Raman Peak Research Articles

Structural Stability of γ-Boron under High Pressure up to 126 GPa with Fine Pressure Increments

The structural stability of γ-boron is investigated using Raman spectra and DFT calculations under high pressures, up to 126 GPa, at ambient temperature. The pressure dependence of all the Raman-active modes of the γ-boron is reported. We also observe amusing changes within the B3g and B1g Raman-active vibrational modes, which result in the phenomenon of first merging and then separating the Raman peaks. In addition to the Raman measurements, the changes in crystal structure and force constants are calculated to reasonably explain the discrepancy between the two Raman modes in response to pressure. The results of the continuous shifts for all Raman modes and the unit-cell parameters, as well as volume with increasing pressure, indicate that there is no structural transformation of γ-boron below this pressure value, with no changes in either symmetry or structure.

Galvanic engineering of interior hotspots in 3D Au/Ag bimetallic SERS nanocavities for ultrasensitive and rapid recognition of phthalate esters

The ecological and health risks of plasticizer accumulation have reached the global public agenda. For early screening of phthalate esters (PAEs), in the present study, we developed ultrasensitive and reliable bimetallic surface-enhanced Raman spectroscopy (SERS) platforms with Ag nanocavities galvanically replaced by Au (Au/AgNCs) at room temperature. A galvanic reaction (GR) coupled with the Kirkendall effect led to a large population of nanoscale hollow regions within 60 s. The interstitials at the bimetallic shells were activated as both interior hotspots for field confinement and diffusion pathways for small target molecules. The GR based on the intrinsic material properties resulted in an Au/AgNC platform with reliable sensing operation, including a relative standard deviation of <10 % at the individual analytic Raman peaks. The qualified and densified interior hotspots of the Au/AgNC platform led to sub-ppm sensitivity (i.e., the average limit of detection of ∼2.1 × 10−2 ppm) for four different PAEs. As a demonstration of the Au/AgNC platform's performance in actual sample environments, the detection and identification of various PAE combinations were also investigated. Subtle differences in the PAEs' spectral characteristics (i.e., peak positions and intensity ratios) were successfully classified using a machine learning algorithm based on a principal component analysis–linear discriminant analysis model. Furthermore, the amount of PAE released from the real sample and evaluated by SERS was consistent with that evaluated by gas chromatography–mass spectrometry. These results indicate that the SERS platforms with Au/AgNC substrates and portable Raman instruments are suitable for on-site safety monitoring of toxic substances in food and the environment.

Laser induced diamond/graphite structure for all-carbon deep-ultraviolet photodetector

Graphite was formed by in-situ structural conversion from sp3 to sp2 hybridized carbon via KrF excimer. The surface morphology of diamond was changed to nanoparticles after laser irradiation. Raman peak related to amorphous carbon emerged after laser treatments with energy of 10 ∼ 25 mJ cm−2. X-ray photoelectron spectroscopy exhibited that surface graphitization could take place under low laser energy of 2 mJ cm−2. The structural transformation of diamond after laser irradiation was further studied by cross-sectional transmission electron microscopy (TEM) analysis. The TEM results displayed that the diamond/graphite interface was gradually transformed from diamond to graphite, and the transformation process was verified by molecular dynamics simulations. The specific contact resistance of 7.83 × 10-5 Ω cm2 for the diamond/graphite structure was acquired by transmission line model. Meanwhile, the barrier height of the graphite/diamond contact was obtained to be 0.54 eV. In the end, an all-carbon deep-ultraviolet photodetector with diamond/graphite structure was developed. The all-carbon photodetector exhibited relatively high responsivity of 15 mA/W under 220 nm illumination, and a fast transient response of 86 μs.

