As their name indicates, liquid crystals simultaneously exhibit some characteristics common to both ordinary isotropic liquids and solid crystals. This ambivalence is also found in the effects of surfaces on these systems which lead to a great diversity of phenomena. These phenomena are reviewed focusing on nematic liquid crystals which have the simplest structure among the many existing types and which have been the most extensively studied. Three main kinds of effects can be distinguished. The first concerns the perturbation of the liquid crystalline structure close to the surface. Beyond this transition region, the bulk liquid crystalline structure is recovered with an orientation which is fixed by the surface: this phenomenon of orientation of liquid crystals by surfaces is the so-called anchoring. Finally, close to bulk phase transitions, critical adsorption or wetting can occur at surfaces as is also seen in isotropic systems.

https://iopscience.iop.org/article/10.1088/0034-4885/54/3/002/pdf

Surface effects and anchoring in liquid crystals

Nanomechanical resonators can now be realized that achieve fundamental resonance frequencies exceeding 1 GHz, with quality factors (Q) in the range 10^3<=Q<=10^5. The minuscule active masses of these devices, in conjunction with their high Qs, translate into unprecedented inertial mass sensitivities. This makes them natural candidates for a variety of mass sensing applications. Here we evaluate the ultimate mass sensitivity limits for nanomechanical resonators operating in vacuo that are imposed by a number of fundamental physical noise processes. Our analyses indicate that nanomechanical resonators offer immense potential for mass sensing—ultimately with resolution at the level of individual molecules.

/pdf/ultimate-limits-to-inertial-mass-sensing-based-upon-vjlphpx903.pdf

Ultimate limits to inertial mass sensing based upon nanoelectromechanical systems

Two-dimensional molecular patterns were obtained by the adsorption of long-chain alkanes, alcohols, fatty acids, and a dialkylbenzene from organic solutions onto the basal plane of graphite. In situ scanning tunneling microscopy (STM) studies revealed that these molecules organize in lamellae with the extended alkyl chains oriented parallel to a lattice axis within the basal plane of graphite. The planes of the carbon skeletons, however, can be oriented either predominantly perpendicular to or predominantly parallel with the substrate surface, causing the lamellar lattice to be either in or near registry with the substrate (alkanes and alcohols) or not in registry (fatty acids and dialkylbenzenes). In the case of the alcohols and the dialkylbenzene the molecular axes are tilted by +30 degrees or -30 degrees with respect to an axis normal to the lamella boundaries, giving rise to molecularly well-defined domain boundaries. Fast STM image recording allowed the spontaneous switch between the two tilt angles to be observed in the alcohol monolayers on a time scale of a few milliseconds.

https://science.sciencemag.org/content/sci/253/5018/424.full.pdf

Commensurability and mobility in two-dimensional molecular patterns on graphite.

Vacuum scanning tunneling microscopy has been used to investigate the hydrogen‐terminated Si(111) surfaces obtained upon dissolution of the native oxide in HF and NH4F solutions. Whereas etching in aqueous HF acid produces an atomically rough surface, comparable treatment in NH4F results in atomically flat surfaces. These atomically flat surfaces are extremely well ordered and exhibit terraces which extend thousands of angstroms.

Comparison of Si(111) surfaces prepared using aqueous solutions of NH4F versus HF

This review provides a general introduction into the theory of cantilever sensors, including practical design concepts, examples for liquid-phase sensing with particular emphasis on biological applications, and a discussion of future prospects.

Cantilever-based biosensors

A bending and stretching mode crystal oscillator as a friction vacuum gauge

Vibration isolation technology for scanning tunneling microscopy (STM) to suppress the external mechanical perturbation down to a subatomic scale is described. The system is simplified into two subsystems, a tunneling assembly and a supporting table. Each of them has its own mechanical eigenfrequency. The principle of the isolation exists in making the two eigenfrequencies very different from each other. A theory of isolation developed is based on a model of multiply coupled oscillators with damping. Experimental results of the isolation characteristics for the two types of isolators constructed, one consisting of two‐stage coil springs and the other of multiply stacked metal plates with rubber pieces among them, are well explained by the theory. STM images of graphite are obtained by using these isolators combined with various tunneling assemblies. Thereby the basis for design of the isolators is clarified.

Vibration isolation for scanning tunneling microscopy

THE existence of Fermi-liquid electronic states in the high-Tc superconductor Bi2CaSr2Cu2O8 has been experimentally established by angle-resolved photoemission spectroscopy1. The nature of these states has been studied by various high-energy spectroscopies1–5, all of which indicate that the electronic states at the Fermi energy reside mainly in the oxygen 2p orbital with in-plane symmetry. The question remains as to which plane in the crystal, BiO or CuO2, provides the O 2p orbitals at the Fermi energy. This point is important in modelling the high- Tc mechanism, because if the Fermi-liquid states were supplied by the BiO plane, which is not present in the copper oxide high-Tc superconductors, mechanisms based on the Fermi-liquid states would lose their direct experimental basis. Here we present results from scanning tunnelling spectroscopy (STS), combined with photoemission (PES) and inverse photoemission (IPES) spectroscopies, which show that the BiO planes are non-metallic and the O 2p orbitals in the CuO2 planes form the Fermi-liquid states.

Evidence for non-metallic nature of the BiO plane in Bi2CaSr2Cu2O8 from scanning tunnelling spectroscopy

Voltage‐dependent images of liquid crystals on graphite were observed in air by scanning tunneling microscopy (STM). Molecular rows of liquid crystals and the atomic pattern of the graphite substrate were imaged with high (above 1 V) and low (below 0.1 V) bias voltages, respectively. Patterns of molecules, grain boundaries, and distinguishable defects of the liquid crystal arrangement were reproduced even after imaging the substrate in the same area. This indicates that the graphite lattice can be seen by STM without touching or disturbing the adsorbed molecules on it. A resonant tunneling model is proposed to explain the phenomenon.

Voltage‐dependent scanning tunneling microscopy images of liquid crystals on graphite

The initial stages of the adsorption processes of oxygen and hydrogen on the Si(111)‐7×7 surface were studied at room temperature in real time using a ultrahigh vacuum scanning tunneling microscopy (UHV STM). We have found several specific features for each process. (1) the [112] steps are relatively insensitive to oxygen or hydrogen exposure: more resistant to hydrogen than to oxygen. (2) The adsorption proceeds with different chemical reactivities among the adatoms: the adatoms in the faulted half of the 7×7 unit cell are more active than the unfaulted half; the center adatoms in each half are more active and the corner adatoms are the next; the corner holes in the 7×7 unit cell are less active indicating that the 7×7 structure still exists even for fairly high coverages. (3) At initial stages of adsorption, oxygen is adsorbed in the on‐top site of the surface adatom forming Si–O and then in the bridge site forming Si–O–Si which causes the disorder in the image, whereas hydrogen is adsorbed in the on‐...

M. Ono

Papers

A bending and stretching mode crystal oscillator as a friction vacuum gauge

Vibration isolation for scanning tunneling microscopy

Evidence for non-metallic nature of the BiO plane in Bi2CaSr2Cu2O8 from scanning tunnelling spectroscopy

Voltage‐dependent scanning tunneling microscopy images of liquid crystals on graphite

Real-time observation of oxygen and hydrogen adsorption on silicon surfaces by scanning tunneling microscopy