Coatings

Research

Jump to: Other

17 pages, 6151 KiB

Open AccessArticle

Ternary Holey Carbon Nanohorn/Potassium Chloride/Polyvinylpyrrolidone Nanohybrid as Sensing Film for Resistive Humidity Sensor

by Bogdan-Catalin Serban, Octavian Buiu, Marius Bumbac, Nicolae Dumbravescu, Cristina Pachiu, Mihai Brezeanu, Gabriel Craciun, Cristina Mihaela Nicolescu, Vlad Diaconescu and Cornel Cobianu

Coatings 2024, 14(4), 517; https://doi.org/10.3390/coatings14040517 - 22 Apr 2024

Viewed by 436

Abstract

The study presents findings on the relative humidity (R.H.) sensing capabilities of a resistive sensor. This sensor utilizes sensing layers composed of a ternary nanohybrid, consisting of holey carbon nanohorn (CNHox), potassium chloride (KCl), and polyvinylpyrrolidone (PVP), with mass ratios of 7/1/2, 6.5/1.5/2, [...] Read more.

The study presents findings on the relative humidity (R.H.) sensing capabilities of a resistive sensor. This sensor utilizes sensing layers composed of a ternary nanohybrid, consisting of holey carbon nanohorn (CNHox), potassium chloride (KCl), and polyvinylpyrrolidone (PVP), with mass ratios of 7/1/2, 6.5/1.5/2, and 6/2/2 (w/w/w). The sensing structure comprises a silicon substrate, a SiO₂ layer, and interdigitated transducer (IDT) electrodes. The sensing film is deposited on the sensing structure via the drop-casting method. The sensing layers’ morphology and composition are investigated through Scanning Electron Microscopy (SEM) and RAMAN spectroscopy. The resistance of thin-film sensors based on ternary hybrids increased with exposure to a range of relative humidity (R.H.) levels, from 0% to 100%. The newly designed devices demonstrated a comparable response at room temperature to that of commercial capacitive R.H. sensors, boasting excellent linearity, swift response times, and heightened sensitivity. Notably, the studied sensors outperform others employing CNHox-based sensing layers in terms of sensitivity, as observed through manufacturing and testing processes. It elucidates the sensing mechanisms of each constituent within the ternary hybrid nanocomposites, delving into their chemical and physical properties, electronic characteristics, and affinity for water molecules. Various alternative sensing mechanisms are considered and discussed, including the reduction in holes within CNHox upon interaction with water molecules, proton conduction, and PVP swelling. Full article

(This article belongs to the Special Issue Advanced Thin Films Technologies for Optics, Electronics, and Sensing)

► Show Figures

Figure 1

11 pages, 10583 KiB

Open AccessCommunication

Mid-Infrared (MIR) Complex Refractive Index Spectra of Polycrystalline Copper-Nitride Films by IR-VASE Ellipsometry and Their FIB-SEM Porosity

by Emilio Márquez, Eduardo Blanco, José M. Mánuel, Manuel Ballester, Marcos García-Gurrea, María I. Rodríguez-Tapiador, Susana M. Fernández, Florian Willomitzer and Aggelos K. Katsaggelos

Coatings 2024, 14(1), 5; https://doi.org/10.3390/coatings14010005 - 19 Dec 2023

Viewed by 929

Abstract

Copper-nitride (Cu

_{3}

N) semiconductor material is attracting much attention as a potential, next-generation thin-film solar light absorber in solar cells. In this communication, polycrystalline covalent Cu

_{3}

N thin films were prepared using reactive-RF-magnetron-sputtering deposition, at room temperature, onto glass and silicon [...] Read more.

