This article reviews the state of the art in the gas-phase synthesis of graphene in atmospheric plasmas. The substrate-free process involves the delivery of a carbon-containing precursor into a microwave-generated Ar plasma. Factors that influence the synthesis of graphene include precursor composition, reactor design, and the flow rates of gases. These factors have elucidated the mechanisms of graphene formation in atmospheric plasmas. Gas phase–synthesized graphene is pure and highly ordered and possesses unique features that make the material useful in applications such as catalysis, energy storage, lubrication, and the transmission electron microscopy imaging of nanomaterials. However, the main challenge in the synthesis process is the low rate of graphene production. This article anticipates future research aimed at overcoming this challenge and compares the atmospheric plasma method with contemporary graphene production techniques.

Photochromic (PC) ZnO nanoparticles are synthesized for the first time by using a VHF plasma enhanced CVD apparatus. The prepared ZnO film changes from transparent to PC state under UV irradiation; on being subjected to heat treatment, it changes back to transparent state. There is a threshold temperature for attaining the PC phase. The Debye-Waller factor of Zn atoms is specifically large for the PC ZnO. The ZnO nanoparticles contain carbon as impurity. The effects of C-O bonds on the ZnO crystal structure and density of states (DOS) are simulated based on density-functional theory. The results reveal that the crystal structure is slightly distorted and a sufficient DOS for PC light absorption is formed in the band gap.

The atmospheric pressure plasma sources with a coaxial geometry were used for generation of the radio frequency, microwave and pulsed dc plasmas inside water and aqueous solutions. Pulsed dc plasma generated in ethanol-water mixtures leads to production of the hydrogen-rich synthesis gas with hydrogen content up to 65 %. The effect of various plasma generation regimes on the performance of plasma, on the hydrogen production efficiency and on the hydrogen-rich synthesis gas production was examined. A role of the composition of the ethanol-water mixture was investigated.

An investigation of the effect of experimental parameters on the temperature and uniformity of material deposition by atmospheric pressure dielectric barrier discharge (DBD) planar plasma reactors was conducted. The apparatus consisted of a pulsed AC high voltage power source with various electrode materials (aluminum, copper wire mesh, and aluminum/copper wire mesh) operating under a range of load resistances. Possible effects of non-ideal interfacial conditions for the contact surface between the electrode and the substrate were also studied with various modified surface thermal conditions. It was found that a hybrid electrode design with a fine copper (Cu) wire mesh attached to an aluminum plate of approximately 3 mm thickness produced the most visually uniform deposit, presumably as a result of both the superior conductivity provided by the Al metal plate and the stable plasma resulting from the relatively low breakdown voltage by using helium (He) as the dilution gas. Although the experimental conditions of plasma-enhanced chemical vapor deposition (PECVD) are often specific to particular systems and applications, this work provides insights on technical details which can be applied to various plasma DBD reactors.

In this study we compare light trapping in hydrogenated amorphous silicon (a-Si:H) solar cells deposited directly onto polycarbonate (PC) at low temperature (< 130°C). To that end, we embossed PC substrates with 400 nm and 10 μm square based pyramids to induce light trapping based on diffraction and on geometric effects. As a comparison, we deposited a-Si:H cells on flat glass substrates and on Asahi U-type TCO glass. The cells on PC generate current densities comparable (slightly higher) than cells on Asahi TCO glass, but suffer from a slightly lower Voc, resulting in cells with an initial efficiency of 6.8% and 7.4% on sub-micron pyramid and micro-pyramid structured PC substrates respectively, compared to 7.6% for cells on Asahi. This shows great potential for a-Si:H cells deposited directly onto cheap plastics.

A one-dimensional model has been developed for radio frequency (RF) glow discharge of SiH4/GeH4/H2 3-gases mixture at a high pressure regime based on the fluid model. The behavior of electrons, neutrals, radicals and ions with corresponding rate constants is described by driftdiffusion equations that are coupled with the Poisson’s equation and solved with an explicit central-difference discretization scheme. The germanium (Ge) content in the deposited film and germane (GeH4) radical fraction in the gas phase are found to decrease as total gas pressure increases in contrast to the increased deposition rate, which are explained by the fact that GeHx-group species are more thoroughly depleted and less promoted by the denser plasma at high pressure compared to SiHx-group species. The multiplied population of electrons and hydrogen atoms in the quadratically denser plasma also boosts secondary reactions which are favorable for SiH3 and GeH3 and consume SiH2 and GeH2for high order radicals.

