Quevedo-López, Manuel A.

Permanent URI for this collectionhttps://hdl.handle.net/10735.1/2380

Manuel Quevedo-López is a Professor of Material Sciences and Engineering and serves as the head of the department. Learn more about Professor Quevedo-López from the Department of Materials Science and Engineering, his Curriculum Vitae, and his Research Explorer page.

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Toxicological Assessment of Cross-Linked Beads of Chitosan-Alginate and Aspergillus australensis Biomass, with Efficiency as Biosorbent for Copper Removal
(MDPI, 2019-01-30) Gabriela Contreras-Cortés, Ana; Javier Almendariz-Tapia, Francisco; Gómez-Álvarez, Agustin; Burgos-Hernández, Armando; Guadalupe Luque-Alcaraz, Ana; Rodríguez-Félix, Francisco; Quevedo-López, Manuel A.; Plascencia-Jatomea, Maribel; Quevedo-López, Manuel A.
Sorbent materials of biological origin are considered as an alternative to the use of traditional methods in order to remove heavy metals. Interest in using these materials has increased over the past years due to their low cost and friendliness to the environment. The objective of this study was to synthesize and characterize cross-linked beads made of chitosan, alginate, and mycelium of a copper-tolerant strain of Aspergillus australensis. The acute toxicity of the biocomposite beads was assessed using brine shrimp Artemia salina nauplii and the phytotoxicity was determined using lettuce (Lactuca sativa) and chili pepper 'Anaheim' (Capsicum annuum) seeds. The biosorption capacity for copper removal in simulated wastewater was also evaluated. Results showed that the biosorbent obtained had a maximal adsorption of 26.1 mg of Cu²⁺ per g of biocomposite, and removal efficiency was around 79%. The toxicity of simulated residual water after treatment with the biocomposite showed low toxicity toward seeds, which was highly dependent on the residual copper concentration. The toxicity of the biocomposite beads to A. salina was considered medium depending on the amount of the biocomposite, which was attributed to low pH. Biocomposite shows promise as biosorbent for the removal process of heavy metals.
Application of ZnO Schottky Diodes in Rectifier Circuits for Implementation in Energy Harvesting
(Inst Materials Physics, 2019-02-21) Gomez-Alvarez, M.; Mejia, Israel; Cabrera, V.; Avila-Avendano, Carlos; Garcia, R.; Diaz-Cano, A.; Leon-Nataret, Y.; Quevedo-López, Manuel A.; Resendiz, L.; Mejia, Israel; Avila-Avendano, Carlos; Quevedo-López, Manuel A.
This work presents the results obtained from the SPICE simulation of a full-wave bridge rectifier circuit, a double half-wave rectifier circuit and a half-wave rectifier circuit, each at a frequency of 816MHz and low amplitude. The results match the experimental I-V curves obtained with the parameters extracted from the electrical characteristics of the experimental Schottky diodes: Si/SiO₂/Cr/Au/ZnO/Al, glass/Al/ZnO/Au and glass/Al/ZnO/Pd. The results of the simulation show that the devices fabricated in this work can be a useful alternatives for rectifier circuits commonly used in energy harvesting systems, because they are capable of delivering output rectified voltages higher than 1V.
Optical Properties of P-Type SnOₓ Thin Films Deposited by DC Reactive Sputtering
(Springer, 2018-11-23) Guzman-Caballero, D. E.; Quevedo-Lopez, Manuel A.; Ramirez-Bon, R.; Quevedo-Lopez, Manuel A.
Refractive index (n), extinction coefficient (k), effective complex dielectric function (epsilon) and band gap energy (Eg) of p-type SnOₓ thin films from 0.75 to 4eV are studied. 25 nm thick films were deposited by direct current (DC) magnetron sputtering in reactive argon and oxygen atmosphere at different relative oxygen partial pressure (OPP) followed by a post annealing treatment at 250 °C in air atmosphere for 30 min. The relative high Hall effect mobility (μ) of the SnOₓ was attributed to the dominant SnO phase in films grown at 15% OPP. Films deposited at 5 and 11% OPP showed incomplete Sn oxidation resulting in a mixture of Sn and SnO phases with lower hole mobility. Optical transmittance (T) and reflectance (R) are described by assuming a model where the p-type SnOₓ films are defined by a dispersion formula based on a generalization of the Lorentz oscillator model. The roughness of the films (r) was modeled by a Bruggeman effective medium approximation (BEMA). From the optical analysis, k in the visible spectral region show high values for films with phase mixture, while films with single SnO phase presented negligible values. Films with single SnO phase have low n, this latter result from the lower compact microstructure of these films. Also, energies associated to direct and indirect transitions of the Brillouin zone of the SnOₓ films were identified from the evaluated epsilon. Finally, the increase in the values of Eg energy was related to the increase in the SnO phase.