Electrochemical Surface-Enhanced Raman Spectroscopy for Aniline Adsorbed on Silver Electrodes: A DFT Study of the Anharmonic Effects of Amino Wagging Vibrational Modes

Aniline molecules exhibit a special amino wagging vibrational mode on the surface of the silver electrode. The corresponding Raman peak not only displays enhanced Raman signals in surface-enhanced Raman spectroscopy (SERS) experiments but also shows a shift toward higher wavenumbers. This work adopts a molecule-metal cluster model to investigate the normal Raman spectra of aniline molecules and their SERS spectra adsorbed on silver electrode surfaces by density functional theory (DFT) approaches. Based on the harmonic approximation, the influence of anharmonic effects on the normal Raman and SERS spectra of aniline is further considered. Our calculated results of the anharmonic Raman spectra of free aniline molecules show that their anharmonic effect mainly comes from the amino wagging vibrational mode. Then, the anharmonic Raman spectra of aniline binding to neutral and positively charged silver clusters were calculated and compared with the harmonic Raman spectra. It was found that the coupling effect between vibrational modes also greatly affects the Raman spectral characteristics. Finally, the excited state energy gap and pre-resonance Raman spectra of the aniline–silver cluster complexes are studied, and it is believed that there may be a charge-transfer enhancement mechanism.

Defect-induced Sr1−xPrxTiO3 crystallites by burial sintering and its optoelectronic applications

The band structure of SrTiO3 was altered by introducing Pr3+ in the Sr2+ site and subsequent graphite burial sintering. The asymmetric nature of the (310) peak in XRD and the emergence of Eg and B1g modes in the Raman spectrum suggest the transformation from cubic to tetragonal phase for the Sr1-xPrxTiO3 system with x ≥ 0.1. The development of the forbidden first-order Raman peaks and novel spectral properties are attributed to the local vibrational modes linked to oxygen vacancies. Structural variations in terms of lattice strain were investigated using a W–H plot, and morphological changes were analyzed by high-resolution FE-SEM. High infrared absorption in UV–Vis–NIR spectra and a significant reduction in band gap from 2.8 eV to 1.8 eV were accomplished through increased disorder in the lattice and the reduction of Ti4+. The blue shift in absorption spectra with Pr concentration can be used to tune the absorption range for sensing purposes. The formation of new electronic states observed here offers a novel approach for band gap modification in perovskites for photocatalytic and photovoltaic applications.

Reduction of amorphous carbon clusters from the highly disordered and reduced graphene oxide NPs by acoustical shock waves — Towards the formation of highly ordered graphene

The journey of exploring the acoustical shock wave-induced solid state phase transitions on polymorphic and allotropy materials have gained enormous momentum in recent years after the invention of the tabletop Reddy tube, but, the knowledge of shock wave-induced phase transitions on allotropy materials is very limited in comparison to the polymorphic materials. Hence, in this framework, we report the shock wave-induced transitions based on the reduction of the amorphous carbon clusters in the highly disordered and reduced graphene oxide nanoparticles (rGO NPs) [rGO — is also called as modified graphene]. The reduction of the disordered carbon in the rGO NPs under shocked conditions is examined by the techniques such as X-ray diffractometry and Raman spectrometer. X-ray crystallographic studies clearly present that as the shock pulses are increased, the intensity of the (002) peak is increased for which the authentication is observed by the Raman spectral analyses wherein it is clearly indicated the decrement and increment of the D and G bands against the exposure of the shock pulses thereby the ID/IG ratios are found to be 1.24, 1.17, 1 and 0.927 for 0, 100, 200 and 400 shocks, respectively. According to the Raman spectral results, the area of the amorphous Raman peak is reduced against the shock pulses such that the values are 98, 82, 81 and 48 for the 0, 100, 200 and 400 shocks, respectively. The removal of amorphous carbon clusters in the rGO NPs can be explained on the basis of the conversion of sp3 to sp2 hybridizations based on the shock wave induced hot-spot nucleation mechanism.

On the Origin of Raman Activity in Anatase TiO2 (Nano)Materials: An Ab Initio Investigation of Surface and Size Effects.

Titania-based materials are abundant in technological applications, as well as everyday products; however, many of its structure-property relationships are still unclear. In particular, its surface reactivity on the nanoscale has important consequences for fields such as nanotoxicity or (photo)catalysis. Raman spectroscopy has been used to characterize titania-based (nano)material surfaces, mainly based on empirical peak assignments. In the present work, we address the structural features responsible for the Raman spectra of pure, stoichiometric TiO2 materials from a theoretical characterization. We determine a computational protocol to obtain accurate Raman response in a series of anatase TiO2 models, namely, the bulk and three low-index terminations by periodic ab initio approaches. The origin of the Raman peaks is thoroughly analyzed and the structure-Raman mapping is performed to account for structural distortions, laser and temperature effects, surface orientation, and size. We address the appropriateness of previous experimental use of Raman to quantify the presence of distinct TiO2 terminations, and provide guidelines to exploit the Raman spectrum based on accurate rooted calculations that could be used to characterize a variety of titania systems (e.g., single crystals, commercial catalysts, thin layered materials, facetted nanoparticles, etc.).

