Low Temperature Aqueous Synthesis Research Articles

Low-temperature aqueous synthesis and biocompatibility of manganese whitlockite

In this work, manganese whitlockite (Mn-WH, Ca18Mn2(HPO4)2(PO4)12) was successfully synthesized and comprehensively characterized. This material is a manganese-containing analog of the biomineral magnesium whitlockite (Mg-WH, Ca18Mg2(HPO4)2(PO4)12). The synthesis was performed via a low-temperature dissolution-precipitation process in aqueous medium under ambient pressure at 75 °C using dicalcium phosphate dehydrate and manganese acetate tetrahydrate as starting materials. The crystal structure of the synthesized powder was determined by powder X-ray diffraction, FTIR and Raman spectroscopies, demonstrating the presence of characteristic structural units. Morphological features and elemental distribution within the synthesized powder were studied by SEM/EDX analysis. XPS, EPR and magnetic studies confirmed the presence of Mn ions in a divalent state. Temperature-dependent magnetic measurements revealed a paramagnetic behavior of Mn-WH down to 5 K. In vitro cytotoxicity experiments were performed with MC3T3-E1 preosteoblastic cell line.

Tetragonal phase-free crystallization of highly conductive nanoscale cubic garnet (Li6.1Al0.3La3Zr2O12) for all-solid-state lithium-metal batteries

The synthesis and processing of garnet-type conductors is usually done at temperatures above 1100 °C to reach the high Li-ion conducting cubic phase resulting in micron-sized particles and potential Li-loss, which are unfavorable for further processing and electrode-electrolyte assembly. Here, we tackle this problem and report a novel low-temperature aqueous synthesis route to stabilize the cubic phase of Li6.1Al0.3La3Zr2O12 (c-Al-LLZO) at a temperature as low as 600 °C, while obtaining nano-crystallites at around 100 - 200 nm. Moreover, a dual-reaction mechanism was proposed to describe the process of c-Al-LLZO crystallization. The as-synthesized nanoscale c-Al-LLZO particles facilitate the densification of the solid-state electrolyte (SSE) pellets with less endowed grain boundaries (exhibiting a high relative density of 97.8 %). The ionic conductivity reaches 0.42 mS cm−1 at 21 °C and the low activation energy (half of the published values) is 0.17 eV. The results presented here show that symmetric cells with Li metal exhibit excellent stability at the current density of 0.2 mA/cm2 and 0.5 mA/cm2, and an improved critical current density (CCD) of 2.16 mA/cm2. This work provides a feasible method of low-temperature crystallization of nanoscale cubic garnet SSEs with good performance for the fabrication of stable SSLBs.

Sequential, low-temperature aqueous synthesis of Ag-In-S/Zn quantum dots via staged cation exchange under biomineralization conditions.

The development of high quality, non-toxic (i.e., heavy-metal-free), and functional quantum dots (QDs) via 'green' and scalable synthesis routes is critical for realizing truly sustainable QD-based solutions to diverse technological challenges. Herein, we demonstrate the low-temperature all-aqueous-phase synthesis of silver indium sulfide/zinc (AIS/Zn) QDs with a process initiated by the biomineralization of highly crystalline indium sulfide nanocrystals, and followed by the sequential staging of Ag+ cation exchange and Zn2+ addition directly within the biomineralization media without any intermediate product purification. Therein, we exploit solution phase cation concentration, the duration of incubation in the presence of In2S3 precursor nanocrystals, and the subsequent addition of Zn2+ as facile handles under biomineralization conditions for controlling QD composition, tuning optical properties, and improving the photoluminescence quantum yield of the AIS/Zn product. We demonstrate how engineering biomineralization for the synthesis of intrinsically hydrophilic and thus readily functionalizable AIS/Zn QDs with a quantum yield of 18% offers a 'green' and non-toxic materials platform for targeted bioimaging in sensitive cellular systems. Ultimately, the decoupling of synthetic steps helps unravel the complexities of ion exchange-based synthesis within the biomineralization platform, enabling its adaptation for the sustainable synthesis of 'green', compositionally diverse QDs.

