Nanographite Films Research Articles

Photoelectric skin effect in conducting films

The effect of high-intensity laser radiation on the surface of conducting films is considered as the interaction of photons with free electrons in the skin layer of the films, which induces longitudinal and transverse currents controlled by the laser beam intensity, free electron concentration in the film material, and the angle of incidence of the laser beam on the film surface. The experimentally observed optoelectric effect in nanographite films, which was explained earlier by the optical rectification effect, may be due to the longitudinal photoelectric skin effect due to metal-type conduction of graphite.

Anisotropy of the photoelectric properties of porous nanographite films

The influence of the orientation of platelike grains in nanographite (NG) films on the efficiency of photoelectric conversion of pulsed laser radiation has been studied. The initial orientation of NG grains perpendicular to the substrate surface was determined by a plasmachemical process used for the film deposition. A change in the orientation of grains in the film as a result of mechanical smoothing action leads to the appearance of anisotropy in the photoelectric properties of samples.

A device for testing a fast nanographite photodetector at high temperatures

The results of tests of a fast photodetector based on a nanographite film grown on a silicon substrate are presented. The temperature dependence of the optoelectric signal from the photodetector in the range 300–800 K has been studied under the vacuum conditions. It has been shown experimentally that, when the temperature increases from 300 to 625 K, the photodetector’s sensitivity decreases by approximately 30%. When the temperature increases to higher values, the optoelectric-signal amplitude drops linearly and is halved at T = 740 K as compared to room temperature. Extrapolation of the experimental data shows that the optoelectric response of the photodetector disappears at T > 1000 K.

Double resonant Raman scattering in nanographite films

Experimental results are presented on Raman scattering in graphite films produced by DC plasmaenhanced chemical vapor deposition from a methane-hydrogen gas mixture. Scanning electron and probe microscopy data show that, depending on substrate material and deposition time, the deposited film is either a mesoporous material consisting of graphite nanocrystallites with basal planes oriented perpendicular to the substrate surface or an atomically flat, nanometer-thick stack of graphene layers parallel to the substrate. A comparative Raman spectroscopy analysis is performed for film samples deposited on nickel and silicon substrates for 5 and 60 min, as well as for highly ordered graphite samples. The Raman spectra of the examined samples correspond to the double resonant scattering mechanism. The behavior of Raman peak position and intensity as functions of excitation wavelength suggests a high degree of structural order in the graphite films deposited on nickel for 5 min. The results obtained are used to show that the thickness of these films is 1.5 ± 0.5 nm.

Nanographite films produce a strong DC response under laser irradiation

Nanographite films produce a strong DC response under laser irradiation

Enhanced electron field emission from preferentially oriented graphitic films

The electron field emission properties of nanographite films, whose basal planes display a degree of preferred orientation perpendicular to the surface, are reported. It was found that nanometric thick films which display a high degree of preferred orientation perpendicular to the substrate emit electrons at a high turn on field (TOF), while thicker films which display a much lower degree of preferred orientation emit electrons at a significantly lower TOF. It is suggested that the observed effect is mainly associated with the degree of basal planes orientation of the nanostructures and not just to their length.

A glossmeter for inspection of surface quality of low gloss nano-carbon surfaces

The nano-carbon films consisting of nanometrically thin graphite crystallites were produced by chemical vapor deposition method. The nano-graphite crystallites standing perpendicular to substrate surface form mesoporous film with very low gloss. Originally developed glossmeter techniques were applied for inspection of the nano-graphite films to evaluate their homogeneity and level of gloss. In the paper we describe technical details related to the glossmeter techniques and experimental results obtained for the nano-graphite films.

Effect of substrate material on the structure of carbon films obtained by plasmachemical deposition

Carbon films were obtained on nickel and silicon substrates by plasmachemical deposition from a hydrogen-methane gas mixture activated by dc discharge. The deposits were characterized by Raman scattering and scanning electron microscopy. Nanographite films on nickel are formed at a significantly lower substrate temperature and methane concentration in the gas phase than on silicon.

Quick-response film photodetector of high-power laser radiation based on the optical rectification effect

The efficiency of conversion of high-power laser radiation to an electric signal based on the optical rectification effect in nanographite films is studied experimentally. The amplitude of the signal is found to significantly depend on the size of the film, as well as on the length and arrangement of measuring electrodes. The maximal sensitivity of the photodetector (above 500 mV/MW at a wavelength of 1064 nm) consisting of the film with electrodes and operating without an external power supply and add-on components is shown to be achieved when the size of the film is comparable to the laser beam diameter. The sensitivity of the photodetector is studied under the condition when a nanosecond beam from a pulsed laser scans the surface of the film in two mutually perpendicular directions. The local sensitivity increases near the free ends of the photodetector. It is shown that the nanographite detector and a similar photodetector made of a polished silicon wafer have radically different parameters.

A Nanographite Film-Based Fast Response Detector for Intense Laser Radiation

A simple high-speed photodetector of high-power laser radiation, based on the optical rectification effect, is described. It operates without an external power source. A nanographite film deposited onto a silicon substrate using the plasmochemical deposition technique and having two conducting surface electrodes is used as the photodetector's photosensitive element. The performance of this device was demonstrated by detecting pulsed laser radiation in a spectral range of 0.266-1.9 µ m using the second, third, and fourth harmonics of radi- ation from an YAG : Nd 3+ laser with passive Q -switching and radiation from light oscillators based on stimu- lated Raman scattering in compressed hydrogen. It was shown that the photodetector sensitivity is proportional to the optical radiation frequency and its response time is shorter than 0.5 ns.

Spectral Dependence of the Optical Rectification Effect in Nanographite Films

The spectral dependence of the optical rectification effect in nanostructured carbon (nanographite) films obtained by plasmachemical deposition was studied in a wavelength range from 266 to 1900 nm. In this range, the amplitude of the electric signal observed when films were irradiated by nanosecond light pulses of constant power increases in inverse proportion to the laser wavelength. The experimental results confirm the assumptions made previously concerning the mechanism of the observed effect. It is suggested that nanographite films are promising materials for detectors of ultrashort laser pulses in the IR, visible, and UV spectral intervals and for generators of electromagnetic radiation operating in the terahertz frequency range.

Effect of the Nanographite Film Thickness on the Optical Rectification Pulse

The phenomenon of optical rectification during pulsed laser irradiation was studied in nanographite films of various thicknesses obtained by plasmachemical deposition on silicon substrates. The amplitude of the optical rectification pulse (ORP) strongly depends on the film thickness h and reaches a maximum at h ∼ 2.5 μm. At a smaller film thickness, the ORP is accompanied by a photoelectric signal of microsecond duration, which arises in the silicon substrate. For the nanographite films with h > 2.5 μm, the ORP is observed in the absence of any signal from the substrate, which allows such films to be used in fast-response detectors of pulsed laser radiation in a broad spectral range.

Preparation of Nano-Graphite Films and Field Emission Properties

Nano-graphite films have been deposited on n-Si substrates by microwaveplasma chemical vapour deposition. The surface morphology andmicrostructure of the films were tested by scanning electronmicroscopy, x-ray diffraction and Raman spectroscopy. In the fieldemission measurement, a turn-on field of 0.5 V/μm and a highemission-site density of 105/cm2 on a tested emission areaof (34×35 mm2) have been obtained.