Copper-nitride (Cu

_{3}

N) semiconductor material is attracting much attention as a potential, next-generation thin-film solar light absorber in solar cells. In this communication, polycrystalline covalent Cu

_{3}

N thin films were prepared using reactive-RF-magnetron-sputtering deposition, at room temperature, onto glass and silicon substrates. The very-broadband optical properties of the Cu

_{3}

N thin film layers were studied by UV-MIR (0.2–40

μ

m) ellipsometry and optical transmission, to be able to achieve the goal of a low-cost absorber material to replace the conventional silicon. The reactive-RF-sputtered Cu

_{3}

N films were also investigated by focused ion beam scanning electron microscopy and both FTIR and Raman spectroscopies. The less dense layer was found to have a value of the static refractive index of 2.304, and the denser film had a value of 2.496. The iso-absorption gap,

E_{04}

, varied between approximately 1.3 and 1.8 eV and could be considered suitable as a solar light absorber. Full article

(This article belongs to the Special Issue Advanced Thin Films Technologies for Optics, Electronics, and Sensing)

► Show Figures

Graphical abstract

21 pages, 10110 KiB

Open AccessArticle

Effect of Substrate Bias on the Microstructure and Properties of Non-Equimolar (AlCrSiTiZr)N Films with Different Cr/Zr Ratios Deposited Using Reactive Direct Current Magnetron Sputtering

by Hao-En Peng, Ching-Yin Lee, Hsin-Yi Chang and Jien-Wei Yeh

Coatings 2023, 13(12), 1985; https://doi.org/10.3390/coatings13121985 - 22 Nov 2023

Viewed by 691

Abstract

To reduce the cost of tools operated in extreme environments, we developed films with excellent corrosion/oxidation resistance. Two high-entropy nitride films, (AlCrSi_0.3TiZr)N and (AlCr_1.5Si_0.3TiZr_0.5)N, were deposited using reactive DC magnetron sputtering under different substrate biases. [...] Read more.

To reduce the cost of tools operated in extreme environments, we developed films with excellent corrosion/oxidation resistance. Two high-entropy nitride films, (AlCrSi_0.3TiZr)N and (AlCr_1.5Si_0.3TiZr_0.5)N, were deposited using reactive DC magnetron sputtering under different substrate biases. The films exhibited a maximum hardness of 32.5 GPa ((AlCrSi_0.3TiZr)N) and 35.3 GPa ((AlCr_1.5Si_0.3TiZr_0.5)N) when deposited at −150 V, corresponding to 27 and 142% increases compared to those deposited at 0 V. This indicates that the bias strengthened (AlCr_1.5Si_0.3TiZr_0.5)N (higher Cr/Zr ratio) more significantly. The enhancement of the mechanical properties was highly correlated with the interstitial point defects and densification of the film microstructures. The corrosion resistance of the films deposited on 6061 Al alloy substrate under different biases was tested in 0.1 M H₂SO₄. (AlCrSi_0.3TiZr)N and (AlCr_1.5Si_0.3TiZr_0.5)N displayed the lowest corrosion currents of 0.75 and 0.19 μA/cm² when deposited at −100 and −150 V, respectively. These values are two orders of magnitude lower than that of the uncoated substrate. The (AlCr_1.5Si_0.3TiZr_0.5)N film showed better oxidation resistance than the (AlCrSi_0.3TiZr)N film and remained partially oxidized after heat treatment at 1000 °C. The (AlCr_1.5Si_0.3TiZr_0.5)N film deposited at −150 V exhibits excellent mechanical properties and corrosion/oxidation resistances, making it suitable for protecting tools operating in harsh environments. Full article

(This article belongs to the Special Issue Advanced Thin Films Technologies for Optics, Electronics, and Sensing)

► Show Figures

Figure 1

18 pages, 15532 KiB

Open AccessArticle

The Relationship between Annealing Temperatures and Surface Roughness in Shaping the Physical Characteristics of Co₄₀Fe₄₀B₁₀Dy₁₀ Thin Films

by Chi-Lon Fern, Wen-Jen Liu, Chia-Chin Chiang, Yung-Huang Chang, Yuan-Tsung Chen, Yu-Zhi Wang, Jia-Wei Liu, Shih-Hung Lin, Ko-Wei Lin and Sin-Liang Ou

Coatings 2023, 13(11), 1895; https://doi.org/10.3390/coatings13111895 - 05 Nov 2023

Viewed by 1276

Abstract

Co₄₀Fe₄₀B₁₀Dy₁₀ thin films, with thicknesses varying between 10 nm and 50 nm, were grown on a Si(100) substrate. Subsequently, they underwent a 1 h annealing process in an Ar atmosphere at temperatures of 100 °C, 200 [...] Read more.

