Hydrogen Plasma Processing Research Articles

Supporting plasma processes for fabrication of n-doped nano-crystalline silicon thin film on low-cost glass substrates

Nano-crystalline silicon is an excellent material for applications in the optoelectronics industry. This intermediate material combines both the advantages of amorphous and crystalline silicon. However, the typical fabrication process of nano-crystalline silicon previously required high-quality substrates such as quartz or silicon wafers, which limited its potential applications. Recently, plasma treatments have been recognized as the most efficient and customizable methods for transforming materials. In this study, corona plasma was used to treat the low-cost glass substrates to improve their adhesion to silicon thin films. It allowed the film to become more uniform with a surface roughness of less than 10% at the thickness of about 1 μm. The conventional thermal annealing process was replaced by a high-power hydrogen plasma process, which does not cause harmful effects on the glass substrates and stimulates the amorphous-crystalline phase transition. The increasing of the crystalline fraction, which is known as the order of arrangement of silicon atoms network, affects the doped concentration as well as the electrical properties of the nc-Si:H thin films. The resulting n-doped nano-crystalline silicon thin film has a crystalline fraction of 32.8%, corresponding to a sheet resistance of 104 Ω/square.

Surface De-Fluorination and Bond Modification of CFx by High-Density Hydrogen Plasma Processing

Surface De-Fluorination and Bond Modification of CF<i>_x</i> by High-Density Hydrogen Plasma Processing

Experimental and molecular dynamics studies of an ultra-fast sequential hydrogen plasma process for fabricating phosphorene-based sensors

Low concentration phosphorene-based sensors have been fabricated using a facile and ultra-fast process which is based on an exfoliation-free sequential hydrogen plasma treatment to convert the amorphous phosphorus thin film into mono- or few-layered phosphorene sheets. These sheets have been realized directly on silicon substrates followed by the fabrication of field-effect transistors showing the low leakage current and reasonable mobility for the nano-sensors. Being capable of covering the whole surface of the silicon substrate, red phosphorus (RP) coated substrate has been employed to achieve large area phosphorene sheets. Unlike the available techniques including mechanical exfoliation, there is no need for any exfoliation and/or transfer step which is significant progress in shortening the device fabrication procedure. These phosphorene sheets have been examined using transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Raman spectroscopy and atomic-force microscopy (AFM). Electrical output in different states of the crystallization as well as its correlation with the test parameters have been also extensively used to examine the evolution of the phosphorene sheets. By utilizing the fabricated devices, the sensitivity of the phosphorene based-field effect transistors to the soluble L-Cysteine in low concentrations has been studied by measuring the FET response to the different concentrations. At a gate voltage of − 2.5 V, the range of 0.07 to 0.60 mg/ml of the L-Cysteine has been distinguishably detected presenting a gate-controlled sensor for a low-concentration solution. A reactive molecular dynamics simulation has been also performed to track the details of this plasma-based crystallization. The obtained results showed that the imparted energy from hydrogen plasma resulted in a phase transition from a system containing red phosphorus atoms to the crystal one. Interestingly and according to the simulation results, there is a directional preference of crystal growth as the crystalline domains are being formed and RP atoms are more likely to re-locate in armchair than in zigzag direction.

Optical Properties of the SiOx (x &lt; 2) Thin Films Obtained by Hydrogen Plasma Processing of Thermal Silicon Dioxide

The optical properties and composition of thermal silicon oxide thin films processed in a hydrogen electron cyclotron resonance plasma have been studied by ellipsometry, quantum-chemical modeling, and photoluminescence spectroscopy. It has been found that the plasma processing of the films leads to their oxygen depletion and the formation of nonstoichiometric oxide SiOx < 2. The parameter x of the obtained SiOx films has been determined by comparing the experimental spectral dependence of the refractive index with the dependence obtained theoretically using the ab initio calculation. It is shown that an increase in the time of processing of thermal dioxide SiO2 in a hydrogen plasma leads to an increase in the refractive index of the film, as well as in the degree of its oxygen depletion. The dependence of the parameter x of the investigated films on the hydrogen plasma processing time is plotted.

