Reflection anisotropy spectroscopy (RAS) is a non-destructive optical probe of surfaces that is capable of operation within a wide range of environments. In this review we trace the development of RAS from its origins in the 1980s as a probe of semiconductor surfaces and semiconductor growth through to the present where it is emerging as a powerful addition to the wide range of existing ultra-high vacuum (UHV) surface science techniques. The principles, instrumentation and theoretical considerations of RAS are discussed. The recent progress in the application of RAS to investigate phenomena at metal surfaces is reviewed, and applications in fields including electrochemistry, molecular assembly, liquid crystal device fabrication and remote stress sensing are discussed. We show that the experimental study of relatively simple surfaces combined with continuing progress in the theoretical description of surface optics promises to unlock the full potential of RAS. This provides a firm foundation for the application of the technique to the challenging fields of ambient, high pressure and liquid environments. It is in these environments that RAS has a clear advantage over UHV-based probes for investigating surface phenomena, and its surface sensitivity, ability to monitor macroscopic areas and rapidity of response make it an ideal complement to scanning probe techniques which can also operate in such environments.

http://iopscience.iop.org/article/10.1088/0034-4885/68/6/R01/pdf

Reflection anisotropy spectroscopy

We used near-edge x-ray absorption fine structure (NEXAFS) spectroscopy to link the orientational bond order at three carbonaceous surfaces-rubbed polyimide, ion beam-irradiated polyimide, and ion beam-irradiated diamondlike carbon films-with the direction of liquid crystal (LC) alignment on these surfaces. We show that, in general, LC alignment can be created on any carbonaceous substrate by inducing orientational order at its surface. Our results form the scientific basis for LC alignment layers consisting of amorphous carbon films in which orientational order near the surface is induced by a directional low-energy ion beam.

https://science.sciencemag.org/content/sci/292/5525/2299.full.pdf

Liquid crystal alignment on carbonaceous surfaces with orientational order.

Nanocrystalline intermetallic powders have been synthesized from metal salt precursors at low temperatures using a modified polyol process with tetraethylene glycol as the solvent. This solution route has yielded several phase-pure compounds in the M−Sn (M = Ag, Au, Co, Cu, Fe, Ni), Pt−M‘ (M‘ = Bi, Pb, Sb, Sn), and Co−Sb bimetallic systems. In the Co−Sb system, CoSb and CoSb3 can be selectively produced by controlling the initial metal concentrations and the reaction temperature. The Co−Sn and Cu−Sn systems can selectively form Co3Sn2 vs CoSn and Cu6Sn5 vs Cu41Sn11 during a single reaction as a function of temperature. These results demonstrate kinetic control over crystal structure in these intermetallic systems. The reaction progress may be monitored at different times and temperatures by XRD, giving insight into the reaction pathways. TEM micrographs show that the particle sizes in the M−Sn systems range from 5 to 50 nm, while the Pt−M‘ systems range from 10 to 100 nm. SEM micrographs show that these p...

Low-Temperature Solution Synthesis of Nanocrystalline Binary Intermetallic Compounds Using the Polyol Process

From simple pocket calculators, to mobile telephones and LCD-TV, over the past few decades devices based on liquid crystal display technology have proliferated into just about all conceivable aspects of everyday life Although used in cutting-edge technology, it is surprising that a vital part in the construction of such displays relies essentially on a process invented almost 100 years ago This essential part, the alignment layer, dictates the macroscopic uniform alignment of liquid crystalline molecules (mesogens) near its surface The current method for manufacturing such layers is the mechanical rubbing of spin-coated polymers with a piece of velvet cloth This very successful method is still at the basis of the production process of even the largest displays currently manufactured in industry Unfortunately, the construction of ever larger displays with this technique is becoming a technological nightmare for engineers Therefore, over the past decades, many alternatives to rubbing have been explored This review will focus on advances towards achieving one of the most important goals in LCD technology: attaining rational control over the properties of nematic liquid crystal domains

LCD alignment layers. Controlling nematic domain properties

We present ion beam erosion experiments performed in ultrahigh vacuum using a differentially pumped ion source and taking care that the ion beam hits the Si(001) sample only. Under these conditions no ion beam patterns form on Si for angles ?45? with respect to the global surface normal using 2?keV Kr+ and fluences of ??2 ? 1022?ions?m?2. In fact, the ion beam induces a smoothening of preformed patterns. Simultaneous sputter deposition of stainless steel in this angular range creates a variety of patterns, similar to those previously ascribed to clean ion-beam-induced destabilization of the surface profile. Only for grazing incidence with 60???83? do pronounced ion beam patterns form. It appears that the angular-dependent stability of Si(001) against pattern formation under clean ion beam erosion conditions is related to the angular dependence of the sputtering yield, and not primarily to a curvature-dependent yield as invoked frequently in continuum theory models.

https://iopscience.iop.org/article/10.1088/0957-4484/21/8/085301/pdf

Is keV ion-induced pattern formation on Si(001) caused by metal impurities?

The technique used to align liquid crystals—rubbing the surface of a substrate on which a liquid crystal is subsequently deposited1,2,3—has been perfected by the multibillion-dollar liquid-crystal display industry. However, it is widely recognized that a non-contact alignment technique would be highly desirable for future generations of large, high-resolution liquid-crystal displays. A number of alternative alignment techniques have been reported4,5,6,7, but none of these have so far been implemented in large-scale manufacturing. Here, we report a non-contact alignment process, which uses low-energy ion beams impinging at a glancing angle on amorphous inorganic films, such as diamond-like carbon. Using this approach, we have produced both laptop and desktop displays in pilot-line manufacturing, and found that displays of higher quality and reliability could be made at a lower cost than the rubbing technique. The mechanism of alignment is explained by adopting a random network model of atomic arrangement in the inorganic films. Order is induced by exposure to an ion beam because unfavourably oriented rings of atoms are selectively destroyed. The planes of the remaining rings are predominantly parallel to the direction of the ion beam.

Kei Hsuing Yang

Papers

Atomic-beam alignment of inorganic materials for liquid-crystal displays