Influence of Thickness of Field Emission Characteristics of Nanometre Boron Nitride Thin Films

Nanometre boron nitride (BN) thin films with various thickness (54-135nm) were prepared on Si(100) by rf magnetic sputtering physical vapour deposition. The field emission characteristics of the BN thin films were measured in an ultrahigh vacuum system. A threshold electric field of 11V/μm and the highest emission current density of 240μA/cm^2 at an electric field of 23V/μm were obtained for the about 54-nm-thick BN film. The threshold electric field increases with increasing the thickness in the nanometre range. The Fowler-Nordheim plots show that electrons were emitted from BN to vacuum by tunnelling through the potential barrier at the surface of BN thin films.     

Field Emission Characteristics of BN Films Treated with H2 and O2 Plasma

BN films were synthesized on the (100)-oriented surface of n-Si (0.008-0.02Ωm) by rf magnetron sputtering physical vapor deposition (PVD). A BN film was first treated with H2 plasma for 60 rain and then the H2 treated sample was treated with O2 plasma for 15rain. The films were characterizes by using Fourier transform infrared spectra (FTIR) and atomic force microscopy (AFM). The field emission characteristics of BN films were measured in an ultrahigh vacuum system. A turn-on electric field of 8 V/μm and a current of 400μA/cm^2 were obtained for the BN film treated with H2 plasma. The results show that the surface plasma treatment makes no apparent influence on the surface morphology of the BN films. The transformations of the sample emission characteristics have to do with the surface negative electron affinity (NEA) of the films possibly. The turn-on electric field of the BN film treated with H2 plasma is lower than that without treatment, which possibly attributes to the surface NEA effect. The surface NEA of the H2 treated BN film is lost after O2 plasma treatment.     

Thin film micro-scaled cold cathode structures of undoped and Si-doped AlN grown on SiC substrate with low turn-on voltage

The field emission characteristics of the AlN thin films with micro-scaled cold cathode structures are tested in the high vacuum system. The aluminum nitride(AlN) thin films with a thickness of about 100 nm are prepared on the n-type 6H-SiC(0001) substrate at 1100°C by metal organic chemical vapor deposition(MOCVD) under low pressure. The I–V curves and surface micro-images of undoped and Si-doped AlN films are investigated. From the I–V and Fowler–Nordheim plots,it can be seen that the Si-doped Al N shows better field emission characteristics compared with the undoped AlN sample.The obtained turn-on field is 6.7 V/μm and the maximum emission current density is 154 m A/cm2 at 69.3 V for the Sidoped AlN film cathode after proper surface treatment. It is proposed that the relatively low electric resistivity of Si-doped Al N films is significant for electron migration to the surface region, and their rougher surface morphology is beneficial to a higher local electric field enhancement for the field emission.     

A New Method to Prepare Boron Nitride Thin Films

We report a new method to prepare boron nitride (BN) thin films on Si (100) substrates in an Ar-N2-BCl3-H2 gas system by magnetron arc enhanced plasma chemical vapour deposition. Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD) are used to characterize the films. The FTIR spectra show that the deposited boron nitride films experienced a transition from pure h-BN phase to a cubic-containing phase with the variation of arc current ranging from IOA to 18A. The BN film with 42% c-BN was obtained without substrate bias voltage. In the gas system of Ar-N2-BCl3-H2, h-BN can be preferentially etched by chlorine. The chemical etching effect of chlorine allows the formation of c-BN without substrate bias voltage, which may develop a new perspective for the deposition of high quality c-BN film with low stress.     

STRESS ANALYSIS IN CUBIC BORON NITRIDE FILMS BY X-RAY DIFFRACTION USING sin2 ψ METHOD

The boron nitride (BN) films containing cubic boron nitride (c-BN) and hexagonal boron nitride (h-BN) were prepared by radio frequency a ssisted thermal filament chemical vapor deposition. The stress and strain in BN films were investigated by X-ray diffraction analysis using the sin² ψ method. The results showed that both c-BN and h-BN in the same film have similar values of elastic strain, however, the compressive stress in c-BN is much greater than that in h-BN for the same film. Both stress and strain gradually decre ased with the increase of substrate temperature (T_s). The effective stress in the films calculated by the effective stress model increased with the increase of T_s. Furthermore, the dependence of effective stress in the films on T_s was also investigated.     