Characterization and Performance of PAni-TiO2 Photovoltaic Cells Treated by RF Plasma

Severe research attempts are still in progress to improve the performance of polyaniline (PAni) based photoactive layers as one of the cheapest materials used for manufacturing organic solar cells. Herein, polymer solar cells were fabricated with ITO/(PAni-TiO2)/Au system. The photoactive layers (PAni-TiO2) were treated with a hydrogen-plasma discharge for low processing time of 0, 3 and 5 min to enhance the synthesized solar cells efficiency. The morphology, micro structure and optical properties of the prepared samples and plasma treated nanocomposite layers were investigated and discussed. The performance of bulk heterojunction (BHJ) cell samples have been systematically investigated before and after plasma treatment. The absorption and optical band gap energy is increased after the treated PAni-TiO2 photoactive layers. It is found that, the efficiency was enhanced to 0.7% after 5 min of hydrogen plasma process compared to 0.36% for the pristine cell. The efficiency increase is ascribed to a structural change that accompanied by a rapid increase in surface roughness, which leaded to a decrease in the reflected photons and in turn an increase in the produced charge carriers.

Possibility of generating H+, or H2 +, or H3 + dominated ion beams with a 2.45 GHz permanent magnet ECR ion source.

At Peking University (PKU), experimental research as well as theoretical study on how to produce high intense H+, H2 +, or H3 + dominated ion beams with a compact permanent magnet 2.45 GHz electron cyclotron resonance (PMECR) ion source have been continuously carried out in the past few decades. Based on the comprehension of hydrogen plasma processes inside a 2.45 GHz PMECR discharge chamber, a three-phase diagram of ion fraction dominant regions that illustrates the relationship between the H+, H2 +, and H3 + ion species and working parameters was presented. Meanwhile, a numerical model based on the particle population balance equations was developed for quantitative comprehension of electron cyclotron heated hydrogen plasma. Calculated results of H+, H2 +, and H3 + fractions against gas pressure, microwave density, and wall material obtained with this numerical model agree well with the measured ones. Recently, a miniaturized ECR ion source has been developed, and a 52 mA hydrogen beam was extracted. Under the guidance of the model, H+, H2 +, and H3 + beams with a fraction of 88%, 80%, and 82%, respectively, were obtained with this miniaturized ECR ion source under suitable working parameters. A PMECR ion source for a proton therapy facility has been built at PKU recently. A 34 mA beam H+ fraction of 91% was obtained at the first attempt.

Evolution of Silicon-Nickel Nanosheets on (111) Silicon Substrates to Realize Reduced Graphene Oxide-Silicide Heterostructures

We report the evolution of ultra-thin silicon-nickel nanosheets on (111) silicon substrates using a hydrogen plasma processing. A novel stress-induced lateral-diffusion method has been employed to realize thin layers of Si-Ni flakes containing nickel quantum dots. The presence of carbon during the growth is critical to form carbon-silicon nanostructures and subsequently induce strain on (111) planes of silicon substrate. The lateral diffusion of Ni between (111) planes is enhanced at the presence of strain to realize silicon-nickel sheets. These sheets have been examined using TEM, AFM, SEM, EDS, XRD, Raman spectroscopy and photo-luminescence analyses. In addition, we have used graphene-oxide (GO) foils to place on the surface of these layers. By a hydrogen plasma treatment, the GO foil is reduced into rGO on silicon-nickel sheets. Finally, an rGO/Si-Ni nanosheet hetero-structures on (111) silicon substrates is formed. To have electrical contacts to the top rGO layer, we have used an indium tin oxide (ITO)-coated glass to complete the device. A preliminary light emission device has been realized and tested.

Characterization of Al-doped ZnO nanorods grown by chemical bath deposition method

Introduction: In recent years a metal oxide semiconductors have been paid attention due to their excellent chemical and physical properties.ZnO (Zinc oxide) is considered as one of the most attractive semiconductor materials for implementation in photo-detectors, gas sensors, photonic crystals, light emitting diodes, photodiodes, and solar cells, due to its novel electrical and optoelectronic properties. There are different uses of metal oxide semiconductors such us, UV photodetectors which are useful in space research’s, missile warning systems, high flame detectors, air quality spotting, gas sensors, and precisely calculated radiation for the treatment of UV-irradiated skin. ZnO is a metal oxide semiconductors and it is used as a transparent conducting oxide thin film because it has the best higher thermal stability, best resistance against the damage of hydrogen plasma processing and relatively cheaper if one compares it with ITO. Materials and Methods: On glass substrates, Al-doped ZnO (AZO) nanorods have been grown by a low -cost chemical bath deposition (CBD) method at low temperature. The seed layer of ZnO was coated on glass substrates. The effect of the Al-doping on the aligned, surface morphology, density, distribution, orientation and structure of ZnO nanorods are investigated. The Al-doping ratios are 0%, 0.2%, 0.8% and 2%. The Aluminum Nitrate Nonahydrate (Al (NO3)3.9H2O) was added to the growth solution, which is used as a source of the aluminum dopant element. The morphology and structure of the Al-doped ZnO nanorods are characterized by field emission scanning electron microscopy (FESEM) and high-resolution X-ray diffractometer (XRD). using the radio RF (Radio frequency) magnetron technique. Results and Discussion: The results show that the Al-doping have remarkable effects on the topography parameters such as diameter, distribution, alignment, density and nanostructure shape of the ZnO nanorods. These topography parameters have proportionally effective with increases of the Al-doping ratio. Also, X-ray diffraction results show that the Al-doping ratio has a good playing role on the nanostructure orientation of the ZnO nanorods. Conclusions: The Aluminum Nitride Nanohydrate considered as a good Aluminu source for doping ZnONR. It is clear from FESEM results that the Al-doping of ZnONR has a remarkable effect on the surface topography of nanorods for all aluminum doping ratios. From XRD patterns, it concludes that as the Al-doping ratio increases, the reorientation of the nanostructure of ZnO increases towards [100] direction. The results obtained also have shown that the average diameter of a nanorod is increased with increasing the ratio of Al-doping.

