Fluorine Plasma Treatment Research Articles

Plasma fluorination of vertically aligned carbon nanotubes: functionalization and thermal stability.

Grafting of fluorine species on carbon nanostructures has attracted interest due to the effective modification of physical and chemical properties of the starting materials. Various techniques have been employed to achieve a controlled fluorination yield; however, the effect of contaminants is rarely discussed, although they are often present. In the present work, the fluorination of vertically aligned multiwalled carbon nanotubes was performed using plasma treatment in a magnetron sputtering chamber with fluorine diluted in an argon atmosphere with an Ar/F2 ratio of 95:5. The effect of heavily diluted fluorine in the precursor gas mixture is investigated by evaluating the modifications in the nanotube structure and the electronic properties upon plasma treatment. The existence of oxygen-based grafted species is associated with background oxygen species present in the plasma chamber in addition to fluorine. The thermal stability and desorption process of the fluorine species grafted on the carbon nanotubes during the fluorine plasma treatment were evaluated by combining different spectroscopic techniques.

Passivation of oxide traps and interface states in GaAs metal-oxide-semiconductor capacitor by LaTaON passivation layer and fluorine incorporation

GaAs metal-oxide-semiconductor capacitor with TaYON/LaTaON gate-oxide stack and fluorine-plasma treatment is fabricated and compared with its counterparts without the LaTaON passivation interlayer or the fluorine treatment. Experimental results show that the sample exhibits better characteristics: low interface-state density (8 × 1011 cm−2/eV), small flatband voltage (0.69 V), good capacitance-voltage behavior, small frequency dispersion, and small gate leakage current (6.35 × 10−6 A/cm2 at Vfb + 1 V). These should be attributed to the suppressed growth of unstable Ga and As oxides on the GaAs surface during gate-oxide annealing by the LaTaON interlayer and fluorine incorporation, and the passivating effects of fluorine atoms on the acceptor-like interface and near-interface traps.

Normally-off AlGaN/GaN high-electron-mobility transistor on Si(111) by recessed gate and fluorine plasma treatment

We have studied the efficiency of using both recessed gate and fluorine plasma treatment to achieve normally-off high-electron-mobility transistor (HEMT). It is found that, by a simple recess process, one cannot achieve normally off device with high drain current because of gate leakage problem after inductively coupled plasma (ICP) etching for recessed structure. The proper method is adding fluorine treatment based on recess gate. The normally off GaN HEMTs with recess gate and fluorine treatment show very good performance. It is found that the threshold voltages can be shifted to +1.1 V, and the drain current at VGS − Vth = 2 V and VDS = 20 V was 218 mA/mm.

Improved performance of Pd/WO3/SiC Schottky-diode hydrogen gas sensor by using fluorine plasma treatment

A high-performance Pd/WO3/SiC Schottky-diode hydrogen gas sensor was fabricated by using fluorine plasma treatment on the WO3 film. From the electrical measurements under various hydrogen concentrations and temperatures, the plasma-treated sensor exhibited a maximum barrier-height change of 279 meV and a static gas sensitivity of more than 30 000, which is 30 times higher than that of the untreated sensor. This significant improvement is attributed to the larger adsorption area caused by the plasma-roughened WO3 film and the lower baseline leakage current induced by fluorine passivation of oxide traps. Additionally, the kinetics analysis and hydrogen coverage of the devices were studied to demonstrate the temperature dependence of the gas sensing behaviors. The hydrogen adsorption enthalpy at the Pd-WO3 interface significantly decreased from −31.2 kJ/mol to −57.6 kJ/mol after the plasma treatment. Therefore, the adsorption process on the plasma-treated sample is much easier and the suppression of sensing properties is more obvious at elevated temperatures above 423 K.

