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By P. H. Wendland

Calculations are presented for the design of a silicon photodiode in which the incident light beam makes multiple passes between the detector surfaces. Total internal reflection is used for this "light-trapping" effect. By this means, the optical path length can be extended to several millimeters, while the electrode separation remains less than 102 cm, as required for nanosecond response time. Data are presented for a Schottky barrier photodiode constructed on a multiply reflecting silicon base wafer. It is shown that the long-wavelength response is considerably extended in such structures without a corresponding sacrifice in high-speed response. The development of efficient and powerful lasers at 1.06 p has stimulated interest in detectors which operate at this wavelength. In typical silicon photodiodes, for detecting 1.06 p radiation, the requirements for high speed and high sensitivity are mutually exclusive. Since the absorption coefficient is only 25 cm-', a lo-'-cm path length is required to absorb 92 pct of the incident 1.06 p radiation. If the electrode separation is greater than 10 cm, however, the carrier transit time will be greater than 1 nsec. This problem can be solved by allowing the incident light beam to make multiple passes between the electrodes. The optical path length can then be extended to several millimeters, as required for complete absorption, while the electrode separation remains less than 10' cm, as required for nanosecond response time. In a typical photodiode geometry, one ohmic contact and one rectifying contact are formed on the two opposite surfaces of a base wafer, and the wafer thickness determines the electrode separation. The objective of the multiple reflection design is to allow all 1.06 p radiation to enter the detector front surface and to form the back detector surface so that no 1.06 radiation can exit. Total internal reflection at the back detector surface is well-suited for light trapping of 1.06 p radiation because the relatively large dielectric constant of silicon leads to a critical angle of 16.5 deg for total internal reflection. LIGHT TRAPPING It is well-known that, as light passes from one medium such as air into another medium such as glass or silicon, the angle of refraction is always less than the angle of incidence. In the limiting case, where the incident rays approach an angle of 90 deg with the normal, the refracted rays approach a fixed angle +, beyond which no refraction is possible: this is called the critical angle. It follows from Snell's law that where = critical angle, n - index of refraction of air, n' - index of refraction of the medium. Applying the principle of reversibility of light rays, all internal angles of incidence greater than +, will produce total internal reflection and "light trapping". The index of refraction of silicon at 1.06 p is 3.5,' and the critical angle is thus 16.5 deg. Fig. 1 shows these relationships for silicon. This very small critical angle in silicon is significant because all incident angles between 16.5 and 90 deg will produce total internal reflection and "light trapping". This effect can be implemented with a "prismlike" geometry, so that incident light can be introduced into the sample without loss and "trapped". PHOTOSIGNALS A precise knowledge of the absorption coefficient at 1.06 in silicon is of critical importance to the design of fast and efficient silicon photodiodes for 1.06 radiation. Dash and newman2 show a value of 25 cm-l, and our measurements have corroborated this value. Assuming that the collection of photoinduced minority carriers is perfect, the quantum efficiency of a photodiode is dependent only on the absorption coefficient. It then follows from Lambert's law that where QE is the quantum efficiency in pct, a is the absorption coefficient, d is the optical path length, and the reflectivity at the surface is assumed to be completely suppressed by an optical interference layer. Fig. 2 gives the maximum quantum efficiency for 1.06p radiation of a silicon photodiode with optical path length d, using Eq. [2]. The ultimate response time of a fully depleted photodiode to an incident light pulse can be considered to be the arrival times of all photoinduced carriers at the contacts, i.e., the minority carriers at the junction interface and the majority carriers at the oppo-