We report the dry etch of GaSb(001) by inductively coupled plasma reactive ion etcher. Silicon Oxide, deposited by PECVD, was used as a mask. The oxide layer proved to be almost unaffected compared to the GaSb, when using chlorine compound gases as etchants (Cl2, BCl3, and SiCl4) as well as argon. This provides high selectivity for GaSb to the mask layer. The sample holder has no silicon that may contribute to the etching process. Etching using Cl2 + Ar showed increase in the etching rate as the chlorine ratio increases; however, the process led to grassy surface and chemical like reaction. The use of SiCl4+Cl2+Ar mixture with low chlorine ratio resulted in anisotropic etch with smooth sides. It has been found for this case that the increase of the chlorine ratio led to an increased etching rate as well. The repeat of previously reported result by Swaminathan et al. [Thin Solid Films 516 (2008) 8712.] yet with a sample holder not having silicon, proved the effect of Si-contribution in producing vertical profile etch with smooth surfaces.

As an alternative to crystalline silicon or thin film solar cells on rigid glass substrates, we aim to fabricate amorphous silicon (a-Si)/nanocrystalline silicon (nc-Si) tandem thin film solar cells on cheap flexible substrates. We have chosen polycarbonate as the superstrate and adapted the a-Si and nc-Si deposition processes for deposition at a maximum temperature of 130°. Because a-Si deposited at low temperatures has a high band gap, we were able to fabricate very thin (<1.2 μm) a-Si/nc-Si solar cells, because the high band gap of the a-Si shifts the current generation more towards the bottom cell, allowing for a much thinner (900 nm) bottom cell. The somewhat lower Jsc of the complete cell is partly compensated by a higher Vocwhich results in an initial conversion efficiency of 9.5% for the low temperature tandem solar cells on glass.

Morphologies of silicon nanowires grown by plasma-assisted metalorganic chemical vapor deposition were studied in the presence of various dopant precursors. The varied precursors affected the axial and radial growth rates over orders of magnitude where triethylborane showed the strongest enhancements for both axial and radial growth, and triethylarsenic and triethylantimony retarded axial growth. Native oxide thickness is also shown to depend strongly on doping condition resulting in increased oxide thicknesses for increased carrier concentration, using shifts in the measured binding energy of the silicon 2p3/2 state as a proxy for carrier concentration.

The fabrication of low-dimensional diamond materials in form of nanowires is a stringent requirement for advanced electronic applications. However, the nanometric control of diamond materials into desired and tailored geometries, as those ones required for applications in the field of nano-photonics, is a really challenging and complex task using currently available processes. In the present paper we describe some recent results obtained using plasma-induced processes for the shaping of diamond films in fascinating 1D structures, such as nanowires, nanowhiskers and nanopillars, to be integrated in devices of technological interest.

In this work, the effect of bandgap grading of hydrogenated amorphous silicon germanium (a-Si1-xGex:H) absorber near the p/i and the i/n interfaces was investigated. The a-Si1-xGex:H single-junction solar cells were improved by applying both p/i grading and i/n grading. Our results showed that both the p/i and the i/n grading can increase the open-circuit voltage (VOC) as compared to the cell without grading. The i/n grading can further improve the FF. Presumably the potential gradient created by the i/n grading can facilitate the hole transport thus it can improve the FF. However, the JSC decreased as the i/n grading width increased. The reduction of JSC was due to the loss in the red response, which can be attributed to the replacement of lower bandgap material by the larger ones. Combining the effects of VOC, JSC and FF, a suitable thickness of the p/i and the i/n grading was 20 nm and 45 nm, respectively. Finally, the grading structures accompanied with further optimization of doped layers were integrated to achieve a cell efficiency of 8.59 %.

A growth of high quality thick diamond film has been carried out on high pressure and high temperature diamond substrate by microwave plasma chemical vapor deposition system. First, the effect of growth parameters on the growth film morphologies was investigated, indicating that the diamond film is very sensitive to the growth temperature and input microwave power. Then, sample holders with different geometries were used in our experiment, illustrating that high quality diamond film can be grown by using the sample holder with flat surface. Finally, the characterization of the as grown samples has been carried out.

The effect of the rapid thermal annealing (RTA) and hydrogenation step on the electronic properties of the n+ and p+ solid phase crystallized (SPC) poly-crystalline silicon (poly-Si) thin films was investigated using Hall effect measurements and four-point-probe measurements. Both the RTA and hydrogenation step were found to affect the electronic properties of doped poly-Si thin films. The RTA step was found to have the largest impact on the dopant activation and majority carrier mobility of the p+ SPC poly-Si thin films. A very high Hall mobility of 71 cm2/Vs for n+ poly-Si and 35 cm2/Vs for p+ poly-Si at the carrier concentration of 2×1019 cm-3 and 4.5×1019 cm-3, respectively, were obtained.