Co₄₀Fe₄₀B₁₀Dy₁₀ thin films, with thicknesses varying between 10 nm and 50 nm, were grown on a Si(100) substrate. Subsequently, they underwent a 1 h annealing process in an Ar atmosphere at temperatures of 100 °C, 200 °C, and 300 °C. The oxide characteristic peaks of Dy₂O₃(440), Co₂O₃(422), and Co₂O₃(511) were revealed by X-ray diffraction (XRD). The low-frequency alternating current magnetic susceptibility (χ_ac) decreases with frequency. Due to thickness and the anisotropy of the magnetic crystal, the maximum χ_ac and saturation magnetization values rise with thicknesses and annealing temperatures. As the thickness and heat treatment temperature rise, the values for resistivity and sheet resistance tend to fall. The results of atomic force microscopy (AFM) and magnetic force microscopy (MFM) show that average roughness (Ra) lowers as the annealing temperature increases, and the distribution of strip-like magnetic domain becomes more visible. As thickness and annealing temperature increase, there is a corresponding rise in surface energy. Nano-indentation testing shows that hardness initially decreases from 10 nm to 40 nm, followed by an increase at 50 nm. Notably, annealing at 300 °C leads to a significant hardening effect, marking the highest level of hardness observed. Young’s modulus increased as thicknesses and annealing temperatures increased. The magnetic, electric, and adhesive characteristics of CoFeBDy films are highly dependent on surface roughness at various annealing temperatures. Full article

(This article belongs to the Special Issue Advanced Thin Films Technologies for Optics, Electronics, and Sensing)

► Show Figures

Figure 1

21 pages, 11978 KiB

Open AccessFeature PaperArticle

Optical Properties of Reactive RF Magnetron Sputtered Polycrystalline Cu₃N Thin Films Determined by UV/Visible/NIR Spectroscopic Ellipsometry: An Eco-Friendly Solar Light Absorber

by E. Márquez, E. Blanco, M. García-Gurrea, M. Cintado Puerta, M. Domínguez de la Vega, M. Ballester, J. M. Mánuel, M. I. Rodríguez-Tapiador and S. M. Fernández

Coatings 2023, 13(7), 1148; https://doi.org/10.3390/coatings13071148 - 25 Jun 2023

Cited by 2 | Viewed by 1297

Abstract

Copper nitride (

{Cu}_{3} N

), a metastable poly-crystalline semiconductor material with reasonably high stability at room temperature, is receiving much attention as a very promising next-generation, earth-abundant, thin film solar light absorber. Its non-toxicity, on the other hand, makes it [...] Read more.

Copper nitride (

{Cu}_{3} N

), a metastable poly-crystalline semiconductor material with reasonably high stability at room temperature, is receiving much attention as a very promising next-generation, earth-abundant, thin film solar light absorber. Its non-toxicity, on the other hand, makes it a very attractive eco-friendly (greener from an environmental standpoint) semiconducting material. In the present investigation,

{Cu}_{3} N

thin films were successfully grown by employing reactive radio-frequency magnetron sputtering at room temperature with an RF-power of 50 W, total working gas pressure of

0.5 Pa

, and partial nitrogen pressures of

0.8

and

1.0

, respectively, onto glass substrates. We investigated how argon affected the optical properties of the thin films of Cu

_{3}

N, with the aim of achieving a low-cost solar light absorber material with the essential characteristics that are needed to replace the more common silicon that is currently in present solar cells. Variable angle spectroscopic ellipsometry measurements were taken at three different angles,