STRESS ANALYSIS IN CUBIC BORON NITRIDE FILMS BY X-RAY DIFFRACTION USING sin2 ψ METHOD

The boron nitride (BN) films containing cubic boron nitride (c-BN) and hexagonal boron nitride (h-BN) were prepared by radio frequency a ssisted thermal filament chemical vapor deposition. The stress and strain in BN films were investigated by X-ray diffraction analysis using the sin² ψ method. The results showed that both c-BN and h-BN in the same film have similar values of elastic strain, however, the compressive stress in c-BN is much greater than that in h-BN for the same film. Both stress and strain gradually decre ased with the increase of substrate temperature (T_s). The effective stress in the films calculated by the effective stress model increased with the increase of T_s. Furthermore, the dependence of effective stress in the films on T_s was also investigated.     

Growth-Parameter Spaces and Optical Properties of Cubic Boron Nitride Films on Si（001）

Cubic boron nitride （c-BN） films were deposited on Si（001） substrates in an ion beam assisted deposition （IBAD） system under various conditions, and the growth parameter spaces and optical properties of c-BN films have been investigated systematically. The results indicate that suitable ion bombardment is necessary for the growth of c-BN films, and a well defined parameter space can be established by using the P/a-parameter. The refractive index of BN films keeps a constant of 1.8 for the c-BN content lower than 50%, while for c-BN films with higher cubic phase the refractive index increases with the c-BN content from 1.8 at χc =50% to 2.1 at χc = 90%. Furthermore, the relationship between n and p for BN films can be described by the Anderson-Schreiber equation, and the overlap field parameter γ is determined to be 2.05.     

Thick c-BN films deposited by radio frequency magnetron sputtering in argon/nitrogen gas mixture with additional hydrogen gas

The excellent physical and chemical properties of cubic boron nitride(c-BN) film make it a promising candidate for various industry applications. However, the c-BN film thickness restricts its practical applications in many cases. Thus, it is indispensable to develop an economic, simple and environment-friend way to synthesize high-quality thick, stable c-BN films. High-cubic-content BN films are prepared on silicon(100) substrates by radio frequency(RF) magnetron sputtering from an h-BN target at low substrate temperature. Adhesions of the c-BN films are greatly improved by adding hydrogen to the argon/nitrogen gas mixture, allowing the deposition of a film up to 5-μm thick. The compositions and the microstructure morphologies of the c-BN films grown at different substrate temperatures are systematically investigated with respect to the ratio of H_2 gas content to total working gas. In addition, a primary mechanism for the deposition of thick c-BN film is proposed.     

Optical properties of hexagonal boron nitride thin films deposited by radio frequency bias magnetron sputtering

The optical properties of hexagonal boron nitride (h-BN) thin films were studied in this paper. The films were characterized by Fourier transform infrared spectroscopy, UV--visible transmittance and reflection spectra. h-BN thin films with a wide optical band gap E_g (5.86 eV for the as-deposited film and 5.97 eV for the annealed film) approaching h-BN single crystal were successfully prepared by radio frequency (RF) bias magnetron sputtering and post-deposition annealing at 970~K. The optical absorption behaviour of h-BN films accords with the typical optical absorption characteristics of amorphous materials when fitting is made by the Urbach tail model. The annealed film shows satisfactory structure stability. However, high temperature still has a significant effect on the optical absorption properties, refractive index n, and optical conductivity σ of h-BN thin films. The blue-shift of the optical absorption edge and the increase of E_g probably result from stress relaxation in the film under high temperatures. In addition, it is found that the refractive index clearly exhibits different trends in the visible and ultraviolet regions. Previous calculational results of optical conductivity of h-BN films are confirmed in our experimental results.     

Field Emission from Amorphous carbon Nitride Films Deposited on silicon Tip Arrays

Amorphous carbon nitride films (a-CNx) were deposited on silicon tip arrays by rf magnetron sputtering in pure nitrogen atmosphere. The field emission property of carbon nitride films on Si tips was compared with that of carbon nitride of silicon wafer. The results show that field emission property of carbon nitride films deposited on silicon tips can be improved significantly in contrast with that on wafer. It can be explained that field emission is sentitive to the local curvature and geometry, thus silicon tips can effectively promote field emission property of a-CNx films. In addition, the films deposited on silicon tips have a smaller effective work function (F=0.024eV) of electron field emission than that on silicon wafer (F=0.060eV), which indicates a significant enhancement of the ability of electron field emission from a-CNx films.     