Wafer Scale Quasi Single Crystalline MoS₂ Realized By Epitaxial Phase Conversion
(IOP Publishing Ltd, 2018-12-17) Xu, Xiangming; Wang, Zhenwei; Lopatin, Sergei; Quevedo-López, Manuel A.; Alshareef, Husam N.; Quevedo-López, Manuel A.
Vapor-solid phase reaction (VSPR) is a two-step process for synthesizing 2D MoS₂. In the first step, a precursor film such as molybdenum oxide is grown on a substrate, followed by a sulfurization process at elevated temperature. This process offers a scalable fabrication of wafer-scale film with feasible control in thickness and uniformity. However, the properties of MoS₂ films from this VSPR process often suffer from poor electrical properties. The major reason is their polycrystalline (PC) structure with large concentrations of defects and grain boundaries, which are inherited from the amorphous precursor films. Here, we report a new and scalable VSPR process in which epitaxial MoO₂ films (grown over a 2-inch wafer) are used as high-quality precursors, which are converted into quasi-single-crystalline (QSC) MoS₂. We demonstrate that the field effect mobility of transistors fabricated using a QSC MoS₂ channel is almost 35 times larger, compared to a PC MoS₂ channel, also better than most previously reported MoS₂ films by other two-step MoS₂ formation processes. Our process presents a new approach in which the epitaxial growth of the precursor phase can be used to improve 2D semiconductor and device performance.
Positive Bias Instability in ZnO TFTs with Al₂O₃ Gate Dielectric
(Institute of Electrical and Electronics Engineers Inc., 2019-03-31) Bolshakov, Pavel; Rodriguez-Davila, Rodolfo A.; Quevedo-López, Manuel A.; Young, Chadwin D.; 0000-0003-0690-7423 (Young, CD); Bolshakov, Pavel; Rodriguez-Davila, Rodolfo A.; Quevedo-López, Manuel A.; Young, Chadwin D.
Positive bias instability stress (PBI) was done on ZnO thin-film transistors (TFTs) with Al₂O₃ deposition at 100°C and 250°C. The threshold voltage (VT), transconductance (g ₘ), and subthreshold slope (SS) were monitored where the 100°C samples demonstrated a 'turn-around' phenomenon in the ΔVₜ compared to the 250°C samples. The 250°C samples show consistent ΔVₜ, suggesting a higher Al₂O₃ deposition temperature results in the absence of the defect responsible for the 'turn-around' effect. Both sets also demonstrate negligible degradation in Δgₘ and ASS -suggesting little to no influence on the Vₜ shift by interfacial state generation. © 2019 IEEE.
Structural, Chemical and Electrical Properties of CdS Thin Films Fabricated by Pulsed Laser Deposition Using Varying Background Gas Pressure
(Elsevier B.V., 2019-05-07) Martínez-Landeros, V. H.; Hernandez-Como, N.; Gutierrez-Heredia, G.; Quevedo-López, Manuel A.; Aguirre-Tostado, F. S.; Quevedo-López, Manuel A.
The present study outlines the evolution of the composition, strain and electrical properties of cadmium sulfide (CdS) thin films deposited via pulsed laser deposition (PLD), under varied chamber pressure ranging from 0.13 to 13.33 Pa. The CdS thin films presented a hexagonal crystalline structure at the various deposition pressures as well as improved crystallinity at higher deposition pressures. The electrical resistivity of the resulting films ranged from 10⁻¹ to 10⁷ Ω-cm for deposition pressures of 2.66 to 10.66 Pa. Such a change is closely related to stoichiometry variations in the CdS films, which comprise an excess of Cd compared to S. This change in chemical composition is accompanied by an increase in deposition rate, a decrease in electrical resistivity and grain size, and a broadening of the longitudinal optical (LO) Raman peak, which indicates structural disorder in the CdS films. This disorder is attributed to defects in the crystalline lattice that manifest as a cadmium excess and/or sulfur vacancy left by the evaporated material at low deposition pressures, due to the increased kinetic energy of depositing species during PLD and the desorption of sulfur. ©2019 Elsevier B.V.
