 2.65 µΩ-cm), Ti (ρ = 42.0 µΩ-cm), Zr (ρ = 42.1 µΩ-cm) are lower than Cu-TFMG 3.2~85.7 times. Speculated the deposited Cu-TFMG is non-crystalline and nonuniform to cause high resistance. Figures 9(b)-9(c) schematically illustrate the 3nm-CuTFMG/NWs and 3nm-Cu-TFMG/NTs under UV illumination. The amount of reflected light from the 3nm-Cu-TFMG/NTs should be less than the 3nm-Cu-TFMG/NTs because the hollow morphology functions in the same way as the compound parabolic concentrator (CPC) to collect UV light. Table 1 presents the photoresponse of the Cu-TFMG/ZnO NSs compared with various noble/ZnO NSs.23-27 The photoresponse of the ZnO NTs is larger than the ZnO NWs due to the hollow morphology enhancing the UV photocurrent. The photoresponse of the ZnO 1-D NSs can be enhanced by doping with various elements and decorating with noble metal nanoparticles, such as Au and Ag.23-27 In this study, a few TFMG layers were for the first time used for the enhancement of the photoresponse of a UV photodetector. Although the photoresponse of the TFMG sample is comparable with these noble-nanoparticle samples, the TFMG/ZnO 1-D NSs sample has much higher mechanical strength due to the TFMG being uniformly coated on the ZnO 1-D NSs.


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Figures 10(a)-(d) show the band diagram of the ZnO and ZnO/TFMG in the dark and under － UV illumination. O2 was absorbed on the ZnO and attracted an electron from the ZnO to create

a depletion region on the ZnO surface. The UV photons generated numerous e－ and h+ pairs to －－ eliminate depletion, due to the h+ reacting with O2 (abs) to become O2(gas). The remaining e

increase the conductivity of the ZnO NWs and NTs. The TFMG/ZnO interface created a Schottky barrier of ~0.65eV, which formed a larger depletion region on the ZnO that decreased the dark current of the TFMG/ZnO samples. Under UV illumination, the ultra-thin Cu-TFMG has a high transmittance that allows most UV light to be exposed on the ZnO. The UV photogenerated a lot of e－ and h+ pairs. Some e－ were excited by UV light and jumped to the CuTFMG region, which enables the Cu-TFMG to store many e－. Accordingly, the ultra-thin CuTFMG absorbed and stored numerous photo-generated e－, which is similar to a large capacitor. As such, the long photoresponse and recovery time were caused by the larger resistive-capacitive delay.

Conclusions High density ZnO NWs and ZnO NTs were hydrothermally synthesized on glass substrates at 95°C. The IUV/Idark ratio (~2.69×103) of the 7hr-ZnO NTs was higher than the ZnO NWs (~2.52×102) by around 10.7-fold, due to its hollow structure enabling more absorption of UV light. According to EDS analysis, the sputtered Cu-TFMG is comprised of 46.5% Cu, 42.3% Zr, 7.34% Al and 3.94% Ti. The PL INBE/IDLE ratio of the 3nm-Cu-TFMG/NTs is around 2~3-fold higher than that of the 3nm-Cu-TFMG/NWs owing to the NTs having a lower defect density and


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higher UV photoresponse. The HR-TEM analysis confirmed that the ZnO NWs and NTs are single crystalline and wurtzite structure. The Cu-TFMG layer was uniformly coated on the NWs and NTs samples. The Cu-TFMG thickness of NWs and NTs samples was ~2.67 nm and 0.98~1.23 nm, respectively, which comprises only a few atomic layers. The 3nm-CuTFMG/NWs (1.94×104) and 3nm-Cu-TFMG/NTs (4.52×104) featured the maximum UV photoresponse. Consequently, this demonstrated that ultra-thin Cu-TFMG can effectively increase the UV photoresponse by 16.8~77-fold. The long UV photoresponse/recovery time of the 3nm-Cu-TFMG/NTs sample implies the existence of a large capacitor CTFMG to absorb the UV photocurrent and release current in the dark. The visible band transmittance of the 3nm CuTFMG is ~90%, and so has the possibility of replacing TCO application.


