A syllabary is a set of written symbols that represent the syllables or moras which make up words. A symbol in a syllabary, called a syllabogram represents an consonant sound followed by a vowel sound —that is, a CV or V syllable—but other phonographic mappings such as CVC, CV- tone, C are found in syllabaries. A writing system using a syllabary is complete when it covers all syllables in the corresponding spoken language without requiring complex orthographic / graphemic rules, like implicit codas silent vowels or echo vowels; this loosely corresponds to shallow orthographies in alphabetic writing systems. True syllabograms are those that encompass all parts of a syllable, i.e. initial onset, medial nucleus and final coda, but since onset and coda are optional in at least some languages, there are middle, start and full true syllabograms. Most syllabaries only feature one or two kinds of syllabograms and form other syllables by graphemic rules. Syllabograms, hence syllabaries, are pure, analytic or arbitrary if they do not share graphic similarities that correspond to phonic similarities, e.g. the symbol for ka does not resemble in any predictable way the symbol for ki, nor the symbol for a.
Otherwise they are synthetic, if they vary by onset, nucleus or coda, or systematic, if they vary by all of them. Some scholars, e.g. Daniels, reserve the general term for analytic syllabaries and invent other terms as necessary; some system provides katakana language conversion. Languages that use syllabic writing include Japanese, Vai, the Yi languages of eastern Asia, the English-based creole language Ndyuka, Shaozhou Tuhua, the ancient language Mycenaean Greek. In addition, the undecoded Cretan Linear A is believed by some to be a syllabic script, though this is not proven. Chinese characters, the cuneiform script used for Sumerian and other languages, the former Maya script are syllabic in nature, although based on logograms, they are therefore sometimes referred to as logosyllabic. The contemporary Japanese language uses two syllabaries together called kana, namely hiragana and katakana, which were developed around 700; because Japanese uses CV syllables, a syllabary is well suited to write the language.
As in many syllabaries, vowel sequences and final consonants are written with separate glyphs, so that both atta and kaita are written with three kana: あった and かいた. It is therefore sometimes called a moraic writing system. Languages that use syllabaries today tend to have simple phonotactics, with a predominance of monomoraic syllables. For example, the modern Yi script is used to write languages that have no diphthongs or syllable codas. Few syllabaries have glyphs for syllables that are not monomoraic, those that once did have simplified over time to eliminate that complexity. For example, the Vai syllabary had separate glyphs for syllables ending in a coda, a long vowel, or a diphthong, though not enough glyphs to distinguish all CV combinations; the modern script has been expanded to cover all moras, but at the same time reduced to exclude all other syllables. Bimoraic syllables are now written with two letters, as in Japanese: diphthongs are written with the help of V or hV glyphs, the nasal coda is written with the glyph for ŋ, which can form a syllable of its own in Vai.
In Linear B, used to transcribe Mycenaean Greek, a language with complex syllables, complex consonant onsets were either written with two glyphs or simplified to one, while codas were ignored, e.g. ko-no-so for Κνωσός Knōsos, pe-ma for σπέρμα sperma. The Cherokee syllabary uses dummy vowels for coda consonants, but has a segmental grapheme for /s/, which can be used both as a coda and in an initial /sC/ consonant cluster; the languages of India and Southeast Asia, as well as the Ethiopian Semitic languages, have a type of alphabet called an abugida or alphasyllabary. In these scripts, unlike in pure syllabaries, syllables starting with the same consonant are expressed with graphemes based in a regular way on a common graphical element; each character representing a syllable consists of several elements which designate the individual sounds of that syllable. In the 19th century these systems were called syllabics, a term which has survived in the name of Canadian Aboriginal syllabics. In a true syllabary there may be graphic similarity between characters that share a common consonant or vowel sound, but it is not systematic or close to regular.