Low-Temperature Thin Film Transistors Based on Pulsed Laser Deposited CdS Active Layers
(Institute of Physics Publishing) Martinez-Landeros, V. H.; Hernández-Como, N.; Gutierrez-Heredia, G.; Ramirez-Bon, R.; Quevedo-López, Manuel A.; Aguirre-Tostado, F. S.; Quevedo-López, Manuel A.
Cadmium sulfide (CdS) thin films as n-type semiconductor material were deposited by pulsed laser deposition by varying the argon pressure at room temperature. The structural, morphological and stoichiometric characteristics of the CdS films were studied as a function of the deposition pressure. The results show that the argon deposition pressure had a dramatic impact on the CdS film properties. The CdS electrical resistivity increased 10 4 times when argon pressure was increased from 8 to 10.66 Pa. These films were employed on fully-patterned thin film transistors (TFTs) fabricated by a photolithography-based process, and their electrical characteristics were measured. The TFTs electrical performance achieved a mobility of ∼24 cm² /V-s with a threshold voltage from 1.5 to 12.6 V after testing. The deposition pressure of CdS for transistors fabrication, which optimizes the resulting electrical characteristics, was determined from this study. ©2019 IOP Publishing Ltd.
Effects of Titanium Oxide Surface Properties on Bone-Forming and Soft Tissue-Forming Cells
(Wiley) Wheelis, Sutton E.; Montaño-Figueroa, Ana Gabriela; Quevedo-Lopez, Manuel A.; Rodrigues, Danieli C.; 0000-0003-4068-9896 (Wheelis, SE); 0000-0002-0389-0833 (Rodrigues, DC); Wheelis, Sutton E.; Montaño-Figueroa, Ana Gabriela; Quevedo-Lopez, Manuel A.; Rodrigues, Danieli C.
Background: Previous studies have concluded that certain titanium oxide (TiO₂) surface properties promote bone-forming cell attachment. However, no comprehensive studies have investigated the effects of TiO₂ surface and film morphology on hard and soft tissues. Purpose: The aim of this study is to understand the effects of TiO₂ morphology on the proliferation and differentiation of murine preosteoblasts (MC3T3-E1) and proliferation of human gingival fibroblasts (HGF-1) using in vitro experiments. Materials and Methods: Samples were fabricated with several TiO₂ thickness and crystalline structure to mimic various dental implant surfaces. in vitro analysis was performed for 1, 3, and 7 days on these samples to assess the viability of MC3T3-E1 and HGF-1 cells in contact with the modified oxide surfaces. Results: Results showed that HGF-1 cells exhibited no significant difference in viability on modified oxide surfaces versus a titanium control across experiments. MC3T3-E1 cells exhibited a significantly higher viability for the modified oxide surface in 1 day experiments, but not in 3 or 7 day experiments. Alkaline phosphatase expression in MC3T3-E1 was not significantly different on modified oxide surfaces versus the control across all experiments. A slight positive trend in viability was observed for cells in contact with rougher modified oxide surfaces versus a titanium control in both cell types. Conclusions: These observations suggest that crystallinity and thickness do not affect the long-term viability of hard or soft tissue cells when compared to a cpTi surface. Therefore, treatments like anodization on implant components may not directly affect the attachment of hard or soft tissue cells in vivo. © 2018 Wiley Periodicals, Inc.
Dual-Gate MoS₂ Transistors with Sub-10 NM Top-Gate High-K Dielectrics
(American Institute of Physics Inc.) Bolshakov, Pavel; Khosravi, Ava; Zhao, Peng; Hurley, P. K.; Hinkle, Christopher L.; Wallace, Robert M.; Young, Chadwin D.; 0000-0002-3530-6400 (Zhao, P); 0000-0001-5566-4806 (Wallace, RM); 0000-0003-0690-7423 (Young, CD); Bolshakov, Pavel; Khosravi, Ava; Zhao, Peng; Hinkle, Christopher L.; Wallace, Robert M.; Young, Chadwin D.
