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Conventional atomic layer deposition (ALD) is a thermo-chemical process that is now used extensively in the manufacture of ultrathin films. In addition to substrate heating, various forms of other “assisted” ALD processes are actively being developed, where supplementary energy is supplied for example, from a plasma discharge or from light. This paper presents a critical review of the exploitation of light in ALD to stimulate photochemical processes. The range of light sources that are exploitable for photochemical ALD processes is considered and the chemical mechanisms that are stimulated in the ultraviolet spectrum are interpreted. The use of light as an excitation source lends itself to area selective deposition using lithographic methods or focused beams. The exploitation of photochemical processes for the deposition of patterned ALD films is reviewed in the context of the current alternatives. Finally, the potential for photo-etching is introduced. Atomic layer etching is a complimentary process to ALD and the application of photochemistry in layer-by-layer subtraction processes is considered.

This research has focused on the sensitized photoisomerization step of a solar energy storage system based on the interconversion of norbornadiene (NBD) and quadricyclane (Q). Sensitizers studied in the photoisomerization were arylphosphine complexes of copper(I) halides [(Ph3P)3CuX, (MePh2P)3CuX, (DIPHOS)CuCl; X = Cl, Br, I and DIPHOS = Ph2P(CH2)2PPh2]. The lowest electronic excited state of the complexes can be an effective triplet energy sensitizer as evidenced by a maximum quantum yield of 1.0 with (MePh2P)3CuX. The sensitization mechanism of the L3CuX complexes is proposed as a bimolecular energy transfer process in which energy transfer takes place through the metal centered orbitals. The efficiency of the (MePh2P)3CuX sensitizers is unprecedented by other reported inorganic or organic sensitizers; however, ligand dissociation of the complexes in dilute solutions detracts from their otherwise attractive features. The free ligands undergo rapid photodecomposition and are extremely poor sensitizers of the NBD/Q system. The ligand dissociation of the LmCunCln (L = Ph3P, MePh2P; m:n = 3:1, 2:1, 4:2, 3:2, 2:2) complexes was modeled by use of vapor pressure osmometry and UV absorption. The equilibria and equilibrium constants of dissociation were determined for benzene solutions at 37 °C. The stability of the LmCunCln complexes (Ph3P

Department of Chemistry, Faculty of Science, M. S. University of Baroda, Baroda-390 002 Manuscript received 21 November 1980, revised 19 June 2981, accepted 2 February 1982 The reaction of benzoyl chloride with different potassium-O-alkyl xanthates (n-propyl, iso-propyl, n-butyl) around 0º afforded good yields of corresponding S-benzoyl-O-alkyl xanthates. The structure of these aroyl xanthates were consistent with the spectral data. Aroyl xanthates have been reported to be resistant to photolysis. It has, however, been observed in the present investigation that the fragmentation of these S-benzoyl-O-alkyl xanthates does occur on prolonged photolysis. Irradiation of these xanthates in benzene solution with mercury lamp for 60-70 hr resulted in the formation of benzoyl disulfide. Thermal decomposition around 250º for 15 min gave beam benzoyl disulfide, corresponding ester and carbon disulfide.

Physical Chemistry Section, Jadavpur University, Calcutta-700 032 Manuscript received 10 October 1977, accepted 26 January 1978. Oxygen quenching of excited singlet state or anthracene sulphonate (1-mono sulphonate (1AS), 2- mono sulphonate (2AS) and 1,5· disulphonate (1,5AS)) and their photoperoxidation are studied in aqeous medium. Oxygen quenclling constant is found to be nearly the same within the experimental error for different anthracene sulphonates. Theoretically calculated rate constant for oxygen quenching of fluorescence is compared with those obtained experimentally. However photoperoxidation is highly sensitive to number and position of the sulphonate group in the ring. The rate constant for peroxidation step is found to follow the order 1AS>2 AS> 1,5AS and involve singlet oxygen.

Trans, Z-1, 4-diphenyl-1, 3-butadienecarboxylic acid, recently prepared was exposed to the UV irradiation in the methanol under the influence of the high pressure mercury arch lamp light. After 24 hrs of irradiation it was possible to isolate trans, trans-1, 4-diphenyl-1, 3-butadiene, together with trans, cis-1, 4-diphenyl-1, 3-butadiene, a lot of white polymer material of propose structure as poly-(1, 4-diphenyl)-2-butene and oily compound of proposed structure as 1-4-diphenyl-1-methoxy 2-butene. The proposed structures of all photochemically prepared and isolated compounds is in examination.