For example, the characters for'ke','ka', and'ko' in Japanese hiragana have no similarity to indicate their common "k" sound. Compare this with Devanagari, an abugida, where the characters for'ke','ka' and'ko' are के, का and को with क indicating their common "k" sound. English, along with many other Indo-European languages like German and Russian, allows for complex syllable structures, making it cumbersome to write English words with a syllabary. A "pure" syllabary would require a separate glyph for every syllable in English, thus one would need separate symbols for "bag", "beg", "big", "bog", "bug", "bad", "bed", "bid", "bod", "bud", "bead", "bide", "bode", etc. Since English has well over 10,000 different possibilities for individual syllables, a s
Shorthand is an abbreviated symbolic writing method that increases speed and brevity of writing as compared to longhand, a more common method of writing a language. The process of writing in shorthand is called stenography, from the Greek stenos and graphein, it has been called brachygraphy, from Greek brachys and tachygraphy, from Greek tachys, depending on whether compression or speed of writing is the goal. Many forms of shorthand exist. A typical shorthand system provides symbols or abbreviations for words and common phrases, which can allow someone well-trained in the system to write as as people speak. Abbreviation methods use different abbreviating approaches. Many journalists use shorthand writing to take notes at press conferences or other similar scenarios. In the computerized world, several autocomplete programs, standalone or integrated in text editors, based on word lists include a shorthand function for used phrases. Shorthand was used more in the past, before the invention of recording and dictation machines.
Shorthand was considered an essential part of secretarial training and police work, as well as useful for journalists. Although the primary use of shorthand has been to record oral dictation or discourse, some systems are used for compact expression. For example, healthcare professionals may use shorthand notes in medical charts and correspondence. Shorthand notes are temporary, intended either for immediate use or for typing, data entry, or transcription to longhand, although longer term uses do exist, such as encipherment: diaries are a common example; the earliest known indication of shorthand systems is from the Parthenon in Ancient Greece, where a mid-4th century BC marble slab was found. This shows a writing system based on vowels, using certain modifications to indicate consonants. Hellenistic tachygraphy is reported from the 2nd century BC onwards, though there are indications that it might be older; the oldest datable reference is a contract from Middle Egypt, stating that Oxyrhynchos gives the "semeiographer" Apollonios for two years to be taught shorthand writing.
Hellenistic tachygraphy consisted of word stem signs and word ending signs. Over time, many syllabic signs were developed. In Ancient Rome, Marcus Tullius Tiro, a slave and a freedman of Cicero, developed the Tironian notes so that he could write down Cicero's speeches. Plutarch in his "Life of Cato the Younger" records that Cicero, during a trial of some insurrectionists in the senate, employed several expert rapid writers, whom he had taught to make figures comprising numerous words in a few short strokes, to preserve Cato's speech on this occasion; the Tironian notes consisted of word ending abbreviations. The original Tironian notes consisted of about 4000 signs, but new signs were introduced, so that their number might increase to as many as 13,000. In order to have a less complex writing system, a syllabic shorthand script was sometimes used. After the decline of the Roman Empire, the Tironian notes were no longer used to transcribe speeches, though they were still known and taught during the Carolingian Renaissance.
After the 11th century, they were forgotten. When many monastery libraries were secularized in the course of the 16th-century Protestant Reformation, long-forgotten manuscripts of Tironian notes were rediscovered. In imperial China, clerks used an abbreviated cursive form of Chinese characters to record court proceedings and criminal confessions; these records were used to create more formal transcripts. One cornerstone of imperial court proceedings was that all confessions had to be acknowledged by the accused's signature, personal seal, or thumbprint, requiring fast writing. Versions of this technique survived in clerical professions into the modern day, influenced by Western shorthand methods, some new methods were invented. An interest in shorthand or "short-writing" developed towards the end of the 16th century in England. In 1588 Timothy Bright published his Characterie. Bright's book was followed by a number of others, including Peter Bales' The Writing Schoolemaster in 1590, John Willis's Art of Stenography in 1602, Edmond Willis's An abbreviation of writing by character in 1618, Thomas Shelton's Short Writing in 1626.