Comparative studies of DFT and experimental Raman spectra of pure 5O.14 liquid crystalline compound

ABSTRACT This article studies the density functional theory (DFT) and experimentally measured Raman spectrum of 5O.14 monomeric liquid crystalline compound. Raman spectroscopy in liquid crystal (LC) is very sensitive to temperature and with the variation of temperature every bond in the molecule shows different Raman peaks. Some important changes in the peaks were also noticed in different phases with the change in temperature. These changes occurred basically due to the changes in the molecular orientation with varying temperature. The structural and dynamics changes of the LC undergoing phase transitions have been analysed from the investigations of peak positions and linewidths. Finally, the results obtained from experimental and DFT generated Raman spectra confirm some interesting features to understand the behaviours of 5O.14 LC.

Quartz under stress: Raman calibration and applications of metamorphic inclusions to geobarometry

Abstract. An experimental calibration of the shifts of three major Raman peaks of quartz with hydrostatic pressure and uniaxial differential stress is presented, and implications for their use in geobarometry based on Raman spectroscopy of quartz inclusions are discussed. The position of the 206 cm−1 peak depends only on hydrostatic pressure P, and its pressure dependence is recalibrated with a peak-fitting procedure that is more adequate for Raman barometry than previous calibrations. The position of the 128 and 464 cm−1 peaks depends on P and also on differential stress σ, which can be determined from the position of these two peaks knowing hydrostatic pressure from the position of the 206 cm−1 peak. The results obtained here are different from those inferred previously from first-principles calculations. The present calibration provides direct relationships between Raman shifts and stress, with a simple formulation of residual pressure and differential stress assuming uniaxial stress along the c axis of quartz inclusions. It is tested on data from experimental and natural inclusions. Residual pressures from the present calibration are similar within uncertainties to those obtained with previous experimental calibrations. Residual differential stresses obtained from the 128 and 464 cm−1 peaks are very sensitive to the precision of Raman measurements. Experimental inclusions yield residual pressures consistent with synthesis pressure. Differential stresses obtained on some experimental inclusions are sometimes incompatible, providing a criterion for identifying inclusions under complex stress conditions that are not appropriate for geobarometry. Recent data on natural inclusions show self-consistent differential stress, consistent with the assumption of major stress along the symmetry axis of the inclusion crystals. The average pressure values from the 128 and 464 cm−1 peaks are similar to the residual pressure from the 206 cm−1 peak that depends only on hydrostatic pressure. It can be used to obtain pressure when the 206 cm−1 peak position cannot be used due to interference with host mineral peaks. Using the 128 and 464 cm−1 peaks alone, or averaging either 128 and 206 or 206 and 464 cm−1 peaks, can induce systematic bias in the residual pressure determination. Applications of the present results to natural inclusions suggest that combined determination of residual pressure and differential stress may be used for both barometry and thermometry pending further calibration.

Surface-enhanced Raman spectroscopy analysis reveals biochemical difference in urine of patients with perianal fistula

Background & aimsPerianal fistulising Crohn's disease (PFCD) is different from the characteristics and outcomes of traditional non-inflammatory bowel disease (IBD) anal fistulas. The presence of perianal disease was a poor prognostic indicator for Crohn's disease (CD) patients and PFCD patients were more likely to bear an increased risk of recurrence. However, the effective and accurate diagnosis methods to early distinguish PFCD from simple perianal fistula were still scarce. The purpose of this study is to develop a non-invasive detecting approach to predict CD in patients with perianal fistulas. MethodsData on patients with anal fistulizing disease were collected from July 2020 to September 2020 in two IBD centers. Urine samples from PFCD and simple perianal fistula patients were investigated by surface-enhanced Raman spectroscopy (SERS). Principal component analysis (PCA)-support vector machine (SVM) was utilized to establish classification models to distinguish PFCD from simple perianal fistula. ResultsAfter a case-matched 1:1 selection by age and gender, 110 patients were included in the study. By analyzing the average SERS spectra of PFCD and simple perianal fistula patients, it revealed that there were significant differences in intensities at 11 Raman peaks. The established PCA-SVM model distinguished PFCD from simple perianal fistula with a sensitivity of 71.43%, specificity 80.00% and accuracy 75.71% in the leave-one-patient-out cross-validation. The accuracy of the model in validation cohort was 77.5%. ConclusionsInvestigation of urine samples by SERS helps clinicians to predict Crohn's disease from perianal fistulas, which make patients achieve benefit from a more individualized treatment strategy.