Colloidal sol-gel: A powerful low-temperature aqueous synthesis route of nanosized powders and suspensions

The colloidal sol-gel is a well-established method for the synthesis of nanoparticles with high reproducibility, homogeneity and low cost. It is a versatile route which allows synthesising many ceramic materials at the nanometric scale. The process starts with the hydrolysis of the metal precursor and ends with the formation of a colloidal suspension/sol with high stability. The particle size can be easily tuned by synthesis parameters such as temperature, metal precursor-water ratio and/or metal precursor-catalyst ratio. Depending on the applications, the sol can be directly used for the preparation of coatings or it can be dried to be used as powder. In this review, the fundamentals of the colloidal sol-gel process are provided, highlighting the great capacity of this synthesis route. Its use in combination with other synthesis methods and the influence of the parameters controlling the process is presented, together with applications and examples of the synthesised powders.

Pt/Co3O4 Surpasses Benchmark Pt/C: An Approach Toward Next Generation Hydrogen Evolution Electrocatalyst

Rational design of composite hybrid structures tuned in atomic level interaction can circumvent the instability of the water splitting catalysts. Here, low-temperature aqueous phase synthesis of a hybrid hydrogen evolution electrocatalyst made of a few nanometer Pt clusters anchored on Co3O4 nanosheets with remarkable stability and superiority over the state-of-the-art Pt/C is achieved. Manipulation of cluster binding energy to support material gives rise to superior activity (3.8 times) and extraordinarily enhanced durability. Pt/Co3O4 composite achieved current densities of 10 and 50 mA/cm2 at overpotentials as low as of 70 and 170 mV, respectively. A combinatorial approach of theory and experiment opens an avenue to design HER catalyst beyond Pt/C.

The effect of nickel precursors on the electrochemical properties of spinel LiMn2−xNixO4 cathode: a comparative study of Ni(NO3)2·6H2O and NiSO4·6H2O as nickel sources

A comparative study was carried out with the effect of nickel precursors on the electrochemical performance of spinel LiMn2−xNixO4 (x = 0, 0.1 and 0.2) cathode materials. The spinel materials were prepared by employing a low temperature aqueous reduction synthesis route using locally sourced low-cost manganese precursor electrolytic manganese dioxide (EMD), and Ni(NO3)2·6H2O as a nickel source. The EDS result has confirmed that the use of nickel nitrate provides more nickel content in the synthesized samples as compared to using nickel sulphate as a nickel source. Importantly, LiMn1.9Ni0.1O4 prepared with the nitrate salt showed the low impedance value (∼294.7 Ω) than that of the nickel sulphate used spinel (∼431.8 Ω), inferring that the nitrate salt generates low resistance in the spinel. The improved conductivity was observed with the small amount of nickel in both precursor used spinel, nickel salt used spinel showed high electrical conductivity (225.4 Ω) than the sulphate salt (330.7 Ω). A small amount of nickel addition showed the significant enhancement in capacity retention of LiMn1.9Ni0.1O4 and LiMn1.8Ni0.2O4 by retaining 88% and 145% of its initial capacity for nickel salt used spinel and the sulphate salt used spinel showed 83% and 92% of its initial capacity, respectively whereas the pristine LiMn2O4 showed only 56% of its initial capacity. The investigation clearly indicates that the substitution of small amounts of nickel into the spinel, irrespective of the precursor used effectively reduces the Jahn-Teller effects in the LiMn2O4.

Optical properties from photoelectron energy-loss spectroscopy of low-temperature aqueous chemically synthesized ZnO nanorods grown on Si

The optical properties of zinc oxide (ZnO) nanorods (NRs) synthesized by the low-temperature aqueous chemical method on top of silicon (Si) substrate have been investigated by means of photoelectron energy loss spectroscopy (PEELS). The ZnO NRs were obtained by the low temperature aqueous chemical synthesis on top of Si substrate. The measured valence band, the dynamical dielectric functions and optical absorption of the material show a reasonable agreement when the trending and shape of the theoretical calculations are considered. A first-principle calculation based on density functional theory (DFT) was performed using the partially self-consistent GW approximation (scGW0) and compared to the experimental results. The application of these two techniques brings a new analysis of the electronic properties of this material. The experimental results regarding the density of states (DOS) obtained for the valence band using x-ray photoelectron spectroscopy (XPS) was found to be consistent with the theoretical calculated value. Due to this consistency, the same wavefunctions was then employed to calculate the dielectric function of the ZnO NRs. The experimentally extracted dielectric function was also consistent with the calculated values.