Shelton's system became popular and is well known because it was used by Samuel Pepys for his diary and for many of his official papers, such as his letter copy books. It was used by Sir Isaac Newton in some of his notebooks. Shelton borrowed from his predecessors Edmond Willis; each consonant was represented by an arbitrary but simple symbol, while the five vowels were represented by the relative positions of the surrounding consonants. Thus the symbol for B with symbol for T drawn directly above it represented "bat", while B with T below it meant "but". A vowel at the end of a word was represented by a dot in the appropriate position, while there were additional symbols for initial vowels; this basic system was supplemented by further symbols representing common suffixes. One drawback of Shelton's system was that there was no way to distinguish long and short vowels or diphthongs; the reader needed to u
In writing and typography, a ligature occurs where two or more graphemes or letters are joined as a single glyph. An example is the character æ as used in English; the common ampersand developed from a ligature in which the handwritten Latin letters e and t were combined. The origin of typographical ligatures comes from the invention of writing with a stylus on fibrous material or clay. Businessmen who needed a way to speed up the process of written communication found that conjoining letters and abbreviating words for lay use was more convenient for record keeping and transaction than the bulky long forms; the earliest known script, Sumerian cuneiform, includes many cases of character combinations that, over time evolve from ligatures into separately recognizable characters. Ligatures figure prominently in many historical manuscripts, notably the Brahmic abugidas, or the bind rune of the Migration Period Germanic runic inscriptions. Medieval scribes who wrote in Latin increased their writing speed by combining characters and by introducing notational abbreviations.
Others conjoined letters for aesthetic purposes. For example, in blackletter, letters with right-facing bowls and those with left-facing bowls were written with the facing edges of the bowls superimposed. In many script forms, characters such as h, m, n had their vertical strokes superimposed. Scribes used notational abbreviations to avoid having to write a whole character in one stroke. Manuscripts in the fourteenth century employed hundreds of such abbreviations. Modifications to script bodies like these originate from legal and monastic sources, with the emphasis shifting from business to monastic sources by around the 9th and 10th centuries. In hand writing, a ligature is made by joining two or more characters in atypical fashion by merging their parts, or by writing one above or inside the other. In printing, a ligature is a group of characters, typeset as a unit, so the characters do not have to be joined. For example, in some cases the fi ligature prints the letters f and i with a greater separation than when they are typeset as separate letters.
When printing with movable type was invented around 1450, typefaces included many ligatures and additional letters, as they were based on handwriting. Ligatures made printing with movable type easier because one block would replace frequent combinations of letters and allowed more complex and interesting character designs which would otherwise collide with one another. Ligatures began to fall out of use due to their complexity in the 20th century. Sans serif typefaces used for body text avoid ligatures, though notable exceptions include Gill Sans and Futura. Inexpensive phototypesetting machines in the 1970s generally avoid them. A few, became characters in their own right, see below the sections about German ß, various Latin accented letters, & et al.. The trend against digraph use was further strengthened by the desktop publishing revolution starting around 1977 with the production of the Apple II. Early computer software in particular had no way to allow for ligature substitution, while most new digital typefaces did not include ligatures.
As most of the early PC development was designed for the English language dependence on ligatures did not carry over to digital. Ligature use fell as the number of traditional hand compositors and hot metal typesetting machine operators dropped due to the mass production of the IBM Selectric brand of electric typewriter in 1961. A designer active in the period commented: "some of the world's greatest typefaces were becoming some of the world's worst fonts."Ligatures have grown in popularity over the last 20 years due to an increasing interest in creating typesetting systems that evoke arcane designs and classical scripts. One of the first computer typesetting programs to take advantage of computer-driven typesetting was Donald Knuth's TeX program. Now the standard method of mathematical typesetting, its default fonts are explicitly based on nineteenth-century styles. Many new fonts feature extensive ligature sets. Mrs Eaves by Zuzana Licko contains a large set to allow designers to create dramatic display text with a feel of antiquity.
A parallel use of ligatures is seen in the creation of script fonts that join letterforms to simulate handwriting effectively. This trend is caused in part by the increased support for other languages and alphabets in modern computing, many of which use ligatures somewhat extensively; this has caused the development of new digital typesetting techniques such as OpenType, the incorporation of ligature support into the text display systems of macOS, applications like Microsoft Office. An increasing modern trend is to use a "Th" ligature which reduces spacing between these letters to make it easier to read, a trait infrequent in metal type. Today, modern font programming divides ligatures into three groups, which can be activated separately: standard and historical. Standard ligatures are needed to allow the font to display without errors such as character collision. Designers sometimes find contextual and historic ligatures desirable for creating effects or to evoke an old-fashioned print look.
