なかのにっき

The throw distance of Al and W atoms was determined (A) by investigating the pressure-dependent deposition rate and applying the Keller-Simmons one-dimensional model. The power density at the target as a parameter was varied over more than one order of magnitude. Whereas the values determined for Al are not influenced by power, the values for tungsten strongly increase with power. This effect is related to strong gas density reduction related to gas heating for W sputtering, which reduces the probability of collisions between sputtered atoms and the gas. The gas heating was experimentally determined by simultaneous measurements of the pressure in the sputtering chamber and at the end of a tubular probe inserted into the hot plasma region. For tungsten, a strong heating and related gas density reduction was found. An analytical expression describing the spatially resolved temperature profile in a sputtering discharge is developed by means of the Keller-Simmons formulas. The influence of various process parameters on gas heating can be easily studied by the model. There is good agreement between the model calculations with the experiments performed as well as with Monte Carlo simulations and experimental findings from the literature. Forward simulations by the model result in a power-independent throw distance (B) for both elements, which are in agreement with the values (A) resulting from the pressure-dependent deposition rate. Existing differences are explained by the rough assumptions of the model, which is critically discussed.

By chemisorption of oxygen on an aluminum target, an absolute target voltage increase is noticed which can be attributed to the reduction of the secondary electron emission from the target. By following the target voltage behavior during magnetron sputtering of the aluminum target precovered with a chemisorbed oxygen layer, the cross section for removing the chemisorbed layer could be calculated based on a proposed model that relates the measured target voltage to the target coverage.

Using an energy selective mass spectrometer, ion energy distribution functions (IEDFs) in a low pressure radio frequency (rf) argon discharge have been measured. This experiment has been done in the diffusion chamber of a helicon source. Two kinds of IEDF have been observed depending on the gas pressure: classical "one-peak" spectra at high pressure (>1 μbar) and "two-peak" spectra at low pressure (<1 μbar). These results have been correlated with the plasma potential and density profiles along the axis of the reactor obtained with a Langmuir probe and the IEDF have been fitted using a simple analytical model. In this way, noncollisional diffusion of energetic ions from the source chamber to the diffusion chamber has been shown.

Nanoindentation of crystalline and amorphous silicon nitride films is studied using 10-million-atom molecular dynamics simulations. A rigid pyramid-shaped indenter tip is used. Load-displacement curves are computed and are used to derive hardness and elastic moduli of the simulated crystalline and amorphous films. Computer images of local pressure distributions and configuration snapshots show that plastic deformation in the film extends to regions far from the actual indent.

Si nanoclusters have been formed by 5 keV Si+ implantation at a fluence of 1×10^16 atoms/cm2 into a 200 Å thin thermally grown SiO2 film on Si (100), followed by thermal treatment at 1000 ℃ with different annealing times. All the annealed samples show a broad photoluminescence spectrum with increasing intensity as function of annealing time. The use of a dual beam time of flight secondary ion mass spectrometry in negative mode with Cs+ ions at low energy for sputtering allows us to observe variations in Si_n- signal due to excess of silicon atoms introduced by implantation. With the high sensitivity achieved using this instrumental configuration it is possible to follow Si signals which give information about the chemical enviroment of the Si atoms. The possibility of studying the time evolution of the nucleation and growth of nanoclusters has been investigated.

The built-in electrical potential of Cu(In,Ga)Se2 (CIGS) solar cells was measured quantitatively and resolved spatially using scanning Kelvin probe microscopy. Profiles of the electrical potential along cross sections of the device demonstrate that the p?n junction is a buried homojunction, and the p/n boundary is located 30?80 nm from the CIGS/CdS interface in the CIGS film. The built-in electric field terminates at the CIGS/CdS interface, indicating that the CdS and ZnO layers of the device structure are inactive for the collection of photoexcited carriers.

We report on experiments on vertically shaken binary granular mixtures, which separate into their components due to the external excitation. This well-known phenomenon, where large particles rise to the top of the mixture, is called the Brazil-nut effect. Recent theoretical findings predict also a reverse Brazil-nut effect, where large particles sink to the bottom of the container. We choose spherical beads of various diameters and materials in order to observe the transition from Brazil-nut effect to its reverse form. The direction of demixing depends sensitively on the external excitation, so that it is possible to switch between both effects for a given mass density ratio.

The scaling exponents α, β, and 1/z in thin films of the organic molecule diindenoperylene deposited on SiO2 under UHV conditions are determined. Atomic-force microscopy, x-ray reflectivity, and diffuse x-ray scattering were employed. The surface width displays power law scaling over more than 2 orders of magnitude in film thickness. We obtained α= 0.684±0.06, β= 0.748±0.05, and 1/z = 0.92±0.20. The derived exponents point to an unusually rapid growth of vertical roughness and lateral correlations. We suggest that they could be related to lateral inhomogeneities arising from the formation of grain boundaries between tilt domains in the early stages of growth.