Low temperature aqueous synthesis of size-controlled nanocrystals through size focusing: a quantum dot biomineralization case study.

Traditional quantum dot synthesis techniques rely on the separation of nucleation and growth to control nanocrystal size. However, the same goal can be achieved through slow and continuous introduction of reactive precursors to keep the growth mechanism in the size focusing regime throughout synthesis. In this work, we demonstrate the efficacy of this approach within the framework of functional material biomineralization where, despite simultaneous nucleation and growth of particles, this growth mechanism enables size-controlled nanocrystal synthesis. Herein, the single enzyme cystathionine γ-lyase (CSE) is utilized to biomineralize CdS nanocrystals via the slow, but continuous turnover of the amino acid l-cysteine to produce H2S. Nanocrystal nucleation and growth theories confirm that consistent addition of monomers will result in a high supersaturation term, driving the nanocrystal growth mechanism into the size focusing regime. We further confirm this theory by mimicking biomineralization via chemical routes and demonstrate the influence of varying supersaturation, to further control the average nanocrystal size. Finally, altering the chelation strength of the capping agent l-cysteine is found to play a key role in balancing nanocrystal growth in solution and long-term stability.

An effective low-temperature solution synthesis of Co-doped [0001]-oriented ZnO nanorods

We demonstrate an efficient possibility to synthesize vertically aligned pure zinc oxide (ZnO) and Co-doped ZnO nanorods (NRs) using the low-temperature aqueous chemical synthesis (90 °C). Two different mixing methods of the synthesis solutions were investigated for the Co-doped samples. The synthesized samples were compared to pure ZnO NRs regarding the Co incorporation and crystal quality. Electron paramagnetic resonance (EPR) measurements confirmed the substitution of Co2+ inside the ZnO NRs, giving a highly anisotropic magnetic Co2+ signal. The substitution of Zn2+ by Co2+ was observed to be combined with a drastic reduction in the core-defect (CD) signal (g ∼ 1.956) which is seen in pure ZnO NRs. As revealed by the cathodoluminescence (CL), the incorporation of Co causes a slight red-shift of the UV peak position combined with an enhancement in the intensity of the defect-related yellow-orange emission compared to pure ZnO NRs. Furthermore, the EPR and the CL measurements allow a possible model of the defect configuration in the samples. It is proposed that the as-synthesized pure ZnO NRs likely contain Zn interstitial (Zni+) as CDs and oxygen vacancy (VO) or oxygen interstitial (Oi) as surface defects. As a result, Co was found to likely occupy the Zni+, leading to the observed CDs reduction and hence enhancing the crystal quality. These results open the possibility of synthesis of highly crystalline quality ZnO NRs-based diluted magnetic semiconductors using the low-temperature aqueous chemical method.

Investigations of BaFe0.5Nb0.5O3 nano powders prepared by a low temperature aqueous synthesis and resulting ceramics

A facile method to prepare nanoscaled BaFe0.5Nb0.5O3 via synthesis in boiling NaOH solution is described herein. The nano-crystalline powder has a high specific surface area of 55m2g−1 and a crystallite size of 15nm. The as-prepared powder does not show any significant crystallite growth up to 700°C. The activation energy of the crystallite growth process was calculated as 590kJmol−1. Dense ceramics can be obtained either after sintering at 1200°C for 1h or after two-step sintering at 1000°C for 10h. The average grain sizes of ceramic bodies can be tuned between 0.23μm and 12μm. The thermal expansion coefficient was determined as 11.4(3)·10−6K−1. The optical band gap varies between 2.90(5) and 2.63(3)eV. Magnetic measurements gave a Néel temperature of 20K. Depending on the sintering regime, the ceramic samples reach permittivity values between 2800 and 137,000 at RT and 1kHz.

