Superconductivity in heavily B-doped diamond layers deposited on highly oriented diamond films

We deposited a [100]-oriented B-doped diamond layer by three methods to clarify the effects of film morphology on the transition from metallic to superconducting diamond. Heavily B-doped [100]-oriented diamond layers were deposited on [first method] undoped polycrystalline diamond films with [111] faces, [second method] highly oriented undoped diamond (HOD) thin films with a pyramidal surface, and [third method] thick undoped HOD films with a pyramidal surface. We confirmed that the B-doped layer in the third method was oriented in the [100] direction by scanning electron microscopy (SEM). The highest transition temperatures were T_c(onset) = 5.0 K and T_c(zero) = 3.1 K for the B-doped layer deposited on a thick HOD film with a pyramidal surface under a zero magnetic field. By contrast, T_c(onset) was 4.1 K for a heavily B-doped diamond layer deposited on a thin HOD film with a pyramidal surface, and was 3.9 K for a heavily B-doped diamond layer deposited on an undoped polycrystalline diamond film. These differences in T_c for our samples are affected by disorder and effective hole-carrier doping in each sample. Using the third method, we successfully deposited a high-quality B-doped [100] layer in three steps: (first step) depositing a [100] HOD film on a Si [100] substrate, (second step) depositing an HOD film with a pyramidal surface, and (third step) depositing a [100]-oriented B-doped layer. The change in the electronic states due to the B-doping of diamond films and the film morphology were investigated by x-ray photoelectron spectroscopy (XPS) measurements and band calculations.     

Synthesis of highly oriented CVD diamond films by ultra short bias enhanced nucleation step

Highly oriented diamond films have been deposited on silicon substrate by the MPCVD technique (microwave plasma assisted chemical vapour deposition) using an ultra short bias enhanced nucleation process (so called USBEN). We focus our attention on two points: the homogeneity of the deposit in order to perform a precise characterisation whatever surface location (on 1×1 cm² of single silicon substrate); and the simplification of the successive steps usually performed in the BEN process. This is carried out by optimising the microwave cavity and the d.c. discharge extension and by keeping the pretreatments just necessary to obtain high nucleation density with an acceptable epitaxial ratio and a good homogeneity. This leads to a drastic reduction of the bias time of only 30 s for low bias voltage. As we obtain a highly oriented diamond film with a short bias pretreatment without preliminary carburation step, we discuss the substrate transformation under a weak bombardment duration of ions having a quite low energy. We think that the bias step probably consists to a slight modification of the substrate surface.     

Wafer bonding of highly oriented diamond to silicon

Polished, highly oriented diamond (HOD) with an RMS roughness of less than 3 nm was bonded to single-side polished silicon wafers in ultra-high vacuum (UHV) at 32 MPa of applied uniaxial pressure. Successful fusion of HOD to silicon was achieved at temperatures above 850 °C. Fusion resulted in the formation of an abrupt interface between the wafers in the areas away from diamond grain boundaries. Voids, partially filled with amorphous material, were observed at the fused interface near the diamond grain boundaries. Preferential diamond polishing, potential out-diffusion of hydrogen from diamond and oxygen from silicon are believed to have contributed to the observed non-uniformity of the bonded interface.     

Temporal response of UV sensors made of highly oriented diamond films by 193 and 313 nm laser pulses

Ultraviolet sensors were fabricated on a Si substrate using an undoped, highly oriented diamond film with Pt and Al interdigited electrodes with a gap length of 5, 10 and 15 μm. Transient voltage outputs due to photocurrent of the sensors under a bias voltage of 20, 40 and 80 V were measured by the pulsed irradiation of an ArF excimer laser (λ=193 nm, pulse width=5 ns) or a dye laser (λ=313 nm, pulse width=7 ns). It was found that the transient voltage output by the ArF laser irradiation on a sensor (Pt electrodes with a 15-μm gap) consisted of main and second peaks at 1.1 and 3.8 ns, respectively, when the bias voltage was 20 V. The FWHM was approximately 4 ns. The second peak was observed in the output signals of most sensors. On the other hand, the voltage output was two orders of magnitude weaker when the sensors were irradiated by the dye laser.     

Microscopic measurements of the electrical properties of highly oriented B-doped diamond films: influence of grain boundaries

In this work we present electrical measurements with a current flow being spatially defined on a μm scale. We examine the effect of the grain structure on the electrical transport properties of B-doped diamond films grown on large-area HOD films depending on temperature and field strength. The results are discussed with regard to film morphology. Bridges as narrow as 3.0 μm are etched and contacted in a well-defined way using Ti/Pt/Au contacts. Our experiments and analysis indicate that the electrical transport is not dominated by grain boundaries perpendicular to current flow. Using HOD films with a grain size of up to 10 μm as determined by scanning electron microscopy (SEM) we prepare bridges where a single grain boundary intersects the bridge or connects the two ends, as well as bridges where no grain boundary is present. These measurements on single grain boundaries are a tool to reveal the fundamentals of the current transport properties.     