Predicting the storage time of green tea by myricetin based on surface-enhanced Raman spectroscopy

The quality of green tea changes rapidly due to the oxidation and degradation of polyphenols during storage. Herein, a simple and fast Surface-enhanced Raman spectroscopy (SERS) strategy was established to predict changes in green tea during storage. Raman spectra of green tea with different storage times (2020–2015) were acquired by SERS with silver nanoparticles. The PCA-SVM model was established based on SERS to quickly predict the storage time of green tea, and the accuracy of the prediction set was 97.22%. The Raman peak at 730 cm−1 caused by myricetin was identified as a characteristic peak, which increased with prolonged storage time and exhibited a linear positive correlation with myricetin concentration. Therefore, SERS provides a convenient method for identifying the concentration of myricetin in green tea, and myricetin can function as an indicator to predict the storage time of green tea.

Influence of current density on constant current electric field enhanced aluminum induced crystallization of amorphous silicon thin films

In this study, electric field-enhanced aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) thin films was investigated considering various current densities. Constant electric currents of 4, 5, and 6 A were applied to assess the Joule heating characteristics during specific durations (40, 15.5, and 9 s). The samples were prepared by depositing a 200-nm thick a-Si layer on a glass substrate and sputtering a 300-nm thick aluminum (Al) layer onto the a-Si layer. During the AIC process, layer exchange occured via the diffusion of silicon (Si) into the Al layer. This phenomenon was verified by the in-situ reflectivity, which was in excellent agreement with thin-film optics calculations. During the annealing, processing temperatures were lower than 470 °C, which is less than the Al-Si eutectic temperature of 577 °C. The Raman peak observed near a wavenumber of 519 cm−1 revealed the formation of polycrystalline silicon films through Joule heating processes. Field-effect scanning electron microscopy images were captured and analyzed to investigate the surface morphology of the samples, specifically focusing on grain growth.

BNNS formation through surface modification of hBN nanopowders with a silane coupling agent

The production of BNNSs through the surface modification of nano-sized hBN powders with vinyltrimethoxysilane (VTS) as a silane coupling agent was realized using the newly introduced process route. It aimed to investigate the effects of shear forces generated by ultrasonication and stirring, which were applied during hydroxylation before silanization, and also VTS concentration on surface chemistry, exfoliation, dispersibility, and stabilization of hBN nanopowder. SEM images exhibited that stirring used before ultrasonication throughout hydroxylation improved the dispersibility of BN platelets. Followed by hydroxylation through ultrasonication, the silanization with 0.5 mg/mL VTS resulted in weak absorbances between 1225–995 cm−1 on FTIR spectrum, dispersed and translucent BN platelets, reduction of Raman peak intensity at 1368 cm−1, and an increase of zeta potential (from −10.1 mV to −19.0 mV) as indications of BNNS formation and also improved dispersibility and stability of dispersions. A higher VTS concentration than 0.5 mg/mL concluded with aggregation and poor dispersibility, associated with depletion flocculation. In addition, the number of translucent BN platelets with a lateral size of ∼ 200 nm increased, Raman peak intensity further decreased, and zeta potential reached −28.8 mV after silanization with optimal VTS content (0.5 mg/mL) since both stirring and ultrasonication were applied along hydroxylation. These results indicate the production of thinner BNNSs with high crystallinity and higher dispersion stability.