Many ligatures combine f with the following letter. A prominent example is ﬁ; the tittle of t
In written language, a logogram or logograph is a written character that represents a word or phrase. Chinese characters are logograms; the use of logograms in writing is called logography, a writing system, based on logograms is called a logographic system. In alphabets and syllabaries, individual written characters represent sounds only, rather than entire concepts; these characters are called phonograms in linguistics. Unlike logograms, phonograms do not have word or phrase meanings singularly until the phonograms are combined with additional phonograms thus creating words and phrases that have meaning. Writing language in this way, is called phonetic writing as well as orthographical writing. Logographic systems include the earliest writing systems. A purely logographic script would be impractical for most languages, none is known, apart from one devised for the artificial language Toki Pona, a purposely limited language with only 120 morphemes. All logographic scripts used for natural languages rely on the rebus principle to extend a limited set of logograms: A subset of characters is used for their phonetic values, either consonantal or syllabic.
The term logosyllabary is used to emphasize the phonetic nature of these scripts when the phonetic domain is the syllable. In both Ancient Egyptian hieroglyphs and in Chinese, there has been the additional development of fusing such phonetic elements with determinatives. Logographic writing systems include: Logoconsonantal scripts These are scripts in which the graphemes may be extended phonetically according to the consonants of the words they represent, ignoring the vowels. For example, Egyptian was used to write both sȝ'duck' and sȝ'son', though it is that these words were not pronounced the same apart from their consonants; the primary examples of logoconsonantal scripts are:Hieroglyphs and demotic: Ancient Egyptian Logosyllabic scripts These are scripts in which the graphemes represent morphemes polysyllabic morphemes, but when extended phonetically represent single syllables. They include:Anatolian hieroglyphs: Luwian Cuneiform: Sumerian, other Semitic languages, Hittite, Luwian and Urartian Maya glyphs: Chorti and other Classic Maya languages Han characters: Chinese, Japanese, Zhuang Derivatives of Han characters: Chữ nôm: Vietnam Dongba script written with Geba script: Naxi language Jurchen script: Jurchen Khitan large script: Khitan Sawndip: Zhuang languages Shui script: Shui language Tangut script: Tangut language Yi: various Yi languagesNone of these systems is purely logographic.
This can be illustrated with Chinese. Not all Chinese characters represent morphemes: some morphemes are composed of more than one character. For example, the Chinese word for spider, 蜘蛛 zhīzhū, was created by fusing the rebus 知朱 zhīzhū with the "bug" determinative 虫. Neither *蜘 zhī nor *蛛 zhū can be used separately; this is incorrect. In Archaic Chinese, one can find the reverse: a single character representing more than one morpheme. An example is Archaic Chinese 王 hjwangs, a combination of a morpheme hjwang meaning king and a suffix pronounced /s/. In modern Mandarin, bimorphemic syllables are always written with two characters, for example 花儿 huār'flower'. A peculiar system of logograms developed within the Pahlavi scripts used to write Middle Persian during much of the Sassanid period; these logograms, called hozwārishn, were dispensed with altogether after the Arab conquest of Persia and the adoption of a variant of the Arabic alphabet. Logograms are used in modern shorthand to represent common words.
In addition, the numerals and mathematical symbols are logograms – 1'one', 2'two', +'plus', ='equals', so on. In English, the ampersand & is used for'and' and for Latin et, % for'percent', # for'number', § for'section', $ for'dollar', € for'euro', £ for'pound', ° for'degree', @ for'at', so on. All historical logographic systems include a phonetic dimension, as it is impractical to have a separate basic character for every word or morpheme in a language. In some cases, such as cuneiform as it was used for Akkadian, the vast majority of glyphs are used for their sound values rather than logographically. Many logographic systems have a semantic/ideographic component, called "determinatives" in the case of Egyptian and "radicals" in the case of Chinese. Typical Egyptian usage was to augment a logogram, which may represent several words with different pronunciations, with a determinate to narrow down the meaning, a phonetic component to specify the pronunciation. In the case of Chinese, the vast majority of characters are a fixed combination of a radical that indicates its nominal category, plus a phonetic to give an idea of the pronunciation.