Young’s modulus of highly oriented polypropylene films

Anomalously high values of Young’s modulus were established in polypropylene films with λ = 33.7 and the range of a nonlinear increase in the region of λ = 5–7 was found, caused by recrystallization processes. To explain these results, we proposed considering Young’s modulus in polypropylene as a linear combination of constituents which are only a function of the temperature and degree of drawing separately. __________ Translated from Khimicheskie Volokna, No. 4, pp. 12–14, July–August, 2007.     

Spray-grown highly oriented antimony-doped tin dioxide transparent conducting films

Undoped and Sb-doped tin dioxide films of varying thickness with a remarkable crystallographic orientation in the [200] direction were grown by spray-pyrolysis from tin(II) chloride solutions. Films grown on silica-coated glass substrates were completely crystalline and showed a higher degree of orientation with respect to films that were grown on uncoated glass. The presence of the silica barrier was seen to have increased the degree of orientation and to have enhanced the resulting electrical properties. Transmission electron microscopy revealed that the silica layer may have played the crucial role of a nucleation layer. Moreover, the developed microstructures were correlated with the optical and electrical behaviour of the films. Dense conducting films with thicknesses between 280–450 nm and visible transmittances of 80-70 % showed resistivities of about 10⁻³ Ωcm.     

Surface morphology and electrochemical properties of highly boron-doped homoepitaxial diamond films

Highly boron-doped diamond films were grown on (100) diamond substrates that were mechanically repolished at an off-axis angle of 4° with respect to the (100) surface, tilted toward the [110] direction. The surface morphology and crystallinity were examined with atomic force microscopy, and it was found that the deposited surfaces have high crystallinity, with steps running parallel to the [110] direction. The terrace width was ∼30 nm. Atomic resolution images obtained on these terraces showed a disordered atomic arrangement, with no evidence for the 2×1 or 1×2 reconstruction usually observed for non-doped samples, suggesting that the high level of boron doping affects the surface structure. The electrochemical behavior of the films showed a wide working potential window and low capacitance.     

Highly oriented growth of n-type ZnO films on p-type single crystalline diamond films and fabrication of high-quality transparent ZnO/diamond heterojunction

We present the results on the fabrication and characterization of high-quality transparent heterojunction between n-type ZnO film and p-type diamond single crystalline film on the substrate of diamond bulk single crystal. The results indicated that the current density of the fabricated p-n junction reaches 110 A/m² when the forward bias voltage is 2.5 V, and the turn-on voltage value is about 0.75 V and agreement with the expected value. Moreover, a good rectification characteristic and transparent in the visible light range was obtained in the device.     

Dipolar-decoupled carbon-13 NMR study of highly oriented polyethylene films

Summary High-resolution solid-state ¹³C NMR spectra and ¹³C relaxation times T₁ and T₁ have been measured at 40–100° C for uniaxially oriented polyethylene films with the drawing direction parallel to the magnetic field; this sample has a unique morphological structure that the noncrystalline chains are nearly disordered irrespective of the high degree of drawing. A sharp resonance line(line A) appears at the position corresponding to the principal value ₃₃ of the chemical shift tensor for the CH₂ carbons with the trans-trans conformation. Another sharp linedine B) is observed at almost the same chemical shift as for the CH₂ carbons of polyethylene in solution. Although these observations are similar to those for a cold-drawn polyethylene sample reported previously, line B is much enhanced in intensity and the linewidth is narrower in the present sample, reflecting the disorientation of the noncrystalline component. It is found from T₁ measurements that line A contains two components with different molecular mobility, both being assigned to the crystalline components. On the other hand, the line B is composed of a single component assignable to the noncrystalline component with liquid-like molecular mobility.     

Origin of friction in films of horizontally oriented carbon nanotubes sliding against diamond

Carbon nanotube films were fabricated by a new deposition technique that can minimize carbon nanotube rolling/slipping when sliding against diamond. Molecular dynamics simulations were performed to understand the friction mechanisms. Results clarify the controversial arguments in the literature and conclude that the atomically smooth surface without dangling atoms and durability of the atomic lattice structure of carbon nanotubes makes them a good solid lubricant with an ultra-low coefficient of friction of around 0.01.     

Angle-dependent reflectometry as a technique for fast assessment of highly oriented diamond film quality

An expedient technique for assessing the quality of highly oriented diamond films is described. This analysis is based on light reflection from the {111} faces of oriented diamond octahedra as a function of azimuthal sample orientation. Significant light reflection was detected at 90° rotation intervals and the full-width-at-half-maximum of these periodic peaks was determined to be adequate for gauging the upper limit of crystal misorientation. In addition, a two-dimensional surface mapping of the distribution of highly oriented diamond across the sample was determined by analyzing reflectivity properties at equally spaced spots on the surface.     

Development of high resolution position sensitive UV detector based on highly oriented polycrystalline diamond

UV position-sensitive sensor using a polycrystalline highly-oriented diamond film with a sensitive area of 2 × 4.5 mm² developed, and a proof-of-concept study was conducted. The charge division method was employed to establish the position when the light hits the sensitive area. A fifth higher harmonic of a Nd:YAG laser with pulse width of 100 ps was used as a light source. The position resolution was 0.25 mm, and there was good position linearity throughout the sensitive area. Considering the possibility of light-spot broadening due to diffraction by the slit, the sensor may have a better resolution than that indicated by the result. But the electric-field strength of some parts of the crystal was insufficient, the response time was relatively slow, approximately 0.5 ms.     

