摘要:

Two extreme cases can be solved for electron charging effects where the first one ignores the electron correlation and the second one treats only one‐electron scattering. So far, Coulomb blockade has been treated by the orthodox theory [Likharev, IBM J. Res. Dev.32, 144 (1988)], where the charging energy is expressed ase2/2Cusing the capacitanceCof a tunnel junction. On the other hand, one‐electron scattering can be solved exactly by using the Schrödinger equation. But it is difficult to solve for a many‐body system by the Schrödinger equation. In this article, stress is placed on the case where the electric field cannot be ignored anymore. A treatment of the charging energy is proposed using a screening model or an electromagnetic field model by employing a cavity model in the field of photon.

ISSN:0734-211X    

DOI:10.1116/1.588868

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The operation of the scanning tunneling microscope (STM) in the near field emission regime provides a direct, noninvasive approach for investigating surfaces at nanometer scale. Here, we present a study of the current characteristics in a near field emission STM. The influence of tip’s geometry is analyzed. We show that the electron field emission from the sample is stable against tip‐shape changes due to adsorbate diffusion or atomic rearrangements.

ISSN:0734-211X    

DOI:10.1116/1.588869

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Due to the finite size of the probe tip, atomic force microscopy (AFM) images of biomolecules, and other structures similar in size, are laterally enlarged. We use mathematical morphology, a non‐linear image processing method, to model the interaction between probe tip and sample. In a typical imaging situation, baseline dimensions are most affected by the probe and widths can be 80% tip and 20% molecule. Using the morphological model and a known tip, we can restore the image so that it more closely resembles the actual surface. Morphological restoration is ideal in some regions, giving the exact sample surface, and improved in others. In the case of a carbon probe, restoration increases the perfectly obtained surface area by as much as 160 times. Following restoration, lateral widths at fixed heights are improved by as much as 75%. Restoration greatly improves image resolution even if one uses probes consisting of very small candidate structures, e.g., nanotubes and Bucky balls. The tip imaging process is also modeled, and we find that calibration spheres should be larger than the molecules of interest and that for many tips, there is little or no advantage to using smaller spheres. A blood plasma protein, fibrinogen, is modeled, and AFM and restored images of single molecules are computed.

ISSN:0734-211X    

DOI:10.1116/1.588870

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

A recently developed optical‐scatter instrument, the scanning scattering microscope (SSM) produces two‐dimensional images of very small surface features and of variations in surface topography. In its present configuration, the lateral resolution is better than 10 μm and its sensitivity to surface roughness is in the angstrom (rms) range. The performance of the SSM has been demonstrated using calibration gratings, Si(100) surfaces, and Ge thin films grown on silicon; intercomparison also was made with atomic force microscope measurements. These results indicate that this scanned optical technique is a very useful noncontact method for evaluating surface microtopography.

ISSN:0734-211X    

DOI:10.1116/1.588871

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

As‐terminated Si surfaces are model semiconductor interface systems with a wide range of technological applications. We have studied As‐terminated Si (001) surfaces with scanning tunneling microscopy which reveals that it is possible to produce a well ordered surface. Some characteristic types of defects do occur on this surface, however, which are found to be of particular interest. These include antiphase domain boundaries, step edges, and long, atomically straight trenches running perpendicular to the dimer rows across the surface. The nature and origin of these defects are discussed.

ISSN:0734-211X    

DOI:10.1116/1.588872

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The reconstructed Si (111) 7×7 surface was imaged in several operation modes of the combined ultrahigh vacuum atomic force microscope/scanning tunnel microscope. By imaging single atom defects on the sample surface a clear proof of the atomic resolution in noncontact mode of the force microscope was possible. By simultaneous measurements of several interaction parameters and by the investigation of force‐distance curves, it was possible to explain the origin of the interaction.