Jan 1, 1968

By C. E. Lesher

Coal has been fighting a rear-guard action since the last World War. The battle against competitive fuels has been largely guerilla warfare with more sniping within the ranks than of organized opposition. Oil and natural gas are the fuels that over these twenty odd years have driven coal backward and out of many profitable markets. Now, somewhat timidly, the coal industry is trying a new weapon; namely, Research, or let us more properly say, Organized Research. Engineers have been designing this weapon for many years, supported by those interested in coal, including some coal producers. A part of this pioneer work has been Fundamental Research, the Ph.D. kind that is over the heads of most of us. Another part has been aimed at immediate objectives and realizable profits, the practical, man-in-the-street sort. That is Industrial Research. Enough has been accomplished to make a fair exhibit, but whether this new weapon will have sufficient fire power to rout the opposition, whether the industry will really go into production and use it, the next few years will tell. Need foR Coal Research To utter "Research" is to use the modern magic word; to conjure up the miraculous—rubber from weeds; radar; magnesium from sea water; yes, even gasoline from coal. Research is a very general term. It means something different to every man. What is the coal industry seeking with its research; or what should it seek? And, specifically, how is it going about the job; and is it taking the best way? There are many who say that Coal has been asleep at the switch, while Oil and Gas have been taking the energy business. In an organized way this is true. Large-scale, privatelyfinanced research is just started in the Pennsylvania anthracite industry, and it is still a dream for bituminous coal. What has been done so far collectively is purely defensive; as, for instance, to improve mechanical devices for burning coal so as to be able to recover markets for house-heating fuel long since abandoned to oil and gas. To appreciate just how seriously bituminous coal has slipped back in the national economy in the past 2 5 years, one has only to recall that, in the last war the Navy required for its operations all the high-grade, low-volatile coal that could be produced, and that anthracite was withdrawn from the middle and northwest markets to keep the eastern seaboard warm. All coal was "rationed" by zones, if not to individuals. Now the Navy, the Armed forces and the Merchant Marine are propelled by oil and gasoline. Gasoline and heating oil are rationed to individuals. Production of all coal in this country in 1918 reached the historic figure of 678,200,-000 tons, and in 1943, after 25 years, it is expected to reach a special wartime total of 660,000,000 tons. Meanwhile, production of crude oil this year may exceed 1 ,500,000,000 bbl., and like that of natural gas, reach four times the amount produced in 1918.

Jan 1, 1944

By C. E. Lesher

Coal has been fighting a rear-guard action since the last World War. The battle against competitive fuels has been largely guerilla warfare with more sniping within the ranks than of organized opposition. Oil and natural gas are the fuels that over these twenty odd years have driven coal backward and out of many profitable markets. Now, somewhat timidly, the coal industry is trying a new weapon; namely, Research, or let us more properly say, Organized Research. Engineers have been designing this weapon for many years, supported by those interested in coal, including some coal producers. A part of this pioneer work has been Fundamental Research, the Ph.D. kind that is over the heads of most of us. Another part has been aimed at immediate objectives and realizable profits, the practical, man-in-the-street sort. That is Industrial Research. Enough has been accomplished to make a fair exhibit, but whether this new weapon will have sufficient fire power to rout the opposition, whether the industry will really go into production and use it, the next few years will tell. Need foR Coal Research To utter "Research" is to use the modern magic word; to conjure up the miraculous—rubber from weeds; radar; magnesium from sea water; yes, even gasoline from coal. Research is a very general term. It means something different to every man. What is the coal industry seeking with its research; or what should it seek? And, specifically, how is it going about the job; and is it taking the best way? There are many who say that Coal has been asleep at the switch, while Oil and Gas have been taking the energy business. In an organized way this is true. Large-scale, privatelyfinanced research is just started in the Pennsylvania anthracite industry, and it is still a dream for bituminous coal. What has been done so far collectively is purely defensive; as, for instance, to improve mechanical devices for burning coal so as to be able to recover markets for house-heating fuel long since abandoned to oil and gas. To appreciate just how seriously bituminous coal has slipped back in the national economy in the past 2 5 years, one has only to recall that, in the last war the Navy required for its operations all the high-grade, low-volatile coal that could be produced, and that anthracite was withdrawn from the middle and northwest markets to keep the eastern seaboard warm. All coal was "rationed" by zones, if not to individuals. Now the Navy, the Armed forces and the Merchant Marine are propelled by oil and gasoline. Gasoline and heating oil are rationed to individuals. Production of all coal in this country in 1918 reached the historic figure of 678,200,-000 tons, and in 1943, after 25 years, it is expected to reach a special wartime total of 660,000,000 tons. Meanwhile, production of crude oil this year may exceed 1 ,500,000,000 bbl., and like that of natural gas, reach four times the amount produced in 1918.

