John M. Lindquist

Photoelectron spectroscopy studies of the hydrogenation of cyanogen on Pt(111): Comparison with HCN and ethylenediamine

Abstract X-ray photoelectron spectra as a function of anneal temperature are used to compare the thermally initiated chemistry of C2N2 + H2 on Pt(111) with that of C2N2, HCN and ethylenediamine. These spectra show that the product of the reaction of C2N2 with coadsorbed hydrogen (the γ state of C2N2 + H2/Pt(111)) is not HCN but is more likely to be a surface di-imine species. The N1s binding energy of this partially hydrogenated species is ∼ 399.3 eV. HCN adsorption on Pt(111) leads to two distinct chemical species with N1s binding energies of 398.6 and 396.9 eV which are interpreted in terms of molecular and dissociative adsorption respectively.

Beam-induced modifications of TCNQ multilayers

Abstract We report on the investigation of electron and ion-beam-induced modifications of multilayer quantities of tetracyanoquinodimethane (TCNQ) adsorbed on a metal substrate. X-ray and ultraviolet photoelectron spectroscopy, thermal desorption spectroscopy, Auger electron spectroscopy and Raman spectroscopy have been used to study the beam-induced chemistry. The changes induced by electron or ion-beam exposure include: (i) stabilization against thermal decomposition as indicated by TDS, (ii) changes in the UPS and Raman spectra, (iii) binding energy shifts in the XPS carbon and nitrogen peak position as well as changes in the chemical reactivity of the beam exposed film. In particular the beam modified material is stable to temperatures of 625 K at which point the onset of decomposition is observed with evolution of HCN, H 2 and N 2 . In comparison, unmodified TCNQ multilayers sublime at 350 K leaving behind a few layers which decompose beginning at 475 K. The integrity of the modified material below the decomposition temperature is verified by temperature dependent UPS measurements. The work function, derived from the UPS, increases upon modification. As the multilayer is modified the Raman spectrum characteristic of molecular TCNQ converts into a broad, featureless spectrum. The Raman and XPS spectra have been used to follow the effect of beam dosage. The N 1s peak of the XPS spectrum broadens and becomes a doublet with beam dosage while the carbon peaks narrow to become a singlet. These changes appear to be consistent with beam induced polymerization of TCNQ.

The interface chemistry of HgCdTe passivated with native sulfide layers grown from nonaqueous and aqueous polysulfide solutions

We have grown anodic sulfide passivation layers on HgCdTe from both nonaqueous and aqueous polysulfide solutions. In both cases CdS layers are nominally obtained. The growth behavior of the sulfide layers is found to be quite different in the different electrolytes. Capacitance–voltage measurements on metal‐insulator semiconductor device structures that incorporated a ZnS cap and Pd gate metal over the CdS have been used to compare the electrical properties of the interfaces produced. Preliminary evidence suggests that aqueous anodic sulfide layers may be more stable than nonaqueous ones, but contain more positive fixed charge and mobile ion charge. Auger electron spectroscopy depth profiles indicate that the aqueous anodic sulfides are oxide free, but appear to contain more Hg and Te contamination than nonaqueous anodic sulfides.

Passivation of HgCdTe with CdS thin films: Correlation of device characteristics with surface spectroscopy

We present results on the passivation of HgCdTe with thin films of CdS grown anodically from nonaqueous polysulfide electrolytes. Electrochemical measurements have been carried out to develop an understanding of the film growth. Capacitance‐voltage measurements on metal‐insulator‐semiconductor (MIS) device structures that incorporated a ZnS cap and Pd gate metal over the CdS are used to compare electrical properties of the interface with Auger electron spectroscopy (AES) and x‐ray photoelectron spectroscopy (XPS) depth profiles. The surface spectroscopies were carried out using a sample temperature of 170 K, which allowed us to easily observe Hg by Auger electron spectroscopy. XPS and AES results show that Hg and Te are partially incorporated into the CdS layer, as sulfides that did not completely dissolve during the film growth. The interdiffusion of Zn into the interface resulted in large hysteresis in the C‐V data. By minimizing the Zn interdiffusion, MIS devices with low hysteresis (∼0.25 V) that are ...

Ion beam removal of water and dioctyl phthalate from cryogenic mirrors

This study details recent work on spectroscopic detection and ion beam removal of molecular contaminants on mirror surfaces. Results are presented for initial experiments that investigate the effects of irradiating contaminated, low-temperature mirror surfaces with ion beams. Effects of the ion beam on the clean cryogenic substrates are examined as well as the physical process occurring during ion bombardment of the contaminant films. Water and dioctyl phthalate are studied as principal contaminants on beryllium and copper mirror surfaces. Conditions necessary to remove these contaminants by ion beam bombardment were determined. lonbeam-induced chemistry is observed for removal of water from a beryllium surface. These results demonstrate the importance of the chemical and physical nature of mirror surfaces with respect to contaminant removal by this method.

An x‐ray photoelectron spectroscopy study of water removal from beryllium at 160 K: Evidence for ion beam induced oxidation

We present data for the ion beam removal of H2O from beryllium at 160 K. The removal rate of H2O from beryllium is qualitatively slower than that from copper. Evidence from x‐ray photoelectron spectroscopic measurements indicates the ion beam causes surface oxidation up to a point where the oxide thickness prohibits further reaction. The mechanism for this ion beam induced surface oxidation is discussed and points toward H2O bond breakage by the ion beam as a significant contributing factor.