Atomic layer deposition(ALD), a chemical vapor deposition technique based on sequential self-terminating gas–solid reactions, has for about four decades been applied for manufacturing conformal inorganic material layers with thickness down to the nanometer range. Despite the numerous successful applications of material growth by ALD, many physicochemical processes that control ALD growth are not yet sufficiently understood. To increase understanding of ALD processes, overviews are needed not only of the existing ALD processes and their applications, but also of the knowledge of the surface chemistry of specific ALD processes. This work aims to start the overviews on specific ALD processes by reviewing the experimental information available on the surface chemistry of the trimethylaluminum/water process. This process is generally known as a rather ideal ALD process, and plenty of information is available on its surface chemistry. This in-depth summary of the surface chemistry of one representative ALD process aims also to provide a view on the current status of understanding the surface chemistry of ALD, in general. The review starts by describing the basic characteristics of ALD, discussing the history of ALD—including the question who made the first ALD experiments—and giving an overview of the two-reactant ALD processes investigated to date. Second, the basic concepts related to the surface chemistry of ALD are described from a generic viewpoint applicable to all ALD processes based on compound reactants. This description includes physicochemical requirements for self-terminating reactions,reaction kinetics, typical chemisorption mechanisms, factors causing saturation, reasons for growth of less than a monolayer per cycle, effect of the temperature and number of cycles on the growth per cycle (GPC), and the growth mode. A comparison is made of three models available for estimating the sterically allowed value of GPC in ALD. Third, the experimental information on the surface chemistry in the trimethylaluminum/water ALD process are reviewed using the concepts developed in the second part of this review. The results are reviewed critically, with an aim to combine the information obtained in different types of investigations, such as growth experiments on flat substrates and reaction chemistry investigation on high-surface-area materials. Although the surface chemistry of the trimethylaluminum/water ALD process is rather well understood, systematic investigations of the reaction kinetics and the growth mode on different substrates are still missing. The last part of the review is devoted to discussing issues which may hamper surface chemistry investigations of ALD, such as problematic historical assumptions, nonstandard terminology, and the effect of experimental conditions on the surface chemistry of ALD. I hope that this review can help the newcomer get acquainted with the exciting and challenging field of surface chemistry of ALD and can serve as a useful guide for the specialist towards the fifth decade of ALD research.

Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process

The Colloid Chemical Approach to Nanostructured Materials

A technique is described for fabricating arrays of uniform CdS nanowires with lengths up to 1 μm and diameters as small as 9 nm by electrochemically depositing the semiconductor directly into the pores of anodic aluminum oxide films from an electrolyte containing Cd2+ and S in dimethyl sulfoxide. The nanowire arrays were characterized by powder X-ray diffraction (XRD) and electron microscopy. The deposited material is found to be hexagonal CdS with the crystallographic c-axis preferentially oriented along the length of the pore. The effects of annealing on the crystallinity of the deposited semiconductor were investigated by XRD and resonance Raman spectroscopy. The deposition technique is, in principle, generalizable as a means of fabricating nanowires of a wide range of semiconductors.

Electrochemical Fabrication of CdS Nanowire Arrays in Porous Anodic Aluminum Oxide Templates

Ordered anion adlayers on metal electrode surfaces.

Attenuated total reflection infrared spectroscopy of proteins and lipids in biological membranes.

Electrochemical atomic layer epitaxy (ECALE)

In this paper the method of electrochemical atomic layer epitaxy (ECALE) is described. It involves the alternated electrochemical deposition of atomic layers of elements to form compound semiconductors. It is being investigated as a method for forming epitaxial thin films. Presently, it appears that the method is applicable to a wide range of compound semiconductors composed of a metal and one of the following main group elements: S, Se, Te, As, Sb, or Br. Initial studies have involved CdTe deposition. Factors controlling deposit structure and composition are discussed here. Preliminary results which show that ordered electrodeposits of CdTe can be formed by the ECALE method are also presented. Results reported here were obtained with both a polycrystalline Au thin-layer electrochemical cell and a single-crystal Au electrode with faces oriented to the (111), (110), and (100) planes. The single-crystal electrode was contained in a UHV surface analysis instrument with an integral electrochemical cell. Deposits were examined without their exposure to air using LEED and Auger electron spectroscopy. Coverages were determined using coulometry in the thin-layer electrochemical cell.

Conditions for the Deposition of CdTe by Electrochemical Atomic Layer Epitaxy

Thin-layer electrochemical studies of the underpotential deposition of cadmium and tellurium on polycrystalline Au, Pt and Cu electrodes

This paper is the first report of the formation of thin films, thicker than ten monolayers, using electrochemical atomic layer epitaxy (ECALE). Thin films of CdTe have been electrodeposited on polycrystalline gold substrates in an electrochemical thin-layer flow-cell deposition system using the ECALE methodology. Studies of the deposit morphology have been performed using scanning electron microscopy and atomic force microscope. Significant improvements in deposit morphology are reported as a result of changes to the ECALE cycle program and deposition hardware. Deposit compositions analyzed using electron probe microanalysis and inductively coupled plasma atomic emission spectrometry, were found to be stoichiometric and nearly independent of the number of cycles and the Cd deposition potential. In addition, the deposition rate was shown to be one CdTe monolayer per cycle (half monolayer of Cd and half monolayer of Te per ECALE cycle).

Preliminary Studies of the Use of an Automated Flow‐Cell Electrodeposition System for the Formation of CdTe Thin Films by Electrochemical Atomic Layer Epitaxy

Infrared spectroscopy (IR) and scanning tunneling microscopy (STM) have been used to analyze a model membrane bilayer structure consisting of a phospholipid outer monolayer deposited onto alkane-derivatized surfaces, which were constructed using Langmuir-Blodgett (L-B) and self-assembly methods. The phospholipid used as the outer monolayer was 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG). The hydrocarbon-covered substrates which formed the inner half of the bilayer consisted of either (1) a perdeuterated stearic acid (d-SA) L-B monolayer on a Ge-attenuated total reflectance (ATR) element or (2) vapor-deposited Au-on-mica derivatized with a self-assembled monolayer of 1-octadecanethiol

Structural characterization and nanometer-scale domain formation in a model phospholipid bilayer as determined by infrared spectroscopy and scanning tunneling microscopy

Brian W. Gregory

Papers

Electrochemical atomic layer epitaxy (ECALE)

Conditions for the Deposition of CdTe by Electrochemical Atomic Layer Epitaxy

Thin-layer electrochemical studies of the underpotential deposition of cadmium and tellurium on polycrystalline Au, Pt and Cu electrodes

Preliminary Studies of the Use of an Automated Flow‐Cell Electrodeposition System for the Formation of CdTe Thin Films by Electrochemical Atomic Layer Epitaxy

Structural characterization and nanometer-scale domain formation in a model phospholipid bilayer as determined by infrared spectroscopy and scanning tunneling microscopy