Trap states in enhancement-mode double heterostructures AlGaN/GaN high electron mobility transistors with different GaN channel layer thicknesses

This is the report on trap states in enhancement-mode AlGaN/GaN/AlGaN double heterostructures high electron mobility transistors by fluorine plasma treatment with different GaN channel layer thicknesses. Compared with the thick GaN channel layer sample, the thin one has smaller 2DEG concentration, lower electron mobility, lower saturation current, and lower peak transconductance, but it has a higher threshold voltage of 1.2 V. Deep level transient spectroscopy measurements are used to obtain the accurate capture cross section of trap states. By frequency dependent capacitance and conductance measurements, the trap state density of (1.98–2.56) × 1012 cm−2 eV−1 is located at ET in a range of (0.37–0.44) eV in the thin sample, while the trap state density of (2.3–2.92) × 1012 cm−2 eV−1 is located at ET in a range of (0.33–0.38) eV in the thick one. It indicates that the trap states in the thin sample are deeper than those in the thick one.

Passivation of oxide traps in gallium arsenide (semiconductor) metal-oxide-semiconductor capacitor with high-k dielectric by using fluorine incorporation

Gallium arsenide (semiconductor) (GaAs) metal-oxide-semiconductor capacitors with fluorine-incorporated TaHfON as gate dielectric are fabricated by pre- or postdeposition fluorine plasma treatment and their electrical and physical properties are compared with a control sample without the treatment. Among the three devices, the one with postdeposition fluorine treatment exhibits better characteristics: low oxide-charge density (−3.5 × 1012 cm−2), low interface-state density (2.2 × 1012 cm−2eV−1), small flatband voltage (0.7 V), small hysteresis (45 mV), and good capacitance–voltage behavior. These should be attributed to (1) the passivating effects of fluorine atoms on the acceptorlike interface and near-interface traps, and (2) fluorine-induced suppressed growth of unstable Ga and As oxides on the GaAs substrate during postdeposition annealing.

Repulsive effects of hydrophobic diamond thin films on biomolecule detection

The repulsive effect of hydrophobic diamond thin film on biomolecule detection, such as single-nucleotide polymorphisms and human immunodeficiency virus type 1 trans-activator of transcription peptide protein detection, was investigated using a mixture of a fluorine-, amine-, and hydrogen-terminated diamond surfaces. These chemical modifications lead to the formation of a surface that effectively resists the nonspecific adsorption of proteins and other biomolecules. The effect of fluorine plasma treatment on elemental composition was also investigated via X-ray photoelectron spectroscopy (XPS). XPS results revealed a fluorocarbon layer on the diamond thin films. The contact angle measurement results indicated that the fluorine-treated diamond thin films were highly hydrophobic with a surface energy value of ∼25mN/m.

Fluorine plasma treatment of bare and nitrilotris(methylene)triphosphonic acid (NP) protected aluminum: an XPS and ToF-SIMS study

Nitrilotris(methylene)triphosphonic acid (NP) is a technologically important molecule that has been used for years as a corrosion inhibitor and/or adhesion promoter on aluminum and other metal surfaces. However, to the best of our knowledge, the detailed surface characterization of NP adsorbed on aluminum, or on any other surface, has not been reported. Herein, we report an X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis of a series of untreated and NP-coated aluminum substrates that were exposed to the downstream products of a fluoroalkane + oxygen plasma for different amounts of time (from 0 to 20 s). As indicated by P 2p, N 1s, Al 2p, O 1s, and F 1s narrow scans, even a 4-s plasma treatment significantly damages the NP protective layer and converts the native aluminum oxide into aluminum oxyfluoride. Heat treatment of the fluorine plasma-treated samples in the air substantially converts the aluminum oxyfluoride back to aluminum oxide, while similar heating under vacuum results in little change to the materials. A slow loss of fluorine from the samples occurs over the course of weeks when they are stored in the air. A ToF-SIMS analysis reveals sets of signals that are consistent with no surface treatment, NP treatment, or fluorine plasma treatment. A principal component analysis of the negative ion ToF-SIMS spectra from the samples shows the expected differentiation of the samples. Copyright © 2014 John Wiley & Sons, Ltd.