50^{\circ}

,

60^{\circ}

, and

70^{\circ}

, to determine the two ellipsometric parameters psi,

ψ

, and delta,

Δ

. The bulk planar

{Cu}_{3} N

layer was characterized by a one-dimensional graded index model together with the combination of a Tauc–Lorentz oscillator, while a Bruggeman effective medium approximation model with a

50 %

air void was adopted in order to account for the existing surface roughness layer. In addition, the optical properties, such as the energy band gap, refractive index, extinction coefficient, and absorption coefficient, were all accurately found to highlight the true potential of this particular material as a solar light absorber within a photovoltaic device. The direct and indirect band gap energies were precisely computed, and it was found that they fell within the useful energy ranges of

2.14

–

2.25

eV and

1.45

–

1.71

eV, respectively. The atomic structure, morphology, and chemical composition of the Cu

_{3}

N thin films were analyzed using X-ray diffraction, atomic force microscopy, and energy-dispersive X-ray spectroscopy, respectively. The Cu

_{3}

N thin layer thickness, profile texture, and surface topography of the

{Cu}_{3} N

material were characterized using scanning electron microscopy. Full article

(This article belongs to the Special Issue Advanced Thin Films Technologies for Optics, Electronics, and Sensing)

► Show Figures

Figure 1

14 pages, 9447 KiB

Open AccessArticle

Evolution of Nanocrystalline Graphite’s Physical Properties during Film Formation

by Mariuca Gartner, Mihai Anastasescu, Hermine Stroescu, Jose Maria Calderon-Moreno, Silviu Preda, Octavian-Gabriel Simionescu, Andrei Avram and Octavian Buiu

Coatings 2022, 12(9), 1274; https://doi.org/10.3390/coatings12091274 - 01 Sep 2022

Cited by 2 | Viewed by 1376

Abstract

Nanocrystalline graphite (NCG) layers represent a good alternative to graphene for the development of various applications, using large area, complementary metal-oxide semiconductor (CMOS) compatible technologies. A comprehensive analysis of the physical properties of NCG layers—grown for different time periods via plasma-enhanced chemical vapour [...] Read more.

Nanocrystalline graphite (NCG) layers represent a good alternative to graphene for the development of various applications, using large area, complementary metal-oxide semiconductor (CMOS) compatible technologies. A comprehensive analysis of the physical properties of NCG layers—grown for different time periods via plasma-enhanced chemical vapour deposition (PECVD)—was conducted. The correlation between measured properties (thickness, optical constants, Raman response, electrical performance, and surface morphology) and growth time was established to further develop various functional structures. All thin films show an increased grain size and improved crystalline structure, with better electrical properties, as the plasma growth time is increased. Moreover, the spectroscopic ellipsometry investigations of their thickness and optical constants, together with the surface roughness extracted from the atomic force microscopy examinations and the electrical properties resulting from Hall measurements, point out the transition from nucleation to three-dimensional growth in the PECVD process around the five-minute mark. Full article

(This article belongs to the Special Issue Advanced Thin Films Technologies for Optics, Electronics, and Sensing)

► Show Figures

Figure 1

8 pages, 1848 KiB

Open AccessArticle

Dependence of Structural and Optical Performance of Lanthanum Fluoride Antireflective Films on O Impurities

by Wenli Lu, Bo Pan, Ruiying Miao, Bingzheng Yang, Chuang Yu, Dongwei Zhang, Dehong Chen, Liguo Han and Zhiqiang Wang

Coatings 2022, 12(8), 1184; https://doi.org/10.3390/coatings12081184 - 16 Aug 2022

Viewed by 1191

Abstract

Lanthanum fluoride (LaF₃) thin films were deposited on the Ge substrate using the molybdenum boat evaporation method. The effect of films’ oxygen impurity on the infrared optical properties has been investigated for the first time in this report. With the increase [...] Read more.