Band alignment at the CdTe/InSb (001) heterointerface

CdTe/InSb heterojunctions have attracted considerable attention because of its almost perfect lattice match and the presence of nonoctal interface bonding. This heterojunction is a model heterovalent system to describe band offsets. In this research, molecular beam epitaxy was used to deposit a ∼5 nm epitaxial CdTe (001) layer on an InSb (001) surface. Monochromatic x-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy were used to characterize the electronic states of clean InSb and CdTe surfaces and CdTe/InSb (001) heterostructures. A room temperature remote hydrogen-plasma process was used to clean the surfaces prior to characterization. The results indicate a valence band offset of 0.89 eV and a type-I (straddling gap) alignment for the CdTe/InSb (001) heterostructure interface. In addition, In-Te bonding was observed at the interface. Downward band bending of the InSb is attributed to excess electrons introduced by nonoctal In-Te interface bonding.

Non-thermal hydrogen plasma processing effectively increases the antibacterial activity of graphene oxide

Graphene-based materials (GMs) are promising antibacterial agents which provide an alternative route to treat pathogenic bacteria with resistance to conventional antibiotics. To further improve their antibacterial activity, many methods have been developed to functionalize the GMs with chemicals. However, the application of additional chemicals may pose potential risks to the environment and human being. Herein, a radio-frequency-driven inductively coupled non-thermal hydrogen plasma was used to treat and reduce graphene oxide (GO) without using any other chemicals, and we found that the plasma-reduced GO (prGO) is with significantly higher bactericidal activity against Escherichia coli. The mechanism of the increased antibacterial activity of prGO is due to that plasma processing breaks down the GO sheets into smaller layers with more rough surface defects, which can thus induce more destructive membrane damages to the bacteria. This work sets another good example, showing that plasma processing is a green and low-cost alternative for GM modification for biomedical applications.

Hydrogen Treatment Technology of Ti-based Nano-Diamond Field Emission Cathode

Abstract The field emission cathode coating of nano-diamond on titanium substrate was prepared by electrophoretic deposition, the hydrogen plasma process was carried out after heat treatment, and then the microstructure, field emission properties and the luminescence performance of the samples were characterized. The results show that the adsorption of H + and the etching of H + collectively affect the morphology of diamond coating. Deficient hydrogen treatment can't reach the requirement and excessive hydrogen treatment can lead to serious etching for the diamond coating, resulting in worse field emission properties of the coating and luminescence effect. The appropriate hydrogen treatment is helpful to improve the field emission properties and luminescence effect. Finally, the field emission mechanism of nano-diamond coating on titanium substrate was discussed, and the reasons of luminescence effect difference were explained.

Understanding hydrogen plasma processes based on the diagnostic results of 2.45 GHz ECRIS at Peking University**Project supported by the National Natural Science Foundation of China (Grant Nos. 11175009 and 11575013).

Optical emission spectroscopy (OES), as a simple in situ method without disturbing the plasma, has been performed for the plasma diagnosis of a 2.45 GHz permanent magnet electron cyclotron resonance (PMECR) ion source at Peking University (PKU). A spectrum measurement platform has been set up with the quartz-chamber electron cyclotron resonance (ECR) ion source [Patent Number: ZL 201110026605.4] and experiments were carried out recently. The electron temperature and electron density inside the ECR plasma chamber have been measured with the method of line intensity ratio of noble gas. Hydrogen plasma processes inside the discharge chamber are discussed based on the diagnostic results. What is more, the superiority of the method of line intensity ratio of noble gas is indicated with a comparison to line intensity ratio of hydrogen. Details will be presented in this paper.