The Mayan system used logograms
Times New Roman
Times New Roman is a serif typeface designed for use in body text. It was commissioned by the British newspaper The Times in 1931 and conceived by Stanley Morison, the artistic advisor to the British branch of the printing equipment company Monotype, in collaboration with Victor Lardent, a lettering artist in the Times' advertising department. Although no longer used by The Times, Times New Roman is still common in book and general printing, it has become one of the most popular and influential typefaces in history and a standard typeface on desktop computers. Times New Roman's creation took place through the influence of Stanley Morison of Monotype. Morison was an artistic director at Monotype, historian of printing and informal adviser to The Times. Asked to advise on a redesign, he recommended that they change their text typeface from a spindly and somewhat dated nineteenth-century face to a more robust, solid design, returning to traditions of printing from the eighteenth century and before.
This matched a common trend in printing tastes of the period. The new face was drawn by Victor Lardent, an artist from the advertising department of The Times, with Morison consulting, before refinement by the Monotype drawing office. Morison proposed an older Monotype typeface named Plantin as a basis for the design, Times New Roman matches Plantin's dimensions; the main change was. As a typeface designed for newspaper printing, Times New Roman has a high x-height, short descenders to allow tight linespacing and a condensed appearance; the new design made its debut in The Times on 3 October 1932. After one year, the design was released for commercial sale. Although Morison may not have drawn the design, his influence on its concept was sufficient that he felt that he could take credit for it as "my one effort at designing a font". In Times New Roman's name, Roman is a reference to the regular or roman style, the first part of the Times New Roman family to be designed. Roman type has roots in Italian printing of the late 15th and early 16th centuries, but Times New Roman's design has no connection to Rome or to the Romans.
The Times stayed with Times New Roman for 40 years, but new production techniques and the format change from broadsheet to tabloid in 2004 have caused it to switch typeface five times from 1972 to 2007. However, all the new fonts have been variants of the original New Roman typeface. Once released for commercial sale, Times New Roman became successful, becoming Monotype's best-selling typeface of all time in metal type. Times New Roman has a robust colour on the page and influences of European early modern and Baroque printing; the design is condensed, with short ascenders and descenders and a high x-height, all effects that save space and increase clarity. The roman style of Plantin was loosely based on a metal type created in the late sixteenth century by the French artisan Robert Granjon and preserved in the collection of the Plantin-Moretus Museum of Antwerp; this style is sometimes categorised as part of the "old-style" of serif fonts. Indeed, the working title of Times New Roman was "Times Old Style".
However, Times New Roman modifies the Granjon influence further than Plantin due to features such as its'a' and'e', with large counters and apertures, its ball terminal detailing and an increased level of contrast between thick and thin strokes, so it has been compared to fonts from the late eighteenth century, the so-called'transitional' genre, in particular the Baskerville typeface of the 1750s. Historian and sometime Monotype executive Allan Haley commented that compared to Plantin "serifs had been sharpened...contrast was increased and character curves were refined," while Lawson described Times's higher-contrast crispness as having "a sparkle never achieved." Other changes from Plantin include a straight-sided'M' and'W' with three upper terminals not Plantin's four, both choices that move away from the old-style model. Morison described the companion italic as being influenced by the typefaces created by the Didot family in the late 18th and early 19th centuries: a "rationalistic italic that owed nothing to the tradition of the sixteenth or seventeenth centuries.