ISSN:0734-211X    

DOI:10.1116/1.588873

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The complex pattern of the nanowire skeletons of different light emitting porous silicon structures is investigated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Diffraction lines and dark field images are used to identify and determine the crystallite specimen long range order. TEM images give the size and particle orientation, and AFM images show a three‐dimensional pattern formed by an interconnecting skeleton of particles. Near infrared photoluminescent porous silicon (0.006 Ω cm) structures show a skeleton of nanosized silicon aggregates which form domains of spatially oriented crystallites. For red photoluminescent samples (4.9 Ω cm) the electron diffraction spots are discontinuously split into tiny intensity maxima. The diameter of the wire structure forming porous silicon as measured by TEM allows us to estimate the distortion of the AFM images due to the finite size of the tip radius. A critical angle α0=2 arctan[K/(1−K)]1/2, whereKis the ratio of the height of the structure to the tip diameter was defined and it was shown that for structure walls steeper than α0the distortion may be substantial.

ISSN:0734-211X    

DOI:10.1116/1.588874

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

We present a systematic study of the performance of scanning tunneling microscope (STM)‐based, low energy electron beam lithography, using simulations of field emission from STM tips, emphasizing realistic conditions of tip geometry and operation. We calculate the potentials and electric field for a hemispherical model emitter in an axially symmetric system. Emission current density at the tip is calculated using the Fowler–Nordheim equation, and current density at the sample is obtained by calculating trajectories of emitted electrons. We characterize the beam diameter at the sample as a function of emitter radius, tip–sample bias, emission current, resist thickness, and tip work function. The beam diameter is primarily affected by the tip–sample gap, increasing at larger gaps, characteristic of high bias and large tip curvature. For optimal tip radius the beam diameter increases linearly with bias from approximately 2 nm at 5 V to 25 nm at 50 V. Beam diameter is nearly independent of emission current over the range 0.05–50 nA. Dielectric resist films cause an increase in beam diameter due to increased tip–substrate gap. Beam diameter is very sensitive to tip work function, increasing dramatically for low work function tips. Tips comprised of asperities on flat surfaces produce significantly smaller beams compared to ‘‘standard’’ tips of the same emitter radius. However, for low bias (<15 V) beam diameter becomes insensitive to tip geometry. We compare these simulations to selected experimental results to evaluate the limitations to performance and assess the feasibility of routine sub‐10 nm structure fabrication using STM‐based low energy electron beam lithography.

ISSN:0734-211X    

DOI:10.1116/1.588751

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The resolution of electron‐beam lithography is limited by the proximity effect, which is due to the scattering of incident electrons. This scattering leads to exposure of neighboring areas and, therefore, to pattern degradations. It can be modeled by convolving the incident dosage distribution with a point spread function and the subsequent developing process by a pointwise nonlinear function. This article presents an iterative algorithm that exploits this overall model to compute corrections of the proximity effect in the nanometer range. A convex error function is derived that satisfies all physical constraints and the problem is set up as a convex, constrained, and nonlinear minimization problem. The correction algorithm is a hybrid of the conjugate gradient and gradient projection algorithms. Its performance for a test pattern is evaluated and then a detailed analysis of the effect of inaccuracies of the model parameters and of the necessary quantization of the corrected incident dosage distribution is presented.

ISSN:0734-211X    

DOI:10.1116/1.588752

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Independent parallel features have been lithographically patterned with a 2×1 array of individually controlled cantilevers using an atomic force microscope. Control of the individual cantilevers was achieved with an integrated piezoelectric actuator in feedback with a piezoresistive sensor. Patterns were formed on 〈100〉 single crystal silicon by using a computer controlled tip voltage to locally enhance the oxidation of the silicon. Using the piezoresistor directly as a force sensor, parallel images can be simultaneously acquired in the constant force mode. A discussion of electrostatic forces due to applied tip voltages, hysteresis characteristics of the actuator, and the cantilever system is also presented.

ISSN:0734-211X    

DOI:10.1116/1.588753

出版商:American Vacuum Society    

年代:1996

数据来源: AIP