Seed layer synthesis effect on the concentration of interface defects and emission spectra of ZnO nanorods/p‐GaN light‐emitting diode

As the low‐temperature aqueous chemical synthesis (LT‐ACS), holds great promises for the synthesis of one‐dimensional (1D) ZnO nanostructure‐based light‐emitting diodes (LEDs) and hence require parameter tuning for optimal performance. N‐ZnO nanorods (NRs)/p‐GaN heterojunction LEDs have been synthesized by the LT‐ACS using ZnO nanoparticle (NPs) seed layers prepared with different precursor solutions. The effect of these seed layers on the interface defect properties and emission intensity of the as‐synthesized n‐Zn/p‐GaN heterojunction LEDs has been demonstrated by spatially resolved cathodoluminescence (CL) and electroluminescence (EL) measurements, respectively. A significant reduction of the interface defects in the n‐ZnO NRs/p‐GaN heterostructure synthesized from a seed layer prepared from zinc acetate (ZnAc) with a mixture of potassium hydroxide (KOH) and hexamethylenetetramine (HMTA) (donated as ZKH seed) compared with those prepared from ZnAc and KOH (donated as ZK seed) is observed as revealed by spatially resolved CL. Consequently, the LEDs based on n‐ZnO NRs/p‐GaN prepared from ZKH seed show an improvement in the yellow emission (∼578 nm) compared to that based on the ZK seed as deduced from the electroluminescence measurements. The improvement in the yellow EL emission on the ZKH LED probably attributed to the low presence of the non‐radiative defect as deduced by light‐output current (L–I) characteristics analysis.

Influence of ZnO seed layer precursor molar ratio on the density of interface defects in low temperature aqueous chemically synthesized ZnO nanorods/GaN light-emitting diodes

Low temperature aqueous chemical synthesis (LT-ACS) of zinc oxide (ZnO) nanorods (NRs) has been attracting considerable research interest due to its great potential in the development of light-emitting diodes (LEDs). The influence of the molar ratio of the zinc acetate (ZnAc): KOH as a ZnO seed layer precursor on the density of interface defects and hence the presence of non-radiative recombination centers in LT-ACS of ZnO NRs/GaN LEDs has been systematically investigated. The material quality of the as-prepared seed layer as quantitatively deduced by the X-ray photoelectron spectroscopy is found to be influenced by the molar ratio. It is revealed by spatially resolved cathodoluminescence that the seed layer molar ratio plays a significant role in the formation and the density of defects at the n-ZnO NRs/p-GaN heterostructure interface. Consequently, LED devices processed using ZnO NRs synthesized with molar ratio of 1:5 M exhibit stronger yellow emission (∼575 nm) compared to those based on 1:1 and 1:3 M ratios as measured by the electroluminescence. Furthermore, seed layer molar ratio shows a quantitative dependence of the non-radiative defect densities as deduced from light-output current characteristics analysis. These results have implications on the development of high-efficiency ZnO-based LEDs and may also be helpful in understanding the effects of the ZnO seed layer on defect-related non-radiative recombination.

Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods

Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 °C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (μ-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.

Low Temperature Aqueous Precipitation Synthesis of LiMnPO4 Nano Particles for Li Ion Battery Cathodes