Self-Passivation by Fluorine Plasma Treatment and Low-Temperature Annealing in SiGe Nanowires for Biochemical Sensors

Nanowires are widely used as highly sensitive sensors for electrical detection of biological and chemical species. Modifying the band structure of strained-Si metal-oxide-semiconductor field-effect transistors by applying the in-plane tensile strain reportedly improves electron and hole mobility. The oxidation-induced Ge condensation increases the Ge fraction in a SiGe-on-insulator (SGOI) and substantially increases hole mobility. However, oxidation increases the number of surface states, resulting in hole mobility degradation. In this work, 3-aminopropyltrimethoxysilane (APTMS) was used as a biochemical reagent. The hydroxyl molecule on the oxide surface was replaced by the methoxy groups of the APTMS molecule. We proposed a surface plasma treatment to improve the electrical properties of SiGe nanowires. Fluorine plasma treatment can result in enhanced rates of thermal oxidation and speed up the formation of a self-passivation oxide layer. Like a capping oxide layer, the self-passivation oxide layer reduces the rate of follow-up oxidation. Preoxidation treatment also improved the sensitivity of SiGe nanowires because the Si-F binding was held at a more stable interface state compared to bare nanowire on the SiGe surface. Additionally, the sensitivity can be further improved by either the N2 plasma posttreatment or the low-temperature postannealing due to the suppression of outdiffusion of Ge and F atoms from the SiGe nanowire surface.

DC and RF characteristics of enhancement-mode InAlN/GaN HEMT with fluorine treatment

We report an enhancement-mode InAlN/GaN HEMT using a fluorine plasma treatment. The threshold voltage was measured to be +0.86 V by linear extrapolation from the transfer characteristics. The transconductance is 0 mS/mm at VGS = 0 V and VDS = 5 V, which shows a truly normal-off state. The gate leakage current density of the enhancement-mode device shows two orders of magnitude lower than that of the depletion-mode device. The transfer characteristics of the E-mode InAlN/GaN HEMT at room temperature and high temperature are reported. The current gain cut-off frequency (fT) and the maximum oscillation frequency (fmax) of the enhancement-mode device with a gate length of 0.3 μm were 29.4 GHz and 37.6 GHz respectively, which is comparable with the depletion-mode device. A classical 16 elements small-signal model was deduced to describe the parasitic and the intrinsic parameters of the device.

Influence of Fluorine Plasma Treatment of TiO2Films on the Behavior of Dye Solar Cells Employing the Co(II)/(III) Redox Couple

Fluorine plasma treatment was investigated as an appropriate means for the surface modification of TiO2 thin film electrodes and the optimization of their performance as photoanodes in dye solar ce...

Increasing the creation yield of shallow single defects in diamond by surface plasma treatment

Single Nitrogen-Vacancy (NV) centers in diamond close to the crystal surface are very promising magnetic field sensors with very high sensitivity. Here, we report the enhanced creation of very shallow (less than 3 nm below the diamond surface) NV centers by using fluorine and oxygen plasma treatment. We observe a four fold increase—from 0.11% to about 0.45% in the production yield when the sample surface is terminated with fluorine or oxygen atoms. This effect is explained by the stabilization of the NV's negative charge state which is influenced by the various defects present on the diamond surface.

Effect of fluorine plasma treatment with chemically reduced graphene oxide thin films as hole transport layer in organic solar cells

The inorganic materials such as V2O5, MoO3 and WO3 were investigated to replace PEDOT:PSS as hole transport layer (HTL) in organic electronic devices such as organic solar cells (OSCs) and organic lighting emission diodes. However, these methods require vacuum techniques that are long time process and complex. Here, we report about plasma treatment with SF6 and CF4 using reactive ion etching on reduced graphene oxide (rGO) thin films that are obtained using an eco-friendly method with vitamin C. The plasma treated rGO thin films have dipoles since they consist of covalent bonds with fluorine on the surface of rGO. This means it is possible to increase the electrostatic potential energy than bare rGO. Increased potential energy on the surface of rGO films is worth applying organic electronic devices as HTL such as OSCs. Consequently, the power conversion efficiency of OSCs increased more than the rGO films without plasma treatment.