Optical properties of ultrathin layers (<50 Å) of Au and Pb quench condensed on amorphous germanium (α-Ge) have been measured in situ at 10 K. The development of these films from an insulating state to a metallic state is traced as a function of the film thickness as well as the sheet resistance, R□. Of particular interest is the regime of R□ near 3000 Ω where there is an anomaly in the optical transmission. This anomaly is due to a singularity in the dielectric function when the system undergoes an electronic percolation or insulator-to-metal (I/M) transition.

「選択を変えない場合に当たる確率は1/3。選択を変えてハズレるのは最初に当たりを引いていた場合で，それ以外は当たるわけだから選択を当たる確率は1-1/3=2/3となる。したがって選択を変えた方が有利」j

結局，答えを知っている相手(司会者)による選別を経たほうが確率が高いということだ．自分が最初に選んだ一つだけは相手の選別の対象となっていないので，確率が上昇しない．

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A high-density surface-wave magnetized argon plasma operated in the very low pressure regime together with a rf biased system is used to study the pure physical etching characteristics of platinum thin films. It is shown that, for a given dc self-bias voltage, the platinum etch rate strongly decreases as the operating pressure increases, which results from a decrease of the ion density at the sheath edge and from enhanced redeposition. It is found that using a high-density plasma in the very low pressure regime yields high etch rates with a good selectivity over resist. Fence-free features can also be achieved at bias voltages that, in contrast with reactive ion etching reactors, are only slightly above the platinum sputtering threshold.

We analyze a real-space expression for the local stress tensor. This tensor rigorously satisfies conservation of linear momentum. From this expression a coarse-grained tensor is obtained for use in atomistic simulations of solids. Our formulation is then validated by considering both a homogeneously strained crystalline solid and one containing an oversized inclusion. In the latter case a direct comparison is made with results from anisotropic elasticity theory. We find that we are able to obtain good agreement with the suitably averaged continuum solutions in the far-field regime. Moreover, the coarse-grained tensor derived here appears to offer superior accuracy as compared to a stress tensor that has been widely used in atomistic analysis.

Based on our previous Monte Carlo simulation model of electron interactions with solids, including cascade secondary electron production, in which an optical dielectric function was used to describe electron energy loss and the associated secondary electron excitation, we have systematically investigated secondary electron generation and emission for 19 metals. The calculated secondary yield curve for primary beam energy ranging from 100 eV to 2 keV was found to correspond with the experimental universal curve. The dependence of the secondary yield on the work function was studied numerically, leading to a remarkable scattered deviation from Baroody's relationship. This deviation shows that the secondary yield relates to different aspects of behavior by electrons in a metal, such as the cascade production process, the stopping power and specific energy loss mechanism for a sample, and the dependence on the electron density of states. The results provide an explanation for the scattered data on the experimental yield versus the work function. The calculations indicate that the characteristic energy loss of primaries may result in a corresponding feature in the energy distribution of secondaries.

The control of reactive sputter processes has been dynamically simulated by integrating the Larsson differential equations. This was done by employing a fast Runge?Kutta step control algorithm, allowing us to simulate sputtering with more than 20-fold real time speed on a pentium 166 Mhz. A simple proportional integral differential (PID) algorithm was implemented to simulate (i) the partial pressure control via reactive gas flow at a fixed current and (ii) the partial pressure control via current at a fixed reactive gas flow. The control cycle time was varied with respect to real life process control. These simulations show that arbitrary setpoints on the stationary s curve resulting from the steady state Larsson equations can be stabilized. However, the cycle time of the PID controller has to be small enough, e.g., less than 600 ms, for a reliable control. The setpoints in the transition mode are highly unstable, so that the process drifts immediately into one of the two corresponding stable steady states (typically within about 3?15 s) after freezing the control. In addition these computations were compared with experimental control results of reactively sputtered TiO2 and Nb2O5 films deposited by the midfrequency technique. In both cases the total s curve was stabilized at a constant oxygen flow. The process stabilization was performed at power densities of up to 5 W/cm2, limited by the generator output. For the oxygen partial pressure measurements a -probe with optimized speed was used.

An expansion of a bicomponent laser plume into a dilute ambient gas is simulated using a combined direct simulation-random trajectory Monte Carlo method. The stoichiometry of thin films deposited from laser-desorbed material on a flat substrate is examined. In the case of energy-dependent particle adsorption probability, the dependencies of deposition rate on the background pressure are shown to be nonmonotonic with maximums at low gas pressure. In addition, an increase in the ratio of light to heavy species was obtained at low pressure. We demonstrate that these results can be attributed to the interplay between the effects of collisions with the background gas on the fluxes of particles arriving at the substrate and on the adsorption probability of the species. The calculation results are consistent with recent experiments. The study is of interest for the optimization of the experimental conditions during pulsed laser deposition of multicomponent materials.