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FIGURES Figure 1. FE-SEM images of the 3, 6, 10, and 15 nm TFMG deposited on (a)-(d) ZnO NWs and (e)-(h) ZnO NTs. Figure 2. (a) XRD, (b) Raman and (c) PL spectra of the ZnO NWs coated with various thicknesses of Cu-TFMG. Figure 3. (a) XRD, (b) Raman and (c) PL spectra of the ZnO NTs coated with various thicknesses of Cu-TFMG. Figure 4. (a)-(c) TEM, (d) HR-TEM and EDX mapping of the 3nm Cu-TFMG/ZnO NWs. Figure 5. (a)-(b) TEM, (c) HR-TEM, (d)-(e) TEM, (f) HR-TEM images and EDX mapping of the 3nm Cu-TFMG/ZnO NTs. Figure 6. I-V curves of the 3nm Cu-TFMG/ZnO NWs sample (a) in the dark , (b) under UVLED illumination, and (c) cycled switch on/off UV-LED with a period of 6 minutes. Figure 7. I-V curves of the 3nm Cu-TFMG/ZnO NTs sample (a) in the dark, (b) under UV-LED illumination, and (c) cycled switch on/off UV-LED with a period of 6 minutes. Figure 8. Schematic illustrations of oxygen absorption and equivalent circuit of (a) ZnO NTs and 3nm-Cu-TFMG/ZnO NTs (b) in the dark and (c) under UV illumination. Figure 9. (a) Transmittances of 3~15 nm Cu-TFMG/ZnO NTs samples. Schematic illustrations of the reflected and refracted light of (b) Cu-TFMG/ZnO NWs and (c) Cu-TFMG/ZnO NTs.


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Figure 10. Band diagram of the ZnO and Cu-TFMG/ZnO (a)-(b) in the dark and (c)-(d) under UV illumination.

TABLES Table 1. List the photoresponses of the Cu-TFMG/ZnO NSs samples compared with various noble metal/ZnO NSs samples.

ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge. FE-SEM images, I-V curves, XRD, Raman, PL spectra of ZnO nanowires and nanotubes. (PDF)

AUTHOR INFORMATION Corresponding Author * Tel: +886-2- 2730-3273 ext. 7785; Fax: +886-2- 2737-6428; E-mail: [email protected]


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* Tel: +886-6-260-6123 ext. 7785; Fax: +886-6- 2602305; E-mail: [email protected]

Author Contributions ∥

B. R. Huang and C. L. Hsu contributed equally to this work; C. L. Hsu wrote the paper.

Funding Sources The authors would like to thank the Ministry of Science and Technology, Taiwan, for financially supporting this research under Contract No. MOST 105-2221-E-024-015-.


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BRIEFS Few layers thin film metallic glass enhanced UV photodetector based on ZnO nanotubes and nanowires


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Figure 1


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Figure 2


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Figure 3


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Figure 4


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Figure 5


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Figure 6


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Figure 7


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Figure 8


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Figure 9


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Figure 10


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Table 1. List that photoresponse of Cu-TFMG/ZnO NSs compared with various noble/ZnO NSs. Ohmic /Schottky contact

UV lamp

3nm-Cu-TFMG/ZnO NTs

MSM-Ohmic

365 nm, 1 mW/cm2

4.52×104

This work

3nm-Cu-TFMG/ZnO NWs

MSM-Ohmic

365 nm, 1 mW/cm2

1.94×104

This work

7hr-ZnO NTs

MSM-Ohmic

365 nm, 1 mW/cm2

2690

This work

ZnO NWs

MSM-Ohmic

365 nm, 1 mW/cm2

252

This work

p-ZnO:La NWs

MSM-Ohmic

365 nm, 0.25 mW/cm2

212.1

13

p-ZnO:Cu/n-ZnO NWs

MSM-Ohmic

365 nm, 0.25 mW/cm2

6.1

15

Au NPs/ ZnO NW

MSM-Ohmic

367nm, 256 mW

145.3

18

MSMSchottky

350 nm, 1.3 mW/cm2

5×106

23

Au NPs/p-ZnO:K NSs/n-ZnO NW

MSM-Ohmic

365 nm, 6.0 mW/cm2

1168

24

Ag NPs/Single ZnO NW

MSM-Ohmic

365nm

1.6×107

25

Au NPs/ZnO Nanosheet

MSM-Ohmic

335nm

~2×103

26

Pt NPs/Single GaN NW

MSMSchottky

380nm, 6.41 µW/cm2

101

27

Materials

Au NPs/Single ZnO NW

Photoresponse Ref. IUV/IDark


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43x50mm (300 x 300 DPI)


Few-Layer Thin-Film Metallic Glass-Enhanced ... - ACS Publications

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