Jan 1, 1944

Upon the recommendation of its Technical Committee, The Com-pressed Air Society has adopted the following definitions of, certain terms. Displacement.-The displacement of an air compressor is the volume displaced by the net area of the compressor piston. Capacity.-The capacity should be expressed in cubic feet per minute, and is the actual amount of air compressed and delivered, expressed in terms of free air at intake temperature and at the pressure of dry air at the suction. Volumetric Efficiency.-Volumetric efficiency is the ratio of the capacity to the displacement of the compressor, all as defined above. Compression Efficiency.-Compression efficiency is the ratio of the work required to compress isothermally all the air delivered by an air compressor to the work actually clone within the compressor cylinder, as shown by indicator cards, and may he expressed is the product of the volumetric efficiency (the intake pressure and the hyperbolic logarithm of the ratio of compression), all divided by the indicated mean effective pressure within the air cylinder or cylinders.

Jan 8, 1918

Mining Methods LUCIEN EATON, Chairman S. R. ELLIOTT, Vice-chairman CHARLES W. WRIGHT, Secretary Alluvial Mining CLINTON BERNARD CHARLES JANIN O. J. EGGLESTON CHARLES H. MUNRO N. L. WIMMLER Open-cut Mining Iron MAX H. BARBER J. A. MACKILLICAN KENNETH DUNCAN W. R. VAN SLYKE

Jan 1, 1932

By Fenton Scott, Patrick Hannon

Some occurrences of lead-zinc mineralization in Mississippian carbonates of central Nova Scotia are briefly described. The results of geophysical and geochemical prospecting are presented. Because the deposits do not give a positive response to these indirect techniques it is necessary to site exploratory drilling through the development of geological concepts.

Jan 1, 1976

Society of Economic Geologists, 65 East 56th St., Princeton, N. J. Edward Sampson, Secretary. Publications of the Society constitute a part of "Economic Geology," a semiquarterly journal published by: The Economic Geology Publishing Co., W. S. Bayley, Business Editor, University of Illinois, Urbana, Ill.

Jan 1, 1933

[Year of Election 1944. WALTER HULL ALDRIDGE New York, N. Y. 1946. PETER M. ANDERSON Johannesburg, South Africa 1946. CHARLES CAMSELL Ottawa, Ont., Canada 1946. CHARLES AUGUSTUS CARLOW Fife, Scotland 1946. CECIL DESCH London, England 1946. WILLIAM FRASER London, England 1922. FEDERICO GIOLITTI Torino, Italy]

Jan 1, 1946

Discussion of the paper of Ernest Stütz, presented at the New York Meeting, October, 1913, and printed in Bulletin No. 79, July, 1913, pp. 1257 to 1265. H. 0. HOFMAN, Boston, Mass.:-I have hunted in vain for a figure which gives a dehydration temperature of cement. I was wondering if Mr. Stütz had a figure of that kind. E. STÜTZ :-No, I am afraid I have not. H. 0. HOFMAN :-I believe some figures have been published that cement disintegrates at 400° or 500° C. It seems tome a very low temperature. Mr. Stütz just made the statement that the disintegration of this briquette begins at the temperature at which the briquette begins to sinter. E. STÜTZ :-Above the sintering point. H. 0. HOFMAN :-The sintering point would be about 1,200° C. E. STÜTZ :-Yes, roughly speaking. I am afraid I have no information about the exact degree of dehydration. H. O. HOFMAN :-I have looked a great deal for such a figure and I have not been able to obtain it. Professor Howe says I might have tried myself. But my interests were directed in another line; although-that is, perhaps, a good suggestion. CHAIRMAN RICHARDS:-Is not Portland cement sometimes used for the test in a cupellation furnace and a drying-out furnace ? H. O. HOFMAN :-Yes, it is used, but that is a higher temperature, of course. But I have been trying to get a figure as to where it loses all its water. I understand it begins to lose water at 500° C. But there are different silicates or hydrosilicates in the cement, so that one would have four or five or sit figures to show the different stages at which the cement loses its water. CHAIRMAN RICHARDS :-I would ask whether the use of this material in blast furnaces has shown increased capacity of furnace or decreased consumption of fuel.