It has, more in common with the eighteenth century." Morison had several years earlier attracted attention for promoting the radical idea that italics in book printing were too disruptive to the flow of text, should be phased out. He came to concede that the idea was impractical, wryly commented to historian Harry Carter that Times' italic "owes more to Didot than dogma." Morison wrote in a personal letter of Times New Roman's mixed heritage that it "has the merit of not looking as if it had been designed by somebody in particular." Rather than creating a companion boldface with letterforms similar to the roman style, Times New Roman's bold has a different character, with a more condensed and more upright effect caused by making the horizontal parts of curves the thinnest lines of each letter, making the top serifs of letters like'd' purely horizontal. This effect is not found in sixteenth-century typefaces; some commentators have found Times' bold unsatisfactory and too condensed, such as Walter Tracy
A writing system is any conventional method of visually representing verbal communication. While both writing and speech are useful in conveying messages, writing differs in being a reliable form of information storage and transfer; the processes of encoding and decoding writing systems involve shared understanding between writers and readers of the meaning behind the sets of characters that make up a script. Writing is recorded onto a durable medium, such as paper or electronic storage, although non-durable methods may be used, such as writing on a computer display, on a blackboard, in sand, or by skywriting; the general attributes of writing systems can be placed into broad categories such as alphabets, syllabaries, or logographies. Any particular system can have attributes of more than one category. In the alphabetic category, there is a standard set of letters of consonants and vowels that encode based on the general principle that the letters represent speech sounds. In a syllabary, each symbol correlates to a syllable or mora.
In a logography, each character represents morpheme, or other semantic units. Other categories include abjads, which differ from alphabets in that vowels are not indicated, abugidas or alphasyllabaries, with each character representing a consonant–vowel pairing. Alphabets use a set of 20-to-35 symbols to express a language, whereas syllabaries can have 80-to-100, logographies can have several hundreds of symbols. Most systems will have an ordering of its symbol elements so that groups of them can be coded into larger clusters like words or acronyms, giving rise to many more possibilities in meanings than the symbols can convey by themselves. Systems will enable the stringing together of these smaller groupings in order to enable a full expression of the language; the reading step expressed orally. A special set of symbols known as punctuation is used to aid in structure and organization of many writing systems and can be used to help capture nuances and variations in the message's meaning that are communicated verbally by cues in timing, accent, inflection or intonation.
A writing system will typically have a method for formatting recorded messages that follows the spoken version's rules like its grammar and syntax so that the reader will have the meaning of the intended message preserved. Writing systems were preceded by proto-writing, which used pictograms and other mnemonic symbols. Proto-writing lacked the ability to express a full range of thoughts and ideas; the invention of writing systems, which dates back to the beginning of the Bronze Age in the late Neolithic Era of the late 4th millennium BC, enabled the accurate durable recording of human history in a manner, not prone to the same types of error to which oral history is vulnerable. Soon after, writing provided a reliable form of long distance communication. With the advent of publishing, it provided the medium for an early form of mass communication; the creation of a new alphabetic writing system for a language with an existing logographic writing system is called alphabetization, as when the People's Republic of China studied the prospect of alphabetizing the Chinese languages with Latin script, Cyrillic script, Arabic script, numbers, although the most common instance of it, converting to Latin script, is called romanization.
Writing systems are distinguished from other possible symbolic communication systems in that a writing system is always associated with at least one spoken language. In contrast, visual representations such as drawings and non-verbal items on maps, such as contour lines, are not language-related; some symbols on information signs, such as the symbols for male and female, are not language related, but can grow to become part of language if they are used in conjunction with other language elements. Some other symbols, such as numerals and the ampersand, are not directly linked to any specific language, but are used in writing and thus must be considered part of writing systems; every human community possesses language, which many regard as an innate and defining condition of humanity. However, the development of writing systems, the process by which they have supplanted traditional oral systems of communication, have been sporadic and slow. Once established, writing systems change more than their spoken counterparts.
Thus they preserve features and expressions which are no longer current in the spoken language. One of the great benefits of writing systems is that they can preserve a permanent record of information expressed in a language. All writing systems require: at least one set of defined base elements or symbols, individually termed signs and collectively called a script. In the examination of individual scripts, the study of writing systems has developed along independent lines. Thus, the terminology employed differs somewhat from field to field; the generic term text refers to an instance of writte
Graphene is an allotrope of carbon consisting of a single layer of carbon atoms arranged in a hexagonal lattice. Graphene can be considered as an indefinitely large aromatic molecule, the ultimate case of the family of flat polycyclic aromatic hydrocarbons. Graphite, the most common allotrope of carbon, is a stack of graphene layers held together with weak bonds. Fullerenes and carbon nanotubes, two other forms of carbon, have structures similar to that of graphene. Graphene has many uncommon properties, it is the strongest material tested, conducts heat and electricity efficiently, is nearly transparent, yet opaque for a 1-atom-thick layer. Graphene shows a large and nonlinear diamagnetism, greater than that of graphite, can be levitated by neodymium magnets, it is a semimetal with small overlap between the conduction bands. Scientists theorized about graphene for years, it had been produced unintentionally in small quantities for centuries through the use of pencils and other similar graphite applications.