Hydrogen Plasma Processing of Iron Ore

Iron is currently produced by carbothermic reduction of oxide ores. This is a multiple-stage process that requires large-scale equipment and high capital investment, and produces large amounts of CO2. An alternative to carbothermic reduction is reduction using a hydrogen plasma, which comprises vibrationally excited molecular, atomic, and ionic states of hydrogen, all of which can reduce iron oxides, even at low temperatures. Besides the thermodynamic and kinetic advantages of a hydrogen plasma, the byproduct of the reaction is water, which does not pose any environmental problems. A review of the theory and practice of iron ore reduction using a hydrogen plasma is presented. The thermodynamic and kinetic aspects are considered, with molecular, atomic and ionic hydrogen considered separately. The importance of vibrationally excited hydrogen molecules in overcoming the activation energy barriers, and in transferring energy to the iron oxide, is emphasized. Both thermal and nonthermal plasmas are considered. The thermophysical properties of hydrogen and argon–hydrogen plasmas are discussed, and their influence on the constriction and flow in the of arc plasmas is considered. The published R&D on hydrogen plasma reduction of iron oxide is reviewed, with both the reduction of molten iron ore and in-flight reduction of iron ore particles being considered. Finally, the technical and economic feasibility of the process are discussed. It is shown that hydrogen plasma processing requires less energy than carbothermic reduction, mainly because pelletization, sintering, and cokemaking are not required. Moreover, the formation of the greenhouse gas CO2 as a byproduct is avoided. In-flight reduction has the potential for a throughput at least equivalent to the blast furnace process. It is concluded that hydrogen plasma reduction of iron ore is a potentially attractive alternative to standard methods.

Activating basal-plane catalytic activity of two-dimensional MoS2 monolayer with remote hydrogen plasma

Two-dimensional layered transition metal dichalcogenide (TMD) materials such as Molybdenum disufide (MoS2) have been recognized as one of the low-cost and efficient electrocatalysts for hydrogen evolution reaction (HER). The crystal edges that account for a small percentage of the surface area, rather than the basal planes, of MoS2 monolayer have been confirmed as their active catalytic sites. As a result, extensive efforts have been developing in activating the basal planes of MoS2 for enhancing their HER activity. Here, we report a simple and efficient approach—using a remote hydrogen-plasma process—to creating S-vacancies on the basal plane of monolayer crystalline MoS2; this process can generate high density of S-vacancies while mainly maintaining the morphology and structure of MoS2 monolayer. The density of S-vacancies (defects) on MoS2 monolayers resulted from the remote hydrogen-plasma process can be tuned and play a critical role in HER, as evidenced in the results of our spectroscopic and electrical measurements. The H2-plasma treated MoS2 also provides an excellent platform for systematic and fundamental study of defect-property relationships in TMDs, which provides insights for future applications including electrical, optical and magnetic devices.

The application of plasma treatment for Ti3+ modified TiO2 nanowires film electrode with enhanced lithium-storage properties

Hydrogen plasma processing offers improved thermodynamics, kinetics and optimal reductive environment over conventional, thermal processing. In the current work, we report the first demonstration of hydrogen plasma treatment as a simple and effective strategy to fundamentally improve the performance of TiO2 nanowires for lithium storage. In comparison to pristine TiO2 nanowires, the hydrogen plasma treated TiO2 (H-TiO2) samples show substantially enhanced electron conductivity due to Ti3+ introduction, which are successfully confirmed by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and four-probe testing instrument. More importantly, the H-TiO2 electrode exhibits a higher rate capability and better reversibility. At charge/discharge current of 200, 800, 1600 and 3350mA/g (10C), the discharge capacity of the H-TiO2 electrode is 200, 162, 144 and 130mAhg−1. After 200 cycles at current of 200mA/g, its capacity retention was 99.8% with almost no capacity fading. The electrochemical impedance spectra analyses and theoretical energy calculations using density functional theory (DFT) finally suggest that the hydrogenation process not only improves electronic conductivity due to the formation of Ti3+ in the hydrogenation process but also dramatically augments lithium-ion mass transport within the crystalline lattice due to the introduction of Ti3+.

Reduction of Copper Oxide by Low-Temperature Hydrogen Plasma

The paper presents experimental results of reduction of cupric oxide (CuO) by low-temperature hydrogen plasma in a microwave-assisted plasma set-up. The experiments were carried out at low microwave powers in the range of 600–750 W and low hydrogen flow rates in the range of 0.833 × 10−6 to 2.5 × 10−6 m3 s−1. In all the experiments for reduction of CuO with hydrogen plasma, an initial induction period was observed in the kinetic plots. The induction period decreases with increase in pressure or temperature. The induction period leads to the formation of active sites for adsorption of H2. After the induction period, fast autocatalytic reduction takes place followed by a sluggish period towards the end. The reduction process proceeds in sequential steps through the formation of sub-oxides. The kinetic data fits the Avrami-Erofeev equation with ‘n’ value close to 3. The resultant activation energy measured during hydrogen plasma processing is around 75.64 kJ mol−1. This is lower compared to activation energies measured by other methods of reduction indicating a clear advantage.