Jan 12, 1913

By J. B. Goddard

The discovery of rhenium on the ion exchange resin used at the uraniun in-situ leach operations at Palangana, TX, led to a laborabory study of possible recovery methods. Rhenium was present in small amounts in the ammonium carbonate leach liquors as the perrhenate anion, ReO4-. It concentrated on the anion exchange resin, which was a factor of 10 more selective for rhenium than for uranium. Various elution systems were investigated for stripping the rhenium from the columns after the uranium had been eluted with chloride or nitrate solutions. Although the per-chlorate ion was most efficient on a molar basis, nitrate ion combined the benefits of efficiency and low cost. A 3N or stronger concentration of nitrate containing up to 0. 5N H + was found to be the system of choice. A rhenium sulfide concentrate containing up to 14010 Re was obtained from these effluents by hydrogen sulfide precipitation. Preliminary experiments were run to produce rhenium metal powder by oxidation of the concentrate to NH4ReO4 followed by hydrogen reduction at elevated temperature.

Jan 1, 1984

By R. S. Sandhu, S. H. Advani, J. K. Lee, B. L. Aboustit

A comprehensive finite element formulation for thermo-elastic consolidation based on a general variational principle is presented Sample one dimensional problems associated with isothermal consolidation, heat conduct ion, and thermo-elastic consolidation are presented. In addition, evaluations of thermo-elastic consolidation for an underground coal conversion field site are conducted.

Jan 1, 1982

(Members are urged to send in for this column, any notes. of interest concerning themselves or their fellow-members.) The following members registered at Institute headquarters during the month of May: Emil Gathmann, Baltimore, Md. Philip Argall, Denver, Colo. Albert H. Fay, Washington, D. C. A. C. Hodge, F.R.G.S., St. Austell, Eng. Alfred E. Barlow, Montreal, Canada. S. M. Marshall, Johnstown, Pa. B. C. Yates, Lead, S. D. Miltiades Armas, Paris, France. Leonard S. Austin, Salt Lake City. Albert Sauveur, Cambridge, Mass. Henry A. Wentworth, Boston, Mass. G. A. Reinhardt, Cambridge, Mass. Frank M. Leland, Mackay, Idaho. Fred Crabtree, Pittsburg, Pa. W. N. Crafts, Cleveland, Ohio. T. A. Rickard, London, England. Louis Hasbrouck, Kingston, N. Y. F. Lynwood Garrison, Philadelphia, Pa. F. V. Desloge, Desloge, Mo. S. B. Christy, Berkeley, Cal. E. C. Templeton, Palo Alto, Cal. H. A. Buehler, Rolla, Mo. L. D. Ricketts, Warren, Ariz. F. W. DeWolf, Urbana, Ill. J. E. Johnson, Jr., Ashland, Wis. Howland Bancroft, Denver, Colo. A. O. Granger, Cartersyille, Ga.

Jan 6, 1913

By D. L. Rainey, E. R. Goter, W. R. Hudspeth

THE area in which spodumene-bearing pegmatites occur extends from Gaffney, S. C., in a northerly direction to Lincolnton, N. C., a distance of about 16 miles. The zone averages 2 miles in width. Interest in this area was first aroused by the discovery of small amounts of cassiterite in the pegmatites and in greissen which occurs on the walls of some of the pegmatites. Attempts were made from 1880 into the 1920's to mine and concentrate cassiterite, but there were no successful operations. In 1935 L. M. Williams became interested in the area and began prospecting by trenching and sinking several small shafts. He gradually gained control of a considerable acreage south of the city of Kings Mountain, N. C. Mr. Williams states that he produced some ore from a shaft which he shipped to the Maywood Chemical Co. in the late 1930's. In 1937 G. H. Chambers of the Foote Mineral Co. visited the area and examined several properties, but the lithium market was too small to support the necessary concentrating plant.

Jan 9, 1953

(Members are urged to send in for this column any notes of interest concerning themselves or their fellow-members.) Members and guests who called at Institute headquarters during the period May 10, 1916 to June 10, 1916: G. Aertsen, Philadelphia, Pa. Hennen Jennings, Washington, D. C. Frederick C. Alsdorf, Wickenburg, Ariz. H. M. LaFollette, LaFollette, Tenn. A. H. Anderson, Worcester, Mass. E. T. Lednum, Chicago, Ill. J. H. Batcheller, Mattapoisett, Mass. Francis Church Lincoln, Reno, Nev. Arthur B. Clark, Sheridan, Mont. H. Mortimer-Lamb, Montreal, Canada. J. Murray Clark, Toronto, Canada. Andrew W. Newberry, San Francisco, Cal. J. H. Collier, Oakland, Cal. C. E. Pettibone, Cleveland, 0. H. S. Emlaw, Spring Lake, Mich. Heinrich Ries, Ithaca, N. Y. E. L. Estabrook, Platteville, Wis. C. S. Robinson, Youngstown, 0. James W. Hambleton, El Paso, Tex. - M. K. Rodgers, Basin, Mont. James Henderson, London, England. E. J. Rossbach, St. Louis, Mo. G. P. Hulst, East Chicago, Ind. J. B. Tyrrell, Toronto, Canada. William F. Jahn, Riebeling, Mont. G. B. Waterhouse, Buffalo, N. Y.