Improved characteristics of MoS2 transistors with selective doping using 1,2-dichloroethane

We demonstrate area-selective doping of MoS2 field-effect transistors using 1,2-dichloroethane (DCE) solution. In the device manufacturing process, area-selective chemical doping was used to implement contact engineering in the source/drain region. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy measurements were performed to confirm the blocked layer (BL) using a photoresist, which suppressed the doping effect of the DCE treatment. In the XPS results, the main core level of the MoS2 flake with BL did not shift, whereas that of the MoS2 flake without BL changed by approximately 0.24 eV. In the case of the MoS2 flakes with a BL, the vibrational modes of the Raman scattering did not shift. Conversely, the two Raman peaks of the MoS2 flake without BL red-shifted because of increasing electron–phonon scattering. The effect of area-selective doping was confirmed by electrical measurements. The field-effect mobility and the subthreshold swing were enhanced from 4.07 to 31.5 cm2 (V s)−1 and from 1.26 to 0.401 V/decade, respectively.

Laser tweezer Raman spectroscopy combined with deep neural networks for identification of liver cancer cells

Rapid identification of cancer cells is crucial for clinical treatment guidance. Laser tweezer Raman spectroscopy (LTRS) that provides biochemical characteristics of cells can be used to identify cell phenotypes through classification models in a non-invasive and label-free manner. However, traditional classification methods require extensive reference databases and clinical experience, which is challenging when sampling at inaccessible locations. Here, we describe a classification method combing LTRS with deep neural network (DNN) for differential and discriminative analysis of multiple liver cancer (LC) cells. By using LTRS, we obtained high-quality single-cell Raman spectra of normal hepatocytes (HL-7702) and liver cancer cell lines (SMMC-7721, Hep3B, HepG2, SK-Hep1 and Huh7). The tentative assignment of Raman peaks indicated that arginine content was elevated and phenylalanine, glutathione and glutamate content was decreased in liver cancer cells. Subsequently, we randomly selected 300 spectra from each cell line for DNN model analysis, achieving a mean accuracy of 99.2%, a mean sensitivity of 99.2% and a mean specificity of 99.8% for the identification and classification of multiple LC cells and hepatocyte cells. These results demonstrate the combination of LTRS and DNN is a promising method for rapid and accurate cancer cell identification at single cell level.

Study on defect imaging technology of optical elements based on micro-Raman spectroscopy.

An optical element defect detection imaging method based on micro-Raman spectroscopy is proposed to achieve high-precision imaging of optical element defects and their distribution. The detection precision of the system is immediately reflected in the imaging quality. The sharpness value of the mapping images is calculated using the Sum of Modulus of Gray Difference function. The selection of the Raman peak is an important step, and when a borosilicate glass sample with standard defects is measured for verification, it is found that the Raman peak light intensity changes at -37 and 28cm-1. When these two peaks were used for 2D mapping, obvious defect contours can be obtained, while the light intensity at other sites could not be used for imaging, and remained essentially constant. Through the detection of laser burning defects, new peaks appear at the burned defect location that could be used for imaging, and the burning defect area can be clearly distinguished from the non-burning area. By changing the laser burning conditions, the Raman shift changes, which verifies that there is a certain correlation between the laser burning degree and the Raman shift, which also provides a basis for 2D mapping imaging of defect detection.

Assessment of glycosaminoglycan content in bone using Raman spectroscopy.

Glycosaminoglycans (GAGs) are responsible for preserving bone tissue toughness as well as regulating collagen formation and mineralization in the extracellular matrix. However, current methods for characterization of GAGs in bone are destructive, thus unable to capture in situ changes or differences in GAGs between experimental groups. As an alternative, Raman spectroscopy is a non-destructive method and can detect concurrent changes in GAGs and other bone constituents. In this study, we hypothesized that the two most prominent Raman peaks of sulfated GAGs (at ~1066cm-1 and at ~1378cm-1) could be used to detect differences in GAGs content of bone. To test this hypothesis, three experimental models were utilized: an in vitro model (enzymatic removal of GAGs from human cadaver bone), an ex vivo mouse model (biglycan KO vs. WT), and an ex vivo aging model (comparing cadaveric bone samples from young and old donors). All Raman measurements were compared to Alcian blue measurements to confirm the validity of Raman spectroscopy in detecting GAGs changes in bone. Irrespective of different models, it was found that the ~1378cm-1 peak in Raman spectra of bone was uniquely sensitive to changes of GAGs content in bone when normalized with respect to the phosphate phase (~960cm-1); i.e., 1378cm-1/960cm-1 (peak intensity ratio) or 1370-1385cm-1/930-980cm-1 (integrated peak area ratio). In contrast, the 1070cm-1 peak, which includes another major peak of GAGs (1066cm-1), seemed to be compromised to detect changes of GAGs in bone due to concurrent changes of carbonate (CO3) in the similar peak range. This study validates the ability of Raman spectroscopy to detect in situ treatment-, genotype-, and age-related changes in GAG levels of bone matrix.