Plasma functionalization for cyclic transition between neutral and charged excitons in monolayer MoS2.

Monolayer MoS2 (1L-MoS2) has photoluminescence (PL) properties that can greatly vary via transition between neutral and charged exciton PLs depending on carrier density. Here, for the first time, we present a chemical doping method for reversible transition between neutral and charged excitons of 1L-MoS2 using chlorine-hydrogen-based plasma functionalization. The PL of 1L-MoS2 is drastically increased by p-type chlorine plasma doping in which its intensity is easily tuned by controlling the plasma treatment duration. We find that despite their strong adhesion, a post hydrogen plasma treatment can very effectively dedope chlorine adatoms in a controllable way while maintaining robust structural integrity, which enables well-defined reversible PL control of 1L-MoS2. After exhaustive chlorine dedoping, the hydrogen plasma process induces n-type doping of 1L-MoS2, degrading the PL further, which can also be recovered by subsequent chlorine plasma treatment, extending the range of tunable PL into a bidirectional regime. This cyclically-tunable carrier doping method can be usefully employed in fabricating highly-tunable n- and p-type domains in monolayer transition-metal dichalcogenides suitable for two-dimensional electro-optic modulators, on-chip lasers, and spin- and valley-polarized light-emitting diodes.

Surface modification of optical materials with hydrogen plasma for fabrication of Bragg gratings.

We investigate the hydrogen plasma process as a route for creating Bragg gratings (BGs) on optoelectronic materials such as undoped lithium niobate (LiNbO(3)), proton-exchanged LiNbO(3), and soda-lime glass. Photopatterns (periodic modulations, Λ=323-2000 nm) were created on those substrates and the hydrogen plasma process was investigated for its ability to transfer the microstructures and the underlying mechanisms involved in this process. The diffraction efficiency and surface topology of the BG were characterized, as well as the optical properties of corresponding bulk materials undergoing the same plasma treatment. It is shown that the hydrogen plasma treatment changes the complex refractive index and modifies the surface topology with a volume expansion in the near-surface region, and both features are connected to the appearance of structural defects in the materials. The hydrogen plasma offers unique flexibility and advantages that can be explored for the fabrication of integrated photonic components.

VUV diagnostics of electron impact processes in low temperature molecular hydrogen plasma

Novel methods for diagnostics of molecular hydrogen plasma processes, such as ionization, production of high vibrational levels, dissociation of molecules via excitation to singlet and triplet states and production of metastable states, are presented for molecular hydrogen plasmas in corona equilibrium. The methods are based on comparison of rate coefficients of plasma processes and optical emission spectroscopy of lowest singlet and triplet transitions, i.e. Lyman band () and molecular continuum (), of the hydrogen molecule in the VUV wavelength range. Comparison of rate coefficients of spin-allowed and/or spin-forbidden excitations reduces the uncertainty caused by the non-equilibrium distributions of electron energy and molecular vibrational level, which are typically known poorly in plasma sources. The described methods are applied to estimate the rates of various plasma processes in a filament arc discharge.

Ultralow field emission from thinned, open-ended, and defected carbon nanotubes by using microwave hydrogen plasma processing

Ultralow field emission is achieved from carbon nanotubes (CNTs) by using microwave hydrogen plasma processing. After the processing, typical capped CNT tips are removed, with thinned, open-ended, and defected CNTs left. Structural analyses indicate that the processed CNTs have more SP3-hybridized defects as compared to the pristine ones. The morphology of CNTs can be readily controlled by adjusting microwave powers, which change the shape of CNTs by means of hydrogen plasma etching. Processed CNTs with optimal morphology are found to have an ultralow turn-on field of 0.566V/μm and threshold field of 0.896V/μm, much better than 0.948 and 1.559V/μm of the as-grown CNTs, respectively. This improved FE performance is ascribed to the structural changes of CNTs after the processing. The thinned and open-ended shape of CNTs can facilitate electron tunneling through barriers and additionally, the increased defects at tube walls can serve as new active emission sites. Furthermore, our plasma processed CNTs exhibit excellent field emission stability at a large emission current density of 10.36mA/cm2 after being perfectly aged, showing promising prospects in applications as high-performance vacuum electron sources.