High quality sub-10 nm high-k dielectrics are deposited on top of MoS₂ and evaluated using a dual-gate field effect transistor configuration. Comparison between top-gate HfO₂ and an Al₂O₃/HfO₂ bilayer shows significant improvement in device performance due to the insertion of the thin Al₂O₃ layer. The results show that the Al₂O₃ buffer layer improves the interface quality by effectively reducing the net fixed positive oxide charge at the top-gate MoS₂/high-k dielectric interface. Dual-gate sweeping, where both the top-gate and the back-gate are swept simultaneously, provides significant insight into the role of these oxide charges and improves overall device performance. Dual-gate transistors encapsulated in an Al₂O₃ dielectric demonstrate a near-ideal subthreshold swing of ~60 mV/dec and a high field effect mobility of 100 cm²/V·s.
Developing Analysis Criteria to Adjust the Growth of CdS and CdTe Thin Films Using the PLD Technique, for Solar Cell Purposes
(Inst Materials Physics) Ruiz-Preciado, M.; Quevedo-López, Manuel A.; Rojas-Hernandez, A. G.; de Leon, A.; Apolinar-Iribe, A.; Ochoa-Landin, R.; Valencia-Palomo, G.; Castillo, S. J.; 6602171886 (Quevedo-Lopez, MA)
The goal of this research is to obtain technical information of the conformation of the CdTe/CdS junctions deposited on an ITO/Glass substrate. Their physical conditions to deposit each single layer will enable appropriate configurations to be applied on electronic devices such as alternative solar cells on silicon technology. Firstly, CdS thin films were deposited upon an ITO/Glass substrate at room temperature, with 9,000 shots at the rate of 10 shots/s, at different pressures of 20, 40, 60, 65, 70, 75 and 90 mTorr. Afterwards, CdTe thin films were grown on glass substrates all with 100,000 shoots at the rate of 10 shots/s, at the same pressure of 100 mTorr, but at different substrate temperatures: 100, 200, 300 and 400 degrees C. For CdS at the rate of 0.1 nm/s good films of 150 nm were produced in 1,500 seconds (25 min), while for CdTe at the rate of 0.0696 ≈ 0.07 nm/s, films of 696 nm in 10,000 s (166.66 min) were produced. Their morphologies, crystallite size and resistivities were also studied to propose the optimized CdTe/CdS junction for a photovoltaic application.
Dielectric Gate Applications of PMMA-TiO₂ Hybrid Films in ZnO-Based Thin Film Transistors
(Electrochemical Science Group) Alvarado-Beltrán, C. G.; Almaral-Sánchez, J. L.; Quevedo-López, Manuel A.; Ramirez-Bon, R.
In this paper we report a low temperature sol-gel deposition process of organic-inorganic PMMA-TiO₂ hybrid films for applications to gate dielectric layers in field-effect (FE) thin film transistors (TFT), using sputtered n-type ZnO as semiconductor active layer . The PMMA-TiO₂ hybrid thin films were prepared by a modified sol-gel route using titanium butoxide (TBT) as the inorganic (titania) source, methyl methacrylate (MMA) as the organic source, and 3-trimetoxy-silyl-propyl- methacrylate (TMSPM) as the coupling agent between organic and inorganic phases. The hybrid precursor solution for the deposition of the films contained the three precursors with molar ratio 1:0.25:0.25 for TBT, TMSPM and MMA, respectively. For characterization purposes, the hybrid thin films were deposited by dip coating on glass slides substrates and subsequently heat-treated at 100 °C for 24 h. Previous to the device applications, the hybrid films were analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier Transform Infra-Red (FTIR) spectroscopy, transmission and reflection spectroscopy and thermogravimetric analysis (TGA) measurements. The macroscopic characteristics of the hybrid films such as high homogeneity and high optical transparence evidenced the formation of a cross-linked, interpenetrated organic-inorganic network. The dielectric characteristics of the PMMA-TiO₂ hybrid films were studied by measuring capacitance-voltage (C-V) and current-voltage (I-V) curves in metal-insulator-metal (MIM) structures, using gold as metal contacts. Finally, the hybrid films were tested as gate dielectric layers in thin film transistors with structure ZnO/PMMA-TiO₂/ITO/Glass, with a common bottom gate and patterned Al source/drain contacts. We analyzed the output electrical response and transfer characteristics of the hybrid dielectric gate TFTs to determine their performance parameters.