Oxygen‐rich coating promotes binding of proteins and endothelialization of polyethylene terephthalate polymers

The formation of endothelial cell monolayer on prosthetic implants has not sufficiently explored. The main reasons leading to the development of thrombosis and/or intimal hyperplasia is the lack of endothelialization. In the present work, we have studied the influence of oxygen and fluorine plasma treatment of polyethylene terephthalate (PET) polymers on human microvascular endothelial cell adhesion and proliferation. We characterized the polymer surface, wettability, and oxidation potential upon plasma treatment. Moreover, binding of serum and media compounds on PET surface was monitored by Quartz crystal microbalance method, X-ray photoelectron spectroscopy, and atomic force microscopy. Cell adhesion and morphology was assessed by light and scanning electron microscopy. The influence of plasma treatment on induction of cellular oxidative stress and cell proliferation was evaluated. The results obtained showed that treatment with oxygen plasma decreased the oxidation potential of the PET surface and revealed the highest affinity for binding of serum components. Accordingly, the cells reflected the best adhesion and morphological properties on oxygen-treated PET polymers. Moreover, treatment with oxygen plasma did not induce intracellular reactive oxygen species production while it stimulated endothelial cell proliferation by 25% suggesting the possible use of oxygen plasma treatment to enhance endothelialization of synthetic vascular grafts.

Fluorination of Al2O3 blocking layer for improving the performance of metal‐oxide‐nitride‐oxide‐silicon flash memory

AbstractThe characteristics of Al2O3 film grown by atomic‐layer deposition as blocking layer with and without fluorine plasma treatment were investigated based on a capacitor structure of Al/Al2O3/TaON/SiO2/Si. The physical structure was studied by transmission electron microscopy, and the chemical composition of the blocking layer was analyzed by X‐ray photoelectron spectroscopy and secondary ion mass spectroscopy. Moreover, the surface roughness of the blocking layer was investigated by atomic force microscopy. Compared with a capacitor with Al2O3 blocking layer, the one with fluorinated Al2O3 displayed higher programming/erasing speeds, better endurance property and better charge retention characteristic because the fluorination could reduce excess oxygen and traps in the blocking layer, thus forming a larger barrier height at the interface between the charge‐trapping layer and the blocking layer. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

An Ultrathin AlGaN Barrier Layer MIS-HEMT Structure for Enhancement-Mode Operation

A GaN-based enhancement-mode (E-Mode) metal-insulator-semiconductor (MIS) high electron mobility transistor (HEMT) with a 2 nm/5 nm/1.5 nm-thin GaN/AlGaN/AlN barrier is presented. We find that the formation of a two-dimensional electron gas (2DES) in the GaN/AlGaN/AlN/GaN heterostructure can be controlled by the presence of the plasma-enhanced chemical-vapor deposition (PECVD) Si3N4 on the barrier layer, and the degree of decrease in sheet resistance Rsh is dependent on the Si3N4 thickness. We choose 13 nm Si3N4 as the gate insulator to decrease gate current and to improve the threshold voltage of devices. With selective etching of the passivation Si3N4 under gate and over fluorine plasma treatment, the MIS-HEMT exhibits a high threshold voltage of 1.8 V. The maximum drain current Id,max and the maximum transconductance are 810 mA/mm and 190 mS/mm, respectively. The devices show a wide operation range of 4.5 V.