Carbon nanofibers were used as building blocks for two-dimensional photonic crystal slabs. Electron beam lithography and chemical vapor deposition were used to fabricate regular arrays and random patterns of nanofibers. The optical properties of the samples were investigated using a diffraction measurement setup, as well as reflection ellipsometry. We find that carbon nanofiber regularity has a strong effect on both diffractive and specular optical properties. This shows that ellipsometry can be a valuable tool to study properties of carbon nanofiber arrays. It also shows that carbon nanofibers provide an interesting candidate as building blocks for nanostructured optical components.

CNT arrays were synthesized by Chemical Vapor Deposition (CVD) and spun into ribbons, which were coated using Atmospheric Pressure Microwave Plasma system. Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) characterization of CNT ribbons indicated the presence of polymer films with CF2 as a repeat unit. Atomic concentration of C, F and O in the coated films was estimated from X-ray Photoelectron Spectroscopy (XPS) data. Types of bonding between the elements in the coated films was studied by curve fitting of C 1s XPS spectra.

In this work, we examined the Ge incorporation and the accompanied defect formation during PECVD deposition of hydrogenated amorphous silicon-germanium alloys (a-Si1-xGex:H). In particular, we studied the effect of hydrogen on film growth, defect formation, Ge and Si incorporation efficiencies, and the H-bonding configuration. Our results indicate that hydrogen has a strong effect on improving the a-Si1-xGex:H film quality and the Ge incorporation in a-Si1-xGex:H. With adequate hydrogen dilution, the a-Si1-xGex:H thin-film quality significantly improved. However, excessive hydrogen dilution degraded the film properties. A number of analytical tools were employed, including FTIR, XPS, UV-Visible spectroscopy, photoconductivity, etc. The a-Si1-xGex:H material having 24% Ge content and a bangap of 1.61ev produced the solar cell with a conversion efficiency of 7.07%.

Organosilicate materials with dielectric constants (k) ranging from 3.0 to 2.2 are in production or under development for use as interlayer dielectric materials in advanced interconnect logic technology. The dielectric constant of these materials is lowered through the addition of porosity which lowers the film density, making the patterning of these materials difficult. The etching kinetics and surface roughening of a series of low-k dielectric materials with varying porosity and composition were investigated as a function of ion beam angle in a 7% C4F8/Ar chemistry in an inductively-coupled plasma reactor. A similar set of low-k samples were patterned in a single damascene scheme. With a basic understanding of the etching process, we will show that it is possible to proactively design a low-k material that is optimized for a given patterning. A case study will be used to illustrate this point.

Silicon nanowires (Si NWs) were grown directly on transparent conductive oxide layers using a single pump down process in a plasma enhanced chemical vapour deposition (PECVD) system. Layers of ITO and SnO2 on glass substrates were exposed to a hydrogen plasma leading to the reduction of the oxide and to the agglomeration of the metal into catalyst droplets of a few tens of nanometers diameter. The diameter and the density of the nanowires depend on the catalysts droplets size and density, we studied step by step the evolution of the surface prior to and at the initial stage of the nanowire growth. The catalyst droplets size and distribution were essentially investigated through Scanning Electron Microscopy (SEM).

We have grown tree-like vertically-aligned carbon nanotubes (CNTs) on silicon substrate, suitable for highly sensitive interdigital capacitive sensors. As an application, we present a sensitive pressure sensor with branched CNTs as its capacitance plates.

After realization of the interdigital structure, the growth of CNTs has been achieved through direct-current plasma enhanced chemical vapor deposition (DC-PECVD) method. A sequential growth and hydrogenation has led to the formation of multiple branched structures of nanotubes. The growth of tree-like CNTs on the interdigitally patterned substrate results in a high overlap between adjacent fingers and consequently a significant response to mechanical variations of the membrane as a result of the applied pressure.

We compare the turn-on voltage, P-I, and EL responses between the MISLEDs made by Si-rich SiNx and SiOx films. Active layer thickness enlarged from 120 to 360 nm is achieved by lengthening deposition time from 10 to 30 min, which inevitably increases the forward turn-on voltage from 3 to 41 V. We observe that the forward turn-on voltage of SiNx based MISLED is only 10.43 V and that of SiOx based one is 69 V with the same film thickness of 100 nm. The tunneling-based carrier transport mechanism is dominated due to the exponential like V-I behavior, while the tunneling probability is strongly dependent on the height of the barriers between metal/dielectric and dielectric/nc-Si matrices. The P-I slope of SiNx and SiOx based MISLEDs are 1.6 and 115.2 mW/A, respectively. The SiNx MISLED reveals threshold current and voltage of only 4 A and 12 V due to lower barrier height of both ITO/SiNx and SiNx/nc-Si, whereas the threshold current and voltage of SiOx based MISLED are 400 A and 78 V, respectively. In comparison, the higher tunneling current through the SiNx MISLED fails to promote the larger external quantum efficiency of the MISLED, indicating that such lower barriers are not beneficial to the confinement of tunneling carriers and the enhancement of light-emission efficiency.