Jan 7, 1916

Institute of Metals Division Iron and Steel Division Extractive Metallurgy Division Council J H Scaff (IMD) Chairman, Robert W Shearman, Secretary, J S Smart, (IMD), P T Stroup, (EMD), A W Schlechten, (EMD), J S Marsh, (ISD), A W Thornton, (ISD), M E Violin, (MED), D S Eppelsheimer, (MIED) Journal of Metals Editorial Advisory Committee J S Smart, Jr, Chairman, W A Dean, J C Kinnear, Jr, T D Jones, Evan Just, John Marsh, M Tenenbaum Pacific Northwest Regional Conference A Y Bethune, General Chairman, Frank N Marr, Chairman, General Arrangements, R J Lapee, Chairman, C P Love, (EMD Program), W M Armstrong, Chairman, Physical Metallurgy Program, L W Heinzinger, Chairman (ISD Program), J P Spielman, Chairman, (MIED Program) New England Regional Conference K H Mairs, Chairman, W A Backofen, Vice-Chair¬man, Delmar E Trout, Secretary, G W Coleman, Treasurer, F H Wilson, Past Chairman, Members at Large Sidney Siegel, Boston, G F Donahue, Connecti¬cut Representatives from Connecticut Frank Chudy, J E Chafey Representa¬tives from Boston N L Reed, E Gordon

Jan 1, 1955

COMMITTEES. Iron and Steel. Albert Sauveur, Chairman. A. A. Stevenson, Vice-Chairman. Herbert M. Boylston, Secretary, Abbot Bldg., Harvard Sq., Cambridge, Mass. LOCAL COMMITTEES. Program Committee.-A. A. Stevenson, Chairman. Herbert A3. Boylston, J. E. Johnson, Jr., Henry D. Hibbard, E. Gybbon Spilsbury. Reception Committee.-J. R. Johnson, Jr., Chairman. Felix A. Vogel, William R. Walker. Dinner Committee.-E. Gybbon Spilsbury, Chairman. The opening session was held on Thursday morning, Oct. 16, 1913, at the Institute Headquarters in the Engineering Societies Building, 29 West 39th Street, New York, N. Y., and was called to order by President Rand, who addressed the meeting briefly before presenting Albert Sauveur, who responded to the President's address, and presided at the meeting. The following papers were then presented in oral abstract by their authors or authors' representatives: The Cleaning of Blast-Furnace Gas, by W. A. Forbes. Discussed by S. K. Varnes, H. N. Diehl, F. H. Wagner, Joseph Hartshorne, S. B. Marshall, J. W. Richards, J. E. Johnson, Jr., W. A. Forbes, and others.

Jan 12, 1913

H. N. EAVENSON, Gary, W. Va.-Judging from our own experience, the statement that only 40 per cent. of the accidents are caused by the human element is very low. We have adopted all the measures that Mr. Wilson recommended, such as systematic timbering, use of permissible expolsives and practically everything that anybody has suggested or can think of, and even after all that has been done, done for several years, and a systematic campaign maintained all the time to reduce accidents, we still