Structure and mechanical properties of highly oriented poly(ethylene terephthalate) films

The relationships between the supermolecular structure of poly(ethylene terephthalate) films subjected to cold drawing and subsequent zone annealing and their mechanical properties are investigated. The effectiveness of zone annealing is compared to that of annealing with fixed ends. Microstructural changes occurring during heat treatment and zone annealing are monitored using wide angle X-ray scattering, small angle X-ray scattering, infrared spectroscopy, differential scanning calorimetry, and static mechanical tests. The very high modulus and strength of the zone-annealed films are directly attributed to the large number of the molecules connecting the crystallites.     

High-resolution STM-imaging of highly oriented ultra thin poly(ethylene) films

Poly(ethylene) (PE) ultra thin films drawn from the melt have been deposited on highly oriented pyrolytic graphite (HOPG) substrates for an investigation with the scanning tunneling microscope (STM). Similar to earlier examinations of poly (1-butene) (PB-1) ultra thin films (1), the STM investigations exhibited images of PE flakes extending over some hundered nanometers. Their thickness was determined to be much larger than the normal established tunneling distance between the tip and a good conducting (metallic) sample surface. It is supposed that the STM-tip penetrates the film and reduces its thickness by scanning over the film. Thus, a destruction of the film is likely leaving only a monomolecular layer of PE macromolecules on the graphite surface. At higher resolutions an ordered structure pseudomorphic to the simple chain nature of the PE macromolecule is revealed.     

Growth and characterization of highly oriented CuBr thin films through room temperature electrochemical route

A simple electrochemical process has been demonstrated to grow highly oriented copper(I) bromide thin films on indium-doped tin oxide (ITO) glass through reducing CuBr₂ in aqueous solutions at room temperature. The copper(I) bromide thin films grow preferential orientation along the 〈1 1 1〉 crystal axis from the X-ray diffraction patterns. The orientation growth of the CuBr thin films is little affected by the solution pH and applied potentials. The possible mechanism of the orientation growth has been discussed, and the surface energy of different crystal plane of CuBr crystal is believed to play an important role to control the orientation growth of the CuBr thin films. The oriented films exhibit intense free-exciton photoluminescence at room temperature.     

A study of the crystalline growth of highly boron-doped CVD diamond: preparation of graded-morphology diamond thin films

An investigation was made of graded-morphology diamond thin films deposited on Si substrates by use of the microwave plasma chemical vapor deposition (CVD) technique. The preparation of graded diamond thin films not only offers new perspectives into functional materials, but it also gives clues to the growth mechanism of CVD diamond. Although it is clear that the substrate temperature and the deposition time affect the grain size in particular, the difference depending on the boron concentration in the growing process was studied in the present work. As a result, in highly boron-doped (10⁴ ppm) diamond films, the Raman peak which was ascribed to the boron-doping was not observed at the very initial growth stage. However, the crystal growth process was almost irrelevant for the boron-doping quantity. Furthermore, we showed the morphology dependence of electrochemical properties as one example of the excellent functions of the graded-morphology highly boron-doped diamond film.     

The preparation of high quality oriented diamond thin films via low temperature and hydrogen ion etched nucleation

A three-step process was used to prepare high quality [001]-oriented diamond films. First, diamond crystallites were nucleated for 20 min on Si(001) at a temperature around 740 °C by bias-enhance method, during this step the portion of [001]-oriented diamond nuclei was increased in comparison with the nuclei deposited by a two-step method. Then hydrogen ion etching was performed for 30 min by setting an electric potential of −140 V. After the etching step most of the crystallites were [001]-oriented and twinned crystallites disappeared. Finally, diamond thin films were deposited under conventional conditions for [001]-textured growth. SEM was used to analyse the morphology of diamond crystallites and films. The results indicate that large area, uniform and [001]-oriented diamond thin films can be prepared by three-step growth. The films show good Raman characteristics and higher thermal conductivity than those deposited by a two-step process.     

Self-assembly of nano-sized arrays on highly oriented thin films of poly(tetrafluoroethylene)

Self-assembly of nano-sized arrays by casting a dilute solution of a guest material on the friction-transferred poly(tetrafluoroethylene) (FT-PTFE) substrate was newly discovered. Long axis of the rod-like structures forming the arrays is aligned perpendicular to the chain direction of FT-PTFE, and accordingly, the arrays are highly anisotropic. This phenomenon was observed for aqueous or organic solutions of polymers or organic materials. Each rod-like structure forming the arrays is composed of small grains. The arrays in question are formed regardless to the crystallinity of the guest materials. The formation mechanism of the nano-sized arrays is still unclear. However, we guess that they are formed as a result of microscopic flow pattern at the edge of the solution film. The arrays in question may be a new type of dissipative structure.