CdCl₂ Treatment on Chemically Deposited CdS Active Layers in Thin Film Transistors
(Electrochemical Science Group) Mendívil-Reynoso, T.; Ramírez-Rodríguez, L. P.; Quevedo-López, Manuel A; Ramírez-Bon, R.; Castillo, S. J.; Erik Jonsson School of Engineering and Computer Science; 6602171886 (Quevedo-Lopez, MA)
In this work CdS layers were deposited by an ammonia-free chemical bath deposition process on SiO₂/p-Si substrates as active layers of thin film transistors (TFT). The electrical characteristics of the CdS-based TFT with different channel lengths were analyzed after thermal annealing in forming gas combined with previous immersion in CdCl₂ saturated solution. The annealing temperatures were 100, 200 and 300°C. To determine the effects of the CdCl₂ treatment on the device electrical parameters, devices with and without previous immersion in CdCl₂ were thermal annealed in forming gas and analyzed. The results show that the thermal annealing processes at 100 and 200 °C do not improve the electrical characteristics of the devices in both conditions. The annealing at 300 °C in both conditions improves noticeably the electrical performance of the devices attaining mobilities of the order of 5 cm²/Vs, threshold voltage in the range -1.5-10 V, swing voltage in the range of 1.65-9 V and I(on)/I(off) current ratio of the order 10³-10⁶.
Thin Film Cadmium Telluride Charged Particle Sensors for Large Area Neutron Detectors
(Amer Inst Physics) Murphy, John W.; Smith, Lindsey; Calkins, J.; Mejia, Israel; Cantley, Kurtis D.; Chapman, Richard A.; Quevedo-Lopez, Manuel A.; Gnade, Bruce E.; 0000 0003 8371 1336‏ (Gnade, BE); 00049719‏ (Gnade, BE); C-2327-2008‏ (Gnade, BE)
Thin film semiconductor neutron detectors are an attractive candidate to replace ³He neutron detectors, due to the possibility of low cost manufacturing and the potential for large areas. Polycrystalline CdTe is found to be an excellent material for thin film charged particle detectors−an integral component of a thin film neutron detector. The devices presented here are characterized in terms of their response to alpha and gamma radiation. Individual alpha particles are detected with an intrinsic efficiency of >80%, while the devices are largely insensitive to gamma rays, which is desirable so that the detector does not give false positive counts from gamma rays. The capacitance-voltage behavior of the devices is studied and correlated to the response due to alpha radiation. When coupled with a boron-based neutron converting material, the CdTe detectors are capable of detecting thermal neutrons.
Evaluation of CdS Interfacial Layers in ZnO Nanowire/Poly(3-Hexylthiophene) Solar Cells
Murphy, John Winter; Mejia, Israel; Gnade, Bruce E.; Quevedo-Lopez, Manuel A.; 0000 0003 8371 1336 (Gnade, BE); 00049719‏ (Gnade, BE)
We prepare ZnO:poly(3-hexylthiophene) (P3HT) thin-film solar cells and ZnO nanowire:P3HT nanostructured solar cells and evaluate the effect of adding an interfacial layer between the ZnO and P3HT as a function of the nanowire height. We evaluate several different interlayers of CdS deposited, using two different chemical bath deposition (CBD) recipes. The height of the nanowire array is varied from a bilayer device with no nanowires up to arrays with a height of 2 mu m. We find that achieving a conformal coating of the ZnO with the interfacial layer is critical to improve device performance and that CBD can be used to grow conformal films on nonuniform surfaces.
Optimizing Diode Thickness for Thin-Film Solid State Thermal Neutron Detectors
(American Institute of Physics, 2012-10-04) Murphy, John W.; Mejia, Israel; Quevedo-López, Manuel A.; Gnade, Bruce E.; 0000 0003 8371 1336 (Gnade, BE); 00049719‏ (Gnade, BE); Erik Jonsson School of Engineering and Computer Science
In this work, we investigate the optimal thickness of a semiconductor diode for thin-film solid state thermal neutron detectors. We evaluate several diode materials, Si, CdTe, GaAs, C (diamond), and ZnO, and two neutron converter materials, 10B and 6LiF. Investigating a coplanar diode/converter geometry, we determine the minimum semiconductor thickness needed to achieve maximum neutron detection efficiency. By keeping the semiconductor thickness to a minimum, gamma rejection is kept as high as possible. In this way, we optimize detector performance for different thin-film semiconductor materials.

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