In situ Monitoring of Double Metal Cyanide (DMC) Catalyst Synthesis by Raman Spectroscopy

Double metal cyanide (DMC) catalyst is widely used for the alkoxylation reaction to produce polyether polyol from ethylene/propylene/butylene oxides. It is challenging to optimize the synthesis process, due to the lack of real-time understanding of the speciation of the reaction mixture. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and actual alkoxylation reaction performance are effective ways for the evaluation of success of each synthesis, but it is difficult to guide process optimization. An in situ Raman method is developed in this study to monitor the DMC catalyst synthesis in real time to accelerate the process optimization. The synthesis involves the reaction of ZnCl2 and K3Co(CN)6 (KHCC) to form Zn3[Co(CN)6]2 (ZHCC). ZHCC is then converted to DMC in the presence of excess of t-butanol and ZnCl2 in the second step. Characteristic KHCC Raman peaks were observed at 2138 and 2153 cm-1, ZHCC at 2185 and 2206 cm-1, and DMC at 2203 and 2225 cm-1, respectively. This enables realtime tracking of both steps’ conversion. Both t-butanol and ZnCl2 concentrations were found to substantially influence the kinetics of DMC formation, but not the Raman spectra of the final DMC products. The reaction time could be adjusted from hours to minutes through the control of reactant concentrations.

On the preparation and characterization of AlSi12-graphene powder for powder bed fusion additive manufacturing applications

This study investigates the possibility of using dry mechanical mixing techniques to prepare ideal composite powders for L-PBF applications. For this purpose, two AlSi12-reinforced composite powders with 0.5 and 1 wt% graphene were prepared by ball milling and regular mixing processes. The powder attributes (size, size distribution and shape), behaviors (absorptivity, packing density, and flowability), relative humidity, and O/C/H content of the composite powders were quantitatively assessed after mixing and compared to those of monolithic AlSi12. The attachment of the graphene particles and their evolutions during each mixing technique were qualitatively investigated. The quality of the graphene powder before and after mixing was studied by Raman spectroscopy, and the nature of the carbonaceous constituent in the composite powders was identified based on the Raman peak positions, shapes and relative intensities. The results of this study prove that only through ball milling ideal composite powders for the L-PBF applications can be achieved.

The effect of Ag doping on the structure, optical, and electronic properties of ZnO nanostructures deposited by atmospheric pressure MOCVD on Ag/Si substrates

Atmospheric pressure metal–organic chemical vapour deposition was used to synthesize Ag-containing ZnO nanostructures of different morphology on Si substrates coated by Ag. Ag from Ag/Si substrates and Ag from silver acetylacetonate after its decomposition were used as a catalyst for ZnO nanocrystal growth for deposition of ZnO nanostructures with different morphologies. We investigated the relation of the structural parameters and chemical composition probed by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy with the photoluminescence (PL) properties and electron–phonon coupling (EPC) reflected in the multi-phonon Raman spectra. The Raman and PL spectra were studied at different powers of the exciting laser radiation (P exc). The spectral position and width of the phonon Raman peaks and the near bandgap PL band at low P exc are supposed to be determined by the structural quality of the surfaces/boundaries of the crystallites. The intensity of the near-bandgap and defect-related PL and the magnitude of the EPC are additionally affected by the dopant concentration. Because of the large crystallite size (>30 nm, determined from XRD), the effects of phonon or electron confinement are negligible in these nanostructures. The behaviour of the position and width of phonon and PL bands with increasing P exc indicates that the heat dissipation in the film, which is dependent on the nanostructure morphology and Ag content, plays an important role. In addition, the cytotoxicity of ZnO:Ag nanostructures was investigated by using monolayer cell cultures of epithelioid origin Madin-Darby bovine kidney and Madin-Darby canine kidney cells at a MTT assay revealing that the level of silver doping of ZnO nanostructures, their morphology, and geometric dimensions determine their toxic effects.