Department of Pure Chemistry, University College of Science, Calcutta-700 009 Department of Applied Chemistry, University College of Technology, Calcutta 700 009 Manuscript received 28 April 1930, revised 21 August 1983, accepted 26 November 1983 The effect of viscosity, concentration and pH on the photochemical reduction of Co(III) to Co(II) on irradiation with light of 254, 313, 365 nm have been investigated for complexes of the type [CoL2(N3)2,]+1 (L =ethylene diamine, 2,2'-bipyridyl, 1,10- phenanthroline, biguanide) and also for cis- and trans-[Co(en)2(NO2)(H2O)]2+. Results show that for a particular exciting light \(\phi\)C 2+ is affected only by the viscosity of the photolytic medium and is independent of the concentration of the complex, and pH. It has also been observed that for cis- and trans-[Co(en)2(N3)2]CIO4 the redox quantum yield goes through a maximum and the\(\phi\) redox vs wave length profile is almost parallel to the contour of the uv absorption spectra. Investigations show that the bisazido complexes on excitation in the charge transfer spectral region in nonaqueous media undergo photodecomposition without the formation of Co(II).

The photochemical formation of hydrogen peroxide from water with zinc oxide as a sensitiser has been studied in detail both in sunlight as well as in artificial-ultraviolet and visible light. The yield of hydrogen peroxide increases in presence of some organic compounds which presumably act as stabilisers. Of the nine organic substances employed for this purpose, phenol was found to be the best. An increase in the amount of zinc oxide produces a corresponding increase in the reaction rate which, however, tends to a limit with a constant intensity of light. An increase in the pa has been found to increase the yield of hydrogen peroxide. The formation of hydrogen peroxide also takes place in the total tight from a tungsten filament lamp as well as in the violet region of the visible spectrum isolated by means of filters, although in the latter case the reaction is very slow. This indicates that the photosensitive range of zinc oxide extends up to the violet. The photosensitising activity of zinc oxide, prepared. by different methods, has been studied and it has been found that zinc oxide, prepared from carbonate by ignition, has the greatest activity.

On Induction Period and After-effect in Photochemical Reactions.

The Photochemical Decomposition of Acetaldehyde Solution

Chemical Reactivity and Light Absorption Part I.&nbsp

Photochemical Oxidation of Leuco-Malachite Green by means of Uranyl Nitrate in Monochloracetic Acid Solution.

The kinetics of the photochemical reduction of molybdic acid in presence of d-tartarid acid have been studied and the quantum efficiency of theprocess has been measured. The dependence of the rate of reduction on the concentrations of both complex and uncombined molybdic acid, its variation with change of PHof the system and the appearance of different shades of the reduced solutions, have been explained. Evidence from rotation measurements of the reduced solutions indicates. that, the complex does not break into its components by reduction.

The Decomposition of PotassiumManganioxalate in Plane Polarised, Circularly Polarised and Ordinary Light.

Zinc Oxide as a general Sensitiser for Photochemical Reactions.

The photochemical reactions occurring in aqueous solutions of octacyanomolybdate(V) ion, Mo(CN)_8^3-, during irradiation with light of 365 and 436 nm wavelengths were studied. The quantum yields and reaction products were determined for neutral, unbuffered solutions as well as solutions buffered at pH 4.0, 7.0, and 9.0. The results of these studies showed that the Mo(CN)_8^3- ion is rapidly reduced by light to a Mo(IV) complex. In neutral or acidic media, the initial photoreduction product was found to be the red heptacyanoaquomolybdate(IV) ion, Mo(CN)_7(H_2O)^3-. Photolysis in basic solution gave the yellow heptacyanohydroxomolybdate(IV) ion, Mo(CN)_7(OH)^4-, as an unstable intermediate. Hydrolysis of this complex to the blue tetracyanohydroxooxomolybdate(IV) ion, Mo0(OH)(CN)_4^3-, occurred rapidly in base. In each case, cyanogen, (CN)_2, and cyanate ion, OCN^-, were formed. Additionally, in neutral solutions, the formation of hydrogen ion during the irradiation of the sample gave a rapid drop in the pH of the solution. Measurements of the product quantum yields for Mo(IV) complexes, *_Mo(IV), gave values that were always greater than one and which increased rapidly with increasing pH of the irradiated solutions, The values were the same for both irradiating wavelengths, showing no wavelength effect for the reaction, The quantum yields determined for *_Mo(IV) were 1.51, 1.59, 3.10, and 4.29 for pH 4 , neutral pH, pH 7, and pH 9 solutions respectively. From the experimental results, a reaction mechanism is suggested for each of the aqueous media used, The initial photolytic reactions are the same in all solutions with subsequent thermal reactions being responsible for the variation of *_Mo(IV) with the pH of the solution.

Decomposition of Hydrogen Peroxide by Potassium Ferro- and Ferricyanides.&nbsp

The Phenomenon of After-effect in certain Photochemical Reactions.&nbsp

Photochemical Reaction between lodine and Oxalate.