Improvement of Field Emission Characteristics of Copper Nitride Films with Increasing Copper Content

A copper nitride （Cu3N） thin film is deposited on a Si substrate by the reactive magnetron sputtering method. The XPS measurements of the composite film indicate that the Cu content in the film is increased to 80.82 at. % and the value of the Cu/N ratio to 4.2：1 by introducing 4% 112 into the reactive gas. X-ray diffraction measurements show that the film is composed of Cu3N crystallites with an anti-ReO3 structure. The effects of the increase of copper content on the field emission characteristics of the Cu3N thin film are investigated. Significant improvement in emission current density and emission repeatability could be attributed to the geometric field enhancement, caused by numerous surface nanotips, and the decrease of resistivity of the film.     

Deposition of hexagonal boron nitride thin films on silver nanoparticle substrates and surface enhanced infrared absorption

Silver nanoparticle thin films with different average particle diameters are grown on silicon substrates. Boron nitride thin films are then deposited on the silver nanoparticle interlayers by radio frequency （RF） magnetron sputtering. The boron nitride thin films are characterized by Fourier transform infrared spectra. The average particle diameters of silver nanoparticle thin films are 126.6, 78.4, and 178.8 nm. The results show that the sizes of the silver nanoparticles have effects on the intensities of infrared spectra of boron nitride thin films. An enhanced infrared absorption is detected for boron nitride thin film grown on silver nanoparticle thin film. This result is helpful to study the growth mechanism of boron nitride thin film.     

Enhanced field emission characteristics of thin-Au-coated nano-sheet carbon films

This paper reports that the nano-sheet carbon films (NSCFs) were fabricated on Si wafer chips with hydrogen--methane gas mixture by means of quartz-tube-type microwave plasma chemical vapour deposition (MWPCVD). In order to further improve the field emission (FE) characteristics, a 5-nm Au film was prepared on the samples by using electron beam evaporation. The FE properties were obviously improved due to depositing Au thin film on NSCFs. The FE current density at a macroscopic electric field, E, of 9~V/μ m was increased from 12.4~mA/cm² to 27.2~mA/cm² and the threshold field was decreased from 2.6~V/μ m to 2.0~V/μ m for Au-coated carbon films. A modified F-N model considering statistic effects of FE tip structures in the low E region and a space-charge-limited-current effect in the high E region were applied successfully to explain the FE data of the Au-coated NSCF.     

The electrical properties of sulfur-implanted cubic boron nitride thin films

Cubic boron nitride (c-BN) thin films are deposited on p-type Si wafers using radio frequency (RF) sputtering and then doped by implanting S ions. The implantation energy of the ions is 19 keV, and the implantation dose is between 10 15 ions/cm 2 and 10 16 ions/cm 2 . The doped c-BN thin films are then annealed at a temperature between 400°C and 800 C. The results show that the surface resistivity of doped and annealed c-BN thin films is lowered by two to three orders, and the activation energy of c-BN thin films is 0.18 eV.     

Electron Field Emission of CNx Thin Films Prepared by Low Pressure Plasma Enhanced Chemical Vapour Deposition

CNx thin films were prepared using low pressure plasma enhanced chemical vapour deposition,and then bombarded by low-energy N2^ .The compositions before and after N2^ bombardment were compared using x-ray photoelectron spectroscopy.The electron field emission characteristics of CNx thin films before and after N2^ bombardment were studied under the pressure of 10^-6pa.For the samples,the turn-on emission field decreased from 2.5V/μm to 1.2V/μm while the stable current density increased from 0.5mA/cm^2 to a value larger than 1mA/cm^2 before and after the bombardment.Our results illustrate that the field emission characteristics were improved after the bombardment of N2^ .     

Preparation of p—n Junction Diode by B—Doped Diamond Film Grown on Si—Doped c—BN

A heterojunction diode has been fabricated by boron-doped p-type diamond thin film grown epitaxially on a silicon-doped n-type cubic boron nitride bulk crystal using the conventional hot filament chemical vapour deposition method.The ohmic electrode of Ti(50nm)/Mo(100nm)/Au(300nm)for the p-type diamond film and the bulk crystal of the c-BN were deposited by the rf planar magnetron method.Then the device was annealed at 410℃ in air for 1h in order to form ohmic metal alloy,The current-voltage characteristics of the heterojunction diode were measured and the result indicated that the rectification ratio reached 10^5,and the turn-on voltage and the highest current were 7V and 0.36mA,respectively.     