It was observed in electron microscopes in 1962, but it was studied only while supported on metal surfaces. The material was rediscovered and characterized in 2004 by Andre Geim and Konstantin Novoselov at the University of Manchester. Research was informed by existing theoretical descriptions of its composition and properties; this work resulted in the two winning the Nobel Prize in Physics in 2010 "for groundbreaking experiments regarding the two-dimensional material graphene." The name "graphene" is a combination of "graphite" and the suffix -ene, named by Hanns-Peter Boehm and colleagues, who produced and observed single-layer carbon foils in 1962. Boehm et al. introduced the term graphene in 1986 to describe single sheets of graphite. Graphene can be considered an "infinite alternant" polycyclic aromatic hydrocarbon; the International Union of Pure and Applied Chemistry notes, "previously, descriptions such as graphite layers, carbon layers, or carbon sheets have been used for the term graphene...it is incorrect to use for a single layer a term which includes the term graphite, which would imply a three-dimensional structure.
The term graphene should be used only when the reactions, structural relations or other properties of individual layers are discussed."Geim defined "isolated or free-standing graphene" as "a single atomic plane of graphite, which – and this is essential – is sufficiently isolated from its environment to be considered free-standing." This definition is narrower than the IUPAC definition and refers to cloven and suspended graphene. Other forms such as graphene grown on various metals, can become free-standing if, for example, suspended or transferred to silicon dioxide or silicon carbide. Graphene is a crystalline allotrope of carbon with 2-dimensional properties, its carbon atoms are packed densely in a regular atomic-scale chicken wire pattern. Each atom has four bonds: one σ bond with each of its three neighbors and one π-bond, oriented out of plane; the atoms are about 1.42 Å apart. Graphene's hexagonal lattice can be regarded as two interleaving triangular lattices; this perspective was used to calculate the band structure for a single graphite layer using a tight-binding approximation.
Graphene's stability is due to its packed carbon atoms and a sp2 orbital hybridization – a combination of orbitals s, px and py that constitute the σ-bond. The final pz electron makes up the π-bond; the π-bonds hybridize together to form the π ∗ - bands. These bands are responsible for most of graphene's notable electronic properties, via the half-filled band that permits free-moving electrons. Graphene sheets in solid form show evidence in diffraction for graphite's layering; this is true of some single-walled nanostructures. However, unlayered graphene with only rings has been found in the core of presolar graphite onions. TEM studies show faceting at defects in flat graphene sheets and suggest a role for two-dimensional crystallization from a melt. Graphene can self-repair holes in its sheets when exposed to molecules containing carbon, such as hydrocarbons. Bombarded with pure carbon atoms, the atoms align into hexagons filling the holes; the atomic structure of isolated, single-layer graphene is studied by TEM on sheets of graphene suspended between bars of a metallic grid.
Electron diffraction patterns showed the expected honeycomb lattice. Suspended graphene showed "rippling" of the flat sheet, with amplitude of about one nanometer; these ripples may be intrinsic to the material as a result of the instability of two-dimensional crystals, or may originate from the ubiquitous dirt seen in all TEM images of graphene. Atomic resolution real-space images of isolated, single-layer graphene on SiO2 substrates are available via scanning tunneling microscopy. Photoresist residue, which must be removed to obtain atomic-resolution images, may be the "adsorbates" observed in TEM images, may explain the observed rippling. Rippling on SiO2 is caused by conformation of graphene to the underlying SiO2 and is not intrinsic. Ab initio calculations show that a graphene sheet is thermodynamically unstable if its size is less than about 20 nm and becomes the most stable fullerene only for molecules larger than 24,000 atoms. Analogs are two-dimensional systems. Analogs can be systems in which the physics is easier to manipulate.
In those systems