Lanthanum fluoride (LaF₃) thin films were deposited on the Ge substrate using the molybdenum boat evaporation method. The effect of films’ oxygen impurity on the infrared optical properties has been investigated for the first time in this report. With the increase in oxygen content in the films, the F content decreases, and the O/F ratio decreases from 0.160 to 0.055. XRD patterns reveal that the presence of O impurity destroys the crystal structure integrity of the LaF₃ films and leads to the intensification of infrared absorption. The average transmittance decreases from 58.1% to 52.2%, and the peak transmittance decreases from 59.9% to 54.5%. Additionally, the refractive index and extinction coefficient of LaF₃ films with different oxygen content are obtained by fitting the transmittance test data. The results show that the refractive index and extinction coefficient of the films in 8–12 μm increase with the increase in oxygen content, the average refractive index increases from 1.339 to 1.478, and the extinction coefficient increases from 0.001 to 0.030. In this paper, the influence of oxygen impurity in the LaF₃ film on its infrared optical properties is revealed, which lays a theoretical foundation for the development of high-performance LaF₃ infrared antireflective film. Full article

(This article belongs to the Special Issue Advanced Thin Films Technologies for Optics, Electronics, and Sensing)

► Show Figures

Graphical abstract

Other

Jump to: Research

12 pages, 3347 KiB

Open AccessBrief Report

High-Performance ε-Ga₂O₃ Solar-Blind Photodetectors Grown by MOCVD with Post-Thermal Annealing

by Zeyuan Fei, Zimin Chen, Weiqu Chen, Tiecheng Luo, Shujian Chen, Jun Liang, Xinzhong Wang, Xing Lu, Gang Wang and Yanli Pei

Coatings 2023, 13(12), 1987; https://doi.org/10.3390/coatings13121987 - 23 Nov 2023

Cited by 1 | Viewed by 761

Abstract

High-temperature annealing has been regarded as an effective technology to improve the performance of Ga₂O₃-based solar-blind photodetectors (SBPDs). However, as a metastable phase, ε-Ga₂O₃ thin film may undergo phase transformation during post-annealing. Therefore, it is necessary [...] Read more.

High-temperature annealing has been regarded as an effective technology to improve the performance of Ga₂O₃-based solar-blind photodetectors (SBPDs). However, as a metastable phase, ε-Ga₂O₃ thin film may undergo phase transformation during post-annealing. Therefore, it is necessary to investigate the effect of the phase transition and the defect formation or desorption on the performance of photodetectors during post-annealing. In this work, the ε-Ga₂O₃ thin films were grown on c-plane sapphire with a two-step method, carried out in a metal-organic chemical vapor deposition (MOCVD) system, and the ε-Ga₂O₃ metal-semiconductor-metal (MSM)-type SBPDs were fabricated. The effects of post-annealing on ε-Ga₂O₃ MSM SBPDs were investigated. As a metastable phase, ε-Ga₂O₃ thin film undergoes phase transition when the annealing temperature is higher than 700 °C. As result, the decreased crystal quality makes an SBPD with high dark current and long response time. In contrast, low-temperature annealing at 640 °C, which is the same as the growth temperature, reduces the oxygen-related defects, as confirmed by X-ray photoelectron spectroscopy (XPS) measurement, while the good crystal quality is maintained. The performance of the SBPD with the post-annealing temperature of 640 °C is overall improved greatly compared with the ones fabricated on the other films. It shows the low dark current of 0.069 pA at 10 V, a rejection ratio (R_peak/R₄₀₀) of 2.4 × 10⁴ (R_peak = 230 nm), a higher photo-to-dark current ratio (PDCR) of 3 × 10⁵, and a better time-dependent photoresponse. These results indicate that, while maintaining no phase transition, post-annealing is an effective method to eliminate point defects such as oxygen vacancies in ε-Ga₂O₃ thin films and improve the performance of SBPDs. Full article

(This article belongs to the Special Issue Advanced Thin Films Technologies for Optics, Electronics, and Sensing)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Advanced Thin Films Technologies for Optics, Electronics, and Sensing

Share This Special Issue

Special Issue Editor

Special Issue Information

Published Papers (8 papers)

Research

Other

Further Information

Guidelines

MDPI Initiatives

Follow MDPI