LiMnPO4 (LMP) is regarded as a promising material for improved Li ion batteries. It is, like the already commercially applied LiFePO4 (LFP), an olivine cathode material. The main advantage is its higher potential (4.1V vs. 3.5V for LFP, with respect to Li+/Li), resulting in an energy density, about 20% higher than for LFP. The main drawbacks are its low electronic and ionic conductivities (compared to LFP). This results in reduced experimental capacities, especially at elevated (dis)charging rates1. This drawback can be circumvented, by reducing particle sizes to nano dimensions, resulting in shorter Li ion diffusion distances. Here, we describe an optimized LMP low temperature (100°C) aqueous precipitation synthesis method2, resulting in nanoparticles (NP), with typical sizes of 50-200 nm, of which the reaction time could be significantly reduced, by modifying the base, used for inducing the precipitation. By an in-depth study of several synthesis parameters such as the flow rate, reaction time, temperature, base, … the complexity of this thermodynamically and even kinetically fragile system is emphasized. Our results show that phase pure LMP NP are only obtained in a particular small subset of these parameter values. Outside this range, secondary phases (like Li3PO4, MnHPO4 hydrate and Mn5(HPO4)2(PO4)2.4H2O (hureaulite)) are formed, or LMP is even completely absent. The figure shows a TEM image of the LMP NP as synthesized after 24 hours at 100°C. T. Vranken is a Ph.D. fellow of the Research Foundation – Flanders (FWO). References (1) Wang, H.; Yang, Y.; Liang, Y.; Cui, L.-F.; Casalongue, H. S.; Li, Y.; Hong, G.; Cui, Y.; Dai, H. Angew. Chemie Int. Ed. 2011, 50, 7364–7368. (2) Delacourt, C.; Poizot, P.; Morcrette, M.; Tarascon, J.-M.; Masquelier, C. Chem. Mater. 2004, 16, 93–99. Figure 1

Directing the growth of ZnO nano structures on flexible substrates using low temperature aqueous synthesis

c-Axis versus a-axis growth in seed-mediated grown ZnO nanowires controlled by the physical position of the substrate in the growth-solution.

Aqueous Solution Process for the Synthesis and Assembly of Nanostructured One-Dimensional α-MoO3 Electrode Materials

A low-temperature aqueous solution synthesis of nanostructured one-dimensional (1D) molybdenum trioxide (MoO3) was developed. The subsequent self-assembly of the fibers to form large-scale freestanding films was achieved without any assistance of organic compounds. Indeed, the whole process, from synthesis to assembly, does not require toxic organic solvents. As an example of the application of our synthesized materials, we built two types of half-cell lithium-ion batteries: (i) the cathode made out of 1D MoO3, having the width in 50–100 nm, with the length in micro scale, and with thickness in ∼10 nm, and (ii) the anode made out of the macroscopic oxide papers consisting of 1D MoO3 and carbon materials. As a cathode material, 1D MoO3 showed a high rate capability with a stable cycle performance up to 20 A g–1 as a result of a short Li+ diffusion path along the [101] direction and less grain boundaries. As an anode material, the composite paper compound showed a first specific discharge capacity of 800 mAh g–1. These findings indicate not only an affordable, eco-efficient synthesis and assembly of nanomaterials but also show a new attractive strategy toward a possible full aqueous process for a large-scale fabrication of freestanding oxide paper compounds without any toxic organic solvent.

A Novel Green Approach to Synthesis of Nanostructured Li4Ti5O12 Anode Material

Li4Ti5O12 (LTO), which is strongly advocated as anode material for lithium ion batteries destined for land transport and grid-integration PV applications, was prepared via a novel low-temperature aqueous synthesis followed by annealing route using only inorganic compounds, including lithium hydroxide and inexpensive titanium tetrachloride as precursors. The synthesis of nanostructured LTO is done via the thermal transformation (annealing) of the aqueous synthesized intermediate phase, Li1.81H0.19Ti2O5·2H2O (LTH). The nanostructure of the prepared LTO material was found to depend on the preceding intermediate phase formation conditions and applied annealing protocol. Thus nanoflower-structured LTO with “petals” 17-50 nm thick was produced by annealing the LTH intermediate phase at 400 oC. However, the morphology changed from flower structure into particulate, when annealing was done at a temperature higher than 500 oC. Finally, after annealing at 700 oC an LTO-rutile TiO2 composite with average particle size of 100 nm was obtained. Possible mechanisms responsible for the different LTO nanocrystal morphologies are proposed.