PHOTOCHEMICAL REACTION WITH SOME INORGANIC COLLOIDS AS ACTIVE AGENTS UNDER THE INFLUENCE OF LIGHT IN VARIOUS STATESOF POLARISATION PART XIV. INFLUENCE OF CIRCULARLY POLARISED LIGHT ON PHOTOCHEMICAL REACTIONS WITH PREEXCITED COLLOIDS AS PHOTOSENSITISERS.

The photochemical changes of jute fibre do not appear to be influenced by the uronic acid consti­tuent. The acidic and reducing types of substances, which are generated in the fibre daring irradia­tion, are derived mainly from the lignin component. The acidic reaction products or the constituent uronic acid hive no hydrolytic influence on the fibre, indicating that in the photochemical degradation of jute, acidic components do not contribute to the accelerated degradation.

" After-effect " in certain Photochemical Reactions. Part II.&nbsp

A NOTE ON THE PHOTOCHEMICAL PREPARATION AND PROPERTIES OF TETRAIODOACETONE

Influence of Light on Nitrification in Soil.

The phenomenon of so-called " activation " of oxalic add by the addition of KMnO4 in deficiency in aqueous solution is not shown by other polycarboxylic acids. Enhanced reducing power towards certain metallic slats. Such as mercuric chloride and gold chloride (chloroauric acid) thereby acquired, has hitherto been erroneously regarded as being the result of a process of chemical induction. The experimental results can be explained, however, by the formation of intermediate oxidation products of varying degrees of stability; in general oxy-car­boxylic acids which strongly reduce certain metallic salts. The reactions are stoichiometric in nature and thus have nothing in common with the permanganate-oxalate-mercuric chloride reaction.

Influence of Intensity on the Velocity of Photochemical Reactions.&nbsp

Studies on the Effect of Ultra-violet Light on Colloids. Part II.&nbsp

On the Photochemical Oxidation of Formaldehyde by Hydrogen Peroxide in Acid Medium with Tungstic Acid Sol as Photo-catalyst

Separation of uranium from thorium, zirconium, and manganese has been effected by photochemical process using their sulphate solution. Role of alcohol on the recovery of uranium has been investigated.

A series of controlled laboratory experiments are carried out in dual Teflon chambers to examine the presence of oligomers in secondary organic aerosols (SOA) from hydrocarbon ozonolysis as well as to explore the effect of particle phase acidity on SOA formation. In all seven hydrocarbon systems studied (i.e., α-pinene, cyclohexene, 1-methyl cyclopentene, cycloheptene, 1-methyl cyclohexene, cyclooctene, and terpinolene), oligomers with MW from 250 to 1600 are present in the SOA formed, both in the absence and presence of seed particles and regardless of the seed particle acidity. These oligomers are comparable to, and in some cases, exceed the low molecular weight species (MW < 250) in ion intensities in the ion trap mass spectra, suggesting they may comprise a substantial fraction of the total aerosol mass. It is possible that oligomers are widely present in atmospheric organic aerosols, formed through acid- or base-catalyzed heterogeneous reactions. In addition, as the seed particle acidity increases, larger oligomers are formed more abundantly in the SOA; consequently, the overall SOA yield also increases. This explicit effect of particle phase acidity on the composition and yield of SOA may have important climatic consequences and need to be considered in relevant models.

Background Trichloroethene and tetrachloroethene are the most common pollutants in groundwater and two of the priority pollutants listed by the U.S. Environmental Protection Agency. In previous studies on TCE and PCE photolysis and photochemical degradation, concentration ranges exceeding environmental levels by far with millimolar concentrations of TCE and PCE have been used, and it is not clear if the obtained results can be used to explain the degradation of these contaminants at more realistic environmental concentration levels. Methods Experiments with micromolar concentrations of TCE and PCE in aqueous solution using direct photolysis and UV/H2O2 have been conducted and product formation as well as transformation efficiency have been investigated. SPME/GC/MS, HPLC/UV and ion chromatography with conductivity detection have been used to determine intermediates of degradation. Results The results showed that chloride was a major end product in both TCE and PCE photodegradation. Several intermediates such as formic acid, dichloroacetic acid, dichloroacetaldehyede, chloroform, formaldehyde and glyoxylic acid were formed during both, UV and UV/H2O2 treatment of TCE. However chloroacetaldehyde and chloroacetic acid were only detected during direct UV photolysis of TCE and oxalic acid was only formed during the UV/H2O2 process. For PCE photodegradation, formic acid, di- and trichloroacetic acids were detected in both UV and UV/H2O2 systems, but formaldehyde and glyoxylic acid were only detected during direct UV photolysis. Conclusions For water treatment UV/H2O2 seems to be favorable over direct UV photolysis because of its higher degradation efficiency and lower risk for the formation of harmful intermediates.