Field Emission from Silicon Nanocrystallite Films with Compact Alignment and Uniform Orientation

Patterned silicon nanocrystallite (SINC) films were fabricated on (100) orientation p-type boron-doped sificon wafer by the hydrogen ion implantation technique and the anodic etching method. The efficient field emission with low turn-on field of about 3.5V/μm at current density of 0.1μA/cm^2 was obtained. The emission current density from the SiNC films reached 1mA/cm^2 under a bias field of about 9.1V/μm. The experimental results demonstrate that there are great potential applications of the SiNC films for fiat panel displays. A surface treatment with hydrogen plasma was performed on the SiNC films and a significant improvement of emission properties was achieved.     

Field emissions of graphene films deposited on different substrates by CVD system

<正>Graphene films are deposited on copper(Cu) and aluminum(Al) substrates,respectively,by using a microwave plasma chemical vapour deposition technique.Furthermore,these graphene films are characterized by a field emission type scanning electron microscope(FE-SEM),Raman spectra,and field emission(FE) I-V measurements.It is found that the surface morphologies of the films deposited on Cu and Al substrates are different:the field emission property of graphene film deposited on the Cu substrate is better than that on the Al substrate,and the lowest turn-on field of 2.4 V/μm is obtained for graphene film deposited on the Cu substrate.The macroscopic areas of the graphene samples are all above 400 mm~2.     

Multi-layer structures including zigzag sculptured thin films for corrosion protection of AISI 304 stainless steel

To increase corrosion resistance of the sample,its electrical impedance must be increased.Due to the fact that electrical impedance depends on elements such as electrical resistance,capacitance,and inductance,by increasing the electrical resistance,reducing the capacitance and inductance,electrical impedance and corrosion resistance can be increased.Based on the fact that these elements depend on the type of material and the geometry of the material,multilayer structures with different geometries are proposed.For this purpose,conventional multilayer thin films,multilayer thin film including zigzag structure(zigzag 1)and multilayer thin film including double zigzag structure(zigzag 2)of manganese nitride are considered to protect AISI 304 stainless steel against corrosion in salt solution.These multilayer coatings including zigzag structures are prepared by alternately using the conventional deposition of thin film and glancing angle deposition method.After deposition,the samples are placed in a furnace under nitrogen flux for nitriding.The cross sections of the structures are observed by field emission scanning electron microscopy(FESEM).Atomic force microscope(AFM)is used to make surface analyses of the samples.The results show that the multilayer thin films including zigzag structures have smaller grains than conventional multilayer thin films,and the zigzag 2 structure has the smaller grain than the other two samples,which is attributed to the effect of shadowing and porosity on the oblique angle deposition method.Crystallography structures of the samples are studied by using x-ray diffraction(XRD)pattern and the results show that nitride phase formation in zigzag 2 structure is better than that in zigzag 1 structure and conventional multilayer thin film.To investigate the corrosion resistances of the structures,electrochemical impedance spectroscopy(EIS)and potentiodynamic polarization tests are performed.The results reveal that the multilayer thin films with zigzag structures have better corrosion protection than the conventional multilayer thin films,and the zigzag structure 2 has the smallest corrosion current and the highest corrosion resistance.The electrical impedances of the samples are investigated by simulating equivalent circuits.The high corrosion resistance of zigzag 2 structure as compared with conventional multilayer structure and zigzag 1 structure,is attributed to the high electrical impedance of the structure due to its small capacitance and high electrical resistance.Finally,the surfaces of corroded samples are observed by scanning electron microscope(SEM).     

Electron field emission characteristics of nano-catkin carbon films deposited by electron cyclotron resonance microwave plasma chemical vapour deposition

This paper reported that the nano-catkin carbon films were prepared on Si substrates by means of electron cyclotron resonance microwave plasma chemical vapour deposition in a hydrogen and methane mixture. The surface morphology and the structure of the fabricated films were characterized by using scanning electron microscopes and Raman spectroscopy, respectively. The stable field emission properties with a low threshold field of 5V/μm corresponding to a current density of about 1μA/cm^2 and a current density of 3.2mA/cm^2 at an electric field of 10V/μm were obtained from the carbon film deposited at CH4 concentration of 8%. The mechanism that the threshold field decreased with the increase of the CH4 concentration and the high emission current appeared at the high CH4 concentration was explained by using the Fowler-Nordheim theory.