Low temperature aqueous phase synthesis of silver/silver chloride plasmonic nanoparticles as visible light photocatalysts

A one pot and environmentally benign synthetic route for plasmonic photocatalytic Ag@AgCl nanoparticles in a PVA-dissolved aqueous solution system is presented. The synthesized AgCl has a cubic-shape and its edge length can be controlled from ~57 to ~170 nm by varying the reaction temperature. In this system, PVA was used as a stabilizer for the formation of Ag@AgCl nanoparticles through interaction with Ag(+) ions. After partial reduction with l-arginine, the metallic Ag is formed on the surface of the AgCl substrates and the contents of the metallic Ag mainly affect both the visible-light absorption properties and the plasmonic photocatalytic efficiency of the Ag@AgCl nanocomposites. A plausible growth mechanism of metallic silver during the reduction process is proposed. More importantly, it is verified that the size of the AgCl substrate affected the light absorption region of the Ag@AgCl nanocomposite.

Aqueous Synthesized Nanostructured Li4Ti5O12 for High-Performance Lithium Ion Battery Anodes

Nanostructured Li4Ti5O12 (LTO) was prepared via a novel process comprising low-temperature (<100°C) aqueous synthesis and annealing of the hydrous intermediate phase Li1.81H0.19Ti2O5·2H2O (LTH) using only LiOH and TiCl4 as precursors. Nanosheet-structured LTH converted to either LTO nanosheets (102 m2·g−1) or LTO nanoparticles (28 m2·g−1) upon annealing at 400 and 600°C respectively, each exhibiting unique electrochemical performance properties. The nanosheet-structured LTO exhibited higher initial charge capacity (228.3 vs. 187.3 mAh ·g−1 at 1.0 V cutoff and C/24 rate) than the nanoparticle-structured LTO. Furthermore, the LTO nanosheets taking advantage of their short diffusion path exhibited better rate capability than the LTO nanoparticles; for example their discharge capacity at 15 C was 115 mAh ·g−1 vs. 68.4 mAh ·g−1 at 1.2 V cutoff for the LTO nanoparticles. Meanwhile, the LTO nanoparticles exhibited better cyclability than the LTO nanosheets because of their higher crystallinity. Thus after 130 1 C cycles with cut off at 1.2 V (vs. Li/Li+), the discharge capacity of the nanosheets was 132.9 mAh ·g−1 while that of nanoparticles was 150.7 mAh ·g−1, corresponding to 85 and 97% discharge capacity retention respectively. The newly synthesized nanostructured LTO material can offer a low cost scalable solution for high-performance LIB anodes.

Improved Low-Temperature Aqueous Synthesis of ZnO Nanorods and Their Use in SERS Detection of 4-ABT and RDX

The growth-controlled synthesis of zinc oxide nanorods (ZnO NR) in the aqueous phase has been investigated. The rods were grown on ZnO films previously deposited onto Si(100) and indium tin oxide (ITO) substrates by RF magnetron sputtering. The formation of the rods took place in the presence of hexamethylenetetramine (HMT) as habit-control reagent. The grains in the base ZnO film acted as seeds that promoted the longitudinal growth of the oxide. As-synthesized base films and rods were characterized by X-ray diffraction, scanning electron microscopy (SEM), field emission SEM, optical absorption and photoluminescence spectroscopy techniques. Subsequently, a wet chemistry procedure was performed to achieve ZnO NR growth. This methodology was conducive to the formation of rods of a relatively narrow distribution of diameters (60 - 70 nm) with lengths in the 1 - 3 μm range. Photoluminescence spectra were characterized by a dominant near-band-edge (NBE) peak followed by a green luminescence (GL) broad band, indicative of higher oxygen vacancy concentration in the ZnO NR grown on ZnO/ITO in comparison with those grown on ZnO/Si(100). A UV process was used for coating the ZnO NR with gold (Au). Au coating on ZnO NR was used to evaluate the detection capability by SERS of different analytes such as: 4-aminobenzenethiol (4-ABT) and 1,3,5-trinitroperhydro-1,3,5- triazine (RDX) at low levels. A strong SERS Raman spectrum was observed for 4-ABT. A limit of detection (LOD) of 1 × 10-8M for 4-ABT was achieved corresponding to a minimum of 5.4 × 105molecules detected under the experimental conditions at excitation wavelength of 785 nm with a sensitivity of the ZnO NR in the range of 1.1 × 10-16g under the laser spot.