H.M. Liu

Numerical calculation of the temperature distribution and evolution of the field‐ion emitter under pulsed and continuous‐wave laser irradiation

The temperature distribution and evolution of metal field‐ion emitters under pulsed and continuous‐wave (cw) laser irradiation are obtained numerically using implicit alternating direction method. For the cw laser irradiation, the temperature distribution in the emitter reaches a steady‐state value after approximately 2 μs of laser heating. The peak temperature of the tip apex reached depends almost linearly on the incident energy flux of the laser beam, and also on the cone angle of the emitter. For the fast laser pulse, both the waveform and the spatial intensity variation of the laser beam are considered. The numerical result is found to differ only slightly from that obtained by assuming a square shape of the laser pulse. The feasibility and advantages of using a laser beam as a means of heating the emitter in the study of single atom surface diffusion and adatom‐adatom interaction, laser‐induced silicide interface formation, and other studies with the Atom Probes and Field Ion Microscope are also dis...

Atomic structures of several silicon surfaces: A direct field ion microscope observation

Atomically resolved and well‐ordered field ion images of several silicon surfaces have been obtained. For a carefully cleaned Si tip, after annealing at 800 °C for several minutes, very well‐ordered atomic structures develop on high index planes such as the (230), (135), (124), (234), (123), (113), (115), and (317). Many of them are reconstructed. Two structures coexist for the (230) plane. Also, many two‐dimensional defects can be seen.

Atomic structures in reconstruction of high index surfaces of silicon

Abstract Recently we have succeeded in obtaining atomically resolved and well ordered field ion images of silicon surfaces. We present here methods of analysis of these images, and also details of the experiment. By thermal annealing of a silicon emitter, several high index surfaces such as the {023}, {155}, {123} and {137} develop into large facets with very well ordered atomic structures. Therefore these are surfaces of greater stability and lower surface free energy, and should be of particular interest even though only a few studies of silicon high index surfaces exist. The best developed facets depend very sensitively on the annealing temperature, and very well ordered structures are observed only if the emitter is annealed in a narrow temperature range, between 700 and 850°C. By comparing with the (1 × 1) structures of these silicon surfaces, we conclude that most of these surfaces are reconstructed. Based on two different methods of distance calibration, two sets of atomic structures consistent with the images are proposed. Further studies with other techniques are needed to clarify the atomic structures in the reconstruction of these high index surfaces.

Growth of thin single crystal NiSi2 films on Si surfaces, a field ion microscope study

Thin single crystal NiSi2 films have been grown epitaxially on the [111] oriented Si tip surface in ultrahigh vacuum (UHV). A 180° change in the axial symmetry is found for the field ion images taken before and after the growth of the silicide layers. From this observation and a computer simulation of the field ion images we conclude that the Si‐NiSi2 interface has the B‐type structure. The field ion image of the NiSi2 films is good enough to reveal the atomic structure of the (111) Ni layer.

Atomic structures of silicon and metal surfaces; pulsed-laser tof atom-probe and field ion microscopy

Abstract The atomic structure of a solid surface can be imaged with the field ion microscope and the chemical species of surface atoms can be identified by the time-of-flight atom-probe. By combining a pulsed-laser technique to field ion microscopy, atomic processes in surface reconstruction and growth of thin films can be studied with a resolution of 2.5 A, and in time steps of a few nanoseconds. The mass resolution and material applicability of a pulsed-laser time-of-flight atom-probe are greatly improved. Thus materials of poor conductivity such as high purity silicon can be analyzed with excellent mass resolution. It is also ionion energy analyzer with an accuracy and resolution of 2 parts per 100 000 and an ion reaction and dissociation time analyzer of 20 fs time resolution. Some recent studies with these techniques such as (1) surface reconstruction of Pt and Ir(001) and (110) surfaces, (2) observation of well ordered and atomically resolved images of pure silicon surfaces and surface reconstruction of many surfaces of silicon, and (3) formation of multiple charge cluster ions and dissociation of compound ions by atomic tunneling in an electric field etc., will be briefly described. We want to emphasize that recent studies of Si and metal surfaces are concerned with atomic structures of thermally equilibrated surfaces, and not with field evaporated surfaces as in earlier studies.

Initial stages of iridium-semiconductor compound formation and the interface atomic structures: A field ion microscope study

Abstract The early stages of formation of thin layers of IrSi and IrGe on clean Ir surfaces and the interface atomic structures have been studied in the field ion microscope. Distinctive stages of growth of Ir-silicide have been observed. In the earliest stage, two atomic layers of silicide are formed on the Ir(001) plane. Atomically resolved images show a structure resembling the C(2×2) overlayer structure of the substrate, which we believe to have the (011) Ir-layer structure of the (011) plane of IrSi crystal. In the second stage, the (2×1) image structure observed on the Ir(011) is identified to be the Ir-layer of the IrSi(001) fundamental planes. Formation of IrGe on the Ir(001) is similar to the earliest stage of silicide formation. We believe that the ordered interface atomic structures we have observed with the FIM should also be observable at flat interfaces with conventional techniques.

Atomic structures at IrSi(IrGe)/Ir(001) interfaces

The interface atomic structure of very thin IrSi(IrGe) films grown on the Ir(001) plane has been studied with the field ion microscope. Two distinctive types of structures have been observed. One shows the C(2×2) structure of the substrate. As the size of the layer is reduced by field evaporation, the surface relaxes into a rhombic structure resembling the (011) Ir layer of the IrSi(IrGe) crystal. The other shows a rectangular unit cell of a larger size, which is not yet successfully correlated to the structure of the IrSi(IrGe) crystal.