Jan 4, 1918

By Paul Pietrokowsky

THE formation of intermediate phases in the solid state reaction of titanium with silicon, germanium. and tin (of subgroup 4B in the periodic table) was the subject of a recent paper.' Further investigation of the system Ti-Sn revealed the presence of a new compound on the titanium-rich side of this phase diagram. Metallographic evidence indicated that this new phase was situated very close to 75 atomic pct Ti. The present work is concerned with the crystal structure of the intermediate phase Ti3Sn. Iodide-process titanium metal, furnished by the New Jersey Zinc Co., was used in this investigation. The metallic tin was received in powder form from Charles Hardy Inc., New York; its purity was 99.80 pct. The titanium rod was machined into small cups 1 cm in diam and about 1.5 cm in height. The tin powder was compacted, melted, and then placed in the titanium cups and alloyed by electric arc melting in a helium atmosphere. The alloys, weighing approximately 8 g, were sealed in evacuated quartz tubes and homogenized at 1030°C for 5 days. This isothermal heat treatment was terminated by a water quench from the soaking temperature. Filings of the alloyed pellets were sealed in evacuated quartz bulbs and quenched from 1030°C into liquid argon. A 14.32 cm Debye Scherrer X-ray camera was used for the powder diffraction study. The copper radiation was filtered. X-ray diffraction data for the compound Ti3Sn are given in Table I. The data were indexed on the basis of a hexagonal lattice. Good agreement between observed and calculated values of the square of the reciprocal interplanar spacings was obtained with the following expression: (1/d)2 = 0.03810 (h2 + hk + k2) + 0.04410 (l2) Unit cell parameters were calculated by the method of least squares from the reflections (20.3), (22.2), (40.1), and (42.1); ao = 5.916 & 0.004A, co = 4.764 ± 0.004A, and co/ao = 0.805. The relatively small size of the unit cell allowed the unambiguous indexing of most of the reflections from planes of large spacing. An inspection of the assigned indices (Table I) reveals the absence of (hk.l) reflections when 1 2n. A systematic absence of this type leads to the space group C 6/mmc or one of its subgroups. Assuming, for a first approximation, a linear increase in the density of titanium with the addition of tin, it follows that there are two stoichiometric molecules of Ti3Sn per unit cell. The density calculated from X-ray measurements is 5.194 g cm-'. At this point it became clear that Ti3Sn might be isomorphous with Mg3Cd. The 6 Ti and 2 Sn atoms were placed in the following positions of space group D4 6h, C 6/mmc: 6Tiin (h): X 2X 1/4; 22;; 1/4;Xx 1/4;x2x3/4; 2x x 3/4; x x 4; with x = 516 2 Sn in (c): 1/3 2/3 1/4; 2/3 1/3 3/4.

Jan 1, 1953

By Albert L. Toenges

Alaska requires an adequate fuel supply for its development, and has large potential coal reserves ranging from lignite to subbituminous and anthracite. Coal production in the Territory now is less than the requirements. In 1947, production was 361,000 tons, divided about equally between bituminous coal from the Matanuska field and subbituminous coal from the Nenana field. There is need for development of modern mechanized mines, which should produce the required output with a minimum of workers. These mines should not be thought of in the light of large potential capacity, as in the States. However, these new mines should be developed by modern methods, which should result in lower costs than at present. Because of the diverse physical conditions in the coal fields, intensive investigation by diamond drilling is necessary to properly plan the development and equipment of mine sites at minimum cost. The Bureau of Mines is doing this now in the Wishbone Hill area of the Matanuska field. All coal land in Alaska is government-owned and subject to the Coal Leasing Act.

Jan 1, 1949

Executive Committee, Board of Directors Howard C Pyle, Chairman, J L Gillson, Vice¬Chairman, A W Thornton, Elmer A Jones, Augustus B Kinzel Finance Committee, Board of Directors J S Vanick, Chairman, John P Hammond, J W Woomer Investments Gail F Moulton, '60, Chairman, Andrew Fletcher, '62, John M Lovejoy, '61, C R Dodson, ex off as AIME Treasurer, J S Vanick, ex off as Chairman of Finance Committee Endowment Andrew Fletcher, Chairman, N G Alford, W J Coulter, Harold Decker, J V N Dorr, R B Gilmore, J B Haffner, Kenneth Hill, 0 H Johnson, J D MacKenzie, D H McLaughlin, J R McMillan, W S Morris, L F Reinartz, H DeWitt Smith, Wilfred Sykes, J R Suman, C E Weed Honorary Memberships C E Reistle, Jr, '60, Chairman, Grover J Holt, '61, Augustus B Kmzel, '62, (ex off as Past Presidents of AIME) M L Haider, '60, D H McLaughlin, '61, John M Lovejoy, '62, L F Reinartz, '63, Howard C Pyle, ex off as President of AIME

Jan 1, 1959