Analysis and reduction of the gate forward leakage current in AlGaN/GaN HEMTs employing energy-band modulation technology

The gate forward leakage current in AlGaN/GaN High Electron Mobility Transistors (HEMTs) is investigated. It is known that the gate forward leakage current reduces as effective electron barrier height (qϕb) grows. Therefore, an energy-band modulation (EBM) technology using fluorine-plasma treatment or P-type doping is presented to introduce the negative fixed charges into AlGaN layer. The introduced negative fixed charges can modulate the conduction-band profile in AlGaN layer, resulting in higher effective electron barrier. An analytical model is proposed to illustrate the conduction-band profile. It is suggested that as introduced negative fixed charge concentration exceeds a critical value, an additional electron barrier (qΔϕb) is achieved, contributing to reducing the gate forward leakage current. Based on this theory, the fluorine-plasma treatment is implemented to carry out EBM technology in this work. Experimental results confirm that the additional electron barrier qΔϕb of 0.3eV is obtained for the fluorine-plasma treatment condition of 60W and 120s. Thus, the gate forward leakage current is decreased by one order magnitude lower than that of HEMT device without fluorine-plasma treatment. The analytical results are in good agreement with numerical simulation and experiment results.

High Priority of Nanocrystalline Diamond as a Biosensing Platform

Here we report the performance of surface functionalized diamond surfaces as biosensing platform for human immunodeficiency virus trans-activator of transcription (HIV-Tat) peptide detection. Comparative investigations were conducted on nanocrystalline diamond (NCD) and polycrystalline diamond (PCD) films. Scanning electron microscopy (SEM) images revealed the morphology differences between NCD and PCD films. X-ray photoelectron spectroscopy (XPS) data showed that functional components and corresponding coverages, demonstrating denser carboxyl acid groups and fluorinated groups on NCD than that PCD films after UV/ozone and fluorine plasma treatment respectively. Contact angle results showed the differences in surface wettability and free energy between functionalized NCD and PCD biosensors. Fluorescence observations confirmed that higher biosensing performance can be obtained on NCD biosensors with high sensitivity selectivity, and stability. The NCD films with denser surface coverages of functionalizations made NCD films much more priority as an effective biosensing candidate than PCD films.

Ice friction of ultra-high molecular weight polyethylene: The effects of fluorine additives and plasma (PECVD) treatment

Various new polymer additives were blended into ultra-high molecular weight polyethylene (UHMWPE) in order to examine their effects on ice friction. A certain type of a new liquid perfluoropolyalkylether was proven to improve the surface and sliding characteristics of UHMWPE on ice. It was shown for the first time that an optimum amount of additive (about 2.5wt%) reduces the ice friction coefficient significantly at temperatures greater than −7°C. Moreover, plasma chemical vapour deposition of UHMWPE under a fluorinated gas was also utilized to examine its effect on its surface and sliding characteristics. This treatment increased the static water contact angle, from 85° to 138° and decreased the friction coefficient to about 25% at the highest sliding velocity of 1.96m/s.

Effect of O2, Ar/H2 and CF4 plasma treatments on the structural and dielectric properties of parylene-C thin films

Plasma treatment of parylene-C surfaces not only causes structural modification of the surface during the plasma exposure, but also leaves active sites on the surfaces, which decreases the dielectric properties. In this work, the effects of oxygen, argon/hydrogen and fluorine plasma treatment on the surface and dielectric properties of parylene-C thin films were investigated using Fourier transform-IR spectroscopy, energy dispersive x-ray analysis and dielectric spectroscopy measurement. The results showed that the plasma treatment successfully introduced fluorine functional groups and decreased the oxygen content on the parylene-C surfaces. It appears that the replacement of oxygen and hydrogen by fluorine atoms led to a decrease in the local orientational polarizability of parylene-C. Consequently, it was found that the atmospheric fluorine plasma-treated parylene-C possessed lower dielectric characteristics, 16% lower than the untreated parylene-C at industrial frequencies (10–104 Hz). The Ar/H2 plasma treatment is also an experimental means to reduce the dielectric properties and to decrease the oxygen content in parylene-C. In contrast, the oxygen plasma increases the dielectric constant and can cause deterioration of the leakage current associated with carbon depletion showing C–O and C=O formation. CF4 and Ar/H2 plasma treatment does not significantly affect the long molecular motion (α-relaxation). Additional extrinsic oxygen content due to O2 plasma treatment in the parylene-C structure reproduces the increase in the time constant of both the short (β-relaxation) and long molecular motion.